Dictionary of Ceramics_A.Dodd-1994

DICTIONARY OF

CERAMICSArthur Dodd

THIRD EDITION

Revised and updated by

David Murfin

THE INSTITUTE OF MATERIALS

Book 588This edition first published in 1994 by

The Institute of Materials1 Carlton House Terrace

London SWlY 5DB

© The Institute of Materials 1994All rights reserved

British Library Cataloguing-in-Publication Data

Dodd, Arthur EdwardDictionary of Ceramics. - 3Rev.ed

I. Title II. Murfin, David666.03

ISBN 0-901716-56-1

Typeset byDorwyn Ltd, Rowlands Castle

Printed and bound atThe University Press, Cambridge

The first and second editions carried no dedications, but A.E. Dodd might like to beremembered for other reasons than this dictionary. Some lines from his Weaver Hillsand Other Poems seem appropriate:

Rock, crag, Earth's skullKnown by lens and X-ray beam;Soil, silt, Earth's skin,Analysed to micron grain;Grass, tree, Earth's hair,Numbered, classified and named;Atom tagged, star docketed,Computed by electron brain.

These myriad facts all knownAnd yetAnother's mind unknownExceptBy Mind, by Mind alone.

Words are as leaves,They shrivel, trees stand bare.Words are as leaves,Leaf-mould, seeds root there.We once more tread the pack-horse wayAnd smile to think how small the lasting worthMay be of so much toil.

A.E. Dodd, 1967

For my own part I might hope to fulfil:

The Preacher sought to find out acceptable words, and that which was written wasupright, even words of truth.

Ecclesiastes 12:10

and be allowed to put my dedication to the third edition in the form of a silicatetrahedron:

To

Dedication

CR and especially SW

When I joined BCRA (as it was then known) to work for Dr A.E. Dodd, the secondedition of this dictionary was well in hand. As a newly-qualified physicist, Icontributed a few specialised entries. Nearly 30 years later, many more are required.The dictionary has been considerably expanded to take account of newdevelopments in engineering ceramics, electroceramics; of new processes inwhitewares; of new machinery and new test methods; of the impact of environmentallegislation. The same broad scope has been adopted and coverage of glass, vitreousenamel and cement industries widened. It has seemed wise, in an industry which hasmoved much further to being science-based rather than craft-based, to include someterminology in relevant areas of basic science: in particular crystal structure, fracturemechanics and sintering. Here, and for some advanced ceramics produced in a widevariety of forms, some longer entries have been introduced to avoid extensive use ofcross-references and to provide a coherent understanding of closely-related materialsand processes.

Abbreviations have become something of a disease. Those in general use havebeen listed in their appropriate alphabetical positions, but where authors substitute(unrecognized and sometimes unrecognizable) initials for well-known processes as ashorthand, the obscurity resulting from carrying them over unexplained to anothercontext cannot be clarified even by a multitude of dictionary entries. Such have beenomitted.

About 2000 new terms have been added. Though some existing terms have beenmodified to take account of changed emphases (roller hearth kilns are not the raritiesof 30 years ago), very few have been removed. This is a twofold tribute to Dodd'soriginal work. His definitions, concentrating on the essence of the meaning, have stoodthe test of time, even when the words now have much broader application in details.Where words have become obsolete, it has been thought worthwhile to preserve hisaccurate and authoritative definitions for historical record.

My thanks are due to The Institute of Materials for giving me the opportunity torevive Dodd's Dictionary; to Mrs Dodd for permission to use the original copyrightmaterial; to Dr R.C.P. Cubbon, then Deputy Chief Executive of British CeramicResearch Ltd, for allowing me to use the Company's library - without which thisrevision would have been impossible; to the staff of the Information Departmentthere, past and present, who have all shared in gathering the information on whichthis book is based; and finally, to all my other ex-colleagues and friends in theindustry, whose continued penchant for asking awkward questions has been thedriving force and reason for that collection.

D. MurfinMadeley, 1994

Preface to the Third Edition

vii This page has been reformatted by Knovel to provide easier navigation.

Contents

Dedication ...................................................................................... v

Preface to the Third Edition ............................................................ vi

7.6 Temperature to 12.0 Temperature ......................................... 1

'A' Glass to AZS Refractories ...................................................... 1

B25 Block to Bwlchgwyn Quartzite ............................................ 18

°C to Czochralski Technique ....................................................... 45 °C to Coking ......................................................................................... 45 Colburn Process to Czochralski Technique ......................................... 67

Dam Ring to Dyer Method ............................................................ 84

E.B. Gun to Eykometer ................................................................. 102

°F to Fuzzy Texture ...................................................................... 113

G Stone to Gyratory Crusher ....................................................... 136

H Cassette to Hysteresis ............................................................. 148

IC Silicon Carbide to Izod Test .................................................... 162

JC to Jumpers ............................................................................... 170

KIC to Kyanite ................................................................................ 172

Laboratory Glassware to Lytag ................................................... 179

viii Contents

This page has been reformatted by Knovel to provide easier navigation.

MA to Mylius Test ......................................................................... 191

Nabarro-Herring Creep to NZP .................................................... 212

Obsidian to Oxynitride Glasses .................................................. 217

Packing Density to PZT ................................................................ 223

Quality Assurance to Quoin ........................................................ 249

R-curve to Ryolex ........................................................................ 251

S-brick to Syphon ........................................................................ 269 S-brick to Slop Glaze ........................................................................... 269 Slop Moulding to Syphon ..................................................................... 297

‘T’ Glass to TZP ............................................................................ 319

U-type Furnace or Hair-pin Furnace to Uviol Glass .................. 340

V-bricks to Vycor .......................................................................... 343

Wad to Wythe ................................................................................ 349

Xerography to XRF - X-ray Fluorescence Spectrometry ........... 358

YAG to Zyttrite .............................................................................. 359

Appendices Appendix A: The Definition of ‘Ceramics’ ............................................ 363 Appendix B: Other Sources of Information .......................................... 365 Appendix C: Hardness of Materials ..................................................... 367 Appendix D: Nominal Temperatute (°C) Equivalents of

Pyrometric Cones ........................................................................ 368 Appendix E: Comparison Table for Sieve Sizes .................................. 370

7.6 Temperature. See SOFTENING POINT.12.0 Temperature. See ANNEALINGPOINT.

'A' Glass. A glass composition first usedfor making glass fibre, it was a container-glass type containing 10-15% alkali, andwas soon superseded by specialcompositions.Abbe Number or Abbe Value. A measureof the optical dispersion of a glassproposed by the German physicist E.Abbe (1840-1905). Its usual symbol is vand is defined by v = (nD -1) (nF - nc)-

{

where nc nD and nF are the refractiveindices at wavelengths equivalent to thespectral lines C, D and F. Also known asCONSTRINGENCE and as the V-VALUE.Aberson Machine. See SOFT MUDPROCESS.

Abbreviations. Abbreviations havebecome a disease, in that authorssubstitute (unrecognized and sometimesunrecognizable) initial letters for well-known general processes whose namesare more than a few letters long, e.g.LPS for liquid-phase sintering, CTE forcoefficient of thermal expansion. What isexplained and used as a shorthand in onetechnical paper gets carried over toothers, and becomes a source ofobscurity. This dictionary listsabbreviations in general use in theirappropriate alphabetical positions.Ablation. The removal of a surface skin;the term has been applied to thevolatilization or burning away of aspecial protective coating, of ceramic orother material, on space vehicles. Theheat absorbed during ablation effectivelydissipates the heat generated by re-entryof the space vehicle into the Earth'satmosphere.Abradability Index. See ABRASIONRESISTANCE and BS 1902 Pt 4.6Abrams9 Law. States that the strength, S,of a fully compacted concrete is related

to the ratio, R, of water to cement by theequation S = A/BR where A and B areconstants. (D. A. Abrams, Struct. Mat.Res. Lab. Lewis Inst, Bull. 1, Chicago,1918.)Abrasion. Wear caused by themechanical action of a solid, e.g. wear ofthe stack lining of a blast furnace by thedescending burden (cf. CORROSION andEROSION).Abrasion Resistance. The ability of amaterial to resist mechanical rubbing.Some ceramic products are speciallymade to have this property, for exampleblue engineering bricks for the paving ofcoke chutes. There are several types ofapparatus for the evaluation of thisproperty; see BENDER ABRASION

METHOD, KESSLER ABRASION TESTER,

MIDLAND IMPACT TEST, MORGAN-

MARSHALL TEST, RATTLER TEST, SCC

TEST, TABER ABRASER. BS 1902 PtS 4.6and 4.7 specify its determination forrefractories at ambient and elevatedtemperatures, the first using air-blownalumina abrasive, the second alumina/zirconia abrasive fed by gravity. BS 6431Pt 20 specifies a wet test (PEI TEST)and a dry test (MCC TEST) for thesurface abrasion of glazed tiles. Pt 14specifies a deep abrasion test forunglazed tiles, in which aluminaabrasive, grain size 80, is fed under avertical rotating wheel to cut a groove inthe tile, whose depth is measured after astandard number of revolutions of thewheel. BS 1344 Pt 4 is an obsolescenttest for vitreous enamels. ASTM C.704specifies a test for refractory bricks andcastables, using an air blast with lkg ofgraded SiC abrasive.Abrasive. A hard material used in theform of a wheel or disk for cutting, or asa powder for polishing. The usualabrasives are silicon carbide and fusedalumina. Abrasive wheels are commonly

made by bonding abrasive grains withclay and feldspar (a proportion of FRIT(q.v.) is also often added) and firing theshaped wheel; organic bonds e.g.synthetic resins, rubber or shellac, arealso used, in which case the wheels arenot fired. For the standard markingsystem see under GRINDING WHEEL.Abrasive Jet Machining. Abrasiveparticles are entrained in a high-velocityfluid jet which acts as the cutting tool. Ifthe fluid is a gas, up to 50g/min ofabrasive powder is carried through thejet nozzle at supersonic speed bypressures of 200 to 850 kPa. InWATERJET CUTTING, discharge pressuresup to 400MPa provide jet velocites up to700 m/s, carrying 1.5 to 2.0 kg/min ofabrasive in a jet which can be confined toa smaller diameter without spreading.Absolute Temperature (°Abs). SeeKELVIN TEMPERATURE SCALE.Absorption. See POROSITY; WATERABSORPTION.

Absorption Ratio. See SATURATIONCOEFFICIENT.

Accelerated Tests. Test methods whichattempt to determine the effect of slowchanges on materials by adopting moresevere or more rapid changes, andcorrelating the test result with actualbehaviour in service. Examples are testsfor weathering, wear, moistureexpansion. ASTM-E632 gives criteria fordesigning such accelerated tests.Accelerator. A material that, whenadded to hydraulic cement or to plaster,accelerates the setting. With cement,care must be taken to distinguishbetween the effect on the initial set andthe effect on the longer-term hydration -some additions accelerate setting butinhibit the final development of strength;also, a compound that acts as anaccelerator at one level of concentrationmay become a retarder at some other

concentration. In general, alkalicarbonates are strong accelerators forportland cement. For plaster, the bestaccelerator is finely-ground gypsum,which provides nuclei for crystallization;potash alum has also been used.Acceptance Angle of an optical fibre, seeNUMERICAL APERTURE.

Acceptance Testing. With increasedemphasis on quality control andquality assurance, raw materials orintermediates are subjected to a seriesof tests of relevant properties to ensurethat they match the producers'specification. The acceptance qualitylevel, which is the percentage which isacceptable to the buyer, is usuallyspecified, and compliance checked bytesting and statistical analysis of theresults. BS 3921 lays down a detailedsampling scheme for building bricks.See also ACTION LIMIT, QUALITYCONTROL; ATTRIBUTES.Accessory Mineral. A mineral that ispresent in a rock or clay in relativelysmall quantity, usually as an impurity;e.g. mica is usually found as an accessorymineral in china clay.Acheson Furnace. An enclosed electricresistance furnace, of the type first usedby Acheson in 1891 to make siliconcarbides from carbon and sand, whichcan attain temperatures of 2500 0C.Acicular. see MORPHOLOGY.Acid Annealing. Dipping of the metalbase for vitreous enamelling into diluteacid (generally HCl) followed byannealing; this promotes scaling beforethe pickling process.Acid Embossing. The etching of glasswith HF or a fluoride.Acid Frosting. The etching of glasshollow-ware with HF or a fluoride.Acid Gold. A form of gold decorationfor pottery introduced in 1863 by J. L.Hughes at Mintons Ltd., Stoke-on-Trent.

The glazed surface is etched with diluteHF prior to application of the gold; theprocess demands great skill and is usedfor the decoration only of ware of thehighest class. A somewhat similar effectcan be obtained by applying a pattern inlow-melting flux on the glaze andgoldbanding on the fluxed area; this isknown as MOCK ACID-GOLD, c.f. BRIGHT

GOLD and BURNISH GOLD.Acid Open-hearth Furnace. An OPEN-HEARTH FURNACE (q.v.) used in therefining of hematite iron; little such ironis now made. The particular feature isthat the hearth is made of acidrefractories - silica bricks covered with afritted layer of silica sand.Acid Refractory Material. General termfor those types of refractory materialthat contain a high proportion of silica,e.g. silica refractories (> 92% SiO2) andsiliceous refractories (78-93% SiO2).The name derives from the fact thatsilica behaves chemically as an acid andat high temperatures reacts with basessuch as lime or alkalis.Acid Resistance. In USA, the acidresistance of ceramic decorations onglass is specified in ASTM C724 andC735. The acid resistance of vitreousenamelled ware at (nominal) roomtemperature is determined by exposingthe enamelled surface to 10% citric acidfor 15 min at 26 ± 1°C (ASTM C282)Five classes of enamelware aredistinguished according to theirsubsequent appearance:AA: no visible stain and passes dry-

rubbing testA: passes blurring-highlight test and

wet-rubbing testB: passes blurring-highlight test: fails

wet-rubbing testC: fails blurring-highlight test; passes

disappearing-highlight testD: fails disappearing-highlight test.

A similar classification has been adoptedin B.S. 1344 (Part 2) but the time ofexposure to the 10% citric acid is 20 minand the temperature is 20 0C. BS 1344 Pt3 tests resistance to H2SO4; other partstest resistance to hot acids, alkalis anddetergents.Acid-resisting Brick or Tile. A fired claybrick or tile of low porosity and highresistance to a variety of chemicals. B.S.1902 Pt 3.12 specifies an acid resistancetest for refractories, Pt 3.15 a test forbulk material. ASTM C-279 specifiesthree grades according to resistance toH2SO4. ASTM C-410 specifies industrialfloor bricks.Acid-resisting Cement. The principaltypes are as follows: 1. Silicate: an inertfiller bonded with silica gel that has beenprecipitated in situ from Na- or K- silicatein the presence of Na2SiF6, or fromsilicon ester. 2. Rubber Latex: essentiallycement sand mixes impregnated withrubber. 3. Synthetic Resin: with an inertfiller. 4. Sulphur Cements: usually withsand as filler. 5. Bituminous Cements.ASTM specifications for these materialsare listed in VoI 4-05 of the Annual Bookof ASTM Standards, and number some25, including specifications for mortarsand grouts.Acid Scaling. Dipping or spraying metalwith acid, then annealing at red heat, toremove oil, rust and dirt before vitreousenamelling, cf. ACID ANNEALING.Ackerman Blocks. Hollow extruded clayblocks, with thin walls and large voids,for ceiling and floor construction,available in sizes from 150 to 220 mm.(Polish Stand. PN B-12005, 1969).ACL Kiln or Lepol Kiln. ACL is a trade-mark of the Allis Chalmers Mfg Co.,USA: Lepol is a trade-mark of PolysiusCo., Germany. Both terms refer to atravelling-grate preheater for portlandcement batch prior to its being fed to a

rotary cement kiln; with this attachment,the length of a rotary cement kiln can behalved.ACOP. Approved Code of Practice (inHEALTH and SAFETY, q.V.).Acoustic Emission. Internal structuralchanges in materials (crack growth,phase transitions, plastic deformation)may release strain energy manifested asultrasonic waves, whose detection andanalysis gives an insight into the type ofchanges taking place. In particular, crackgrowth may be continuously monitoredand warning of impending failureobtained.Acoustophoresis. Dense suspensions aresubjected to ultrasonic vibrations. (~ 1MHz) The amplitude of the resultingparticle vibration is considered to beproportional to the ZETA POTENTIAL.ACS. American Ceramic Society.Actinic Green. An emerald green glassof the type used for poison bottles.Action Limit. In statistical QUALITYCONTROL (q.v), the number of defectiveitems per sample which will only beexceeded by chance in a given number oftests, in practice usually taken to be 1 in1000. The warning limit is usually takento be 1 test in 40 revealing a defectiveitem.Activated Alumina. A synthetic high-surface area alumina, produced byappropriate heat-treatment, and usuallya transition alumina containing a smallproportion of OH- ions.Activated Carbon. According to ASTMD-2652, activated carbons are a family ofcarbonaceous substances manufacturedby processes that develop absorptiveproperties. This standard defines over100 terms relating to the use of granularand porous carbons as absorbantmaterials, and the ASTM Annual Bookof Standards VoI 15-01 contains some 20test methods for relevant properties.

Activated Clay. Acid treatment ofbentonite and other clays to improvebleaching and absorption properties.Activated Sintering. Sintering in thepresence of a sintering aid - a materialsuch as a foreign oxide which producessupersaturated surface phases providinghigher surface energy.Activation Energy. A threshold energyvalue which must be acquired by asystem before some types of reaction orchange can occur. See ARRHENIUS' LAW.Active Brazing. Joining ceramics withmetal brazes which wet well the surfaceof the ceramic, obviating the need forprior metallising.Active Filler-Controlled Pyrolysis.(AFCOP) In this technique for makingmultiphase ceramic matrix composites,an active filler material (a transitionmetal or compound thereof which willyield a carbide or other ceramic) ismixed with an organometallic polymerand pyrolysed. The kind, content andstructure of the filler control the kineticsof the polymer pyrolysis and theresulting microstructure, which maycontain disordered or glassy areas. (M.Seibold and P. Greil, 1st European Confon Adv. Mater & Processes.)ACZS. Alumina-Chrome-Zirconia-Silicarefractory, used in glass tanks.A-D Goodness-of-Fit Test. See K-STEST.Adams Chromatic Value System. Amethod for the quantitative designationof colour in terms of (1) lightness, (2)amount of red or green, and (3) amountof yellow or blue. The system has beenused in the examination of ceramiccolours (E. Q. Adams, /. Opt. Soc. Am.,32,168,1942).Adams Process. A method for theremoval of iron compounds from glass-making sands by washing with a warmsolution of acid (Na oxalate containing a

small quantity of FeSO4; see /. Soc.Glass Tech., 19,118,1935).Adams-Williamson Annealing Schedule.A procedure, derived from firstprinciples, for determining the optimumannealing conditions for a particularglass; (L. H. Adams and E. D.Williamson, /. Franklin Inst, 190, 597,835,1920).Adapter. A connecting-piece, usuallymade of fireclay, between a horizontalzinc-retort and the condenser in whichthe molten zinc collects.Adherence. The strength of the bondbetween two materials, especially thatbetween a coating and the substrate.ASTM C313 specifies a test for the'Adherence of Porcelain Enamel andCeramic Coatings to Metal.' Adherencefailure is measured as the ratio of brightmetal to remaining adherent enamelafter indentation by a specified plunger.ASTM C633 specifies a text for the'Adhesion or Cohesive Strength ofFlame-sprayed Coatings'.Adiabatic Diesel Engines. Ceramiccomponents have been made towithstand the high operatingtemperatures in uncooled (waterless)diesel engines designed for minimumheat loss, usually incorporating exhaustturbochargers. (The term 'adiabatic' isnot used with its strict meaning of noheat gained or lost during athermodynamic process.)Adobe. Mud used in tropical countriesfor making sun-dried (unfired) bricks;the term is also applied to the bricksthemselves.Adsorption. Process of taking up amolecular or multi-molecular film of gasor vapour on a solid surface. This film isnot readily removed except by stronglyheating the body. The adsorption ofmoisture on the internal surface of aporous body may cause the body to

expand slightly; this is known asMOISTURE EXPANSION (see also GASADSORPTION METHOD). Langmuir'sadsorption isotherm, with the equation/ = ap/(l - ap), is based on theassumption that adsorption is limited toa monomolecular layer (f is the fractionof the surface covered; p is the gaspressure; a is a constant).Advanced Ceramics. A general term forceramics, usually of high purity orcarefully controlled composition andmicrostructure, used in technicalapplications where their mechanical,thermal, electrical and/or opticalproperties are important, cf. SPECIAL

CERAMICS, FINE CERAMICS, TECHNICAL

CERAMICS, ENGINEERING CERAMICS,

ELECTROCERAMICS, OPTICAL

APPLICATIONS.

Aebi Kiln. A car tunnel kiln built to thedesign of Robert Aebi, Zurich. One suchdesign is top fired by the CRYPTOSYSTEM (q.v.).Aerated Concrete. Concrete with a highproportion of air spaces resulting from afoaming process; the bulk density mayvary from about 560-1440 kg/m3 (35-90lb/ft3). Aerated concrete is chiefly usedfor making pre-cast building units. It isalso known as GAS CONCRETE,

CELLULAR CONCRETE Or FOAMED

CONCRETE.

Aeration of Cement. The effect of theatmosphere on portland cement duringstorage. Dry air has no effect, but if it isexposed to moist air both moisture andcarbon dioxide are absorbed with erraticeffects on the setting behaviour (cf. AIRENTRAINING).Aeroclay. Clay, particularly china clay,that has been dried and air-separated toremove any coarse particles.Aerogel. A highly porous solid formedby replacing the liquid in a GEL by agas.

Aerograph. A device for sprayingpowdered glaze or colour on the surfaceof pottery by means of compressed air.Aerox. Alumina filter ceramic withuniform micron-sized pores, made byAerox Ltd, which company was acquiredby Doulton Industrial Products, Stone,now part of Fairey Engineering.A.F.A. Rammer. Apparatus designed bythe American Foundrymen's Associationfor the preparation of test-pieces offoundry sand; in 1948 the Associationchanged its name to the AmericanFoundrymen's Society. See A.F.S. andSAND RAMMER.AFNOR. Abbreviation for the FrenchStandards Association; AssociationFranchise de Normalisation, 23 RueNotre-Dame-des-Victoires, Paris 2.AFRSI. Advanced Flexible ReusableSurface Insulation comprises an innerlayer of leached silica glass fabric; acentral layer of high-purity fused silicafibre; an outer layer of quality fabric.The material was developed as ininsulating blanket for the Space Shuttleby NASA, Ames Research Centre andJohns-Manville, USA.After Contraction. The permanentcontraction (usually expressed as a linearpercentage) that may occur if a fired orchemically-bonded refractory product isre-fired under specified conditions oftest. Fireclay refractories are liable toshow after contraction if exposed to atemperature above that at which theywere originally fired (cf. FIRINGSHRINKAGE).After-glow. See JUMP.After Expansion. The permanentexpansion (usually expressed as a linearpercentage) that may occur when arefractory product that has beenpreviously shaped and fired, orchemically bonded, is re-fired underspecified conditions of test. Such

expansion may take place, for example,if the product contains quartz or kyanitc,or if bloating occurs during the test (cf.FIRING EXPANSION).A.F.S. American Foundrymen's Society,Des Plaines, Illinois, USA. This Societyhas issued standard methods for testingfoundry sands.Afwillite. A hydrated calcium silicate,3CaO. 2SiO2 . 3H2O; it is formed whenportland cement is hydrated underspecial conditions and when calciumsilicate is autoclaved (as in sand-limebrick manufacture).Agalmatolite. An aluminosilicatemineral that is very similar toPYROPHYLLITE (q.V.).Agate. A cryptocrystalline variety ofsilica that has the appearance of a hard,opaque glass; it usually containscoloured LIESEGANG RTNGS. It is used inthe ceramic industry for burnishing golddecoration on pottery and for makingsmall mortars and pestles for preparingsamples for chemical analysis.Agate Glass. Decorative glassware,simulating AGATE, made by blendingmolten glasses of two or more colours,or rolling glasses of several colourstogether in the plastic state.Agate Ware. Decorative earthenwaremade, chiefly in the 18th century inStaffordshire, by placing thin layers ofdifferently coloured clays one onanother, pressing them together, slicingacross the layers and pressing the slab ofvariegated coloured clay into a mould.When fired, the ware had theappearance of natural agate.Ageing. (1) A process, also known asSOURING (q.v.), in which moistened clay,or prepared body, is stored for a periodto permit the water to become moreuniformly dispersed, thus improving theplasticity. A similar effect can be achievedmore quickly by TEMPERING (q.v.).

(2) The process of allowing vitreous-enamel slip to stand, after it has beenmilled, to improve its rheologicalproperties.Agglomerate. To form assemblages ofsmaller particles, rigidly joined togetherelectrostatically or by intergrowth. (Or,as a noun, such an assemblage.)Agglomeration defeats mixing on thescale of the finest particles, and canproduce variations in packing densitywhich impair strength and otherproperties.Aggregate. See CONCRETE AGGREGATE;LIGHTWEIGHT EXPANDED CLAY

AGGREGATE.

Aglite. Trade-name: a lightweightexpanded clay aggregate made by theButterley Co. Ltd, Derby, England, fromcolliery shale by the sinter-hearth process.The bulk density is: (12-18 mm) 0.5 kg/1;(5-12 mm) 0.55 kg/1; (<5 mm) 0.8 kg/1.Agricultural Pipes. See FIELD-DRAINPIPES.

Agricultural Tile. See DRAIN TILE.Air BeII. A fault, in the form of anirregularly shaped bubble, in pressed ormoulded optical glass.Air-borne Sealing. A process for thegeneral, as opposed to local (cf. SPRAYWELDING), repair of a gas retort byblowing refractory powder into thesealed retort, while it is hot; the powderbuilds up within any cracks in therefractory brickwork and effectivelyseals them against gas leakage. (West'sGas Improvement Co. Ltd., Brit. Pat.568159; 21/3/45.)Air Brick. A fired clay brick, of the samesize as a standard building brick, buthaving lateral holes for the purpose ofventilation, e.g. below floors. BS 493specifies units for use externally (Class 1)and internally (Class 2).Air Chain. A line of air bubbles, forminga defect in glass or vitreous enamel.

Air Content. The volume of air voids incement paste, morter or concrete,excluding the pore space in theaggregate. Air entrained by mixing orgases generated chemically may beincluded. (ASTM C-125).Air Entraining. The addition of amaterial to portland cement clinkerduring grinding, or to concrete duringmixing, for the purpose of reducing thesurface tension of the water so that 4-5vol.% of minute air bubbles becometrapped in the concrete. This improvesworkability and frost resistance anddecreases segregation and bleeding. Theagents used as additions include: 0.025-0.1% of alkali salts of wood resins,sulphonate detergents, alkalinaphthenate, or triethanolamine salts; or0.25-0.5% of the Ca salts of glues (fromhides); or 0.25-1.0% of Calignosulphonate (from paper-making).Air-floated. Material, e.g. china clay, thathas been size-classified by means of anAIR-SEPARATOR (q.V.).

Air-hardening Refractory Cement orMortar. See CHEMICALLY BONDEDREFRACTORY CEMENT.

Airless Drying. The drying chamber issurrounded by an airtight inner shell andan insulated outer shell. The original airatmosphere is recirculated and heated,so that it is progressively replaced asheat transfer medium by superheatedsteam from the drying product. No air isallowed to enter the dryer during thedrying process.Air Line. A fault, in the form of anelongated bubble, in glass tubing- alsoknown as HAIR LINE.Air Permeability. See PERMEABILITY.Air Pollution. BS 1747 specifies methodsof test for the determination of finesuspended particles (smoke); SO2, NOx.See also TA-LUFT and HEALTH AND

SAFETY.

Air Ramming. US term for the processof shaping a refractory brick or furnacehearth with a pneumatic rammer.Air Seal. A method for the prevention ofthe escape of warm gases from theentrance or exit of a continuous furnace,or tunnel kiln, by blowing air across theopening.Air Separator. A machine for the sizeclassification of fine ceramic powders,e.g. china clay; the velocity of an aircurrent controls the size of particlesclassified.Air-setting Refractory Cement orMortar. See CHEMICALLY BONDEDREFRACTORY CEMENT.

Air-swept Ball Mill. See BALL MILL.Air Twist. Twisted capillaries as a formof decoration within the stem of a wineglass.Aired Ware. Pottery-ware that has apoor glaze as a result of volatilization ofsome of the glaze constituents. The termwas used more particularly when warewas fired in saggars in coalfired kilns,'air' escaping from a faulty saggar intothe kiln while kiln gases at the same timepenetrated into the saggar. The term isalso sometimes applied to a glaze thathas partially devitrified as a result ofcooling too slowly between 900 and 7000C; the most common crystallization isthat of calcium silicate or zinc silicate.Akermanite. 2CaO.MgO.2SiO2; m.p.1454°C; sp.gr. 3.15; thermal expansion(~1200°C) 10.6 x 10-* K-i. This mineralis found in some slags.Alabaster Glass. A milky-white glassresembling alabaster; transmitted light isdiffused without any fiery colour.Albany Clay. A clay found in theneighbourhood of Albany, New York; aquoted analysis is (%) SiO2 57.6; Al2O3

14 .5; Fe2O3 5.2; CaO 5.7; MgO 2.7;Alkalis 3.1. A somewhat similar clayoccurs in Ontonagon County, Michigan.

Because of its fine particle size and highflux content, this clay fuses at acomparatively low temperature to form agreenish-brown glaze suitable for use onstoneware; it is also used as a vitrifyingbonding material.Alberene Stone. A US stone havingproperties similar to those ofPOLYPHANT STONE (q.V.).

Albite. See FELDSPAR.Albolite. A silica and magnesia plasticcement.Alcove. A narrow covered extension tothe working end of a glass-tank furnace;it conveys molten glass to a forehearthor revolving pot.AIginates. Organic binders andsuspending agents derived from seaplants. Ammonium alginate and sodiumalginate have found some use asadditions to suspensions of glazes andenamels.AIi Baba. Popular name for a largechemical stoneware jar of the type usedfor the bulk storage of acids; these jarsare made in sizes up to 5000 litrescapacity.Alite. The name given to one of thecrystalline constituents of portlandcement clinker by A. E. Tornebohm(Tonindustr. Ztg., 21,1148,1897). Alitehas since been identified as the mineral3CaO. SiO2

Alkali-Aggregate Reaction. Thesiliceous components of aggregates mayreact detrimentally with the alkalicomponenets of Portland cement, afterthe concrete has hardened.Alkali Attack. See DURABILITY OF ON-GLAZE DECORATION.

Alkali Neutraliser. See underNEUTRALISER.

Alkoxide. Compounds formed from thereaction of an alcohol with an alkalimetal. They are used in SOL-GELprocesses (q.v) for preparing ceramics.

All-basic Furnace. Abbreviation for All-Basic Open Hearth Steel Furnace. Thewhole of the superstructure of such afurnace-hearth, walls, roof, ports, ends, isbuilt of basic refractories These furnaceswere introduced in Europe in about1935, the object being to make itpossible to operate at a highertemperature than that possible with basicO.H. furnaces having a silica roof.Alligator Hide. (1) A vitreous-enamelware fault in the form of severeORANGE PEEL (q.v ) and TEARING (q.v.);causes include too-rapid drying and too-heavy application of enamel.(2) A decorative glaze effect, having theappearance indicated by its name,sometimes used by studio potters; it isachieved by loading the glaze withrefractory oxides to increase the viscosity sothat during firing, the glaze does not flowuniformly over the surface of the ware.Alon. Aluminium Oxy-Nitride (q.v).(Alon has previously been used as atradename for fused alumina, by theCabot Corp, USA.)Allophane. An amorphous gelconsisting, usually, of 35-40% Al2O3,20-25% SiO2 and 35% H2O. It is oftenfound in association with halloysite.Allport Oven. A pottery BOTTLE OVEN(q.v.) in which the hot gases from thefiremouths entered the oven nearer to itscentre than the usual points of entryaround the oven walls; another featurewas preheating of the secondary air. (S.J. Allport, Brit. Pat. 570 335; 3/7/45; 606084; 5/8/48.)Alluvial Clay. A brickmaking clay ofriver valleys typified in England by theclays of the Humber estuary, the Thamesvalley, and the Bridgwater district. Thecomposition is variable.Aloxite. Trade-name: Fused aluminaabrasives and abrasive products made bythe Carborundum Co., Ltd.

Alsing Cylinder. An early type of BALLMILL (q.v.) invented by J. R. Alsing in1867.Alumina. Aluminium oxide, Al2O3. Thisoxide exists in several forms: principallyY-Al2O3, stable up to about 10000C andcontaining traces of water or of hydroxylions, and CX-Al2O3, the pure formobtained by calcination at hightemperature. The so-called P-Al2O3 isthe compound Na2OIlAi2O3. BS 4140specifies powder properties and methodsof determining chemical contaminants ofaluminium oxide powders, which arealso specified in ASTM F.7. See alsoALUMINA (FUSED); ALUMINA (SINGLECRYSTAL); ALUMINA (SINTERED);ALUMINA (TABULAR); CORUNDUM.Alumina Cement. See HIGH-ALUMINA

CEMENT.Alumina Clogging. Nozzles forsecondary steelmaking ladles canbecome blocked by build-up of denseproducts of the reaction between thenozzle refractories and the steel and slag,in particular by attack on the aluminaphase of the refractory.Alumina (Fused). In spite of its highm.p. (2050 0C), alumina can be fused inan oxy-hydrogen flame or in an electricarc. By the former method, large singlecrystals (boules) can be produced; theyare used as bearings, and as dies forwire-drawing, and for other purposesdemanding high abrasion resistance.Fused alumina made in the electric arcfurnace is usually crushed, and sievedinto a range of grit sizes for use as anabrasive; when re-bonded and sintered itis used as a special refractory material.Alumina Porcelain. Defined in ASTM-C242 as: A vitreous ceramic whiteware,for technical application, in whichalumina is the essential crystalline phase.Alumina (Single Crystal). Made bythe flame-fusion of the powder; used

in bearings, lasers, fibre-drawing dies,etc.Alumina (Sintered). Alumina,sometimes containing a small amount ofclay or of a mineralizer, and fired at ahigh temperature to form a denseceramic. Sintered alumina has greatmechanical strength: compressivestrength 3 GN/m2 (20 0C), 0.9 GM/m2

(10000C), 1 GN/m2 (1500 0C); tensilestrength 175 MN/m2 (200C), 140 MN/m2

(1000 0C), 35 MN/m2 (1400 0C); Young'sModulus, 350 GN/m2 (20 0C), 140 MN/m2 (1000 0C), 140 GN/m2 (15000C).Sintered alumina also has high abrasionresistance, high dielectric strength, andlow power factor. Thermal expansion (0-1000 0C) 8 x 1(H\ Because of theseproperties, sintered alumina is used inthread guides, tool tips, and grindingmedia; as the ceramic component ofsparking plugs, electronic tubes, ceramic-to-metal seals, etc. Sintered aluminacoatings can be applied to metals byflame-spraying. Alumina ceramics forelectrical and electronic applications arespecified in ASTM D2442.Alumina (Tabular). A pure (99.5%)alumina calcined at 16500C andcontaining very little (e.g. 0.02%) Na2O;it consists of coarse tablet-like crystals ofCORUNDUM (q.v.).Alumina Whiteware. Defined in ASTM- C242 as: Any ceramic whiteware inwhich alumina is the essential crystallinephase.Aluminalon. A composite, 90% alumina,10% aluminium nitride, formed by hot-pressing. It has high strength andductility to 1400 0C, and is acid resistantto 1200 0C.Aluminium Borates. Two compoundshave been reported: 9Al2O3 2B2O3,which melts incongruently at 1950 0C;2Al2O3 B2O3, which dissociates at10350C. The compound 9Al2O3. 2B2O3,

when made by electrofusion, has beenproposed as a special refractory material:R.u.L., 15000C; thermal expansion, 4.2 x10-6 (20-14000C); good thermal-shockresistance.Aluminium Boride. The usual compoundis AlB2; sp.gr. 3.2. AlB2 dissociatesabove 9800C to form AlB12 (sp.gr. 2.6)and Al.Aluminium Carbide. Al4C3; thedissociation pressure at 14000C isapprox. 1 x 10-5 atm.; m.p. 2800 0C;sp.gr. 2.99. This carbide is slowlyattacked by water at room temperature.Aluminium Enamel. A vitreous enamelcompounded for application toaluminium. There are three main types:containing lead, phosphate glass, orbarium. Lithium compounds have alsobeen used in these enamels.Aluminium Nitride. AlN; m.p. 22000C in4 atm. N2; dissociates at 1700-18000C invacuo. The theoretical density is 3.26.Thermal expansion (25-10000C) 5.5 x10-6. Thermal conductivity 550 W/m.K.That of alumina is about 30 W/m.K, soAlN is tape cast (q.v) into substrates andchip carriers for printed circuits, usingCaO or Y2O3 as densification additives.AlN is a raw material for SIALONS (q.v),forming a series of POLYTYPOIDS (q.v)with constant (Si+Al):(O+N) ratio.When shaped into crucibles AlN can beused as a container for moltenaluminium. It is a good electricalinsulator, the resistivity exceeding 1012

ohm. cm at 25 0C. Modulus of rupture,250 MN/m2 at 25°C and 120 MN/m2 at1400 0C. Hardness, 1230 (KlOO).Aluminium Oxynitride. AlON is aninfrared transmitter in the wavelengthrange 1 to 4|im.Aluminium Phosphate. Generally refersto the orthophosphate, AlPO4; sp.gr.2.56, m.p. approx. 2000 0C butdecomposes. It is supplied in various

grades, particularly for use as a binder inthe refractories industry. The bondingaction has been attributed to reactionbetween the phosphate and basic oxidesor Al2O3 in the refractory. This typeof bond preserves its strength atintermediate temperatures (500-10000C), a range in which organic bonds aredestroyed and normal ceramic bondinghas not yet begun.Aluminium Titanate. Al2O3TiO2 meltsat 1860 0C, but slowly dissociates below1150 0C to Al2O3 and TiO2, producing amicrostructure with a network of finecracks. This gives good thermal shockresistance and a thermal expansioncoefficient up to 7000C which is almostzero, but non-uniform. It may bestabilized with small amounts of Fe2TiO5

or MgTiO3 to provide more uniformexpansion.Alumino-silicate Refractory. A generalterm that includes all refractories of thefireclay, sillimanite, mullite, diaspore andbauxite types. BS 1902 Pt 2 defines it asa refractory containing 8 to 45% Al2O3,the balance being predominantly silica.Aluminous Cement. See CIMENT FONDU.Aluminous Fireclay Refractory. Thistype of refractory material is defined inB.S. 1902 Pt 2 as a refractory containingin the fired state, > 45% Al2O3, thebalance being predominantly silica.Alundum. Trade-name: Fused aluminamade by Norton Co.Alunite. KAl3(SOJ2(OH)6 occurs inAustralia, USA (Arizona, Nevada,Utah), Mexico, Italy, Egypt, andelsewhere. The residue obtained aftercalcination and leaching out of the alkalican be used as raw material for high-alumina refractories.Amakusa. The Japanese equivalent ofCHINA STONE (q.V.).Amberg Kaolin. A white-firingmicaceous kaolin from Hirschau,

Oberpfalz, Germany. A quoted analysisis (per cent): SiO2, 48.0; Al2O3 37.5;Fe2O3 0.5; TiO2 0.2; CaO 0.15; alkalis2.6; loss-on-ignition 12.2.Amber Glass. Whilst other colours ofCONTAINER GLASS are selected foraesthetic reasons (clear and green beingthose generally available) the amber orbrown glass is designed to absorbultraviolet light to protect some foodsand pharmaceutical products sensitive toUV. The amber colour is imparted byiron and sulphur.Ambetti or Ambitty. Decorative glasscontaining specks of opaque material;the effect is produced by allowing theglass to begin to crystallize.Amblygonite. A lithium mineral ofvariable composition,(Li,Na)AlPO4(F,OH); sp. gr. 3 0; m.p.11700C. It occurs in various parts ofsouthern Africa, but is relativelyuncommon and therefore finds less useas a source of lithium than do PETALITEand LEPIDOLITE (q.v.).Amborite. Hot-pressed fine-grainedboron nitride with a ceramic bond, usedas an abrasive (de Beers Co).Amboy Clay. An American siliceousfireclay; it is plastic and has a P.C.E.above 32.AMDCB. Applied Moment DoubleCantilever Beam. See FRACTURETOUGHNESS TESTS.American Bond. Brickwork of stretchercourses with a header course every 5th,6th or 7th course.American Hotel China. A vitreous typeof pottery-ware. A typical bodycomposition is (per cent): kaolin, 35;ball clay, 7; feldspar, 22; quartz, 35;whiting, 1.Ammonium Bifluoride. NH4F.HF; usedas a saturated solution in hydrofluoricacid (usually with other additions) forthe etching of glass.

Ammonium Vanadate. NH4VO3; usedas a source of vanadium in ceramicpigments, e.g. tin-vanadium yellow,zirconium vanadium yellow andturquoise, etc.Ampelite. A carbonaceous schistcontaining alumina, silica and sulphur,sometimes used as a refractory.Amperit. Tradename. Mixed alumina-titania powders supplied by HoechstAG.Amphiboles. See SILICATE STRUCTURES.Amphoteric. Capable of reacting as acidor base (e.g. Al2O3).Ampoule. A small glass container that issealed (after it has been filled withliquid) by fusing the narrow neck. Theglass must resist attack by drugs andchemicals, but must be readily shaped bymass-production methods; normally, aborosilicate glass of fairly low alkali andlime contents is used.Amsler Volumeter. An apparatus for themeasurement of the bulk density ofpowdered or granular materials (see BS1902 Pt 3.6). It comprises a cylindricalsteel container, whose lid is retained by ascrewed collar to provide a mercury seal.A guarded capilary tube with a referencemark is fitted into the domed lid. Aplunger with a graduated micrometer,fitted into the side of the cylinder,controls and measures the displacementof mercury within.Anaconda Process. A method for theshaping of silica refractories formerlyused at some refractories works in USA.The bricks were first 'slop-moulded',then partially dried, and finally re-pressed. The name derives from thetown of Anaconda, Montana, USA,where the process was first used, early inthe present century, by theAmalgamated Copper Co.Analysis. See DIFFERENTIAL THERMALANALYSIS; PARTICLE-SIZE ANALYSIS;

RATIONAL ANALYSIS; ULTIMATE

ANALYSIS.

Anatase. A tetragonal form of titania,TiO2; sp. gr. 3.84. The other forms areBROOKiTE (q.v.) and RUTILE (q.v.). Allthree structures have similar Ti-O bonddistance but differ in the linking of theTiO6 octahedra. Anatase has beenobserved in some fireclays and kaolins. Itis rapidly converted into rutile whenheated above about 700 0C.Anchors. Specially shaped metal orceramic pins to hold ceramic fibreblankets or panels in place to formfurnace linings. Other heavier unshapedlinings (of refractory concrete) are alsoanchored to the furnace structure bynotched or shaped rods and bars.Andalusite. A mineral having the samecomposition (Al2SiO5) as sillimaniteand kyanite but with different physicalproperties. The principal source is S.Africa; it also occurs in California,Nevada, and New England (USA).When fired, it breaks down at 13500C toform mullite and cristobalite; thechange takes place without significantchange in volume (cf. KYANITE).Andalusite finds some use as arefractory raw material.Andreasen Pipette. An instrument usedin the determination of the particle sizeof clays, by the SEDIMENTATIONMETHOD (q.v.); it was introduced by A.H. M. Andreasen, of Copenhagen(Kolloid Zts., 49, 253,1929).Andrews' Elutriator. A device forparticle-size analysis. It consists of: afeed vessel or tube; a large hydraulicclassifier; an intermediate classifier; agraduated measuring vessel. (L.Andrews, Brit. Pat. 297 369; 14/6/27.)Angle Bead. A special shape of wall tile(see Fig. 7, p350).

Angle of Drain. The angle at whichvitreous enamel ware is placed on a rack

after dipping, to obtain the requiredthickness of coating.Angle of Nip. The angle between thetwo tangents to a pair of crushing rolls atthe point of contact with the particle tobe crushed. This angle is important inthe design of crushing rolls for clay; itshould not exceed about 18°.Angle Tile. A purpose-made clay orconcrete tile for use in an angle invertical exterior tiling.Angstrom Method. See THERMALDIFFUSIVITY.Angstrom Unit, A. lOnm, still met inX-ray crystallography.Angular. See MORPHOLOGY.Anhydrite. CaSO4; there are soluble andinsoluble forms. Anhydrite begins toform when gypsum is heated attemperatures above about 2000C. Thepresence of anhydrite in plaster used formaking pottery moulds can causeinconsistent blending times; the mouldstend to be soft, and to give slow casting,slow release of casts from the mould,and flabby casts.Anionic Exchange. See IONIC

EXCHANGE.Anisotropy. The state of havingproperties whose values differaccording to the direction ofmeasurement. This is quite frequentlymet in ceramics, and can arise from thebasic crystal structure (e.g. sheet-likecrystal structures with weaker,asymmetric forces between the layers,have much lower tensile strengthperpendicular to the sheet). On themicrostructural scale, directional formingprocesses such as uniaxial PRESSING(q.v) can make anisotropic suchproperties as strength and shrinkage.Anneal. To release stresses from glass bycontrolled heat treatment; the process isusually carried out in a LEHR (q.v.). Seealso ADAMS-WILLIAMSON ANNEALING

SCHEDULE; REDSTON-STANWORTHANNEALING SCHEDULE*, TREBUCHON-KIEFFER ANNEALING SCHEDULE.Annealing Point or AnnealingTemperature. The temperature at whichglass has a viscosity of 1013 poises; alsoknown as the 13.0 TEMPERATURE. Whenannealed at this temperature glassbecomes unstressed in a few minutes. Amethod of test by fibre elongation isgiven in ASTM - C336; C598 specifies abeam bending test.Annealing Range. The range oftemperature in which stresses can beremoved from a glass within areasonable time, and below which rapidtemperature changes do not causepermanent internal stress in the glass.When comparing glasses, the AnnealingRange is taken as the temperatureinterval between the ANNEALING POINT(q.v.) and the STRAIN POINT (q.v.).Annular Kiln. A large continuous kiln,rectangular in plan, of a type much usedin the firing of building bricks. Thebricks are set on the floor of the kiln andthe zone of high temperature is made totravel round the kiln by progressivelyadvancing the zone to which fuel is fed.There are two principal types:LONGITUDINAL-ARCH KILN (q.V.) andTRANSVERSE-ARCH KILN (q.V.)Annuliis Brick. A DOME BRICK with thelarge faces equally inclined to each otherin breadth and length, so that one endface is smaller than the other.Anode Pickling. See ELECTROLYTICPICKLING.Anorthite. See FELDSPAR.Anorthosite. A coarse-grained rockconsisting almost exclusively ofplagioclase (see under FELDSPAR). Itoccurs in Canada, New York State,Norway and Russia; trials have beenmade with this material as a flux inceramic bodies.

Antiferroelectric. A dielectric of highpermittivity which undergoes a change incrystal structure on cooling through aCURIE TEMPERATURE (q.V.) but whichpossesses no spontaneous polarisation.The state is visualised as polarisation ofadjacent lines of atoms in oppositedirections.Antiferromagnetic. A material in whichthe atomic magnetic moments arealigned antiparallel so that the totalmoment is zero and there is noobservable spontaneous magnetization.The alignment disappears at the CURIETEMPERATURE (q.v.). Antiparallelordering gives rise to anantiferromagnetic or to a ferrimagneticdepending on the crystal structure.Antimony Oxide. Sb2O3; m.p. 655°C; sp.gr. approx. 5.5. Used as an opacifier inenamels and as a decolorizing and finingagent in glass manufacture, particularlyin pot melting; in pottery manufacture itis a constituent of Naples Yellow.Antimony Yellow. See LEADANTIMONATE.

Antioch Process. Plaster moulds areproduced by pouring an aqueous plasterof Paris slip over a mould, steamtreating, allowing to set in the air andoven drying.Anti-piping Compound, HOT-TOPPINGCOMPOUND, (q.v).Antique Glass. Flat glass made by theCYLINDER PROCESS (q.v.) and withtextured surfaces resembling old glass; itis used in the making of stained-glasswindows (cf. CATHEDRAL GLASS).Anti-static Tiles. Floor tiles of a typethat will dissipate any electrostaticcharge and so minimize the danger ofsparking; such tiles are used in rooms,e.g. operating theatres, where there isflammable vapour. One such type ofceramic tile contains carbon. TheNational Fire Protection Association,

USA, stipulates that the resistance of aconductive floor shall be less than 1megohm as measured between twopoints 3 ft (1 m) apart; the resistance ofthe floor shall be over 25 000 ohmbetween a ground connection and anypoint on the surface of the floor orbetween two points 3 ft (1 m) apart onthe surface of the floor.A.P. US abbreviation for ANNEALINGPOINT (q.v.).Apatite. Calcium phosphate, CaPO4

though other negative ions (F, Cl, CO3

or OH) may be present in natural rocks.Apatite is a chief constituent of bone.Apatite and hydroxyapatite (containingthe OH- ion) are used in bioceramics,particularly if it is desired to achievebone intergrowth with the artificialcomponent or prosthesis.APGS. Advanced Plasma Gun Systemfor thermally sprayed coatings.Aplite. A rock mined in Virginia for usein glass manufacture; it consistsprincipally of albite, zoisite and sericite.Apparent Initial Softening. Whenapplied to the REFRACTORINESS-UNDER-LOAD TEST (q.v.), this term has thespecific meaning of the temperature atwhich the tangent to the curve relatingthe expansion/contraction and thetemperature departs from the horizontaland subsidence begins. (For typical curvesee Fig. 5, p230.)Apparent Porosity. See under POROSITY.Apparent Solid Density. A term usedwhen considering the density of a porousmaterial, e.g. a fireclay or silicarefractory. It is defined as the ratio ofthe mass of the material to its APPARENT

SOLID VOLUME (q.V.) (cf. TRUEDENSITY).Apparent Solid Volume. A term usedwhen considering the density andvolume of a porous solid, particularly arefractory brick. It is defined as the

volume of the solid material plus thevolume of any sealed pores and also ofthe open pores.Apparent Specific Gravity. For a porousceramic, the ratio of the mass to themass of a quantity of water that, at 4°C,has a volume equal to the APPARENTSOLID VOLUME (q.v.) of the material atthe temperature of measurement. ASTMC20 specifies a boiling water test; ASTMC830 a vacuum pressure test.Application Weight. The weight ofvitreous enamel coating applied, per unitarea covered.Applied Moment Double CantileverBeam. See FRACTURE TOUGHNESS

TESTS.

Apron. See under SAND SEAL.APS. Air plasma spraying - see PLASMASPRAYING.

AQL. Acceptance Quality Level. SeeACCEPTANCE TESTING.

Arabian Lustre. The original type of on-glaze lustre used by the Moors from the9th century onwards for the decorationof pottery; the sulphides or carbonates ofcopper and/or silver are used, the firing-on being in a reducing atmosphere sothat an extremely thin layer of the metalis formed on the glaze.Arbor. US term for the spindle of agrinding machine on which the abrasivewheel is mounted.Arc Furnace. See ELECTRIC FURNACE.Arc ion plating. Metal is evaporated andionised, then a reactive gas of non-metallic elements is introduced andreacted with the metal vapour at thesurface of a substrate, whereon aceramic film is formed. Usually thesubstrate is given a negative bias voltage.Arc-image Furnace. See IMAGE

FURNACE.

Arc-spraying. See PLASMA SPRAYING.Arch. In addition to its normal meaningthis term is sometimes applied to a

furnace roof. See also ARCH BRICK;ARCHING; POT ARCH.Arch Brick. A building brick or refractorybrick having the two large faces inclinedtowards each other. This may be done intwo ways: in an END ARCH (q.v.) one ofthe end faces is smaller than the oppositeend face; in a SIDE ARCH (q.v.) one of theside faces is smaller than the opposite sideface. Arch bricks are used in theconstruction of culverts, furnace roofs, etc.(See Fig. 1, p 15.)Arching. (1) The preheating of glass-potsbefore use. (2) The jamming of materialin a hopper or shaft furnace, an emptyspace being formed beneath the 'arch'thus produced.Architectural Glass. Glass used in theconstruction industry. ASTM C-724specifies Test Methods for AcidResistance of Ceramic Decorations onArchitectural Glass. Four drops of eachof 10% citric acid and nominal 3.7%HCl are placed on the glass surface for15 min, and acid attack assessed visuallyagainst a 7-point scale.Archless Kiln. Alternative name forscovE (q.v.).Argillaceous. Containing clay; clayey.(From French argile, clay).Argillite. A sedimentary rock rich in clayminerals; the term is now generallyapplied to thick-bedded clay rock thathas no distinct cleavage.Aridised Plaster. Plaster that has beentreated, while being heated in the'kettle', with a deliquescent salt, e.g.CaCl2; it is claimed that this produces astrong plaster having more uniformproperties.Ark. A large vat used in the potteryindustry for the mixing or storage of clayslip.Arkose. A rock of the sandstone typebut containing 10% or more of feldspar;it is formed by decomposition of granite.

Armour. Ceramic armour stopsprojectiles by absorbing their kineticenergy to generate cracks in the hard,brittle ceramic. Of light weightcompared to metal armour, ceramicssuch as boron carbide and alumina areuseful as body armour.Armouring. Metal protection for therefractory brickwork at the top of thestack of a blast furnace; its purpose is toprevent abrasion of the refractories bythe descending burden (i.e. the rawmaterials charged to the furnace).Arrest Line. A RIB MARK (q.v) definingthe crack front shape of an arrestedcrack, before the crack is spread againby a new stress.Arrhenius' Law. A logarithmicrelationship between reaction rate andtemperature which applies to creep,diffusion and solid state phasetransformations (among many otherchemical and physical reactions).

log V-A- q/kTwhere v is the reaction rate, A is aconstant, q is the activation energy, T isthe temperature and k is Boltzmann'sconstant. The activation energy is athreshold energy value which the systemmust have before the reaction can occur.Arris. The sharp edge of a building brickor ridge-tile; an ARRIS TILE is a speciallyshaped tile for use in the ridge or hip ofa roof. The ARRIS EDGE on glass is abevel up to 1/16 in. (1.5 mm) wide and atan angle of 45°.Arsenic Oxide. As2O3; sublimes at193°C; sp. gr. 3.87. Used as a fining anddecolorizing agent (particularly inassociation with selenium) in glassmanufacture.ASA. Prefix to specifications of theAmerican Standards Association, 70East 45th Street, New York 17.Artifical Porcelain. See SOFT PASTE

PORCELAIN.

Asbestine. A fibrous mineral consistingof mixed hydrated silicates of Mg andCa; it occurs in New York State.Asbestos. A fibrous, heat-resistantmineral, which may be formed intoboards or woven into fabric or paper.Formerly much used as a heat insulatingmaterial, the health hazard of ASBESTOSIShas led to its replacement by forms ofcalcium silicate board. There are twotypes of asbestos. Chrysotile is a hydratedmagnesium silicate, stable up to 500 0C. Itis used as a reinforcing fibre in asbestoscement, when mixed with water andPortland cement. Heat-resistant boards,sheets and pipes can be made, containingabout 10% asbestos. Relevant Britishstandards are BS486, 567, 690, 835, 3497,3656, 4624 and 5247. Amphiboles (e.g.tremolite, a hydrated calcium magnesiumsilicate, or crocidolite, a hydrated sodiumiron silicate) also known as blue asbestos,cause ASBESTOSIS. They are less strongthan chrysotile, though with higher elasticmoduli, and weaken markedly above 3000C. The Annual Book of ASTMstandards, VoI 4.05, lists some 50standards for asbestos fibre and asbestos-cement products and relevant testmethods.Asbestosis. A severe inflammatorydisease of the lungs, caused by inhalingamphibole (blue) asbestos.Asbolite. Impure cobalt ore used by theold Chinese potters to produceunderglaze blue.Ascera Method. A tensile testingtechnique using test pieces of simplegeometry and large test volume(cylinders 9 to 10 mm diameter, 120 mmlong). Non-tensile forces are minimisedby careful design of the gripping,alignment and force application devices.(ASEA Ceramica AB, Sweden).Ashfield Clay. A fireclay associated withthe Better Bed coal, Yorkshire, England.

The raw clay contains about 57% SiO2,27% Al2O3, 1.7% Fe2O3 and 1.5%alkalis.ASTM. American Society for Testingand Materials. This Society isresponsible for most of the Americanstandard specifications for ceramics.Address: 1916 Race St., Philadelphia 3,Pa., USA.Ashlar Brickwork. Clay brick orblockwork, made to resemble stoneworkby the size, arrangement and surfaceappearance of the units.Aspirating Screen. A vibrating SCREEN(q.v) through which the fines are drawnby suction.Astbury Model. A theoretical model todescribe the plasticity of clays, and inparticular their non-elliptical (exceptbentonite) hysteresis loops. The clay isrepresented as an arrangement of purelyelastic elements (springs) and purelyviscous elements (dashpots) with theproviso that as more energy is stored,the elastic elements break down and areconverted into viscous elements. (N.F.Astbury. Science of Ceramics ,Vol. 2,1965).Atomiser. A device to produce a finespray of small particles or liquiddroplets. In a SPRAY DRYER, theatomiser may be a nozzle, or a spinninghead which produces the spraycentrifugally.Atritor. Trade-name: a machine thatsimultaneously dries and pulverizes rawclay containing up to 18% moisture; itconsists of a feeder, metal separator,pulverizer, and fan. (Alfred HerbertLtd., Coventry, England.)Attaclay. See ATTAPULGITE.Attapulgite. One of the less commonclay minerals; it was first found atAttapulgus, USA, and is characterizedby a high (10%) MgO content. It has alarge surface area and is used in oil

refining, as a carrier for insecticides, etc.Also known as PALYGORSKITE (q.v.).Atterberg Test. A method fordetermining the plasticity of clay interms of the difference between thewater content when the clay is justcoherent (tested by rolling out the clayby hand) and when it begins to flow as aliquid; the difference is the AtterbergNumber. The test was first proposed byA. Atterberg (Tonindustr. Ztg., 35,1460,1911).Attributes. Qualitative characteristics ofproducts, whose presence or absence issubject to inspection to assess theacceptance quality level of a sample.(Inspection by variables involvesnumerical measurement) BS 1902 Pt 3.13relates to the attributive properties ofcorner, edge and surface defects inrefractories. See ACCEPTANCE TESTING.Attrition. Particle-size reduction by aprocess depending mainly on impactand/or a rubbing action.Attrition Mill. A disintegrator dependingchiefly on impact to reduce the particlesize of the charge. Attrition mills aresometimes used in the clay buildingmaterials industry to deal with thetailings from the edge-runner mill.Attritor. Tradename. A bead mill, madeby Torrance & Sons, Bristol.Aubergine Purple. A ceramic colour,containing Mn, introduced in the 18thcentury, when it was used for underglazedecoration.Auger. (1) An extruder for clay, or claybody, the column being forced throughthe die by rotation of a continuous screwon a central shaft. (2) A large'corkscrew' operated by hand or bymachine to take samples of soft material,e.g. clay, during prospecting.Autoclave. A strong, sealed, metalcontainer, fitted with a pressure gaugeand safety valve; water introduced into

the container can be boiled underpressure, the gauge pressure developedat various temperatures being as follows:Gauge pressure (p.s.i.): 0 25 50 100 150(0 175 350 700 1050 kPa)Temperature (0C): 100 130 148 170 186A common method of testing glazedceramic ware for crazing resistance is toexpose pieces of ware to the steam in anautoclave, at 50 p.s.i. in B.S. 3402 andB.S. 4034, or at 5-250 p.s.i. (increasingthe pressure in steps of 50 p.s.i.) inASTM - C424. The method isunsatisfactory because it confuses theeffects of moisture expansion (the primecause of crazing) and thermal shock. Anautoclave test is also sometimes used inthe testing of vitreous enamelware. Asapplied to the testing of portlandcement, the autoclave test revealsunsoundness resulting from the presenceof any MgO or CaO.Autocombustion System. Anelectronically controlled impulse systemfor the oil firing (from the top or side) ofceramic kilns.Autogenous Grinding Mill. In this typeof rotating cylinder mill, the onlygrinding medium is the incoming coarsefeed. (Autogenous = self-produced).Automation. The operation of processesunder automatic control (nowadaysusually by digital computer) withouthuman intervention. Older U.S.literature, especially that relating to thebrick industry, used the term whenmechanisation was meant - powerassistance without automatic control.Autosieve. An automatic sievefractionation system for particle sizeanalysis. Four sieves are mounted on theoutside of a hollow plastics cylinder, intowhich powder is fed through an axialpart. Cylinders are interchangeable, withdifferent sets of sieves. The finest sieve isat the bottom. Sieves are mechanically

oscillated and fluid jets blown throughthe sieves to fluidize the powder. Thefines are automatically weighed at eachoscillation of the sieves.Auxiliary Metal Bath Process. Moltenmetals act as solvents to promotereactions between inorganic materials toform powders of borides, carbides ornitrides. (Powder Metallurgy Int. 4, (4),191,1972).Autostic. A water-based, air-settingcement much used for small tasks suchas mounting thermocouple sheaths.(Tradename of Carlton, Brown &Partners, Sheffield).Aventurine. A decorative effectachieved on the surface of pottery orglass by the formation of small, bright,coloured crystals (generally hematite,Fe2O3, on pottery bodies, but chrome orcopper on glassware).Ayrshire Bauxitic Clay. A non-plasticfireclay formed by laterisation of basaltlava and occurring in the Millstone Gritof Ayrshire, Scotland; there are twotypes, the one formed in situ, the otherbeing a sedimentary deposit. Chemicalanalysis (per cent) (raw): SiO2 42; Al2O3

38; TiO2, 3-4; Fe2O3, 0.5; alkalis, 0.2.AZS Refractories. Alumina-zirconia-silica refractories, used in contact withthe molten glass in glassmaking. Theserefractories are fusion-cast for highdensity, low porosity, and resistance tocorrosion by ingress of molten glass.ASTM C1223 tests for glass exudationfrom AZS refractories, on heating to1510 0C.B25 Block. A hollow clay building block,25x30x13.5 cm, introduced by the Swissbrick industry in 1953. It is economicalto lay (22 blocks per m2), giving a wall25 cm thick with low thermaltransmittance.Babal Glass. Name for BariumBoro-Aluminate glass proposed by

M. Monneraye, J. Serindat and C.Jouwersma (Glass Techn., 6, (4), 132,1965).Babic's Mortar. A cement mortar madewater-repellant by incorporating anaqueous siliconate. (Build Trades J. 183(5439) 34 1982)Babosil. Trade-name: a frit forpottery glazes, so-named becauseit contains barium, boron and silica.It comprises:

0.06 K2O 0.125 Al2O3 0.43 BaO0.50 Na2O 0.68 B2O3 2.45 SiO2

Backbone. A system of polystyrenebacking for brick panels. (UnitedResearch & Development Corp, andBASF).Backface Wear. Abrasion of the rearface of a refractory by differentialmovement between it and a rotating orflexing structure, e.g. in a rotary cementkiln.Back Heat. In an annular kiln, thetemperature in the furthest back of thechambers being fired; sometimes theterm is extended to include the hottest ofthe chambers being cooled.Back Ring. See HOLDING RING.Back Stamp. The maker's name and/ortrademark stamped on the back ofpottery flatware or under the foot ofhollow-ware.Backing. The common brickwork behindfacing bricks in a brick building, or low-duty refractories or heat insulationbehind the working face of a furnace.Backing Strip. A strip of metal welded tothe back of a metal panel prior to itsbeing enamelled; the purpose is toprevent warping.Bacor; Bakor. A Russian corundum-zirconia refractory for use moreparticularly in the glass industry; thename is derived from BADDELEYITE(q.v.) and CORUNDUM (q.v.). There are

various grades, e.g. BAKOR-20 (62%Al2O3,18% ZrO2, 16% SiO2) andBAKOR-33 (50% Al2O3, 30% ZrO2,15%SiO2).Baddeleyite. Natural zirconia, ZrO2;there are deposits of economicimportance in Australia, Brazil andRussia.Badging. The application, usually bytransfer or silk-screen, of crests, trademarks, etc. to pottery or glass-ware (cf.BACK STAMP).Baffles. Thin detachable batts, placedvertically around the edge of a kiln caras a shield, held in place by small wedgesknown as baffle pegs.Baffle Mark. A fault that may occur on aglass bottle as a mark or seam caused bythe joint between the blank mould andthe baffle plate.Baffle Wall. See SHADOW WALL.Bag Wall. A wall of refractorybrickwork built inside a downdraughtkiln around a firebox, each fireboxhaving its own bag wall. The purpose isto direct the hot gases towards the roofof the kiln and to prevent the flamesfrom impinging directly on the setting(cf. FLASH WALL).Bain Deformation. The conversion ofone crystal lattice into another by asimple expansion or contraction alongthe orthogonal axes. A MARTENSITICTRANSFORMATION (q.v.) can bedescribed by a Bain deformationcombined with a lattice-invariantdeformation (one which does not changethe crystal structure) to produce anundistorted plane; the transformed(product phase) lattice is then rotated tocoincide with the present lattice alongthe habit plane.Bait. (1) A tool used in the glassindustry- it is dipped into the moltenglass in a tank furnace to start thedrawing process.

(2) To shovel solid fuel into the fireboxof a kiln.Bakor. See BACOR.Balance; Balancing. A grinding wheel issaid to be in STATIC BALANCE if it willremain at rest, in any position, when it ismounted on a frictionless, horizontalspindle; such a wheel is also in DYNAMICBALANCE if, when rotated, there is nowhip or vibration. The process of testingfor balance, and the making of anynecessary adjustment to the wheel, isknown as BALANCING.Baldosin Catalan. A Spanish type ofextruded ceramic floor tile.Ball Clay. A sedimentary kaolinitic claythat fires to a white colour and which,because of its very fine particle size, ishighly plastic. The name is derived fromthe original method of winning in whichthe clay was cut into balls, each weighingabout 15kg. As dug, ball clays are oftenblue or black owing to their high contentof carbonaceous matter. In England, ballclays occur in Devon and Dorset; inUSA, they are found in Kentucky andTennessee. Ball clays are incorporated inceramic bodies to give them plasticityduring shaping and to induce vitrificationduring firing. In addition to their use inmost pottery bodies and as suspendingagents for vitreous enamels, ball claysare used to bond nonplastic refractoriessuch as sillimanite. Current consumptionis about 400 000 tons in USA and 100000 tons in Britain.Ball-in-hand Test. A ball of mixedcastable refractory, shaped by hand, isallowed to fall from a specified heightand caught in the open fingers of thehand. The consistency is judged with theaid of photographs. The test is specifiedin ASTM C-860 and in BS 1902 Pt. 7.3.Ball Mill. A fine-grinding unit of a typemuch used in the pottery, vitreousenamel, and refractories industries. It

consists of a steel cylinder or truncatedcone that can be rotated about itshorizontal axis (see CRITICAL SPEED);the material to be ground is charged tothe mill together with alloy-steel balls,pebbles, or specially made ceramicgrinding media (generally high-alumina).The mill may be operated dry or wet;wet ball-milling is usually a batch processbut dry ball-milling may be continuous,the 'fines' being removed by an aircurrent (AIR-SWEPT BALL MILL).Ball Test. See KELLY BALL TEST.Balling. (1) The tendency of someceramic materials or batches, whenmoist, to aggregate into small balls whenbeing mixed in a machine.(2) One method of shaping potteryhollow-ware in a JOLLEY (q.v.); a ball ofthe prepared body is placed in thebottom of the plaster mould and is then'run up' the sides of the mould as itrotates.Ballotini. Transparent glass spheres lessthan about 1.5 mm diameter; presumablya derivative of the Italian ballotta, asmall ball used for balloting.Baltride. Tradename. A coating ofTITANIUM NITRIDE (q.v.) applied,especially to twist drills, by plasmavapour deposition. (Balzer's HighVacuum Co).Bamboo Tile. A term used in Africa andAsia for SPANISH TILE (q.v.) on accountof their resemblance, when placed inposition, to a roof of split bamboo.Bamboo Ware. A bamboo-like type ofCANE WARE (q.v.), somewhat dark incolour, first made by Josiah Wedgwoodin 1770.Banbury Mixer. A heavy-duty mixer forviscous pastes, with a pair of counter-rotating rotors.Banding. The application, by hand or bymachine, of a band of colour to the edgeof a plate or cup.

Band Theory of Solids. The outerelectrons of the atoms in a crystal latticebehave as though unbound, but subjectto a periodic electrical potentialcorresponding to the lattice spacing.Their possible energies fall into bands ofallowed and forbidden states. See alsoELECTRICAL CONDUCTIVITY.

Bank Kiln. A primitive type of potterykiln used in the Far East; it is built on abank, or slope, which serves as achimney.Banks. The sloping parts between thehearth of an open-hearth steel furnaceand the back and front walls. They wereconstructed of refractory bricks coveredwith fritted sand (Acid O.H. Furnace) orburned-in magnesite or dolomite (BasicO.H. Furnace), cf. BREASTS.Bannering. Truing the rim of a saggar(before it is fired) by means of flat metalor a wooden board, to ensure that therim lies in one horizontal plane and willin consequence carry the load ofsuperimposed saggars uniformly.Bansen. A unit of gas permeabilityexpressed in [(m3/h.).cm]/ [m2(mm waterpressure)] (H. Bansen, Arch.Eisenhuttenw. 1, 667, 1927-28).Baraboo Quartzite. A quartzite ofthe Devil's Lake region of Wisconsin,USA, used in silica brick manufacture.A quoted analysis is (per cent): SiO2,98.2; Al2O3, 1.1; Fe2O3, 0.2; Na2O +K2O, 0.1.Barbotine. French word for SLIP (q.v.).Barelattograph. A French instrument forthe automatic recording of thecontraction and loss in weight of a claybody during drying under controlledconditions; (for description see Bull Soc.Franc. Ceram. No. 40, 67, 1958).Barium Boride. BaB6; m.p., 22700C; sp.gr., 4.32; thermal expansion, 6.5 x 10-6;electrical resistivity (200C), 306jLiohm.cm.

Barium Carbonate. BaCO3; decomposesat 14500C; sp. gr. 4.4. Occurs naturally inDurham, England, as witherite. Theprincipal use in the ceramic industry ofthe raw material is for the prevention ofefflorescence on brickwork; for thispurpose it is added to brick-clayscontaining soluble sulphates. The purematerial is used in the manufacture ofbarium ferrite permanent magnets, andin some ceramic dielectrics to give lowerdielectric loss. In the glass industry thiscompound is used in optical glass andtelevision tubes; it is also used in someenamel batches.Barium Chloride. BaCl2 a solublecompound sometimes used to replaceCaCl2 as a mill-addition in themanufacture of acid-resisting vitreousenamels. It also helps to preventscumming. Poisonous.Barium Osumilite. A glass-ceramicformulation BaMg2Al3(Si9Al3O30)patented by J. J. Brennan et al (U.S. Pat4589900,1986, used as the foundationmaterial for composites.Barium Oxide. BaO; m.p. 19200C; sp. gr.5.72.Barium Stannate. BaSnO3; it issometimes added to barium titanatebodies to decrease the Curietemperature. An electroceramiccontaining approx. 90 mol% BaTiO3 and10 mol%, BaSnO3 has a very highdielectric constant (8000-12000 at 200C).Barium Sulphate. BaSO4; m.p. 15800C;sp. gr. 4.45.Barium Titanate. BaTiO3; m.p. 1618°GMade by heating a mixture of bariumcarbonate and titania at 1300-13500C.Because of its high dielectric constant(1350-1600 at 1 MHz and 25°C) and itspiezoelectric and ferroelectric properties,it finds use in electronic components; itsCurie temperature is 120-1400C. Theproperties can be altered by the

formation of solid solutions with otherferroelectrics having the perovskitestructure, or by varying the BaOiTiO2

ratio on one or other side of thestoichiometric.Barium Zirconate. BaZrO3; m.p. 2620 C;sp. gr. 2.63. Synthesized from bariumcarbonate and zirconia and used as anaddition (generally 8-10%) to bariumtitanate bodies to obtain high dielectricconstant (3000-7000) and other specialproperties.Barker-Truog Process. A processdescribed by G. J. Barker andE. Truog (/. Amer. Ceram. Soc,21, 324, 1938; 22, 308, 1939; 24, 317,1941) for the treatment of brickmakingclays with alkali, this being claimed tofacilitate shaping and to reduce theamount of water necessary to giveoptimum plasticity. According to theirpatent (US Pat. 2 247 467) the clay ismixed with alkali to give pH 7-9 if itwas originally acid, or pH 8-10 iforiginally non-acid; it is also stipulatedthat the total amount of alkali addedshall be limited by the slope of thecurve relating the pH to the quantity ofalkali added, this slope being reduced tohalf its original value. The alkali isusually added as soda ash (Na2CO3)and the amount commonly required isabout 0.2%.Bar Kiln, Bar Dryer. A pre-fabricated,steel-cased tunnel kiln for the rapidfiring of heavy clay products is combinedin a two-storey arrangement with a rapiddryer in which the ware is set on thesame kiln cars as are used for firing.(Occidental Industries, Paris).Barratt-Halsall Firemouth. A design fora stoker-fired firemouth for a potteryBOTTLE OVEN (q.v.); a subsidiary fluesystem links all the firemouths aroundthe oven wall to assist in temperatureequalization. The design was patented by

W. G. Barratt and J. Y. M. Halsall (Brit.Pat. 566 838; 16/1/45). Also known as theGATER HALL DEVICE because it was firstused at the factory of Gater, Hall & Co.,Stoke-on-Trent, where J. Y. M. Halsallwas General Manager and which was atthe time associated with the Barrattpottery.Barrelling. The removal of surfaceexcrescences and the general cleaning ofmetal castings by placing them in arevolving drum, or barrel, together withcoarsely crushed abrasive material suchas broken biscuit-fired ceramic ware (cf.RUMBLING).Barton Clay. A clay of the Eoceneperiod used for brickmaking near thecoast of Hampshire and in the Isle ofWight.Barytes. Naturally occurring BARIUMSULPHATE (q.v.) It is the principalsource of BARIUM CARBONATE (q.v.)but is also used to some extent in thenatural state in glass manufacture.Basalt Ware. A type of ceramic artwareintroduced in 1768 by Josiah Wedgwoodand still made by the firm that hefounded. The body is black and vitreous,iron oxide and manganese dioxide beingadded to achieve this; a quotedcomposition is 47% ball clay, 3% chinaclay, 40% ironstone and 10% MnO2.The ware has something of theappearance of polished basalt rock (cf.FUSION-CAST BASALT).

Base Coat. A fired coating over whichanother coating is applied. See GROUND-C O A T ; ENGOBE.Base Code. Alternative name for PUNTCODE (q.v.).Base Exchange. See IONIC EXCHANGE.Base Metal. (1) In the phrase'base-metal thermocouple, this termsignifies such metals and alloys ascopper, constantan, nickel, tungsten,etc.

(2) In the vitreous-enamel industry, theterm means the metal (steel or cast iron)to which the enamel is applied.Basic Fibre. Glass fibres before theyhave been processed. A number of fibresmay subsequently be bonded together toform a strand.Basic Open-hearth Furnace. An OPEN-HEARTH FURNACE (q.v.) used in therefining of basic pig-iron. The hearth isbuilt of basic refractory bricks coveredwith burned dolomite or magnesite.Basic Oxygen Steelmalring. Variousrelated processes in which oxygen isblown into the molten iron bath by aretractable refractory lance. The vesselsare lined with basic refractories, andlime may also be injected through thelance. The BOS, BOF or LD/AC processis top-blown, in that the oxygen isintroduced from above. The Q-BOP(quiet or quick BOP) or OBM (oxygenbottom Maxhuette) process is bottom-blown through a nozzle in the lowerlining, which shrouds the oxygen with aconcentric jet of hydrocarbons to protectthe lining. See L-D PROCESS.Basic Refractory. A general term forthose types of refractory material thatcontain a high proportion of MgO and/orCaO, i.e. oxides that at hightemperatures behave chemically asbases. The term includes refractoriessuch as magnesite, chrome-magnesite,dolomite, etc.Basket-weave Checkers, CHECKERS(q.v.) built to form continuous verticalflues.Basse-taille. Vitreous enamelled artwarein which a pattern is first cut in low reliefon the metal backing, usually silver; thehollows are then filled with translucentenamel, which is subsequently fired on.Basset Process. For the simultaneousproduction of hydraulic cement and pig-iron by the treatment, in a rotary kiln, of

a mixture of limestone, coke, and ironore. (L. P. Basset, French Pat. 766 970,7/7/34; 814 902, 2/7/37.)Bastard Ganister. A silica rock havingmany of the superficial characters of atrue GANISTER (q.v.) such as colour andthe impression of rootlets, but differingfrom it in essential details, e.g. anincreased proportion of interstitialmatter, variable texture, and incompletesecondary silicification.Bat. (1) A refractory tile or slab as used,for example, to support pottery-warewhile it is being fired.(2) A slab of plaster used for variouspurposes in the pottery industry.(3) A roughly shaped disk of potterybody - as prepared on a batting-outmachine prior to the jiggering offlatware, for example.(4) A short building brick, either madeas such or cut from a whole brick.(5) In USA, a piece of brick that hasbeen broken off.Bat Printing. A former method ofdecorating pottery; it was first used, inStoke-on-Trent, by W. Baddeley in 1777.A bat of solid glue or gelatine was usedto transfer the pattern, in oil, from anengraved copper plate to the glazedware, colour then being dusted on. Theprocess was still in use in 1890 and hasnow been developed into the MURRAY-

CURVEX MACHINE (q.V.).Batch. A proportioned mixture ofmaterials. The term is used in mostbranches of the ceramic industry; inglass-making, the batch is the mixture ofmaterials charged into the furnace.Batch-type Mixer. See MIXER.Ban. See BAT.Batdorf Theory. A theory of brittlefracture which assumes random flaworientation and a consistent crackgeometry, proposing that reliabilitypredictions should be based on linear

elastic fracture mechanics combinedwith the weakest link theory. SeeFRACTURE MECHANICS. (S. B. Batdorfand J. G. Crose. J Appl.Mech 41 (1974)p459).Batt Wash. See REFRACTORY COATING.Batter. In brickwork, the name given toan inclined wall surface or to the angleof such a surface to the vertical.Battery. Term applied to the largerefractory structure in which coke isproduced in a series of adjacent ovens(cf. BENCH).Battery Casting. A system of mechanisedhandling, tilting and automatic filling ofthe heavy plaster moulds used to slip-cast sanitaryware. Several moulds aregrouped together in a 'battery' andhandled as one unit. The sytem wasinvented by Shanks Ltd of Glasgow(Br.Pat. ), and developed by theArmitage-Shanks Group.Battery Top Paving. Refractorybrickwork, cast blockwork or castrefractory concrete laid or placed on thetop of a coke-oven BATTERY.Batting Out. The process of making adisk of prepared pottery body forsubsequent shaping in a JIGGER

(q.v.).Battledore. A tool used in the hand-made glass industry for shaping the footof a wine glass; also known as aPALLETTE.Baudran Expansion Apparatus. A devicefor measuring the thermal expansion ofceramics up to 15000C; expansion of thetest-piece is directly transmitted by alever system to an inductivedisplacement detector. This procedure isused for testing refractories (B.S. 1902,Pt. IA); it was devised by A. Baudran(Bull Soc. Franc. Ceram. (27), 13, 1955).Baume Degrees (°Be). A system,introduced by a Frenchman, A. Baume,in 1768 for designating the specific

gravity of liquids. There are two scales,one for liquids lighter than water andone for heavier liquids; only the latter isnormally of interest in the ceramicindustry, where it is sometimes used indescribing the strength of sodium silicatesolutions. The precise equivalencebetween the Baume scale and thespecific gravity is in some doubt but thefollowing conversion factor has beenstandardized in USA and may begenerally accepted:

sp. gr. = 145/(145-°Be)Bauxite. A mineral containing a highproportion of aluminium hydroxides,formed by weathering in tropicalclimates. Its principal sources areAustralia, Brazil, France, FrenchGuinea, Guyana, Hungary, Jamaica,Surinam, Russia and former Yugoslavia.It is purified in the BAYER PROCESS(q.v.) to produce calcined alumina usedin the abrasives, electroceramics,refractories and other branches of theceramics industry.Bauxitland Cement. See KUHL CEMENT.Bayer Process. A process for theextraction of alumina from bauxite,invented by K. J. Bayer in 1888. Thebauxite is digested with hot NaOH andthe Al2O3 is then extracted as the solublealuminate. Because of this method ofextraction, the calcined alumina used inthe ceramic industry usually containssmall quantities of Na2O.Bayerite. A trihydrate of alumina,Al2O3.3H2O, named after K. J. Bayer,originator of the BAYER PROCESS, (q.v.);however, the trihydrate formed in thisprocess is GIBBSITE (q.v).BDKG. Berichte der DeutschenKeramische Gesellschaft.Bead. (1) Any raised section roundglass-ware.(2) A small piece of glass or ceramictubing surrounding a wire.

Beading. (1) The application of vitreousenamel slip, usually coloured, to theedge of enamelware.(2) Removal of excess vitreous enamelslip from the edges of dipped ware.Bead Test. The softening and flowcharacteristics of a glass are assessed bycomparing the bahaviour of a bead ofspecified size and shape with beads ofstandard compositions.Bear. See SALAMANDER

Bearer Arch. See RIDER BRICKS.

Bed Alternative name for a SETTING

(q.v.) of gas retorts.Bed Joint. A horizontal joint inbrickwork.Bedder. A plaster shape conforming tothat of the ware to be fired and used toform the bed of powdered alumina onwhich bone china is fired.Bedding. (1) The placing of potteryflatware on a bed of refractory powder,e.g. silica sand or calcined alumina, toprovide uniform support during thefiring process, thus preventing warpage.(2) The compacted base (of gravel orother material) on which sewer pipes arelaid and supported. ASTM C896. TheClay Pipe Development Association, UKhas published tables relating to beddingand loads on vitrified clay pipes.Beehive Kiln. See ROUND KILN.

Beer-Lambert Law. = LAMBERT'S LAW

(q.v.).Beidellite. A clay mineral first found atBeidell, Colorado, USA; it is an Al-richmember of the montmorillonite group.Belfast Sink. A domestic or industrialsink with an overflow and with its topedge plain; cf. EDINBURGH SINK andLONDON SINK.

Belgian Kiln. A type of annular kilnpatented by a Belgian, D. Enghiens(Brit.Pats.18281,1891; 22008,1894;7914,1895). It is a longitudinal-arch kilnwith grates at regular intervals in the kiln

bottom; it is side-fired on to the grates.Such kilns have been popular for thefiring of fireclay refractories at 1200-13000CBelite. The name given to one of thecrystalline constituents of portlandcement clinker by A. E. Tornebohm(Tonindustr. Ztg., 21,1148,1897). Thismineral has since been identified as oneform of 2CaO-SiO2.Bell. The socket of a sewer pipe, intowhich the SPIGOT fits. See also TRUMPET.

Bellarmine. A fat, salt-glazed bottle orjug, usually decorated with a beardedface stamped on the narrow neck.Bell Damper. A damper of the sand-seal type, and bell-shaped. Suchdampers are used, for example, inannular kilns.Belleek Ware. A distinctive type ofpottery made at Belleek, CountyFermanagh, Northern Ireland. Thefactory was established in 1857 and theware is characterized by its thinness andslightly iridescent surface; the bodycontains a significant proportion of frit.Bell Kiln. See TOP HAT KILN.

Bench Paving. Brickwork on the topsurfaces of coke oven side benches, toresist coke spillage, heat and abrasion.Belly. (1) The part of a blast furnacewhere the cross-section is greatest,between the STACK (q.v.) and the BOSH

(q.v.); this part of a blast furnace is alsoknown as the WAIST.

(2) The part of a converter in which therefined steel collects when the converteris tilted before the steel is poured.Bender Abrasion Method. The ConcreteMasonry Association of Australia testfor ABRASION RESISTANCE (q.v.) basedon the test developed by Perth CityCouncil, derived from ASTM C779-82.The abrasion index Ia is given byIa = (number of thousands ofrevolutions)V2/depth of penetration.

Steel ball bearings are driven at constantload across the surface and the depth ofpenetration measured.Belshazzar. A 16-quart wine bottle.Belt Kiln. A tunnel kiln through whichware is carried on an endless belt madeof a wire-mesh woven from heat-resisting alloy. Such belts, if slightlyoverheated, can leave belt marks on theware, a common fault with glasswarefrom the lehr. In the pottery industrysuch kilns have found some use for glostand decorating-firing.Bench. (1) A series of chamber ovens orgas retorts built of refractory bricks toform a continuous structure.(2) The floor of a pot furnace for makingglass.(3) A clay pit, if beyond a certain depth,may be worked in a a series of horizontallayers, known as Benches: these maycoincide with different strata in theworking face.Bend Test. See MODULUS OF RUPTURE.Beneficiation. US term for any process,or combination of processes, forincreasing the concentration of a mineralin an ore; the term is now replacing theolder term 'mineral dressing' in the UK.An example of beneficiation in theceramic industry is the treatment ofcertain pegmatites to produce aSPODUMENE (q.v.) concentrate.Bent Glass, FLAT GLASS (q.v.) which hasbeen reshaped when hot.Bentonite. A natural clay, named fromFort Benton, USA, where it was firstfound. It consists chiefly ofMONTMORILLONITE (q.v.). It occurs astwo varieties - sodium bentonite andcalcium bentonite; the former swells veryconsiderably when it takes up water. Theprincipal source is USA: Westernbentonite (the Na variety from theWyoming area) and Southern bentonite(the Ca variety from the Mississippi

area). The particle size of bentonite is allless than 0.5|im; It has remarkablebonding properties and is used as abinder for non-plastics, particularly forfoundry sands.Bentonite Number. A measure ofsedimentation resistance, expressed interms of the heights of clear and turbidportions of the liquid column, and itsoverall density. A sharp boundarybetween the suspension and the clearliquid is formed by adding bentonite.(Glass Ceram. 39 (5) 224 1983).Berg Method. See DIVER METHOD.Berkeley Clay. A plastic, refractorykaolin from S. Carolina; P.C.E.34.Berkovich Indenter. A 3-faced diamondpyramid for indentation hardness tests.A sharper tip can be maintainedcompared to the 4-faced Vickerspyramid indenter.Berl Saddle. A chemical stonewareshape for the packing of absorptiontowers; it is saddle-shaped, size about25mm, and approx. 60000 pieces arerequired per m3. A packing of BerlSaddles provides a very large contactsurface and is a most efficient type ofceramic packing. (Patented in Germanyby E. Beri 1928).Berlin Porcelain. Porcelain, particularlylaboratory porcelain, made at the BerlinState Porcelain Factory. A quoted bodycomposition is 77% purified Halle clayand 23% Norwegian feldspar, all finerthan 10mm. The ware is fired at 10000Cand is then glazed and refired at 14000C.Bernitz Blocks. Perforated refractoryblocks designed for the passage of airand steam in water-gas plant.Berry Machine. See SOFT MUD

PROCESS.

Beryl. 3BeO.Al2O3.6SiO2; this mineralis the only economic source of berylliumoxide and other beryllium compounds. Itoccurs in Brazil, South Africa, India, and

Madagascar. Beryl has a low, butanisotropic, thermal expansion.BeryIIia. See BERYLLIUM OXIDE.Beryllides. A group of intermetalliccompounds of potential interest asspecial ceramics. Cell dimensions andtypes of structure have been reported forthe beryllides of Ti, V, Cr, Zr, Nb, Mo,Hf and Ta (A. Zalkin el ai, Acta Cryst,14, 63,1961).Berylliosis. A serious lung diseaseacquired by exposure to very smallquantities of the dust of beryllia or otherberyllium compounds. It may take manyyears to reveal itself.Beryllium Carbide. Be2C; decomposes at21000C with volatilization of Be; sp. gr.approx. 2; Knoop hardness (25-g load)2740; thermal expansion (25-8000C),10.5 x 10-6. This refractory carbide isslowly attacked by water at roomtemperature and by O2 and N2 at10000C. It has been used as a moderatorin nuclear engineering.Beryllium Nitride. Be3N2; m.p. 22000Cbut oxidizes in air when heated to above6000C. There are two forms: cubic andhexagonal.Beryllium Oxide or Beryllia. BeO; m.p.approx. 25300C; sp. gr. 3.02. A specialrefractory oxide notable for itsabnormally high thermal conductivity (1.4W/mK at 600C) and mechanical strength(crushing strength 1.5 GN/m2; transversestrength, 200 MN/m2 tensile strength 100MN/m2-all at 200C). Thermal expansion(20-10000C), 9 x 1(H. Thermal-shockresistance is good. Electrical properties:Volume resistivity (3000C) 1013-1015

ohm-cm; dielectric constant (IMHz) 6-7;power factor (1 MHz) 6.5 x ICH. ASTMF356 relates to its electrical and electronicapplications. It acts as a moderator forfast neutrons and is used for this purposein nuclear reactors; it is also sometimesused as a constituent of special porcelains.

Instruments have been mounted on BeOblocks in space-craft. Berylliumcompounds are toxic.Bessemer Converter. See CONVERTER.Best Gold. See BURNISH GOLD.Besto wing. The cover of fired bricks(usually three courses) for the setting ofa CLAMP (q.v.).Beta-Alumina, (p-alumina) Thecompound Na2O-IlAl2O3. It hasapplications as a solid electrolyte.Bethel-Bagnall Nozzle. A compositerefractory nozzle designed to give aconstant teeming rate in the casting ofsteel. A nozzle having the diameterrequired for the latter part of theteeming is fitted in the ladle well, and asecondary nozzle of smaller diameter isthen fitted below the primary nozzle; thenozzle of smaller diameter is removedwhen the ladle has been partly emptied.(H. A. Bethel and F. T. Bagnall, BritPat, 549 212, 11/11/42).B.E.T. Method. See BRUNAUER,

EMMETT and TELLER METHOD.Better Bed Fireclay. A siliceous fireclayoccurring under the Better Bed Coal ofthe Leeds area, England.Bevel Brick. A brick having one edgereplaced by a bevel (see Fig. 1, p39).Bevelled. Cut at an angle. Flat glass isgiven bevelled edges for aesthetic effect,especially on mirrors. Bevelled bricks areso made to fit corners, or to enhance theappearance of the top of a wall. Bevelledpipes have angled ends to fitcomplementary ends or othercomponents at an angle.BG-sign. A sign that the slip resistanceof a surface has been tested by theBerufsgenossenschaftliche Institut ftirArbeitssicherheit. The sign isaccompanied by a classification of theopen voids and the slip resistance.BHN. BRINELL HARDNESS (q.V.)NUMBER.

BI. Bridge Indentation. See FRACTURETOUGHNESS TESTS.Bicheroux Process. A method developedin 1918 by Max Bicheroux, of Aachen,for the production of plate glass; moltenglass from a pot is cast between rollers.Bidet. A low ceramic bowl speciallydesigned for washing the private parts.BS5505 provides a specification.Bierbaum Scratch Hardness. A diamondpoint is drawn across the surface to bemeasured, under a specified pressure,and the scratch width is measured with atravelling microscope.Bigot Curve. Drying shrinkage curvesfor clays which correlate lineal shrinkagewith water loss in air-drying to 1100C.Plasticity figures are derived bymultiplying the shrinkage by the ratio ofweights of water of plasticity to totalwater absorbed. (A. Bigot, ComptesRendues, 172, 755,1921).Binder. A substance added to a ceramicraw material of low plasticity to facilitateits shaping and to give the shaped waresufficient strength to be handled;materials commonly used for thispurpose include sulphite lye, sodiumsilicate, molasses, dextrin, starch,gelatine, etc. The term BOND (q.v.) isalso sometimes used in this sense but isbetter reserved to denote theintergranular material that gives strengthto the fired ware.Bingham Body or Bingham Material. Amaterial that behaves elastically up to ayield stress but at higher stressesdeforms at a rate proportional to thestress in excess of the yield value.(Named after E. C. Bingham; seeBINGHAM PLASTOMETER).Bingham Plastometer. A device for themeasurement of the rheologicalproperties of clay slips by forcing the slipthrough a capillary under variouspressures; a curve is drawn relating the

rate of flow to the pressure. E. C.Bingham, Proc. A.S.T.M., 19, Pt.2,1919;20, Pt. 2, 1920.)Bioceramics. Ceramics used inbiomedical applications. The chiefapplications are as DENTAL CERAMICS(q.v.) and PROSTHESES (q.v.). Aluminaand synthetic apatite or hydroxyapatiteare the most frequently used forprostheses, which must be compatiblewith body fluids.Bioglass. Registered Tradename ofUniversity of Florida for a series ofbioactive glasses.Bioglass-Ceramics. Glass-ceramics (q.v.)usually based on calcium phosphates,used in biomedical applicationsBiomimetic Process. The gradualincorporation into the body, by a naturalprocess, of a synthetic materialmimicking a natural material. Forexample, the gradual intergrowth ofbone material into synthetic poroushydroxyapatite prostheses.Biot Number. The heat-transfer ratiohr/k, where h is the heat transfercoefficient, r is the distance from thepoint or plane under consideration to thesurface, and k is the thermalconductivity. The Biot Number is auseful criterion in assessing thermal-shock resistance. (M. A. Biot, Phil. Mag.,19, 540,1935.)Biotite. A mica containing appreciableamounts of iron and magnesium; itsometimes occurs as an impurity in suchceramic raw materials as feldspar andnepheline syenite.Bird's Beak. A special type of wall tile(see Fig. 7, p350).Birdcage. An imperfection occasionallyoccurring in bottle manufacture, a glassthread (or threads) spanning the insideof the bottle.Birefringence. Double refraction, withthe formation of two images through a

crystal such as calcite, which hasdifferent refractive indexes for the twoplanes of polarization of the incidentlight. The greater this difference, thegreater the birefringence, or separationof the images. BS 7604 specifies two tests(Pt. Ia tensile test; Pt.2 a bending test)for determining the stress opticalcoefficient of glass, allowing stresses tobe computed from birefringencemeasurements.Biscuit. (1) Pottery that has been firedbut not yet glazed. Biscuit earthenwareis porous and readily absorbs water;vitreous ware and bone china are almostnon-porous even in the biscuit state.(2) In the vitreous-enamel industry, thedried (but still unfired) coating ofenamel slip.Biscuit Firing. The process of kiln firingpotteryware before it has been glazed.Earthenware is biscuit-fired at 1100-11500C; bone china is biscuit-fired at1200-12500C.Bismuth Oxide. Bi2O3; m.p. 825°C; sp.gr. approx. 8.5. Four crystalline formsexist.Bismuth Stannate. Bi2(SnO3)3:sometimes added to barium titanatebodies to modify their dielectricproperties; particularly to producebodies having an intermediate dielectricconstant (1000-1250) with a negligibletemperature coefficient.Bismuth Telluride. Bi2Te3; m.p. 585°C.A semiconductor that has found someuse as a thermoelectric material.Bisque. The older form, still preferred inUSA, of the term BISCUIT (q.v.).Bit Gatherer. The man whose job is togather small quantities of glass for use indecorating hand-blown glass-ware.Bitstone. Broken pitchers or calcinedflints (in either case crushed to about25mm) formerly used in the bottom of asaggar for glost firing to prevent sticking.

Black Ash. This term has been appliedto crude barium sulphide, which hasbeen used as a substitute for bariumcarbonate as an additive to clay toprevent scumming.Black Body. As applied to heatradiation, this term signifies that thesurface in question emits radiant energyat each wavelength at the maximum ratepossible for the temperature of thesurface, and at the same time absorbs allincident radiation. Only when a surfaceis a Black Body can its temperature bemeasured accurately by means of anoptical pyrometer.Black Core or Black Heart. Mostfireclays and brick-clays containcarbonaceous matter; if a brickshaped from such clays is fired toorapidly, this carbonaceous matter willnot be burned out before vitrificationbegins. The presence of carbon and theconsequent reduced state of any ironcompounds in the centre of the firedbrick result in a 'Black Core' or 'BlackHeart'.Black Edging. A black vitreous enamelapplied over the GROUND-COAT (q.v.)and subsequently exposed, as an edging,by brushing away the COVER-COAT(q.v.) before the ware is fired.Black Speck. A fault, in glass,particularly in the form of a smallinclusion of chrome ore. On pottery-ware the fault is generally caused bysmall particles of iron or its compounds.In vitreous enamelware also, the fault iscaused by contamination.Black Silica. A carbonaceous silica ashproduced by the controlled incinerationof rice husks (q.v.)Blackboard Enamel. A slightly rough,matt vitreous enamel which will acceptwriting in chalk.Blade. A section of a setting in a batchkiln.

Blaes. A Scottish name for carbonaceousshales, of a blue-grey colour, associatedin the Lothians with oil-shales butdiffering from these in having a muchlower proportion of bituminous matter,in being brittle rather than tough, and inproducing when weathered a crumblingmass which, when wetted, is plastic.Blaine Test. A method for theevaluation of the fineness of a powder onthe basis of the permeability to air of acompact prepared under specifiedconditions. The method was proposed byR. L. Blaine (Bull A.S.T.M., (123), 51,1943) and is chiefly used in testing thefineness of portland cement. Theequipment is essentially the same asRIGDEN'S APPARATUS (q.v.).Blake's Profiles. Auxilary tools to ensureaccurate brickwork.Blake-type Jaw Crusher. A jaw crusherinvented by E. W. Blake in 1858. Onejaw is fixed, the other being pivoted atthe top and oscillating at the bottom.Output is high but the product is not ofuniform size (cf. DODGE-TYPE JAWCRUSHER).Blakely Test. See TUNING FORK TEST.Blank. (1) In the vitreous-enamelindustry, a piece cut from metal sheetready for the shaping of ware. (2) Apiece of glass that has receivedpreliminary shaping. See also CLOT;

OPTICAL BLANK.Blanc-de-Chine. White, glazed Chineseporcelain.Blanc Fixe, BARYTES (q.v.)Blank Mould. The metal mould in whichthe PARisoN (q.v.) is shaped in glasshollow-ware production.Blanket Feeding. The charging of batch(to a glass tank furnace) as a broad, thinlayer; this gives a uniform distributionacross the width of the furnace.Blast Furnace. A shaft furnace, 30-36mhigh, for the extraction of iron from its

ore; a smaller type of blast furnace isused for the extraction of lead. In iron-making, ore, limestone and coke arecharged at the top and hot air is blasted(hence the name) in near the bottom.The whole furnace is lined withrefractory material carbon/SiC in boshand stack; aluminosilicate, siliconcarbide, firebrick or gunnedaluminosilicate in the upper stack;alumina-chrome, mag-chrome or SiC/graphite castables may be used in thehearth.Bleaching Clay. A clay, usually of thebentonite or fuller's earth type, used fordecolorizing petroleum products etc.; theliquid is allowed to percolate through alayer of the clay, which adsorbs thecolouring matter on its surface.Bleb. A raised blister on the surface offaulty pottery-ware.Bleeding. (1) The appearance of water atthe surface of freshly placed concrete,hence the alternative name WATERGAIN; it is caused by sedimentation ofthe solid particles, and can to someextent be prevented by the addition ofplasticizers and or by AIR ENTRAINING(q.v.). A test for the bleeding of cementpastes and mortars is provided in ASTMC243. See also LAITANCE.(2) The movement of gold or platinumdecoration on pottery ware during theearly stages of the firing-on; themovement is caused by the passage of anexcess of hot vaporized solvent over theware as a result of overloading the kilnor inadequate draughting.Blending Batch. A batch charged to aglass furnace during a changeover incomposition of the finished glass. It has acomposition intermediate between thatof the glass already in the furnace andthat finally required.Bleu Persan. A form of potterydecoration in which a white pattern was

painted over a dark blue background;the name derives from the fact that thepattern generally had a Persian flavour.Blibe. A fault, in glass-ware, in the formof an elongated bubble intermediate insize between a seed and a blister, GREYBLIBE consists of undissolved sodiumsulphate.Blinding. (1) The clogging of a sieve orscreen.(2) US term for a glaze fault revealed bya reduction in gloss, and caused bysurface devitrification.Blister. A large bubble sometimespresent as a fault in ceramic ware. Inglass-ware, if near the surface it is a SKINBLISTER and if on the inside surface ofblown glass-ware it is a PIPE BLISTER(q.v.). The common causes of blisters invitreous enamelware are flaws in thebase-metal, surface contamination of thebase-metal, and too high a moisturecontent in the atmosphere of theenamelling furnace.Bloach (US). A blemish on plate glassresulting from stopping the grindingbefore all the hollows have beenremoved; a 'bloach' is an area of theoriginal rough surface.Bloating. The permanent expansionexhibited by some clays and bricks whenheated within their vitrification range; itis caused by the formation, in thevitrifying clay, of gas bubbles resultingeither from entrapped air or from thebreakdown of sulphides or otherimpurities in the clay (cf. EXFOLIATIONand INTUMESCENCE).Block. (1) Denned in the UK (B.S. 3921)as: 'A walling unit exceeding in length,width or height the dimensions specifiedfor a BRICK' (q.v.).(2) A rectangular piece of KILNFURNITURE (q.v.), with cavities in itsupper surface to hold small items such asspark plugs.

Block Handle. A cup handle of the typethat is attached to the cup by a solid barof clay (which is, of course, integral withthe handle) (cf. OPEN HANDLE).Block Mill. See PAN MILL.Block Mould. A one-piece mould,especially a glassmaking mould.Block Rake. A surface blemish, havingthe appearance of a chain, sometimesoccurring on plate glass.Block Reek, CULLET CUT (q.v.)Blocking. (1) The shaping of glass in awooden or metal mould.(2) POLING (q.v.) with a block of wood.(3) The removal of surface blemishesfrom glass-ware by reprocessing.(4) The setting of optical glass blanks ina carrier prior to grinding and polishing.(5) A US meaning is: running a glass-furnace idle at a reduced temperature.(6) Synonym of THWACKING (q.v.).Bloom. (1) Surface treatment of glass(e.g. lenses) by vapour deposition; thisdecreases reflection at the air/glassinterface.(2) A surface film on glass caused byweathering or by the formation ofsulphur compounds during annealing.(3) A fault on vitreous enamels,especially blacks, caused by theirreaction with sulphur gases in the dryeror enamelling furnace to form a surfacefilm of sodium sulphate; the fault maynot become visible until the enamelwarehas been in a moist atmosphere for sometime.Blotter. US term for a disk ofcompressible material, e.g. blotting-paper stock, for use between a grindingwheel and its mounting flanges.Blow-and-Blow. The process used toblow small-neck glass containers withthe is MACHINE (q.v.). The PARISON(q.v.) is blown and the second blowingprocess produces the final shape of theware.

Blow-in Lining. A sacrifical refractorylining to protect the permanent lining ofa blast furnace when recommissionedafter re-lining. It normally covers BOSHtO HEARTH.Blow Mould. The metal mould in whichblown glass-ware is given its final shape.Blow pipe Spray Welding. See SPRAYWELDING.Blowing. See LIME BLOWING, GLASSBLOWING.Blowing Iron. An iron tube used inmaking hand-blown glasswareBlown Away. See HOLLOW NECK.Blown Enamel. Vitreous enamelshowing surface ridges. They formduring wet-spraying with too thick or toofluid a coating, or too high an airpressure.Blowpipe. See BLOWING IRON.Blue Brick. See ENGINEERING BRICKS.Blue Coring. A blue colouring at thecentre of fired ware, caused by residualreduction of iron- or titanium-bearingmaterials in the body, after the organicshave been burned out.Blue Enamel. An area in dry-processvitreous enamelware where the coatingis too thin and the ware appears blue.Blueing. The production of blueengineering bricks, quarries or roofingtiles by controlled reduction during thelater stages of firing; this alters thenormal state of oxidation of the ironcompounds in the material and results ina characteristic blue colour.Blunger. A machine for mixing clayand/or other materials to form a slip;it usually consists of a large hexagonalvat with a slowly rotating verticalcentral shaft on which are mountedpaddles. The process of producing a slipin such a machine is known asBLUNGING.Blurring-highlight Test. A test todetermine the degree of attack of a

vitreous-enamelled surface after an acid-resistance test; (see ASTM - C282).Blushing. A pink discolorationsometimes occurring during the glost-firing of pottery. It can be caused bytraces of Cr in the kiln atmospherearising, for example, from CHROME-TINPINK (q.v.) fired in the same kiln, or byfiring a tin-opacified glaze in a kilncontaining traces of Cr vapour from thefiring of Chrome Green.Board. See WORK BOARD.Boccaro Ware. Red, unglazed stonewarewith relief decoration.Bock Kiln. See BULL'S KILN.Body. (1) A blend of raw materialsawaiting shaping into pottery orrefractory products.(2) The interior part of pottery, asdistinct from the glaze.(3) The condition of molten glassconducive to ready working.(4) The cylindrical part of a steelconverter.Body Mould. In the pressing of glass,that part of the mould which gives shapeto the outer surface of the ware.Body Stain. See STAIN (4).Boehme Hammer. A device for thecompaction of test-pieces of cement ormortar prior to the determination ofmechanical strength, it consists of ahammer, pivoted so that the head fallsthrough a definite are on the test-piecemould to cause compaction understandard conditions.Boehmite. A monohydrate of alumina:often a constituent of bauxite andbauxitic clay.Boetius Furnace. A semi-direct coal-fired pot furnace for melting glass; thiswas the first pot-furnace to usesecondary air to increase the thermalefficiency.Bogie Kiln or Truck Chamber Kiln. Anintermittent kiln of the BOX KILN (q.v.)

type distinguished by the fact that theware to be fired is set on a bogie which isthen pushed into the kiln; the bogie hasa deck made of refractory material (cf.SHUTTLE KILN).Bohemian Glass. A general term forCzechoslovakian glass, particularly table-ware and chemical ware; it is generallycharacterized by hardness and brilliance.Boiling. A fault in vitreous enamelware(particularly in enamelled sheet-steel)visible as blisters, pinholes, specks,dimples or a spongy surface. The usualcause is undue activity of the GROUND-COAT (q.v.) during the firing of thefirst COVER-COAT (q.v.), but gases arealso sometimes evolved during thefiring of the cover-coat (cf. BOTLTNGTHROUGH).

Boiling Through. A fault in vitreousenamelware, small dark specksappearing on the surface of the ware,usually in consequence of gas evolutionfrom the base metal.Bole. A friable earthy clay highlycoloured by iron oxide.Bolley's Gold Purple. A colour that hasbeen used on porcelain. A solution ofstannic ammonium chloride is left forsome days in contact with granulated tinand is then treated with dilute goldchloride solution. The gold purple isprecipitated.Bolt-hole Brush. A stiff brush with astraight metal guide, used to removevitreous enamel from the edges of wareto prevent chipping and to neaten thefired product.Bolus Alba, CHINA CLAY (q.v.)Bomb. The large, approximatelyhemispherical pad of silicone rubber or,originally, gelatine which transfers thecolour in the MURRAY-CURVEX printingprocess (q.v.).Bond. (1) The arrangement of bricks ina wall; the bond is usually such that any

crossjoint in a course is at least onequarter the length of a brick from jointsin adjacent courses. For special types ofbonds see AMERICAN BOND, DUTCHBOND, ENGLISH BOND, FLEMISH BOND,FLYING BOND, IN-AND-OUT BOND,MONK BOND, QUETTA BOND. To beginor end a course, a bonder, a brick ofspecial size or shape, may be required.(2) The placing of roofing tiles so thatthe joint between two tiles in one courseis at or near the centre of the tile of thecourse below.(3) The intergranular material, glassy orcrystalline, that gives strength to firedceramic ware.(4) The bond in abrasive wheels may beceramic, silicate of soda, resin, shellac,rubber, or magnesium oxychloride.Bond Fireclay. A U.S. term for a fireclayof sufficient natural plasticity to bondnonplastic materials.Bond's Law. A theory of grinding whichpostulates that the grinding rate of asolid is proportional to the crackpropagation speed in the solid.(F.C.Bond, Trans. Amer. Inst. Min.(metall) Engrs. 193,1952, p484).Bond Strength. In ASTM C952 for thebond strength of mortar to masonry, acrossed-brick couplet tensile test is usedfor clay bricks; a stacked bond flexuraltest for concrete blocks. ASTM E518 is aflexural test for the bond strength ofmasonry, in which a transverse force isapplied to a beam of bricks, using an airbag.Bond and Wang Theory. A theory ofcrushing and grinding: the energy (H)required for crushing varies inversely asthe modulus of elasticity (E) and specificgravity (S), and directly as the square ofthe compressive strength (C) and as theapproximate reduction ratio (n). Theenergy in hp.h required to crush a shortton of material is given by the following

The theory is due to F. C. Bond and J. T.Wang (Trans. Amer. Inst. Min(metall)Engrs., 187, 875,1950).Bondaroy's Yellow. An antimony yellowdeveloped by Fourgeroux de Bondaroyin 1766: white lead, 12 parts; potassiumantimonate, 3 parts; alum, 1 part; salammoniac, 1 part.Bonded Roof. A term for the roof of afurnace when the transverse joints in theroof are staggered (cf. RIGGED ROOF).Bonder. A brick that is half as wideagain as a standard square (rectangularor arch); such bricks are sometimes usedto begin or end a course of bondedbrickwork. (See Fig. 1, p39).Bondley Process. See underMETALLIZING.Bone Ash. Strongly calcined bone,approximating in composition toCa3(PO4). The m.p. of bone ash is about16700C, density 3.14. It is used in themaking of CUPELS (q.v.). Less stronglycalcined bone constitutes about 50% ofthe BONE CHINA body. It isoccasionally used, to the extent of about2%, in some vitreous enamels. See alsoCALCIUM PHOSPHATE.Bone China. Vitreous, translucentpottery made from a body of thefollowing approximate composition (percent): calcined bone, 45-50; china clay,20-25, china stone, 25-30. TheCOMBINED NOMENCLATURE (q.V.)defines this ware as: 'Completelyvitrified, hard, impermeable (even beforeglazing), white or artificially coloured,translucent and resonant. Bone Chinacontains calcium phosphate in the formof bone ash; a translucent body is thusobtained at a lower firing temperature

than with hard porcelain. The glaze isnormally applied by further firing at alower temperature, thus permitting agreater range of underglaze decoration.'The British Pottery Manufacturers'Federation defined this material as:'Ware with a translucent body containinga minimum of 30% of phosphate derivedfrom animal bone and calculated ascalcium phosphate. B.S.5416 'ChinaTableware' now specifies that bone chinashall contain 'at least 35% by mass of thefired body of tricalcium phosphate'.Inthe USA, ASTM-C242 permits the term'bone china' to be applied to anytranslucent whiteware made from a bodycontaining as little as 25% bone ash.Bone china, though delicate inappearance, is very strong. It was firstmade by Josiah Spode, in Stoke-on-Trent, where by far the largest quantityof this type of high-class pottery is stillmade (cf. PORCELAIN).Bonnet Hip. See HIP TILE.Bonnybridge Fireclay. A fireclayoccurring in the Millstone Grit in theBonnybridge district of Scotland. Atypical per cent analysis (fired) is: SiO2,56-57; Al2O3, 36; Fe2O3, 3-4; alkalis,0.75. P.C.E. 32-33.Bont. N. Staffordshire term for one ofthe iron hoops used to brace the outsidebrickwork of a BOTTLE OVEN (q.v.).Boost Melting. The application ofadditional heat to molten glass in a fuel-fired tank furnace by the passage of anelectric current through the glass.Boot. Alternative name, preferred inUSA, for POTETTE (q.v.).Borax. NaB4O7-IOH2O; sp. gr. 2.36(anhydrous), 1.7 (hydrated). Occurs inwestern USA and is an importantconstituent of vitreous enamel and glazefrits, and of some types of glass. Onheating, the water of crystallization islost by a series of steps:

equation, in which all quantities are inf.p.s. units:

The anhydrous borax, (sodiumtetraborate) melts at 7410C.Borax Glass. Vitreous, anhydrous,sodium tetraborate (NaB4O7).Borazon. Trade-name (General ElectricCo., USA); cubic form of BORONNITRIDE (q.v.).Boric Oxide. B2O3; m.p. 4500C; sp. gr.1.84. Solid B2O3 is commonly availableonly in the vitreous state; two crystallineforms exist, however, Ct-B2O3

(hexagonal) and (3-B2O3 (a denser form).Borides. A group of special ceramicmaterials. Typical properties are greathardness and mechanical strength, highmelting point, low electrical resistivityand high thermal conductivity; impactresistance is low but the thermal-shockresistance is generally good. For theproperties of specific borides see underthe borides of the following elements:Al, Ba, Ca, Ce, Cr, Hf, La, Mo, Nb, Si,Sr, Ta, Th, Ti, U, V, W, Zr.Boroaluminate. See ALUMINIUM

BORATE.Borocalcite. See COLEMANITE.Boron Carbide. B4C; synthesized by thereaction of C and B2O3 at hightemperatures. Boron carbide has aKnoop Hardness (10Og) of 2300-2800,which is second only to that of diamond;for this reason it is used for grinding anddrilling. Its transverse strength is approx.280 MN/m2 and compressive strengthover 3GN/m2 Boron carbide is alsorefractory (m.p. 24500C) althoughoxidation becomes severe above 11000C;it is otherwise chemically resistant andabrasion resistant, and finds use innozzles and other high-temperature

locations. The sp. gr. is 2.52. Thermalexpansion (25-8000C) 4.5 x 10-6;(25-20000C) 6.5 x 1(H.Boron Nitride. BN; oxidizes in air at8000C. but its m.p. under a pressure ofnitrogen is >3000°C. Sp. gr. 2.2. Thisceramic exists in forms that correspondto the graphite (hexagonal) and thediamond (cubic) forms of carbon. Thecubic form is as hard as diamond andwas originally made (R. H. Wentorf, /.Chem. Phys., 26, 956,1957) by thesimultaneous application of very highpressure (85 000 atm.) and temperature(18000C). It has since been found that, inthe presence of a catalyst, both thetemperature and pressure can bereduced. It is made under the trade-name Borazon by General Electric Co.,USA. The hexagonal form of BN isreadily produced by high-temperaturereaction between B2O3 or BCl3 andammonia. Hot-pressed hexagonal BN ismachinable. Its electrical resistivity is 1.7x 1013 ohm.cm at 200C and 2.3 x 1013

ohm.cm at 5000C. Uses include dielectricvalve spacers, crucibles and rocketnozzles; it is not wetted by some moltenglasses.Boron Oxide. See BORIC OXIDE.Boron Phosphate. BPO4; vaporizes at14000C; sp. gr. 2.81; related structurallyto high-cristobalite. It has been used as aconstituent of a ceramic body that firesto a translucent porcelain at 10000C.Boron Phosphide. There are twocompounds: BP, Sp. gr. 2.97; KnoopHardness (10Og) 3200; decomposes at11300C; B13P2, sp. gr. 2.76; KnoopHardness (100 g) 3800; melts or sublimesat approx. 20000C.Boron Silicides. See SILICON BORIDESBorosilicate Glass. A silicate glasscontaining at least 5% B2O3 (ASTMdefinition); a characteristic property ofborosilicate glasses is heat resistance.

Bort. Industrial diamond of the typeused as an abrasive for cutting andgrinding.Bosh. (1) The part of a blast furnacebetween the tuyere belt and the lintel; itis usually lined with high-grade fireclayrefractory and is water-cooled.(2) In the glass industry, a tankcontaining water for cooling glass-making tools.Boson Box. Incorrect form of BOZSINBox (q.v.).Boss; Bossing. In the process of potterydecoration known as GROUND-LAYING(q.v.), brush marks are removed byBOSSING, i.e. striking, the ware with apad, or Boss, made by stuffingcottonwool into a silk bag.Bottger Ware. A dark red stoneware.Botting Clay. Prepared plastic refractorymaterial for use in the stopping of thetap-holes in cupolas. A typicalcomposition would be 50-75% fireclay,up to 50% black sand, 10% coal dustand up to 5% sawdust.Bottle Brick. A hollow clay building unitshaped like a bottomless bottle, 305mmlong, 76mm o.d., 50mm. i.d. andweighing lkg. The neck of one unit isplaced in the end of another to buildbeams, arches or flat slabs; steelreinforcement can be used. Bottle brickshave been used in France (where theyare known as 'Fusees Ceramiques'), inSwitzerland, the Netherlands, and in S.America.Bottle Oven. A type of intermittent kiln,usually coal-fired, formerly used in thefiring of pottery; such a kiln wassurrounded by a tall brick hovel or cone,of typical bottle shape.Bottom Pouring or Uphill Teeming. Amethod of teeming molten steel from aladle into ingot moulds. The steel passesthrough a system of refractory fireclaytubes and enters the moulds at the

bottom; the refractory tubes are ofvarious shapes. See TRUMPET, GUIDE-T U B E , CENTRE BRICK and RUNNERBRICKS.Bottom Stirring Elements. Refractoryblocks including apertures or pipes forpassing gas or powder into the steelcharge, built into the bottom lining of aBASIC OXYGEN FURNACE (q.V.).Bottom Tuyeres. Refractory blocksinserted separately to introduce gasesinto the charge of a BASIC OXYGENFURNACE (q.V.). Cf. BOTTOM STIRRINGELEMENTS.Boudouard Reaction. The reactionleading to dissociation of CO into CO2;See CARBON MONOXIDEDISINTEGRATION. (O. Boudouard,ComptRend., 128, 98, 824,1522,1899).Boulder Clay. A glacial clay used inmaking building bricks, particularly inthe northern counties of England.Boule. A fused mass of material, pear-shaped, particularly as produced by theVERNEUiL PROCESS (q.v.). Sapphire(99.9% Al2O3) boules, about 50 mmlong, are produced in this way, and areused, for example, in making threadguides, bearings and gramaphoneneedles.Bourry Diagram. A diagram relating thewater-loss and shrinkage of a clay bodyto the drying time; the two curves areshown on the one diagram. (E. Bourry,the 19th century French ceramist.)Bouyoucos Hydrometer. A variable-immersion hydrometer. The originalinstrument was graduated empirically toindicate the weight of solids per unitvolume of suspension; it wassubsequently developed for particle-sizeanalysis. (G. J. Bouyoucos, Soil Sci.,23,319,1927, 25, 365, 1928; 26, 233, 1928.)Bowl. That part of the feeder whichdelivers molten glass to the followingunit.

Bowmaker Test. A method offorecasting the durability of refractoryglass-tank blocks proposed by E. J. C.Bowmaker (/. Soc. Glass Tech., 13,130,1929). The loss in weight of a sample cutfrom the tank block is determined afterthe sample has been immersed for 3 h. inHF/H2SO4 at 1000C; the acid mixture is3 parts by vol. HF (commercial 50-60%HF) and 2 parts by vol. pure cone.H2SO4. The test is no longer consideredvalid.Box-car roof. Popular name for theKREUTZER ROOF (q.V.).Box Feeder. A device for feeding clay topreparation machines. It consists of alarge metal box, open topped, with thebottom usually formed by a steel-bandconveyor or by a conveyor ofoverlapping steel slats; for plastic claythe feeding mechanism may be a numberof revolving screw shafts.Box KtIn. A relatively small industrialintermittent kiln of box-like shapeBoxing. The placing of biscuit hollow-ware, e.g. cups, rim to rim one onanother; this helps to prevent distortionduring firing.Boxing-in. A method of setting in a kilnso that, for example, special refractoryshapes can be fired without beingstressed and deformed; also known asPOCKET SETTING.Boyd Press, A toggle-press in whichpressure is exerted both on the top andbottom of the brick in the mould. It wasintroduced in 1888 and has since beenwidely used for the dry-pressing ofbuilding bricks and refractories.(Chisholm, Boyd and White Co.,Chicago, USA).Bozsin Box. A box, with heat-insulatedwalls, containing a temperature recorder;it was designed by M. Bozsin to travelwith the ware through a vitreous-enamelling furnace.

Brabender Plastograph; BrabenderPlasti-Corder. Trade-names: instrumentsdesigned in USA to assess the plasticityof clays and other materials on the basisof stress measurement during acontinuous shearing process.Brackelsberg Furnace. A rotary furnace,originally fired by pulverized coal, forthe melting of cast iron; the lining of thefirst such furnaces was a rammedsiliceous refractory, but silica bricklinings have also been used successfully(C. Brackelsberg, Brit. Pat. 283 381;13/4/27.)Bracken Glass. Old English glass-waremade from a batch in which the ash fromburnt bracken supplied the necessaryalkali.Bracklesham Beds. Pale-coloured claysintermingled with glauconite sandoccurring in parts of Southern Englandand worked for brickmaking to the S.W.of London and near Southampton.Bragg Angle, Bragg's Law. See X-RAYCRYSTALLOGRAPHY.Brake Linings. See FRICTION ELEMENTS.Brasqueing. A process sometimes usedfor the preparation of the interior of afireclay crucible prior to its use as acontainer for molten metal. The crucibleis lined with a carbonaceous mixture; itis then covered with a lid and heated toredness (From French word with thesame meaning.)Bravais Lattice. See CRYSTALSTRUCTURE; SPACE GROUP.Bravaisite. A clay mineral containing Mgand K, and of doubtful structure; it hasvariously been stated to be a mixture ofkaolinite and illite or of montmorilloniteand illite.Brazing. Ceramics may be joined to eachother, or to metals, by providing amolten interlayer which wets thesurfaces to be joined, then solidifies.Metal alloys are usually used, though

inorganic glasses have been used forsilicon nitride. Brazing may be direct,when the braze material itself (possiblyincluding a suitable activator) wets thesurfaces; or indirect, used for the manyceramic surfaces which are difficult towet with low-melting brazes. Theceramic is first metallized, and thenbrazed using an alloy which wets themetallization layer. The most commonmethod is the MOLY-MANGANESEprocess.Brazilian Test. A method for thedetermination of the tensile strength ofconcrete, ceramic, or other material byapplying a load vertically at the highestpoint of a test cylinder or disk (the axisof which is horizontal), which is itselfsupported on a horizontal plane. Themethod was first used in Brazil for thetesting of concrete rollers on which anold church was being moved to a newSite (cf BRITTLE-RING TEST).Break-out. Defined (ASTM - C286) as:'In dry-process enamelling, a defectcharacterized by an area of blisters withwell-defined boundaries.'Break-up of Matt Glaze. The termBREAK-UP is applied more particularlyto the glazes containing rutile used onwall tiles. Some of the added rutiledissolves in the glaze, the yellow orbrown titanates thus formedsubsequently collecting round theundissolved rutile crystals to give themarbled effect known as the RUTILE

BREAK Or BREAK-UP.Breast Wall. (1) The side-wall of a glass-tank furnace above the tank blocks, alsoknown as CASING WALL, CASEMENTWALL Or JAMB WALL.(2) The refractory wall between thepillars of a glass-making pot furnace andin front of the pot.Breasts. The sloping parts joining thehearth of an openhearth furnace to the

furnace ends below the ports andadjoining brickwork (cf. BANKS).Brecem. High alumina cements blendedwith granulated blast furnace slag,developed by the Building ResearchEstablishment, Watford.Bredigite. The form of CALCIUMORTHOSILICATE (q.v.) that is stable fromabout 800-14470C on heating, persistingdown to 6700C on cooling.Breezing. A thin layer of crushedanthracite or of coarse sand spread onthe siege of a pot furnace before settingthe pots.Bremond Porosimeter. Apparatus forthe evaluation of pore size distributionby the expulsion of water from asaturated testpiece. (P. Bremond, Bull.Soc. Franc. Ceram. (37), 23,1957).Brenner Gauge. An instrument for thenon-destructive determination of thethickness of a coating of vitreousenamel; it depends on the measurementof the force needed to pull a pin fromcontact with the enamel surface against aknown magnetic force acting behind thebase metal.Breunnerite. Magnesite containing5-30% ferrous carbonate; some of theAustrian 'magnesite' used as a rawmaterial for basic refractories is, morestrictly, breunnerite.Brewster. Unit of photoelasticity: 1brewster is equivalent to a relativeretardation of 10~13 cm2/dyne. Namedafter Sir D. Brewster who, in 1816,demonstrated that glass becomesbirefringent when stressed.Brianchon Lustre. A lustre (q.v.) forpottery-ware developed by M.Brianchon, in Paris, in 1856. Thereducing agent necessary to form thethin deposit of metal is incorporated asbismuth resinate so that a reducingatmosphere in the kiln is not needed.Although the easiest lustre to apply, it is

Fig. 1 Brick types

less durable than lustres produced in areducing fire.Brick. A brick is a clay or calciumsilicate walling unit as big as can beconveniently handled in one hand.BS3921 for clay bricks, defines their co-ordinating size to be 225 x 112.5 x 75mm,with a working size (derived bysubtracting a 10mm allowance for amortar joint) of 215 x 102.5 x 65mm.BS3921 also specifies requirements forcompressive strength, water absorption,soluble salt content, efflorescence andsampling, cf. BLOCK.

See following types: ACID-RESISTING;CLAY BUILDING; CONCRETE; FACING;FLOOR; PAVING; PERFORATED; SANDLIME; SEWER. See also CLADDING. ForBrick Shapes, both for building and forfurnace construction, see Fig. 1, andBS 3446 PtI. BS 3056 specifiesdimensions of refractory bricks forvarious applications. BS 1902 Pt 3.11specifies the measurement of dimensionsand shapes of refractory bricks and

blocks. ASTM C861 specifies metricdimensions for refractory bricks; C909 aseries based on a 38-mm module forrefractory rectangular and taperedbricks. Measurement of dimensions andwarpage are specified in C134.Brick Clays. Clays suitable for themanufacture of building bricks occurchiefly in the carboniferous and morerecent geological systems. In the UKabout 30% of the bricks are made fromcarboniferous clays, 30% from theOxford clays, 10% Glacial clays, 6%Keuper Marl; the remaining 24% aremade from Alluvial clays, the so-calledBrick-earths, Tertiary, Cretaceous,Devonian, Silurian, and Ordoviciandeposits. Brick clays are impure andmost of them vitrify to give bricks ofadequate strength when fired at900-11000C.Brick Earth. An impure loamy clay,particularly that of the Pleistocene of theThames Valley, used for brickmaking.Brick Shapes. See Fig. 1 and the furtherreferences in Appendix A. The GermanDIDiER co publishes a detailed codingsystem for refractory bricks and shapes,which is a de facto standard in Europe.Brick Slip. A fired ceramic architecturalfacing varying from about 13 to 38mm inthickness and produced either as a unititself or cut from a larger unit.Bricking Centre. A curved woodenformer for the construction of arches.Bricking Rig. A metal framework withcompressed air plungers, for constructingarches or cylindrical refractorystructures.Bricklaying. The process of building awall or other structure by bondingtogether individual BRICKS with MORTARor other methods. BS 5628 Pt3 includesrecommendations for bricklaying.Brickwork. See MASONRY;

BRICKLAYING.

Standard square Bevel brick Bonder Bullnose

Circle brick Circle brickon edge

Dome brick End arch

End skewon edge

End skewon flat

Feather end Feather endon edge

Feather side Key brick Pup Radial brick

Side arch Side skew Split Whelp

Bridge; Bridge Wall. A refractory wallseparating two parts of a furnace. Thebridge wall (or firebridge) in a boilerfurnace terminates the combustionchamber. In a glass-tank, the bridge wallseparates the melting end from theworking end of the furnace; the wall is inthis case usually double, is pierced by theTHROAT (q.v.) and is spanned at the topby refractory tiles known as bridgecovers.Bridge Crack. A defect sometimes foundin the clay column from an extruder;such a crack is likely to be present if thebridge that supports the auger-shaft istoo close to the mouthpiece.Bridge Wall. See BRIDGE.Bridge Indentation. A modified SINGLE-EDGE PRECRACKED BEAM. See

FRACTURE TOUGHNESS TESTS.

Bridging. A phenomenon preventing thefree flow of powder from a hopper. Theparticles stick together temporarily toform a bridge across the outlet nozzle,effectively reducing its area. See alsoCRACK BRIDGING; TILE BRIDGING.Bridging Oxygen. An oxygen ion placedbetween two silicon ions, e.g. in thestructure of a silicate glass.Bright Annealing. Heating metal to bevitreous enamelled to red heat or abovein a reducing atmosphere, to produce aclean, bright surface.Bright Gold or Liquid Gold. A materialfor the decoration of pottery-ware; itconsists essentially of a solution of goldsulphoresinate together with other metalresinates and a flux (e.g. a bismuthcompound) to give adhesion to the ware.This form of gold decoration is alreadybright when drawn from the decoratingkiln (cf. ACID GOLD and BURNISHGOLD).

Brights. Any portion of decorated glassforming part of a design, but which hasnot been acid treated.

Brilliant Cut. Process of decorating flatglass by cutting a pattern with abrasivewheels followed by polishing.Brimsdown Frit. A lead bisilicate frit forglazes made from 1913 until 1928 byBrimsdown Lead Works, Brimsdown,Middlesex, England. The batch consistedof litharge, silica, and Cornish Stone.Although the frit contained 64% PbO itssolubility, when tested by the HomeOffice method then used, was only 1-2%.Brindled Brick. A building brick madefrom a ferruginous clay and partiallyreduced at the top firing temperature; ithas a high crushing strength.Brinell Hardness. An evaluation of thehardness of a material in terms of thesize of the indentation made by a steelball when pressed against the surface.Symbol - HB supplemented by numbersindicating the diameter of the ball usedand the load applied; the abbreviationadopted by the American CeramicSociety is BHN-Brinell HardnessNumber. The test is primarily for metals;it has been applied to clay products, e.g.building bricks, but without greatsuccess. (I. E. Brinell, Comnm. Congr.Internal Math Essai, 2, 83,1901)Bristol Glaze. A feldspathic type ofglaze, generally opaque, maturing at1200-12500C and suitable for use ononce-fired stoneware. Both thetransparent and the opaque types arecompounded from feldspar, whiting,ZnO, china clay and flint; the opaquetype contains more feldspar and lesswhiting. Bristol glazes tend to be ratherdull and often show pin-holes.BRITE. Basic Research in IndustrialTechnologies in Europe/EuropeanResearch on Advanced Materials - aEuropean Community programme ofresearch including advanced ceramics.Britmag. Trade-name: dead-burnedmagnesia made by the seawater process

in Britain. (Steetley Co. Ltd., Worksop,England).Brittle Fracture, Brittleness. SeeFRACTURE. Brittle, or fast fractureoccurs when the intensified stress at acrack tip exceeds the fracture stress ofthe material (i.e. the force is sufficient tobreak the interactive bonds). The crackthen propagates catastrophically rapidly.Brittle fracture is characterized by a verysmall (sub-millimetre) microcrack zoneat the crack tip, low (0.01 kJm-2)fracture energy and a linear relationshipbetween the load and the load-pointdisplacement in fracture tests. This typeof fracture is typical of low-toughnessceramics such as glass and fine-grainedmonolithic ceramics.Brittle-ring Test. A test to determine thebehaviour of a ceramic material undertensile stress; a test-piece in the form ofan annulus is loaded along a diameter sothat maximum tensile stresses developon the inner periphery of the annulus inthe plane of loading. For theory of thistest see Mechanical Properties ofEngineering Ceramics, p. 383, 1961. (cf.BRAZILIAN TEST.)Broad Glass. Larger panes of flat glasswere made by blowing a tall cylinderinstead of a sphere, and cutting itlengthwise and flattening it by reheating.See CROWN GLASS.Broken-joint Tile. A single-lap roofingtile of a size such that the edge of onetile, when laid, is over the centre of thehead of a tile in the course next below.Broken Seed. See SEED.Brokes. Term used in the English ball-clay mines for clay that will not cut intoballs; such clay is generally of lowplasticity and poor fired colour.Brongniart's Formula. A formularelating the weight (W, oz) of solidmaterial in 1 pint of slip (or slop glaze),the weight (P, oz) of 1 pint of the slip,

The formula was established for slopglazes by A. Brongniart (Traite des ArtsCeramiques, Vol.1, p.249,1854).Brookfield Viscometer. An electricallyoperated rotating cylinder viscometer inwhich the drag is recorded directly on adial; it has been used in the testing ofvitreous-enamel slips (/. Amer. Ceram.Soc, 31,18,1948).Brookite. The orthorhombic form oftitania, TiO2; sp. gr. 4.17. The otherforms are ANATASE (q.v.) and RUTILE(q.v.). It is comparatively rare and israpidly transformed into rutile attemperatures above about 8000C.Broseley Tile. An old name for a plainclay roofing tile; such tiles were made inBroseley, Shropshire, England.Brownies. Term sometimes applied tobrown spots in white vitreous-enamelground-coats; more commonly known asCOPPERHEADS.Brown China, ROCKINGHAM WARE, q.v.Brownmillerite. A calcium aluminoferritethat occurs in portland and high-aluminacements. It was originally thought to havethe composition 4CaO-Al2O3. Fe2O3;there is, however, a continuous series ofsolid solutions in the CaO-Al2O3-Fe2O3

system, the usually accepted Brown-millerite composition being only aparticular point in the series. M.p.1415°C; thermal expansion (0-100O0C),10.1 x 1(H.Brucite. Mg(OH)2; deposits in Ontarioand Quebec (Canada) and in Nevada(USA), are used as a source of MgO.Bruise. A concentration of cracks in thesurface of glass-ware caused by localizedimpact.Brulax System. An impulse system of oilfiring, particularly for the top-firing of

and the specific gravity (S) of the drysolid material:

annular kilns, developed by A. A.Niesper, in Switzerland, in 1955.Brunauer, Emmett and Teller Method.A procedure for the determination ofthe total surface area of a powder or of aporous solid by measurement of thevolume of gas (usually N2) adsorbed onthe surface of a known weight of thesample. The mathematical basis of themethod was developed by S. Brunauer,P. H. Emmett and E. Teller - hence theusual name B.E.T. METHOD (/. Amer.Chem. Soc, 60, 309, 1938). ASTM C1069measures the specific surface area ofalumina or quartz by nitrogenadsorption.Brunner's Yellow. An antimony yellowrecipe given by K. Brunner in 1837: 1part tartar emetic, 2 parts lead nitrate, 4parts NaCl. The mixture is calcined andthen washed free from soluble salts priorto its use as a ceramic colour.Brush Marks. A surface imperfectionfound on the exterior of some bottles;the marks resemble a series of finevertical laps and are also known asSCRUB MARKS.

Brushing. The removal of beddingmaterial from pottery-wareafter the biscuit firing.Brussels Nomenclature. Term given tothe International Tariff Nomenclatureagreed and issued in 1955. Chapter 69related to ceramic products. TheBrussels Nomenclature has beensuperseded for tariff purposes by theCOMBINED NOMENCLATURE OF THE

EUROPEAN COMMUNITIES (q.V.)

BS; BSI. Abbreviations for BritishStandard and British StandardsInstitution. The Institution isresponsible for the preparation(through industry committees on whichinterested parties are represented) ofnational standards for Britain; copies ofthese standards, and of foreign

standards, can be obtained from theInstitution at Linford Wood, MiltonKeynes, MK14 6LEBSCCO. Bi - Sr - Ca ± Cu - OSUPERCONDUCTORS.

Bubble Alumina. Sintered bauxite isfused with carboneous materials andsteel borings in an electric arc furnace. Aslag containing nearly 90% Al2O3 isformed, and dispersed into bubbles byblowing air or steam into the moltenslag. The alumina bubbles are leached indilute sulphuric acid to removeremaining oxide impurities. Aluminaover 99.7% pure is obtainable, either asbubbles for insulating applications, or asvery fine, hard crystals for abrasiveapplications, obtained by crushing thebubbles. (B.T. Horsfield. US Pat1682675, 1925).Bubble Cap. A small, hollow, chemicalstoneware hemisphere with serrationsround the bottom edge; used onstoneware trays in de-acidifying towersin the chemical industry.Bubble Glass. Glass-ware containing gasbubbles sized and arranged to produce adecorative effect (cf. FOAM GLASS).Bubble-pressure Method. A techniquefor the determination of the maximumsize of pore in a ceramic product; thissize is calculated from the pressureneeded to force the first bubble of airthrough the ceramic when it is wettedwith a liquid of known surface tension.The method is used, for example, in thetesting of ceramic filters (B.S. 1752).Bubble Opal, OPAL GLASS (q.v.)containing many tiny pockets of gas,rendering it opaque.Bubble Structure. The relativeabundance, size and distribution of gasbubbles in a ceramic glaze or in avitreous enamel. In the latter, the dullenamels contain most bubbles, glossyenamels being relatively bubble-free.

Bubbling. See GAS BUBBLING BRICK.Bubbly Clay. A clay which, because itcontains small amounts of organicmatter, causes bubbles if used in vitreousenamels.Buck. A support used in the firing ofheavy vitreous enamel-ware.Buckstave or Buckstay. A steel bracingdesigned to take the thrust of thebrickwork of a furnace.Buckyball. See FULLERENES.Buffer Course. Refractory brickworkinstalled to separate two materials, toprevent chemical reaction betweenthem.Buffer Layer. The layer withcomposition and properties intermediatebetween body and glaze, found at thebody/glaze interface.Bugholes. Small holes or pits in thesurface of formed concrete.Biihrer Kiln. The ZIG-ZAG KILN (q.v.)invented by J. Buhrer (Brit. Pat. 562;1867).Building Brick. See CLAY BUTLDINGBRICK; CONCRETE BRICK;SAND-LIME BRICK.Building Clays. See BRICK CLAYS.Bulb Edge. The rounded edge of sheet-drawn glass.Bulged Finish. See FINISH.Bulk Density. A term used whenconsidering the density of a porous solid,e.g. an insulating refractory. It is definedas the ratio of the mass of the material toits BULK VOLUME (q.v.). ASTM C20specifies a boiling water test, ASTMC830 a vacuum pressure test forrefractories; ASTM C914 a waximmersion test. ASTM C357 and C493are boiling water and mercurydisplacement tests for granularrefractory materials. ASTM Cl34specifies a bulk density determinationfrom measurements of the size ofrefractory bricks using steel straight

edges to measure dimensions andwarpage. BS 1902 Pt 3.6 specifies fourtests for the GRAIN DENSITY (q.v.) ofrefractories.Bulk Specific Gravity. For a porousceramic, the ratio of the mass to that of aquantity of water which, at 4°C, has avolume equal to the BULK VOLUME(q.v.) of the material at the temperatureof measurement.Bulk Volume. A term used relative tothe density and volume of a porous solid,e.g. a refractory brick. It is defined as thevolume of the solid material plus thevolume of the sealed and open porespresent.Bulkhead. A panel of thinner brickworkbuilt into a furnace wall to permit earlyreplacement.Bulking. The tendency of fine particles,e.g. sand, to occupy a greater volumewhen slightly moist; the finer theparticles the more pronounced is thiseffect of surface moisture.Bull Float. A long-handled finishingtool for levelling large areas ofconcrete.BuIFs Eye. (1) A thick round piece ofglass or lens.(2) See ELECTRODE RING.Bull's Kiln. A CLAMP (q.v.) of atype designed by W. Bull (Brit. Pat.1977; 31/5/1875) in which the bricks tobe fired are set in a trench belowground level; this type of kiln findssome use in India. (Also known as aBOCK KILN.)Bullers' Rings. Annular rings (63.5mmdia. with a central hole 22mm dia.)made by pressing a blend of ceramicmaterials and fluxes; the rings are notfired. The constituents are soproportioned that the contraction of therings during firing can be used as ameasure of the temperature to whichthey have been exposed in a kiln; the

contraction is measured, after the firingprocess and when the rings are cold, bymeans of a gauge. The rings wereintroduced in about 1900 by BullersLtd., Stoke-on-Trent, England, fromwhom four types are now available foruse in various temperature rangeswithin the overall range 960-14000C.Bullhead. See KEY BRICK.Bullion. Flat glass of uneven thicknessmade by the handspinning of a gob ofglass at the end of an iron rod.Bullnose. A building brick or refractorybrick having one end face rounded tojoin one side face. Such bricks builtabove one another can be used to form arounded jamb, hence the alternativename JAMB BRICK (q.v.) (See Fig. 1,P39).Bump Check, PERCUSSION CONE (q.v.)Bung. (1) A vertical stack of saggars orof ware.(2) A refractory brick shape used in theroof of a malleable iron furnace.Bunsen's Extinction Coefficient. Thereciprocal of the thickness that a layer ofglass, or other transparent material, musthave for the intensity of transmitted lightto be decreased to one-tenth of itsintensity as it falls on the layer.Burgee. Contaminated sand resultingfrom the grinding of plate glass. (N.England dialect; the same word is usedfor poor quality coal).Burger's Vector. See CRYSTAL

STRUCTUREBurgos Lustre. A red lustre for porcelainmade by suitably diluting a gold lustrewith a bismuth lustre; some tin may alsobe present. (From Burgos, Spain.)Burley Clay. A refractory clay,intermediate in alumina content betweena flint clay and a diaspore clay, thatoccurs in Missouri, USA; elsewhere it isknown as Nodular Fireclay. The namederives from the diaspore oolites, known

to the local miners as 'burls', found inthese clays. The Al2O3 content of theraw clay is 55-63%.Burning. An alternative (but lessappropriate) term for FIRING (q.v.)Burner Block. See QUARL BLOCK.Burning Bar; Burning Point; BurningTool. A support, usually made of heat-resisting alloy, for vitreous enamelwareduring firing. Defects in the ware causedby contact with these supports areknown as BURNING TOOL MARKS.Burning Off. See BURN OFF.Burnish Gold or Best Gold. The bestgold decoration on pottery is madebright by BURNISHING, i.e. rubbing,usually with a blood-stone or agate.It is applied to the ware as a suspensionof gold powder in essential oils, with orwithout the addition of a proportion ofBRIGHT GOLD (q.v.); other ingredientsare a flux (e.g. lead borosilicate or abismuth compound) to promoteadhesion to the ware, and an extendersuch as a mercury salt. This type ofgold decoration is dull as takenfrom the kiln, hence the need forsubsequent burnishing, cf. ACIDGOLD.

Burn Off. A fault in vitreous enamellingresulting from the apparent burning-away of the ground coat. The fault maybe due to the enamel having becomesaturated with iron oxide; to preventthis, the fusion temperature of theground-coat should be raised by alteringits composition. Other causes are toothin a coat, wetness of the metal beforedipping, or shaking the dipped metal toovigorously.Burn-out. Heating a green ceramicshape to remove the (usually organic)binder. When this immediatelyprecedes sintering, the rate of heatingmust be carefully controlled, to avoidtrapping the resulting gases in pores as

these close, and to prevent excessporosity.Burnover. An underfired STOCK BRICK(q.v.) from the outside of a clamp; suchbricks are usually re-fired.Burr. (1) A partially fused waste brickfrom a kiln, or several such bricks fusedtogether.(2) A rough edge on the base-metal usedin vitreous enamelling; it must beremoved before the enamel is applied.Burr Mill. A mill for pigmentpreparation, comprising two ribbed discsrotating against each other.Bursting Expansion. In the refractoriesindustry this term has the specificmeaning of surface disintegration ofbasic refractories caused by theabsorption of iron oxide. The expansionthat leads to this form of failure resultsfrom solid solution of magnetite (Fe2O4)in the chrome spinel that forms a majorconstituent of chrome and chrome-magnesite refractories. A laboratory testsubmits a test-piece cut to the size of a50mm cube, to the action of 40 g of mill-scale (crushed to pass a 30 B.S. sieve) forI h at 16000C; the expansion is expressedas a linear percentage.Bursting Off. Breaking blown glass-warefrom the end of the blowing iron.Bushing. (1) An electric glass-meltingunit for the production of glass fibres,which are drawn through platinumorifices in the base.(2) A liner fitted in the feeder thatdelivers glass to a forming machine;this liner is also known as an ORIFICERING.

Bustle Pipe or Hot-blast CirculatingDuct. A metal tube of large diameterwhich surrounds a blast furnace at alevel a little above the tuyeres; it islined with refractory material anddistributes the hot air from the hot-blast-stoves to the pipes known as

GOOSENECKS which in turn carry the airto the tuyeres.Butterfly Bruise, PERCUSSION CONE(q.v.)Button. Part of a piece of pressed glassdesigned to produce a hole whenknocked out; also sometimes called aCAP or KNOCKButton Test. A test for the fusibility of avitreous enamel frit, or powder, firstproposed by C. J. Kinzie (/. Amer.Ceram. 15, 357, 1932) and subsequentlystandardized (ASTM C374); Also knownas the FUSION-FLOW TEST and as theFLOW BUTTON TEST.Bwlchgwyn Quartzite. A quartzite fromBwlchgwyn, N. Wales, used as a rawmaterial for silica-brick manufacture.Chemical analyses are:

SiO2 Al2O3 AlkalisAs quarried 96.6 1.1 0-4Washed 97.4 0.7 0.3

0C. Degrees Celsius (formerly, and stillmore commonly, known as DegreesCentigrade). For conversion toFahrenheit T0C = (9AT+ 32)°F.' C Glass. (Chemical) An acid-resistantglass composition for glass-fibre, itcontains 7-10% Na2O.C 6 0 . See BUCKYBALL.C 8 0 . See CONTRAST RATIO.Cabal Glass. A special glass consistingsolely of Calcium oxide, Boric oxideand Alumina, hence its name. Cabalglass is known for its low dielectricloss. It was first made by H. Jackson forthe UK Ministry of Munitions in1917-19.Cable Cover. A fired clay (in this contextgenerally, but erroneously, known as'earthenware') or concrete conduit forcovering underground electric cables;these covers warn of the cable's presenceand protect it from excavating tools. Forspecification see B.S. 2484.

CACT. Center for Advanced CeramicTechnology, at Alfred University, USA.CAD/CAM. Computer Aided Design/Computer Aided ManufactureCadmium Carbonate. CdCO3. Smallamounts (up to 2%) are sometimesadded to CADMIUM SELENIDE (q.v.) redcolours to improve their stability.Cadmium Niobate. Cd2Nb2O7; an anti-ferroelectric compound; the Curietemperature lies between - 85°C and -100 0C.Cadmium Nitrate. Cd(NO3)2 .4H2Om.pt. 59.5 0C used to add cadmium forcolouring glass to vitreous enamel.Cadmium Oxide. CdO; sp. gr. approx.7.0. The vapour pressure is approx. 1mm at 10000C and 7 mm at 11000C;sublimes rapidly at 15000C. It isoccasionally used in ceramic colours.The oxide is poisonous.Cadmium Selenide. This compound, orthe polyselenide, is responsible for thecolour in selenium ruby glass. With someCdS in solid solution it forms the basis ofCd-Se red ceramic (especially vitreousenamel) colours; the firing temperaturemust not exceed about 8500C. Thepresence of up to 3% V2O5 is claimed tostabilize the colour; blackening in thepresence of a glaze or flux containing Pbis caused by the formation of PbSe.Cadmium Silicate. CdSiO3; sp. gr. 4.9;m.p. 12400C.Cadmium Sulphide. CdS; sp. gr. 4.8; m.p.17500C. A constituent of some ruby-coloured glass, of some yellow enamels,and of Cd-Se red ceramic colours whichcan be fired at temperatures up to about8500C. Sintered CdS can be used as aphotoconductive ceramic.Cadmium Sulphoselenide. CdS..v CdSe.A ceramic pigment, the basis of a rangeof yellow, orange and red ceramiccolours. See CADMIUM SELENIDE;

ENCAPSULATED COLOURS.

Cadmium Titanate. CdTiO3; aferroelectric ceramic having the ilmenitestructure at room temperature; the Curietemperature is approx. -2200C.Cadmium Yellow. Cadmium sulphide,coprecipitated with barium sulphate.Cadmium Zirconate. CdZrO3;occasionally used as an addition tobarium titanate bodies, the effect beingto reduce the dielectric constant andCurie temperature.Calcine: Calcination. Heat treatmentintended to produce physical and/orchemical changes in a raw material. Thecalcination of bauxite, for example,eliminates water and yields a product thatis relatively free from further firingshrinkage; when kyanite is calcined, on theother hand, the change is not in chemicalbut in mineralogical composition, mulliteand cristobalite being formed.Calcite. CaCO3, the mineral constituentof limestone, chalk, and marble. Used asa constituent of soda-lime glass and, asWHITING (q.v.), in some pottery bodies;it is a major component of the batchused in portland cement manufacture.Calcium Aluminates. The five compounds(q.v.) are: TRICALCIUM

ALUMINATE(3CaO.Al2O3);DODECACALCIUM HEPTALUMINATE

(12CaOJAl2O3); CALCIUM MONO-ALUMiNATE (CaO-Al2O3); CALCIUMDIALUMINATE (CaO. 2AI2O3) andCALCIUM HEXALUMINATE (CaO.6AJ2O3).TRICALCIUM PENTALUMINATE (q.v.) is amixture of the mono- and di-aluminates.Calcium Boride. CaB6; m.p. 2235 0C: sp.gr. 2.45; thermal expansion (25-1000 0C.)5.8 x 10^6; electrical resistivity (20 0C),124 jiohm.cm.Calcium Carbonate. See CALCITE;

WHITING.

Calcium Chloride. CaCl2; used forFLOCCULATiON (q.v.) in the preparationof glazes; about 0.05% is normally

sufficient. It is also sometimes used as amill-addition in the preparation ofvitreous enamel slips. Calcium chloridesolution accelerates the rate of setting ofPortland cement; it is also sometimesadded to concrete mixes as an integralwaterproofer.Calcium Dialuminate. CaO. 2Al2O3;melts incongruently at 1762 ± 5 0C;thermal expansion, 5.0 x 10-6 Presentin high alumina cement but does notitself have cementing properties.Calcium Ferrite. In the binary system,two ferrites are formed - CaO-Fe2O3

and 2CaO-Fe2O3; the former may occurin some HIGH-ALUMINA CEMENT (q.v.).Thermal expansion (0-1000 0C): CaO.Fe2O3,11.7 x 10-6; 2CaO-Fe2O3,10.5 x1(H.Calcium Fluoride. See FLUORSPAR.Calcium Hafnate. CaHfO3; m.p. 2470 ±200C; sp. gr. 5.73; thermal expansion(10-1300 0C), 7 x 1(H.Calcium Hexaluminate. CaO.6Al2O3;melts incongruently at 1830 ± 15 0C toform corundum and a liquid.Calcium Metasilicate. SeeWOLLASTONITE.Calcium Monoaluminate. CaO-Al2O3;melts incongruently at 1602 ± 5 0C;thermal expansion (0-1200 0C), 6.8 x10-6. A major constituent of HIGH-ALUMINA CEMENT (q.v.).Calcium Orthosilicate or DicalciumSilicate. 2CaO-SiO2; m.p. 2130 0C.Occurs in four crystalline forms: a,stable above 1447 0C; a1, bredigite,stable from about 800-14470C onheating, 1447 °C-670 0C on cooling; p,larnite, stable or metastable from520-670 0C; y stable below 780-830 0C.Material in which a considerable amountof 2CaO-SiO2 has been formed by high-temperature reaction, falls to a powder -'dusts' - on cooling because of theinversion (accompanied by a 10%

increase in volume) to the y-form at 5200C. The inversion can be prevented bythe addition of a stabiliser, e.g. B2O3 orP2O5. Calcium orthosilicate is aconstituent of portland cement and maybe formed in dolomite refractories.Calcium Oxide. See LIME.Calcium Phosphate. The compound ofmost interest is 3CaO.P2O5 orCa3(PO4)2; melts with some dissociationat 1755 0C. Crucibles made of thisphosphate withstand FeO melts at 16000C and permit the refining of steel to aphosphate content of 0.025%. It is alsoused in the manufacture of opal glass.See also BONE ASH.Calcium Silicate. The four compounds(q.v.) are: WOLLASTONITE (CaO.SiO2);RANKiNITE (3CaO.2SiO2); CALCIUMORTHOSILICATE (2CaO-SiO2); andTRiCALCiuM SILICATE (3CaO-SiO2).Autoclaved calcium silicate boardproducts, reinforced with cellulose fibres,have been developed as substitutes forasbestos. BS 3958 Pt 2 specifies theproperties and dimensions of preformedcalcium silicate insulation suitable foruse up to 6500C and 9500C.Calcium Silicate Bricks. The approvedterm (replacing sand-lime brick and flint-lime brick) for bricks made byautoclaving a mixture of sand (orcrushed siliceous rock) and lime.Requirements and qualities are specifiedin B.S. 187, and in the USA, in ASTMC73 for calcium silicate facing bricks.Dimensions are specified in BS 4729.Calcium Stannate. CaSnO3; sometimesused as an additive to barium titanatebodies, one effect being to lower theCurie temperature.Calcium Sulphate. See ANHYDRITE;GYPSUM; PLASTER OF PARIS.Calcium Sulpho-Aluminates. Twocompounds exist: the 'high' form,3CaO.Al2O3.3CaSO4.30-32H2O; and

the 'low' form, 3CaOAl2O3.CaSO4.12H2O. Both forms may beproduced by reaction between3CaO-Al2O3 and gypsum during thehydration of portland cement. The 'high'form is also produced when cement andconcrete are attacked by sulphatesolutions.Calcium Titanates. Three compoundsexist: CaO-TiO2, m.p. 1915°C;4CaO.3TiO2, melts incongruently at 17550C; 3CaO.2TiO2 melts incongruently at1740 0C. Calcium titanate refractoriesslowly deform under load at hightemperature; they resist attack by basicO.H. slag and portland cement clinkerbut react with materials containing SiO2

and/or Al2O3. CaO-TiO2 has a dielectricconstant of 150-175; it finds use as acomponent of more complex titanatedielectrics.Calcium Zirconate. CaZrO3; a materialhaving useful dielectric and refractoryproperties. As a dielectric it is normallyused in minor amounts (3-10%) intitanate bodies; as a refractory it can beused, even under reducing conditions, upto 17000C provided that it is not incontact with siliceous material. M.p.approx. 23500C, sp. gr. 4.74; thermalexpansion 8-11 x 10"6 (25-1300 0C).Calcrete. Gravel and sand cementedwith calcium carbonate.Calcspar. Old name for CALCITE (q.v.).Calculated Brickwork. Brickworkdesigned according to the engineeringprinciples set out in BS 5628 'Code ofPractice for the Use of Masonry'. Thecalculations take into account the loadon the wall, its height, the crushingstrength of the bricks, the type ofmortar, the stiffening effect of the floors,and other factors. Walls of calculatedbrickwork can be thinner, and hencemore economic, than traditional walls,yet still be fully adequate to withstand

the stresses that will be imposed onthem. See also LIMIT STATE DESIGN.Calculated Mineralogy. Modernterminology for RATIONAL ANALYSIS(q.v.)Calculon. A building-brick size equal to6.75 in (17 cm).Caledonia Body. A ceramic body formaking coarse glazed pottery; typically,it contained 70% yellow-firing clay, 20%china clay and 10% flint.Calgon. Proprietary name for a complexsodium phosphate (q.v.) sometimes usedas a deflocculant for clay slips; (Albrightand Wilson, Ltd., Oldbury, England).Callow. A term, of localised use, for theoverburden of a clay-pit.Calorific Value (CV). The quantity ofheat released when a unit weight (orvolume) of fuel is completely burned.Units: 1 Btu/lb = 0.556 cal/g = 2326 J/kg.Typical values: coal, 25-35 MJ/kg; liquidfuels, 40-50 MJ/kg; natural gas 40 MJ/m3.Calorite. Trade-name: a pyroscopesimilar to a pyrometric cone butcylindrical; they are made for usebetween 500 and 1470 0C (Wengers Ltd,Stoke-on-Trent, England).Cameo. (1) Glass jewellery, etc., made oftwo or more layers of glasses ofdifferent colours and carved in relief.(2) Similar ornamental pieces made ofJASPER WARE (q.V.)Cam Lining. A lining, usually ofrefractory brick, whose thickness variesregularly around a kiln to induce feedmovement and improve heat exchange.Campaign. The working life of anindustrial furnace between major repairs;the term is particularly applied to blastfurnaces and to glass-tank furnaces.Canal. The section of a flat-glass tank-furnace through which molten glass flowsto the drawing chamber.Candle. See CERAMIC FILTER.

Candlot's Salt, CALCIUM SULPHO-ALUMINATE (q.V.).

Cane. Glass rods of small or mediumdiameter.Cane Marl. Local name for one of thelow-quality fireclays associated with theBassey Mine, Littlerow and Peacock coalseams of N. Staffordshire, England.Cane Ware. Eighteenth-century Englishstoneware of a light brown colour; it wasa considerable advance on the coarsepottery that preceded it but, for use astableware, cane ware was soon displacedby white earthenware. During the 19thand the earlier part of the 20th century,however, cane ware continued to bemade in S. Derbyshire and the Burton-on-Trent area as kitchen-ware andsanitary-ware; it had a fine-texturedcane-coloured body with a white engobeon the inner surface often referred to asCANE AND WHITE.

Cank. An indurated clay with cementedparticles, or a useless mixture of clay andstone, the term is chiefly used in theMidlands and North of England.Cannock. South Staffordshire term for aferruginous nodule occurring in afireclay; the name derives from the townof Cannock in that area.Cannon. A small (15-60 ml) thick-walledglass bottle of the type used to containflavouring essences.Cannon Pot. A small POT (q.v.) for glassmelting.Cant. The bottom outside edge of aSAGGAR (q.v.); it is important that thisshould be rounded to help the saggar toresist thermal and mechanical shock.Cantharides Lustre. A silver lustre forartware similar in appearance to thelustre on the wings of the cantharidesbeetle; it is yellow and has usually beenapplied to a blue lead-glaze.Canton Blue. A violet-blue ceramiccolour made by the addition of barium

carbonate to cobalt blue. A quotedrecipe is (per cent): cobalt oxide, 40;feldspar, 30; flint, 20; BaCO3,10.Caolad Flint. A form of cryptocrystallinesilica occurring at Cloyne, Co. Cork,Eire. It has a sp. gr. of 2.26 and is readilyground, without the need for pre-calcination, for use in pottery bodies.Cap. (1) See BUTTON. (2) A COLLAR(q.v.) on the end of a POST (q.v.) toincrease the area of contact.Capacitor. See DIELECTRIC.Capon Abrasion Test. A method for thedetermination of deep abrasion resistance.A flat test-piece is placed to touchtangentially a 200mm diameter steel discrotating at 75 rpm, and white fusedalumina of grain size 80 (32 GB 1971) isfed into the grinding zone at a rate of100g/100 revolutions of the disc. Thevolume of material removed after 150revolutions of the disc is measured bymeasuring the length of groove ground inthe test-piece. The equipment is calibratedagainst Austrian standard granite. The testis the British and European standard testfor unglazed ceramic floor tiles (BS 6431,Ptl4,1983 EN 102) and has also beenadopted for clay pavers.Capping. (1) The formation of a weakregion at the end of a pressed compact.In the region just below the top punch,the compact is subjected to acompressive force only, with no shearcomponent die to interaction with thedie walls. This region is consequentlyweak. This fault is also known as END-CAPPING.

(2) capping is also the term used for thevarious methods (cardboard or cementspacers, grinding) used to ensure that thefaces of crushing strength test specimensare plane, parallel and perpendicular tothe applied force.Carbides. A group of special ceramicmaterials; see under the carbides of the

following elements: Al, Be, Ce, Cr, Hf,La, Nb, Si, Ta, Th, Ti, U, V, W, Zr.Carbon. See CARBON REFRACTORIES;GRAPHITE.Carbon-Ceramic Refractory. SeePLUMBAGO.Carbon Dioxide Process. A method ofbonding refractory grains by mixingthem with a solution of sodium silicate,moulding to the required shape and thenexposing the shape to CO2. The processwas first mentioned in Brit. Pat. 15 619(1898) but did not come into general useuntil about 1955, when it began to beemployed in the bonding of foundrysands and cores. The process has beentried for bonding rammed linings insmall ladles.Carbonisation. The removal of volatilecomponents from pitch-bonded, resin-bonded or impregnated basicrefractories, by heating to 980 to 1000 0Cimmersed in metallurgical coke in anairtight container, to provide a reducingatmosphere. The refractories retainRESIDUAL CARBON (q.v.) Thecarbonisation mass loss is the loss inmass during this process. ASTM C-607specifies a coking or carbonizationprocedure for large shapes of caron-bearing materials. Cf. CARBON YIELD.Carbon Monoxide Disintegration. Thebreakdown of refractory materials thatsometimes occurs (particularly withfireclay refractories) when theyare exposed, within the temperaturerange 400-600 0C, to an atmosphererich in carbon monoxide. Thedisintegration is due to the depositionof carbon around 'iron spots' in thebrick, following the well-knowndissociation reaction:

2CO = CO2 + CBS 1902 Pt 3.10 and Pt 7.6 specify testsfor resistance to CO, as does ASTMC288.

Carbon Refractories. These refractories,consisting almost entirely of carbon, aremade from a mixture of graded coke, oranthracite, pitch and tar; the shapedblocks are fired (packed in coke). Thefired product has an apparent porosity of20-25% crushing strength 50-70 MNm-2;R.u.L. (350 kPa), 17000C; thermalexpansion (0-1000 0C), 0.65%. Theprincipal use is in the lining of blastfurnaces, particularly in the hearth andbosh (cf. PLUMBAGO).Carbon Yield. See RESIDUAL CARBON.Carborundum. Trade-mark of TheCarborundum Co., Niagara Falls, USA,and Trafford Park, Manchester,England. This firm pioneered theindustrial synthesis of silicon carbide andtheir trade-mark is often used as asynonym of SILICON CARBIDE (q.v.),particulary in its use as an abrasive.Carbothermal Reduction. Hightemperature reactions in which carbonacts as a reducing agent so that oneceramic may be prepared from another,e.g. AlN may be prepared by heating C+ Al2O3 mixtures in N2. The carbonreduces the alumina, to Al metal whichreacts with the nitrogen gas.Carboxymethylcellulose (CMC). Anorganic compound that, in the form of itssodium salt, finds use in the ceramicindustry as an additive to glazes andengobes to prevent friability before thecoating is fired; CMC has been added tovitreous enamel slips to prevent settling.Carboy. A glass container for acids, etc.;it has a narrow neck and its capacity is 5gallons or more. (See B.S. 678.)Carburettor. The chamber of a water-gasplant, lined with refractory material andoften filled with CHECKERS (q.v.) onwhich oil is sprayed to enrich the gas (cf.SUPERHEATER).

Carder Tunnel Kiln. A tunnel-kilndesigned in about 1928 by Carder and

Sons, Brierley Hill, England, for thefiring of stoneware at 12000C.CARES, Ceramic Analysis andReliability Evaluation of Structures.(Formerly known as SCARE - StructuralCeramic Analysis and ReliabilityExamination). A Fortran 77 computerprogram using Weibull and Batdorffracture statistics to predict the fast-fracture reliability of isotropic ceramics.Carlton Shape. A tea-cup the top half ofwhich is cylindrical, the bottom halfbeing approximately hemispherical butterminating in a broad, shallow foot. Forspecification see B.S. 3542.Carman Equation. A relationship,derived from KOZENY'S EQUATION(q.v.), permitting determination of thespecific surface, S1, of a powder frompermeability measurements:

S = 14V[p3AKV(l -p2)]where p is the porosity of the bed ofpowder, V is the kinematic viscosity ofthe flowing fluid, and K is a constant. Inhis original application of this equation,Carman used a simple apparatus inwhich liquids were used as permeatingfluids. (P.C. Carman, /. Soc. Chem. Ind.,57, 225, 1938.)Carnegieite. Na2OAl2O3^SiO2, m.p.1526°C. It is formed when NEPHELINE(same composition) is heated above1248°C and is sometimes found infireclay refractories that have beenattacked by Na2O vapour.Carolina Stone. A CHINA STONE (q.v.)used to some extent in the US potteryindustry.Carrara Porcelain. Term sometimesapplied to PARIAN (q.v.).Carrousel. A four-wheeled bogie fittedwith a rotating framework which carriestwo sets of STiLLAGES (q.v.) for thehandling of bricks from a dryer to aHoffmann type of kiln. (From theFrench word for a merry-go-round.)

Carry. Term sometimes used in Scotlandfor OVERBURDEN (q.V.).Car Top. See DECK.Cascading. The behaviour of the chargein a ball mill when it spills from thehighest point without an appreciableproportion passing into free flight.Case Mould. See under MOULD.Cased Glass. Glass-ware with asuperimposed layer of another glasshaving a different composition andusually coloured. The thermalexpansions of the two glasses must becarefully matched (cf. PLY GLASS).Casella Counter. A device for theautomatic counting and size-determination of particles from 1 to200mm. (Casella Electronics Ltd., York,England.)Casement Wall. See BREAST WALL.Casher Box. A metal box used to catch aglass bottle after it had been severedfrom the blow-pipe in the old hand-blown process.Casing Wall. See BREAST WALL.Cassel Kiln. See KASSEL KILN.Cassette. A design of tile CRANK basedon a rectangular refractory module. Thetiles are supported and separatedwithout building up a structure of postsand pins.Castable. BS 1902, Pt 7 defines a castableas a mixture of graded refractoryaggregate and other materials, which,after mixing with water, will set owing tothe formation of a hydraulic and/or achemical bond. Castables are subdividedinto two categories according to theirbulk density. Insulating castables arethose which when cast, cured and driedat 110 0C have a bulk density 1600kg/m3. All other castables are known asdense castables. BS 1902 Pt 7 specifiestests for UNSHAPED REFRACTORIES(q.v.). ASTM C401 defines REGULARCASTABLE REFRACTORIES aS those

containing hydraulic setting cements andhaving a lime content greater than 2.5%.Normal strength castables have amodulus of rupture of at least 2.07 MNirr2 (300 psi); high-strength types have amodulus at least 4.14 MN m~2. They arefurther classified on the basis of volumestability. Insulating castables areclassified on the basis of bulk density.See also LOW-CEMENT CASTABLE; NO-C E M E N T CASTABLE.

Casting. Shaping a fluid material (whichsubsequently solidifies) by pouring it intoa mould. The process is used in potterymanufacture and in glass-making. Tocast pottery-ware, a SLIP (q.v.) is pouredinto a plaster mould which absorbs aproportion of the water so that the bodybuilds up on the walls of the mould. Inthe production of thin-walled ware, e.g.tableware, excess slip is poured out ofthe mould when the required thicknessof ware has been formed. For thick ware,e.g. sanitary fireclay, the SOLID CASTINGprocess is used, with an inner plastercore; slip is in this case poured into thespace between mould and core and thebody is allowed to build up without anyslip being poured off. ASTM C 866, atest for the filtration rate of whitewareclays, is relevant to casting behaviour.Glassware can be cast by pouring moltenglass into a mould. (A telescope mirrorblank 6 m diameter was thus made).Television tubes and radomes are madeby centrifugal casting. The glass flowsupwards in a spinning mould, producinga uniform wall thickness. Complexshapes are made by slip-casting groundglass powder in plaster of Paris moulds,then firing.Casting-pit Refractories. Speciallyshaped refractories (usually fireclay) foruse in the casting of molten steel. Theindividual items included in the term are:LADLE BRICKS, ROD COVERS, STOPPERS,

NOZZLES, MOULD BRICKS, TRUMPETS,GUIDE TUBES, CENTRE BRICKS,RUNNERS, CONES and MOULD PLUGS(q.v.). ASTM C435 classifies nozzles,sleeves and ladle bricks each into typeA, B or C depending on PCE, porosity,reheat linear change and, for ladlebricks, modulus of rupture.Casting Spot. A fault that sometimesappears on cast pottery as a vitrified andoften discoloured spot on the bottom ofthe ware or as a semi-elliptical mark onthe side. It occurs where the stream ofslip first strikes the plaster mould and isattributable to local orientation of platyparticles of clay and mica in the body.The fault can be largely eliminated byadjusting the degree of deflocculation ofthe slip so that it has a fairly low fluidity.The fault is also sometimes calledFLASHING.Castle; castling. Local term for thesetting of bricks on a dryer car, two-on-two in alternate directions.Catalyst Support. Many catalysedchemical reactions require the catalyst topresent a high surface area to thereagents. One way of achieving this is forthe catalyst to be supported on an inertsubstrate itself of high surface area - forexample a ceramic honeycomb.Catalytic Converter. A device to removenoxious components from the hotexhaust gases of diesel and petrolengines, by passing them over a suitablecatalyst to promote their breakdown.Cordierite ceramic honeycombs are theusual catalyst carriers.Cataphoresis. The movement of colloidalparticles in an electric field; this formsthe basis of the purification of clays bythe so-called ELECTRO-OSMOSIS (q.v.)method.Catenary Arch. A sprung arch havingthe shape of an inverted catenary (theshape assumed by a string suspended

from two points that are at an equalheight from the ground). The stresspattern in such an arch is such that thereis no tendency for any bricks to sliprelative to one another.Cateracting. Term used in ball-millingfor the state of the charge when a largeproportion falls in free flight. Thisusually occurs at mill speeds higher thanthat needed for CASCADING (q.v.).Cathedral Glass. Rolled flat-glasstextured on one side to resemble oldwindow glass (cf. ANTIQUE GLASS).Cathode Pickling. See ELECTROLYTIC

PICKLING.Cationic Exchange. See IONICEXCHANGE.Cat Scratch. Surface flaws on glasswareresembling the marks of a cat's claws.Cat's Eye. (1) Glass tubing of thescHELLBACH (q.v.) type for use in spirit-levels. (2) A fault, in glass-ware, in theform of a crescent-shaped blister whichmay contain foreign matter.Cauchy Formula. A formula proposedby A. L. Cauchy, a 19th-century Frenchmathematician, relating the refractiveindex, n, of a glass to the wavelength, X,of the incident light:

n = A + BX-2 + CX-*. . .A closer relationship is the HARTMANFORMULA (q.v.).Caveman. An oddjob man around(frequently under) a glass furnace.Cavity Wall. A wall built so that there isa space between the inner and outerleaves, which are tied together atintervals by metal or other ties. Such awall has improved thermal insulationand damp-proofness.CBN. Cubic Boron Nitride (q.v.)C/B Ratio. A term that has been usedfor the SATURATION COEFFICIENT (q.V.).C & D Hot Top. A HOT-TOP (q.v,)designed by W. A. Charman and H. J.Darlington (hence the name 4C & D') at

the time, about 1925, when they wereboth employed by Youngstown Sheetand Tube Co., USA. The hot top, whichis fully floating, consists of a cast-ironcasing lined with fireclay or insulatingrefractories; a refractory bottom ring isattached to the lower end of the casingto protect the latter from the hot metal.C-D Principle. The Convergence-Divergence principle used in theFRENKEL MIXER (q.V.).ce.c. Cation exchange capacity. SeeIONIC EXCHANGE.Celadon. An artware glaze of acharacteristic green colour, which isobtained by introducing a smallpercentage of iron oxide into the glazebatch and firing under reducingconditions so that the iron is in theferrous state. The name was used by thefirst Josiah Wedgwood for his self-coloured green earthenware.Celeste Blue. A ceramic colour made bysoftening the normal cobalt blue by theaddition of zinc oxide.Celite. The name given to one of thecrystalline constituents of portlandcement clinker by A. E. Tornebohm(Tonindustr. 58 Ztg. 21,1148,1897). Thisconstituent has now been identified as asolid solution of 4CaO.Al2O3-Fe2O3 and6CaO.2Al2O3.Fe2O3.Cell. One of the spaces in a hollow claybuilding block. According to the USspecification (ASTM C212) a cell musthave a minimum dimension of at least0.5 in. (12.5 mm) and a cross-sectionalarea at least 1.5 in2 (950 mm2).Cell Furnace. A glass-tank furnace inwhich glass in the melting end andauxiliary chambers is heated electrically.Cellular Brick or Block. A clay buildingbrick or block which shall not haveholes, but may have frogs or cavities(holes closed at one end) exceeding 20%of the volume of the brick or block. (B.S.

3921). Cellular bricks are usually madeby pressing whereas PERFORATEDBRICKS (q.v.) are made by extrusion.Cellular Concrete. See AERATEDCONCRETE.Cellular Glass. See FOAM GLASS.Celsian. Barium feldspar,BaO.Al2O3.2SiO2; m.p. 1780 0C. Thereare two crystalline forms, resulting in anon-linear thermal expansion curve.Celsian refractory bricks have beenmade and have found some use inelectric tunnel kilns.Celsius. The internationally approvedterm for the temperature scalecommonly known as Centigrade. Thefixed points are 00C, (the triple point ofwater) and 1000C (the steam overboiling water). See 0C, 0F.Cement. See ACID-RESISTING CEMENTS;CIMENT FONDU; HIGH EARLY-STRENGTHCEMENT; HYDRAULIC CEMENT; KEENE'SCEMENT; PORTLAND CEMENT; RAPID-HARDENING PORTLAND CEMENT;REFRACTORY CEMENT, SILICATECEMENT; SOREL CEMENT, SULPHATE-RESISTING CEMENT; SULPHO-ALUMINATECEMENT; SUPERSULPHATED CEMENT. Formethods of testing cement see BS 4550,Pts 0 to 6, which specifies chemicalanalysis, strength and consistency tests,setting times, soundness, heat ofhydration, and standard sands and coarseaggregates for mortar and concrete. BS6432 specifies tests for glass-fibrereinforced cement.Cementation. A process to promote theabsorption and diffusion of onesubstance into the surface of another.(Originally, producing a hard carbonsteel coating on wrought iron by packingit in charcoal and heating strongly for along period).Cement Bacillus. This name hasbeen applied to the compound3CaO.Al2O3.3CaSO4.31H2O, which is

formed by the action of sulphatesolutions on portland cement andconcrete.Cemented Carbide. Metal carbides,chiefly tungsten carbide WC andtitanium carbide TiC, used for cuttingtools, in which the carbide grains arebonded together by a thin layer of metal,usually cobalt, though nickel has alsobeen used. The object is to provide adegree of ductility to an inherentlybrittle material.Cemented Oxide. See TOOL (CERAMIC).Cement-kiln Hood. The head, which maybe mobile or fixed, of a rotary cement kiln;through the hood the burner passes andwithin the hood the clinker dischargesfrom the kiln to the cooler.CEN. Comite Europeen deCoordination des Normes, Boite 5,B-1000, Brussels. EN. Abbreviation forEuropean Standards (Euronorm)Centigrade. See 0C.Centre Brick. A special, hollow,refractory shape used at the base of theGUIDE TUBES (q.v.) in the bottom-pouring of molten steel. The CentreBrick has a hole in its upper face andthis is connected via the hollow centre ofthe brick to holes in the side faces (oftensix in number). The Centre Brickdistributes molten steel from the trumpetassembly to the lines of RUNNER BRICKS.Centre Pip. A fault in tableware madeby the ROLLER-HEAD (q.v.) process. Asmall raised area forms at the centre ofthe ware in firing. The orientation of clayparticles introduced by pugging persistsacross the thickness of the ware at thecentre. Elsewhere the shaping processreorients the particles along a diameter.The result is a central region ofminimum drying and firing shrinkageand a raised centre.Centreless Grinding. The cylindricalworkpiece to be ground is supported on

a workable and rotated by a 'regulatingwheel' (q.v.). It is also sometimes knownas a CROWN BRICK or SPIDER.

Centrifugal Casting. Tubes and otherrotationally synmetric shapes are cast onthe inside of moulds spun at high speedto produce large forces which increaseconsolidation rates. A dense cast results.No central core is needed to cast hollowarticles. The moulds may be of plasticsor metal and need not be porous. Cone-shaped glassware such as television tubesis made in this way.Centrifugal Disc Mill. A horizontal discwithin a chamber is rotated at high speedby an electric motor. Clay is fed in nearthe axis, and comminuted by thecentrifugal action of the mill, at constantmoisture content.Centrifuge. A device in which the rate ofsettling of particles from a liquidsuspension is accelerated by subjectingthem to a high centrifugal force; this isdone by charging the suspension intocarefully-balanced 'buckets' at oppositeends of a diameter of a rapidly spinningdisk or shaft. Such equipment is usedindustrially in the treatment of rawmaterials; in the ceramic laboratory, thecentrifuge is used as a method ofparticle-size analysis, particularly forparticles below about lmm.Centura Ware. Glass-ceramic tablewarethat has been glazed, and sometimesdecorated. (Trade name: Corning GlassWorks, USA).CERABULL. A computer database andelectronic bulletin board operated by theAmerican Ceramic Society.Ceramel. Obsolete term for CERMET

(q.v.).Ceramesh. 0.1 mm pore-size metal meshcoated with zirconia.Ceramic Coating (on Metal). Defined(ASTM - C286) as: 'An inorganicessentially non-metallic, protective

coating on metal, suitable for use at orabove red heat.'Ceramic Colour Standards. This set of 12ceramic tiles provides standard coloursfor the calibration of colour measuringinstruments used in all industries.Specially developed colours and glazesand rigorously precise firing schedulesgive stable and reproducible colours.There are 3 neutral grey standards withflat spectral curves to check linearity ofresponse; 7 strongly coloured standardswith steep spectral curves to checkresponsivity or wavelength andwaveband errors; 2 colour-differencestandards which 'pair' with the mid-greyand the green standards, giving a directcheck on colour differencemeasurements. A black and a whitestandard are available, plus 'specials' toindividual requirements. (Thedevelopment of these tiles, incollaboration with the National PhysicalLaboratory, earned Ceram Research,Stoke-on-Trent, its second Queen'sAward for Technological Achievement).Ceramic Filter. A ceramic characterizedby an interconnected pore system, thepores being of substantially uniform size.Such ceramics are made from a batchconsisting of pre-fired ceramic, quartz oralumina together with a bond that,during firing, will vitrify and bind thesurfaces of the grains together. The poresize of different grades varies from about10 to 500mm; tests for pore size aredescribed in B.S. 1752. The filters arecommonly available as tiles or tubes, thelatter sometimes being known asCANDLES; special shapes can be madeas required. Uses include filtration,aeration, electrolytic diaphrams and air-slides (cf. FILTER BLOCK', SINTERED

FILTER).

Ceramic Process. The ASTM definitionis: 'The production of articles or coatings

from essentially inorganic, non-metallicmaterials, the article or coating beingmade permanent and suitable forutilitarian and decorative purposes bythe action of heat at temperaturessufficient to cause sintering, solid-statereactions, bonding or conversionpartially or wholly to the glassy state.'See also APPENDIX A.Ceramic-to-metal Seal. The joining of ametal to a ceramic is generallyaccomplished by METALLIZING (q.v.) theceramic surface and then brazing-on themetal component. Ceramic-to-metal sealsare used in electrically insulated andvacuum-tight 'lead-throughs', especiallyfor high-power h.f. devices; componentsso made are more rugged and resisthigher temperatures than those having aglass-to-metal seal, thus permitting ahigher bake-out temperature and use in anuclear environment.Ceramics and Ceramic Materials. Non-metallic inorganic or carbon solids,artificially produced or shaped by a high-temperature process, and inorganiccomposites wholly or essentiallycomprising such materials. Ceramics areusually taken to be shaped articles. (Fora discussion of the problems in definingceramics, and for official and quasi-official definitions in various contexts,see APPENDIX A).

Ceramic Whiteware. This term is definedin the USA (ASTM C242) as: 'A firedware consisting of a glazed or unglazedceramic body which is commonly whiteand of fine texture; the term includeschina, porcelain, semivitreous ware andearthenware.'Ceramix. Tradename for a flow controldevice developed by Ideal Standard Incfor hot/cold water mixer taps. Twoalumina discs, one solid, the otherpierced by three holes, rotate againsteach other to open or close the holes to

provide for the passage of water. Thedevice is wear-resistant. (UK Pat.2136544A and 2136545A, 1984)Ceramming. The conversion of a glass toa glass-ceramic.Ceramography. The study ofmicrostructures of ceramics atmagnifications greater than 50 .Ceramoplastic. An electrically insulatingcomposite of synthetic mica bonded toglass.Ceramtec. Tradename of the CeramicDevelopment Co for pyrophyllite, butoften used in a context which impliesthat it is a synthetic ceramic.Ceranox. A collective term for binarycompounds of B, C, N and Si.CeraPearl. A castable apatite ceramic,for dental application. Its tensile strength(150 MPa) is more than twice that offeldspathic dental porcelain.Cercoms. Composites with at least oneceramic component.Cercon. Tradename. Lightweighthoneycomb ceramics (CorningGlassworks).Ceria. See CERIUM OXIDE.Cerium Borides. CeB4: m.p.2100 0C;sp. gr. 5.7. CeB6: thermal expansion(25-1000 0C) 6.7 x 1(HCerium Carbides. CeC2: m.p. 2500 0C;sp.gr. 5.2; decomposed by water. Ce2C6

has also been reported.Cerium Nitride. CeN; produced by theaction of N2 on Ce at 800C or NH3 onCe at 500C.Cerium Oxide. CeO2; m.p. 2600C; sp. gr.7.13; thermal expansion (20-800C), 8.6 x10-6. A rare earth derived from themonazite of India, Brazil, Florida,Australia and Malagasy. Used in thepolishing of optical glass; it is alsoeffective both as a decoloriser and as acolouring agent for glass.Cerium Sulphides. There are threesulphides: CeS, m.p. 2450 0C ± 100 0C;

Ce3S4, m.p. 2050 0C ± 75 0C; and Ce2S3,m.p. 18900C ± 50 0C. Special ceramiccrucibles have been made of thesesulphides, but they can be used only invacuo or in an inert atmosphere; suchcrucibles are suitable as containers formolten Na, K, Ca and other highlyelectropositive metals. The thermal-shock resistance of CeS is good, that ofCe2S3 poor, and that of Ce3S4

intermediate.Cerlite. An Italian body of clay,chamotte and feldspars, which is claimedto combine the strength of vitreous chinawith the lower deformability of fireclay,whereby it is suitable for making largeobjects.Cermet. A material containing bothceramic and metal. According to onedefinition the proportions by weight liebetween 15% and 85%. Cermets appearfirst to have been made by M. Hauser inSwitzerland in 1926. Experiments havebeen made with a wide range of ceramics(oxides and carbides) and metals (iron,chromium, molybdenum, etc.) in anattempt to combine the refractory andoxidation-resistant properties ofceramics with the thermal-shockresistance and tensile strength of metals.Success has been only partial. The mostpromising cermets are TiC/Alloy (thealloy containing Ni, Co, Mo, W, Cr invarious proportions), Al2O3/Cr, Al2O3/Fe and ThO2/Mo. The principal use forcermets would be for the blades of gasturbines and other high-temperatureengineering units. Special cermets arealso currently being used in brake andclutch linings. (Name first proposed byA. L. Berger - see /. Am. Ceram. Soc,32, 81,1949; for general information onthe subject see J. R. Tinklepaugh and W.B. Crandall Cermets, Reinhold, 1960.)Note also that C.A.Calour and A.Mooreclaimed (/. Mat ScL, 7, (5), 543,1972)

that above 700 0C metal matrix cermets,reinforced with ceramic fibres orwhiskers, were not viable. If the fibrereacts sufficiently well with the metalmatrix to form a bond, its lifetime islimited by corrosion; if it is sufficientlyunreactive not to corrode, an inadequatebond is formed.Cerulean Blue. Cobalt stannateCoOwSnO2, a light blue pigment.Chain Hydrometer. A type ofhydrometer that is operated at constantdepth by a chain loading device similarto that used on some analytical balances.It has been used for the determinationof the particle-size distribution of clays.Chain Silicates. See SILICATESTRUCTURES.Chair. ( I)A wooden chair of traditionaldesign used by a glass-blower.(2) A team of workmen producing hand-made glass-ware.Chairman. See GAFFER.Chalcedony. A cryptocrystalline, fibrousform of quartz; flint, for example, ischalcedonic.Chalcogenide Glass. A glass containing ahigh proportion of tellurium, selenium orsulphur. Such glasses are used inelectronic current-switching devices, astheir conductivity differs along differentcrystal panes, but their switching rate hasproved too slow for modern computerapplications. Current research centres ontheir high infra-red transmission, andapplications in solar cells.Chalk. A soft rock consisting of fine-grained calcium carbonate used as analternative material to limestone incement manufacture, and in theproduction of WHITING (q.v.).Chalkboard Enamel, BLACKBOARD

ENAMEL (q.V.)Chalked or Chalky. The condition ofvitreous enamelware that, inconsequence of abrasion or chemical

attack, has lost its gloss and has becomepowdery.Chamber Dryer. A type of dryer inwhich shaped clayware is placed inchambers in which the temperature,humidity, and airflow can be controlled;the ware remains stationary during thedrying process. The Keller Dryer is ofthis type, its distinctive feature being thesystem of handling the bricks to be driedby means of STILLAGES (q.v.) andFINGER-CARS (q.V.).Chamber Kiln. An ANNULAR (q.v.) kilnof the type in which the setting space ispermanently subdivided into chambers;examples include the SHAW KILN (q.v.)and the MENDHEIM KILN (q.v.).Chamber Oven. A refractory-lined gas-making unit; the capacity of such anoven may vary from about 1 to 5 tons ofcoal.Chamotte. A W. European word(originally German) which has now alsobeen adopted in the UK, denotingrefractory clay that has been speciallyfired and crushed for use as a non-plasticcomponent of a refractory batch; it isgenerally made by calcination of lumpsof the raw clay in a shaft kiln or in arotary kiln (cf. GROG)Champleve Enamelware. One type ofvitreous-enamel artware: a pattern is firstcut into the base-metal but, where thepattern requires that enamels ofdifferent colours should meet, a verticalfin of metal is left so that the colourboundary will remain sharp, the twoenamels not running into one anotherwhen they are fused. (French wordmeaning 'raised field'.)Characterisation. The description ofthose material variables that aresufficient to permit reproduction ofmaterial performance in service, in a testor in relation to material processing. Theterm is used loosely for the measurement

of microstructural, textural andmineralogical properties.Charge. As applied to a ball mill thisterm means the material being groundand the grinding media.Charge Pad. Localised thicker or betterquality refractory in a metallurgicalfurnace, to withstand the impact of hotmetal or scrap entering the furnace.Charge Shaft. See FIRE PILLAR.Charlton Photoceramic Process. Apositive print is formed on ceramic wareby a process involving the application ofemulsion to the ware, exposure incontact with the negative, anddevelopment. (A. E. Charlton, CeramicIndustry, 56, No. 4, 127, 1951.)Charp. Trade-name for Calcined High-Alumina Refractory Powder; it is madefrom Ayrshire bauxitic clay.Charpy Test. An impact test for fractureresistance. A V-notched specimen, fixedat both ends, is struck behind the notchby a pendulum. The energy lost by thependulum in fracturing the test-piecegives a measure of the impact strength ofthe material. See FRACTURE TOUGHNESSTESTS.

Chaser Mill. Name occasionally used foran EDGE-RUNNER MILL (q.v.) particularlyof the over-driven fixed-pan type.Chatelier. See LE CHATELIER.Chatter Sleek. = FRICTIVE TRACK (q.v.)Check, Crizzle, Vent. A surface crack inglassware. (See also SMEAR.)Checkers; Checker Bricks. Refractorybricks or special shapes set in aregenerator in such a way as to leavepassages for the movement of hot gases;waste gases passing from a furnacethrough the checkers give up heat which,on reversal of the direction of gas flow inthe furnace, is subsequently transferredto the combustion air and fuel.Checkerwork, Chequerwork. Aconstruction made with many CHECKER

BRICKS (q.v.) to provide a large surfacearea for heat transfer to gases.Checking. (1) A defect in cast-ironenamelware, raised lines appearing onthe surface as a result of cracks in theground-coat. (2) The term has been usedin USA to signify surface cracking orcrazing of clayware.Cheeks. The refractory side-walls of theports of a fuel-fired furnace.Chemically Bonded Refractory Cement.A jointing cement for furnace brickworkthat may be one of two types: Air-settingrefractory cement - finely groundrefractory material containing chemicalagents, such as sodium silicate, whichensure that the cement will harden atroom temperature; Air-hardeningrefractory cement - finely groundrefractory material containing chemicalagents that cause hardening at atemperature below that at whichvitrification begins but above roomtemperature.Chemical Machining. Selective etchingor dissolution of material to shape acomponent. See LEACHABLE GLASS;LITHIUM SILICATE GLASSES.Chemical Porcelain. US term forCHEMICAL STONEWARE (q.V.).Chemical Stoneware. A vitreous type ofceramic product for use in the chemicalindustry and in other locations whereresistance to chemical attack is sought. Atypical body composition is: stonewareclay or plastic fireclay, 25-35%, ball clay,3(M0%, feldspar, 20-25%; grog, 20-30%. The grog may be crushedstoneware or porcelain, fused alumina,or silicon carbide, depending on thecombination of physical propertiessought in the finished product. The firingtemperature is usually 1200-1300 0C.Chemical stoneware has a crushingstrength of nearly 300 MN rrr2; thecoefficient of linear expansion (20-100

0C) is 4 x 10-6. In the USA, this type ofware is termed 'Chemical Porcelain'.Chemical Surface Coating (CSC). Thislow-temperature chemical modificationtechnique has three stages: activation ofthe substrate; formation of the newceramic precursor by chemical action;heat treatment to convert the newprecursor into a new ceramic coating.For instance, a silicon nitride coating canbe produced by activating a silica gelsubstrate by chemisorption oftrichorosilane, reacting with ammoniaand heating to 500 0C.Chemical Vapour Deposition (CVD).Chemical reactions between gaseousreagents at or near a heated surface areused to deposit a material coating onthat surface. Process temperature aretypically above 700 0C. The technique iswidely used both to prepare ceramicmaterials, and to apply ceramic coatingsto other material. It was first developedto fabricate microelectric devices.Compared to other coating methods ithas higher deposition rates and offersbetter control over the microstructure ofthe coating by adjusting the depositionparameters.Chemical Vapour Infiltration (CVI).Vapour phase reactants infiltrate aporous preform. Their chemicalreactions deposit product within thepores to produce a 2-phase composite.Chequers; Chequer Bricks. SeeCHECKERS; CHECKER BRICKS.Chert. A general term for acryptocrystalline siliceous rock that mayoccur in either nodular or tabular form.Chert stones were used as pavers andrunners in the old paddle type of mill forgrinding potters' materials; trimmedchert blocks are now used as a liningmaterial for ball mills.Chest Knife. A tool used in hand-blownglass-making for removing the MOIL (q.v.)

from the blowing-iron; the moils areallowed to crack off while the blowing-irons are in a receptacle called a 'chest'.Chevenard Dilatometer. An apparatusfor the measurement of thermalexpansion; it depends on the recording,by means of an optical lever, of thedifferential expansion of the test-pieceand that of a standard. It finds use inWestern Europe for the testing ofceramic products. (P Chevenard CompteRend., 164, 916,1917.)Chevron Notch Bend Test. SeeFRACTURE TOUGHNESS TESTS.

Chevroning. Fault-like planes in rotarykiln linings. The bricks between adjacentfault planes are tilted out of alignmentwith a V or chevron end to the displacedregion. Ovality of the kiln structure isone cause.Chill Mark. A surface defect on glass-ware characterized by its wrinkledappearance; also known as FLOW LINE(q.v.). It is caused by uneven contact inthe mould prior to the forming.Chimney Linings. Refractory concretesare used line steel chimneys, by gunningor casting. BS 4207 provides a code ofpractice for their formulation andinstallation. See also FLUE LINER.Chimney Pot. The relevant BritishStandard is BS 1181 (1961); cf. FLUE

LINER.

China. BS 5416 specifies this to bepottery with water absorption 0.2% andtranlucency 0.75% (assessed bycomparison with standard test pieces)See also BONE CHINA. In the USA,however, ASTM-C242 defines the wordas any glazed or unglazed vitreousceramic whiteware used for nontechnicalpurposes, e.g. dinnerware, sanitary-ware,and art-ware, provided that they arevitreous. The COMBINEDNOMENCLATURE (q.v.) equates this termwith PORCELAIN (q.v.).

China Clay (Kaolin). A white-firing clayconsisting essentially of KAOLINITE(q.v.). Major deposits occur in Cornwall(England); Georgia, S. Carolina andFlorida (USA); Germany, France,Czechoslovakia, and elsewhere. Annualoutput in USA is 2 500 000 tons; inEngland, 1 500 000 tons. Of thesetonnages only about 20% is used in theceramic industry (pottery andrefractories). Typical composition (percent): SiO2, 47; Al2O3, 38; Fe2O3, 0.8;Alkalis, 1.7; loss-on-ignition, 12.Chinaflow. A specialist distributionservice for china and glassware, operatedby National Carriers.Chinagraph. Specially formulated pencils(Royal Sovereign Pencil Co) for markingpottery, glass and similar smooth, hardsurfaces.China Process. A US term defined(ASTM - C242) as the method ofproducing glazed whiteware in which thebody is biscuit fired and glaze is thenapplied followed by glost firing at alower temperature. (In the UK thisprocess is used in the manufacture bothof earthenware and of bone china.)China Sanitary-ware. US term forvitreous ceramic sanitaryware.China Stone. Partly decomposed granite,consisting of feldspathic minerals andquartz, it is used as a flux in potterybodies. Examples in the UK are CornishStone and Manx Stone. The former isavailable in various grades, e.g. HardPurple, Mild Purple, Hard White andSoft White; the feldspars are leastaltered in the Hard Purple, alteration tosecondary mica and kaolinite beingprogressively greater in the Mild Purple,Hard White, and Soft White; the purplestones are so coloured by the smallamount of fluorspar present. Manx Stone(from Foxdale, Isle of Man) is virtuallyfree from fluorine.

Chinese Blue or Mohammedan Blue.The mellow blue, ranging in tint fromsky-blue to greyish-blue, obtained by theearly Chinese and Persian potters by theuse of impure cobalt compounds ascolorants.Chinese Red, Chrome Red. Red andorange colours made from variousproportions of lead oxide PbO and leadchromate PbCrO4.Chipping. The chipping of vitreousenamelware is often attributable to theenamel coating being too thick, or to thecurvature of enamelled edges being toosharp. Chipping of the edges of ceramictableware is also accentuated by poordesign.Chittering. A fault that may appear as aseries of small ruptures along the edge orrim of pottery-ware. True chittering iscaused by incorrect fettling.Choke. A glass-making fault appearingas a constriction in the neck of a bottle.Choke Crushing. The method of runninga pair of crushing rolls with the spacebetween the rolls kept fully charged withclay; with the rolls operated in this waymuch of the crushing is achieved by theclay particles bearing on each otherwhich gives a finer product than withFREE CRUSHING (q.V.).Chrome-Alumina Pink. A ceramiccolour consisting principally of Cr2O3,Al2O3 and ZnO; when used as a glazestain, the glaze should contain ZnO andlittle, if any, CaO. It is recommendedthat, for use under-glaze, the glazeshould be leadless. The colour dependson diffusion of Cr into the insolubleAl2O3 lattice and is normally stable upto 1300 0C.Chrome Green. See VICTORIA GREEN.Chromel. Tradename. Nickel-chromealloys used in chromel-alumelthermocouples, and kiln accessories andfurniture.

Chrome-Magnesite Refractory. Arefractory material made from chromeore and dead-burned magnesite, thechrome ore preponderating so that thefired product contains 25-55% MgO.Such refractories may be fired or theymay be chemically bonded; they arefrequently metal-cased and find most usein the steel industry. A typical chemicalanalysis is (per cent): SiO2, 3-7; Fe2O3,10-14, Al2O3,12-18; Cr2O3, 25-30; CaO,1-2; MgO, 35-40. See also MAGNESITE-

CHROME REFRACTORY for A S T Mclassification.Chrome Ore. An ore consistingprimarily of chrome spinels, (Fe, Mg)O.(Cr, Fe, Al)2O3; it occurs in ultrabasicigneous rocks and in rocks derived fromthem by alteration, e.g. serpentines. Thechief sources are in S. Africa, Rhodesia,Turkey and Russia; there are otherimportant deposits in Yugoslavia,Greece, India, Philippines and Cuba.The composition varies widely; a typicalrefractory-grade ore contains (per cent)Cr2O3, 40-45; SiO2, 3-6; and Al2O3,FeO, and MgO, 15-20 of each. Theprincipal use in the refractories industryis in the manufacture of chrome-magnesite bricks for the steel industryChrome Red. See CHINESE RED.Chrome Refractory. A refractory brickmade from chrome ore without theaddition of other materials; the Cr2O3

content is 25%. and the MgO content is25%. Chrome refractories are neutral,chemically, and find use as a separatingcourse of brickwork between silicarefractories and basic refractories; theirR.u.L. q.v.) is considerably lower thanthat of chrome-magnesite refractories.Chemical composition (per cent): SiO2

4-7; Fe2O3, 12-15; Al2O3, 16-20; Cr2O3,38-42; CaO, 1-2; MgO, 15-20.Chrome Spinel. A SPINEL (q.v.) in whichthe trivalent metal is Cr.

Chrome-Tin Pink. A colour for ceramicglazes; it was first used in England in the18th century and was originally called'English Pink'. The mechanism by whichthe colour is formed is precipitation offine particles of chromic oxide on thesurface of tin oxide in an opaque glaze;lime must also be present.Chrome-Zircon Pink. About 70% of theSnO2 used in CHROME TIN PINK (q.v.)can be replaced by zircon withoutimpairing the colour or stability.Chromic Oxide. Cr2O3; m.p. approx.2270 0C; sp. gr. 5.21; thermal expansion(0-1200 0C) 7.4 x 10-6. A source of greencolours for the ceramic industry butusually added in the form of a chromate,e.g. potassium dichromate. The oxide ishighly refractory and has been used to alimited extent to improve the bond inCHROME-MAGNESITE REFRACTORIES

(q.v.)Chromite. Ferrous chromite. FeO-Cr2O3;sp. gr. 4.88; thermal expansion (0-12000C) 8.3 x 10-6 Chromite is a majorconstituent of many CHROME ORES(q.v.).Chromium Borides. At least sevenchromium borides have been reported.The compound that has received mostattention is the diboride, CrB2; m.p.approx. 19000C; sp. gr. approx. 5.5;thermal expansion 5.0 x ICh6. Whenheated in air, a coating of B2O3 isformed and prevents further oxidationup to the limiting temperature at whichB2O3 itself ceases to be stable. It hasbeen used for the flame-spraying ofcombustion-chamber linings.Chromium Carbides. At least two Crcarbides exist. Cr3C2; m.p. 1890 0C; sp.gr. approx. 6.7; thermal expansion (20-1000 0C) 10 x 10-6. CrC: m.p. 15500C butoxidizes at 1100 0C. These carbides arehard, refractory, and chemicallyresistant. As such they have found

limited use in bearings and corrosion-resistant nozzles, etc.Chromium Dioxide. CrO2. Aferromagnetic; CURIE POINT (q.v.) 1160C; magnetic coercive force 20-30oersteds; saturation magnetization 130emu/g.Chromium Nitrides. There are twocompounds, Cr2N and CrN; the latterdecomposes at 15000C.Chromium Oxide. See CHROMIC OXIDE;CHROMIUM DIOXIDE.

Chromium Silicides. Several compoundsexist e.g. Cr3Si, Cr2Si, CrSi, Cr3Si2 andCrSi2. The m.p. varies from approx.15500C for CrSi and CrSi2 to approx.17000C for Cr3Si. Hardness varies from76-89 Rockwell A. These silicides resistoxidation up to about 10000C; they havegood resistance to thermal shock butlow resistance to impact.Chromophore. Atoms or ions whosearrangement of electrons leads toselective absorption of particularwavelengths of light, and so impartscolour to their compounds, which maybe used as PIGMENTS (q.v.). Typicalchromophores are multivalent metalssuch as Co, V. In lattice colours thechromophore forms part of the crystallattice. See also ENCAPSULATEDCOLOURS.

Chrysotile. The principal mineral of theASBESTOS (q.v.) group. When pure ithas the composition 3MgO.2SiO2.2H2O.Chuff Brick. A soft, underfired, salmonpink brick (USA).Chiin Glaze. A thick, high-temperatureopalescent glaze, often with red orpurple streaks.Chum. A shaped block of wood orplaster on which a bat of pottery bodycan be roughly shaped before it is placedin the mould for jolleying in the makingof large items of hollow-ware; a piece offlannel is placed over the chum before it

is used and this subsequently slips off thechum when the shaped clay is removed.Chunk Glass. Rough pieces of opticalglass obtained when a pot of glass isbroken open.CICS. Ceramic Industry CertificationScheme. The body which grantsaccreditation certificates for QUALITYASSURANCE under BS 5750, for theceramics industry.CIE System. The name derives from theinitials of the Commission Internationalede TEclairage. It is a trichromatic systemof colour notation that is used, forexample, in the glass industry.Cinpres. Gas assisted injection moulding,a plastics manufacturing technique.Ciment Fondu. Trade-name: aluminoushydraulic cement. (Lafarge AluminousCement Co. Ltd, 73 Brook St., London,Wl) For general properties of this typeof cement see HIGH-ALUMINA CEMENT.See also GORKAL CEMENT.Cimita. A natural mixture of clay andfeldspar occurring in parts of Chile. Thecomposition is not uniform but a typicalanalysis (per cent) is: SiO2, 58; Al2O3,33; Fe2O3, 1; Alkalis, 4; H2O, 4.Cinder Notch. See SLAG NOTCH.Circle Brick. A brick with two oppositelarger faces curved to form parts ofconcentric cylinders (cf. RADIAL BRICK,and see Fig. 1, p39).Circle System of Firing. See underROTARY-HEARTH KILN.Cire-perdue. French words for LOSTWAX (q.v.).Citadur. Trade-name: a HIGH-ALUMINACEMENT (q.v.) made in Czechoslovakia.Citric Acid. An organic acid sometimesused for the treatment of steel prior toenamelling, or in some metal releasetests.Cladding. An external non-load bearingfacing, e.g. of bricks, faience or tiles,used in frame-type buildings (cf.

VENEERED WALL). ASTM C1088 is aspecification for thin veneered brickunits (maximum thickness 1 in., 25.4mm)made from clay or shale.Cladless Hot Isostatic Pressing, SeeSINTER-HIP.Clamming. Local name for the brick andfireclay filling of the WICKETS (q.v.) of anold-type pottery kiln; sometimes spelledCLAMIN.Clamp. A kiln constructed, except forthe permanent foundations, of the bricksthat are to be fired, together withcombustible refuse and breeze, STOCKBRICKS (q.v.) in the London area wereformerly fired exclusively in clamps butthese produced only about 50% of first-quality bricks and were replaced byannular or tunnel kilns.Clark Circle System. See under ROTARY-HEARTH KILN.Clash. Local Scottish term for a thinslurry of clay and water.Classification. The subdivision of apowder according to its particle sizedistribution or its separation intofractions of differing particle sizes. Seealso SIEVES, AIR SEPARATIONS, etc.CLAW. Control of Lead at WorkRegulations, 1980.Clay. A natural material characterizedby its plasticity, as taken from the clay-pit or after it has been ground and mixedwith water. Clay consists of one or moreclay minerals together with, in mostcases, some free silica and otherimpurities. The common clay mineral iskaolinite; most clays consist of kaolinitein various degrees of atomic disorder.See also BRICK CLAYS, CHINA CLAY,FIRECLAY and the clay mineralsHALLOYSITE, KAOLINITE,MONTMORiLLONiTE, etc.Clay Building Brick. A brick for normalconstructional purposes; such bricks canbe made from a variety of BRICK CLAYS

(q.v.). Relevant British Standard is: BS3921. The US Standards are ASTM - C62(Building Brick); ASTM - C216 (FacingBrick); ASTM - C67 (Sampling andTesting); ASTM - C126 (Glazed Bricks).Clay Gun.The modern preferred term(BS 3446 Pt3 1990) for TAPHOLE GUN(q.v.)Clay Lath. BS 2705 describes this ascopper-finished steel wire mesh at theintersections of which suitably shapedunglazed clay nodules have been bondedby a firing process. Clay lath provides astable, well-keyed base to cover thewhole of a surface with the minimumnumber of joints; it is supplied in rolls ormats.Clay Shredder. A unit for thepreliminary preparation of plastic clay.The machine consists of a hopper with aflat or conical base; adjustable knivesoperate from a vertical, central, rotatingshaft. The clay falls from the shredderthrough slots in the casing.Clayite. A term proposed by J. W.Mellor (Trans. Brit. Ceram. Soc, 8, 28,1909) 'for that non-crystalline variety ofthe hydrated aluminium silicate-Al2O3.2SiO2.2H2O - which occurs inchina clay and in most clays yetexamined. Kaolinite is crystallineclayite'. When X-ray analysis wassubsequently able to demonstrate thecrystallinity of all the clay mineralsexcept ALLOPHANE (q.v.), the term wasdiscarded.Clayspar. Trade-name for a siliceous rawmaterial occurring in Scandinavia andcontaining approx. 95% SiO2, 2.5%Al2O3 ,1.5% K2O, 0.5% Na2O.Cleaner. A hot solution of alkalis(strength about 5%) used to removegrease and dirt from the base-metalbefore it is enamelled.Clear Clay. A clay such as kaolin that isfree from organic matter and so does not

give rise to bubbles if used in a vitreousenamel; such clays are used in enamelswhen good gloss and clear colours arerequired.Clear Frit. A frit that remains non-opaque when processed into a vitreousenamel.Clear Glaze. A ceramic glaze that istransparent.Cleavage, Cleavage Plane. Cleavage isthe FRACTURE (q.v.) of a crystal alongspecific crystallographic planes known ascleavage planes. See also CRYSTALSTRUCTURE.

Cleavage Crack. Typically, a plasticallydeformed groove with median andlateral cracks emanating from it, causedby a hard sharp object crossing the(glass) surface. In crystalline materials,cleavage cracks are those proceedingacross the grains.Clinker. (1) Hydraulic cement in theunground state as it issues from therotary or shaft kiln in which it was made.(2) Dead-burned basic refractorymaterial, e.g. stabilized dolomite clinker.(3) Lumps of fused ash from coal orcoke as formed, for example, in thefireboxes of kilns. (4) For the similarword as applied to continentalengineering bricks see KLINKER BRICK.Clinkering Zone. That part of a cementkiln which is in the temperature range(1350-1600 0C) in which the constituentsreact to form the CLINKER (q.v.).Climbing Temperature Programme. Asystematic method to determine theoptimum conditions for HOT PRESSING(q.v.). Full pressure is applied at roomtemperature. The temperature is thenincreased slowly, and densificationmonitored (by observing the presspiston movement) until it stops for apreset time interval, when fulldensification is assumed. Density isplotted against time, at constant

pressure. An elongated S-shaped curveresults, corresponding to the threestages of densification. The isothermalpressing temperature is found by usingregression techniques to fit theapproximately linear second stage.Clino-enstatite. See ENSTATITE.Clinotherm System. A prefabricated lowthermal mass kiln.Clip. A brick which has been cut tolength (USA).Clip Tile. A ceramic unit designed to fitaround the base of a steel I-beam.Clobbering. Decorating anotherproducer's ware without permission(USA).Closed Chip. A fractured corner of edgewhere the material is still in place.Closed Fraction. A controlleddistribution of particle size, betweenupper and lower set limits.Cloisonne Enamelware. One type ofvitreous-enamel artware: a pattern isoutlined on the base-metal by attachingwire fillets to the metal; enamels ofdifferent colours are applied within thepartitions thus made; the ware is thenfired and the surface is polished. (FromFrench word meaning 'partitioned'.)Closed-circuit Grinding. A size-reduction process in which the groundmaterial is removed either by screeningor by a classifier, the oversize beingreturned to the grinding unit. Typicalexamples are a dry-pan with screens,dry-milling in an air-swept ball mill andwet-milling in a ball mill with a classifier.Closed Porosity. See under POROSITY.Closed Pot. See under POT.Closer. See PupCloset Suite. A suite of ceramic sanitary-ware including the closet and theflushing cistern.Closure. US equivalent of CLOSER (q.v.)Clot. Roughly shaped clay or body readyfor a final shaping process.

Clot Mould. The mould, in some types ofstiff plastic brick making machines, intowhich a clot of clay is extruded and fromwhich it is then ejected prior to the finalre-pressing.Clunch. A name used in some parts ofEngland for a tough coarse, clay or for amarly chalk.CMAA. Concrete Masonry Associationof Australia. See BENDER ABRASIONMETHOD.CMC. (1) Abbreviation forCARBOXYMETHYLCELLULOSE (q.V.). (2)Critical Moisture Content. (3) CeramicMatrix Composite - see COMPOSITES.CMZP. Calcium magnesium zirconiumphosphate (Ca1^ Mgx)Zr4(PO4)6. Thematerial is chemically stable to 1500 0C,has thermal conductivity 1-2 W/mKfrom 200 to 12000C, bulk thermalexpansion of 5 x 10~7/K from 25 to750 0C.CNB. Chevron Notch Bend. SeeFRACTURE TOUGHNESS TESTS.CNC. Computer Numerical Control.CO2 Process. See CARBON DIOXIDEPROCESS.Coade Stone. A vitreous ware, used forarchitectural ornament, made in Londonby Mrs Coade from 1771 until her deathin 1796; manufacture finally discontinuedin about 1840. The body consisted of akaolinitic clay, finely ground quartz andflint, and a flux (possibly ground glass).Coated Dolomite Grain. Also known asunfired semi-stable dolomite refractory,this comprises calcined dolomite bondedwith tar or oil.Coating. See METAL PROTECTION;

REFRACTORY COATING.Cob Mill. A disintegrator for breakingdown agglomerates of the raw materialsused in the compounding of vitreous-enamel batches.Cobalt Aluniinate. As used as a stain inthe pottery industry, this is of

indeterminate composition but it is morestable and gives a better blue than mostother cobalt stains. When used to whitena pottery body, up to about 0.1% isrequired.Cobalt Carbonate. CoCO3; sp. gr. 4.1.Sometimes used as a source ofCOBALT OXIDES (q.v.) in ceramiccolours.Cobalt Chloride, CoCl2.6H2O;Cobalt Nitrate, Co(NO3)2.6H2O. Solublecobalt compounds sometimes used in theceramic industry for the purpose ofneutralizing the slightly yellow colourcaused by the presence of iron'impurities; the principle is the same asthe use of a 'blue bag' in the laundry.Cobalt Chromate, CoCrO4. Finds someuse, in admixture with ZnO and Al2O3,as a green or blue colour for vitreousenamels.Cobalt Oxides. Grey or 'prepared' oxide,CoO, m.p. approx 18000C; cobalticoxide, Co2O3; black oxide, Co3O4. Usedto give a blue colour to glass and potteryware, and added (together with nickeloxide) to ground-coat enamels for steelto impove their adherence. The tint ofcobalt oxide colours can be modified byadding other oxides (see MAZARINEBLUE, WILLOW BLUE and CELESTEBLUE). With the addition of the oxidesof manganese and iron a black colourcan be produced.Cobalt Sulphate, CoSO4JH2O. Asoluble cobalt compound used for thesame purpose as COBALT CHLORIDE(q.v.). It is also sometimes used invitreous enamels for mottling single-coatgrey-coloured ware.Cobble Mix. U.S. term for concretecontaining aggregate up to 150mmdiameter. (Cf. CYCLOPEAN).Coble Creep, CREEP (q.v.) in which thecreep rate is controlled by diffusion atthe grain boundaries, and is proportional

to the cube of the grain size. (R.L.Coble, /. Appl. Phys. 32 (5) 1961 p787).Cobo Process. The cold bonding of othermaterials to bricks.Cock-spur. See SPUR.Coconut Piece. A special shape ofceramic wall tile (see Fig 7, p350).COD. Crack Opening Displacement,(q.v.)Cod Placer. See under PLACER.Coefficient of Scatter. A term used inthe testing of vitreous enamelware anddefined (ASTM 286) as: The rate ofincrease of reflectance with thickness atinfinitesimal thickness of vitreous enamelover an ideally black backing; formethod of test see ASTM C347.'Coesite. A form of silica produced at500-8000C and a pressure of 35 kbar;sp.gr. 3.01; insoluble in HF. Named fromL. Coes who first obtained this form ofsilica (Science, 118,131, 1953).Co-generation. The combinedgeneration of heat and electric power,using a diesel or gas-engine generator.Land-fill gas (methane) is a frequentlyused fuel.Coil Building. A primitive method ofshaping clay vessels by rolling clay into a'rope', which is then coiled to form thewall of the vessel; the inner and outersurfaces of the roughly shaped ware arefinally smoothed.Coin Brick. See JAMB BRICK, (a solecismfor QUOIN BRICK).Coke Oven. A large, refractory-linedstructure consisting of a series of tall,narrow chambers in which coal is heatedout of contact with air to form coke.Silica refractories are used for most ofthe coke-oven structure. (See BS 4966)(BS 6886 specifies alumino-silicaterefractories for coke-ovens).Cokilite. A refractory castable based onsilicon nitride.Coking. See CARBONIZATION.

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Colburn Process. The production ofsheet glass by vertical drawing for about4 ft and then bending over a drivenroller so that the cooling sheet thentravels horizontally. The process wasinvented in USA by I. W. Colburn in1905 and was subsequently perfected bythe Libbey-Owens Company.Coldclay. A self-hardening clay,tradename of Fulham Pottery. Cf.DUOCLAY.Cold Crushing Strength. See CRUSHINGSTRENGTH.Cold-end Handling, Operations in themanufacture of glass when the glass iscool after processing.Cold Joint. The surface between a run ofconcrete which has passed to its final set,and a second run poured alongside it butwhich is no longer able to blend into it.Cold-process Cement. Older name forSLAG CEMENT (q.V.).Colemanite. Naturally occurring calciumborate, 2CaO.3B2O3.5H2O; there aredeposits in Nevada and California. It isused in some pottery glazes.Collar. A short fireclay section used tojoin the main (silica) part of a horizontalgas retort to the metal mouthpiece.Collaring. The final process inTHROWING (q.v.) a vase: both bands areused to compress the clay and thusreduce the size of the neck.Collet. A flange for the mounting of anabrasive wheel on a spindle.Colloid. Material in a form so finelydivided that, when dispersed in a liquid,it does not settle out unless flocculatedby a suitable electrolyte. The finestfraction of plastic clays is in this form.The colloidal size range is approx. 0.001-0.20mm.Colloid Mill. A high-speed dispersionunit yielding a suspension of particles ofthe order of lmm size. The original millof this type was designed by H. Plauson

(Brit. Pat. 155 836 and subsequentpatents).Colloidal Colours. Colloidal-sizedparticles in glass scatter light, thewavelength of maximum scatter beingdependent on particle size. Colouredeffects are thus produced (as in sunsets).Colloidal gold, silver or copper are mostused. Red filter glasses are made byprecipitating coloured crystals such asCdS or CdSe. The particles are dispersedin the glass by controlled nucleation andgrowth. The metal to be precipitated isdissolved in the glass along with areducing agent (tin oxide or antimonyoxide). The molten glass is cooled to atemperature at which the nucleation rateis high, then heated to promote crystalgrowth.Colorimeter. An instrument for COLOUR

MEASUREMENT (q.V.).Colour. See also ENCAPSULATEDCOLOURS; LATTICE COLOURS;COLLOIDAL COLOURS; TRISTIMULUSVALUES; TRICHROMATIC PRINTING;MUNSELL SYSTEM; METAMERISM. Colouris important in the ceramics industrybecause of its aesthetic value. Mostceramic 'colours' are solid colouredparticles (PIGMENTS q.v.) suspended in aglass. Such DECORATION (q.v.) must bedurable, non-toxic and stable. It isapplied by a wide range of processes, asdesigns or coloured glazes. Colourmeasurement is important, particularlyfor glazed tiles, sanitaryware andvitreous enamelware. These may have tomatch eachother and other colouredmaterials in e.g. the bathroom. ASTMC609 specifies a photometric method forthe measurement of small colourdifferences between tiles. There are twobasic methods of colour measurement:spectrophotometry, and the TristimulusFilter Method typified by theColourmaster, Hilger and Hunterlab

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instruments. See CERAMIC COLOURSTANDARDS. BS 5252,1976 specifies awide range of colours used in industry.The Methuen Handbook of Colour 1983provides colour charts, the names of awide range of colours, and theirtechnical co-ordinates. See also ISCC-NBSCOLOUR SYSTEM and RAL COLOURREGISTER. See also Colour. Itsmeasurement, computation andapplication. Chamberlin andChamberlin, Heyden 1980. For anelementary discussion of colourmeasurement in the ceramic industry,see W. Ryan and C. RadfordWhitewares.: Production, Quality andQuality Control, Institute of Ceramics,1987.Colour Retention. The colour retentionof red, orange and yellow vitreousenamels containing cadmium sulphide,or sulphoselenide, when exposed toatmospheric corrosion is measured bytreating the enamel surface with cupricsulphate solution; details of the test aregiven in ASTM - C538.Colour Twist. Twisted coloured glassrods as a form of decoration within awine-glass stem.Columbium. Name used in USA forNIOBIUM (q.v.).Comb Rack. A bar of acid-resistingmetal, e.g. Monel, used to support and toseparate metal-ware in a PICKLING (q.v.)basket, while it is being prepared for theapplication of vitreous-enamel slip. Theterm is also applied to a burning tool forvitreous enamelling.Combed. A surface texture of narrowlyspaced lines produced on clay facingbricks by fixing wires or plates above theextruding column of clay so that they'comb' its surface.Combined Nomenclature of theEuropean Communities. Published bythe EC Commission in Luxembourg,

1987, this document replaced theBRUSSELS NOMENCLATURE. It classifiesceramic products in Chapter 69,according to use, dealing withrefractories, bricks, tiles and china andother tableware. Ceramics for electricalapplications are classified in Chapter 85.The 'Explanatory Notes' to theclassification give definitions of differenttypes of ceramics, for international tariffand trade purposes. See APPENDIX A.Comeback. In the vitreous-enamelindustry this term denotes the time thatelapses before a batch-type furnaceregains its operating temperature after afresh load of ware has been placed in it.Comminution. A term covering allmethods of size reduction of materials,whether by crushing, impact, or attrition.Common Bond. Term sometimes used inU S A for AMERICAN BOND (q.V.).Common Pottery. A term used in theCOMBINED NOMENCLATURE (q.V.) for'products obtained from ferriginous andcalcareous clay (brick earth) which,when fractured, present an earthy, mattand coloured (generally brown, red oryellow) appearance. Particles, inclusionsand pores representative of theirstructure are greater than 0.15mm andvisible to the naked eye. Waterobsorption (measured by a specified test)is5wt%.'Commons. Clay building bricks that aremade without attention to appearanceand intended for use in the inner leaf ofcavity walls or for internal walls; for theUK, dimensions are specified in BS 3921.The crushing strength of such bricksvaries from about 10 to 40 MNm-2, thewater absorption from about 10 to30wt%.Compacting Factor. A factor indicatingthe workability of any concrete madewith aggregate not exceeding 40 mm, butof particular value for assessing

concretes of low workability. The factoris the ratio of the bulk weight of theconcrete when compacted by beingallowed to fall through a specifiedheight, to that when fully compacted.For details see BS 1881.Compact Tension. See FRACTURE

TOUGHNESS TESTS.

Compaction. The production of a densemass of material, particularly of apowder, in a mould. Ceramic powdersmay be compacted by dry-pressing,tamping, vibration, isostatic pressing, orexplosive pressing. A.R. Cooper andL.E. Eaton (/. Am. Ceram. Soc. 45,1962, p897) proposed a quantitativemodel for the compaction of ceramicpowders. This equated the reduction involume of the compact to the statisticallydistributed and pressure-activatedprocesses of filling large and small voids.Experimental rate constants for thesetwo processes reveal whethercompaction is dominated by primaryparticles or by agglomerates. Suchanalysis neglects interaction between thepowder and the die walls (see DIE WALLFRICTION). More efficient bondingresults if the particles are subjected toshear forces as well as compressiveforces. (D. Train, Trans Inst ChemEngrs, 35,1957, p258).Compass and Wedge. Term sometimesused for a brick that has a taper both onthe side and on the face, e.g. a 9 in. (228mm) brick tapered 4.5/3.5in. (114/89mm) and 2.5/2 in. (63/50 mm).Compo. A siliceous, highly groggedfireclay composition, with crushed cokeor graphite sometimes added, for use asa general ramming material in thecasting-pit of a steelworks or in afoundry. A typical composition is (percent): crushed firebrick, 65-70; chamotte,15-20; siliceous fireclay, 14; foundryblacking, 1. The batch is made up with

about 10% water. (The word is anabbreviation for 'Composition'.)Composites. Materials comprising two ormore components with differentproperties. The components may exist ascontinuous phases, or one may becontinuous and another discrete. Inceramic matrix composites thecontinuous phase is ceramic - thediscrete phase metallic or a secondceramic. In metal matrix composites, thecontinuous phase is metallic. See alsoCERMETS.

Composite Refractory. A refractorybrick, different parts of which havedifferent compositions and/or textures,e.g. an insulating refractory having adense working face, or a metal-casedbasic refractory having internalpartitions filled alternately withmagnesite and chrome-magnesite.Composition Brick. Scottish term for acommon building brick made by thestiff-plastic process from clay andcolliery waste; characteristically, it has ablack core.Compound Rolls. Two or more pairs ofCRUSHING ROLLS (q.v.) arranged aboveone another, the upper pair acting as aprimary crusher and the lower pair as asecondary crusher. Compound rolls finduse in the size-reduction of brick clays.Compressibility. The compressibility ofceramic fibre is the percentage relaxationafter 5min of the pressure which gives a50% reduction in thickness. Cf.RESILIENCE. BS 1902 Pt section 8specifies tests.Compression Precracking. SeeFRACTURE TOUGHNESS TESTS.

Compressive Strength. The maximumload per unit area, applied at a specifiedrate, that a material will stand before itfails. BS 3921 specifies a compressivestrength test for building bricks,specifying a strength of 5 N/mm2 for all

bricks, but 50 or 70 N/mm2 for Class Band Class A ENGINEERING BRICKS.ASTM E447 gives two tests for masonryprisms, one for comparative laboratorytests with different bricks and mortars;the other for use on-site. The prisms aresingle-wythe, laid in stack bond,containing at least two morter joints, andcured for 28 days.Concrete. A mixture of hydrauliccement, fine aggregate (e.g. sand) andcoarse aggregate, together with water; itis placed in situ or cast in moulds andallowed to set. The ratio of the threesolid constituents is usually expressed inthe order given above, i.e. '1: 2: 5:concrete' means 1 part cement, 2 partsfine aggregate and 5 parts coarseaggregate. The properties are largelydetermined by the cement and 'fines',but, for normal constructional purposes,the coarse aggregate must be graded togive dense packing.Concrete Aggregate. Normal (asopposed to lightweight) concreteaggregate includes sand andgravel, crushed rock of various types andslag. The nomenclature is given in BS812; the mineralogical composition isdealt with in ASTM C294 and C295.Concrete Block. The properties requiredof precast masonry units, both dense andlightweight, are specified in the UK inBS 6073. In USA the properties requiredof a solid concrete building block arespecified in ASTM C.90, C936 forconcrete paving blocks and C 744 forunits faced with resin or cement plusfiller; the properties of hollow concreteblocks are specified in ASTM C90 andC129; for methods of sampling andtesting see ASTM Cl40, C426 andC1006. C139 specifies special units formanhole construction. There are some15 more ASTM specifications forspecialised pre-cast concrete products.

Concrete Brick. A building brick madefrom portland cement and a suitableaggregate. ASTM - C55 specifies twotypes: Type I. Moisture-ControlledUnits; Type II. Non-moisture-ControlledUnits. There are three grades of eachtype, these being classified according tocrushing strength and water absorption.Concrete Pipes. Pipes for water anddrainage are made in large sizes frompre-cast concrete units. BS 5911 specifiesthe pipes, fittings for joints, inspectionchambers etc., including specialrequirements for porous, reinforced orglass composite concrete pipes. TheAnnual Book of ASTM Standards, VoI4.05 lists some 25 standards relating tothe requirements and test methods forconcrete pipes, fittings and joints, thisnumber almost doubling if metricequivalents are counted separately.Condenser. The condenser attached to ahorizontal zinc retort for the cooling ofthe zinc vapour and its collection asmetal is made of fireclay.Conditioning Zone. (1) The part of atank furnace for flat glass where thetemperature of the glass is adjustedbefore it flows into the forehearth ordrawing chamber.(2) That part of the feeder, away fromthe wall of a glass-tank furnace, in whichthe temperature of the molten glass isadjusted to that required for working.Conduit (for Electric Cable). See CABLE

COVER.Cone. (1) The usual term for aPYROMETRIC CONE (q.V.) Or a TESTCONE (q.v.); for nominal squattingtemperatures of Pyrometric Cones seeAppendix 2.(2) A special fireclay shape sometimesused in the bottom pouring of moltensteel; it has a hole through it andconveys the steel from runner brick toingot mould. The cone is frequently

made as an integral part of a runnerbrick, in which case the latter is knownas a RISER BRICK Or END RUNNER (q.V.).Cone and Plate Viscometer. A cone withwide (c. 174°) apical angle is placed on ahorizontal flat plate. The space betweenis filled with the liquid to be studied andthe cone or the plate rotated about theaxis of the cone.Cone Crusher. A primary crusher forhard rocks, e.g. quartzite used in makingsilica refractories; it consists of a hardsteel cone that is rotated concentricallywithin a similarly shaped steel casing (cf.GYRATORY CRUSHER).Cone Hip. See HIP TILE.Cone-screen Test. A works' test for thefineness of milled enamels. A standardvolume of enamel slip is washed througha conical sieve; the amount of oversizeresidue is read from a graduated scalealong one side of the sieve.Cone Wheel. A small cone-shapedabrasive wheel of the type frequentlyused in portable tools.Congruent Melting. The melting point ofa solid is said to be congruent if thematerial melts completely at a fixedtemperature and without change incomposition, (cf. INCONGRUENTMELTING).

Coning and Quartering. A method ofobtaining a random sample of a powderby pouring it out to form a cone, whichis then divided into four by twodiametral 'cuts'. One quarter is selected,and the process may be repeated.Consistency. The flow or mechanicaldisplacement properties of cements,mortars and refractory castables. SeeKELLY BALL TEST and VICAT NEEDLEfor cements; BALL-IN-HAND TEST forcastables, FLOW TABLE TEST for mortarsand concretes.Consistodyne. Trade-name; a device forattachment to the barrel of a pug for

controlling the workability of the clay;(Ceramic Age, 77, No. 11, 34,1961).Consistometer. Term used in thevitreous-enamel industry for variousinstruments designed for the evaluationof the flow properties of enamel slips.The earliest consistometer was that usedby R. D. Cooke (/. Amer. Ceram. Soc.y 7,651,1924); this was of the capillary typeand was developed into an instrumentsuitable for works' control by W. N.Harrison (ibid, 10, 970,1927). Otherinstruments for controlling the propertiesof vitreous-enamel slips include theGARDNER MOBILOMETER (q.V.).Consolidation. Heat treatment ofPOROUS GLASS and RECONSTRUCTEDGLASS (q.v.) to eliminate porosity.Constant Moment Test. See FRACTURETOUGHNESS TESTS.Constringence. See ABBE NUMBER.Contact Stress. The tensile stresscomponent in a (glass) surface near thecontact area of force due to an appliedobject.Container Glass. One of the majordivisions of the glass industry - jars,bottles and other containers. ASTMC147 tests their internal pressurestrength; C225 their resistance tochemical attack; C148 the quality ofannealing; C149 their thermal shockresistance. British standards specifyrequirements for different types ofcontainers for various applications,including bottles for beer and cider (BS6118); soft drinks (BS 6119,7367 and7488); wine (BS 6117); medicine (BS1679); milk (BS 6106 and 3313); food(BS 5771); honey (BS 1777); drinkingglasses for wine tasting BS 5586.Containerless Hot Isostatic Pressing. See

SINTER-HIP and GAS-PRESSURE SINTERING.Continental Porcelain. The true,feldspathic, hard-paste PORCELAIN (q.v.)made in Western Europe.

Continuous Casting. Molten metal flowscontinuously into a shallow, water-cooled mould and the solidified ingot iswithdrawn at a constant rate betweencooled moving belts or rollers.Refractories for such a process musthave long lives.Continuous Chamber Kiln. SeeTRANSVERSE-ARCH KILN.Continuous Kiln. A kiln in which the fullfiring temperature is continuouslymaintained in one or other zone of thekiln. There are two types: ANNULARKILN (q.v.) and TUNNEL KILN (q.v.).Continuous Vertical Retort. A type ofgas retort, built of silica or siliceousrefractories. Coal is charged into the topof the retort, coke is extracted from thebottom, and town gas is drawn off, thewhole operation being continuous (cf.HORIZONTAL RETORT). Continuousvertical retorts are also used in the zincindustry, in which case they are built ofsilicon carbide refractories.Contrast Ratio (C80). A ratio related tothe reflectance of a vitreous enamelcoating and defined in ASTM C347 as:The ratio of the reflectance of an enamelcoating over black backing to itsreflectance over a backing of reflectance0.80 (80%).Contravec. Trade-name: a system for theblowing in of air at the exit end of atunnel kiln to counteract the normalconvection currents. (Gibbons Bros.Ltd., Dudley, England)Conversion. A change in crystallinestructure on heating that is notimmediately reversible on cooling. Themost important example in ceramics isthe conversion of quartz at hightemperature into cristobalite andtridymite (cf. INVERSION).Converter. A refractory-lined vesselsupported on trunnions and used for theproduction of steel by oxidation of the

impurities in the molten pig-iron thatforms the charge; this is done by a blastof air or oxygen. In the originalBESSEMER CONVERTER the blast passedthrough the converter bottom, the basicrefractory lining being pierced withtuyeres for this purpose. In theTROPENAS CONVERTER the blast strikesthe surface of the molten metal viatuyeres passing through the refractorywall - hence the alternative name SIDEBLOWN CONVERTER. In the oxygenprocess of steelmaking, TOP-BLOWNCONVERTERS are used; they are linedwith tarred dolomite or tarredmagnesite-dolomite refractories.Cooke Elutriator. A short-columnhydraulic elutriator for sub-sieve sizesdesigned by S. R. B. Cooke (U.S. Bur.Mines, Kept Invest, No. 3333,1937).Cooler. As used in the portland cementindustry, the term 'cooler' refers to theancillary unit of a cement kiln into whichhot clinker is discharged to cool before itis conveyed to the grinding plant.Cooling Arch. A furnace for theannealing of glassware, which is placedin the furnace and remains stationarythroughout the annealing (cf. LEHR).Co-ordinating Size. The size of a co-ordinating dimension (ISO 1803). E.g.that for a BRICK (q.v.) is 225 x 112.5 x75mm. The target size to which theproduct is actually manufactured is calledwork size, and is less, by the nominalthickness of the joints (10mm for bricks,lmm for tiles). Neither of these is theactual size (obtained by measurement)which must be within a given range of thespecified work size. The nominal size isthe size used to describe the product, andmay again differ.Copacite. Trade-name; a CanadianSULPHITE LYE (q.V.).Coping. The top course of masonry in awall. BS 5642 Pt2 specifies materials,

sizes and design of concrete, stone andclayware copings.Copper Carbonate. The material is thebasic carbonate, CuCO3-Cu(OH)2; it isused as a source of copper for colouredglazes, particularly for those glazes firedunder reducing condions.Copper Enamel. A vitreous enamelspecifically compounded for applicationto copper, the composition is essentiallylead silicate with small additions ofalkalis, arsenic oxide and (sometimes)tin oxide.Copperhead. A fault (reddish-brownspots) liable to appear in the ground-coat during vitreous enamelling; thespots are exposed areas of oxidized basemetal. Causes include boiling from thebase-metal, inadequate metalpreparation, very thin application ofenamel, and the presence of acid salts inthe enamel slip.Copperlight. A glass window pane, 6 mmthick and up to 100 mm2 size, fitted in aspecial copper frame and used as a 'fire-stop'.Copper Oxide. Cupric oxide (black),CuO; cuprous oxide (red) Cu2O. Used ascolouring agents in pottery and glass.Copper oxide normally gives a greencolour but under reducing conditions itgives a red, due to the formation ofcolloidal copper, as in rouge flambe andsang de boeuf art pottery and copperruby glass. Mixed with other metaloxides it yields black colours for glazesand for vitreous enamels.Copper Ruby Glass. See RUBY GLASS.Copper Titanate. CuTiO3; a compoundsometimes added in amounts up to 2%to BaTiO3 to increase the fired density.Co-precipitation. Precipitation of onecompound is assisted by the addition of asecond compound which precipitateswith the same reagent. Co-precipitationcan be used to prepare ceramics or their

precursors with a mixed composition ofcarefully controlled proportions.Coquille. Thin glass with a radius ofcurvature of 90 mm; used in theproduction of sun glasses; from Frenchword meaning 'shell' (see alsoMICOQUILLE).

Coral Red. A ceramic colour. One formof coral red consists of basic leadchromate; this compound is unstable andthe decorating fire must be at a lowtemperature.Corbel. Brickwork in which each courseprojects beyond the course immediatelybelow.Cord. A fault in glass resulting fromheterogeneity and revealed as longinclusions of glass of different refractiveindex from that of the remainder of theglass.Cordierite. A magnesium alumino-silicate 2MgO.2Al2O3.5SiO2; part of theMg can be replaced by Fe or Mn.Cordierite exists in three crystallineforms but only the a-form is commonlyencountered; it melts incongruently at1540 0C. There is a large deposit ofcordierite in Wyoming, USA, but it isusually synthesized by firing a mixture ofclay, steatite and alumina (or anequivalent batch) at 1250 0C or above.The mineral has a low and uniformthermal expansion (2.8 x ICh6 between0° and 1200 0C) and cordierite bodiestherefore resist thermal shock. Theelectrical resistance (108-1010 ohm-cm at300 0C) is adequate for many purposeswhen high thermal shock resistance isalso required, e.g. arc chutes, electricfire-bars, fuse cores, etc. The dielectricconstant (1 MHz) is 5.0 and the powerfactor ( 1 MHz) 0.004-0.008. Cordieritehoneycombs are used as supports forautomobile engine exhaust catalysts.Core. (1) The central part of a plastermould of the type used in SOLID

CASTING (q.v.). (2) The central part of asand-mould as used in foundries. (3) Aone-piece refractory or heat-insulatingshape for use at the top of an ingotmould and serving the same purpose as aHOT-TOP q.v.); this type of core is alsosometimes called a DOZZLE.Cored Brick. A brick that is a least 75%solid in any plane parallel to the load-bearing surface.Corex Process. The direct reduction ofiron ore using non-coking coal.Introduced by Iscor Ltd, S. Africa, andformerly known as the KR process.Corhart. Trade-name for various typesof electrically fused refractories: CorhartStandard is a fused mullite-corundumrefractory (18-20% SiO2, 72-74%Al2O3); Corhart Zac is a similar productcontaining zirconia (8-12% SiO2, 65-75% Al2O3,15-20% ZrO2). Theseelectrocast refractories are used chieflyin glass-tank furnaces. Corhart 104 is afusion-cast chrome-magnesite refractoryfor use in the steel industry. (CorhartRefractories Co. Louisville 2, Kentucky,USA; English agent—Electrocast Ltd.,Greenford, Middlesex.).Cornelius Furnace. A type of glass-melting furnace in which the glass isheated by direct electrical resistance.The design was introduced in Sweden byE. Cornelius (Brit. Pat. 249 554; 23/3/25;303 798; 8/1/29).Corner Wear. The wear of an abrasivewheel along one or both of itscircumferential edges.Cornish Crucible. A small (e.g. 90 mmhigh, 75 diam.) clay crucible of a typeused for the assaying of copper; thesecrucibles are made from a mixture ofabout equal parts of ball clay and silicasand.Cornish Stone. See CHINA STONE.Corridor Dryer. Term sometimes usedfor a CHAMBER DRYER (q.V.).

Corrosion. Wear caused by chemicalaction (cf. ABRASION and EROSION(q.v.). See also SLAG ATTACK. ASTM C621 and C 622 describe tests for theresistance of refractories to corrosion bymolten glass.Corundum. The only form of alumina thatremains stable when heated above about1000 0C; also known as (X-Al2O3; m.p.2050 0C; hardness 9 Moh; sp. gr. 3.98;thermal expansion (20-1000 0C) 8.5 x Kh6;sp. heat 0.18 (20 0C), 0.22 (100 0C). Itoccurs naturally, but impure, in S. Africaand elsewhere but is generally producedby extraction from bauxite followed by afiring process at high temperature.Corundum is used as an abrasive and as arefractory and electroceramic, e.g. insparking plugs (see also ALUMINA).COSHH. Control of SubstancesHazardous to Health Regulations, 1988.See HEALTH AND SAFETY.Co-spray Roasting. A process formaking FERRITES (q.v.) in which asolution of mixed Mn and Fe chlorides issprayed into a large roaster. A mixtureof Mn and Fe oxides is formed, and HClrecovered. Zinc oxide is added, andMnZn ferrites produced.Cotac. Cobalt-bonded TantalumCarbide. Tradename, (ONERA, France)Cottle. Term used in the N. Staffordshirepotteries for the material, e.g. stiffcanvas, used to form the sides of aplaster mould while the plaster is beingpoured in and until the plaster has set.(Probably from N. country. Cuttle a layerof folded cloth.)Cotto. Traditional Italian tiles, extrudedas split tiles from weathered shaly red oryellow clays of Tuscany or Emilia. Thetiles are given a rustic finish bywirebrushing or sandpapering afterdrying, then fired set upright usingspecial steel kiln furniture. Tiles up to 61cm square are produced.

Coulter Counter. A high-speed devicefor particle-size analysis designed by W.H. Coulter (Proc. Nat Electronics Conf:,12, 1034,1956) and now made byCoulter Electronics Inc., Chicago, USA.A suspension of the particles flowsthrough a small aperture having animmersed electrode on either side, withparticle concentration such that theparticles traverse the aperturesubstantially one at a time. Each particle,as it passes, displaces electrolyte withinthe aperture, momentarily changing theresistance between the electrodes andproducing a voltage pulse of magnitudeproportional to particle volume. Theresultant series of pulses is electronicallyamplified, scaled and counted.Counter Blow. In the BLOW-AND-BLOW(q.v.) process of shaping glass-ware, theoperation during which the parison isblown out.Counterflow Kiln. A tunnel kiln withtwo parallel tunnels, through which theware moves in opposite directions. Theresultant air-flow pattern in the linkedtunnels leads to fuel economy.Coupe. A design of plate in the form ofa very shallow bowl, lacking any flat rimat the edge.Course. By convention, a course ofbrickwork includes one layer of mortaras well as the bricks themselves.Cove Skirting. A special shape ofceramic wall tile (see Fig. 7, p350).Cover. An item of KILN FURNITURE(q.v.). The cover is the flat refractoryshape forming the top of a CRANK (q.v.);it protects the top piece of ware and atthe same time holds the PILLARS (q.v.) inposition.Covercoat. (1) The final coat applied tovitreous enamelware resulting in the topsurface. Normally there is a ground-coatand a cover-coat, but some enamels arenow sufficiently opaque for single-coat

application to appropriate grades ofbase-metal.(2) The clear layer covering the inkdesign of a transfer. Commercial DecalInc USA, incorporated a low-meltingglass into the covercoat, to protect thecolour layer during firing. This alsofortuitously served to reduce METALRELEASE (q.v.) from colours containinglead or cadmium. (Br. Pats. 1120486,1968 and 1426219,1976).Covered Pot. See under POT.Covering Power. The ability of a glazeor vitreous enamel to cover, uniformlyand completely, the surface of the firedware.Cowper Stove. See HOT-BLAST STOVE.CPDA. Clay Pipe DevelopmentAssociation.Crack Arresters. Macroscopic designfeatures to prevent or delay CRACKGROWTH (q.v.) Examples are holesdrilled near sharp corners to arrestcracks which may originate there, byreducing stress concentrations.Crack, Cracking. See FRACTURE.Crack Branching. When a single crackdivides into two or more cracks, the rateof crack growth is slowed, because theavailable energy must be shared over theproduction of a greater number of newfracture surfaces (see FRACTURE, CRACKPROPAGATION). This effect can beinduced by the pre-existence ofmicrocracks or zones of weakness (e.g. atgrain boundaries) throughout theceramic. The TOUGHNESS (q.v.) ofziRCONiA (q.v.) ceramics can beenhanced by this mechanism. Crackbranching is also known as FORKING inFRACTOGRAPHY (q.V.).Crack Bridging. A mechanism leading tohigher TOUGHNESS (q.v.) in ceramicsand composites. Intact material behindthe crack tip imparts closure forces onthe crack. The crack is 'bridged' behind

the tip either by reinforcing fibres orwhiskers (fibre-bridging) or by largergrains in the matrix (grain bridging). Asthe crack opens under load (i.e. thecrack opening displacement (COD)increases) the 'bridges' are subject tostresses which rapidly increase, until thewhiskers or grains fracture or pull outfrom the matrix. Whiskers will supportstresses up to a maximum crack openingdisplacement comparable to a fraction ofthe whisker radius, and given fibre-bridging stress which decays rapidly asthe COD increases. Large grains willsupport only much lower bridgingstresses, but the COD required to pullout a matrix grain is of the order of thegrain size, much larger than whiskerdiameters. The grain bridging zone thenextends (e.g. in aluminium with ~10|Limgrains) to several hundred micronsbehind the crack tip, and the (smaller)grain-bridging stress decayscorrespondingly slowly as the crackopens. This leads to greater fractureresistance with increased crack length(R-CURVE (q.v.) behaviour) in ceramicssuch as larger-grained alumina.Crack Deflection. A method forincreasing TOUGHNESS (q.v.) in which adispersed second phase prevents thedirect growth of a crack, diverting it andlengthening its path.Cracking off. The severing of shapedglass-ware from the MOIL (q.v.).Crackle. (1) A multiply crazed orcracked surface on art pottery or glass.To produce the effect on pottery theglaze is compounded so as to have ahigher thermal expansion than the body;the craze pattern is sometimesemphasized by rubbing colouring matter,such as umber, into the fine cracks. Withglass, the ware is cracked by quenchingin water; it is then reheated and shaped.(2) A crackled vitreous enamel - the

surface appearing to be wrinkled due toits mottled texture - can be produced bythe wet process of application.Crack Nucleation. New cracks form inceramics when an external stress forcesDISLOCATIONS towards barriers such asGRAIN BOUNDARIES, impurities or otherPOINT DEFECTS (see CRYSTALSTRUCTURE). This build-up ofdislocations forms a microcrack, whichgrows initially by this PLASTICDEFORMATION PROCESS. See CRACKPROPAGATION.Crack Opening Displacement. The linearseparation of the two surfaces formed bycracking. It significantly affects thediminution in crack propagation due toCRACK BRIDGING (q.V.)Crack Propagation. The movement of adeveloping crack through a solid. SeeFRACTURE; CRACK NUCLEATION. Anewly-formed microcrack grows initiallyby plastic deformation of the materialjust ahead of the crack tip. This absorbsmuch energy, so that initial crack growthis slow. It also tends to blunt the cracktip, reducing the stress concentrationeffect. On the other hand, small cavitiesform in the deformed area, which link tothe tip of the crack, which extends. Inceramics, the nature of the materiallimits the amount of plastic deformation;crack tip blunting is limited and the localstress quickly comes to exceed thefracture stress of the material. Theinteratomic bonds are broken and thecrack propagates rapidly andcatastrophically. See FRACTURE;BRITTLE FRACTURE; GRIFFITH-OROWANCRITERIA; TOUGHNESS; STRESSINTENSITY FACTORS.Crank. This word is used in the potteryindustry in two related senses: (1) A thinrefractory bat (Fig. 4, pl77) used as anitem of KILN FURNITURE (q.v.) in theglost-firing of wall tiles. A number of

cranks, each supporting one or moretiles, are built up to form a stack; thecranks are kept apart by refractorydistance-pieces known as DOTS.(2) A composite refractory structure forthe support of flatware during glost- anddecorating-firing; the crank is designedto prevent the glazed surfaces of theware from coming into contact withother ware or kiln furniture.Craquele. See CRACKLE.Crater. A clearly-defined hole in arefractory brick or block whose diameterand depth are measurable.Crawler. Local term for an apron-feederto a pan mill used in brickmaking.Crawling. (1) A defect that sometimesoccurs during the glazing of pottery,irregular areas that are unglazed, or onlypartially glazed, appearing on the firedware. The cause is a weak bond betweenglaze and body; this may result fromgreasy patches or dust on the surface ofthe biscuit ware, or from shrinkage ofthe applied glaze slip during drying.(2) A similar defect liable to occur invitreous enamelling when one coating ofenamel is fired over another coating thathas already been fired. Causes include atoo-heavy application of enamel, poorlycontrolled drying, and the use of enamelthat has been too finely ground.Crazing. The formation of a network ofsurface cracks. A typical example is thecrazing of a glaze; this is caused bytensile stresses greater than the glaze isable to withstand. Such stresses mayresult from MISMATCH (q.v.) betweenthe thermal expansions of glaze andbody, or from MOISTURE EXPANSION(q.v.) of the body; ASTM specifies awater-quench test from 149 0C forvitreous whitewares (C554) and anautoclave test (C424) for nonvitreous orsemivitreous bodies for which moistureexpansion may be a factor. In the special

case of glazed tiles fixed to a wall, a thirdcause is movement of the wall or of thecementing material between the tile andthe wall. Crazing of vitreous enamelware(particularly cast dry-process enamel)may also occur, the system of fine crackspenetrating through the enamel to thebase-metal. The crazing of cement andconcrete is due partly to naturalshrinkage and partly to volume changesfollowing surface reaction with CO2

present in the atmosphere. (ForCRAZING TESTS see under AUTOCLAVE;HARKORT TEST; PUNCH TEST; RINGTEST; SINGER'S TEST, STEGER'S TEST;TUNING-FORK TEST).Crazing Pot. Popular name in thepottery industry for an AUTOCLAVE(q.v.).Creep. The slow deformation that manymaterials undergo when continuouslysubjected to a sufficiently high stress.With most ceramics, creep becomesmeasurable only when the stress isapplied at a relatively high temperature.A 20-50 h creep test for refractories isdescribed in ASTM C832. BS 1902 Pt4.10 describes a compressive creep testup to 1600 0C for refractories. See alsoSLOW CRACK GROWTH.

Creeper. Correcting, with a mortar wipe, atendency for brick rings to drift outwardaxially in the upper part of an arch.Cremer Kiln. A German design oftunnel kiln that can be divided intocompartments by a series of metal slidesto permit better control of temperatureand atmosphere. The fired ware iscooled by air currents throughpermeable refractory brickwork in thekiln roof or by water-cooling coils. (G.Cremer, Brit. Pats. 697 644, 30/9/53; 740639,16/1/55; 803 691, 29/10/58.)Crescent Crack. See FRICTIVE TRACK.Crespi Hearth. A type of open-hearthsteel furnace bottom characterized by

the fineness of the particles of dolomiteused for ramming; after it has beenburned-in, the hearth is very dense andresistant to metal penetration. (G. B.Crespi, Brit. Pat. 507 715. 10/8/38.)Crimping. The production of a rolled orcurled edge to the base metal prior tovitreous enamelling.Cristobalite. The crystalline form ofsilica stable at high temperatures; itsm.p. is 1723 ± 5 0C. Cristobalite isformed when quartz is heated with amineralizer at temperatures aboveabout 1200 0C and is itself characterizedby a crystalline inversion, thetemperature of which varies but isgenerally between 200 0C and 250 0C;this inversion is accompanied by achange in length of about 1 %.Cristobalite is a principal constituentof silica refractories, causing theirsensitivity to thermal shock at lowtemperatures; it is also present in manypottery bodies and is synthesized foruse as a refractory powder in theinvestment casting of metals, for whichpurpose its high thermal expansion isadvantageous.Cristobalite Squeeze. The process ofputting ceramic glazes intocompression, by taking advantage ofthe INVERSION (q.v.) of cristobalite at220 0C. On cooling from the glost kiln,by 573 0C the glaze has solidified, andthe body contraction, due to the (3 to acristobalite phase change, compressesthe glaze.Critical Moisture Content. The moisturecontent of a clay at which the clayparticles touch, the water occupies thevoids between the particles, and noshrinkage occurs on further drying. Itcorresponds roughly to the LEATHER-

HARD (q.v.) state. Drying can be morerapid below the critical moisture content,without risk of distortion.

Critical Speed. (1) The maximum safespeed of rotation of an abrasive wheel;at higher speed vibration becomesdangerous. (2) In ball-milling, the speedof rotation above which the balls remainagainst the casing, as a result ofcentrifugal force, throughout arevolution of the mill; this speed is givenby the equation: NVR = 54.18 - where Nis the rev/min and R is the radius of theinterior of the mill, less the radius of theball, in feet.Critical Stress Intensity. See STRESS

INTENSITY FACTOR.

Crizzle. See CHECK.

Crockery. A popular term for ceramictableware, sometimes restricted toEARTHENWARE (q.V.).

Crocodile Kiln A type of TOP-HAT KILN

(q.v.) developed by Keller GmbH. Thehood has a swivel bearing at one end,and so opens at an inclined angle, ratherthan being raised vertically.Crookes Glass. A glass, usuallycontaining cerium, that absorbs ultra-violet light and is used for protectivegoggles, etc. This glass resulted from thework of Sir W. Crookes, in 1914, for theGlass Workers5 Cataract Committee ofthe Royal Society.Crop. To cut replacement refractorybricks roughly flush with surroundingworn lining bricks, to equalise behaviourwhen returned to service.Cross-bend Test. (1) Term sometimesused for TRANSVERSE STRENGTH TEST

(q.v.).(2) A test to determine the resistance ofvitreous enamelware to cracking when itis distorted.Cross-fired Furnace. A glass-tankfurnace heated by flames that cross thefurnace perpendicular to the direction offlow of the glass; the furnace has severalpairs of ports along its melting end (cf.END-FIRED FURNACE).

Crouch Ware. Light-colouredStaffordshire salt-glazed stoneware ofthe early 18th century; it was made froma clay from Crich, Derbyshire, the word'crouch' being a corruption.Crowding Barrow. A hand-barrow forbricks; it has a base and front, but nosides.Crown. A furnace roof, particularly of aglass-tank furnace.Crown Blast. The procedure of blowingair at roof level into the exit end of atunnel kiln to counteract the natural flowof gases in this part of the kiln.Crown Brick. See KEY BRICK andCENTRE BRICK.

Crown Glass. Glass of uneven thicknessand slightly convex (thus producingsome optical distortion), hand-made byblowing and spinning (cf. OPTICALCROWN GLASS).Crucible Test. See SLAG ATTACKTESTS.Crush. A defect of flat glass - a lightlypitted dull-grey area.Crush Dressing. Shaping the face of anabrasive wheel to a required contour bymeans of steel rolls.Crushing Rolls. A unit frequentlyused for the size reduction of brickclays, etc. Two steel rolls are arrangedhorizontally and adjacent, with a gapbetween them of a uniform widthequivalent to the maximum size ofparticle allowable in the crushedproduct; the rolls are rotated inopposition, and sometimes at differentspeeds, so that the clay is carrieddownwards and 'nipped' between theapproaching surfaces of the rolls (cf.EXPRESSION ROLLS).

Crushing Strength. The maximum loadper unit area, applied at a specified rate,that a material will withstand before itfails. Typical ranges of values for someceramic materials are:

Fireclay and silica refractories: 14-35MNm-2

Common building bricks: 14-42 MN m~2

Engineering bricks Class 'A': 70 MN m~2

Sintered Alumina: 350 MN m~2

Now usually referred to asCOMPRESSIVE STRENGTH (q.V.). BS

1902 specifies cold crushing strength ofshaped insulating refractories (Pt. 4.1)and dense refractories (Pt. 4.3) andULTIMATE COMPRESSIVE STRENGTH

(q.v.) of dense refractories (Pt. 4.2). BS1902 Pt. 7.6 specifies cold crushingstrength tests for unshaped refractories.ASTM C133 and C93 specify tests forrefractory bricks and insulatingfirebricks respectively; C 773 is a testfor whitewares; E447 for masonryprisms.Crusilite. A silicon carbide heatingelement. (Trade-name: MorganiteElectroheat Ltd, London.).Cryogenic. Relating to (the productionof) low temperatures. SeeSUPERCONDUCTIVITY.

Cryolite. Natural sodium aluminiumfluoride, Na3AlF6; m.p. 980 0C; sp. gr.2.95. Because of its low m.p. and itsfluxing action, it is used in themanufacture of enamels and glass and inthe ceramic coatings of welding rods.Opal glass is often made from batchescontaining about 10% cryolite; a similarpreparation is sometimes used in whitecover-coat enamels.Crypto System. An impulse system of oilfiring, more particularly for the top-firingof annular kilns. Trade-name: R. Aebi &Ge., Zurich.Cryptocrystalline. Crystalline, but withsub-microscopic grain size.Cryptofluorescence. Term proposed byW. A. Mclntyre and R. J. Schaffer(Trans. Brit Ceram. Soc, 28, 363, 1929)for soluble salts that have crystallized inthe interior of a clay building product

and are therefore hidden; the term hasnot gained general currency.Crystal Glass. A popular, but misleading,name for a type of decorative glass thatis usually deeply cut so that the brillianceresulting from its high refractive index isfully displayed. For British Standarddefinitions see FULL LEAD CRYSTALGLASS and LEAD CRYSTAL GLASS.Crystalline. (1) (of solids) having theatoms in a definite long-range order. SeeCRYSTAL STRUCTURE.

(2) (of particles in a powder) having thegeometric shape of a freely-developedcrystal. See MORPHOLOGY.Crystalline Glaze. A glaze containingcrystals of visible size to produce adecorative effect. Typical examples areglazes containing zinc silicate crystalsand the AVENTURINE (q.v.) glazes.Crystal Structure. Crystals are solidswhose constituent atoms have a regularrepetitive arrangement in space.

The basic unit of a crystal structure isthe unit cell, which is the smallest groupof atoms which has the characteristicsand symmetry of the whole crystal. It isthe volume formed by joining adjacentlattice points, those points at which thearrangements of atoms begins to repeatitself. The lines along the edges of theunit cell are the lattice vectors. (Thelattice constants are the lengths of theselines and the angles between them). Thespace lattice is the regular, repetitive andsymmetric three-dimensional arrayformed by placing repeating unit cellsalongside one-another. The space latticedescribes the geometric arrangement ofthe atoms in a crystal. There are only 14such symmetrical arrangements possible,the BRAVAis LATTICES (q.v.) (See fig. 2,p81. See also RECIPROCAL LATTICE,

X-RAY CRYSTALLOGRAPHY, SPACE

GROUP). While it is possible to preparesingle crystals in which such symmetric

arrangements of atoms make up thewhole of the material, most crystallinesolids actually consist of small crystalspacked together at random, andseparated by grain boundaries. TheMiCROSTRUCTURE (q.v.) of thesepoly crystalline materials has animportant influence on their properties.Moreover, the arrangement of the atomsin crystals is not perfect. Defects occur.These may be point defects, affectingsingle atoms, or line defects, affectinglines and planes of atoms. The varioustypes of point defect are SubstitutionalDefect - an atom in the lattice issubstituted by a foreign atom of similarsize. Vacancy - an atom is missing froma lattice site. Interstitial - a (small)foreign atom fitting in between thelattice atoms. Frenkel Defect - thedisplacement of an atom from itsposition in the lattice (leaving a vacancy)to an interstitial position. Schottky defect- a pair of vacancies in an ionic crystal,the two missing atoms being ions ofopposite electric charge. All such pointdefects strain the lattice, and affect themovement of dislocations, the linedefects. Solid-state DIFFUSION (q.v.)occurs by movement of atoms intoneighbouring vacancies. In general, thenumbers of point defects increase as thetemperature is raised. There are twotypes of line defect, or dislocation: Edgedislocations occur when an extra plane ofatoms is present on one side of aperpendicular plane (the slip plane) butnot on the other. Such dislocations arerelatively easy to move by low stresses,making the crystals weaker and moresusceptible to plastic flow. Screwdislocations mark the boundary betweenslipped and unslipped crystal parallel tothe direction of slip, as if a cut had beenmade into the solid crystal and theplanes of atoms sheared one atom space

Triclinic Simple monodinic Base-centred monodinic

Face-centred orthorhombicBase-centred orthorhombicSimple orthorhombic

Body-centredorthorhombic

Rhombohedral

Hexagonal

Simple tetragonal Body centred tetragonal

Simple cubic Body-centred cubic Face-centred cubic

Fig. 2 Bravais Lattices

parallel to the edge of the cut. Thistransforms successive atom planes intothe surface of a helix, hence the name.The Burger's Vector indicates thedirection of displacement due todislocations, which are usually combinededge and screw dislocations. This is thedirection of plastic deformation whenshear forces are applied. The Burger'svector is normal to an edge dislocation,parallel to a screw dislocation. Pointdefects and grain boundaries stop themovement of dislocations, and thusaffect strength as well as otherproperties.Crystar. Tradename. A form ofRECRYSTALLISED SILICON CARBIDE(q.v.) in which SiC and electronic gradeSi react at over 2300 0C, and the grainsrecrystallize to form a continuousnetwork of SiC. Crystar is used toproduce thermal shock resistant kilnfurniture as well as tubes and otherrefractory shapes. (Norton Co, USA).C-Scan Acoustic Microscopy, C-SAM.Focussed transducers from 10 to 100MHz are coupled to the test piece in awater-immersion tank so that the test-piece is located at the desired depthbelow the test-piece surface. (Thereflections from that surface itself are cutout electronically). Scanning thetransducer over the surface produces animage of internal flaws at that depth inthe specimen.CSZ. Cubic Stabilised ZIRCONIA (q.v.)CT. Compact Tension - See FRACTURETOUGHNESS TESTS.CT. Nozzle. Trade-name: a refractorynozzle for steel-pouring designed to givea Constant Teeming rate (hence thename). The nozzle consists of an outerfireclay shell and a refractory insert ofdifferent composition. Strictly speaking,the term refers to a particular type ofinsert developed for the teeming of free-

cutting steels. (Thos. Marshall & Co.(Loxley) Ltd., Brit. Pats. 832 280, 6/4/60;904 526, 29/8/62.)Cubing Rolls, CRUSHING ROLLS (q.v.)having projections and used for breakingdown hard 'slabby' clays into a cube-likeproduct that is more suitable for feedingto a secondary grinding unit.Cuckhold. (1) An iron tool for cuttingoff lumps of prepared clay, from a pug,ready for the hand-moulding of buildingbricks. (2) A two-pronged fork with ataut wire joining the extremities of theprongs; it is used for cutting clay from aWASHBACK (q.v.) for STOCK BRICK(q.v.) manufactureCuckle. See CUCKHOLD.Cull. US equivalent of the EnglishWASTER (q.v.).Cullet. Broken glass that can berecharged to the glass furnace. The wordis derived from the French collet thelittle neck left on the blowing iron whenbottles were hand blown; these 'collets'were returned to the glass-pot andremelted. FACTORY CULLET orDOMESTIC CULLET is from the sameglassworks at which it is to be used;FOREIGN CULLET is from a differentglassworks.Cullet Cut. Scratches on glassware dueto particles of cullet in the polishing felt.Culm. A Carboniferous shale used forbrickmaking in the Exeter area. (Dialectword for coal dust or soot.)Cummings' Sedimentation Method. Anapproximate method of particle-sizeanalysis having the merit of giving aweight/size distribution directly. (D. E.Cummings, /. Industr. Hyg. ToxicoL, 11,245,1929.)Cup Gun. A spray gun, particularly asused for touching-up vitreousenamelware, with a container for theenamel slip forming an integral part ofthe gun.

Cup Wheel. An abrasive wheel shapedlike a cup; such wheels are used, forexample, in the grinding of flat surfaces.Diamond cup-wheels are employed inthe grinding of tungsten carbide tools.Cupel. A small, refractory, taperedcylinder (broad end up) with a shallowdepression in the top; cupels are madefrom bone ash or calcined magnesia andare used for the assay of non-ferrousores.Cupola. A shaft furnace used in afoundry for the melting of iron. Cupolasare generally lined with fireclayrefractories covered with a ganister-claymixture. For the production of cast ironwith a low sulphur content, a basic liningis sometimes used; the lining is in thiscase built of chrome-magnesite ordolomite refractories, or it may berammed with a monolithic basicrefractory composition.Cupola Brick. See KEY BRICK.Cupping. A process in which vitreousenamel slip is poured over selected areasof a piece of ware while it is beingdrained, to ensure that the overallthickness of application shall be uniform.Curb Bend. A special shape of wall tile(see Fig. 7, p350).Curie Law and Curie-Weiss Law.Magnetic susceptibility % - CIT where Cis the Curie constant, and T is theabsolute temperature. AFERROMAGNETIC material may beregarded as a paramagnetic material inwhich the atomic magnetic moments arealigned by an internal interaction the'Weiss field' (P.Weiss, 1907)proportional to the magnetization.Above the CURIE POINT, TC, the (then)paramagnetic behaviour offerromagnetic materials is described bythe CURIE-WEISS LAW, X-CI(T- Tc).Curie Temperature. Originallydiscovered by Pierre Curie in 1895 as the

temperature at which a material changedfrom ferromagnetic to paramagneticbehaviour. Now generally applied to thetemperature at which orderedarrangements of atoms, which give riseto a variety of electric and magneticproperties, break down.Curing. The process of keeping freshlyplaced concrete moist to ensurecomplete hydration so that maximumstrength is developed. Compounds areavailable for spraying on concrete toretard loss of moisture during the curingperiod (see ASTM C156 and C309). Pre-cast concrete units are often STEAMCURED (q.v.).Curling. A defect in vitreous enamellingthat is similar to CRAWLING (q.v.).Curtain Arch. An arch of refractorybrickwork that supports the wallbetween the upper part of a gas-producer and the gas uptake.Curtain Wall. See SHADOW WALL.Curtains. An enamelling defect, in theform of dark areas having theappearance of drapery, liable to occur insheet-steel ground-coats. The probablecause is boiling or blistering when theground-coat is being fired.Cushion Edge. Defined in BS 6431 as: 4Aslight convex radiusing of the peripheryof the glazed surface of a tile and/or tilefitting where the glazed surface meetsthe edges'.Cut-back. The careful removal ofdamaged or worn refractory surroundinga lining failure site, until soundrefractory capable of being patched isreached.Cut Glass. Glass-ware into which apattern has been ground by means of anabrasive wheel; the grinding is followedby polishing (cf. BRILLIANT CUT).Cut Glaze. A faulty glaze, spots orpatches being bare or only very thinlycovered. The common cause is

contaminated areas on the biscuit-ware,i.e. patches of oil, grease, dust, or solublesalts. A fault resulting in a similarappearance is KNOCKING (q.v.)Cut-off Scar. Marks on the base of aglass bottle made by the Owen's suctionmachine; the 'scar' is largely causedduring the final blowing operation,however.Cutlery-marking. See SILVER-MARKING.Cutting-off Table or Cutter. A framecarrying a tightly stretched wire, or asystem of such frames and wires, thatoperates automatically at a shortdistance from the mouthpiece of a pugor auger to cut off clots or finished bricksor pipes from the extruded column.Cutting-off Wheel or Parting Wheel. Athin abrasive wheel of the type used forcutting-off or for making slots. Suchwheels generally have an organic bond.Cutting Tools. See TOOL TIPS.Cutty Clay. A variety of English ball claythat was formerly used for makingtobacco pipes.CVR. Abbreviation for CONTINUOUS

VERTICAL RETORT (q.V.).Cyanide Neutraliser. See underNEUTRALISER.Cyanite. Obsolete spelling of KYANITE(q.v.).Cyclic Fatigue. The breakdown of amaterial by repeated application of aregularly increasing and decreasingstress.Cyclone Classifier. A dust-laden gasenters a cylindrical or conical chambertangentially and leaves through a centralopening. The dust particles, moving in ahelical path, experience a force towardsthe centre of Mv/r, where M is theparticle mass, v the particle velocity andr the radius of the chamber. Thusparticles are separated according to size,by a force which can be 5 to 2500 timesthat due to gravity in a settling tank. The

detailed mechanics and flow patterns inpractical cyclone classifiers are complex.Cyclopean. Concrete containingaggregate large than 150mm, used indams and other large structures.Cylinder Process. An old method ofmaking flat glass by blowing molten glassto form a cylinder, which is then crackedopen and flattened in a special furnaceknown as a flattening kiln. In Belgium ,France and Germany, the cylinder wasmade of a length to correspond to that ofthe glass sheet and the circumferencecorresponded to the width. Bohemianpractice was the reverse of this and onlysmall sheets (about 3 ft square) could bemade.Cylinder Test. See THERMAL SHOCKTESTS.Cylindrical Screen Feeder. One type offeeder for plastic clay. It consists of avertical cylindrical screen though whichclay is forced by blades fixed to a verticalshaft that rotates within the cylinder.This machine not only feeds, but alsomixes and shreds the clay.Czochralski Technique. A method ofgrowing single crystals of the refractoryoxides, and of other compounds, bypulling from the pure melt; thecompound must melt congruently. (JCzochralski Z. Phys. Chem., 92, 219,1917.)Dam Ring Significant local thickening ofthe lining of a rotary kiln in an axialdirection, to expand the upstream feedsurface area to increase residence time,or for other control purpose.Damp Proof Course. An imperviouslayer below the surface of a floor, orthrough the width of a wall, designedto prevent moisture rising from theground below. The usual materialsare bituminous, but a course ofENGINEERING BRICKS (q.v.) is commonin older buildings. B.S.3921 specifies

WATER ABSORPTION limits for bricks fordamp-proof courses of 4.5 (class 1) or 7.0(class 2) the latter being recommendedfor external works.Danielson-Lindemann Deflection Test.A procedure for assessing the ability ofvitreous enamelware to suffer a smalldegree of bending without the enamelcracking (R. R. Danielson and W. C.Lindemann, /. Amer. Ceram Soc, 8, 795,1925). The procedure has beenstandardized by the American CeramicSociety (Bull. Amer. Ceram. Soc, 7, 360,1928; 9, 269,1930).Danneberg Kiln. An ANNULAR KILN(q.v.) in which the products ofcombustion leave each firing chamberthrough holes in the hearth and throughnumerous small interconnecting flues.Danner Process. A method for thecontinuous production of glass tubinginvented by Edward Danner in the USAin 1917. Glass flows from a tank furnaceon to a mandrel, which is inclined andtapered and slowly rotates. The mandrelis hollow and air is blown through it tomaintain a hole through the glass, whichis continuously drawn from the lowerend of the mandrel as tubing, 1.5 to60mm dia., at a rate of up to 250 kg/h.(c.f. VELLO PROCESS.)Danny. An open crack at the base of theneck of a bottle.Dapple. External or internal surfaceirregularity in a glass container.Darcy's Law; Darcy. Darcy's Law statesthat the rate of flow of a fluid, subjectedto a low pressure difference, through apacking of particles is very nearlyproportional to the pressure drop perunit length of the packing. This Lawforms the basis of methods for thedetermination of the permeability ofceramics. The DARCY is the c.g.s. unit ofpermeability: a material has apermeability of 1 darcy if in a section

1 cm2 in area perpendicular to the flow,1 ml of fluid of unit viscosity flows at arate of 1 cm/s under a pressuredifferential of 1 atm.; 1 Darcy = 1.013 x109 PERM (q.v.) (The Law waspropounded by H. P. G. Darcy, whendesigning the fountains at Dijon in1856).Datolite. A boron mineralapproximating in composition toCaO.B2O3.2SiO2.H2O; it occurs inRussia and elsewhere. Trials have shownthat it is a suitable flux for use in glazesfor structural clay products.Datapaq Trade-name. An automaticrecording system of travellingthermocouples, which can pass throughe.g. a tunnel kiln and provide a record ofthe firing schedule.Davis Revergen Kiln. The word'Revergen' is a trade-mark. A gas-firedtunnel kiln of the open-flame type; theflame does not come in actual contactwith the ware. The combustion air ispreheated by regenerators (hence thename) below the kiln. The design wasintroduced by Davis Gas Stove Co. Ltd,Luton, England; this firm was absorbedby Gibbons Bros Ltd, Dudley, England.Day Tank. A periodic glass-tankfurnace, usually consisting of a singlechamber, from which glass is worked outby hand; the furnace is operated(charging, melting, and working) on a24-h cycle.DCB Double Cantilever Beam. SeeFRACTURE TOUGHNESS TESTS.DCCA Drying Control ChemicalAdditives. Chemicals such as oxalic acid,tetramethylorthosilicate (TMOS) anddimethyl formamide, which improvedrying and produce larger pores in gels.See SOL-GEL PROCESS.DCDC Double Cleavage DrilledCompression. See FRACTURETOUGHNESS TESTS.

DCL Fusion-cast Refractory. A USfusion-cast refractory, e.g. glass-tankblock, made by a process that largelyeliminates the cavities liable to occur asa result of shrinkage during cooling; themould is L-shaped and is tilted while it isbeing filled so that the shrinkage cavitiesconcentrate in the smaller leg of the L(the iug'), which is then sawn off anddiscarded. (DCL = Diamond Cut Lug;c.f. RO, RT and SR).DCMA Number. See Dry ColourManufacturers' AssociationDead-burned. Term applied to arefractory raw material, and especially tomagnesite, after it has been heated at asufficiently high temperature for thecrystal size to increase so that the oxidebecomes relatively unreactive withwater. Magnesite is deadburned in shaftkilns or rotary kilns at a temperature of1600-17000C.De-airing. The removal of air fromplastic clay or body, from the moistpowder in dry-pressing, from castingslip, or from plaster during blending.There are various devices for submittingthese materials to a partial vacuumduring their processing. De-airingis most commonly practised inextrusion, shredded plastic clay beingfed to the pug, or auger, via a de-airingchamber. The original patent was thatof R. H. Staley (US Pat., 701, 957,1902.)Debinding The removal of a binder froma green ceramic compact, c.f. BURNOUT.Debiteuse. A refractory block having avertical slot; it is used in the FOURCAULTPROCESS (q.v.) of sheet-glassmanufacture, being depressed below themolten glass which is drawn upwardthrough the slot. (French word for afeeding device.)Debonding The breakdown, underthermal, mechanical or chemical stress,

of the bonds between the components ofa composite.Debye-Scherrer Technique. See X-RAYCRYSTALLOGRAPHY,Decal. The American term for a ceramictransfer or litho which is now alsocurrent in the UK. Decals are used toapply designs to ceramic tableware,ornamental ware and tiles, and to glasscontainers. The decal comprises threelayers: the colour, or image, layer whichcomprises the decorative design; thecovercoat, a clear protective layer, whichmay incorporate a low-melting glass; thebacking paper on which the design isprinted (by SCREEN PRINTING orLITHOGRAPHY q.v.). There are variousmethods of transferring the design whileremoving the backing-paper, some ofwhich are suited to machine application.(See HEAT-RELEASE DECAL, HEAT-ACTIVATED DECAL, SLIDE-OFF DECAL).Decalcomania (USA). A particular typeof transfer printing, now known inEngland as LITHOGRAPHY (q.v). Theterm is derived, via the French, from twoGreek words: decal (off the paper), andmania, this form of printing having had ashort, but extreme, popularity withyoung ladies in 1860/65.Deck. The refractory top of a car used ina tunnel kiln or bogie kiln.Decking. The stacking of vitreousenamelware in several layers ready forfiring.Decolorizer. A material added to glassto counteract the colour imparted byimpurities such as iron; the decolorizermay be an oxidizing agent, removing thecolour by chemical action, or it maycounteract the colour already present byintroducing the complementary colour.The materials used include the oxides ofAs, Ce, Co, Mn, Nd and Se.Decorating Firing or Enamel Firing. Theprocess of firing pottery-ware after the

application of coloured or metallicdeeoration; the temperature is usually700-8000C and this fixes the decorationand makes it durable.Decoration. The application of coloursand designs to ceramic ware. Bodies andglazes may be coloured or enhanced bycrystalline effects, and coloureddecorations applied on or under-glaze byprinting or by applying transfers. Goldand other precious metal is applied tomore expensive ware, and may requireadditional firing. Glassware may also bedecorated by cutting or engraving. Seealso COLOUR; DECAL; MURRAY-CURVEXMACHINE; SCREEN PRINTING; BANDING;GLAZE; GOLD DECORATION; LUSTRE;ENGOBE; ENGRAVING.De-enamelling. The removal of vitreousenamel from the base metal; this can bedone by sand-blasting or by solution inalkali.Deep Cut. Alternative name for CUTGLASS (q.v.).Deflecting Block or Spreader Block. Ablock of refractory material, triangular incross-section, that is built into a coke-oven below a charging hole; the sharpedge of the block is uppermost and thisdeflects or spreads the stream ofdescending coal so that it comes to restmore uniformly in the oven.Deflocculation. The dispersion of a clayslip by the addition of a small amount ofsuitable electrolyte, e.g. sodium silicateand/or sodium carbonate.Defluorinated Stone, CHINA STONE (q.v.)from Cornwall, England, from which thesmall amount of fluoride present hasbeen removed by flotation.Deformation Eutectic. The compositionwithin a ceramic system (e.g. china clay,flint and feldspar) which, when heatedunder specified conditions, deforms at atemperature lower than that required toproduce deformation in any other

composition within the system. This termis used more particularly in USA.Deformation Temperature. Thetemperature at which, when a ceramicmaterial is heated under specifiedconditions, the rate of subsidencebecomes equal to the rate of thermalexpansion. With glass, this temperaturecorresponds to a viscosity of 10n-1012

poises.Degourdi. The preliminary low-temperature (800-9000C) firing offeldspathic porcelain, as practised inEurope; the second (glost) firing is atapprox. 14000C. (French word meaning'warming' as distinct from the high-temperature-grand /ew-glost firing.)Delft Ware. An early type of porousearthenware covered with a tin-opacifiedglaze and decorated in blue before theglost fire; named from Delft, Holland,but the process was already in use inEngland in the 16th century. In USA theterm is defined (ASTM C242) as acalcareous earthenware having anopaque white glaze and monochromeon-glaze decoration.De-hacking. The removal of ware from akiln setting. The term is usually usedwhen this is done mechanically,particularly in brick kilns.Deko-Press. A process intended toreduce the production costs of tablewareby combining the dry-pressing of spray-dried powder with decoration and single-firing in a roller-hearth kiln. Developedby Hutschenreuther AG. (Keram Z 36(1984) 551.)Dekram. Trade-name. A multi-colourprinting machine for ceramic tableware(Brit.Pat. 1247001, 1971, ServiceEngineers Ltd).Dela-Drum. Powder and spray are fedinto the lower end of an inclined rotatingdrum. As the moist powder rises alongthe axis of the drum it agglomerates, and

particles of uniform size are discharged.(DeIa Gesellschaft fur Granuliertechnikm.b.H)Delia Robbia Ware. Terra-cotta artwarewith white or brightly-coloured glaze.Deltek An advanced ceramic developedby FOSECO (FS) Ltd and BirminghamUniversity. It has good thermal shockresistance, high refractoriness andstrength, and can be fabricated tocomplex shapes with good surface finishand dimensional tolerances. Itsapplications are to investment casting,aluminium die casting and other metalcasting processes.Demijohn. A glass container for wine orspirits; it has a narrow neck and acapacity of over 10 litres. The name isderived from the French Dame Jeanne, apopular 17th-century name for this typeof large bottle.Dendritic see MORPHOLOGYDense. When applied to structural clayor refractory products the term generallysignifies 'of low porosity'; when appliedto a glass it means 'of high refractiveindex' (in this context the term issometimes expanded to OPTICALLYDENSE).Densification The processes duringshaping and firing which lead to closerpacking of particles, the removal ofpores, and a denser ceramic compact orarticle.Density. The determination of thevarious densities ascribed to refractorymaterials is specified in B.S.1902 Pts. 3.4to 3.8. See APPARENT SOLID DENSITY;BULK DENSITY; DENSITY FACTORS;PACKING DENSITY; TRUE DENSITY.Density Factors for Glass. Factors forcalculating the density of a glass from itscomposition; the original set of factorswas that of A. Winkelmann andO. Schott (Ann. Physik. Chem., 51, 730,1894). Numerous amendments to these

have since been put forward; probablythe most reliable are those of M. L.Huggins and K. H. Sun, /. Amer. Ceram.Soc.,26,4,1943.Dental Ceramics, DENTAL PORCELAIN(q.v.) has been supplemented by otherBiocERAMics, in particular APATITESand ALUMINA, for general maxillofacialrestorative work, using crowns andimplants. Metallising, metal-ceramicbonding and colour matching areimportant in dental ceramic work. BS3365 specifies dental silicate and silico-phosphate cements; BS 6039 glass-ionomer cements.Dental Porcelain. Feldspathic porcelain,shaped, tinted and fired for use as falseteeth; the firing is sometimes carried outin a partial vacuum to remove small airbubbles and thus ensure maximumdensity and strength. X-ray diffractionstudies have shown fired dentalporcelain to be some 80% glassy phase.Dental porcelain jacket crowns arespecified by BS 5612, denture teeth byBS 6817.Deox. A masonry cleaning solution(National Chemsearch (UK) Ltd).Derby Press. Trade-name; a machine forthe re-pressing of wire-cut buildingbricks. (Bennett & Sayer Ltd., Derby,England.)Design. Traditionally, ceramic designwas governed by aestheticconsiderations. The design of modernceramic engineering components isgoverned by the need to avoid sharpcorners and re-entrant shapes (both forease of shaping and to avoid stressconcentration, leading to crackpropagation), and to take advantage ofthe high compressive strength ofceramics.Detergent. For resistance of thedecoration of tableware see DURABILITYOF ON-GLAZE DECORATION.

Detonation Gun (D-gun). A D-guncomprises a water-cooled barrel aboutIm long and 25mm diameter. Anoxygen/acetylene mixture ignited in thebarrel drives a charge of powder(particle diameter 45 fim) at a velocity ofc. 800 m/s, temperatures c. 40000C beingreached. After ignition, the barrel ispurged with nitrogen and the cyclerepeated 4 to 8 times per second, eachdetonation depositing overlapping 25mmcircles of powder some 20jnm thick, onthe target as the gun is carefullytraversed.Detonation Forming. See EXPLOSIVE

PRESSING.Detonation Plating. Term suggested(Iron & Steel, London, 39, (2), 63,1966)to replace FLAME PLATING (q.v.).Devil's Tongue A starch plant fromwhose tuberous root Konjaku Meal isprepared. This has been used to improvethe filterability of slips.Devitrification. The change from theglassy to the crystalline state; it mayoccur either as a fault or by controlledprocessing to produce a devitrifiedceramic; see GLASS-CERAMIC.Devitrified Glass. The original term forGLASS-CERAMIC (q.v.).Devitrite. A crystalline product of thedevitrification of many commercialglasses; the composition isNa2O.3CaO.6SiO2; its field of stability inthe ternary system is small and farremoved from its own compositionWhen heated to 10450C devitritedecomposes into wollastonite and aliquid. First named by G. W. Morey andN. L. Bowen (Glass Industry, 12,133,1931).De-watering. The removal of water froma ceramic slip, e.g. by filter-pressing.DF Stone. Abbreviation forDEFLUORINATED STONE (q.V.).D-gun. See DETONATION GUN.

Diagonal Bond. Brickwork in whichheaders are laid to form a pattern ofdiagonals.Diamantini. See GLASS FROST.Diamond Pyramid Hardness (DPH). Ahardness test based on the measurementof the depth of indentation made by aloaded diamond; for details see B.S.427.As applied to the testing of glass, thisprocedure affords a measure of the yieldpoint of the glass structure.Diamond Wheel. An abrasive wheelconsisting of graded industrial diamondsset in a ceramic, metal, or resinoid bond.Diaphragm Wall. A wide-cavity brickwall with the two leaves bonded togetherby cross-ribs of brickwork replacing thenormal wall ties. The resulting connectedbox structure gives a wall of greaterresistance to lateral and vertical loading,suitable for tall single-storey structures.Diaspore. One of the monohydrates ofalumina; its equilibrium temperaturewith corundum and water is 3600C. Itoccurs, mixed with a certain amount ofclay (and thus more properly termedDIASPORE CLAY), in Missouri (USA)and in Swaziland (S. Africa). Diaspore,after strong calcination to eliminatefiring shrinkage, is used as a raw materialfor the manufacture of high-aluminarefractories.Diatomite; Diatomaceous Earth. Asedimentary material formed from thesiliceous skeletons of diatoms, which areminute vegetable organisms living inwater (both fresh and marine). Largedeposits occur in USA, Denmark, andFrance; there are smaller deposits inIreland and elsewhere. Because of itscellular nature (porosity about 80%) andthe fact that it can be used up to atemperature of about 8000C, diatomite isused as a heat- and sound-absorbingmaterial; it is employed either as apowder for loose-fill, as shaped and fired

bricks, or as an aggregate for lightweightconcrete.Dice. The small, roughly cubical,fragments produced when toughenedglass is shattered.Dice Blocks. See THROAT.Dichroic Glass. A glass which transmitssome colours, and reflects others.Dickite. Al2O3.2SiO2.H2O. This is thebest crystallized of the kaolin minerals,the crystals consisting of regularsequences of two basic kaolin layers.Dickite is comparatively rare; it isoccasionally found in sandstones.Dicor. Tradename. A castable,machineable glass-ceramic based onmica (tetra-silicic fluormica) with up to7% added ZrO2 to improve chemicaldurability and translucency for dentalapplications. (PJ. Adair, DentsplyInternational and Corning Glass. U.S.Pat, 4431420 1984)Didier-March Kiln. A coal-fired tunnelkiln; typically, there are four fireboxes,two on each side.Didyinium. A mixture of rare earthoxides, chiefly the oxides ofLANTHANUM, NEODYMIUM andPRASEODYMIUM (q.V.).Die. (1) An attachment at the exit of anextruder designed to give the final shapeto an extruded clay column. A brick dieusually has an internal set of steel platesarranged to permit lubrication of theinternal surface presented to the claycolumn.(2) In dry-pressing and plastic shaping,this term is often applied to the metalmould into which the moist powderor plastic clay is charged prior topressing.Die Cast Brick Machine. A machinedeveloped by Machinery Inc. USA tomake special shapes from the extrudedslug, so not disrupting the productionprocess.

Die Pressing. Term used in somesections of the industry for DRYPRESSING (q.v.).Dielectric. A material that is capable ofsustaining an electrical stress, i.e. anelectrical insulator. Electroceramics ofhigh dielectric constant include thetitanates, stannates, and zirconates; withsuitable compositions the dielectricconstant can attain 20 000, the powerfactor varying from 1 x 10"4 to 500 x10"4. They are used in high-capacitycondensers at radio-frequencies.Dielectric Heating. The heating of adielectric by energy loss within thematerial when it is exposed to a high-frequency electric field. Trials have beenmade with this form of heating, at radio-frequencies, as a method of dryingclay ware but it is generally uneconomic.Die-Wall Friction. The interactionbetween the wall of the die and thepowder compact in uniaxial dry-pressing,which leads to a non-uniform pressuredistribution across the compact. Speciallubricants may be used to reduce thiseffect.Differential Thermal Analysis (DTA). Amethod for the identification andapproximate quantitative determinationof minerals. In the ceramic industry,DTA is particularly applied to the studyof clays. The basis of this technique isthe observation, by means of athermocouple, of the temperatures ofendothermic and/or exothermic reactionsthat take place when a test sample isheated at a specified rate; in thedifferential method, one junction of thethermocouple is buried in the testsample and the other junction is buriedin an inert material (calcined Al2O3)that is heated at the same rate as the testsample. In the DTA of a clay, the majoreffect is the endotherm resulting fromthe evolution of the water of

constitution. The temperature of thepeak of this endotherm varies accordingto the particular clay mineral present;the area of the endotherm (as measuredon DTA curve) affords a means ofassessing the quantity of the mineralpresent.Differential Scanning Calorimetry(DSC). The difference in energy inputsto a substance and a reference materialis measured as a function of temperaturewhile both are subjected to a controlledtemperature programme.Differential Sintering. If two separatepowder compacts of different greendensities are sintered to be fullydensified, then the lower densitycompact must shrink more. However, ifthe compacts are joined as one piece, theregion of lower green density ismechanically constrained from shrinkingmore than the adjacent higher densityregion, and so does not sinter to fulldensity. This phenomenon is known asdifferential sintering.Differential Thermogravimetry (DTG). Atechnique for the study of the changes inweight of a material when heated; it hasbeen applied, for example, in followingthe dehydration process of clay minerals.Diffusion. The transport of matter by themovement of atoms, ions or molecules.The process is driven by differences inconcentration of chemical species indifferent parts of the substance, withthermally activated movement. In solids,atoms migrate through the lattice eitherby the diffusion of INTERSTITIALS, or ofVACANCIES moving in the oppositedirection (see CRYSTAL STRUCTURE).Diffusion is important in SOLID-STATESINTERING, (q.v). It may cpccur withinthe grains of a polycrystal (volumediffusion) or along the GRAINBOUNDARIES (q.v.). (Surface or grainboundary diffusion.)

Diffusion Bonding. A group of joiningtechniques in which strong bonds areachieved through solid state diffusionwithout melting of the base materials.The techniques are usually used to joindissimilar materials, either directly, orusing thin interlayers. In diffusionbrazing a melting filler metal isinterposed between the components tobe joined. In diffusion welding theinterlayers do not usually melt. (For areview, see O.M. Akselsen, /. Mater. ScL27, 569,1992).Diffusion Sintering. See SOLID-STATE

SINTERING.

Diffusivity. See THERMAL DIFFUSIVITY.Digs. Deep, short scratches on glass.Dilatancy. The behaviour exhibited bysome materials of becoming more fluidwhen allowed to stand and less fluidwhen stirred; dilatancy is shown by someceramic bodies that are deficient in fine(<2jim) particles, (cf RHEOPEXY andTHIXOTROP Y).

Dilatometry. The measurement ofthermal expansion, strictly, as a functionof temperature. In particular, acontinuous record can reveal phasechanges in materials.D-line Cracks. Fine, closely spacedweathering cracks near the edges ofconcrete.Dimming Test. To determine thedurability of optical glass the surface issubjected to the action of air saturatedwith water vapour at a definitetemperature (usually 800C) for aspecified period. Any dimming of thesurface is then observed.DIMOX. The Directed Metal Oxidationprocess (q.v).Dimple. ( I)A fault in vitreousenamelware appearing as a small shallowdepression. Causes include: (i) Oil orwater spots from spray line, (ii)Contamination of slip by other enamel

frit, (iii) Contamination of dry biscuit bydust of another enamel, (iv)Contamination of dry biscuit by iron orother dust from dryer or racks, (v)Incomplete healing of a burst blister, (vi)Incorrect spraying due to suspension ofslip being too highly set, or to thepresence of large frit particles.(2) A fault in a pottery glaze resultingfrom the failure of the glaze to healcompletely over the depression formedduring the bursting of a large bubbleduring the glost firing.DIN. Abbreviation for DeutscheIndustrie-Norm (German IndustryStandard). These standards arepublished by the DeutscherNormenausschuss (abbreviationDNA) which has its offices inBerlin, W.15.Dinas Brick. The original name for asilica refractory, so called from Dinas, inS. Wales, where the silica rock wasquarried. The name is preserved in theGerman dinas-stein and the Russianequivalent.Dinnerware. An American term (ASTMC242) for ceramic whiteware made in aconsistent pattern and a full range ofarticles to make up a dinner service.Dinosaur. A precision setting machinewhich automatically cuts, faces and setsgreen bricks. (Pearne & Lacy, USA;Craven Fawcett, Leeds).Diopside. MgO.CaO.2SiO2; m.p. 1392°C;sp. gr. 3.3; thermal expansion (0-12000C)8.8 x 10-6. There is a deposit in NewYork State. Trials have been made withsynthetic diopside as a high-frequencyelectro-ceramic. It is formed as adevitrification product of sodalime glassif the CaO is partially replaced by MgO;it is also formed when siliceous slagsattack dolomite refractories.Dip Mould. A one-piece glass formingmould. The molten glass enters at the

top, and the finished ware is removedthrough the same hole.Dipping. (1) BISCUIT-FIRED POTTERY(q.v.) is dipped into a suspension of theglaze ingredients in water; the dippedware is then dried and GLOST-FIRED(q.v.)(2) In vitreous enamelling, the base-metal can be dipped in slip and drained(wet process) or it can be first heatedand then dipped in powdered frit (dryprocess).Dipping Weight. See PICK-UP.Direct-arc Furnace. See under ELECTRICFURNACES FOR MELTING and REFININGMETALS.Direct-bonded ceramics. Ceramics inwhich there is no change in chemicalcomposition at the grain boundaries, butonly of particle orientation, so that thebonds across the grain-boundries are ofthe same nature as those in the bulk ofthe ceramic. Such ceramics have highmechanical strength.Direct Coagulation Casting. In thisNEAR NET SHAPE technique for formingcomplex shapes, an aqueouselectrostatically stabilized suspension oflow viscosity is cast into a non-porousmould and then coagulated by changingthe pH or by a delayed reactioncatalyzed by enzymes, to form a stiff, wetgreen body.Directed Metal Oxidation Process.Ceramic reinforcement is incorporatedin a ceramic matrix formed by thereaction of molten metal with anoxidant.Direct Firing. The firing of pottery orvitreous enamelware in a fuel-fired kilnor furnace without protection of theware from the products of combustion.Directional Solidification. This is atechnique for preparing lamellar orfibrous composites of ceramics and/ormetals by growth from a molten eutectic

composition, using techniques normallyused for growing single crystals. Thesolidification front is made to advanceslowly in one direction, by minimizingconvection in the melt, as in some zone-melting or crucible techniques.Directionally solidified eutectics havelow porosity, stable microstructures upto the eutectic temperature, and goodbonding between the uniformlydistributed phases. (R. L. Ashbrook, /.Amer. Ceram. Soc. 60 (9/10), 428,1977).Direct Teeming or Top Pouring. Thetransfer of molten steel from a ladle,through one or more refractory nozzles,directly into the ingot moulds.Dirty Finish. See FINISH.Dirty Ware. Foreign matter thatoccasionally disfigures potteryware astaken from the kiln; potential sources ofthe 'dirt' include the atmosphere, both inthe factory and in the kiln, the placers'hands, the kiln lining, the kiln furniture.See also WHITE DIRT.Disappearing-filament Pyrometer. Anoptical pyrometer consisting of a smalltelescope with an electrically heatedfilament placed in its focal plane. A hotsurface within a kiln or furnace isfocused through the telescope and thecurrent supplied to the filament isadjusted until the apparent temperatureof the filament and furnace coincide, thefilament then disappearing in the generalcolour of its background. Thecorresponding temperature is read froma scale on the instrument.Disappearing-highlight Test. A test todetermine the degree of attack of avitreous-enamelled surface after an acid-resistance test; (see ASTM - C282).Disc. A thin refractory support used toprotect other KILN FURNITURE fromglaze attack during glost firing.Discharge-end Block. See NOSE-RING

BLOCK.

Disintegration Index. A measure of thedurability of a hydraulic cement proposedby T. Merriman (Engng. News Record,104, 62,1930). The test involves shakingwith a lime-sugar solution followed bytitration of one aliquot against HCl withphenolphthalein as indicator and anotherwith methyl orange as indicator. TheDisintegration Index is the differencebetween the two titrations. The test wassuperseded by the test now known as theMERRIMAN TEST (q.V.).Disintegrator. A machine used for thesize reduction of some ceramic materials.A rotor is rapidly revolved within acasing, both rotor and casing havingfixed hammers which impact on thematerial being ground (cf. HAMMERMILL).

Disk Feeder. A type of clay feeder forattachment to the base of a storage bin.There are various types. In one of thesethere is a short fixed cylinder with a sideoutlet; below the cylinder is a revolvinghorizontal disk. In another design thedisk is stationary, the clay beingdischarged by moving arms inside thecylinder.Disk Wheel. An abrasive wheel of a typethat is usually mounted on a plate so thatgrinding can be done on the side of thewheel.Dispex. Trade-name; ammoniumpolyacrylate, sometimes used as adeflocculant in clay slips. (AlliedColloids Ltd., Bradford, England.)Dislocations. See CRYSTAL STRUCTURE.Disordered clays. Clays in which there issubstantial ISOMORPHOUS SUBSTITUTION(q.v.). Disordered clays have fine particlesize, high plasticity, high unfired strengthand high drying shrinkage. In general,ball clays are disordered, china clays not.Disorp. A process developed by Didier-Werke, Germany, to absorb HF from thehot flue gases from the firing of bauxite

or fireclay, by filtration through a bed oflimestone granules.Dispersion Strengthening. Very fineparticles of a second phase, widelydispersed throughout the crystal latticeof the first phase, inhibit the movementof dislocations, increasing strength andfracture toughness. The technique isused in cements and to strengthen metalsby introducing e.g. thoria. If thedispersion is produced by solid statereactions which precipitate the secondphase chemically, the technique isknown as precipitation hardening. SeeTOUGHNESS.Dissector. A person employed to classifydefective potteryware according to thenature of the fault.Disthene. Obsolete name for KYANITE

(q.v.).Diver Method. A technique for thedetermination of particle size bysedimentation. The specific gravity at agiven depth in a sedimenting suspensionis determined by means of small loadedglass 'divers' of known specific gravitiesin a range between the specific gravity ofthe dispersion medium and that of thehomogeneous suspension. If a 'diver' isplaced under the surface of asedimenting suspension it will descend toa level where its weight is equal to theweight of suspension displaced; it willthen continue to descend at the samerate as the largest particles at the level ofits geometrical centre of gravity and at agreater rate than all the particles in thesuspension located above that level. (S.Berg. Ingeniorvidenskabelige Skrifter,No. 2,1940.)Division Wall. A wall of refractorybricks between two adjacent settings in abench of gas retorts.D-line Cracks. Fine, closely spacedweathering cracks near the edges ofconcrete.

D-load. The strength of a concrete pipein a 3-edge bearing test, expressed as theload per unit length as a fraction ofinternal diameter or horizontal span.The load may be the maximum the pipewill support, or may be that load whichwill produce a 0.001 in (0.025mm) crackthroughout a length of 1 ft (305mm) ofthe pipe.DNA. See under DIN.Dobbin. A type of dryer used in thetableware section of the pottery industry;the ware, while still in the plaster mould,is placed on horizontal turntables withinthe drying cabinet; the turntables can berotated about a vertical axis so that theware moves from the working openinginto the interior of the dryer wheremoisture is removed from the mould andthe ware by means of hot air.Dobie. A hand-shaped clay buildingbrick before it has been fired; fromADOBE (q.v.). In USA a 'dobie' is alump of raw fired clay.Docking. The immersion of buildingbricks in water as soon as they are takenfrom the kiln; this is done only when thebricks are known to contain lime nodulesand is a method for the prevention ofLIME BLOWING (q.V.).Doctor Blade. (1) A thin, flexible, pieceof steel used for smoothing a surface,e.g. for cleaning excess colour from theengraved copper plate used in printingon pottery.(2) A blade used for parting thin ceramicsheets or wafers of the type used inminiature condensers.Document Glass. A glass that absorbsultraviolet rays and thus protectsdocuments from deterioration.Dod Box. An old device for extrudingrods or strips of a pottery body for use inthe making of cup handles or of basket-ware. The term may be a corruption ofWAD BOX (q.v.) or it may be from DOD

the old name for the Reed Mace orBulrush.Dod Handle. A cup- or jug-handle madeby the old DOD BOX (q.v.) method.Dodecacalcium Heptaluminate.12CaOJAl2O3; cubic; sp. gr. 2.68(anhydrous), 2.73 (mono-hydrate); m.p.1392°C; thermal expansion (0-12000C)8.0 x 10-6. A constituent of high-aluminahydraulic cement. This compound hasnot been prepared in a strictly anhydrousform; when sorption of water hasreached a max. the composition is12CaO.7Al2O3.H2O.Dodge-type Jaw Crusher. A jaw-crusher with one jaw fixed, the otherjaw being pivoted at the bottom andoscillating at the top; the output is lowbut of uniform size (cf. BLAKE-TYPEJAW CRUSHER).

DOFP. Direct-On Finish Process ofvitreous enamelling (US abbreviation).Dog-house. In an open-hearth steelfurnace, the arched refractory areathrough which a metallic burner (for oil-firing) is inserted; in a glass-tank furnace,the refractory-lined extension into whichbatch is fed.Dog's Teeth or Dragon's Teeth. A faultsometimes found on the edges of arectangular extruded column of clay, thegreater friction at the corners of the dieholding the clay back relative to thecentre of the extruding column; if thiscorner friction is too great it results in aregular series of tears along the edges ofthe column. Methods for curing the faultare increasing the moisture content ofthe clay, improving the lubrication of thedie, or enlarging the corners of the die atthe back of the mouthpiece.DoJIy. A gathering iron with a refractorytip used in the making of glass-ware insemi-automatic machines.Dolly Dimples. A slight defect in cast-iron vitreous enamelware, blisters in a

leadless enamel having almostcompletely healed.Doloma. Calcined dolomite, i.e. amixture of the oxides CaO and MgO; theterm was introduced by the BasicFurnace Linings Committee of the Ironand Steel Institute (I.S.I. Spec. Rept. 35,1946).Dolomite. The double carbonate ofcalcium and magnesium, (Ca,Mg)CO3.Dolomite occurs abundantly in manycountries: in England it extends as a beltof rock from Durham to Nottingham-shire; in Wales the CarboniferousLimestone has been dolomitized locally.Typical analysis (%): MgO, 20; CaO, 30;CO2, 46; impurities, 4. It is used as asource of magnesia in glass productionbut the principal use is as a refractorymaterial, for which purpose it is calcined.Because of the free lime present calcineddolomite rapidly 'perishes' in contactwith the air; it may be tar-bonded to giveit partial protection, or it can bestabilized by firing it, mixed with steatiteor other siliceous material, so that thelime becomes combined as one or moreof the calcium silicates. Stabilizeddolomite refractory bricks find some usein the lining of electric steel furnaces androtary cement kilns, tarred dolomitebricks or blocks (sometimes with dead-burned magnesite added) are much usedin the newer oxygen steelmakingprocesses. See also TEMPERED

DOLOMITE BLOCK.Domain. In a ferroelectric orferromagnetic crystal, e.g. bariumtitanate, a 'domain' is a small area withinwhich the polarization is uniform. If thecrystal is exposed to a high electric ormagnetic field, those domains in whichthe polarization is in a favourabledirection will grow at the expense ofother domains. A domain structure givesrise to HYSTERESIS (q.v.).

Dome Brick. A brick in which both thelarge and the side faces are inclinedtowards each other in such a way that,with a number of these bricks, a domecan be built. (See Fig. 1, p39.)Dome Plug. A refractory shape,usually made of aluminous fireclayor of a refractory material of stillhigher alumina content, used in the topof the dome of a HOT-BLAST STOVE

(q.v.).Doping. The addition of small quantitiesof other materials to markedly affect theproperties of the main component.Electrical properties of ceramics areparticularly susceptible to modificationin this way.Dorfner Test. A test for stress inglazed ware proposed by J. Dorfner{Sprechsaal, 47, 523, 1914): a cylinderof the ware is partly glazed andthe shrinkage of the glazed portion isnoted.Dorr Mill. A TUBE MILL (q.v.) designedfor operation as a closed-circuit wet-grinding unit.Dorry Machine. Apparatus for testingthe abrasion resistance of a ceramic; theflat ends of cylindrical test-pieces areabraded under standardized conditionsby movement in contact with a speciallygraded sand.Dot. A small refractory distance-piecefor separating CRANKS (q.v.) andSETTERS (q.v.).Dottling. The setting of pottery flatwarehorizontally on THIMBLES (q.v.).Double Cantilever Beam. SeeFRACTURE TOUGHNESS TESTS.Double Cleavage Drilled Compression.See FRACTURE TOUGHNESS TESTS.Double Draining. A further period offlow of slip from dipped vitreousenamelware after the initial draining hasfinished and the enamel appears to haveset. A possible cause of this trouble is

excessive alkalinity of the slip caused bythe solution of alkalis from the frit;alternatively, the amount of electrolyteadded to the slip may have beenincorrect.Double Embossing. Producing threeshades of decoration on glassware, byproducing a design with acid, followedby two additional acid treatments.Double-face Ware. Vitreous enamelwarethat has a finish coat on both sides.Double-frit Glaze. A glaze containingtwo frits of different compositions. As anexample, a glaze may contain a lead fritand a leadless frit; the glaze is thusrendered highly insoluble by theinclusion in the second frit of thoseconstituents liable to increase leadsolubility.Double-layer Extrusion. Making bricksby extruding two layers of claysimultaneously, the outer layer usuallyforming a thin surface layer of enhancedappearance.Double Layer Theory. Ceramic particlesgenerally contain atoms that are easilypolarized, with resulting stronginterparticle attraction.AGGLOMERATION (q.v.) can beprevented by mixing the powders in aliquid with dissolved ions, whereby a"double-layer" of dissolved ions formsround each particle. The double-layertheory describes the electrostaticrepulsion between two particles whoseelectric double-layers overlap. Thisoverlap causes a local increase in theelectrolyte concentration. The resultingosmotic pressure counterbalances theattractive electrostatic van der Waalsforces, and prevents the particles comingtogether in agglomerates.Double-roll Verge Tile. A single-laproofing tile having a roll on both edgesso that verges on the two sides aresimilar.

Double Roman Tile. See under ROMANTILE.Double-screened Ground RefractoryMaterial, A US term defined as: Arefractory material that contains itsoriginal gradation of particle sizesresulting from crushing, grinding, orboth, and from which particles coarserand finer than two specified sizes havebeen removed by screening (cf. SINGLE-SCREENED).Double Standard. A brick (particularly arefractory brick) that is twice as wide asa standard square, e.g. 9 x 9 x 3 in(229 x 229 x 76 mm).Double-thread Method. A procedurefor determining the coefficient ofthermal expansion of a glass by forminga thread by fusing a fibre of the glassunder test to a fibre of a glass of knownexpansion; from the curvature of thedouble-thread, when cold, thecoefficient of expansion of the glassunder test can be calculated. (M.Huebscher, Glashutte, 76, 57, 1949).Double Torsion. See FRACTURE

TOUGHNESS TESTS.Double-wing Auger. An AUGER (q.v.)with two discharge screws.Down-cast. Local term for negativepressure in the atmosphere of somezones of an annular kiln.Down-draught Kiln. A kiln in which thehot gases from the fireboxes first rise tothe roof, then descend through thesetting and are finally withdrawn throughflues in the kiln-floor.Down-draw Process. The production ofglass tubing by continuously drawingmolten glass downward from an orifice.See also overflow process.Downtake or Uptake. One of the twovertical passages, built of refractorybricks, leading from the ports to the slag-pockets of an open hearth furnace. Assuch a furnace operated on the

regenerative principle, the direction ofgas-flow being periodically reversed, theidentical passages at the two ends of thefurnace alternately served as Downtakefor the waste gases leaving the furnaceand Uptake for the hot air forcombustion and (in gas-fired furnaces)the fuel gas.Downward Drilling. Wear on glass-tankfurnace bottoms.Dozzle. See under CORE.DPH. Abbreviation for DIAMONDPYRAMID HARDNESS (q.V.).DPT - Diffuse Phase Transition - seeRELAXORS.Drag-ladle or Dragade. To makequenched CULLET (q.v.) by ladlingmolten glass into water.Drag-line. A type of mechanicalexcavator often used in the winning ofbrick-clays; a 'bucket', suspended from aboom, is lowered on to the clay and isthen dragged towards the excavator by awire rope, thus filling the 'bucket' withclay. An advantageous feature of a drag-line is its ability to work clay below thelevel of the excavator itself.Dragged. A surface texture on clayfacing bricks produced by a tightlystretched wire contacting the column ofclay as it is extruded from the pug in thewire-cut process: this texture is alsoknown as rippled.Dragon's Teeth. See DOG'S TEETH. Alsolarge, tooth-like formations of clinkernear the outlet of the sintering zone of arotary kiln.Drain Casting or Hollow Casting. Termsused (more particularly in USA) for theslip-casting process for making hollow-ware, the excess slip being drained byinversion of the mould.Drain Lines. Lines or streaks liable toappear in badly drained wet-processvitreous enamelware after it has beenfired.

Drain Tile. US term for an unglazedfield-drain pipe. The properties of claydrain tiles are specified in ASTM - C4and C498 (for perforated drain tile); ofconcrete drain tiles in ASTM - C412.Draw. See LOAD.Draw Bar. In the PITTSBURGH PROCESS(q.v.) of drawing sheet glass, the positionof the sheet is defined by a refractoryblock (the draw-bar) submerged in themolten glass.Drawing Chamber. The part of a tankfurnace for flat glass from which thesheet of glass is drawn.Drawn Stem. See STEMWARE.Dredging. A dry process of vitreousenamelling in which powdered frit issifted on to the surface of the hot base-metal.Dresden Green. A ceramic colour foruse up to about 11000C. It consists of(%): CoO, 24; Cr2O3, 52; ZnO, 24.Dressing. The process of removing, fromthe face of an abrasive wheel, thosegrains that have become dulled duringuse.Dressier Kiln. The first successful muffle-type tunnel kiln was that built by ConradDressier in 1912. The name is nowapplied to a variety of kilns designed andbuilt by the Swindell-Dressier Corp.,Pittsburgh, USA.Dri-lok. Tradename. A method for thequick and precise construction of kilncars using interlocking insulating brickswithout mortar. Developed by MPKInsulation, Colchester, the Dri-lok bricksare 230 x 114mm or 230 x 230mm, up to114mm thick.Drip Course. A protruding or recessedcourse inside the crown of a glass tank,to prevent molten material runningdown and corroding the breast walls.Drip Test. See SLAG ATTACK TESTS.Drop Arch. An auxiliary brick archprojecting below the general inner

surface of the arched roof of a furnace,brick conduit or like structure.Drop Forward. The projection ofisolated bricks from the general liningsurface of a newly commissioned rotarykiln.Drop-machine Brick. US term for arefractory brick made by dropping,from a height of about 5 m, a clotof the prepared batch into a mould.The process aims to imitate hand-moulding.Drop Monkey. A system of ropes formoving kiln cars.Dropper. A drop of glaze that hasformed, by condensation of glazevapour, on the inside of the roof of aglost kiln and has subsequently fallen onthe ware that is being fired.Dropping. See SAGGING.Dropping Ball Test. See KELLY BALLTEST. BS 4551 includes a dropping balltest for the consistence of mortars.Drop Throat. A glass-tank THROAT(q.v.) below the level of the floor of themelting tank.Drum Dryer. A rotating drum, heated todry tumbling raw materials.Dry-bag Process. See ISOSTATICPRESSING.

Dry Colour Manufacturers9 Association.This body has devised a scheme for theclassification of pigments, based on thechemical and structural identity of thecolouring substance. It excludes singlemetal oxides and non-oxide PIGMENTS(q.v.) but includes all mixed metal oxidesin one of 14 crystal classes and over 50pigment categories, each having aspecific DCMA Number (E.g. Crystalclass XIII is spinel and DCMA No13-26-2 refers to cobalt aluminate bluespinel.Drum. (1) Term sometimes applied tothe mouth of a port in a glass-tankfurnace.

(2) A wooden former of the type thatwas used in making the side of a saggarby hand.Drum-head Process. A process used inEurope for the shaping of flatware; itwas developed on account of the'shortness' of the feldspathic porcelainbody. A slice of the pugged body isplaced on a detachable 'drum-head'which fits on the BATTING-OUT (q.v.)machine. The'drum-head', with theshaped disk lying on it, is then removedand inverted over the jigger-head, thebat then being allowed to fall on themould for its final jiggering.Dry Body. An unglazed stoneware typeof body. The term has been applied, forexample, to CANE WARE, JASPER WAREand BASALT WARE (q.v.).Dry Edging. A fault sometimesoccurring in pottery manufacture as aresult of insufficient glaze application: itis shown by rough edges and corners.Dry Gauge. See DRAG-LADLE.Dry Laying. A rapid form of refractoryconstruction, chiefly for brick rings inrotary kilns. Mating faces of bricks areplaced in direct contact, and mortar usedsparingly, if at all, for local adjustment.Dry Lining. See DRY LAYING.Dry Mix. See DRY PROCESS.Dry Pan. An EDGE-RUNNER MILL (q.v.)used for grinding relatively dry materialin the refractories and structuralclayware industries. The bottom has asolid inner track on which the mullersrotate and outer perforated gridsthrough which the ground material isscreened, oversize being ploughed backto the grinding track.Dry Pressing. The shaping of ceramicware under high pressure (up to 100MN.m-2), the moisture addition beingkept to a minimum (5-6%) or, withsome materials, eliminated by the use ofa plasticizer, e.g. a stearate. Dry pressing

is used in the shaping of wall and floortiles (when it is often referred to as DUSTPRESSING), most high-grade refractories,abrasive wheels, the Fletton type ofbuilding brick (the moisture content forpressing is in this case 19-20%), andmany articles in the electroceramicindustry. The process is also sometimesreferred to as SEMI-DRY PRESSING.Dry Process or Dry Mix. (1) Term usedin the US whiteware industry anddefined (ASTM - C242) as the methodof preparation of a ceramic body bywhich the constituents are blended dry;liquid may then be added as required forsubsequent processing.(2) The process of cement manufacturein which the batch is fed to the kiln dry.Dry Process Enamelling. In this methodof vitreous enamelling, the base metal ispreheated to a temperature above that atwhich the enamel to be used will mature(usually 850-9500C); the finely powderedenamel is then applied to the hot warewhich is then fired to complete thematuring process.Dry-rubbing Test. A test to determinethe degree of attack of a vitreous-enamelled surface after an acid-resistance test; (see ASTM - C282).Dry Shake. A dry mixture of cement andfine aggregate, spread over a concretefloor before final finishing, to provide awear-resistant surface.Dry Spray. Faulty spraying of vitreousenamel, leading to a rough, sandysurface.Dry-stacked walls. See MASONRY.Dry Strength. The mechanical strengthof a ceramic material that has beenshaped and dried but not fired; it iscommonly measured by a transversestrength test.Dryer. See CHAMBER DRYER; DOBBIN;HOT-FLOOR; MANGLE; TUNNEL DRYER.Dryer Scum. See SCUM.

Drying Shrinkage. Ceramic ware (andparticularly clayware that is shaped froma moist batch shrinks during drying; thedrying shrinkage is usually expressed asa linear percentage, e.g. the dryingshrinkage of china clay is usually 6 to10%; that of a plastic ball clay is 9 to12%. To produce ware (e.g.electroceramics or refractory bricks) ofhigh dimensional accuracy, the dryingand firing shrinkages must be low; this isachieved by reducing the proportion ofraw clay and increasing the proportion ofnonplastic material in the batch, which isthen shaped by dry-pressing, forexample.DT. Double Torsion. See FRACTURE

TOUGHNESS TESTS.D T A . DIFFERENTIAL THERMALANALYSIS (q.v).DTG. DIFFERENTIALTHERMOGRAVIMETRY (q.v)Duck-nesting. Localised pockets oflining scour sometimes affecting high-alumina brickwork.Ductile Reinforcement. See CRACKBRIDGING; STRAIN HARDENING; FIBREREINFORCEMENT.Dulling. A glaze fault characterized bythe ware having poor gloss when drawnfrom the kiln; the cause is surfacedevitrification, which may result fromfactors such as SULPHURING (q.v.) ortoo-slow cooling.Dummy. A foot-operated device formanipulating paste moulds whenblowing glass by mouth.Dumont's Blue. Alternative name forSMALT (q.V.).Dumortierite. A high-alumina mineral,8Al2O3^SiO2B2O3; it occurs sufficientlyabundantly in Nevada, USA, for use inthe ceramic cores of sparking plugsalthough bodies of still higher aluminacontent are now more generally used forthis purpose.

Dump. An item of KILN FURNITURE (q.v.)designed for use in a RING - a bottomlesssaggar - for the support of large hollow-ware, e.g. basins. Dumps may also be usedas spacers in a CRANK (q.v.).Dunite. A rock consisting essentially ofolivine but sometimes also containingchromite; it occurs in many parts of theworld and is used in the manufacture offorsterite refractories.Dunnachie Kiln. A gas-fired chamberkiln designed by J. Dunnachie (Brit. Pat.3862; 1881). The first such kiln was builtat Glenboig, Scotland, in 1881 for thefiring of firebricks. Important featuresare the solid floor and the space betweenthe two lines of chambers.Dunt, Dunting. A crack, or theformation of cracks (which may beinvisible), in ware cooled too rapidlyafter it has been fired.Duo-clay. Trade name for a highlyplastic modelling clay, which can be firedand glazed normally, or may be air driedat room temperature to a hard state inwhich it may be decorated with specialcold glazes. Developed by Podmore &Sons, Stoke-on-Trent.Duplex Ceramics. Spherical pressurezones 10-50(xm diameter arehomogenously dispersed in a ceramicmatrix, to toughen it and to enhance itsthermal shock resistance. The zonescontain a high proportion of unstabilizedzirconia. Spontaneous or stress-inducedtetragonal/monoclinic transformation ofthe zirconia produces compressivestresses in the zones, and radialcompressive and tensile hoop stresses inthe nearby matrix. (H.E. Lutz andN. Claussen, /. Eur. Ceram. Soc. 7 (1991)209)

Dupre's Equation. A relationshipbetween surface energies in ceramic-metal bonding.

where W is the work of adhesion (theenergy required to separate unit area ofthe bonded surface); AG is the change insurface energy; yc, ym and ycm arerespectively the surface energies of theceramic, the metal, and of the interfaceformed by joining, assuming pristine,clean surfaces.Durability of On-glaze Decoration. A testfor the resistance of decorated tablewareto attack by detergents is provided inASTM - C556; the reagent used is asolution of 5 g. Na2CO3 per litre of water;the test is for 2,4 and 6 h at 99 ± 1.1°C.ASTM - C676 is a related test for glasstableware, C675 for alkali attack onceramic decorations in bottles; C1203 aboiling test for the resistance to alkalis ofglassware decorated with fired enamels.Durapatite. A highly translucenthydroxyapatite of near theoreticaldensity, made by sintering a wet compactof recently precipitated hydroxyapatite.Duravit. Tradename. A mechanized(battery) slip casting system forsanitaryware, developed by Netzsch(Germany).Dust. A fault, in electric lamp bulbs orvalves, resulting from localconcentrations of seed or finely-dividedforeign matter; also known as SPEW. Seealso DUSTING.

Dust. Dust is defined by B.S.2955,1958as particles which are or have beenAIRBORNE, with particle size (200 meshBS sieve), RESPIRABLE DUST (q.v.) is ahazard in the ceramics industry, causingsiLicosis (q.v.) and other diseases.Workers wear protective clothing;machines are fitted with dust extractors,and dust concentrations in the workingenvironment routinely measured. SeeDUST SAMPLING.

Dust Coat. A coating of vitreous enamelthat has been sprayed thinly andrelatively dry.

Dust Pressing. See DRY PRESSING.

Dusting. (See also DUST) (1)Spontaneous falling to a powder,particularly of material containing alarge amount of CALCIUM

ORTHOSILICATE (q.v.), which suddenlyexpands when it is cooled from red heat.(2) In dry-process vitreous enamelling, asynonym of DREDGING (q.v.)(3) In wet-process vitreous enamelling, adefect during spraying resulting inlocalized concentrations of almost dryslip.(4) The cleaning of an applied coating ofvitreous enamel slip after it has dried,preparatory to firing.Dust Sampling, RESPIRABLE DUST (q.v.)concentrations are routinely measured inthe workplace. Measurements may betaken over a long period in the generalenvironment (see GRAVIMPINGER) or bypersonal dust samples such as theCasella, carried by the operative. Dustsamples collect specimens in filters, andthe collected samples are weighed andanalysed, (see THRESHOLD LIMIT

VALUE). The methods for sampling arespecified in the UK by MDHS 14,1993(q.v.) and in the USA by NIOSH (q.v.)Manual of Analytical Methods, DHEWPub. No. 84-100, revised 1987. The dustis collected on special filters (see below),and weighed and analysed.Dust Sampling, Filters. Glass fibrefilters are adequate for measurementsof dust concentration, but not if thedust is to be analysed. Also fibre loss inhandling can be significant if dust iscollected. Silver or membrane filters arethen used. The Gelman DM800 is aproprietary membrane filter exemplifiedin MDHS 14. (Gelman Sciences Ltd).Millipore Ltd filters are of a range oftypes. The Gelman DM800 is madefrom a copolymer of acrylonitrileand PVC. Such membrane filters and

those made from mixed esters ofcellulose do not show excessive weightcharge due to moisture absorption (asdo cellulose nitrate filters), nor (as dopure PVC) do they show excessivestatic build-up.Dutch Bond. Brickwork with alternateheader and stretcher courses andalternate stretchers in vertical alignment.Dutch Kiln. An early type of up-draughtintermittent kiln for the firing of bricks;it had a number of small chimneys in theroof.Dutch Oven. A simple furnace of smallsize and usually fired with solid fuel; itcan be constructed outside a newly-builtfurnace, for example, and used as an air-heater for drying-out and warming up(cf. DUTCH KILN).

Dwell Mark. A fracture surface markingresembling a pronounced RIPPLE MARKOR WALLNER LINE, indicating a pause incrack propagation at that point.Dye Absorption or Dye Penetration. Atest for porosity in ceramic products thatare nominally non-porous. It is applied,for example, to porcelain insulators forwhich B.S.137 stipulates that there shallbe no sign of dye penetration after afractured specimen has been immersedfor 24 h in a 0.5% solution of fuchsine inalcohol under a pressure of 14 MNnr2.Dyer Method. A procedure for shapingthe socket of a clay sewer-pipe proposedby J. J. Dyer (Brick Clay Record 105 (3),27,1944).E.B. Gun. Trade name; a cement gun ofa type designed for use in repairing therefractory lining of gas retorts. (E. B.Refractory Cement Co. Ltd.,Stourbridge, England.)'E' Glass. (Electrical.) A glass of lowalkali content (<1%Na2O), used to makeelectrically insulating glass fibre.Earthenware. Non-vitreous, opaque,ceramic whiteware. The COMBINED

NOMENCLATURE (q.v.) definesearthenware products as thosemade from selected clays, sometimesmixed with feldspars and with varyingamounts of chalk, characterized by awhite or light-coloured fragment(slightly greyish, cream or ivory).The fragment, which has a fine grain,is homogeneous; the diameter ofthe non-homogeneous elements(particles, inclusions, pores)representative of the structure of thegeneral mass should be less than 0.15mm: these elements are therefore notvisible to the naked eye. In additiontheir porosity as measured by themethod specified in the Nomenclature,(6912 00 10) (coefficient of waterabsorption) is 5% or more by weight.(See also FINE POTTERY, which iscoloured.) The general bodycomposition is (per cent): china clay, 25;ball clay, 25; calcined flint, 35; chinastone, 15. The biscuit firing temperatureis 1100 to 11500C.Easing Air. The air that is admittedthrough the feed-holes of an annular kilnat one stage in the firing of FLETTON(q.v.) bricks; the purpose is to check therapid rise of temperature consequent onthe ignition of the organic matter presentin such bricks.Easy Fired. Clay ware, particularlyearthenware, is said to be easy fired if ithas been fired at too low a temperatureand/or for too short a time.Eaves Course; Eaves Tile. A course ofspecial-size roofing tiles (eaves-tiles) foruse at the eaves of a roof to obtain thecorrect lap.Ebonex. Titanium suboxide material forelectrodes for electrochemistry, and foruse as a high temperature lubricant.Specific properties depend on theproportions of suboxides present. SeeMAGNELI PHASE.

Eccospheres. Tradename forMiCROBALLONS (q.v.) made byEmerson-Cuming Corp, USA.Ecosmalt. A process to apply vitreousenamel by a two-coat, one-fire process,in which the enamel is applied byelectrostatic powder coating in twosuccessive stages.Edge Bowl. A hollow bowl about 7 in.deep and containing the slot throughwhich glass is drawn in the PITTSBURGHPROCESS (q.v.).Edge-defined film growth. Amodification of the CZOCHRALSKITECHNIQUE (q.v.) for growing singlecrystals. In the EFG technique a new diewith a capillary hole is immersed in themelt, which is wicked to the top of thedie by surface tension. A seed crystal istouched to its surface there, and slowlypulled away. A film of the melt spreadsover the top of the die, and the growingcrystal assumes the cross-sectional shapedefined by the sharp edges of the die.Shapes similar to extruded cross-sectionscan be produced.Edge Lining. The painting, by hand ormachine, of a coloured line round theedge of pottery.Edge-runner Mill. A crushing andgrinding unit depending for its action onheavy mullers, usually two in number,that rotate relative to a shallow panwhich forms the base; the pan bottommay be solid or perforated (cf. END-RUNNER MILL).

Edging. (1) The removal of driedvitreous enamel cover-coat from theedge of ware, to reveal the underlyingcoating of enamel.(2) The application of differentlycoloured slip around the rim of enamel-ware.Edinburgh Sink. A domestic orindustrial sink having an overflowand with its top edge projecting

outwards; cf. BELFAST SINK and LONDONSINK.EDS Energy Dispersive Spectroscopy.Efflorescence. A deposit of soluble saltsthat sometimes appears on the surface ofbuilding bricks after they have been builtinto a wall. If the salts are derived fromthe bricks themselves they consist chieflyof CaSO4, MgSO4, K2SO4 and Na2SO4;soluble sulphates present in the raw claycan be rendered insoluble by theaddition of BaCO3 to the clay while it isbeing mixed; this precipitates thesulphate as insoluble BaSO4.Efflorescence may arise, however, fromsoluble salts in the mortar or, if a wallhas no damp course or is backed by soil,from the soil itself. A test for thelikelihood of bricks to effloresce is givenin B.S.3921, which categorizesefflorescence 'nil', 'slight' (area marked),'moderate' or 'heavy' (50% covered).Efflorwick Test. A test for the likelihoodof the formation of EFFLORESCENCE(q.v.) on a clay building brick. A 'wick',made by shaping and firing a red clayknown to be free from soluble salts, isallowed to absorb any soluble saltsdissolved by distilled water from thecrushed sample to be tested; the 'wick' isthen dried and examined forefflorescence. The conditions of the testhave been standardized by the NewYork State College of Ceramics {Brick& Clay Record, 101, No. 5, 25,1944).EFG. Edge-defined Film Growth (q.v.)Eggshell Porcelain. A very thin, andhence highly translucent, porcelainoriginally made by the Chinese andJapanese for the European market.Bone China has also for long beenavailable of 'eggshell' thinness.Eggshelling. (1) A glaze fault resulting inpotteryware coming from the glost-kilnwith an egg-shell appearance. The faultis caused by gas bubbles that have burst

on the surface of the glaze, which hassubsequently failed to heal; the glaze istoo viscous at the firing temperatureused.(2) A similar surface fault in vitreousenamelware (unless this surface appearson the ground-coat, when it can be anadvantage as providing a good base forthe cover-coat).Egyptian Blue. A colour resulting fromthe formation of a complex coppersilicate in an alkaline glaze or glass; thecolour was much used by the ancientEgyptians and subsequently by thePersians.Ehecoat. Tradename. A high-emissivityrefractory coating of silicon carbide,made by MPK Insulation, Colchester.Einecs. European Inventory of ExistingCommercial Chemical Substances. Aswell as listing thousands of individualsubstances, the Inventory includesgeneral definitions. Those relevant to theceramics industry include:2660434 Portland Cement2660455 High Alumina Cement2660460 Glass, oxide2660476 Frits2663409 Ceramic materials and wares(for the text of this definition,see Appendix A).From 2690474 to 2691059, and 2701852,2702086, 2702107, 2704654 variouscolours and pigments, mainly spinels.2704235 Bone Ash2706599 Portland cement flue dust2706667 Feldspar group minerals2957317 Nonoxide glasses.The purpose of the Inventory is toestablish whether a substance is'existing', or 'new' and so subject to wideranging health and safety testing. TheInventory is published in severalvolumes. The general definitions are inAdvance Edition VoI VIII, SubstanceDefinitions Index, EINECS, Commission

of the European Communities,Luxembourg 1987.Eirich Mixer. An under-driven wet-panmixer. The original design was that oftwo Germans L. Eirich and J. Eirich(Brit. Pat. 379265; 25/8/32).Elastic After-effect. When glass andcertain ceramic materials are subjectedto stress for a long period they remainpartly deformed when the stress isremoved: the elastic after-effect is theratio of the deformation remaining aftera given time to the deformationimmediately after removal of thestress.Elastic Fractionation. Soft aggregateparticles are separated from hard byprojecting them against a steel plate, theharder rebounding further.Electret. An electrical analogue of apermanent magnet: a material that is'permanently' electrified and exhibitselectrical charges of opposite sign at itsextremities. In order to retain theircharge for a long period (days or weeks)ceramic electrets must be polarized athigh temperature; materials that havebeen treated in this way include thetitanate dielectrics.Electrical Conductivity. A measure ofthe ease with which an electric currentcan be made to flow in a material by anapplied voltage.Electric current is the flow of charge,which in ceramics can be carried bypositively charged, mobile ions (ionicconductivity), or by electrons or holes.Electrons in a solid can have one of arange of energies. These availableenergies are in bands, the bands beingseparated from each other by quite wideenergy gaps. If all the available energystates in a conduction band (so called)are full, electrons must acquire sufficientenergy to cross the gap to the nexthigher conduction band, before they can

move freely and carry charge. A materialexhibiting this behaviour is called anelectrical insulator. If about half theavailable energy states in a conductionband are occupied, most of the electronsin that band can easily reach a moreenergetic state, and are thus able tomove freely, A material of this type is anelectrical conductor - typically a metal.If the conduction band is almost empty,only a few electrons can easily acquiremore energy (the rest must cross theenergy gap to the nearly empty bandabove them). Conduction is thus limited,and the material is an intrinsicsemiconductor. If the conduction band isnearly full, a few electrons can reach thevacant higher energy states, leaving'holes' behind them. These behave aspositive charge carriers otherwise likeelectrons. (Hole conduction). Again thematerial is an intrinsic semiconductor.The number of such mobile electronsand holes increases as the temperaturerises, so the electrical conductivity ofsemiconductors increases withtemperature. The number of mobileelectrons (or holes) can be increased byDOPING (q.v.) the material with anotherof higher or lower valency respectively,producing n-type (negative) or p-type(positive) doped or extrinsicsemiconductors.ASTM D1829 is a test for the electricalconductivity of ceramics at elevatedtemperatures.Electrical Discharge Machining. EDM.The cutter (a profile tool or cutting wire,forms the anode and the workpiece thecathode, about 40mm apart, separatedby a fluid dielectric such as paraffins inthe EDM machine. Sub-micron solidimpurities in the fluid migrate to form abridge; a 'spark' passes through the fluid,and material is removed from thecathode by melting, evaporation and by

thermal spalling. The fluid concentratesthe spark plasma into a very smallvolume, with energy densities up to 3J/mm2 and plasma temperatures of400000C. The rate of removal of materialdepends on its electrical and thermalproperties and not on its hardness orbrittleness. Mirror finishes can beachieved.Electric Furnaces for Melting andRefining Metals. Several types of electricfurnace are used in the metallurgicalindustries, both ferrous and non-ferrous:all these furnaces are lined withrefractory materials, the larger furnacesgenerally being bricked, the smallerfurnaces usually having a monolithicrefractory lining which is rammed intoplace. The chief types of such furnacesare DIRECT ARC, in which the electriccurrent passes through the charge:INDIRECT ARC, in which the arc is struckbetween the electrodes only; INDUCTIONFURNACE, in which the metal charge isheated by eddy-currents induced in it.Induction furnaces may be operated athigh frequency (h.f. induction furnaces)or at low frequency (Lf. inductionfurnaces).Electrical Porcelain. Porcelainmade for use as an electrical insulatingmaterial. A typical batch composition is18% ball clay, 22% china clay, 30%quartz, 15% china stone, 15% feldspar.Low-tension porcelain for the insulatorsused for normal supply lines and high-tension porcelain for the high voltagegrid are of essentially the samecomposition, but the latter is generallymade to a lower porosity. Largeinsulators may be jolleyed or, wherenecessary, thrown and turned; sometypes of insulator for suspension linesare warm-pressed. Relevant BritishStandards include: B.S.16, 137, 223,3288, 3297.

Electrocast Refractory. A refractorymaterial that has been made by FUSION-CASTING (q.v.).Electroceramics. A general term forceramics specially formulated forelectrical and electronic applications.B.S.6045 gives eight classes:Group ClOO PORCELAINS (alkalinealumino-silicates)C.200 STEATITE, FORSTERITE(magnesium silicates)C.300 high permittivity ceramics:TITANIA, TITANATES,STANNATES and NIOBATES.C.400 alkaline earth alumino-silicates.C.500 porous aluminium and magnesiumsilicate.C.600 MULLITEC.700 HIGH ALUMINA ceramicsC.800 OXIDE CERAMICSThe standard also defines six classes ofglass insulating materials, based oncomposition: G.100 alkali-lime-silica;G.200 and G.300, borosilicates(chemically and electrically resistantrespectively) G.400 alumina-lime-silicates; G.500 lead oxide alkali silica;G.600 barium oxide alkali silica.B.S.4789 specifies ceramic envelopes forelectron tubes.Electrode Ring or Bull's Eye. Specialrefractory shapes, in the roof of anelectric arc steel furnace, forming anopening through which an electrode isinserted.Electrofusion. The process of fusion inan electric furnace. See FUSION-CASTING.Electroless Plating. The formation ofmetal coatings by autocatalytic chemicalreduction of metal ions from solution.The metal being deposited itselfcatalyses the continous chemicalreduction of the metal ions, the electronsare supplied by the reducing agent, andnot by an external source of electric

current, and uniform coatings oftheoretically unlimited thickness can bedeposited at a constant rate solely on thearticle to be plated. The process is usedto apply Ni, Co, Cu or noble metalcoatings to ceramics, as well as toplastics and metals.Electrolyte. A compound which, whendissolved in water, partially dissociatesinto ions, i.e. into electrically chargedatoms, molecules, or radicals. Electrolytesare added to clay slips and to vitreous-enamel slips to control their flowproperties.Electron Beam Perforation. Holes aremelted in ceramics by precise localisedheating with an electron beam focussedwith a magnetic lens.Electronic Ceramics. Ceramics whoseapplications in a wide range of electronicdevices, use such properties assemiconduction, piezoelectricity, ionicconduction, as well as the more widelyknown electrical insulating properties oftraditional electroceramics.Electron Microscopy. Electrons from acathode can be focused by electric andmagnetic fields, to form an enlargedimage of the cathode on a fluorescentscreen. In TRANSMISSION ELECTRONMICROSCOPY, the electrons pass throughthe specimen to be studied; its magnifiedimage can then be examined. Theresolving power is some 1000 times thatobtainable with optical microscopes. InSCANNING ELECTRON MICROSCOPY, theelectron beam is focussed on thespecimen, and made to perform a rasterscan (as in a TV tube) across its surfacepoint by point. This causes secondaryelectrons to be emitted point by point.These are processed electronically toproduce an image of the surface featureson a cathode ray tube screen.Electrolytic Pickling. A method (notmuch used) for the preparation of the

base-metal for vitreous enamelling;chemical PICKLING (q.v.) is assisted(ANODE PICKLING) or replaced(CATHODE PICKLING) by electrolysis.Electro-osmosis. The de-watering andpartial purification of clay by a processOf ELECTROPHORESIS (q.V.) firstproposed by Elektro-Osmose A. G.(Brit. Pats., 135815-20 25/6/18). Theprocess has had only limited applicationbecause of its high cost; it has been usedat Karlovy Vary (formerly Karlsbad) inCzechoslovakia, and at Grossalmerodeand Westerwald (Germany).Electrophoresis. The movement of fineparticles in a suspension as a result ofthe application of an electric field. Use ismade of this effect in the electricallubrication of the dies in someclayworking machinery, the migration ofthe clay particles leaving a concentrationof water between the clay and the metaldie. Clay particles become negativelycharged and migrate towards the anode.Casting is thus possible. See ELEPHANTand VOLUPHANT.Electro-optic Materials. SeeOPTOELECTRONICS, FERPICS.Electrostatic Spraying. A process in whichparticles that are to be sprayed are givenan electrostatic charge opposite to that onthe ware to be sprayed; this attracts thesprayed particles to the ware. Althoughtechnically applicable to vitreousenamelling, this method of spraying has sofar been little used in the ceramic industry.Electrostriction. A second-orderelectromechanical coupling effect,usually a much smaller effect thanPIEZOELECTRICITY (q.v.) Some leadmagnesium niobates have significantelectrostrictive strains (0.1%) with nearabsence of hysteresis. (L.E. Cross et al,Ferroelectrics 23, 1980, pl87).Elephant. An electrophoretic castingmachine which produces a single

continuous band of clay. Two cylindricalanodes rotate in opposite directions. Thecathode is placed in the nip betweenthem, and slip fed in from above. A claydeposit is built up on the cylinders. Whenthe deposits are thick enough, they uniteto form a continuous band, whose widthdepends on the length of the cylindersand whose thickness depends on theirspeed of rotation. (Karl Handle,Germany. Interceram 27,1978, p 33)Elevator Kiln. A kiln into which asetting of ware is raised from below; theware is set (outside the kiln) on arefractory base which is subsequentlyelevated by jacks into the firing position.Kilns of this type have been used, forexample, in the firing of abrasive wheels.Elutriation. The process of separation ofparticles, according to their size and/ordensity, by submitting them to anupward current of water, air or otherfluid (Cf. SEDIMENTATION).Embossing. The decoration of pottery bymeans of a raised pattern (flowers, figures,etc.); the effect is usually obtained bydepressions in the plaster mould in whichsuch ware is made (Cf. SPRIGGING).Emery. A naturally occurring, impure,CORUNDUM (q.v.); used as an abrasive.Emissivity. A surface property, being theratio of its emissive power for heat tothat of a BLACK-BODY (q.v.) for a givenwavelength and at the sametemperature. Some reported values forrefractory materials are:Type of Refractory 10000C 15000CFireclay 0.8 0.7Silica 0.85 0.7Siilimanite 0.55 0.6Sintered alumina 0.4 0.4Chrome-magnesite 0.85 0.7Emley Plastometer. An instrumentdesigned primarily for assessment of theplasticity of building plaster; it has alsobeen used for the testing of clay. The

material to be tested is placed on aporous disk which is mounted on avertical shaft; as the shaft revolves itrises, pressing the sample against aconical metal disk, the motion of whichis resisted by a lever. Equilibrium isreached when the force of the sampleunder test against the metal disk is equalto the stress acting through the lever; theaverage relative tangential force for thefirst 5-min. period is taken as an index ofplasticity. (W. E. Emley, Trans. Amer.Ceram. Soc.,19,523,1917.)Emperor Press. Trade-name. A dry-press brickmaking machine of the rotary-table type. (Sutcliffe Speakman Ltd.,Leigh, Lanes., England.)Enamel. See ENAMEL COLOUR; GLASSENAMEL; VITREOUS ENAMEL.Enamel-back Tubing. Glass tubing, theback half of which (the tube being heldvertically) is seen to consist of white orcoloured PLY GLASS (q.v.)Enamel Colour. A ceramic colour forthe on-glaze decoration of pottery.Enamel Firing. In the British potteryindustry this term is synonymous withDECORATING FIRING (q.V.)Enamelled Brick. A hard, smooth brickwith a fired (usually coloured) washcoating.Enamelling Iron. Cold-rolled sheetspecially made from steel of very lowcarbon content for the vitreous-enamelindustryEncapsulated Colours. Ceramic coloursin which the CHROMOPHORE (q.v.) isphysically trapped or encapsulated inthe crystal matrix, not forming a part ofthe crystal lattice itself (cf. LATTICECOLOURS). The pink cadmiumsulphoselenide inclusion pigments(Degussa, Br. Pat. 1403470, 1975) wereof this type, with the pigment trapped inthe ZIRCON (q.v.) lattice. Laterdevelopments have led to means to

entrap much greater concentrations ofchromophore to enhance coloursaturation, producing bright yellow,orange and red cross colours. (BritishCeramic Research Ltd UK Pat.2106530A, 1983). The technique canalso be used to impart stability topigments which would be difficult orimpossible to use, either by reducingflow problems caused by reaction withglazes (cobalt blue colours) orincreasing thermal stability of thepigment - grey colours based oncarbon black pigment encapsulated inzircon.Encapsulated HIPing. The ceramicpowder is contained in a thin glassenvelope during HOT ISOSTATICPRESSING, excluding the furnaceatmosphere from the compact. Thetechnique has proven particularlyvaluable in HIPing high-Tc ceramicsuperconductors. It allows the oxygenchemistry to be controlled and avoids anadditional treatment stage in anoxidizing atmosphere.Encapsulation. The sealing of anelectronic component, particularly of asemi-conductor, generally with a ceramicsealing compound (cf. POTTINGMATERIAL).

Encaustic Tiles. Ceramic tiles in which apattern is inlaid with coloured clays, thewhole tile then being fired.End. A brick shape used for theconstruction of arches and sprung roofs;the large faces are inclined towards eachother in such a way that one of the endfaces is smaller than the other. (See FigI,p39.)End Feather. See FEATHER BRICK.End-fired Furnace. A type of glass-tank furnace in which the ports are inthe back wall (cf. CROSS FIREDFURNACE).End Runner. See RISER BRICK.

Endoprep. A process for electrostaticpowder enamelling which requires nometal preparation.End-runner MiH. A small grinding unit,primarily for laboratory use, operatingon the principle of the pestle and mortar;the runner is set eccentrically in themortar, which is mechanically driven (cfEDGE-RUNNER MILL).End Skew. A brick (particularly arefractory brick) with one endcompletely bevelled at an angle of 60°.This bevel can be towards a large face(end skew on flat) or towards a side face(end skew on edge). Both types of brickare used in the springing of an arch (SeeFig 1, P39)End Wall. (1) The vertical refractorywall, furthest from the furnace chamber,of the downtake of an open-hearth steelfurnace.(2) One of the two vertical wallsterminating a battery of coke ovens or abench of gas retorts; it is generallyconstructed of refractory bricks andheat-insulating bricks with an exteriorfacing of building bricks.(3) Cf. GABLE WALL.Endell PIastometer. See GAREIS-ENDELLPLASTOMETER.Endellite. Obsolete name for the claymineral HALLOYSITE (q.v.); someauthorities, however, would preserve thename for those halloysites containing anexcess of water.Endothermic Reaction. A chemicalreaction that takes place with absorptionof heat. The dehydration of kaolinite is areaction of this type.Enduro. Tiles made by the FIRESTREAMprocess (q.v.) Fliesen u. Flatten 36 (4) 141986.Energy Dispersive Spectroscopy. X-raysemitted by an element struck by a beamof electrons are detected by a Li-dopedsilicon crystal, in which electron-hole

pairs are generated, the number of pairsbeing proportioned to the energy of theX-rays. The resulting electrical pulsesare displayed as a spectrum of X-rayintensity vs. energy.Enforced-order Mixer. See FRENKELMIXER.

Engine-turning Lathe. A lathe having aneccentric motion and used to incisedecorations on pottery-ware before it isfired.Engineering Bricks. Building bricks thathave been shaped from a clay such as anEtruria Marl which, when fired at a hightemperature, will vitrify to produce a brickof great strength and low waterabsorption. If firing is under reducingconditions, blue bricks are produced; withoxidizing firing the product is a redengineering brick. In either case the brickmust conform, in the UK, to B.S.3921which sub-divides them into two classes:Class A - min. crushing strength 70MNm~2, max. water absorption 4.5 wt%.Class B - min. crushing strength 50MNm~2, max. water absorption 7 wt%.Engineering Ceramics. Simply, ceramicsused for applications in engineering.More precisely, the term usuallyexcludes ceramics based in clay, and isparticularly applied to mechanicalengineering applications in which thethermo-mechanical properties of theceramics are important. Typicalengineering ceramics now widely usedare alumina, zirconia, silicon carbide,and silicon nitride.English Bond. A brick wall built withalternate header and stretcher courses.English Crystal Glass or English FullCrystal. Older name for FULL LEAD

CRYSTAL GLASS (q.V.).English Garden Wall. A brick wall inwhich three stretcher courses arefollowed by one header course, the bondpattern then being repeated.

English Kiln. A transverse-arch chamberkiln with a system of flues and dampersabove the chambers permitting any twochambers to be connected. It wasdesigned by A. Adams in 1899 for thefiring of building bricks made fromhighly bituminous clays.English Pink. See CHROME TIN PINK.English Translucent China. Ceramictableware, etc., introduced in 1959 byDoulton Fine China Ltd, Burslem,England. In contrast to bone china it isfeldspathic, but differs from Continentalporcelain in that it is biscuit fired at ahigher temperature than the glost fire.English and Turner Factors. SeeTHERMAL EXPANSION FACTORS FOR

GLASS.

Engobe. A coating of slip, white orcoloured, applied to a porous ceramicbody to improve its appearance; a glazeis sometimes applied over the engobe, asin sanitary fireclay. A typical engobe forsanitary fireclay consists of 10% ballclay, 40% china clay, 20% flint and 30%china stone; some of the china stone maybe replaced by feldspar and considerablevariation is possible in the proportions ofthe other constituents. (French word.)Enloc. A system for keeping plateswarm. A special conductive decorationon the underside of the plate is heatedinductively by a generator beneath thetable.Epitaxy. Growth of one crystal layeronto another with the same crystalorientation.Engraving. A method of decoration. Forapplication to pottery, the pattern isengraved on a copper plate or roller; theincised pattern is then filled withspecially prepared colour which istransferred to the ware by transferpaper. As a method of decorating glass-ware, the pattern is cut directly into theglass surface by means of copper wheels;

the depth of cut is shallower than inintaglio work.Enslin Apparatus. This apparatus for thedetermination of the water-absorptioncapacity of clays was originally designedby O. Enslin (Chem. Fabrik., 6,147,1933) for testing soils. It consists of aU-tube, one arm of which is connectedvia a 3-way tap to a calibrated horizontalcapillary tube; the other arm ends in afunnel with a sintered-glass base onwhich is placed a weighed sample ofclay. Water is allowed to contact thesample and the amount absorbed is readfrom the capillary tube. The result isexpressed as a percentage of the weightof the dry clay.Enstatite. Magnesium metasilicateMgSiO3: m.p. 15500C. Enstatite(orthorhombic) is stable up to about10500C when it inverts to proto-enstatite(orthorhombic) which is the stable hightemperature form. Clino-enstatite(monoclinic) is formed as a metastablephase when proto-enstatite is cooledrapidly; the transition temperature is865°C. Thermal expansion (300-700°C):enstatite 12 x 10-6; proto-enstatite 10 x10"6 clino-enstatite 13.5 x 10"6, Proto-and/or clino-enstatite are majorconstituents of steatite ceramics: clino-enstatite is found in magnesite re-fractories that have been attacked bysiliceous slags.Envelope Kiln. Alternative name,particularly in USA, for TOP-HAT KILN(q.v.) or SHUTTLE KILN (q.v.).Equilibrium Diagram. See PHASEDIAGRAM.

Equivalent Particle Diameter orEquivalent Free-falling Diameter. Aconcept used in evaluating the size offine particles by a sedimentation process;it is defined as the diameter of a spherethat has the same density and the samefree-falling velocity in any given fluid as

the particle in question (cf. PARTICLESIZE).Eriometry. The measurement of particlesize by using laser-generated diffractionpatterns.Erosion. Wear caused by the mechanicalaction of a fluid, e.g of molten steelflowing through the refractory nozzle ina ladle or of waste gases flowing throughthe downtake of an open-hearth furnace(cf. ABRASION and CORROSION).Erosion-resistant Castable. A term usedin the petrochemical industry to describehigh-strength dense castables used tomake erosion-resistant linings.Erz Cement. A ferruginous hydrauliccement formerly made in Germany; ithas now given place to FERRARICEMENT (q.V.).ESSE A. An Italian clay building block,19 x 40 x 29cm, made with pore-formingadditives. The arrangement ofperforations is varied to emphasisloadbearing, acoustic orthermohygrometric properties.Estuarine Clays. Clays that weredeposited, during the course ofgeological time, in estuaries and deltas.Estuarine clays of the Middle Jurassicoccur in Yorkshire and Lincolnshire andare used as raw material for makingbuilding bricks.E.T.C. ENGLISH TRANSLUCENT CHINA(q.v.).Ethyl Silicate. See SILICON ESTER.Etruria Marl. A brick-clay occurring inthe Carboniferous System and used forthe manufacture of bricks and roofingtiles, particularly in the EnglishMidlands and North Wales. Theseclays have a high iron content; theyfire to a red colour under oxidizingconditions but under reducingconditions they fire to the blue colour ofthe well-known Staffordshireengineering brick.

Etruscan Ware, BASALT WARE (q.v.)having an encaustic decoration, mainlyin red or white in imitation of earlyItalian Etruscan pottery.Ettringite.Ca6Al2(SO4)3(OH)12.26H2O.This mineral is present during the earlystages of the hardening of Portlandcement; it is an essential constituent ofset supersulphated cement, contributingto its high flexural strength.Eucryptite. A lithium mineral,Li2O. Al2O3. 2SiO2. When heated,the a-form changes to the P-format about 9700C; the (3 form expandsin one direction and contracts inanother direction. Eucryptite is aconstituent of special ceramic bodieshaving zero (or even negative) thermalexpansion.Eurite. A feldspathic mineral occurringon the island of Elba and used locally asa ceramic raw material, especially as aflux.Eurolit. A dry screed of tongue-and-grooved clay tiles, on top of which floortiles are fixed.Euronorms. EUROPEAN STANDARDS

(q.v.).Europresse. A continuously operatingextruder developed by Rieterwerke,Konstanz, Germany, in which theconventional auger is replaced by acylindrical body with annular grooves,with only a small clearance between thecylinder and the outer casing. Thegrooves are filled uniformly by afeed rotor on an axis parallel to thecylinder, and emptied by a comb-likeroller with teeth arranged to fit thegrooves.Eutectic. An invariant point on anequilibrium diagram. In the Al2O3-SiO2

system (see Fig. 5) there is a eutecticbetween silica and mullite and a eutecticbetween alumina and mullite. Theeutectic temperature is that at which

a eutectic composition solidifies whencooled from the liquid state. The eutecticcomposition has been defined as 'thatcombination of components of aminimum system having the lowestmelting point of any ratio of thecomponents; in a binary system it is theintersection of the two solubility curves.'Eutectic Joining. The components of aeutectic mixture are present in suchproportions that the mixture melts at alower temperature than mixtures ofslightly different proportions. Eutecticjoining uses such mixtures to form thebond between ceramics, or betweenceramics and metals.Eutit. Cast basalt made by CzechoslovakCeramics.Exadur. An extra hard, smooth plastermade by H & E Borgardts KG,Germany.Excavator. See DRAG-LINE;MECHANICAL SHOVEL; MULTIBUCKETEXCAVATOR; SHALE CUTTER or SHALEPLANER; SINGLE BUCKET EXCAVATOR.Excess Air. The amount of air in acombustion process that is greater thanthat theoretically required for completeconbustion.Exchangeable Bases. See IONICEXCHANGE.Exfoliation. The property of somehydrous silicates, notably VERMICULITE(q.v.). of permanently expandingconcertina-wise when rapidly heated to atemperature above that at which heat isevolved; cf. BLOATING andINTUMESCENCE.Exhaust catalyst. See CATALYTICCONVERTER.Exothermic Reaction. A reaction thattakes place with evolution of heat. Sucha reaction occurs at 900 to 10000C whenmost clays are fired.Expanded Clay. See LIGHTWEIGHTEXPANDED CLAY AGGREGATE.

Expansion Cards. Cardboard inserts, orcards pre-attached to refractory bricks toprovide allowance for thermal expansion.Expansive Cement. A high sulphate andalumina-containing cement, whichshrinks during drying, but then expandson hardening to compensate.Explosive Forming: A process forcompaction by the blast of an explosionwithin the mould containing the powderto be compacted; the rate of energyrelease has been stated to be approx. 33kJs-1 and densities as high as 97% of thetheoretical have been attained.Exposed Finish Tile. US term (ASTM -C43) for a hollow clay building block thesurfaces of which are intended to be leftexposed or painted: the surface may besmooth, combed or roughened.Expression Rolls. A pair of steel rollswhich when rotated will force a claycolumn through a die or along a cutting-off table (as in the shaping of bats forroofing-tile manufacture); cf. CRUSHINGROLLS.

Extra-duty Glazed Tile. US term for aceramic tile with a glaze that issufficiently durable for light-duty floorsand all other surfaces inside buildingsprovided that there is no seriousabrasion or impact.Extrusion. The forcing of clay or othermaterial through a die; this is done by acontinuous screw on a shaft rotatingcentrally in a steel cylinder (an 'auger'),or by a series of knives obliquelymounted on such a shaft (a 'pug'), or,occasionally, by means of a piston (a'stupid'). Ceramic material may beextruded either to mix and consolidate it(as in the extrusion of pottery body priorto jiggering) or to give the body its finalshape (as in the extrusion of bricks andpipes).Eye. An opening in the SIEGE (q.v.) of apot furnace for glass melting; gas and air

for combustion enter the furnacethrough the eye.Eykometer. An instrument for thedetermination of the yield point of claysuspensions; details have been given byA. G. Stern (U.S. Bur. Mines, Kept.Invest. 3495,1940).0F. Degrees Fahrenheit. T0F = 5/9( r -32)°G See 0C.Face. The part of the abrasive wheelagainst which is applied the work to beground.Faced Wall. A wall in which the facingand backing are bonded in such a waythat the wall acts as a unit when loaded(Cf. VENEERED WALL).Fabrication Traces. Anomalousmarkings on crack surfaces due toweaknesses originating duringprocessing.Facing Brick. A clay building brick havingan appearance, and weather-resistance,suitable for use in the outside leaf of a wallor in an external brick panel. Such bricksare made in a variety of textures andcolours; physical properties range from acrushing strength of about 7 to 100MNm~2 and a water absorption of about 5to 30 wt.% Properties are specified in B.S.3921, and in ASTM C216.Faggot. Defined in the S. Africanspecification for building bricks as 'Afacing brick of the normal facedimensions but with the smallest beddimension less than the height'.Fahrenheit. See 0F.Faience. Originally the French name forthe earthenware made at Faenza, Italy,in the 16th century; the ware had a tin-opacified glaze and in this resembledMaiolica and Delft ware. The meaninghas now changed. In France, faience isany glazed porous ceramic ware; faiencefine is equivalent to EnglishEARTHENWARE (q.v.). In England, theterm 'faience' now refers to glazed

architectural ware, e.g. large glazedblocks and slabs (not dust-pressed glazedtiles). In USA, faience ware signifies adecorated earthenware having atransparent glaze.Faience Tiles and Mosaic. US termsdefined (ASTM - C242) as follows:FAIENCE TILE - glazed or unglazed tiles,generally made by the plastic process,showing characteristic variations in theface, edges, and glaze that give an 'art'effect; FAIENCE MOSAIC - Faience tilesthat are less than 6 in2 (3871 mm2 infacial area and usually 8 to 9mm thick.Fairlight Clay. A Cretaceous clay of theHastings (England) area that finds use inmaking building bricks.Falling Slag. Blast-furnace slag thatcontains sufficient CALCIUMORTHOSILICATE (q.v.) to render it liableto fall to a powder when cold. Such aslag is precluded from use as a concreteaggregate by the limits of compositionspecified in B.S. 1047.False Set. Premature, but temporary,stiffening of portland cement resultingfrom overheating of the added gypsumduring grinding of the clinker (cf. FLASHSET).

False Header. A half-brick used tocomplete a course of brickwork.Falter Apparatus. Apparatus designedby A. H. Falter (J.Amer. Ceram. Soc, 28,5,1945) for the determination of theSOFTENING POINT (q.v.) of a glass by thefibre-elongation method as defined by J.T. Littleton (J. Soc. Glass Technol. 24,176,1940).Famille Rose. Red colours based ongold and tin, obtained from PURPLE OFCASSius (q.v.)Famille Verte. Green colours based onchromic oxide, developed in the 18thcentury.Fantail. The opening in the refractorybrickwork that separated the slag pocket

from the regenerator of an open-hearthsteel furnace.Faraday Effect. The rotation of theplane of polarization of a beam ofpolarized light as it passes through glassthat is located in a magnetic field; firstobserved by Michael Faraday in 1830.FARE-gun. Fuel-Air RepetitiveExplosion coating deposition process.Farren Wall. A cavity wall (4-in. cavity)for house construction introduced inUSA; (Brick & Clay Record, 95, No. 4,38, 1939).Fat Clay. Term sometimes used for aclay that is highly plastic.Fastfire Kiln. A kiln for rapid firing.The preferred term according to BS3446 Pt2.Fast Firing, see RAPID FIRINGFast Fracture. See FRACTUREFast ion conductors. Solid electrolyteswith high electrical conductivites due tocharge transport by mobile ions. SeeIONIC CONDUCTIVITY.

Fatigue. The failure of a componentafter prolonged exposure to a stresssignificantly less than the stress whichwould produce immediate failure {staticfatigue)\ or to repeated cyclic stresses atlevel below the immediate fracture stress{dynamic fatigue). A silicon oxynitridesurface film greatly increases the fatigueresistance of silica fibres. See also STRESSCORROSION; THERMAL CYCLING TEST.Fat Oil. A thick oil of turpentine madeby heating turpentine in air at 145°C andthen subjecting it to steam distillation. Itis used as a vehicle, particularly for gold,in the decoration of pottery.Faugeron Kiln. A coal-fired tunnel kilnof a design proposed in 1910 by E. G.Faugeron (French Pat. 421 765;24/10/1910); the distinctive feature is thedivision of the tunnel into a series ofchambers by division-walls on the carsand drop-arches in the roof. Such kilns

have been used for the firing offeldspathic porcelain.Fayalite. Ferrous orthosilicate,2FeCSiO2; m.p. 12050C. This low-melting mineral is formed whenferruginous slags attack, under reducingconditions, aluminosilicate refractories.Feather. (1) A fault, in glass, of feather-like appearance and caused by SEED(q.v.) produced by foreign matter pickedup by the glass during its shaping.(2) A fault in wired glass resulting frombending of the transverse wires.See also FEATHERING.Feather. A STRIATION looking like afeather.Feather Brick. A specially mouldedbrick of the shape that would beproduced by cutting a standard squarediagonally from one edge. This could bedone in three ways to produce aFEATHER END (or END FEATHER) aFEATHER-END-ON-EDGE, or a FEATHERSIDE (or SIDE FEATHER) depending onwhether the diagonal terminates, for a 9x AVi x 3 in. brick, at a 4Vz-in. edge, a3-in. edge or a 9-in. edge. (See Fig. 1,p39).Feather Combing. A method ofdecoration sometimes used by the studiopotter: the ware is first covered withlayers of variously coloured slips and asharp tool is then drawn across thesurface while it is still moist.Feather End. See FEATHER BRICK.Feather Side. See FEATHER BRICK.Feathering. A glaze fault caused bydevitrification. It is particularly liable tooccur in glazes rich in lime. To preventthe fault the initial rate of cooling in thekiln, after the glaze has matured, shouldbe rapid. (See also FEATHER.)Feed Shaft. See FIRE PILLAR.Feeder. (I)A device for supplying rawmaterial, e.g. clay, to a preparationmachine.

(2) A mechanical system for theproduction of gobs of glass for a formingmachine.Feeder Channel. The part of theforehearth of a tank furnace, producingcontainer-glass or pressed glass-ware,that carries the molten glass from theworking end to the feeder mechanism.Feeder Gate or Feeder Plug. A shapedrefractory used to adjust the rate of flowof molten glass in the feeder channel.Feeder Sleeve or Feeder Tube. Acylindrical tube that surrounds thefeeder plunger in a glass-formingmachine.Feeder Spout or Feeder Nose. The partof the feeder in a glass tank furnacecontaining an opening in which theorifice ring is inserted; it forms the endof the forehearth.Feeing. See FEYING.Feed Rate. The rate of advance of acutting tool into the work (in distanceper revolution).Feine Filter. A FILTER-PRESS (q.v.) filter,made from parallel strings instead ofcloth.Feldspar. The internationally agreedspelling is feldspar; previously the usualspelling in Britain was felspar. The feld-spars are a group of minerals consistingof aluminosilicates of potassium, sodium,calcium, and, less frequently, barium.The most common feldspar minerals are:Orthoclase and Microcline:K2O.Al2O3.6SiO2Albite:Na2O. Al2O3. 6SiO2

Anorthite:CaO. Al2O3. 2SiO2

These minerals rarely occur pure,isomorphous substitution being common;most potash feldspars contain sodium,and soda feldspars usually contain bothpotash and calcium. There is acontinuous series of solid solutions,known as plagioclase feldspars, betweenalbite and anorthite. Feldspars are the

chief components of igneous rocks andoccur in economic quantity, and inadequate purity for ceramic use, in USA(N. Carolina, S. Dakota, New England),Canada (Ontario, Quebec, Manitoba),Scandinavia, France, and many othercountries. Over half the world's output isconsumed by the glass industry: in USAand Europe it is a component (20-30%)of practically all pottery bodies, Feldsparconstitutes 25-50% of most vitreousenamel batches.Feldspar Convention. See underRATIONAL ANALYSIS.

Felite. The name given to one of thecrystalline constituents of portlandcement clinker by A. E. Tornebohm(Tonindust Ztg. 211148,1897). Felite isnow known to be one form of2CaO.SiO2.Felspar. See FELDSPAR.Fender. A grate in the floor of achamber kiln immediately in front of theinter-chamber wall: it may consist offireclay blocks or firebars.Felvation. The classification of powdersby fluidisation, elutriation and seiving.Feolite. Tradename. A refractory forstorage heaters, based on ferric oxide,developed by the Electricity Council,UK.Feret's Law. States that the strength(S) of cement or concrete is related toits mixing ratio by the equationS = K [c/(c +w+a)]2 where c, w, and aare the absolute volumes of the cement,water and air in the mix. Thisrelationship was proposed by R. Feret atthe beginning of the century.Ferrari Cement. A sulphate-resistantcement consisting principally of3CaO.SiO2, 2CaO-SiO2 and4CaCAl2O3-Fe2O3. The sulphateresistance results from the formation of aprotective film of calcium ferrite aroundthe calcium aluminate crystals formed by

hydrolysis of the brownmillerite. (F.Ferrari, Cemento Armato, 38, 147,1941.)Feipic Ferroelectric picture devices. TheseOPTO-ELECTRONIC CERAMICS (q.v.) weredeveloped by Bell Telephone Laboratories,USA, to provide low cost, solid statedisplays. The ceramic rotates the plane ofpolarisation of light shone through it, thedegree of rotation depending on thewavelength of the light and the electric fieldapplied to the ceramic. It is possible totransmit light of a single colour, to vary thiscolour by varying the applied field, and toproduce various colours at different pointsin the ceramic surface.Ferric Oxide. Fe2O3, the mineralhematite; m.p. 1565°C, but when heatedin air it loses oxygen below thistemperature to form magnetite, Fe3O4;sp. gr. 5.24; thermal expansion (0-1000°C)12xl(H\ Ferric oxide is presentin the surface layers of blue engineeringbricks: it gives the characteristic sparkleto aventurine glazes.Ferrielectric. A mixed phase material,often a solid solution, which can beregarded as an incompletelycompensated antiferroelectric, theatomic dipoles of the two phases beingunequal. A permanently polarized stateresults, in which antiferroelectric andferroelectric phases coexist, each with itsown CURIE POINT (q.v.).Ferrimagnetic. A material in which theatomic magnetic moments are alignedantiparallel in an unbalanced fashion sothat a spontaneous magnetization occursin the absence of an applied field. Theyhave many properties in common withferromagnetics, but their saturationmagnetization is much less that the sumof the atomic moments.Ferrites. Specifically, this term refers to agroup of electroceramics having FERRO-MAGNETIC (q.v.) properties, combininghigh magnetic permeability (up to 4300)

and low coercive force (0.1-4 oersteds).Attention was first drawn to thesematerials by S. Hilpert (Ber Deuts.Chem. Ges. 42, 2248,1909). The ferritesare synthesized from Fe2O3 and theoxide, hydroxide, or carbonate of one ormore divalent metals, e.g. Ba, Zn, Mn,Ni, Co, Mg or Cu. The firing processmust be carefully controlled to maintainthe required state of oxidation. Mg-Mnferrites have a square hysteresis loop;BaO.6Fe2O3 is a 'hard', or permanent,magnetic material.Ferroconcrete. Concrete reinforced withiron or steel, usually as rods or mesh.Ferroelectric. A dielectric material thatshows a net spontaneous polarizationbelow the electric CURIE POLNT (q.v.)The dielectric constant reaches amaximum value at this temperature. Anapplied electric field governs thedirection of the polarization, and there ishysteresis and a non-linear relationbetween the polarization and the appliedfield. An important property offerroelectric ceramics is theirPIEZOELECTRIC (q.v.) nature.Ferromagnetic. A material in which theatomic moments are aligned parallel,giving rise to spontaneous magnetizationin the absence of an applied field. Themagnetization increases to a saturationvalue equal to the sum of the atomicmoments if an increasing external field isapplied. The materials show magnetichysteresis, and have high susceptibilitiesand permeabilities. Their magnetizationdecreases with increasing temperatureuntil at the CURIE POINT (q.v.) theferromagnetic behaviour disappears andthe materials become paramagnetic. Fora discussion of ceramic ferromagnetics,see FERRITES.

Ferrous Oxide. FeO; m.p. 13700C; sp. gr.5.7. This lower oxide tends to be formedunder reducing conditions; it will react

with SiO2 to produce a material meltingat about 12000C, hence the fluxing actionof ferruginous impurities present in someclays if the latter are fired underreducing conditions.Ferroxdure. Tradename. Ceramicpermanent magnets made by N.V. PhilipsHolland, of BaFe12O19. They have highcoercivity, low remanance and lowsaturation magnetisation.Ferroxplana. Ceramics with the generalchemical formula MO.6Fe2O3 where Mis Ba, Sr or Pb have themagnetoplumbite structure - hexagonalwith a unique 'c' axis. In the basicmagnetoplumbite structure, the 'c' axis isthe easy direction of magnetization. Insome of the more complex substitutedstructures, with interleavedmagnetoplumbite and spinal layers invarious proportions, the 'c9 axis becomesthe difficult direction of magnetization.The easy direction is one in the planeperpendicular to the 'c' axis. Suchmaterials are called ferroxplana.Fettling. The removal, in the 'clay state',and usually by hand, of excess body leftin the shaping of pottery-ware at suchplaces as seams and edges (cf.SCRAPPING). For the purposes ofCOSHH (q.v.) this potentially dustyprocess includes towing, scalloping, sand-papering and sand-sticking. Dampfettling is done either with a wet sponge,or whilst the ware is still damp and nodust is given off.(2) The process of repairing a steel-furnace hearth, with deadburnedmagnesite or burned dolomite, betweentapping and re-charging the furnace.Fettling Refractory. Refractory grain,relatively rich in fluxes, for maintainingfurnace hearths.Feying. A local term in the English brickindustry for the removal of overburdenor for the cleaning up of a clay-pit floor

after an excavator has been at work.FGM. Functionally Gradient Materials.Fiberfrax. Tradename. Aluminiumsilicate fibres, and a wide range of textileproducts made therefrom.(Carborundum Co., USA)Fiberglas. Trade name: Owens-CorningFiberglas Corp., USA.FFF. Finnish Flotation Feldspar, a fluxfor pottery bodies, beneficiated by aflotation process.Fianites. Yttria-stabilized zirconia singlecrystals.Fibre Bridging. See CRACK BRIDGING.Fibre (Ceramic). A mass of thread-likeceramic material, cf. FILAMENT andWHISKER. Typically, these fibres aremade from a batch consisting of aluminaand silica (separate or already combinedas kaolin or kyanite) together with aborosilicate flux; zirconia may also bepresent. Other types of ceramic fibre aremade from fused silica and frompotassium titanate. These fibres are usedin the production of lightweight units forthermal, electrical, and sound insulation;they have also been used for high-temperature filtration, for packing, andfor the reinforcement of other ceramicmaterials. BS 1902 Pt6 specifies require-ments and tests. BS 6466 is a code ofpractice for the design and installation ofceramic fibre furnace linings. See alsoGLASS FIBRE.Fibreglass. Though originally a tradename (of Fibreglass Ltd., St. Helens,England - cf FIBERGLASS, OwensCorning Fiberglass, USA) these wordsare now generally used for GLASS FIBRE(q.v.) products.Fibrekote. A sprayed refractory lining,comprising a mixture of alumina-silicafibres with an inorganic binder, stable to16000C.Fibre Pullout. The DEBONDINGmechanism in fibre-reinforced

composites. If a small crack develops inthe matrix, the load is transferred byshear forces to the still intact fibres,becoming greater than the bondstrength. The bond fails and a cylindricalcrack propagates down the fibre. Testmethods aim at measuring the forcesrequired to pull out fibres. As this maybe practically difficult to achieve, fibrepushout tests, using indenters alignedwith the fibres, are sometimessubstituted. See also CRACK BRIDGING.Fibre Reinforcement. Incorporatingcontinuous fibre reinforcement into aceramic matrix leads to composites withvery high TOUGHNESS (q.v.), andessentially ductile behaviour. The fibresand the matrix may separately be brittle(fracture toughness of a few MPaVm)but in combinations with appropriatelymismatched properties and carefulmicrostructural control, CRACKPROPAGATION (q.v.) may be virtuallycompletely checked. The fibre elasticmodulus is chosen to be higher than thatof the matrix, to promote load transferto the fibre. The fibre should also havehigher thermal expansion, so that oncooling from processing temperatures,the matrix is in compression. Medium-strength fibre-matrix bonding allows forcrack redirection, crack branching andcrack energy dissipation by propagationalong the fibre-matrix interface. Thefibres then remain intact and bear theloads until they fracture separately.Extra energy is then absorbed infracturing the fibres and in FIBREPULLOUT (q.v.) from the matrix. AfibrOUS FRACTURE SURFACE (q.V.)results, rather than the smoothcontinuous surface which would resultfrom BRITTLE FRACTURE (q.V.) of bothcomponents were the fibre-matrix bondstrength high. Most continuous fibrereinforcement is unidirectional, and

strengths anisotropic, being low(-2OMPa) normal to the fibre direction.Two-dimensional composites have fewerfibres and lower strengths thanunidirectional composites tested in theirstrongest direction (parallel to thefibres), but are strong in two directions.Fibretech. Refractory castablesreinforced with steel fibres.Fibrous. See MORPHOLOGY.Fiburloc. Trade name of U.S. ConcretePipe Co., Cleveland, Ohio, for vitrifiedclay pipes with joints comprisingfibreglass/polyester sockets and urethanespigots.Fick's Law. The rate of diffusion isproportional to the negative of theconcentration gradient of the diffusingspecies (Adolf Fick, 1855).Fidler-Maxwell Kiln. A straight tunnelkiln designed to be fired with gas, coal,or oil; a distinctive feature was the use ofcast-iron recuperators in the coolingzone. (F. Fidler and J. G. Maxwell, Brit.Pat. 141 124 and 141 125, 6/1/19.)Field-drain Pipe. An unglazed, fired claypipe, generally 75 or 100 mm dia. andabout 305 mm long, for the drainage offields; occasionally these pipes have aflattened base, or longitudinal ribs, tofacilitate alignment during laying. Forspecification (which includes pipes from63.5 to 305 mm dia) and joints see B.S.1196.Figuier's Gold Purple. A tin-gold colour,produced by a dry method; it has beenused for porcelain decoration.Figured Glass. Flat glass with a patternon one or both surfaces.Filament. A single long thread ofceramic material which may, or may not,be a single crystal, cf. FIBRE (CERAMIC)and WHISKER.

Filler. A general term for a solidmaterial that is chemically inert underthe conditions of use and serves to

occupy space and improve physicalproperties; an example is the use ofchina clay in some paints and plastics. Invitreous enamelling a filler (or pluggingcompound) consisting of a mixture ofinorganic compounds is used to fill anyholes in iron castings, thus providing auniform surface on which to apply theenamel.Film Strength. The mechanical strength,determining its resistance to damage byimpact or abrasion, of the dried coatingon vitreous enamel slip prior to firing.Filling Packet, In a glass-tank, the DOG-HOUSE (q.v.).Filter Block. The properties required ofa clay filter-block for use in tricklingfilters in the chemical industry arespecified in ASTM-C159 (cf. CERAMICFILTER).Filter Candle. A porous ceramic tube,which may be rounded and closed at oneend, made with a high porosity and ofsubstantially uniform pore size.Filter Cloth. Cloths form the actualfiltering medium in the FILTER PRESSES(q.v.) used to de-water clay slips.Originally, these cloths were made ofcotton, subsequently of twill with abacking cloth of jute; cotton and jutecloths need to be proofed againstmildew, usually by cuprammoniumtreatment. Nylon or terylene filter clothshave the advantage of being rot-proofand are stronger than cotton; they arenow much used in the ceramic industry.Filter Press. Equipment for thedewatering of a slurry by compressionbetween two filter cloths, which aresupported by metal frames; a number ofsuch filtering compartments are set sideby side, the compression being appliedthrough the whole series of units. Filterpresses are much used in the potteryindustry, in which it is customary toblend the constituents of the body in slip

form. ASTM C866 is a test for thefiltration of whiteware clays.Fin. A fault, sometimes occurring inpressed or blown glass-ware, in the formof a thin projection following the linebetween the parts of the mould. (Alsocalled FLASH).Final Set. The time required for ahydraulic cement to develop sufficientstrength to resist a prescribed pressure.In the usual VICAT'S NEEDLE (q.v.) testthis stage of the setting process is definedas that at which the needle point will,but its circular attachment will not, makea depression on the surface of thecement. In B.S. 12, the conditions of thetest are 14.4 to 17.8°C (58-64°F) and£90% relative humidity; for normalcements, the Final Set must not exceed10 h (the usual time is 3-4 h).Findlings Quartzite. A compact,cemented quartzite of a type occurring inGermany as erratic blocks - hence thename, which is the German word for'foundling'. This type of quartzite, whichis used as a raw material for silica-brickmanufacture, is composed of about 60%of quartz grains set in 40% of achalcedonic matrix. In Germany theterm is being displaced by the moreinformative term 'cemented quartzite'.Fine Ceramics. The term is used forhigh-quality ceramics, particularlywhitewares, but latterly for engineeringceramics, for which it is the usual term inJapanese literature.Fine China. A term used, without beingprecisely defined, to describe ware ashigh-quality CHINA (q.v.). Fine china isnot necessarily BONE CHINA, and theterm may aptly be applied to ware (e.g.E.T.C.) which does not contain bone ash.Fine Grinder or Pulverizer. A machinefor the final stage of size reduction, i.e.to -100 mesh. Such machines includeball mills, tube mills, and ring-roll mills.

Fine Pottery. Products similar toEARTHENWARE (q.v.) defined similarlyby the COMBINED NOMENCLATURE(q.v.) except that the body is made froma mixture of selected clays, to producefine-grain, homogeneous porous body ofwater absorption > 5 wt %, colouredfrom yellow to brown or reddish brown.Fineness Modulus. Defined in USA asone-hundredth of the sum of thecumulative values for the amount ofmaterial retained on the series of Tyleror US sieves (excluding half sizes) up to100 mesh. Example:

On 4 mesh 2%On 8 mesh 13On 16 mesh 35On 30 mesh 57On 50 mesh 76On 100 mesh 93Sum = 276 +• 100 = 2.76 FinenessModulusFinger-car. A small four-wheeled bogiehaving two uprights from which projectpairs (usually 10 in number) of 'fingers';these can be raised or lowered by a leverand cam. Finger-cars are used in theKELLER SYSTEM (q.v.) of handling bricks.Finger Dip Test. See SLAG ATTACKTESTS.Finial. An ornamental piece of firedclayware formerly much used to finishthe ends of roof ridges.Fining. See REFINING.Finish. The top section of a glass bottle.The finish may be DIRTY (rough orspotted) or SHARP; other faults include:BULGED FINISH - distended so that thebung will not fit; FLANGED FINISH -having a protruding fin of glass; OFFSETFINISH - unsymmetrical relative to theaxis of the bottle.Finish Mould. See NECK MOULD.Finite Element Analysis. A method forthe numerical approximation of a

continuous variable. The system isconsidered as an array of discrete smallelements, interconnected at separatenode points. The technique is used fornumerical calculations of heat flow,stresses and electrical behaviour.Fin Wall. A piered cavity wall in whichthe piers are narrow and deep 'fins',instead of being wide shallow structureswhich merely increase the wall thicknesslocally. The fins increase the structuralstrength of the wall by converting it intoa series of 'T' sections, (cf. DIAPHRAGMWALL).

Fireback. The refractory shape,sometimes made as two or more sectionsto improve thermal-shock resistance,that forms the back of an open domesticfire. A typical batch composition is 60-70% fireclay and 30-40% grog. B.S. 1251specifies four sizes 350, 400, 450 and 500mm; and a minimum P.C.E. of Cone 26.Firebox. One of the small refractory-lined chambers, built wholly or partly inthe wall of a kiln, for combustion of thefuel.Firebrick. Popular term for a FIRECLAY

REFRACTORY (q.V.).Firebridge. See BRIDGE.Fire-Chek Keys. Trade-name:pyrometric cones made by Bell ResearchInc., E. Liverpool, Ohio, USA.Fireclay; Fireclay Refractory. A clay,commonly associated with the CoalMeasures, that is resistant to hightemperatures; it normally consists ofkaolinite together with some free silica,other impurities rarely exceeding a totalof 5%. The most important deposits inthe UK are in the Central Valley ofScotland and Ayrshire,Northumberland and Durham, in theStourbridge district, S. W. Yorkshire,and the Swadlincote area. In thesedistricts fireclays of various grades areworked for the manufacture of

refractories; in Scotland, S.W.Yorkshire, and Swadlincote the fireclaysare also used for making sanitary-wareand glazed sewer-pipes; BS 1206specifies fireclay sinks. In a few otherareas fireclays are also worked for lessexacting purposes. The P.CE. offireclay, and of refractories made fromit, generally increases with the aluminacontent from about 1 5500C for thepoorer qualities to 17500C for gradescontaining 42% Al2O3 when fired; B.S.3446 defines a fireclay refractory ascontaining less than 78% SiO2 and lessthan 38% Al2O3, those gradescontaining 38-45% Al2O3 being termedAluminous Fireclay Refractories. Theprincipal uses of fireclay refractories arein blast-furnace linings, casting-pitrefractories, boiler-furnace linings, andmany general purposes where theconditions are not too severe.Fireclay Plastic Refractory. A US termdefined as: A fireclay material temperedwith water and suitable for ramming intoplace to form a monolithic furnace liningthat will attain satisfactory physicalproperties when subjected to the heat offurnace operation.Fire Crack; Firing Crack. A fire crack isa crack in glass-ware caused by localthermal shock: a firing crack is a crackcaused in clay-ware, or in a non-clayrefractory, by too-rapid firing.Fire Finished. Glass-ware that hasreceived its final surface gloss by heatingthe ware, usually in a flame. See FrREPOLISH.

Fire Mark. A defect, in the form of aminute indentation, that may occur invitreous enamelware if it is over-fired.Fire Pillar. One of the vertical shafts,beneath each firehole, left in a setting ofbricks in a top-fired kiln. (Also known asA CHARGE SHAFT, FEED SHAFT OR FIRESHAFT).

Fire Polished. The final surface glossapplied to glass by heating, in a flame oras the last stage in high temperatureproduction. See FIRE FINISHED.Firepower. Tradename. A small cross-section LTM tunnel kiln for tableware.(N. Barsby, Br. Ceram. Rev. (90), 1979,p l 4 . Cf. QUICKFIRE KILN).Fireproofing Tile. US term for a hollowfired-clay building block for use as aprotection for structural membersagainst fire.Fire Resistance. This term has at timesbeen used indiscriminately to denote theresistance of a material to ignition or tothe spread of flame. In the relevantBritish Standard (B.S. 476) the meaningis restricted to the performance ofcomplete elements of a buildingstructure without regard to theperformance of the materials of whichthey are composed. In USA, fire tests forbuilding construction and materials arethe subject of ASTM - E119.Firesand. An intermediate product in themanufacture of silicon carbide.Fire Shaft. See FIRE PILLAR.Firestone. A siliceous rock (80-90%SiO2) suitable for use, when trimmed, asa furnace lining material in its naturalstate. Firestone has been worked inEngland at Mexborough and Wickersley,and in Co. Durham, but is now little used.Firestream Process. Unglazed tiles arefired in a roller hearth kiln, and glazepowder is sprayed on to the glowing hottiles. The process was developed byMarazzi, Sassuolo, Italy. (UK Pat Appl.GB 2193205A, 1988).Fire Travel. The movement of the zoneof highest temperature around thegallery of an annular kiln. A typical rateof fire travel is one chamber per day,often a little faster.Fire Trough. A long trough, about 20 in.broad, on which, instead of on a grate,

solid fuel is burned in some annularkilns.Fired-on. Decoration fused into thesurface of glazed pottery or glass-ware.Firing. The process of heat treatment ofceramic ware in a kiln to develop avitreous or crystalline bond, thus givingthe ware properties associated with aceramic material.Firing Crack. See FIRE CRACK.Firing Expansion. The increase in sizethat sometimes occurs when a refractoryraw material or product is fired; it isusually expressed as a linear percentageexpansion from the dry to the fired state.Firing expansion can be caused by acrystalline conversion (e.g. of quartz intocristobalite, or of kyanite into mulliteplus cristobalite), or by BLOATING (q.v.).Cf. AFTER EXPANSION.Firing Range. See FIRING TEMPERATURE.Firing Schedule. The intendedrelationship between temperature andtime during the firing of a ceramicproduct.Firing Shrinkage. The decrease in sizethat usually occurs when ceramic ware isfired; it is usually expressed as a linearpercentage contraction from the dry tothe fired state. Firing shrinkage alwaysoccurs with shaped products containingplastic clay and often amounts to 5-6%(cf. AFTER CONTRACTION).Firing Temperature. Typical ranges offiring temperature of traditional ceramicwares are as follows:

0CAluminium enamels 430-540Wet-process cast-iron 620-760enamelsDecorating firing of pottery 700-800Sheet-iron cover-coat 730-840enamelsSheet-iron ground-coat 760-870enamelsDry-process cast-iron enamels 820-920

Building bricks 900-1100Glost firing of pottery 1050-1100Engineering bricks 1100-1150Earthenware biscuit 1100-1150Salt-glazed pipes 1100-1700China biscuit 1200-1250Fireclay refractories 1200-1400Hard porcelain 1300-1400Silica refractories 1400-1450Basic refractories 1550-1750Firsts. Pottery Ware that has beenselected as virtually free from blemishs(cf. SECONDS, LUMP).Fisher Sub-Sieve Sizer. An air-permeability apparatus for themeasurement of particle sizes between0.2 and 50 um. (Fisher Scientific Co.,USA).Fisheye. A bubble on the outer surfaceof a glaze or vitreous enamel.Fish-scaling. A fault sometimesoccurring in vitreous enamelware, smallsemicircles ('fish scales') of enamelbecoming detached - often some daysafter the ware has been fired. The sourceof this defect is always the ground-coatand the ultimate cause is release ofhydrogen followed by a build-up ofpressure; the hydrogen may originate inthe base metal, in the water used in thepreparation and application of theenamel, or in the furnace atmosphereduring the process of firing.Fittings (UK); Trimmers (USA). Specialsizes and shapes of wall and floor tiles(see Fig. 7, p350). For another meaningof Fittings see ODDMENTS.Fitz Mill. A type of fine-grinding unitused, for example, in the preparation ofthe body for sparking plugs; trade name- W. J. Fitzpatrick Co., Chicago 7, USA.Fixing Block; Fixing Brick. A buildingunit that may be made of clay, light-weight concrete or breeze, and that issufficiently soft to permit nails to bedriven in but sufficiently non-friable to

hold the nails firmly in position. Clayfixing blocks are made to have a highporosity, the pores being of controlledsize.Flabby Cast. A fault sometimesencountered in the casting of pottery-ware. The article appears satisfactory ascast but subsequently deforms, either asa result of a thixotropic effect or becausethe interior of the cast is still fluid; if thecause is thixotropy, the amount of Nasilicate and Na2CO3 used as deflocculantshould be increased; the second cause ismost common in the casting of thickware and is prevented by increasing thecasting rate.Flake enamel. Vitreous enamel frit inthe form of thin fragments.Flaking. The detachment of thin patchesof refractory from the silica lining of agas retort. It is probable that flaking isinitiated during the working period ofthe retort and that the removal of SCURF(q.v.) may be a contributory, but not theprincipal, factor.Flambe. See ROUGE FLAMB£.Flaky. See MORPHOLOGY.Flame Gunning. The application ofrefractory powder through a hightemperature burner to deposit a fusedmass onto a worn area of a refractorylining.Flame Plating. This term has beenproposed for the application of a thincoating of refractory material to asurface by the introduction of the platingpowder, oxygen and acetylene into achamber where the explosive gasmixture is detonated, the plating powderthus being melted and projected on theinner surface of the chamber and on anyobject within it. The process wasdeveloped in USA by Linde AirProducts Co., the original patent being inthe name of R. M. Poorman (US Pat. 2714 563. 2/8/55).

Flame-spraying. The process of coating asurface (of metal or of a refractory) byspraying it with particles of oxides,carbides, silicides or nitrides that havebeen made molten by passage throughan oxy-acetylene or oxy-hydrogen flame;the coating material can be fed into theflame either as a powder or as acontinuous rod. The object is to providea thin protective coating usually toprevent oxidation - as in the flame-spraying of alumina on to steel. ASTMC63 specifies a test for the 'Adhesionand Cohesive Strength of Flame-SprayedCoatings'.FIameless Combustion. Term sometimesused for SURFACE COMBUSTION (q.v.).Flanged Finish. See FINISH.Flare Bed. The refractory-lined duct thatconveys gas from the producers to thecombustion chambers in a setting ofhorizontal gas retorts.Flaring Cup. An abrasive wheel shapedlike a cup but with a larger diameter atthe outer (open) edge than at the bottomof the cup, the bottom being the diskthat fits on the spindle.Flash Calcination. Cold powdered clay ispassed through a gas or oil flame, thenquenched with cold air. Steam isgenerated within the clay particles fasterthan it can escape by diffusion, and theparticle structure is disrupted. Flashcalcined kaolin is of lower density thannormally calcined kaolin, and does notcontain mullite or cristobalite.Flash, Flashing. (1) The formation, bysurface fusion or vitrification, of a film ofdifferent texture and/or colour on clayproducts or on glass-ware. In the firingof clay products flashing may occurunintentionally; it is then a defectbecause of its uncontrolled nature.Bricks that are intentionally flashedmake possible pleasing architecturaleffects. Flashed glass-ware is made by

fusing a thin film of a different glass(usually opaque or coloured) on thesurface of the ware.(2) In structural brickwork, a sheet ofimpervious material secured over a jointthrough which water might otherwisepenetrate.(3) A fault in glass-ware (see FIN).(4) The fin of excess body formed duringthe plastic-pressing of ceramic ware, e.g.electrical porcelain; it is removed by anauxiliary process.(5) Alternative name for CASTING SPOT(q.v.).Flash Method. See THERMALDIFFUSIVITY.Flashing. See FLASH.Flashover. A discharge of electricityacross the surface of an insulator.Damage may result.Flash Reaction Hot Pressing. Material ispressed in a mould which has beenpreheated to a temperature above that atwhich the material decomposes. Themore rapid temperature rise (comparedto reaction hot pressing) producesalmost simultaneous decompositions inmixtures of materials with differingdecomposition temperatures. Theprocess has been used to produce rareearth silicate glasses, ferrites and othermixed ceramics. (D.B. Black /. Canad.Ceram. Soc. 45, 47, 1976).Flash Set. Premature and permanentstiffening of portland cement that has notbeen adequately retarded; cf. FALSE SET.Flash Wall. A continuous wall ofrefractory brickwork built inside adowndraught kiln in front of thefireboxes; its purpose is to direct the hotgases towards the roof of the kiln and toprevent the flames from impingingdirectly on the setting.Flask. Local term for the mould, made ofwood or cast iron, used in the shaping ofcrucibles for steel melting.

Flat Arch. See JACK ARCH.Flat Drawn. Sheet glass made by thevertical drawing process.Flat glass. One of the major divisions ofthe glass industry - windows, automobileglass, and other forms of sheet and plateglass. The structural performance ofglass sheets can be assessed destructively(ASTM E997, an air pressure test) ornon-destructively (ASTM E998,observation of deflections and strainsunder a standard pressure).Flatter. See STONER.Flatting. A process for trueing-up hand-made fireclay refractories while they arestill only partially dried. Handmaking isnow little used except for some specialshapes.Flat-ware. Plates, saucers, dishes, etc. (cf.HOLLO w-w ARE) .FIaunching. The weathering, formed inmortar, at the top of a chimney or at thebase of a chimney pot.Flemish Bond. A brick wall built withalternate headers and stretchers in eachcourse. Single Flemish Bond is sobonded on one face of the wall only;Double Flemish Bond is bonded in thisway on both faces of the wall.Fletton. An English building brickoriginally made at Fletton, now a suburbof Peterborough; centres of Flettonbrickmaking also include Bedford andBletchley. The bricks are made by thesemi-dry process from Oxford Clay; thisclay is shaly and contains much organicmatter, which assists in the firing process.The crushing strength varies from about14 to 35 MNm~2 and the waterabsorption from about 17 to 25 wt%.Flexmesh. A type of HEXMESH,constructed to be flexible on one axis,rigid on the other.Flexmould. Tradename. Flexiblepolyvinyl chloride or room temperaturevulcanizing silicone rubber is used for

the block mould. The flexibility of thematerial allows sharp undercuts to bedesigned into the mould. (FlexmouldInc. USA).Flexural Strength. See MODULUS OFRUPTURE.Flint. Nodular chalcedonic silica fromthe chalk deposits of W Europe andelsewhere. These flint pebbles arecalcined and ground for use inearthenware and tile bodies. In USA theterm 'flint' is often applied to otherfinely ground high-silica rocks used inwhiteware manufacture. See alsoCALCINED FLINT.Flint Clay. A non-plastic refractory clayof a type found in Missouri (USA),Southern France, and a few otherlocalities. Flint clays are kaolinitic, butlaterization (See LATERITE) hasoccurred so that the Missouri deposit,for example, may also contain diasporewhereas the French may containboehmite. Flint clays contain (fired) 40-45% Al2O3; P.C.E. 34-35.Flint Glass. 'White Flint' is a termapplied to many colourless glasses;'Optical Flint' is any glass of highdispersion for optical equipment (cf.OPTICAL CROWN). The introduction oflead oxide into the batch to produce theoriginal flint glass, in the 17th centurywas an English contribution to glass-making; silica was introduced into thebatch in the form of crushed flints.Flintlime Brick, CALCIUM SILICATEBRICKS (q.v.) in which part or all of theaggregate is crushed flint.Flint Shot. US term for the sharp sandsometimes used in sandblasting the basemetal as part of the preparation processfor vitreous enamelling.Flintless Stoneware. Defined in the UKPottery (Health and Welfare) SpecialRegulations of 1950 as: Stoneware thebody of which consists of natural clay to

which no flint or quartz or other form offree silica has been added.Flip-flop. A glass decanter with a thinbase.Float Glass Process. A process formaking sheet glass introduced in 1959 byPilkington Bros. Ltd, at St. Helen's,England. A ribbon of glass is floated onmolten tin, the product being sheet glasswith truly parallel surfaces, both fire-polished. The process is limited to soda-lime-silica glasses but can produce50000m2 (500-800 ton) of glass per day.It was improved in 1975 by the PPGdelivery system. The stream of moltenglass is of the required production width(c. 4m) from the melting furnace. Thisreduces optical distortion in the finishedglass arising from flow problems whenthe glass stream passed from meltingfurnace to the molten tin through arestricted opening.Floater. A refractory shape that isallowed to float on the surface of moltenglass in a tank furnace in order to holdback any scum that may be present (cf.RING).

Floating. (1) Slight displacement of apattern applied to potteryware; it iscaused by the presence of grease ormoisture on the glaze at the time whenthe decoration was applied.(2) The smoothing of freshly-placedconcrete to give a good surface finish.Floating Agent. In the vitreous-enamelindustry, the US equivalent of theEnglish term SUSPENDING AGENT (q.v.).Floating-die Press. The punches, die setand core rods can be controlled to moveduring the press cycle. Such multiplesynchronised movements can producecomplex shapes, and minimize densitygradients in the pressed parts. Both areof value in producing technical ceramics.Flo-con. Tradename. A SLIDING-GATEVALVE originally developed by United

States Steel Corp. (U.S. Pat 3685707,1972) (Now Flo-Con Corp. USA;Flogates, Sheffield).Floe Test or Water Test. A test for thedurability of hydraulic cement: Ig of thecement is shaken with 100 ml of water ina test-tube which is then placed on itsside and allowed to stand for 7 days; ifthe amount of floe formed is very smallthe cement is considered to be durable.The test was proposed by I. Paul (Proc.Assoc. Highway Officials, N. AtlanticStates, 12, 140, 1936).FIocculation. The addition of a suitableelectrolyte to a colloidal suspension toagglomerate the particles and so hastentheir settling; the sediment thus formedis usually more readily removed from thecontaining vessel than is the sedimentfrom a deflocculated suspension. Anexample is the addition of up to 0.05%CaCl2 to flocculate slop glaze.Floe Rock. US term for quartzite thatoccurs as loose boulders, e.g.TUSCARORA QUARTZITE (q.V.).Flood Casting. Term used in the Britishsanitary-ware industry for the process ofslip casting in which excess slip isremoved from the mould by draining. Inother sections of the pottery industry theprocess is referred to merely as 'casting';in USA the process is known as 'DrainCasting'.Floor Brick. A brick having mechanical,thermal, and chemical resistance to theconditions to which it is likely to beexposed when used in an industrial floor.Properties are specified in ASTM-C410:'Industrial Floor Brick'.Floor Quarry. (UK) or Quarry Tile(USA). A heavy ceramic flooringmaterial. Floor quarries (as distinct fromFLOOR TILES q.v.) are usually made by aplastic process. They are relatively thickand are hard fired to produce a bodyresistant to heavy abrasion and to attack

by most industrial liquids - hence theirwide use for factory floors. For sizes,tolerances and trueness of shape, seeB.S. 1286.Floor Tile. (1) Ceramic tiles, normallyunglazed, for flooring. It is difficult todraw a sharp distinction between floortiles and FLOOR QUARRIES (q.v.) but theformer are always dry-pressed, and theyare relatively thin and do not normallyexceed 152x152 mm in size. For standardsizes see B.S. 6431. Concrete floor tilesand fittings are specified in BS 1197.(2) One of the refractory shapes used inthe construction of a gas retort; a groupof these tiles is laid horizontally to bracethe retorts of a vertical setting and tolimit the combustion flues.(3) In the USA the term is used for ahollow fired-clay block for use in theconstruction of floors and roofs; twogrades, FTl and FT2, are specified inASTM - C57.Floridin. An older name forATTAPULGITE (q.v.); now a tradenameof the Floridin Co., New York, USA.Flotation. A process for theconcentration of a mineral by crushingthe rock in which it is dispersed,suspending the crushed material in waterand causing a froth to form one of theconstituents of the mineral adhering tothe air bubbles so that it can be floatedoff, leaving the remainder to settle out.Three types of reagent are required:frothers, collectors, and controllers.Flotation has been applied industrially tothe preparation of the following ceramicraw materials; feldspar, talc, magnesite,kyanite, glass-sands, lithium ores.Flow Blue. A deep cobalt blue whichwas used for under-glaze printing onpottery. As the name indicates, thecolour tended to flow into the glaze,giving a blurred effect; this result wasobtained by placing FLOW POWDER

(q.v.) in the saggar containing the ware.Chlorine evolved from the powder andcombined with some of the cobalt, thusrendering it slightly soluble in the glaze.Flow-button Test. See FUSION-FLOWTEST.Flow Coating.The application of vitreousenamel slip by allowing it to flow overthe metal and then to drain.Flow Cup. An orifice-type VISCOMETER,of which there are several patterns:FORD, REDWOOD, SAYBOLT, ZAHN.Their method of use is specified in BSEN 535, which superseded BS 3900 andthe earlier BS 1753. Not all the earlytypes are now specified.Flow Line. Streaks of differentreflectance from the surrounding area,arising in glass and in injection mouldedparts, from the flow pattern of materialduring forming the part; see CHILLMARK; WELD MARK.Flow Machine. A machine used in glass-making; molten glass flows into it from afeeder under the action of gravity.Flow Powder. A mixture formulated toevolve chlorine at the temperature of theglost firing of pottery and used in theproduction of FLOW BLUE (q.v.). Forware covered with a lead glaze, asuitable composition is (per cent): NaCl,22, white lead, 40; CaCO3, 30; borax, 8.For use with a leadless glaze a suitablemixture is (per cent): NaCl, 15; MgCl2,55; KNO3,15; CaCO3,15.Flow Process. A method of producingflat glass by allowing molten glass toflow continuously from a tank furnacebetween rollers. The term is sometimesalso applied to a process for makinghollow-ware, but this is more correctlyreferred to as the GOB PROCESS;(q.v.).Flow Table Test. A test for theconsistency of concrete in terms of itstendency to spread when placed on a

metal table and jolted under specifiedconditions. (ASTM C124). The test isalso applicable to refractory concretes(ASTM C860) and to tests on hydrauliccement for mortars (ASTM C230). BS1902 Pt 11 describes its use for refractorymortars, BS 4551 its use for testingbricklaying mortars, wherein the flowtable is described.Flowers. See MOTTLING (of silicarefractories).Flue Liner. A fireclay shape for use inthe flues and chimneys of domesticheating appliances; BS 6461 is a code ofpractice for the design and installation ofdomestic masonry chimneys and flues.See also CHIMNEY LININGS.ASTM C315 is the US standard, andASTM E835 gives metric sizes related toa 100-mm module.Fluid-energy Mill. A size-reduction unitdepending for its action on collisionsbetween the particles being ground, theenergy being supplied by a compressedfluid (e.g. air or steam) that enters thegrinding chamber at high speed. Such millswill give a product of 5|um or less; theyhave been used for the fine grinding offrits, kaolin, zircon, titania, and calcinedalumina, but the energy consumed per tonof milled product is high.Fluidity of liquids, see VISCOSITY; ofpowders, see MOHR-COULOMB FAILURELAW.

Fluidized Bed. A bed of solid particlesmaintained in suspension in a gas, andthus behaving rather like a fluid; thepowder to be fluidized is supported on aporous base, e.g. a trough of specialporous ceramic material, through whichthe gas (usually air) is fed from belowand under pressure. The principle is usedas a method of conveying powders alonga slightly inclined porous ceramic trough;the powder can be simultaneously driedand/or calcined.

Flume. Local term for the alkali vapourvolatilized from the glass in a glass-tankfurnace; it causes corrosion of thefurnace roof, downtakes, andregenerator refractories. (A corruptionof 'Fume'.)Fluorapatite. The fluorine-containingmodification of APATITE (q.v.)Fluorspar. CaF2; m.p. 14200C; sp. gr. 3.1.The largest deposits of this mineral arein Mexico, China, USA and USSR, but itis also worked in England and mostother European countries. It is used asan opacifier in glass and vitreous enamel.Fluorspar crucibles have been used inthe melting of uranium for nuclearengineering.Flux. A substance that, even in smallquantities, lowers the fusion point ofmaterial in which it is naturally present(e.g. alkalis in clays) or of material towhich it has been added (e.g. boraxadded to glazes). The term is also usedfor the prepared low-melting glasses thatare added to ceramic colours to fusethem to the ware on which they arebeing used as decoration.Flux Factor. A factor for assessing thequality of steelworks grade silicarefractories. It is defined in ASTM-C416as the percentage of Al2O3 in the brickplus twice the total percentage of alkalis;for first-quality (Type A) bricks the fluxfactor must not exceed 0.50.Flux Line. The level of the molten glassin a tank furnace; this level is generallymarked by a horizontal line of maximumattack on the refractories. The term isalso sometimes applied to the boundarybetween unmelted batch and moltenglass in a tank furnace.Flux-line Block. A refractory block foruse in the upper course of the walls of aglass-tank furnace. The flux line is thesurface level of the molten glass andattack on the refractories is more severe

at this level than beneath the moltenglass.Fly-ash. The ash carried by the wastegases in a furnace or kiln (cf.PULVERIZED FUEL ASH).Flying Arch. In a modern glass-tankfurnace the double-walled bridge builtacross the furnace to separate the workingend from the melting and refining end; theflying arch is independent of the generalfurnace structure.Flying Bond. See MONK BOND.Foam Glass. Cellular glass, in the formof blocks, usually made by mixingpowdered glass with a gasifying agent(e.g. carbon or a carbon compound) themixture then being heated for a shorttime to fuse the glass and trap theevolving gas bubbles. Foam glass is usedas a structural heat-insulating material(cf. BUBBLE GLASS).Foamed Ceramic. Highly porousceramics made by generating a foam ofbubbles in a ceramic slip, using achemical agent, then drying and firing.Foams differ from honeycomb in havinga random varied pore-size distribution,rather than regular uniform holes.Foamed Clay. Lightweight cellularclayware for heat and sound insulation.Foam is generated in a clay slip, eithermechanically or by a chemical reactionthat evolves gas bubbles, and the slip isthen caused to set. Some insulatingrefractories are made by this process.Foamed Concrete. See AERATED

CONCRETE.Fold. See LAP.Folded Foot. The foot of a wine glass issaid to be folded if the outer edge hasbeen raised by folding it back on itself.Font. (1) An alternative term for a VOID.(2). A reservoir above the mould forfusion-casting refractories; moltenmaterial from the font helps to fill thePIPE (q.v.).

Foot-boards. Wooden boards, hingedtogether, for hand-shaping the foot ofglass stern-ware.Ford Cup. An orifice-type viscometer. Ithas been used to a limited extent in thetesting of the flow properties of ceramicsuspensions. The aperture sizes, lengthof orifice and method of use were givenin B.S. 1733 and ASTM-D333. Thisviscometer was introduced by the FordMotor Co., England, in 1925.Forehearth. (1) An extension to thebottom of a CUPOLA (q.v.) serving as areservoir for molten iron.(2) An extension of a glass-tank furnacefrom which glass is taken for forming.Fork. A metal device for placing vitreousenamelware in, and subsequentlyremoving it from, a box furnace.Forking. The separation of a propagatingfracture into two or more new fracturesat acute angles. See CRACK BRANCHING.Forshammer Feldspar. A Swedishfeldspar used as a flux in tablewarebodies, to replace DF Stone, comparedto which it was higher in alkalis andlower in silica.Forsterite. Magnesium orthosilicate,2MgO. SiO2: sp. gr. 3.2; m.p. 18900C;thermal expansion (0-12000C) 12.2 x10-6 In economic amounts forsteriteoccurs naturally only in association withFAYALiTE (q.v.) in the mineral OLIVINE(q.v.). Forsterite refractories are madefrom olivine or SERPENTINE (q.v ), dead-burned magnesite being added to thebatch to combine with the fayalite andproduce the more refractory mineralMAGNESIOFERRITE (q.v.). Pure syntheticforsterite is used as a low-loss dielectricceramic; it is particularly suitable (onaccount of its relatively high thermalexpansion) for making vacuum-tightseals with metallic Ti.Fotalite. Tradename of Corning Glassfor a PHOTOSENSITIVE GLASS (q.v.)

Fotoform Process. Tradename. Animage is nucleated and crystallizedwithin a lithium silicate glass, doped withan appropriate sensitizer. The patterncan then be preferentially etched awayto produce holes, patterns, and internalchannels, with an accuracy of a fewmicrons.Founder. See TEASER.Founding (of glass). See REFINING.Fourcault Process. A method of makingsheet glass invented in 1902 by E.Fourcault of Lodelinsard (Belgium). Theglass is drawn vertically and continuouslyfrom the glass-tank through aDEBITEUSE (q.V.).Four-colour Printing. SeeTRICHROMATIC PRINTING.Fourier Transform Specroscopy. Twobeams of radiation are used to producean interference pattern, and thespectrum is produced by taking itsFourier transform - a mathematicaltechnique for building up a complexpattern as the sum of a set of waves ofdifferent harmonic wavelengths.Fractal. 'A shape made of parts similarto the whole in some way' (B.B.Mandelbrot 'The Fractal Geometry ofNature' W.H. Freeman, San Francisco,1982).More mathematically strictly, a fractal isa set such that two standard definitionsof a dimension give different answers.For example, a 1-dimensional curve suchas a coastline may have one lengthaccording to one definition, but mayhave arbitrarily small irregularities givingrise to a different, larger length byanother definition. This is a fractal curve.The fractal dimension DF is defined byDF = [(log L0 - log L )/log S] + D whereL0 is a constant, L is a measured length,S is the scale of measurement and D isthe number of dimensions (1 for a line, 2for a plane). Fractal curves of surfaces

are self-similar, in the sense that amagnification of their small-scalefeatures looks like their larger scalefeatures. Fractal geometry can be usedto study particle morphology, or aid infracture mechanics through the study offracture surfaces, which have beenshown experimentally to be fractalsurfaces. Their fractal dimensions arerelated to the FRACTURE TOUGHNESS(q.v.) of the materials. For example, thearea of the FRACTURE SURFACE (q.v.),which is one determinant of the energyrequired to produce FRACTURE (q.v.) isscale-dependent. If L and L0 are theirregular and straight path lengths of thecrack respectively, the real area of thefracture surface is L/Lo times the areaused if fractal effects are omitted. By theequation defining fractal dimension DF,L/Lo = S1-0F and values for (e.g.) criticalcrack extension forces and energiesrequired to produce fracture should becorrespondingly increased by amountsdeducible from the fractal geometry.Fractional Porosity. See POROSITY.Fractography. The study of the featuresof the fracture surfaces of brittlematerials, to elucidate the causes of thecracks. ASTM C 162-92 and ASTM STP827 define many terms.Fracture. Cracking. The physicalseparation of parts of a solid subjected tomechanical stress. When a crackdevelops (see CRACK NUCLEATION) twonew surfaces are formed. The energy tobreak the interatomic bonds to do this issupplied by the external stress. It isequal to twice the product of the surfaceenergy of the solid and the area of thenew fracture surface. Mechanisms whichabsorb this energy restrain cracking (seeTOUGHNESS), CRACK PROPAGATION(q.v.) is controlled by conditions at thecrack tip: macroscopically, by the stressdistribution which is concentrated at the

crack tip; also by the microstructure and,on the atomic scale, by the CRYSTALSTRUCTURE (q.v.) See alsoFRACTOGRAPHY; SLOW CRACKGROWTH; FRACTALSFracture Mechanics. The study of theways in which crack geometry, materialstrength and TOUGHNESS (q.v.) andstress patterns affect the FRACTURE(q.v.) of materials. The objective is todetermine the critical size of crack ordefect which will cause the crack topropagate rapidly and cause catastrophicfailure. See also FRACTALS; WEIBULLDISTRIBUTION; BATDORF THEORY;GRIFFITH OROWAN CRITERIA; SHETTY'SCRITERION; R-CURVE.Fracture Mirror. A very smooth,reflective fracture surface indicating thatthe fracture was moving relatively slowlyalong a single spreading front.Fracture Modes. Mode I - the openingmode - the stress is perpendicular to thecrack plane.Mode II - the sliding mode - shear stressbetween the crack faces in the directionof crack propagation.Mode III - the tearing mode - shearstress between the crack faces acting in adirection parallel to the crack front.See also SHETTY'S MIXED MODE

EQUATION.

Fracture Surface. The newly-formedsurface within a solid formed bycracking. See also FRACTOGRAPHY.Fracture Toughness. A measure of theease of crack propagation through amaterial. The units are MPa.m0 5.Values for ceramics range from below 1for glasses and most single crystals ; 1 to3 for glass-ceramics, clay-based ceramicsand MgO; 2.5. to 4 for early engineeringceramics (alumina, boron carbide, siliconcarbides, RBSN); 4 to 6 for hot-pressedsilicon nitride and SRBSN and fortransformation-toughened alumina

composites; 6 to 12 for sialons, PSZ,TZP and low binder content hardmetals; over 15 for Ceria-stabilized TZP,fibre-reinforced engineering ceramicsand high binder content hardmetals. SeeFRACTURE TOUGHNESS.Fracture Toughness Tests. There arenumerous techniques but no standardspecimen. The choice is set by the typeof information required; the nature ofthe material; the test geometrycompared to the component geometry;the fracture energy around large or smallflaws; the test temperature; serviceenvironment. See FRACTURE; STRESSCORROSION; J-BASED FRACTURE

TESTING.Most tests involve the preparation oftest-pieces of more or less complexgeometry, containing cuts or notches ofprescribed size and shape. Some requirethe careful introduction of a sharpstarter crack tip in the appropriatelocation - a matter of some delicacy.Cyclic compression can produce acontrolled fatigue flow through thespecimen thickness. The specimen canthen be tested in flexure by the single-edge notched beam technique. Directmeasurements on the FRACTURESURFACE (q.v.) and other techniques ofFRACTOGRAPHY (q.v.) can yieldinformation on fracture toughness.Pertinent features of specificallydesigned tests are as follows.The Compact Tension (CT) test appliesa separating force to the blind end of asawn notch by tensile forces applied tobolts in holes either side of the notch. Ashort, stable crack is first establishedwith minimum possible force, then theincreased crack lengths due to repeatedapplications of the force are measured.The test is simple, and applicable to non-porous materials at ambient temperaturefor slow rates of loading.

The Constant Moment (CM) test openup a V-shaped notch in the specimen byforces parallel to the long axis of the Von moment arms to either side. Thetechnique is applicable to porousmaterials at ambient temperature withslow loading rates, and can measurecritical fracture toughness as a functionof crack growth rate.In the Double Torsion (DT) test upwardforces are applied on either side of aprepared notch, with a pair of downwardforces at a greater distance on eitherside. The test is a common one, with K1

independent of the crack length. Theloading arrangements are simple but alarge volume of material is required, andthe crack front is curved, with non-uniform stress intensity. The test isuseful for slow crack growth studies onboth porous and non-porous materials. Itcan be used at high temperature insevere environments and will give KIC asa function of crack growth rate.The indentation fracture (IF) test issimple and requires only small volumesof material. Cracks develop around aVickers indentation in a flat ceramicsurface in proportion to its fracturetoughness. KIC can be estimated fromcrack lengths. The ratio of force to cracklength is independent of load andmaterial hardness, and so is a usefulparameter. The test is suitable for densematerials (97% theoretical) at ambienttemperature.The indentation strength (IS) methodinduces Vickers indentations into flexurestrength bars with smooth surfaces. Thecritical stress intensity at fracture ismeasured, and KIC calculated. It is notnecessary to measure crack lengths, butresults are dependent on the indenterload.In the Chevron Notched Bar (CNB) test,a chevron or M-shaped notch is sawn in

a short bar or rod and forces appliedeither side as in the CM test. The test isapplicable at high temperature, requiresno knowledge of material properties, butcalculates KIC from the load andspecimen geometry. Specimenpreparation is complex, requireingcareful machining of the sawn 'M' notch.In the Double Cantilever Beam (DCB)test, tensile forces are applied at rightangles to a sawn notch cut parallel to thelong axis of a bar. KIC is derived fromthe load and the geometry. K1 isindependent of crack length for constantmoment loading. The test procedure andthe sample preparation are simple, butthe specimen must be very carefully pre-cracked to produce a sharp crack tipfrom the blunt sawn notch. The test isapplicable to non-porous materials atambient temperature, and can give KIC

as a function of crack growth rate. Slowloading rates are used.The Tapered Cantilever Beam (TCB)test is a variant of the DCB requiring amore complex, wedge-shaped specimenwith notches running the length of bothtapered faces of the wedge. The test isapplicable to porous materials at slowloading rates at ambient temperature,and will give KIC as a function of crackgrowth rate.The Single Edge Notched Beam (SENB)test can be used for rapid rates ofloading. It is simple. A narrow notch cutacross the width of a long specimen iseasier to make and measure than a sharpcrack. The test is performed in 4-pointbend, with the inner pair of forcesapplied to the opposite face to thenotched one. It is applicable to non-porous materials at both ambient or hightemperature. The results are sensitive tonotch size, and they are improved byprecracking the specimen at the end ofthe notch.

The Single Edge Precracked Beam(SEPB) test is thus a refinement of theSENB, to introduce a precrack. Thespecimen is held in a loading fixturewhich generates a Vickers indentation ora single notch at the centre of the tensilesurface of the specimen, which is thenloaded in 4-point bend to failure, as inthe SENB. The specimen must be madewith accurately parallel faces andsquared corners.ASTM C1212 describes how to makereference specimens from SiC and Si3N4,containing known discontinuities orseeded voids, by making surfacedepressions with small spheres in pre-pressed compacts and then isostaticalypressing them.Framework Silicates. See SILICATE

STRUCTURES.

Franchet Lustre. A LUSTRE (q.v.) for thedecoration of pottery. Metal salts areincorporated with the glaze and the wareis then fired reducing at 550-6000C. (L.Franchet, La Fabrication Industrielle desEmaux et Couleurs Ceramiques, Paris,1911.)FRCI. Fibrous Refractory ConcreteInsulator. A lightweight refractoryconcrete incorporating ceramic fibres toact as a thermal insulator.Free-blown. Alternative term for OFF-HAND (q.v )

Free Silica. The amount of silica presentin a ceramic body or raw materials mix,as SiO2 uncombined with any otherelement. Free silica may present arespirable dust hazard, and may give riseto thermal expansion changes in a bodyat the temperatures at which silica issubject to phase changes.Free Crushing. The method of running apair of crushing rolls so that virtually allthe crushing occurs as the particles passbetween the rolls, only a smallproportion of the particles being crushed

by bearing on one another. Whencrushing rolls are operated in this way,the product contains less fines than withCHOKE CRUSHING (q.V.).Freehand Grinding or Off-handGrinding. The method of grinding inwhich the object to be ground is held byhand against an abrasive wheel.Freeze-casting. A process for makingintricate shapes of special ceramicmaterial, e.g. turbo-supercharger blades.Refractory powder, with a smallproportion of binder, is made into a thickslip, which is cast into a mould and thenfrozen; the cast is then dried and sintered.Freeze-Drying. A method for preparingfine powders. A liquid solution of asoluble precursor salt is sprayed into acryogenic medium. The resulting finedispersion can be calcined or reacted toproduce the required product, afterheating to drive off the frozen solvent.French Chalk. See STEATITE.Frenkel Defect. See CRYSTAL

STRUCTUREFrenkel Mixer. A screw-type, 'enforcedorder', mixer depending on interlayerdisplacement of the material betweenmachined screw surfaces; it operates onthe convergence divergence (C-D)principle. (M. S. Frenkel, Brit. Pat. 888864, 7/2/62).Fresnel Formulae. A beam of lightstriking a glass surface is partly reflected.If / and r are the angles of incidence andrefraction respectively, for an incidentbeam of unit amplitude polarized in theplace of incidence, the reflected waveamplitude B is given by -B = tan (i-r)lsin(i+r) for an incident beam polarized atright angles to the place of incidence, thereflected wave amplitude b is given by-b = sin(/-r)/sin (i+r). (and if A and a arethe respective amplitudes of the refractedwaves, A2 + B2 = 1 and a2 + b2 = 1 by theLaw of Conservation of Energy).

Freudenbergite. Na2Al2Ti6O16. ASYNROC (q.v.) phase, for immobilizingsodium.Frey Automatic Cutter. Trade name: amachine for cutting an extruding columnof clay into bricks by one or morehorizontal wires that cut downwardswhile the clay is moving forward. (G.Willy A.G., Chur, Switzerland.)Friability. The tendancy for particles of apowder to break down in size under lightforces during handling and storage.Friction Element. Some clutches andbrakes for use in severe conditions arenow lined with CERMETS (q.v.) Amongstthe materials used are corundum andsillimanite as the ceramic component,and Mo, Cr, Fe, and Cu alloys as themetallic bond.Friction Press or Friction-screw Press. Amachine for dry-pressing: a plunger isforced into the mould by a verticalscrew, the screw shaft being driven byfriction disks or rollers - downwards forpressing by one disk and upwards forrelease of pressure by a second disk onthe opposite side of the driving wheel.This type of press is used for specialshapes of tiles and sometimes for makingsilica refractories, etc.Friction Welding. A method of joiningceramics in which the components areheated by rubbing together at highspeed.Frictive Track. A series of crescent-shaped cracks, lying along a commonaxis parallel to the direction of rubbingcontact.Frigger. A small whimsically shapedpiece of hand-blown glass ware - a glass-blower's bagatelle.Fringe. A thin layer of material on oneface of a brick, projecting beyond theedge.Frischer Ring. A type of TOWERPACKING.

Frit. A ceramic composition that hasbeen fused, quenched to form a glass,and granulated. Frits form an importantpart of the batches used in compoundingenamels and glazes; the purpose of thispre-fusion is to render any soluble and/or toxic components insoluble by causingthem to combine with silica and otheradded oxides.Frisket. A stencil (usually paper) whichdefines the area of pottery to be glazed,or decorated. (USA).Fritted Glass. See SINTERED GLASS.Fritted Glaze. A glaze in which some ofthe constituents have been previouslyfused together to form a frit, theconstituents so pretreated include leadoxide, which fritting converts into aninsoluble silicate, and other constituentsthat would otherwise be soluble.Fritted Porcelain. Alternative name forSOFT-PASTE (q.V.).Fritting Zone. See SOAKING AREA.Frizzling. A fault liable to developduring the firing of potteryware that hasbeen decorated with lithographictransfers - if the varnishes are burnedaway too rapidly in the early stages ofthe enamel fire, the colour is liable tocrack and curl up. To prevent this fault,the layer of size should be thin and therate of firing between 200° and 4000Cshould not greatly exceed l°C/min.Frog. A depression in the bedding face ofsome pressed building bricks to decreasethe weight and improve the keying-in ofthe mortar. The term is probably derivedfrom the same word as applied to thesimilar depression in the centre of ahorse's hoof. BS 3921 specifies that thevolume of the frog(s) shall not exceed20% of the volume of the brick.Frost Glass. Glass whose surface hasbeen treated chemically, sandblastedlightly, or decorated with very thincrushed glass like tinsel, (frost) to scatter

light and produce decorative andobscurative effects.Frost's Cement. An early form ofhydraulic cement patented in England in1811 by James Frost; it was made fromtwo parts chalk to one part clay.Frosting. See ACID FROSTING.Frost Resistance. Porous buildingmaterials may be damaged by thepressures generated by the freezing ofmoisture which has penetrated the pores.Frequent freeze-thaw cycles are morelikely to cause damage than prolonged lowtemperatures. Waterproofing treatmentswhich seal most of the pores but leavesome route for the ingress of moisture canworsen the damage. Frost resistance testsare based on (i) indirect appraisal fromproperties such as strength and/or porosity;(ii) long-term exposure tests or experience;(iii) accelerated simulation. BS 3921,1974was based on (i) and (ii); ASTM C62-75on (i) and (iii). Accelerated tests may beomni-directional, in which all faces of thebricks or tiles are exposed to the freeze-thaw conditions. Only a simple freezingcabinet is then required. In uni-directiontests, only one face is exposed to the lowtemperature, a more realistic simulation ofservice conditions. The BCRA PanelFreezing Test subjects a panel of tencourses of three bricks soaked for 7 days,to a 100-cycle freeze-thaw regime, eachcycle comprising 132 min freezing at-15°C, followed by 20 mins thawing byradiant heaters at 25°C, with 5 min water-spray and drain treatment to replaceevaporated water. BS 3921 classifies bricksinto 3 categories of frost resistance. BS6431 specifies a cyclic freeze-thaw test fortiles.

Froth Flotation. See FLOTATION.FSCS. Fibre Sandwich ConstructionSystems. In the construction of a LOWTHERMAL MASS KILN (q.v.) ceramic fibreis sandwiched between a thin refractory

hot-face tile and the kiln casing. The tilesare held in place by a pin which rotates90° to lock into a stainless steel socketwelded to the casing. (Shelley Furnaces,UK)FSZ. Fully stabilized ZIRCONIA.FTIR. Fourier Transform Infra-Red(spectroscopy)Fuch's Gold Purple. A tin-gold colour,produced by a wet method; it has beenused in the decoration of porcelain.Fugitive Wax Slip-casting. A process forshaping complex ceramic components. Apositive model of the component ismachined from a water insoluble/organicsoluble wax. The positive model isrepeatedly dipped into liquid wax, andthen dissolved out. The wax mould isplaced on a plaster mould which draws thewater from the slip, forming aunidirectional casting. The wax mould isdissolved in an appropriate organic solventwhen the ceramic cast has solidified. (FordMotor Co, U.S. Pat 4067943 1978).Full Lead Crystal Glass. A CRYSTALGLASS (q.v.) specified in B.S. 3828 ascontaining >30% PbO and >12% alkali;Cf. LEAD CRYSTAL GLASS.Fullerenes, Fullerides. Molecularstructures of atoms arranged on thesurface of a sphere or a cylinder, inhexagonal and pentagonal arrays, inconfigurations similar to R. BuckminsterFuller's geodesic domes. Nanometer-sized tubes are being developed basedon cylindrical Fullerenes. 28 to 540carbon atoms in such a sphericalarrangement form the most symmetricpossible molecules - BuckminsterFullerene or 'Buckyballs'.Fuller's Earth. A type of clay formerlyused in the cleansing of cloth. The clayminerals present are of the montmoril-lonite and/or beidellite types. It is usedfor decolorizing oils and has also beenused as a bond for foundry sands.

Fuller's Grading Curve. A method ofgraphical representation of particle-sizeanalysis: the grain size (in fractions of aninch) is shown on the abscissa and thecumulative percentage on the ordinate.In the original paper (W. B. Fuller andS. E. Thompson, Trans. Amer. Soc. CivilEngrs, 59, 67,1907) the concept of 'ideal'grading curves was introduced, thesebeing selected to be ellipses with straightlines tangential to them; more strictly,the 'ideal' curves are parabolas havingthe form d = P2D/10 000, where d is anyselected particle diameter, D is thediameter of the largest particles and P isthe percentage finer than d.Fumed Silica. A pure colloidal form ofsilica produced by reacting silicontetrachloride in a flame. Particle size issome 12nm, and BET surface area 230m2/g.(Tradenames include Cab-O-Sil M5and Degussa OX-50).Functionally Gradient Materials.Composites with graded properties. SeeGRADED CERMETS.Furring Brick. An American term for ahollow brick with surface grooves toretain plaster.Furring Tile. US term for a hollow fired-clay building block for lining the insideof walls and carrying no superimposedload.Fused Grain Refractory. Refractoriesmade from raw material which has beenmelted, destroying its natural crystalstructure; solidified; crushed to anappropriate particle size and sintered.Fused Quartz. This term is often appliedto Transparent Vitreous Silica (See underVITREOUS SILICA) that has beenobtained by the fusion of quartz crystalelectrically or in a flame.Fused Silica. In the UK this term has, inthe past, often been applied toTranslucent Vitreous Silica; this hascaused confusion because the same term

has frequently been used in the literature(especially in USA) when referring tothe transparent variety. For preferredterms see VITREOUS SILICA.Fusion-cast Basalt. An abrasion-resistantmaterial made by fusing natural basaltand casting the molten material intomoulds to form blocks. The hardness is8-9 Mohs; crushing strength, 500MNm-2. These blocks can be used forindustrial flooring and for the lining ofbunkers, chutes, and other equipmentwhere abrasion is severe.Fusion Casting, A process for themanufacture of refractory blocks andshapes of low porosity and a high degreeof crystallinity; the refractory batch iselectrically fused and, while molten is castinto a mould and carefully cooled. Theusual types of fusion-cast refractory arethose consisting of mullite, corundum,and zirconia in various proportions; suchrefractories find considerable use as tankblocks for glass-melting furnaces. Trialshave been made with fusion-castrefractories in steel furnaces.Fusion-flow Test. A method for theevaluation of the fusion flow propertiesof a vitreous enamel or of a glaze. Asused for testing enamel frits, the methodis standardized in ASTM - C374.Fuzzy Texture. A fault sometimesoccurring in vitreous enamelware, the'fuzziness' resulting from minute cratersand bubbles in and near the enamelsurface. Also known as GASSY SURFACE.G Stone. A name that has been used forPYROPHYLLITE (q.V.).G-Value. The basis of a method ofcalculation for compounding slips andglazes, the 'G-value' being the grams ofsuspended solids per cm3 of suspension:G = SP/100, where S is the sp. gr. of thesuspension and P is the percentage ofsolids in the suspension. (K. M. Kautz,/. Amer. Ceram. Soc, 15, 644, 1932).

Gabbrielli Penetrometer. The pressurerequired to penetrate an unfired bodywith a flat-headed needle parallel to itssurface is measured. This provides arapid estimate of porosity as a controltest on the effectiveness and uniformityof pressing dust-pressed tiles. (Gabbriellis.r.l., Italy).Gable Tile. A roofing tile that is half aswide again as the standard tile. Gable tilesare used to complete alternate courses atthe VERGE (q.v.) of a tiled roof.Gable Wall. The refractory wall above thetank-blocks at the end of a glass-makingfurnace; it is also sometimes referred to asthe END WALL Or BACK WALL.Gadget. A tool, used in the hand-madeglass industry, for holding the foot of awine glass while the bowl is beingfinished.Gadolinium Oxide. Gd2O3; m.p. approx.23500C; sp. gr. 7.41; thermal expansion(20-10000C), 10.5 x 10-6. A whitecrystalline solid, with properties similarto MgO and CaO. It is a neutronabsorber, and is used in nuclearapplications 'diluted' with alumina ormagnesia, as a 'burnable poison'. Suchmaterials control the flow of neutrons ina nuclear reactor by absorbing them,being converted to a higher isotope ofthe same material. Gadolinium has ahigh neutron capture cross-section but isused as a minor constituent of theceramic control material to avoidexcessive degradation of mechanicalproperties as the neutrons are absorbedand the 1^J Gd transformed to 1If Gd.Gaffer. The foreman of a SHOP (q.v.)making glass-ware by hand; also called aCHAIRMAN.Gahnite. See ZINC ALUMINATE.Gaize. A siliceous rock, containing someclay, found in the Ardennes and MeuseValley (France). It has been used as apozzoLANA (q.v.).

Galena. Natural lead sulphide, PbS;formerly used in the glazing of pottery.Gall. Molten sulphates sometimesformed on the surface of glass in afurnace; the cause is inadequatereduction of the salt cake to the morereactive sodium sulphite. Otheraggregations of unfused material floatingon molten glass are also sometimesreferred to as gall, e.g. batch gall.Galleting. Small pieces of roofing tilebedded in the top course of single-lap tilesto give a level bedding for the ridge tiles.Galleyware or Gallyware. Term for theearly (16th century) tin-glazedearthenware; the name derives eitherfrom the importation of the ware inMediterranean galleys or from the use ofthe tin-glazed tiles in ships' galleys.Gallium Arsenide. GaAs. Asemiconductor used in electro-luminescent devices, photocells.Gallium Nitride. GaN; m.p. 8000C.A special ceramic of high electricalresistivity 4xlO8 ohm.cm at 200C)Gallium Oxide. Ga2O3; m.p. 18000C:sp. gr. 6.4.Gamut. See TRI-STIMULUS VALUES forcolours.Gangue. The impurities surrounding theimportant constituent(s) in an ore, e.g.the silicate matrix in chrome ore.Ganister. Strictly, this term should bereserved for a silica rock formed bydeposition of dissolved silica in thesiliceous seat-earth of a coal seam; thetrue ganister was typically found as theseat-earth of some of the coal seams ofthe Lower Coal Measures in the Sheffielddistrict of England and was the rawmaterial on which the manufacture ofsilica refractories in that area was based.The term 'ground ganister' is used todenote the highly siliceous patching andramming material used in cupolas andfoundry ladles. In some parts of the USA,

'ganister' alone is used for such materials,including crushed firebrick, possiblymixed with clay and/or silica rock.Gap Grading. See GRADING.Gardner-Coleman Method. A methodfor determining the absorption of oil bypowders. (ASTM D1483/60 Pt 20).Gardner Mobilometer. An instrumentfor the evaluation of the flow propertiesof vitreous-enamel slips. It consists of aplunger ending in a disk, which may besolid or may have a standardized systemof perforations; the plunger is inserted ina tall cylinder containing slip and isloaded so that it descends through theslip; the time taken to fall through aspecified distance is a measure of themobility of the slip. (H. A. GardnerLaboratory, Bethesda, Maryland, USA.)Gareis-Endell Plastometer. Consists oftwo disks between which a cylinder ofclay is squeezed; the upper disk isrotated while the lower disk is slowlyraised by a revolving drum; a stressdeformation curve is recorded. (F.Gareis and K. Endell, Ber. Deuts.Keram. Ges., 15, 613, 1934.)Garnet. (1) A group of mineralscrystallizing in the isometric system andof general composition3RO.R2O3.3SiO2, for example:3CaO.AI2O3.3SiO2 (grossularite),3MgO.Al2O3.3SiO2 (pyrope)3CaO.Fe2O3.3SiO2 (andradite). Naturalgarnet occurs in economic quantity inUSA, Canada, India, S. Africa, andelsewhere: it is used as an abrasive,particularly in the woodworking industryand for the lapping of bronze wormwheels.(2) Mixed oxides with the general formulaA3B2X3O12, with body-centred cubicstructure. Yttrium and rare earth garnetsare FERRIMAGNETIC MATERIALS, (q.v.) ofwhich YTTRIUM IRON GARNET (q.v.) is themost important.

Garnex. A lining system of preformedboards, for continuous casting tundishes.(Steel Times Feb 1977, pi65).Garspar. Finely-ground quartz and glass,a by-product of polishing plate glass,used as a substitute for feldspar.Gas Adsorption Method. A techniquefor the determination of SPECIFICSURFACE (q.v.); variants of the methodinclude the BRUNAUER, EMMETT ANDTELLER METHOD (q.V.) and the HARKINSAND JURA METHOD (q.V.).Gas Bubbling Brick. A special porousbrick shape, set into the base lining of aLADLE (q.v.) or GLASS TANK for theinjection of gases for bubbling or stirringto improve the homogeneity of the steel orcontrol teeming temperature. Adjoiningbubbler blocks form a bubbler strip.Gas Concrete. See AERATED CONCRETE.Gas-fire Radiant. The radiants for gasfires are made of refractory materialhaving good resistance to thermal shock.The usual composition is a mixture ofclay and crushed fused silica; this isshaped and then fired at about 10000C.Gas Pickling. A method of preparingsheet steel for vitreous enamelling bytreatment, while hot, with gaseous HCl.Gas-pressure Bonding, ISOSTATICPRESSING (q.v.) at high temperature withgas (e.g. argon) as the fluid fortransmission of the pressure (cf.EXPLOSIVE PRESSING).Gas Pressure Sintering. The specimen isfirst sintered until all pores are closedpores, under vacuum or at low pressureusing a gas which readily diffuses throughthe material (e.g. oxygen for oxides). Thenthe external gas pressure is raised (to c.10MPa) using a gas which does not easilydiffuse through the material. Thetechnique does not require cladding anddecladding of the products, and combinessintering with low-pressure containerlessHiping in one continuous operation, cf.

SINTER-HIP, (q.v.) which uses pressures of70 to 200 MPa.Gas Retort. A refractory structure usedfor the conversion of coal into coke withthe simultaneous distillation of town gas.There are two types: CONTINUOUS VER-TICAL RETORT (q.v.) and HORIZONTALRETORT (q.v.). In the UK the refractoriesused must meet the specifications issuedby the Gas Council (1 Grosvenor Place,London, S.W.I) in collaboration with theSociety of British Gas Industries and theBritish Coking Industry Association.Gas Turbine. A device for theconversion of the energy of hot gases,derived from internal combustion, intorotary motion of a machine element. Theefficiency increases with operatingtemperature and is at present limited bythe safe temperature at which heat-resisting alloys can be used. There hasbeen much research on the possible useof cermets and other special ceramics inthese turbines, particularly in the blades.Gassy Surface. See FUZZY TEXTURE.Gate. See STOPPER.

Gate Scar. The U.S. term for a VOID (2).Gater Hall Device. See BARRATT-HALSALL FIREMOUTH.Gather. To take molten glass from a fur-nace for shaping; the amount of glass sotaken (gathered) is called a 'gather' also.Gathering Hole. An opening in theworking-end of a glasstank furnace, or inthe wall of a pot furnace, to permit thegathering of molten glass.Gator-Gard Process. A development ofPLASMA SPRAYING (q.v.) in which aconstricted throat in the gun acceleratesthe powder particles before they join theplasma. Tradename.Gatorizing. A superplastic forgingtechnique used to attach ceramic bladesto a metal turbine disc.Gaudin's Equation. An equation for theparticle-size distribution that can be

expected when a material is crushed ina ball mill or rod mill; it is of the formP = 100(x/D)m, where P is the per-centage passing a sieve of aperture x, Dis the maximum size of particle, and m isa constant which is a measure ofdispersion. The equation holds goodonly if the ratio of size of feed to size ofballs is below a critical value which, forquartz, is 1:12. (A. M. Gaudin, Trans.Amer. Inst. Min. Met. Engrs., 123, 253,1926.) Cf. SCHUHMANN EQUATION.Gauge. The exposed length of a roofingtile as laid on a roof; also sometimesknown as a MARGIN.Gauged Brickwork. Brickwork built tofine tolerances, sometimes using bricksspecially made or ground to accuratesizes, (see RUBBER).Gauging of Cement. The process ofmixing cement with water. For thepreparation of a cement paste ofstandard consistency prior to testing,B.S. 12 stipulates that the time ofgauging shall be 3-5 min.G-brick. A large French hollow block withgood thermal insulating properties, due toits many perforations and thin cell walls.Gault Clay. A calcareous clay with ashort vitrification range used for makingbuilding bricks in S. E. England. Bricksmade from this clay are generally porousand cream coloured, but in a fewlocalities red bricks are made from it.Gee Casting-Rate Meter. A metal ring isplaced on top of a clean, dry standardplaster base, which has been blended to afixed consistency. The ring is filled with slipof known density and a close-fitting coverput in place. The space within the ring isconnected to a manometer via a valve inthe cover. The pressure drop in that spacegives a measure of the casting rate.Gehlenite. 2CaO. Al2O3. SiO2; m.p.1593°C; thermal expansion (0-12000C)8.7 x 10-6 This mineral is sometimes

formed by the action of lime onfirebricks; it may occur in the slaggedparts of blast-furnace linings.Gelatine-pad Printing. See MURRAY-CURVEX MACHINE.Gelman Membrane. See DUSTSAMPLING, FILTERS.Generator. In a water-gas plant, therefractory-lined chamber in which solidfuel is gasified by blowing in steam andair alternately.Geomod. Tradename. CAD software fortableware (SDRC CAE International,Stevenage).Geopolymer. Geopolymers are semiamor-phous three-dimensional networks of poly-meric sodium, potassium, lithium andmagnesium silicoaluminates of the poly(sialate) type (-Si-O-Al-O-) or of thepoly sialate-siloxo) type (-Si-O-Al-O-Si-).Geopolymers harden between 20 and1200C and are similar to thermosettingorganic resins, but stable up to 1200/14000C without shrinkage. Hardeninginvolves the chemical reaction of alumino-silicate oxides (Al3+ in IV-fold coordina-tion) with alkali polysilicates yeildingpolymeric Si-O-Al bonds. A wide rangeof alkaline resistant inorganic reinforce-ments were combined with geopolymermatrices (in particular SiC fibre) withouthigh temperature, high energy processing.SiC fibre/K-poly (sialate-siloxo) matrixcomposites shaped and hardened at 700Cfor 1 h 30 min develop flexural meanstrengths of at least 380 MPa, unchangedafter firing at 4500C, 7000C and 900C.{Ceram. Eng. ScL Proc. 9 (7/8), 835,1988).Georgian Glass, WIRED GLASS (q.v.) inwhich the wire mesh is square.Germanium Nitride. Ge3N4; decomposesat 8000C. A special electro-ceramic ofhigh resistivity.Germanium Oxide. GeO2; m.p. 1115°C;sp. gr. 43. This oxide has been used tomake glasses of high refractive index.

Gerstley Borate. A sodium-calciumborate produced at the Gerstley Mine,Death Valley, California. (US Borax andChemical Corp., Los Angeles).Getting. The actual process of diggingclay, by hand or bv excavator; gettingand transporting form the successivestages of winning.Gibbsite. Aluminium trihydrate,Al2O3JH2O. Occurs in Dutch Guiana,the Congo, and some other areas wherelaterization has occurred. A typicalanalysis is 65% Al2O3, 33% H2O and2% impurities, but many samplescontain clay. Gibbsite requirescalcination at a very high temperature toeliminate all the shrinkage that resultsfrom the loss of water.Gilard and Dubrul Factors. SeeTHERMAL EXPANSION FACTORS FORGLASS.Gild. The painting of pottery with liquidgold, this is subsequently fired on atabout 70O0CGillmore Needle. Apparatus for thedetermination of the initial and final setof portland cement (Q. A. Gillmore,Practical Treatise on Limes, HydraulicCements and Mortars, New York, 1864).The present form of apparatus consistsof two loaded rods which slide verticallyin a frame: the rod ('needle') for thedetermination of initial set is Vu in. (2mm) dia. and weighs 1A Ib (HOg), theneedle for the final set is Vi* in. (1 mm)dia. and weighs Ub (446g). Details aregiven in ASTM-C266 (cf. VICATNEEDLE).

Ginneter. Term in the N. Staffordshirepotteries for a person who grinds fromchina-ware, after it has been taken fromthe glost kiln, any adhering particles ofrefractory material from the kilnfurniture; cf. SORTING. (From Ginnet, anold term for a tool used by carpenters toremove excrescences from wood.)

GIaceramic. A term that has been usedin USA for devitrified glass products ofthe type exemplified by PYROCERAM(q.v.)Glarimeter. See INGERSOLLGLARIMETER.Glascol. Tradename. Acrylic copolymerused as sealers for porous glazes and asmedia for colours. (Allied Colloids, UK).Glas-lok. Tradename. A glass-fibre jointfor clay sewer pipes. (Pomona Pipe,USA)Glass. A solid with no long-range orderin the arrangement of its atoms. ASTMCl62-92 defines a glass as an inorganicproduct of fusion that has cooled to arigid condition without crystallizing, andnotes that glasses are typically hard andbrittle, with a conchoidal fracture. Theword is used loosely as a synonym forGLASSWARE (q.v.) The Annual Book ofASTM standards VoI 15.02 lists overfifty test methods and propertyrequirements for glass and glassproducts. The names of many types ofglass indicate their main constituents,e.g. soda-lime glass (the presence ofsilica being understood); for the systemof designating types of optical glass seeOPTICAL GLASS CLASSIFICATION. Amajor advance in the understanding ofthe fundamental nature of a glass wasmade when W. H. Zachariasen (/. Amer.Chem. Soc, 54, 3841,1932) deduced thatthe characteristic properties of glassesare explicable if the interatomic forcesare essentially the same as in a crystal,but if the three-dimensional atomicnetwork in a glass lacks the symmetryand periodicity of the crystallinenetwork. Zachariasen's rules for theformation of an oxide glass are (1) thesample must contain a high proportionof cations that are surrounded by oxygentetrahedra or by oxygen triangles; (2)these tetrahedra or triangles must share

only corners with each other; (3) someoxygen atoms must be linked to only twosuch cations and must not form furtherbonds with any other cations. The ions ina glass are thus divided into NETWORK-FORMING (q.v.) and NETWORK-MODIFYING (q.v.). See also STRUCTON;viTRON. See also HALIDE GLASSES,CHALCOGENIDE GLASSES.Glassblowing. Shaping hot glass by airpressure. This may be done by hand andmouth by a craftsman glassblower, ormay be an element of various formingprocesses: see BLOW-AND-BLOW; PRESS-

AND-BLOW; PUFF-AND-BLOW.Glass-bonded Mica. See MICA (GLASS-BONDED).Glass-Ceramic. A type of ceramicmaterial that, while in the form of amolten glass, is shaped by one of theconventional glassmaking processes, andis subsequently devitrified in a controlledmanner so that the finished product iscrystalline. The crux of the process is theprecipitation, during cooling of theshaped ware, of nucleating agentspreviously added in small amounts to theglass batch; the nucleated article is thenheated to a temperature at which thenucleated crystals can grow. Devitrified-glass products can be made in a widerange of compositions; the propertiescan thus be varied, but typically the wareis impermeable and has high strengthand good thermal-shock resistance. Usesinclude RADOMES (q.v.), high-temperature bearings, thread-guides anddomestic ovenware. (See also NEO-CERAMIC GLASS).Glass-coated Steel or Glass-lined Steel.A grade of vitreous enamelled ware thathas good resistance to chemical attack athigh temperatures and pressures; alsoknown as Glassed Steel.Glass Enamel. A mixture of colouredmetallic oxides, or salts, and low-melting

flux, e.g. lead borosilicate, used for thedecoration or labelling of glass-ware; theenamel is fired-on at a red heat.Glass-encapsulated HIPing. SeeENCAPSULATED HIPING.Glass Eye. A large unbroken blister onvitreous enamelware.Glass Fibre. Filamentous glass made bymechanical drawing or centrifugalspinning; or by the action of a blast of airor steam to produce Staple Fibre. Theunprocessed filaments are known asBasic Fibre; a number of filamentsbonded together form a Strand. Longglass fibres are known as 'Silk', a fleece-like mass of fibres is 'Wool'; feltymaterial is 'Mat'. Formerly glass formaking fibres was produced as marbleswhich were remelted in an electricfurnace to form filaments. Nowadays thedirect-melt method is used. Fibres aredrawn directly from holes in an alloybush, at winding speeds of 50 m/s. TheOwens STEAM-BLOWING PROCESS (q.v.)is used to make glass wool. Glassfilaments are a few jLim diameter, andmuch stronger than ordinary glassbecause free of surface flaws. There areover 20 British Standards for glass fibreproducts and plastics and cementproducts with glass fibre reinforcement.Glass Frost. Very thin glass that hasbeen crushed for use as a decorativematerial (cf. TINSEL).Glass-ionomer Cements. Translucentdental cements, made by the reactionbetween aluminosilicate glass powders,and polymers and copolymers of acrylicacid. Developed by A.D. Wilson andB.E. Kent at the Laboratory of theGovernment Chemist. (/. Appl Chem.Biotechnol 21, (11), 313, 1971). Forspecification, see B.S. 6039.Glassivation. Passivation ofsemiconductor devices by completeencapsulation in glass. An Americanism.

Glass-like Carbon, Vitreous Carbon. Amonolithic, non-graphitic form ofcarbon, made by shaping a thermosettingorganic resin and pyrolysing at 20000Cand above. The material is hard,impervious, has high compressive (700-1400 MPam-2 and tensile (1-200MPanrr2 strengths, retained at hightemperatures, but low impact strength.Higher temperature fabrication giveshigher thermal conductivity (0.012 cal/cm°C.s) at the expense of some strength.The material was developed byLockhead Missile and Space Co. PaloAlto. AD 708314, 1969).Glassmakers Soap. A seleniumcompound, or manganese dioxide, usedto remove green coloration due to ironcompounds.Glass-making Sands. High purity silicasand, with low iron content especially,suitable for making clear glass. BS 2975specifies sampling and analysis.Glass-to-Metal Seal. Metal componentsvarying in size from fine wires to heavyflanges are sealed to glass for manypurposes, e.g. electric lamp bulbs andradio valves. Metals that have been usedfor this purpose include Pt, Cu, W, Moand alloys such as Fe-Cr, Ni-Fe and Ni-Fe-Co; the SOLDER GLASS (q.v.), whichis used as a powder suspended in avolatile liquid, is essentially lead borate.See Kohl.'Handbook of Materials and Techniquesfor vacuum devices' Reinhold, New York& London 1967; or the article on GlassSealing in 'Encyclopaedia of MaterialsScience and Engineering' VoI 3, M.B.Bever (ed) Pergamon 1986.Glassware. The products of the glassindustry, usually CONTAINER GLASS;FLAT GLASS. The other major branchesof the glass industry produceFiBREGLASS and special OPTICAL andELECTRICAL GLASS.

Glaze. A thin glassy layer formed on thesurface of a ceramic product by firing-onan applied coating, by firing in thepresence of alkali vapour (as in SALTGLAZING (q.v.), or as a result of slagattack on a refractory material. A glazemay, however, be partially crystalline(see CRYSTALLINE GLAZE and MATTGLAZE). The term 'glaze' is also appliedto a prepared mixture, which may beeither a powder or a suspension in water(SLOP GLAZE q.v.) ready for applicationto ceramic ware by dipping or spraying.Glaze Fit. The matching of the thermalexpansion of a glaze to that of the bodyon which it is held. To prevent CRAZING(q.v.) the glaze must be in compressionwhen the ware has been cooled from thekiln to room temperature; to achievethis, the thermal expansion of the glazemust be less than that of the body.Glazing. (1) The process of applying aglaze to ceramic ware; the latter may beunfired or in the biscuit state.(2) The formation of a glazed surface ona refractory material as a result ofexposure to high temperature and/orslagging agents. Occasionally, a glaze isdeliberately applied to a refractory toseal the surface pores.(3) The dulling of the cutting grains inthe face of an abrasive wheel, generallyas a result of operating at an incorrectspeed.(4) Inserting glass sheets into windows,doors etc.Glenboig Fireclay. A fireclay occurringin the Millstone Grit in the region ofGlenboig, Lanarkshire, Scotland. Atypical per cent analysis (raw) is: SiO2,50-51; Al2O3, 33; Fe2O3, 2.5; alkalis 0.5.The P.C.E. is 32-33.Glide Planes, SLIP PLANES (q.v.)Globar. A silicon carbide heatingelement. (Trade-name: CarborundumCo., USA and England.)

Glory Hole. An opening in a furnaceused in the glass industry for reheatingglass-ware preparatory to shaping.Gloss. A surface property, for exampleof a glazed ceramic or of vitreousenamelware, related to the reflectivity.For a quantitative definition seeSPECULAR GLOSS.Gloss Point. When a layer of glazepowder is heated, a temperature isreached at which the surface changes itsappearance from dull to bright; thistemperature has been termed the 'glosspoint'. (R. W. P. de Vries, Philips Tech.Rev., YJ, 153,1955.)Glost. This word, meaning 'glazed',is used in compound terms such as'Glost ware', 'Glost firing' and 'Glostplacer'.Glost Box. A form of CRANK for totallyenclosing flatware during glost firing.Gluing. The construction of a rotary kilnlining in axial strips, alternatively gluedand seated normally on the kiln shell.Individual brick rings are keyed on theside, between glued strips.Glut Arch. A brick arch below thefiremouth of a pottery BOTTLE OVEN(q.v.) for the admission of primary airand the removal of clinker.Gob. A lump of hot glass delivered, orgathered, for shaping.Gob Process. A method of makinghollow glass-ware, gobs of glass beingdelivered automatically to a formingmachine.Gold Decoration. See BURNISH GOLDand BRIGHT GOLD.Gold Ruby Glass. See RUBY GLASS.Gold Scouring. Alternative term forburnishing; see under BURNISH GOLD.Goldstone Glaze. An AVENTURINE(q.v.) glaze; a quoted composition is(parts): white lead, 198.7; feldspar, 83.4;whiting, 8; ferric oxide, 11.2; flint, 41.4.This glaze matures at cone 04.

Gold-tin Purple. A mixture of goldchloride and brown tin oxide, used as apigment.Gonell Air Elutriator. A down-blast typeof ELUTRIATOR (q.v.) designed by H. W.Gonell (Zeit. Ver. Deutsch. Ing., 72, 945,1928); it has found considerable use inEurope for assessing the fineness ofPortland cement.Gorkal Cement. The Polish equivalentof Ciment Fondu (q.v.)Gooseneck. See under BUSTLE PIPE.Goskar Dryer. A chamber dryer forbricks and tiles designed by T. A.Goskar (Trans. Brit. Ceram. Soc, 37, 62,1938). Each chamber has a false floorand a false roof; air enters the chambervia the space above the false roof and iswithdrawn via the corresponding spacebelow the false floor.Gossler Process. The drawing of glassfibres from streams of molten glassissuing from holes at the bottom of amelter. (O. Gossler, Br. Pat. 354 763,1930).Gothic Pitch. See under PITCH.Gottignies Kiln. The original electricMULTI-PASSAGE KILN (q.v.); it wasintroduced in 1938 by two Belgians, R.Gottignies and L. Gottignies (BelgianPat. 430 018).Gouging Test. A procedure for theevaluation of the resistance of a vitreous-enamelled surface to mechanical wear.In the procedure laid down in a SpecialBulletin issued by the Porcelain EnamelInstitute (Washington, D.C., USA), asmall steel ball is rolled on the enamelsurface under various loads.Gouy-Freundlich Double Layer. SeeDOUBLE-LAYER THEORY.Grade. As applied to an abrasive wheelthis term refers to the tenacity of thebond for the abrasive grains, i.e. theresistance to the tearing-out of theabrasive grains during use.

Grading. (1) The relative proportions ofthe variously sized particles in a batch,or the process of screening and mixing toproduce a batch with particle sizescorrectly proportioned. A batch with agrading for low porosity will contain highproportions of coarse and fine particlesand a low proportion of intermediatesize; if a particular particle size, e.g. themedium size, is excluded from the batchthis is said to be a GAP GRADING.(2) In the abrasives industry, the processof testing to determine the GRADE (q.v.)of a wheel; testing machines areavailable for this purpose.Graded Cermet. A CERMET (q.v.) inwhich the proportion of metal to ceramicin continuously, gradually and uniformlyvaried along the length of the article, sothat one end is pure metal, the other thepure ceramic, or any section from thelength of such a cermet.Gradient Kiln. A kiln in which thetemperature changes uniformly along itslength.Grain. (1) Abrasive material, dead-burned magnesite, or similar materialsthat have been size graded. (2) A crystalor microcrystal in a polycrystallinematerial.Grain Boundary. The narrow, disorderedregions separating individual grains in apolycrystalline material. They maycomprise glassy material of this is formedduring SINTERING (q.v.) Grain boundariesprovide a second route (as well as throughthe grains) for DIFFUSION processes, andare important to the related processestaking place in SINTERING and in CREEP.Grain boundaries interface with themovement of DISLOCATIONS and CHARGECARRIERS, and are this important indetermining how the MICROSTRUCTURE(q.v.) affects mechanical and electricalproperties. See also CRYSTAL

STRUCTURE.

Grain Bridging. See CRACK BRIDGING.Grain Density. B.S. 1902 Pt 3.6 definesgrain density as the BULK DENSITY (q.v.)of granular materials with grain sizelarger than 2mm. It specifies fourtechniques for its determination(mercury with vacuum; arrested waterabsorption; mercury in burette; mercuryin Amsler volumeter) of which the firstis the referee method, but the others arepreferred on health grounds for routinetesting, as they do not involve largequantities of mercury in glass containers.Grain Growth. In general, inpolycrystalline materials, the largergrains tend to grow at the expense of thesmaller. Grain growth is more marked athigher temperatures, which facilitateatomic mobility. Grain growth may beby DIFFUSION processes and themovement of GRAIN BOUNDARIES, or byselective dissolution processes such asOSTWALD RIPENING (q.V.).Graining; Graining Oxide; GrainingPaste. The production on vitreousenamelware of a patterned surfaceresembling grained wood; this is doneby transferring, by means of a metalroller, GRAINING PASTE (ALSO KNOWNAS GRAINING OXIDE) from an etchedplate to the enamel surface. This pasteconsists of very finely ground colouringoxides and a flux; it is made to therequired consistency with an oil, e.g.clove oil.Grain-size Analysis. See PARTICLE SIZE

ANALYSIS.Grain Spacing. A term in the USabrasives industry equivalent toSTRUCTURE (q.V.).Granite Ware. This term has had variousmeanings wilhin the vitreous-enamelindustry but the definition given inASTM - C286 would restrict themeaning to: a one-coat vitreous-enamelled article with a mottled pattern

produced by controlled corrosion of themetal base prior to firing.Granito. The Italian word meaning'granite' applied to a vitrified 'porcelain-stoneware' tile body.Granny Bonnet. Term sometimes usedfor a Bonnet Hip Tile - see under HIPTILE.

Granular. See MORPHOLOGY.Granulate. Components of a powderwhich behave as units of a given sizedistribution, although each may be madeup of many smaller particles adheringtogether. For example, spray-driedgranulate may be in the form of roughlyspherical or toroidal grains, of uniformsize, each made up of large numbers ofmuch smaller platelike particles.Granulometry. The measurement ofparticle size distribution, or of grain size.Graphite. A crystalline form of carbonoccurring naturally in Korea, Austria,Mexico, Ceylon, Madagascar, andelsewhere; it is produced when amorphouscarbon is heated, out of contact with air, ata high temperature. The m.p. exceeds35000C, the electrical and thermalconductivities are high. Graphite is used(under reducing conditions) as a specialrefractory for electrodes and electricalheating elements; mixed with fireclay it isused in the manufacture of plumbagocrucibles and stoppers for use in the metalindustry. See also CARBONREFRACTORIES. ASTM Annual Book ofStandards VoI 15.01 lists some twenty-fivestandards and tests relating specifically tographite and manufactured carbonproducts.Grappier Cement. A cement made fromfine-ground underburned or overburnedslaked lime.Grave. Decoration on glass, bysandblasting to various depths.Gravimpinger. A simple gravimetricdust sampler developed at British

Ceramic RA. The dust is collected byhigh-velocity impingement in a fluidwhich wets clay particles well and has alow vapour pressure minimizingevaporation over the sampling period ofa week. (Annals Occup. Hyg. 9 (1) 291966).Gravity Process. See GOB PROCESS.Green. Of ceramics, shaped but notdried or fired.Green House. A heated room in whichpottery-ware is inspected and storedbetween the shaping process and thefiring process.Green Spot. A fault that occasionallybecomes serious in the manufacture ofsanitary fireclay and glazed bricks. Thegreen spots are comparatively large andfrequently of an intense colour. Theusual causes are the presence ofchalcopyrite (CuFeS2) in the raw clay oraccidental contamination by a particle ofcopper or copper alloy, e.g. a chip off abronze bearing.Green Strength. The mechanicalstrength (usually measured by atransverse test) of ceramic ware in theGREEN (q.v.) state.Green Vitriol. Ferrous sulphateFeSO4JH2O, produces a red colourwhen used as a source of iron inpigments.Grey Stock. A clamp-fired STOCK BRICK(q.v.) that is off-colour.Griffith Cracks. Minute cracks assumedto be present in the surface of a piece ofglass; their existence was suggested byA. A. Griffith (Phil. Trans., A, 221,163,1920) to explain the low strength of glasscompared with that calculated from theforces of molecular cohesion.Griffith-Orowan Criteria. When cracktip stresses are accommodated only byelastic deformation, the fracture stress isinversely proportional to the square rootof the flaw size, which is often the size of

the largest most highly stressed defect.See FRACTURE, CRACK PROPAGATION.Grin. Gradient Refractive Index lens.Instead of by variation in thickness, thelight path through the lens is determinedby controlled variations in refractiveindex obtained by ion exchange. Theusual form is a cylinder or rod with therefractive index higher on the outside.Grinding. (1) Particle-size reduction byattrition and/or high-speed impact; in thesize reduction of ceramic raw materialscoarse crushing usually precedes finegrinding.(2) Final shaping to close tolerance, e.g.of an electroceramic component, bymeans of abrasive wheels.Grinding Aid. An additive to the chargein a ball mill or rod mill to accelerate thegrinding process; the additive hassurface-active or lubricating properties.Grinding aids find particular use in thegrinding of portland cement clinker, butin the UK their use is precluded by theconditions laid down in B.S. 12.Grinding Wheel. A disk, or comparablesymmetrical shape, of bonded abrasivematerial. The abrasive is either alumina

or silicon carbide; the bond may be ofthe vitrified ceramic type, or it mayconsist of sodium silicate (here called aSILICATE BOND), resin, rubber, orshellac. A standard marking system forgrinding wheels was adopted many yearsago by the Grinding WheelManufacturers' Association of America;in 1952 this system was also adopted inthe UK as British Standard 1814. Thismarking system is reproduced in Fig. 3.BS 1814 is now withdrawn and replacedby BS4481 PtI.Grinstead Clay. A Cretaceous clay forbrickmaking in parts of Sussex, England.Grip-coat. See GROUND-COAT.Grisaille. A method of decorating, atone time used on pottery vases, etc., inwhich different shades of grey were usedto produce the effect of low relief; fromFrench word meaning grey shading.Gritting. The process of forming asmooth surface on blocks of marble, orother natural stones, by means ofabrasive blocks known as 'rubbingblocks .Grizzle. A clamp-fired STOCK BRICK(q.v.) that is soft and suitable only for

Sequence:PrefixW

AbrasiveA

Grain size46

GradeK

Structure5

Bond typeV

Suffix17

Manufacturer'sabrasive type symbol(use optional)Aluminium oxide-ASilicon carbide-C

Coarse8101214162024

Medium3036465460

Gradescale

Soft MediumABCD E FG H IJ K L M N O P Q R S T U VWXYZ

Hard

Fine80100120150180

Veryfine220240280320400500600

Dense12345678

To open9101112131415Etc.(Use optional)

Manufacturer'swheel type symbol(use optional)V-vitrifiedB-resinoidR-rubberE-shel!acS-silicate

Fig, 3 See GRINDING WHEEL

internal walls. The term went out of usebefore 1940.Grizzly. The name used in the Englishstructural-clay products industry for asimple, stationary, screen consistingmerely of a frame and perforated metalplate, or wire mesh; the screen is set atan angle, the inclination depending onthe angle of repose of the material beingscreened.Grizzly Crusher. A machine with movingbars which crush material and sparate itby size.Grog. Firebrick, which may already havebeen used in a furnace lining orelsewhere, crushed to a size suitable forincorporation in a batch, either forremaking into bricks or for use in arefractory cement, ramming, or patchingmaterial. The word is probably derivedfrom the French gros grain (coarsegrain) via the English 'grogram' (coarsecloth) (cf. CHAMOTTE).Grog Fireclay Mortar. A US termdefined as: raw fireclay mixed withcalcined fireclay, or with broken fireclaybrick, or both, all ground to suitablefineness.Grossalmerode Clay. A refractory clayfrom Grossalmerode, about 10 miles (16km) E.S.E. of Kassel, West Germany.These clays are of Tertiary origin. Theyhave been used for making glass-potssince A.D. 1503. The typicalGrossalmerode clay is worked at theFaulbach and at the Lengemann depositsand contains (unfired) 70% SiO2 and18% Al2O3; the P.C.E. is 28-29. Analuminous clay (P.C.E. 33-34) is workedat the Salzmann claypit.Grotthuss Chain Reaction. In absorbedwater layers, H3O

+and OH- ions arepresent, with the fraction dissociatedbeing as much as 1%. (106 times that inliquid water). The H3O+ ion releases aproton to a neighbouring water

molecule, which then releases a protonto another. The charge transport whichresults provides a conduction mechanismin the surface layers of humiditysensitive oxides.Ground-coat. The coating on vitreousenamelware that is applied to the metal.The principal constituents of a sheet-iron ground-coat are feldspar, borax,and silica which, together, constitute75-90% of the batch; in addition, thereis about 10% Na2CO3+NaNO3, 5%fluorspar, 0.5% cobalt oxide and 1.5%MnO2. The chief constituents ofground-coats for cast iron are alsofeldspar, borax, and silica, but thebatches are more variable than forground-coats on sheet iron.Ground-hog Kiln. US term for an art-potters kiln (usually fired with solid fuel)partly buried in a convenient hillside tosupport the roof and conserve heat.Ground Laying. A process for theapplication of a uniform coating ofcolour to pottery-ware by painting withoil the area to be coloured and thendusting powdered colour over the ware;the colour sticks only where oil has beenfirst applied. The process is now usedonly for the decoration of someexpensive types of china and porcelain.Ground Mass. See MATRIX.Grout. Mortar or cement mixed to afluid consistency for use in filling thejoints between brickwork or tiles.Grouting. (1) Filling tile joints withGROUT (q.v.) (2) Pumping refractorymaterial from outside the furnace to seallocalised voids formed in the lining inservice, or to make a new lining. (3)Filling the voids in soils to make firm,massive foundations, by injecting ahardenable compound or concrete.Growan. A term in the Cornish chinaclay industry for incompletely andunevenly decomposed granite.

Gruneisen's Law. relates thermalconductivity y, linear thermal expansioncoefficient a, compressibility K andspecific heat Cv, for a solid of volume V,by 3ccV = yKCv.Guard Ring. An arrangement inthermal-conductivity apparatus designedto ensure that heat shall flow through thesample actually under test, in a directionperpendicular to the hot and cold faces,i.e. no heat flows through the sides of thetest-piece.Guide Tube. A fireclay tube having aspigot and socket, for use in theTRUMPET (q.v.) assembly in the bottom-pouring of molten steel. Two sizes arespecified in B.S. 2496: 45/8 in. (117 mm)o.d. and 27/s in. (73 mm) i.d. for tubes upto 12 in. long (305 mm); 6 in. (152 mm)o.d. and 315/i6 in. (100 mm) i.d. for tubes12-15% in. (305-393 mm) long.Gull Wings. Gull wings and WAKE HACKLEform when the fracture front encountersan inclusion, which overlap slightly onrejoining. The mark then appears as aTWIST HACKLE (called a WAKE HACKLE ifso formed) with two outspreading strongWALLNER LINES, the GULL WINGS.Gum. Various natural gums are used asBINDERS (q.v.) in the ceramics industry.e.g. Gum Arabic (or Gum Acacia,Kordofan gum); Gum Tragacanth.Gum Set. Erratic quick setting of cementin concrete.Guncrete. Refractory concrete appliedby GUNNING, (q.v.)Guniting. Hot spraying of refractoryconcrete.Gunning. The placing of a refractorypowder or slurry by means of a cementgun; most commonly, gunning ispractised as a method of repairingfurnace linings without the need to coolthem to room temperature.Gunning Mix. A CASTABLE,MOULDABLE OR RAMMING MIX that has

been designed to be installed bypneumatic projection. (B.S. 1902 Pt7).Guthrie Kiln. A variant of the BELGIANKILN (q.v.), a trough replacing thetransverse grate; the design was patentedby H. Guthrie in 1877.GVC. Abbreviation for GLAZEDVITRIFIED CLAY: term applied to glazedclay pipes.Gypsum. Natural hydrated calciumsulphate, CaSO4. 2H2O, from whichPLASTER of PARIS (q.v.) is produced. InEngland gypsum occurs in the Newarkand Tutbury zones of the Keuper Marl,and in the Purbeck Beds of Sussex. Itoccurs abundantly in USA, Canada,France, USSR and elsewhere.Gyratory Crusher. A primary crusher forhard rocks such as the quartzite used insilica brick manufacture. The material tobe crushed is fed into the space betweena vertical steel cone and a similarlyshaped steel casing; the cone rotateseccentrically to the casing (cf. CONECRUSHER).

H Cassette. A support for handling andfiring tiles, which is shaped so that eachtile is individually supported, with thetile camber moulded into the cassetteshape, to minimise twist during firing.(CERIC, France)Habit. The form and structurecharacteristic of a particular crystallinecompound.Habla Kiln. A ZIG-ZAG KILN (q.v.) thatmay be archless or with a permanent flatroof; top-fired with fine slack; output 25000-50 000 bricks/week. It was designedby a Czech, A. Habla (Brit. Pats. 242 051and 311 884).HAC. High Alumina Cement (q.v.).Hack. A double row of building bricks,with a 1-ft (305 mm)space between themand 8-9 bricks high, set on boards in theopen to dry; the top of a completed hackis protected from rain by a 'cap'. Side

protection, when necessary, is providedby LEE BOARDS usually pronounced LOOor LEW BOARDS. Hack drying has nowlargely been replaced by artificial dryingunder more controlled conditions.Hackle. A finely structured FRACTURESURFACE of rough or matt appearance.Also termed frosted, gray, matte, mist orstippled areas.Hackle Marks. Fine ridges on theFRACTURE SURFACE of glass, parallel tothe direction of crack propagation. Seealso RIB MARKS.Hafnium Borides. HfB: m.p. 30600C: sp.gr. 12.8. HfB2 m.p., 31500C; sp. gr.(theoretical), 11.2; thermal expansion(25-10000C), 5.5 x 10-6; resistivity(200C), 10-12 jiohm.cm.Hafnium Carbide. HfC; m.p. 38900C;theoretical density, 12.6 g/ml.; hardness,2533 (KlOO); modulus of rupture, 200-350 MNm-2 (200C); 170 MNm-2

(10000C); 105 MNm-2 (13000C).Modulus of elasticity 315 GNm-2 (200C);thermal expansion, 8.8 x 10~6 (25-25000C).Hafnium Nitride. HfN; m.p. 33100C;theoretical density, 14.0 g/ml. Thisspecial ceramice can be prepared bysintering Hf in dry N2 at 10000CHafnium Oxide. HfO2; m.p. approx.28000C; sp. gr. 9.68; thermal expansion(20-10000C) 5.8 x 10-6; (20-15000C) 6.5x 10-6. The low-temperature(monoclinic) form changes to the high-temperature (tetragonal) form at 1700-19000CHafnium Silicate. A compoundanalogous to zircon, hence the suggestedname HAFNON. It can be synthesizedfrom the oxides at 15500C Thermalexpansion (150-13000C), 3.6 x 10"6.Hafnium Titanate. Special refractorycompositions have been made bysintering mixtures of HfO2 and TiO2 invarious proportions. The m.p. of these

sintered bodies is approx. 22000C; thereappears to be a phase change at about18500C Some of the compositions havenegative thermal expansions.Hafnon. See HAFNIUM SILICATE.Hager Process. Glass fibre is made frommolten glass dropped on to a horizontalrevolving disc, from which fibres arethrown off radially. (US Pat. 2 234 087,1941).HAGS. Hot Anode Gas Shroudedthermal spray gun.Haigh Kiln. A US type of CHAMBERKILN (q.v.) designed by H. Haigh; it isU-shaped with an open space betweenthe two lines of chambers, permitting thechambers to be fired from both sides. Inone such kiln, as used at a USbrickworks, the chambers were 12-15 ftwide, 16 ft long and 10 ft high; (4-4.5x5x3m); this particular kiln was gas-fired at 11500CHair Cracks appear in concrete whosesurface has dried more rapidly than theinterior.Hair Line. (1) Fine CORD (q.v.) on thesurface of glass-ware; see also AIR LINE.(2) A fault sometimes seen in vitreousenamelware. The hair lines are a seriesof fine parallel, or nearly parallel, cracksthat have healed in the later firings (thusdiffering from crazing). The cause isexcessive stress in the biscuit enamelresulting from slight movement in themetal arising from non-uniform heatingor poor design.(3) A line of separation sometimesfound near the centre of thick ceramicware that has been shaped by SOLIDCASTING (q.v.).Hair-pin Furnace. A type of furnaceused in vitreous enamelling, see U-TYPEFURNACE.Half-bat. A building brick of half thenormal length; also called a SNAP-HEADER.

Half Crystal. This term has been appliedto CRYSTAL GLASS (q.v.) containing onlyabout 15% PbO.Half-penny Crack. A circular or semi-circular flaw developed from anindentation crack when sub-surfacelateral cracks nearly parallel to thesurface reach the surface and thematerial within the ring is removed. SeeFRACTURE TOUGHNESS TESTS.Halide Glasses. Glasses containing heavymetal fluorides have good infra-redtransmission properties, and highthermal expansion coefficients (up to20 x KH/K).Halifax Hard Bed. A siliceous fireclay ofthe Lower Coal Measures extensivelyworked in Yorkshire, England. Itcontains (fired) 68-74% SiO2, 20-25%Al2O3, 2.5-3.0% Fe2O3 and 1.0-1.5%alkalis.Hall Effect. A magnetic field applied atright angles to an electric currentflowing in a conductor generates a forcein the third mutually perpendiculardirection. This deflects the chargecarriers. A net surface charge densitybuilds up until its electrostatic fieldcounterbalances the force due to themagnetic field. The sign of the surfacecharge density gives the sign of thecharge carriers.HaIPs Factors. For calculating thethermal expansion of a glass; seeTHERMAL EXPANSION FACTORS FORGLASS.Halls Kiln. An annular kiln withpermanent walls dividing the chambers;there are openings at the ends of thesepartition walls to give a zig-zag firetravel, but there are also large traceholes through these walls. The kiln wasdesigned by G. Zehner of Wiesbaden,Germany. The name 'Halls Kiln' derivesfrom the hall-like appearance of the longnarrow chambers.

Halloysite. A clay mineral of thekaolinite group approximating incomposition to Al2O3.2SiO2.4H2O.Halloysite is a constituent of the clays ofNew Zealand and Brazil; it also occurs inMissouri and Utah (USA), in N. Africa,Japan, and elsewhere. The specialfeature of halloysite is the tubular shapeof the crystals resulting from the rollingup of the fundamental sheet structure;this causes difficulty when halloysiticclays are used in ceramic manufacturebecause of the consequent high and non-uniform shrinkage. (Named after theBelgian O. d'Halloy, 1783-1875.)Hamaker Constant. A measure of theelectrostatic dipole attraction of twoparticles in a given solid liquid system(See DOUBLE LAYER THEORY).Hamburg Blue. One of a range of iron-bearing pigments.Hammer Mill. An impact mill consisting ofa rotor, fitted with movable hammers, thatis revolved rapidly in a vertical planewithin a closely fitting steel casing.Hammer mills are sometimes used for thesize reduction of clay shales, glass cullet,and some of the minerals used in theceramic industry (cf. DISINTEGRATOR;IMPACT MILL).

Hammer Test. Tapping anchors or curedcastable with an engineer's hammer, todetect flaws or voids by the change ofsound.Hanging Rack. A heat-resistant metalframe for suspending porcelain enamel-ware during manufacturing processes.Hard. As applied to a glass, glaze, orenamel, this word means that thesoftening temperature is high; such aproduct, when cold, is also likely to behard in the normal sense. See alsoHARDNESS.Hard Ferrite. A FERRITE (q.v.)permanent magnet e.g. BaO.6Fe2O3. Seealso SOFT FERRITE.

Hard Metals. IntermetalHc carbides,particularly cemented carbides (q.v.)used as cutting tools and abrasives.Hard-paste. See HARD PORCELAIN.Hard Porcelain. True feldspathicporcelain (CONTINENTAL PORCELAIN),Hard-paste Porcelain being the olderterm still used by collectors. TheCOMBINED NOMENCLATURE (q.V.)defines hard porcelain as made fromkaolin or kaolinitic clays, quartz, feldsparand sometimes calcium carbonate. It iscovered with a colourless transparentglaze fired with the body. SeePORCELAIN.Hardening-on. Biscuit ware that hasbeen decorated prior to glazing is heatedat a comparatively low temperature(c. 7000C) to volatilize the oils used indecorating and to fuse the flux in theapplied colour so that the decorationremains fixed during the subsequentdipping in the liquid suspension.Hardening-on Fire. A low-temperaturefiring of underglaze decoration, to burnoff the organic media used in applyingthe colours, before glazing.Hardinge Mill. A ball mill for continuousoperation in which the casing is in theform of two conical sections joined by ashort, central, cylindrical section; thematerial to be ground is fed into the millthrough one of the hollow trunnions,being discharged through the oppositetrunnion. Named after H. W. Hardinge,USA, who invented this design of ballmill in 1906.Hardness. See KNOOP HARDNESS;MiCROCHARACTER HARDNESS; MOHS'

HARDNESS*, ROCKWELL HARDNESS*,VICKERS HARDNESS.Harkins and Jura Method. A gas-adsorption method for the determinationof the specific surface of a powder. Thesample is first evacuated and thenexposed to a vapour near to its

saturation pressure; the wetted powder isthen immersed in the liquid itself and therise in temperature is measured. Fromthis, the surface energy change, andhence the surface area, is calculated. (W.D. Harkins and G. Jura, /. Chem. Phys.,11, 430,1943.)Harkort Test. Although H. Harkort wasa German, details of his so-called crazingtest for pottery-ware were first publishedin USA (Trans. Amer. Ce ram. Soc, 15,368,1913). The test-piece is heated to1200C and then plunged into cold water;the cycle is repeated, with successiveincreases of 100C in temperature, untilcrazing can be detected after thequenching. The criteria are: no cracksafter quenching from 1500C - crazing atroom temperature likely after 3-4months; 1600C - 15 months; 170-1800C -no crazing after 2Vi years (with a fewexceptions); 1900C - no crazing after IViyears without exception. It is now knownthat crazing may result from moistureexpansion as well as from thermal shock.( A modification of this test forms thebasis of ASTM-C554.)Harrop Kiln. One of the variety oftunnel kilns built to the designs ofHarrop Ceramic Service Co., Columbus,Ohio. The early examples of HarropKilns in the N. Staffordshire potterieswere of the large open-flame type.Harrow. See under WASH-MILL.Hartford-Empire Individual SectionMachine (IS Machine). This in-linemachine is the industry standard formaking glass containers, with up to 12mechanised glass and mouldmanipulating sections (e.g. H.E. IS-12).Each section functions independently,and can handle up to three GOBS (q.v.)of glass at a time, depending on the sizeof the ware. Malfunction in one sectiondoes not stop the whole machine, whichproduces about 10 pieces/min. Narrow-

necked containers are made by a blow-and-blow process (the PARISON (q.v.) isblown, and the second blow into themould imparts the final shape to theware. The only movement is openingand closing the moulds. The machine canbe easily converted to make wide-mouthed containers with screw threads,using a PRESS-AND-BLOW (q.v.) processin iron moulds. A modification (HE-28)uses the press-and-blow process to maketumblers in paste moulds, the ware beingrotated to avoid seams. The glasses areformed as almost closed hollow objects,cut off and fire-polished with a burn-offmachine.Hartman Formula. Relates the refractiveindex (n) of a glass to the wavelength (X)of the incident light: n = no+c(X-X0)-

CL

where X0, c and a are constant and amay have a value from 1 to 2. This is animprovement on the CAUCHY FORMULA

(q.v.).HASAWA. Health and Safety at Work,etc Act, 1975. See HEALTH AND SAFETY.

Hashin's Equations. Expressions for thebulk and shear moduli, and henceYoung's modulus, of compositematerials, including porous materials.(A.G.Hashin and S. Shtrikman, /. Mech.Phy. Solids 11, 1963, pl27-140)Hassall Joint. A type of joint for glazedpipes designed by Wm. Hassall (of JohnKnowles & Co., Woodville, Burton-on-Trent) in the late 19th century. Bitumenrings are attached to the outside of thespigot and the inside of the socket of thefired pipe. A thin smear of cement isrubbed around these rings just beforethe pipes are laid, the spigot of one pipethen being pushed into the socket of thenext. Liquid cement is finally pouredthrough holes in the socket to completethe joint.Hastings Beds. A series of clay and sanddeposits in the Lower Cretaceous of S.E.

England; the Fairlight Clays at the baseof these deposits have been used forbrickmaking near Hastings and Bexhill.Haunch. The part of the furnace roofbetween CROWN and SKEWBACK (q.v.).Hawk Pug. Trade name: a de-airing pughaving two barrels in tandem, the firstrotating around a fixed bladed shaft,whereas the second is fixed while thebladed internal shaft rotates. Each shaftis set slightly off-centre. (ServiceEngineers, Stoke-on-Trent, England.)Hawse Clay. A local English term for aclay that is crumbly but becomes plasticwhen worked up with water.Haydite. Trade name: a lightweightexpanded clay aggregate, made in USA,named after its inventor S. J. Hayde (USPat. 1 255 878 and 1707 395).HB. Symbol for BRINELL HARDNESS

(q.v.).HCFS. Hypersonic Flame Spraying (q.v.)Header. A brick laid with its lengthacross the width of a wall, thus leavingits smallest face exposed. A course ofsuch bricks is known as a Header Course(cf. STRETCHER). A header in a coke-oven is a refractory brick setperpendicular to the wall, separating twoheating flues.Healing. The ability of a glaze to coverany areas of the ware that may havebeen damaged before the glaze has beenfired on; this depends on a correctcombination of surface tension andviscosity at the glost-firing temperature.Healy-SuIIivan Process. See HYDROGEN-

TREATING PROCESS.

Health and Safety and environmentalcontrol have increased in importance.Some British regulations affecting theceramic industry's responsibilities to itsworkers, its customers and the generalpublic include:* Health and Safety at Work etc Act, 1974;London HMSO, 1975 (HASAWA)

(which is explained by Essentials ofHealth and Safety at Work, London,HMSO, revised 1990).^Control of Lead at Work Regulations,1980 (CLAW). London, HMSO.* Control of Substances Hazardous toHealth Regulations, S.I. 165, 1988.London, HMSO, 1988 (COSHH).* Control of Substances Hazardous toHealth in the Production of Pottery.Approved Code of Practice, Health andSafety Commission, (HSC) London,HMSO, 1990. ISBN Oil 8855301(ACOP).^Potteries etc (Modifications) Regulations1990. (These supersede the Pottery(Health and Welfare) SpecialRegulations 1947 and 1950).Some of the HSE Methods for theDetermination of Hazardous Substancesare relevant to the ceramics industries.See MDHS.*The Health and Safety InformationBulletin 107 (6) 2 1984 Classification,Packing and Labelling Regulations 1984,Pt.l gives requirements for labellingdangerous substances.Other more specific regulations deal withnoise, smoke and fume emission, guardson power presses, using abrasive wheels,lighting gas furnaces, storing gaseous andliquid fuels and a whole range of similarand related topics.*B.S. 7750 is a specification forenvironmental management systemsaimed at ensuring compliance withstated objectives.In the USA, the relevant bodies areOSHA (Occupational Safety and HealthAdministration) and NIOSH (NationalInstitute for Occupational Safety andHealth) which publishes a Manual ofAnalytical Methods P13 85-179018,1984.The FDA (Food and DrugAdministration) is responsible forMETAL RELEASE TESTS (q.V.) in the

USA. ASTM Cl 191 describes the safeuse and handling of ceramic slips; Cl 192safe spraying of ceramic glazes; C1023the labelling of ceramic art materials forchronic adverse health hazards.See also TA-LUFT, METAL RELEASE,DUST, RSI.

Hearth. The lower part of a furnace,particularly the part of a metallurgicalfurnace on which the metal rests during itsextraction or refining. In a blast furnacethe hearth is constructed of aluminousfireclay or carbon blocks; in a basic open-hearth furnace or basic electric-arc steelfurnace, the hearth is constructed of basicrefractory bricks which are covered withdead-burned magnesite or burneddolomite rammed in place.Heat Activated Decal. The colour layermedium contains an activable resin. Thetransfer is applied to cold ware, the resinactivated by a heat source, and thebacking paper blown off.Heat Craze. The CRAZING (q.v.) ofvitreous enamelware as a result ofoverheating in service; thick enameland poor design are contributorycauses.Heat Release Decal. This type oftransfer is applied to hot ware. The heatactivates an adhesive layer, to stick thetransfer to the ware, and simultaneouslymelts a wax layer which held the transferto the backing paper.Heat-Setting Mortar. See REFRACTORYMORTAR.Heat-work. An imprecise term denotingthe combined effect of time andtemperature on a ceramic process. Forexample, prolonged heating at a lowertemperature may result in the samedegree of vitrification in a ceramic bodyas a shorter period at a highertemperature; a similar amount of heat-work is said to have been expended inthe two cases.

Heavy Magnesia. A form of magnesiumoxide made (unless intended forpharmaceutical use) by extraction fromsea-water by the dolomite process (seeSEA-WATER MAGNESIA). The extractedhydrate is calcined at 800-10000C and hasa bulk density of 0.5-0.7. On exposure tothe air, heavy magnesia takes up waterand CO2 to form a basic carbonate. It isused in making SOREL CEMENT (q.v.), asa constituent of glass batches, and invarious chemical processes.Heavy Spar. See BARYTES.Hecht's Porcelain. A German refractoryporcelain similar to MARQUARDTPORCELAIN (q.v.).Hectorite. Originally known as HECTORCLAY from its source near Hector,California, USA. It is a hydrousmagnesium silicate related tomontmorillonite and forming an end-member of the saponite series.Hedvall Effect. A brief period ofenhanced reactivity associated with asolid-solid phase transition. (J.A.Hedvall, Chem. Rev. 15, 1934, pl39).Heel Tap. See SLUGGED BOTTOM.Heliglobe. A spherical mixer, disperserand comminutor which can be operatedunder presure or under vacuum.{Industrie Ceram. (635) 921 1970).Helton System. An Austrian system fordry (mortarless) brick masonry (see alsoNOVAMUR).Hepsleve. Plastics joint rings for plain-ended fully-vitrified sewer pipes.(Tradename. Hepworth Iron Co)Heramicor. Gold decoration ontableware, subdivided into dots toprevent the build up of electricalpotential leading to destructive electricaldischarges (Heraeus GmbH, Germany).Hercules Press. Trade name: a semi-drybrickmaking machine of the rotary-tabletype. (H. Alexander & Co. Ltd., Leeds,England.)

Hercynite. Ferrous aluminium spinel,FeO-Al2O3; m.p. 17800C; thermalexpansion (0-10000C) 10.3 x 10-6.Hercynite is sometimes present in solidsolution with other spinels in aluminouschrome ores; it can also be formed whenferruginous slag attacks an aluminousrefractory under reducing conditions.When heated under oxidizing conditions,hercynite changes into a solid solution ofFe2O3 and Al2O3.HERF. High Energy - Rate Forming(q.v.)Hermansen Furnace. A recuperativepot-furnace for melting glass; thefirst furnace of this type was builtin Sweden in 1907 and was soonafterwards introduced into England andelsewhere.Herreshoff Furnace. A multiple-hearthcylindrical muffle roasting furnace; sucha furnace has been used to calcine offireclay.Hessian Crucible. A type of refractorycrucible for use in the small-scalemelting of non-ferrous metals. Thesecrucibles are made from theGROSSALMERODE CLAYS (q.V.).Hertzian Crack. = PERCUSSION CONE(q.v.).Hexite-Pentite Theory. A theory (longsince discarded) for the atomic structureof clays proposed by W. Asch and D.Asch (see Trans. Brit. Ceram. Soc, 13,90, 1914). The theory was based on thehypothesis that silicates are built up ofhexagonal and pentagonal rings ofhydrated silica and hydrated alumina.Hexmesh. Steel strips set vertically, toform a grating with hexagonal aperturesto anchor CASTABLE REFRACTORYlinings. Hexmesh is anchored to 50mmsquare plates {plate heads) drilled andfixed to round studs.HGMS. High-Gradient MagneticSeparation (q.v.).

Higgins Furnace. An electric arc furnacefor the fusion of refractory materials, e.g.alumina. The shell is a truncated cone(small-end up) which fits over a carbonhearth; when the charge has been fused,the shell is raised so that the ingot offused material can be removed from thehearth (A. C. Higgins, US Pat., 775,654,22/11/04).High-alumina Cement. ( I ) A specialhydraulic cement made by fusing (oroccasionally by sintering) a mixture oflimestone and bauxite. Although thesetting time is similar to that of portlandcement, the final strength is virtuallyattained in 24 h. The compositiongenerally lies within the following limits(per cent): CaO, 36-42; Al2O3, 36-42; Feoxides, 10-18; SiO2, 4-7.B.S. 915 stipulates 32% > Al2O3 andAl2O3-CaO (by wt) equal to 0.85-1.3.High-alumina hydraulic cement, if mixedwith crushed refractory material, can beused as a refractory concrete.High-alumina cement (though previouslyso used) was banned for structural workin buildings in 1974. Strength is lost ifHAC is exposed to high temperatureand humidity during setting or in service,or when the water/cement ratio is high.The reasons for loss of strength anddurability are complex, related tocrystalline state changes from ametastable to a more stable state,accompanied by increased porosity andthe production of water. The strength ofin-situ HAC cannot be measured non-destructively, but DTA can giveinformation on the crystal changescausing loss of strength.(2) A refractory cement (non-hydraulic)of high alumina content.High-alumina Refractory. A refractoryof the alumino-silicate type. In the UK itis defined in B.S. 3446 as containing over45% Al2O3. In the USA seven classes of

high-alumina refractory are defined(ASTM - C27): 50%-Al2O3 (P.C.E. >34; Al2O3 content 50 ± 2.5%); 60%-Al2O3 (P.C.E. > 35; Al2O3 content 60 ±2.5%); 70%-Al2O3 (P.C.E. ± 36; Al2O3

content 70 ± 2.5%); 80%-Al2O3 (P.C.E.2 37; Al2O3 content 80 ± 2.5%), plusthree more classes, namely 85%, 90%and 99% - Al2O3. ASTM C673 classifiesHigh Alumina Plastic Refractories andRamming Mixes into 7 grades from 60%Al2O3 on a similar basis, except that thelast two grades are 95 (±2.5%) and 100%(97.5%) Al2O3. The ISO classification is:High-alumina Group I >56% Al2O3;High-alumina Group II, 45-56%, Al2O3.High-duty Fireclay Refractories. Definedin ASTM - C27 as a fireclay brick with aP.C.E. >3iy2. There are three types:Regular, Spall Resistant, Slag Resistant.Further properties are specified for thelast two types. ASTM C673 specifies ahigh duty fireclay plastic refractory withP.C.E. >31.High Early-strength Cement. US termequivalent to the UK RAPID-H A R D E N I N G PORTLAND CEMENT (q.V.).It is Type III Cement of ASTMSpecification C150, which stipulates acrushing strength 1700 p.s.i.(12 MNm-2)after 1 day in moist air and > 3000 p.s.i.(21 MNm-2) after 1 day in moist airfollowed by 2 days in water.High Energy-rate Forming (HERF). Apunch is carried by a ram, and fired intoa closed die by gas pressure which givesan impact velocity of about 50mph, andforming pressures of over 2 GPa.High-frequency Heating. See INDUCTION

HEATING.High-frequency Induction Furnace. Seeunder ELECTRIC FURNACES FORMELTING AND REFINING METALS.High Gradient Magnetic Separation(HGMS). Also known as high intensitymagnetic separation. Magnetic fields of

sufficient intensity (up to 15 000 gauss)are used to separate paramagneticminerals (as well as ferromagneticmaterials) from china clay. (EnglishClays Lovering Pochin & Co. Ltd, Br.Pat 1077242,1967 and subsequentpatents).Highlight Test. A simple, empiricalestimate of the chemical resistance of asurface (of glass, glazes etc) by notingthe decrease in sharpness of reflectedimages in it.High Pressure Self-CombustionSintering. (HPCS). A variation of glassencapsulated hot isostatic pressing, inwhich a compact made by cold isostaticpressing is sealed under vacuum in aglass capsule heated to the glasssoftening point. High (100MPa) pressureinert gas is applied to the capsule, and itscontents ignited electrically, to sinter anddensify. This specialised method hasbeen used to process TiB2.High-velocity Oxyfuel Spraying. Acoating process. Fuel gas and oxygen arefed into the combustion chamber of aspray gun, and there mixed with powdercarried by an inert gas. The powder isheated to 28000C and accelerated to 800m/s in the gun, to produce low porositycoatings of good surface finish up to1.5mm thick.High-velocity Thermocouple. SeeSUCTION PYROMETER.Highway Bridge Loading. BritishStandard B.S. 5400 Pt. 2 1978 specifiesloads on buried rigid pipes due tovehicles, on the basis of their wheelspacing, axle spacing and tyre contactareas.Hillebrandite. A hydrated calcuimsilicate Ca2SiO3(OH)2 whichdecomposes at about 5000C to form lowcrystalline (3-Ca2SiO4.Hinckley Index. A measure of thedegree of crystallinity of a material,

based on X-ray diffraction peaks. Thesum of the heights of the 110 and 111peaks is divided by the height of the 110peak above the background. The firsttwo peak heights are based on a linedrawn from the trough between the 020-110 peaks, to the background justbeyond the 111 peak. (D.N. Hinkley,Clays & Clay Minerals Proc.llth Natl.Conf. p229,1963).Hind Effect. The porosity of a dried cast(deflocculated) pottery body is less thanthat of the same body, dried, if made bythe plastic (flocculated) process; theobservation was first made by S. R. Hind(/. Inst. Fuel 24, 116,1951).HIPing. Hot isostatic pressing(q.v.).Hip Tile. A specially shaped roofing tilefor use on a descending ridge that formsthe junction of two faces of a roof. Hiptiles are available in a number ofpatterns varying from the close-fittinghip of angular section to the broadlycurved types known as BONNET HIPS andCONE HIPS.Hispano-moreseque Ware. A type oflustre or tin-glazed pottery.HIVF. The Hypersonic Velocity ImpactFusion thermal spray coating process.Hob. The so-called ceramic hobs (flatsurfaces for supporting cooking ware oncookers) are usually made from glassceramic sheets.Hob-mouthed Oven. A pottery BOTTLEOVEN (q.v.) in which the firemouthsprojected 0.45-0.6m outwards, coal beingfed to the fire from the top.Hoffmann Kiln. A top-firedLONGITUDINAL-ARCH KILN (q.V.) of atype introduced by F. Hoffmann in 1858;variants of this type of kiln have beenwidely used in the firing of clay buildingbricks.Hofmeister Series. Cations arranged inorder of decreasing flocculating powerfor clay slips: H+, AP+, Ba2+, Sr2+, Ca2+,

Mg2+, NH4+, K+, Na+, Li+. (F.Hofmeister, Arch Exptl Path.PharmakoL, 24, 247, 1888.)Hog's Back. A type of RIDGE TILE (q.v.).Hoimeter. Trade name: a device forcontrolling the softness of an extrudedcolumn of clay; two small sensing rollersrun on the clay column, their axialpositions changing with any change insoftness of the clay; this change can bemade to adjust the rate of water additionto the mixer and so bring the consistencyof the clay back to normal. (BuhlerBrothers, Uzwil, Switzerland.)Hoi-Tronic. A plasticity and moisturecontrol system for ceramics industrymaterials preparation. (ManfredLeisenberg KG).Holdcroft Bars. Pressed and prefiredceramic bars (57 x 8 x 6.5mm) made ofblended materials so proportioned that,when placed horizontally with only theirends supported, and when heated undersuitable conditions, they will sag at astated temperature. The bars arenumbered from 1 (bending at 6000C) to40 (15500C). These bars were introducedin 1898 by Holdcroft & Co., and are nowavailable from Harrison-Mayer Ltd.,Stoke-on-Trent, England.Holding Ring. A BEAD (q.v.) in thefinish of a glass bottle for use when theparison is transferred to the blow mould:sometimes known as the BACK RING orTRANSFER RING.

Holes (in electrical conductivity). Theabsence of an electron from a compoundor crystal structure leaves a hole. Holesmove through the crystal or compoundunder the action of an electric field, inthe opposite direction to that taken byelectrons. They thus behave much likeelectrons, but carrying positive charge.Holey Boy. A type of perforated floor inintermittent downdraught kilns firingsalt-glazed pipes.

Hollow Blocks. See HOLLOW CLAYBLOCKS.Hollow Casting. See DRAIN CASTING.Hollow Clay Blocks. Fired clay buildingblocks, usually of comparatively largesize, with cells (air spaces) within theblock; they are used for wallconstruction and, with metalreinforcement, for floors andprefabricated panels. For specificationssee B.S. 3921; ASTM - C34, C56, C112and C212 (cf. HOLLOW MASONRY UNIT;

PERFORATED BRICK).

Hollow Masonry Unit. Defined inASTM - C43 as: A unit whose net cross-sectional area in any plane parallel to thebearing surface is less than 75% of itsgross cross-sectional area measured inthe same plane.Hollow Neck. A fault in the neck of abottle resulting from an insufficiency ofglass in the gob from which the bottlewas made; if the bottle is of the screw-necked type, the faulty neck is said to beBLOWN AWAY.

Hollow-ware. Cups, basins etc. (cf. FLAT-WARE). Recent American usage spellsthis HOLLOWARE, particularly whenapplied to glassware.Holyboy. A BATT (q.v.) with holes forcombustion gases to pass through.Hommelaya Process. Trade name: aprocedure in which cobalt is depositedon sheet steel before it is enamelled, thepurpose being to eliminate the need fora ground coat; (Hommel Co., Pittsburgh,USA).Hone. A block of fine abrasive, generallySiC; the block is appreciably longer thanit is broad or wide. Hones are used forfine grinding, particularly of internalbores.Honeycomb. Ceramic honeycombs werefirst developed to provide a lightsheathing material for the protection ofthe outer surface of supersonic aircraft,

missiles, and space-craft from the heatgenerated by air friction. A high-aluminaceramic is generally used; experimentshave also been made with zirconia,thoria, and various carbides. Therefractory powder is mixed with a binderand rolled into a thin flexible sheet; thecore is shaped by corrugated rolls. Thesheet and core are bonded with the samemixture and fired together to producethe honeycomb. Thin sheets of glass on apaper substrate can be corrugated,stacked and heated to produce glasshoneycombs. Honeycombs are also usedas catalyst carriers.Hood. (1) A protective casing, with anexhaust system, for use in carrying outdusty operations (e.g. TOWING (q.v.)) inpottery manufacture.(2) Alternative name for POTETTE (q.v.).Hooded Pot. See under POT.Horizontal Retort. (1) An intermittentunit for the production of town gasfrom coal; it is constructed of segmentsof silica or siliceous refractory material(cf. CONTINUOUS VERTICAL RETORT).(2) An intermittent unit formerly usedfor the production of zinc. Horizontalzinc retorts were generally madefrom a siliceous fireclay, suitablygrogged.Horse; Horsing. (1) A 'horse' is a heavystool with a convex rectangular top onwhich roofing tiles, after they have beenpartially dried, can be given the slightcurvature (about 3m radius) necessary toensure ventilation in a tiled roof; theprocess itself is termed 'horsing'.(2) In the old bottle-ovens for firingpottery, a 'horse' was used by the placersto enable them to reach the top parts ofthe bungs of saggars.Hospital. In a vitreous-enamel factory,the department in which ware is repairedthat has faults, not too serious forremedy.

Hot-blast Circulating Duct. See BUSTLEPIPE.Hot-blast Main. A duct, lined withrefractory material, through which hotair passes from a HOT-BLAST STOVE(q.v.) to the BUSTLE PIPE (q.v.) of a blastfurnace.Hot-blast Stove or Cowper Stove. A unitfor heating the air delivered to thetuyeres of a blast furnace. It is acylindrical furnace, about 25m high and6m dia., lined with fireclay refractories.There is a combustion chamber up oneside; refractory checker bricks (usuallyspecial shapes known as STOVE FILLINGS(q.v.) fill the remainder of the space. Thechecker bricks are heated by thecombustion of blast-furnace gas in thecombustion chamber and then, onreversal of the direction of gas flow theydeliver heat to incoming air which thenpasses to the blastfurnace tuyeres. Thesestoves were first proposed by E. A.Cowper (hence their alternative name)in 1857 and were first used atMiddlesbrough, England, in 1860. Theidea of heating the blast, however, hadbeen put forward by J. B. Neilson, aScotsman, in 1824.Hot Extrusion. This term is bestreserved for the process of extrusion inwhich clay that has already beenprepared and has the correct watercontent is heated while passing throughthe extruder; these features distinguishthe process from STEAM TEMPERING(q.v.). The Hot Extrusion process istypified in the extruders designed by theBedeschi Company, Padova, Italy.Hot Floor. A drying floor, heated frombelow by hot gases or by steam pipes, forspecial shapes of heavy clayware,refractories, etc.Hot Forging. Pressure is applied to apartially-densified compact, with thematerial free to flow without lateral

constraint, at a rate selected to avoidcracking or pore formation, bycontrolling the strain rate. Sinteredmaterials are thus densified withpreferred crystallographic orientation.Hot Isostatic Pressing. Shaping andsintering by the simultaneous applicationof heat and isostatic pressure.Hot-metal Ladle. A ladle for the transferof molten iron from a blast furnace to amixer furnace and from there to a steelfurnace; alternatively, the ladle maytransfer molten pig-iron direct from blastfurnace to steel furnace. Such ladies aregenerally lined with fireclay refractoriesbut for severe conditions high-aluminaand basic refractories have been triedwith some success.Hot-metal Mixer. A large holdingfurnace for molten pig-iron. The capacityof these furnaces, which are of the tiltingtype, is up to 1400 tons. Hot-metalmixers may be ACTIVE (i.e. the pig-ironis partially refined while in the furnace)or INACTIVE (i.e. the pig-iron is merelykept molten until it is required fortransfer to a steelmaking furnace). Ineither case the bottom and walls of thefurnace are made of magnesiterefractories and the roof of silicarefractories.Hot Patching. The repair of therefractory lining of a furnace while it isstill hot; this is most commonly done byspraying a refractory slurry through acement gun. See also AIR-BORNE

SEALING and SPRAY WELDING.Hot-plate Spalling Test. A spalling testdesigned specifically for the testing ofsilica refractories; it was standardized inASTM - C439, now withdrawn, though adescription still appears for informationin the ASTM Annual Book ofStandards.Hot Preparation. See STEAM

TEMPERING.

Hot Pressing. The simultaneousapplication of high temperature and highpressure in a mould, to shape and sintera powder compact at below thetemperature of normal sintering, withoutsintering aids. The process is applied toENGINEERING CERAMICS which areoften difficult to shape and fireconventionally to zero porosity.Furthermore, fine-grainedmicrostructures may be developedwithout grain growth inhibitors.Densification takes place in three stages:particle rearrangement; viscous andplastic flow; material transport bydiffusion. The optimum temperature andpressure combination can be found usingthe CLIMBING TEMPERATUREPROGRAMME Or the ISOTHERMALTECHNIQUE (q.v.), though thecharacteristics of the actual powder used,or property limitations of the diematerials, usually prevent the optimumconditions being achieved for the wholeof the pressing operation.(Hot pressing has also an obsolete usage:JIGGERiNG (q.v.) with a heated profiletool. Some electrical insulators wereshaped in that way).Hot-top. A container lined withrefractory or heat-insulating tiles andused at the top of an ingot mould in thecasting of steel: the molten steel isallowed to fill the mould and the hot-top,the extra metal remaining molten so thatit sinks into the ingot as the latter coolsand shrinks, thus preventing theformation of a 'pipe'.Hot-topping Compound. A granular,exothermic insulating refractory addedto the top of an ingot after teeming.Often used in conjunction with HOT-TOPPING TILES, to prevent 'piping' - theformation of cavities at the top ofcastings due to contraction of the melt asit cools.

Hot-topping Tile. Refractory insulatingtiles performing the function of aMOULD BRICK (q.v.), i.e. delayingsolidification of the melt in a HOT-TOP.Hot-wire method. A dynamic methodfor the measurement of THERMALCONDUCTIVITY (q.v.) applied torefractories up to 15000C (PRE/R321978). A linear heat source embedded inthe test piece gives a power outputconstant along its length and in time.The temperature rise in this hot wire is ameasure of the thermal conductivity ofthe material. The method was developedfor solids and powders with thermalconductivities below 1.5 Wm-1K"1. B.S.1902 Pts. 5.6 and 5.7 and ASTM Cl 113-90 now specify the hot-wire method forrefractories.Hotel China. See AMERICAN HOTELCHINA.Hotel-ware. Tableware of extra strength(usually achieved by extra thickness) foruse in hotels and restaurants; for speci-fication see B.S. 4034, which demands nocrazing after 16 hours in an autoclave at340 10 kPa, and a water absorption<0.2%.Hough Kiln. A barrel arch kiln withinternal cross walls.Hounsfield Tensometer. A compactdevice, manual or motor driven, whichwill perform tensile, shear, compressionand bend strength tests on ceramics andother materials at forces up to 2OkN.(Monsanto pic, Swindon).Hourdis. French term for large hollowblocks for ceiling or roof construction,first produced in Switzerland, and namedafter their inventor. Dimensions are 50to 100 x 20 x 7cm.Housekeeper Seals. Ductile metal sealsto glass. For example, a glass bead canbe applied to the thinned end of acopper tube, and then sealed to a glasstube, the ductile thinned copper yielding

to stresses from thermal expansiondifferences, and preventing cracking.Good chemical bonds between glass andcopper are required. (See W.G.Housekeeper, J.Am.Inst.Elec. Eng. 42,(1923) p840).Hovel. The large conical brick structurethat enclosed the old type of potteryoven or glass-pot furnace.Hover Kiln. A tunnel kiln through whichthe ware is carried on a cushion of hotair; the design was developed by ShelleyElectric Furnaces Ltd. Stoke-on-Trent,England (Brit. Pat. 990,589, 28/4/65; USPat. 3,184,224, 18/5/65).HPCS. High Pressure Self-CombustionSintering (q.v.).HPSN. Hot pressed silicon nitride. SeeSILICON NITRIDE.

HPZ. Hydropolysilazane, a precursor forSi3N4 films.HR. Symbol for ROCKWELL HARDNESS

(q.v.).HREX. Symbol for a special shape ofwall tile - Round Edge External Corner,Left Hand (see Fig. 7, p350).HTI. Abbreviation for High-Temperature Insulating refractory; seeINSULATING REFRACTORY.

HuIo System. A system for the handlingof building bricks from setting in the kilnto delivery at the building site. (Tradename: Van-Huet, Pannerden, Holland.)Humboldt Rotary Kiln. A kiln designedfor burning cement; the batch is fed tothe kiln as a suspension in hot gases withconsequent economy in fuelconsumption.Humidity Dryer. A dryer for clay-ware(particularly bricks) in which therelative humidity (r.h.) of theatmosphere in the dryer is controlled sothat the initial stages of drying takeplace at high r.h., this beingprogressively reduced as drying of theclay-ware proceeds.

Humper. A warped item of tablewarewhich rocks on its foot on a flat surface.(Cf. WHIRLER).Huntington Dresser. See STAR DRESSER.Hutch. Scottish term for a waggon ofabout Im3 capacity used for hauling clay.Hutchins Furnace. An electric arcfurnace for the fusion of refractorymaterials, e.g. alumina. The shell is atruncated cone (big-end-up) and thewater-cooled hearth is made from amixture of pitch and coke (O. Hutchins,US Pat, 1310 341, 15/7/19)HV. Symbol for VICKERS HARDNESS(q.v.).h,x diagram. A chart of enthalpy v.humidity. Points on this diagramcorrespond clearly to the continuouslychanging condition of the air in a dryer,and provide a clear way of displaying thechanges.Hydrargillite. An obsolescent name forGIBBSiTE (q.v.).Hydration. Dolomite and other lime-containing refractories are attacked byatmospheric moisture. To protect thembefore use, they may be metal-cased; tar-impregnated, wrapped in polythenesheeting etc.Hydration Tendency. The degree ofHYDRATION in a test sample of a basicrefractory exposed to moisture underspecified conditions of humidity,temperature and pressure. It is measuredby firing the hydrated sample to 10000Cand determining the percentage weightloss. B.S. 1902 Pt 3.14 specifies the test.ASTM specifies tests for the hydrationof granular dead-burned dolomite(C492); of magnesite or periclase grain(C544); for the hydration resistance ofbasic brick (C456) and for the hydrationresistance of pitch bearing basicrefractory brick (C620).Hydraulic Cement. A cement which setsand gains strength through chemical

action with water; such a cement will setunder water. PORTLAND CEMENT (q.v.)is a typical example.Hydraulic Mining. The method used towin china clay; a high-pressure (2 MPa)jet of water is aimed at the exposedvertical clay face and the clay is washeddown. The suspension is then pumped tosettling tanks where the impurities(chiefly mica) settle out. The purifiedsuspension of china clay is thenconcentrated, filtered, and dried.Hydraulic Press. A machine used for drypressing, or semi-dry pressing; thepressure (up to 100 MPa) is appliedhydraulically to the top, and sometimesalso to the bottom, mould-plate. Suchpresses are used, for example, in drypressing basic refractories.Hydraulic Refractory Cement. AREFRACTORY CEMENT (q.v.) containingaluminous hydraulic cement, e.g. CimentFondu, so that it sets at roomtemperature.Hydraulicking. Old term for HYDRAULICMINING (q.v.).Hydrite Process. In this process bricksare fired at 775°C in the presence ofwater. Gas fuel is burnt in steel tubes onthe sides of periodic kilns, in which lowquality clays may be fired more rapidlywithout fluorine emission.Hydrocasing. A form of kiln/dryerconstruction. The dryer and kiln are inthe same tunnel, made in steelprefabricated sections. A pool of waterruns the full length (c.lOOm) of the kiln/dryer. The kiln cars enter this water atthe entrance of the dryer, and a perfectseal against gas leakage is formed,enabling the kiln to operate at higher gaspressures and provide an even flow of airaround the setting (CERIC, Paris).Hydrogen-treating Process. A methodfor the preparation of sheet steel forvitreous enamelling by first driving

hydrogen into the surface of the steel(this is effected electrolytically) and thenremoving the hydrogen by immersion ofthe steel in boiling water. The processwas introduced by J. H. Healy and J. D.Sullivan (US Pat. 2 754 222,10/17/56).Hydrogenic Furnace. A hydrogenatmosphere pressure furnace.Hydrometer. A glass instrument, shapedrather like a fisherman's float, for thedetermination of the specific gravity of aliquid, e.g. of clay slip or of vitreous-enamel slip.Hydrostatic Pressing. See ISOSTATICPRESSING.Hydrothermal Preparation.Hydrothermal crystral growth takes placewhen an aqueous solution is held at highpressure and high temperature, with atemperature gradient along the container.A solute may be transported byconvection from the hotter region to thecooler, where the solution becomessupersaturated and the solute is depositedThe materials and solution conditions canbe chosen to promote chemical reactions.There are many types of suchhydrothermal processes, which may becombined with other ceramic processessuch as sintering, reaction sintering, hot-pressing, isostatic pressing etc.Hydroxyapatite. That variant of APATITE(q.v.) which contains the OH- hydroxylion.Hygrometer. An instrument formeasuring the relative humidity of air,e.g. in a dryer for ciayware.Hypersonic Flame Spraying (HCFS). Ahigh velocity chemical combustionprocess accelerates and melts a powderstream to 500 to lOOOm/s for sprayingcomposite powders.Hysil. Trade name: A borosilicate glassof high thermal endurance and chemicalresistance used for chemical ware.(Chance Bros., England.)

Hyslop Plasticity Diagram. A diagramrelating the extensibility (E) of a clay, asdetermined by a penetration method, toits softness (S); the relationship is of theform E = KSn

y where K and n areconstants. (J. F. Hyslop, Trans, BritCeram. Soc, 35, 247 1936.)Hysteresis. The degree of lag in thereaction of a material to a change in theconditions (of mechanical, electrical, ormagnetic stress) to which it is exposed.Ceramic ferro-electrics, for example,exhibit hysteresis when subjected to achanging external electric field;hysteresis is also shown by plastic claywhen it is stressed cyclically.IC Silicon Carbide. Abbreviation forImpregnated-Carbon Silicon Carbide; itcontains free carbon and silicon and thebulk density is comparatively low (2.60).ICP. Inductively Coupled Plasma. Anemission spectrometry technique for thechemical analysis of ceramics.ICTA. International Committee onThermal Analysis.Ice Colour. A relatively coarse (100mesh) flux used to give a decorativeeffect on glass-ware. The surface to bedecorated is coated with a tacky oil. Theflux is then applied and the ware is firedat a low temperature so that the grainsof flux remain discrete.IF. Indentation Fracture. See FRACTURE

TOUGHNESS TESTS.Ignition Arch. A refractory arch in aboiler furnace fitted with a mechanicalgrate; its purpose is to assist the ignitionof the fuel as the latter moves under thehot brickwork.IIIite. A group name for micaceous clayminerals of variable composition. Thename derives from the fact that it wasfrom Illinois (USA) clays and shales thatsamples were isolated by R. E. Grim, R.H. Bray, and W. F. Bradley (Amer.Mineral, 22, (7), 813,1937) who first

proposed this name. As there has beensome confusion as to the exact meaningof the term, the following statement inthe original paper should be noted: \ . .the term Mite . . . is not proposed as aspecific mineral name, but as a generalterm for the clay mineral constituent ofargillaceous sediments belonging to themica group.'IL/MA. Ignition-Loss/Moisture-Adsorption. The relationship betweenthese properties was proposed as asimple method for assessing the natureand proportion of the clay mineralpresent in clays by P. S. Keeling (Trans.6th. Int. Ceram. Congr., 195, 1958). Forthe purpose of this test, IL is taken asthe difference between the ignition lossunder oxidizing conditions at 10000C andat 375°C; MA is determined bysubjecting samples of dried clay to 75%R.H. at 25°C for 24h); this humidity isprovided by the atmosphere above asaturated solution of sodium chloride).Ilmavit. Trade-name. (VEB TechnischerGlas, Ilmenau). A machineable glassceramic. The material is 35% sodiumfluorphlogopite, and is crystallizeddirectly from the melt without furtherheat treatment. Its thermal expansion issimilar to that of iron alloys.Ilmcnite. Ferrous titanate, FeOTiO2;m.p. 1365°C. This mineral is theprincipal constituent of the heavyminerals in the beach sands of Australiaand elsewhere; it is thus the chief sourceof titania, which is used in the ceramicindustry as an opacifier and as aconstituent of some ceramic dielectrics.Image Furnace. Apparatus for theproduction of a very high temperature ina small space by focusing the radiationfrom the sun (SOLAR FURNACE) or froman electric arc (ARC-IMAGE FURNACE)by means of mirrors and/or lenses. Suchfurnaces have been used for the

preparation and study of some specialceramics.Image Gloss. The distinctness with whicha sharply outlined character is reflectedfrom the surface in question. Thisproperty is important in the selection ofvitreous-enamelled architectural panels,which should not reflect recognisableimages of neighbouring objects. A test isdescribed in ASTM - C540.Imbibition. The particular case ofabsorption or adsorption of a liquid by asolid in which the solid increases involume. A typical example is theswelling of Na-bentonite when it takesup water.Imbrex. See ITALIAN TILE.Imitation Porcelain. See SEMI-PORCELAIN.IMM Sieve. See under SIEVE; for meshsizes see Appendix E.Impact Box. A tile, clamped to an innerface of a 30mm cubic rotating steel box,is subjected to random impacts of 5mmand 8mm diameter steel balls containedin the box. Wear is assessed visually. Thetest, applied to unglazed floor tiles,quarries and brick pavers, is claimed tosimulate pitting attributed to steel-tippedstiletto heels.Impact Bruise. = PERCUSSION CONE(q.v.).Impact Mill. A crushing unit in which arapidly moving rotor projects thecharged material against steel plates;impact mills find use in the size-reduction of such materials as feldspar,perlite, etc. (cf. DISINTEGRATOR;

HAMMER MILL).Impactopus. A pulverised coal firingsystem (see OCTOPUS).Impact Resistance. The resistance of amaterial to impact. A test for thisproperty (which is clearly of importancein the assessment of tableware, forexample) must proceed by a series of

blows - usually delivered by a swingingpendulum - of increasing severity; themajor difficulties in the impact testing ofceramics are to produce homogeneoustest-pieces and to determine theproportion of the impact force causingfracture that is actually used in fracturingthe test-piece. In USA a standard impacttest for ceramic tableware is described inASTM - C368. B.S. 6206 is an impacttest for flat safety glass.Imperiale. A large wine bottle, 61 fortable wines, 4.51 for sparkling wines.Imperial Red. Red pigments based onferric oxide.Impervious. In the USA this word has adefined meaning (ASTM - C242) asapplied to ceramic ware, namely, thatdegree of vitrification shown bycomplete resistance to dye penetration;the term generally implies that the waterabsorption is zero, except for floor tilesand wall tiles which are considered to beimpervious provided that the waterabsorption does not exceed 0.5%.Impulse Burners. Burners for the feedingof fuel oil to a kiln. The oil, supplied athigh pressure in a ring-main, is injectedinto the kiln in metered quantities.Inamori Stones. Synthetic gemstonesmanufactured by Kyocera Corp, Japan.In-and-out Bond. Brickwork consistingof alternate courses of headers andstretchers.Inclination Flowmeter. Powder flowsfrom a funnel to form a cone on aninclined glass plate. The angle ofinclination is increased mechanically tothat value which causes gliding of thecone tip. The cotangent of that angle is anindex of the flowability of the powder{Powder Metallurgy Int. 19, (1), 40, 1987).Inclined Flow Test. A pellet of glaze isfired on a specially made plane of biscuitbody, supported at a fixed angle in thekiln. The distance the glaze flows down

the plane is a measure of its fluidity. (Cf.FUSION FLOW TEST FOR VITREOUS

ENAMELS.).

Inclusion. (1) A foreign atom or ion inthe crystal lattice.(2) A larger foreign particle in thematrix of the material. See also NON-METALLIC INCLUSION; STONE.Inclusion Pigment. See ENCAPSULATEDCOLOURS.

Incongruent Melting. A solid meltsincongruently if, at its melting point, itdissociates into a liquid and a solid ofdifferent composition; for exampleORTHOCLASE melts incongruently atabout 11700C to form LEUCITE and aliquid that is richer in silica.Increment. See PREFERRED INCREMENT.Indenting. In structural brickwork, theomission of a suitable series of bricks sothat recesses are left into which anyfuture work can be bonded.Indentation Fracture. See FRACTURE

TOUGHNESS TESTS.

Indentation Hardness. The values ofhardness obtained by using one of thevariety of test methods in which a hardprobe or indenter is pressed into thesurface to be tested. See VICKERS,KNOOP, BRiNELL hardness.Indentation Strength. See FRACTURETOUGHNESS TESTS.

Indialite. A modified form ofcoRDiERiTE with hexagonalstructure.Indian Red. A red ferric oxide pigmentmade by calcining ferrous sulphate.Indiana Method. A technique for thedetermination of the quantity ofentrained air in concrete on the basis ofthe difference in the unit weights of aconcrete sample with and without air.The name derives from the fact that air-entrained cement was first used to anyextent in Indiana, USA. (Proa A.S.T.M.,47, 865,1947.)

Indirect-arc Furnace. See underELECTRIC FURNACES FOR MELTING ANDREFINING METALS.Induction Furnace. See under ELECTRICFURNACES FOR MELTING AND REFININGMETALS.Induction Heating. The heating of anelectrically conducting material by theeffect of induced electric currents, whichmay be set up by a high-frequency fieldin a small object or a low-frequency fieldin a large object (as in a large inductionfurnace for steel melting). High-frequency heating has been proposed(Brit. Pat. 898 647,14/6/62) as a methodfor the firing of glaze on ceramic tiles.Inductively Coupled Plasma. Stable, hot(10 0000C) highly ionized gas 'flames'are produced by induction heating withan RF generator. Materials of highmelting points can be evaporated. Thetechnique can be used as the source for atype of sophisticated emissionspectrometer for chemical analysis of thevapourised material. It can also be usedas a synthesis technique for high purityultrafine particles, free of contaminationby any electrode materials. When liquidreactants are used, e.g. to produce oxidesfrom solutions of metal salts, thetechnique is known as spray ICP.Indumix. Trade-name. A kilnatmosphere control system developed byManfred Leisenberg KG, Laubach. Apressurised gas stream 6-10mm diameteris injected into a chamber with sideopenings through which the kilnatmosphere is sucked in on the injectorprinciple. In a variant, the VARIOMIXsystem, external air is also introduced, inamounts adequate for burning the gas.Industrial Floor Brick. See FLOOR

BRICK.Inertisation. Biscuit firing which drivesgases from the body, without closing thepores.

Inert Plasma Spraying (IPS). SeePLASMA SPRAYING.Infra-red Drying. Drying by exposure toinfra-red radiation from speciallydesigned electric lamps or gas burners.The process has found some applicationin the vitreous-enamel industry and inthe pottery industry.Infrasizer. An air elutriator for thefractionation of powders into sevengrades within the size range 100 mesh to7]um. It was designed by H. E. T.Haultain (Trans. Canadian Inst. Min.Met, 40, 229, 1937; Mine Quarry Engng.,13, 316, 1947).Infusorial Earth. An obsolete name forDIATOMITE (q.V.).Ingersoll Glarimeter. An instrumentdesigned primarily to measure the glossof paper; it has been used to evaluate theabrasion resistance of a glaze in terms ofloss of gloss after a specified degree ofabrasion. The apparatus was designed byL. R. Ingersoll (/. Opt. Soc. Amer., 5,213,1921).In-glaze Decoration. A method ofdecorating pottery; the decoration isapplied on the surface of the glaze,before the glost fire, so that it maturessimultaneously with the glaze. Suchdecoration can be applied by hand-painting, spraying, or silk screen.Inglis Equation. Relates the stress at thetip of an elliptical flaw in glass to theapplied stress, the flaw length and theradius of curvature of the crack tip.When the stress at the crack tip issufficient to overcome the strength of thechemical bonds there, fracture occurs.Long, sharp cracks produce higherstresses. See FRACTURE MECHANICS.Ingot Head Tile. See HOT TOPPING TILE.Ingot Mould. See MOULD BRICK; MOULDPLUG.

Initial Set. The time interval between theGAUGING (q.v.) of a hydraulic cement

and its partial loss of plasticity. In theVICAT'S NEEDLE (q.v.) test, the end ofthis period is defined as the time whenthe needle will no longer descendthrough the cement test block to within 5mm of the bottom. In B.S. 12, the testconditions are 14.4-17.8°C (58-64°F)and >90% r.h.; for normal cements theInitial Set must not be less than 30 min(the usual period is 1-2 h).Injection Moulding. A processsometimes adopted for the shaping ofnon-plastic ceramics, e.g. alumina. Aplasticizer such as polystyrene or phenolformaldehyde composition is mixed withthe ceramic powder and the batch is thenwarmed and injected into the die.Ink-Jet Printing. A printing process inwhich the ink is applied as a successionof sprayed drops. The drop sizes andspray velocity are determinedelectrostatically.Inside Colour. The reverse side or insidesurface of fired gold decoration on glass.Its appearance is a check on adequateventilation and proper firingtemperature.Instron. Trade-name. A range ofmachines for measuring mechanicalproperties at constant rates of strain.The loads and strain rates arecontrollable; cyclic fatigue testing ispossible; accessories are available to

allow tension, compressive and torsionaltesting of green and fired ceramics atambient and elevated temperatures.Insulating Refractory. A refractorymaterial having a low thermalconductivity and used for hot-faceinsulation in a furnace. Such productshave a porosity of 60-75%. If they aremade from refractory clay this highporosity is produced by theincorporation of a combustible in thebatch or, less commonly, by foaming orby chemical means. In the USA, ASTM- C155 classifies insulating refractories asshow in the table below.Insuloc. A system for protecting water-cooled pipes in steel reheating furnaces.An inner layer of refractory fibre iscovered by a tough outer skin ofinterlocking refractory tiles.Insweep. Term applied to the lower partof a glass container if the sides curveinward or taper towards the base.Intaglio. The decoration of glass-ware bycutting a pattern to a depth intermediatebetween that of deep cutting andengraving (The term Intaglio Printinghas been applied to the decoration ofpottery-ware by transfer-printing from acopper plate.)Integrated Thermal Process. A systemdeveloped in Italy for the firing of tilesby the kilnmaker Poppi and the tile

Insulating Refractories - Classification. ASTM C155Group Identi- Reheat Change not more than Bulk Density not greater thanficationGroup 16 15500F (845°C) 34 lb/ft3 (0.54 g/cm3)Group 20 19500F (10650C) 40 lb/ft3 (0.64 g/cm3)Group 23 22500F (12300C) 48 lb/ft3 (0.77 g/cm3)Group 26 25500F (14000C) 54 lb/ft3 (0.86 g/cm3)Group 28 27500F (15100C) 60 lb/ft3 (0.96 g/cm3)Group 30 29500F (16200C) 68 lb/ft3 (1.09 g/cm3)Group 32 31500F (17300C) 95 lb/ft3 (1.52 g/cm3)Group 33 32500F (17900C) 95 lb/ft3 (1.52 g/cm3)

manufacturer CISA. The tiles are heatedrapidly and uniformly by radiation fromplates below and above the tiles, whichare moved to and fro on rollers in thefiring zone. Single firing in 20 minutes ispossible, and it is easy to change todouble firing. The flexibility of thesystem allows a greater variety of moreartistic tiles to be fired. (Keram Z. 38,(10), 626,1986).Intercalary Decoration. A designtrapped between two layers of glass.Small pieces of gold foil, coloured glassetc. are placed on one surface, which isthen covered by the second layer of hotglass.Interlocking Tile. A large type of roofingtile having one or more longitudinalridges and depressions that interlockwith the complementary contour ofneighbouring tiles on the roof. Such tilesare commonly made in a REVOLVERPRESS (q.v.).Intermediate Crusher. A machine of atype suitable for size reduction fromabout 8 to 20 mesh, e.g. a pan mill orball mill (note, however, that a ball millcan more properly be used as a FINEGRINDER (q.v.)).Intermediate Piece. See MATCHINGPIECE.Intermittent Kiln or Periodic Kiln. Abatch-type kiln in which goods are set,fired, cooled, and then drawn. Theprincipal types in the ceramic industryare ROUND KILNS (or BEEHIVE KILNS),RECTANGULAR KILNS, BOTTLE OVENS,BOGIE KILNS and TOP-HAT KILNS. (Seeseparate entries under these headings).Intersection Scarp. The locus ofintersection of two portions of a crackwith each other.Interstitial. See CRYSTAL STRUCTURE.Interstop. Trade-name for a two-platerevolving SLIDING GATE VALVE (q.v.)developed by Stopinc AG.

Intumescence. The property of somesilicates, notably of PERLITE (q.v.), ofexpanding permanently, when heated, toform a completely vesicular structure; cf.BLOATING and EXFOLIATION.Inverse Spinel. See SPINEL.Inversion; Inversion Point. Aninstantaneous change in the crystallineform of a material when it is heated to atemperature above the INVERSIONPOINT; the change is reversed when thematerial is cooled below thistemperature. An example of importancein ceramics is the a <-> B quartz inversionat 573°C.Investment Casting. A process for thecasting of small metal components to aclose tolerance. In the usual process awax replica of the part to be cast iscoated ('invested') with refractorypowder, suitably bonded, and the wholeis then warmed (1500C) to melt out thewax - hence the alternative name Lost-wax Process; the refractory mould isthen fired at 1000-11000C. Therefractory used may be powderedsillimanite or alumina, or speciallyprepared cristobalite; the latter isparticularly used in the application of theprocess in dentistry. B.S 1902 Pt 10specifies methods for the determinationof resistance to deformation at elevatedtemperatures; permeability and standardair flow capacity at elevatedtemperatures; thermal profiledetermination, for refractories forinvestment casting shell mould systemsprefabricated brickwork, in whichreinforcement is provided by steel rodsrunning horizontally across perforationsin the blocks.Inwall. US term for the refractory liningof the STACK (q.v.) of a blast furnace.Iodoeosin Test or Mylius Test. Fordetermining the durability of opticalglass. The amount of free alkali in a

freshly fractured surface is determinedby means of iodoeosin; the surface isthen exposed to moist air at 18°C for 7days and the free alkali is againdetermined. Any increase in free alkali istaken as a measure of lack of durability;a decrease indicates stability. The test isnot valid for many modern opticalglasses. (F. Mylius, Z. Anorg. Chem.y 67,200,1910; Silikat Z, 1, 2, 25, 45,1913.)Ion Beam Machining. See ELECTRON

BEAM PERFORATION.

Ion Implantation. The introduction offoreign ions into solids, usingaccelerating energies in the range 20-500keV. It is a non-equilibrium process,useful for preparing metastable alloys orfor modifying suface properties such asfriction, wear and corrosion. It can beused to modify superconductivebehaviour.Ion Plating. A vapour phase is createdby evaporation, and transported througha gaseous glow discharge to thesubstrate. In reactive ion plating,metallic species interact with reactivegases to form oxides, nitrides orcarbides. Ion plated coatings tend tohave greater adherence than evaporatedor sputtered coatings.Ionic Conductor. A material in which thecharge carriers are ions rather thanelectrons or holes. Ionic conductors usuallyhave crystal structures containing channels,or planes through which cations can move.8-Al2O3 (NaAl11O17) is an ionicconductor, used as the electrolyte insodium-sulphur storage batteries. SeeELECTRICAL CONDUCTIVITY.

Ionic Exchange. The replacement of ionson the surface, or sometimes within thelattice, of materials such as clay. Theions become adsorbed to balance adeficiency of charge in the clay structure,e.g. in a montmorillonite in which someMg2+ has been replaced by Al3+, or to

satisfy broken bonds at the edges of theclay crystals. Ionic exchange capacity isgenerally expressed in milli-equivalentsper 100 g: typical values are: kaolinite,1-3; ball clay, 10-20; bentonite, 80-100.ASTM C837 tests the absorption ofmethylene blue dye by clays, a measureof the ion exchange capacity.Ipro Brick. An I-shaped clay pavingbrick designed for use in roadmaking,particularly on soils of poor bearingcapacity - as in Holland.IPS. Inert PLASMA SPRAYING (q.v.).Iridizing. The formation of a film ofmetal oxide on the surface of a ceramic,particularly of glass. The surface to betreated is heated and then exposed tothe vapour, or to atomized spray, of ametal salt. Such surface films may beapplied as decoration or to provide asurface that is electrically conducting,e.g. for anti-frosting windscreens.Irising. A surface fault, in the form ofstained patches, sometimes found on flatglass that has been stacked with surfacesin contact. The term originates from theinterference colours that oftenaccompany the fault. It is caused bymoisture. If the glass is annealed in anacid atmosphere and adequately washedirising is unlikely to occur; separation ofthe stacked sheets by paper also preventsthis trouble.Iron Modulus. The Al2O3^e2O3 ratio ina hydraulic cement. In portland cementthis modulus usually lies between 2 and 3.Iron Notch. Alternative name for theTAPHOLE (q.v.) of a blast furnace.Iron Ore Cement. See ERZ CEMENT.

Iron Oxide. See FERROUS OXIDE;

FERRIC OXIDE; MAGNETITE.

Iron Saffron. See Indian Red.Iron Spot. A dark, sometimes slaggy,spot on or in a refractory brick, resultingfrom a localized concentration offerruginous impurities; such spots can

cause carbon deposition, or evendisintegration of the brick, if the latter isexposed to CO attack at 400-5000C or tohydrocarbons at 800-9000C.Iron-Zirconium Pink. See ZIRCONIUM-I R O N PINK.

Ironing. A fault that may arise duringthe firing of decorated ware havingcobalt blue bands, etc.; the band appearsdull and may have a reddish scum causedby the crystallization of cobalt silicate.Ironstone China. See MASON'SIRONSTONE CHINA.Irregular. See MORPHOLOGY.Irridizing. US spelling of IRIDIZING (q.v.).Irwin Consistometer. A simple capillary-flow viscometer designed by J. T. Irwin(/. Amer. Ceram. Soc, 21, 66,1938) fortesting vitreous enamel slips. Twocapillaries are placed in the lower end ofa long wide-bore tube; both capillarieshave the same bore but one is twice aslong as the other. The wide outer tube isfilled with the slip to be tested and isthen allowed to discharge through thetwo capillaries into separate measuringcylinders. The rate of flow through eachcapillary can thus be calculated and acurve can be drawn from which both theyield value and mobility can be read.Irwin Slump Test. A works test forassessing the setting-up of vitreousenamel slips for spraying. It was firstdescribed by J. T. Irwin (Finish, p. 28,Sept. 1946) in the following words: 'Aground-coated plate is placed on a tableand a steel cylinder, 1 13/i6ths in. internaldiameter and 2Vi in. high, (46mm i.d. x63.5mm high) is placed on the plate. Thecylinder is filled with enamel to betested. The cylinder is then liftedvertically, with a rapid motion, by meansof a hook and cord attached to the top ofthe cylinder and passing over a pulley toa weight. When the weight is released,the cylinder is raised vertically. This

action results in a 'pancake' of enamelon the test plate. The diameter of this'pancake' is a function of the set orstiffness of the enamel slip.'IS. Indentation Strength. See FRACTURETOUGHNESS TESTS.IS Machine. The HARTFORD-EMPIREINDIVIDUAL SECTION MACHINE (q.V.).ISCC-NBS Colour System. A system forthe designation of a range of identifiablecolours used industrially, colours drawn upin USA by the Inter-Society Color Counciland the National Bureau of Standards. Forfull details see NBS Circular 553,1955,published jointly by the ISCC and theNBS (Now the National Institute ofStandards and Technology).ISO. International StandardsOrganisation, 1 Rue de Varembe,Geneva.Isoelectric Point. The pH at whichparticles in suspension carry zero netelectric charge.ISO-JET Burner. The burner has acombustion chamber with an aligned fuelnozzle at one end, and is arranged todirect a high velocity stream of gaseouscombustion products from its other end,producing suction in the firing chamberto improve kiln atmosphere circulation.Dilution air is introduced into this gasstream at an acute angle to the flow, toreduce the gas temperature and enhancethe suction effect. (Bickley furnaces Inc.Br.Pat 1461309).Isomorphous. Literally, having the sameshape. Isomorphs are differentcompounds with the same crystalstructure. In isomorphous substitution,one ion in the crystal structure isreplaced by a foreign ion, facilitated bythe crystal structures of the twocompounds being isomorphous. See alsoCRYSTAL STRUCTURE, POINT DEFECTS.Isostatic Pressing. The dry powder mixor preform to be pressed is put in a

flexible rubber or elastomer container,(often called the TOOLING) which is thenplaced in a container with hydraulic fluidand subjected to hydrostatic pressure,generally 70-140 MPa but for specialpurposes up to 6 GPa. With metaltooling the process can be used at hightemperatures. The merit of this processis the uniform manner in which pressureis applied over the whole surface,resulting in uniform density in theshaped component. Uniform non-directional objects or tubes can be madeby incorporating a central MANDRELL.In the WET BAG process the hydraulicfluid is water containing soluble oil.Small batches and large articles aremade. The automatic DRY BAG processis used to mass-produce small articlessuch as spark plug insulators. Thepressure medium is a gas. Isostaticpressing avoids problems of die-wallfriction but does not provide as accuratetolerances as die-pressing. The processwas invented by H. D. Madden (US Pat.1081 618, (1913).Isothermal Technique. A systematicmethod to determine optimumconditions for HOT PRESSING (q.v.). Aseries of hot pressings are conductedunder a set of different isothermalconditions, by heating the materialslowly to the required temperature (theisotherm), then applying pressure whichis maintained until densification iscomplete. The time to achieve a givendensity is plotted against thetemperature. Two straight lines appear,whose point of intersection gives theoptimum hot pressing conditions.Istra. Trade-name: a HIGH-ALUMINACEMENT (q.v.) made in Yugoslavia.Italian Red. One of the red ferric oxidepigments.Italian Tile. An alternative name forOLD ROMAN TILE (q.v.) The term is also

sometimes used erroneously, as asynonym of SPANISH TILE (q.v.).ITO Process. Soft-mud extruded largeblocks are set directly on to kiln cars.(Fuchs Ziegeleimaschinen GmbH, Austria).ITP Process. See INTEGRATEDTHERMAL PROCESS.

IUPAC Rules. The International Unionof Pure and applied Chemistry, 'How toname an Inorganic Substance' A guide tothe use of nomenclature of inorganicchemistry. Definitive Rules 1970,Pergamon Press 1977.Izod Test. A method for measuringimpact strength. The energy required tofracture a (usually notched) specimen iscalculated from the initial height of apendulum, and the height of the swingafter striking the specimen. (Cf. CHARPY

TEST, FRACTURE TOUGHNESS TESTS;

EDGE CHIPPING TEST.).

J c . Critical Current Density, abovewhich a material ceases to be aSUPERCONDUCTOR (q.V.).

J-based Fracture Testing. A method forapplying FRACTURE MECHANICS tocomposites. See also CRACK BRIDGING,and cf. R-CURVE. The crack openingdisplacement is related to the appliedstress by measuring the crack tip stressintensity and the J-integral. This is thesum of the energies needed to form a newcrack tip and to develop the fractureprocess zone. It depends on the specimengeometry and is found by measurementson two specimens with different cracklengths. (V.C. Li in 'Applications ofFracture Mechanics to CementitiousComposites' and (with others) in /. Amer.Ceram. Soc. Tl, 1994, pl553)Jack Arch. A sprung arch of bricksspecially shaped so that the outer surfaceof the arch is horizontal, the innersurface being either horizontal or archedwith a large radius. Also known as aFLAT ARCH.

Jack Bricks. Refractory bricks for theglass industry; they are perforated toaccommodate the prongs of a fork truckand used beneath a newly-set pot.Jacking. Using hydraulic or screw jacks tosecure the brickwork when constructingrefractory rings. Jacks may be usedradially, to hold the partly-completed ringagainst the casing. Spreader jacks areused circumferentially in the KEY ZONEto tighten the ring before insertingclosure bricks and key plates.Jam-socket Machine. A machine forshaping the sockets in clay sewer-pipes.The pipes are extruded plain, cut tolength and fed to the jam-socketmachine in which a ram, having theinternal profile of the socket, is forcedinto the end of the pipe. The machinewas introduced by Pacific Clay ProductsCo., Los Angeles, USA {Brick ClayRecord, 124, No. 4, 55, 1954).Jamb. The brickwork, or other material,forming one of the vertical sides of anopening in a wall of a building orfurnace, e.g. a doorjamb.Jamb Brick. See BULLNOSE, but inparticular, specially-shaped refractorybricks to form the portal around theexternal door of a coke-oven.Jamb Wall. See BREAST WALL.Japanese Red. Alternative name forTHIVIER EARTH (q.V.).Jar Mill. A small BALL MILL (q.v.), therevolving cylinder being a vitreousceramic jar; such mills are used in thegrinding of small batches of ceramiccolours and vitreous enamels.Jardiniere Glaze. A former type ofunfritted lead glaze containing PbO, K2O,CaO, ZnO, Al2O3 and SiO2. There weresoft (cone 02) and hard (cone 4) types.Jasper Ware. A fine coloured stonewarefirst made in 1774 by Josiah Wedgwoodwho referred to it as being 'peculiarly fitfor cameos, portraits and all subjects in

bas relief; as the ground may be of anycolour throughout, and the raised figuresof a pure white'. The body containsbarytes and the colours include bluelavender, and sage green (typically bluewith white bas relief). A quoted bodycomposition is: 26% ball clay, 18% chinaclay, 11% flint, 45% barytes.Jaw Crusher. A primary crusher for hardrocks, e.g. the quartzite used in makingsilica refractories. The crusher has twoinclined jaws, one or both being actuatedby a reciprocating motion so that thecharge is repeatedly 'nipped' betweenthe jaws. For different types see underBLAKE, DODGE and SINGLE-TOGGLE.Jena Glass. Various types of glass (theJena chemically resistant and opticalglasses are particularly well known)made by Jenaer Glaswerk Schott andGen., Jena, Thuringia, Germany.Jeroboam. A 4-quart wine bottle.Jersey Fireclay Brick. A US siliceousrefractory.Jersey Stone. A CHINA STONE (q.v.)occurring in Jersey, C.I. A statedcomposition is (%): SiO2, 77; Al2O3, 12;CaO, 0.5; Fe2O3, 0.5; K2O, 4.5 ; Na2O, 3.Jet Dryer. A type of dryer in which theware is dried chiefly by the action of jets ofwarm air directed over the surfaces of theware; the principle has been successfullyapplied in the drying of pottery.Jet-enamelled Ware. A type of 18thcentury porcelain decorated with blackon-glaze transfers; (cf. JET WARE).Jet Impact Mill. See FLUID-ENERGY MILL.Jet-Kote. A HYPERSONIC FLAMESPRAYING technique, (q.v.).Jet Ware. Pottery-ware, chiefly tea-pots,having a red clay body and a black,manganese-type, glaze; (cf. JET-ENAMELLED WARE).Jeweller's Enamel. A vitreous enamelfusing at a low temperature and suitablefor application to copper, silver, and

other nonferrous metals in theproduction of jewelry or badges.Because the principal European centrefor enamelled jewelry was Limoges,France, the chief types have Frenchnames: BASSE-TAILLE, CHAMPLEVE,CLOISONNE, PLiouE-A-JOUR (for detailssee under each name).Jigger; Jiggering. A jigger is a machinefor the shaping (jiggering) of pottery-ware by means of a tool fixed at a shortdistance from the surface of a plastermould that is mechanically rotated onthe head of a vertical spindle. In themaking of flatware a suitable quantity ofprepared body from the pug is firstshaped into a disk by a batting-outmachine placed alongside the jigger; insemi-automatic jiggers the movements ofthe two machines are co-ordinated. Thedisk of body is placed by hand on aplaster mould which has been fixed onthe head of the vertical spindle of thejigger; the upper surface of the mouldhas the contour required in the uppersurface of the finished ware. The mouldis then set in motion by a clutchmechanism and a tool having the profileof the bottom of the ware is broughtdown on the plastic body which is thenforced to take the required shapebetween mould and tool. The essentiallysimilar process applied to the shaping ofhollow-ware, e.g. cups, is known asJOLLEYiNG. In both processes water isnecessary as a lubricant.Jiggerman. A workman in a glassworkswhose job is to return SCULLS (q.v.) tothe charging end of a glass-tank furnace,(cf. JiGGERER, the man who operates aJIGGER (q.v.) in a pottery.)Jiki. Japanese name for porcelain.Jockey Pot. A POT (q.v.) for glassmaking ofsuch size and shape that it can be supportedin the furnace by two other pots.Joggle. See NATCH.

Joining. The term is particularly appliedto the technology required to bondsimilar or dissimilar materials to formcomponents for mechanical or electricalengineering applications. It is especiallyused of joining ceramics to metals inmachine parts.Joint Line. A visible line on imperfectglass-ware reproducing the line betweenseparate parts of the mould in which theglass was made. Also known as aPARTING LINE, MATCH MARK, MITRE

SEAM MOULD MARK Or SEAM.

Jolley; Jolleying. Terms applied tothe shaping of hollow-ware in thesame senses as JIGGER (q.v.) andJIGGERING are applied to the shaping offlat-ware.Jolt Moulding. A process sometimesused for the shaping of refractory blocks.A mould is charged with prepared batchwhich is then consolidated by jolting themould mechanically; top pressure maysimultaneously be applied via a mouldplate, cf. TAMPING.Journey. The period of emptying of aglass-pot before it is again filled withbatch; the term is also applied to a shiftin which an agreed number of pieces ofglass-ware are made.Jumbo.( I ) A type Of TRANSFER LADLE (q.V.)for the conveyance of molten iron.(2) A hollow clay building block of atype made in USA, its size is 11 Vi x IVix 3V2 in. (292 x 191 x 89mm) and it hastwo large CELLS (q.v.) and a IV -̂irt.(38mm) SHELL (q.v.); the weight is 15-16Ib. (6.7-7.1kg).(3) Roofing tiles (claimed to be theworld's largest) made by Tuiles deLimoux are 53cm x 36cm.Jump. The slight rise in temperaturewhen a kiln is closed.Jumpers. See POPPERS.KIC - See STRESS INTENSITY FACTOR.

Kady Mill. Trade-name: a high-speeddispersion unit consisting principally of abottom-feeding propeller, a maindispersion head containing a rotor and astator, and an upper shroud andpropeller. (Steele & Cowlishaw Ltd.,Stoke-on-Trent, England.)Kaki. An opaque stoneware glaze, inwhich a surface layer of iron oxidecrystal produces a reddish brown colour.Kaldo Process. A process for theproduction of steel by the oxygen-blowing of molten iron in a rotating,slightly inclined vessel; the latter isusually lined with tarred-dolomiterefractories. The name is derived fromthe first letters of the name of the in-ventor, Professor Railing, and of theDomnarvet Steelworks, Sweden, wherethe process was first used.Kaliophilite. K2O.Al2O3.2SiO2.Transforms at about 14000C into anorthorhombic phase that melts at approx.18000C. Crystals of this mineral havebeen found in fireclay refractories thathave been attacked by potash vapour.Kalopor. A hollow clay block, with thevoids filled with polystyrene. The geo-metry of the leaves is designed tomaximize thermal insulation, and toprovide tongue and groove connectionsfor accurate bricklaying. (KLB VertriebsGmbH, Germany).Kalsilite. K2O.Al2O3.2SiO2 togetherwith a small amount of Na2O. Thismineral is sometimes formed when alkalivapour attacks fireclay refractories.Kandite. Group name for the kaoliniteminerals, i.e. kaolinite, nacrite, dickiteand halloysite. (Clay Minerals Bull., 2,294, 1955.)Kankar. An Indian word for limenodules in clay soils.Kanthal. High temperature resistancewire and tape for heaters (A.B. Kanthal,Sweden).

Kaolin. Name derived from ChineseKao-Lin, a high ridge where this white-firing clay was first discovered. SeeCHINA CLAY.Kaoline. Trade-name. A fired china clayinsulator (Richard, Thomas & Baldwins,Staffs.).Kaolinite. The typical clay mineral ofchina clay and most fireclays; itscomposition is Al2O3.2SiO2.2H2O. Theunit lattice consists of one layer oftetrahedral SiO4 groups and one layer ofoctahedral Al(OH)6 groups; a kaolinitecrystal (which is hexagonal) consists of anumber of these alternate layers.Disorder can, and normally does, occurin the stacking of these layers so that theceramic properties of a kaolinitic claymay vary. When heated, kaolinite loseswater over the range 450-6000C; theD.T.A. endothermic peak is at 5800C.When fired at temperatures above11000C mullite is formed.Kaolinization. The geological breakdownof alumino-silicate rocks, usually but notnecessarily of the feldspathic type, toproduce kaolinite.Kaowool. Trade-name. Aluminosilicateceramic fibres. (Morganite CeramicFibres, Neston; originally Babcock &Wilcox, USA).Kassel Brown, A substance containingabout 90% humus compounds and only1% ash from the region of Kassel,Germany; the German name is Kasseler-braun. Its use as a protective colloid in thedeflocculation of slip was the subject ofGerman Patent 201,987 4/8/06.Kassel Kiln. An old type of intermittent,rectangular, fuel-fired kiln whichdiminished in cross-section towards theend leading to the chimney; it originatedin the Kassel district of Germany.Kavalier Glass. An early type ofchemically resistant glass characterized byits high potash content; it was first made

by F. Kavalier at Sazava, Czechoslovakia,in 1837, and the Kavalier Glassworks stilloperates on the same site.Kaye Disk Centrifuge. A device forparticle-size analysis (1-50 |im) bymeans of a beam of light passed througha liquid suspension of the particles whilethe suspension is rotated in a transparentdisk-shaped centrifuge. The prototypewas designed by B. H. Kaye (Brit. Pat,895,222, 2/5/62); now made by CoulterElectronics Ltd., St. Albans, England.Keatite. A form of silica resulting fromthe crystallization of amorphousprecipitated silica at 380-5850C andwater pressures of 350-1250 bars; sp. gr.2.50. Named from its discoverer, P. P.Keat (Science, 120, 328, 1954).Keene's Cement or Keene's Plaster. Amixture of gypsum, that has beencalcined at a dull red heat, and 0.5-1%of an accelerator usually potash alum orK2SO4. Also known as PARIAN CEMENT

Or PARIAN PLASTER.

KeeJ. The refractory-lined lower sectionof the barrel of a HOT METAL MIXERwhich is always in contact with the hotmetal.Kek Mill. Trade-name: (I)A pin-diskmill depending for its action on high-speed centrifugal force; (2) a beater millin which a four-armed 'beater' revolveshorizontally at high speed betweenupper and lower serrated disks. (KekLtd., Manchester, England.)Keller System. A method of handlingbricks to and from a chamber dryer; thebricks are placed on STILLAGES (q.v.)which are lifted by a FINGER-CAR (q.v.),carried into the dryer and set down onledges projecting from the walls of thedrying chamber; when dry the bricks arecarried in the same manner to the kiln.The system was patented by Carl Kellerof Laggenbeck, Westphalia, Germany, in1894. Since that date the firm has

introduced much additional equipmentto advance the degree of mechanizationin the heavy-clay industry.Kelly Ball Test. An on-site method forassessing the consistency of freshly mixedconcrete in terms of the depth ofpenetration, under its own weight of 30 Ib(13.5kg), of a metal hemisphere, 152 mmdia. (J. W. Kelly and M. Polivka, ProaAmer. Concrete Inst., 51, 881,1955.)Kelly Sedimentation Tube. A device formeasuring the rate of settling of particlesfrom a suspension, and hence forparticle-size analysis. To the lower partof a sedimentation vessel, a capillarytube is joined and is bent through 90° sothat it is vertical to a level a little abovethat of the suspension in thesedimentation vessel; above this level thecapillary tube is inclined at a small angleto the horizontal. As particles settle inthe main vessel the position of themeniscus in the capillary tube movesdownward, affording a means ofassessing the rate of settling of theparticles. This apparatus, designed by W.J. Kelly (Industr. Engng. Chem., 16, 928,1924), has been used for the particle-sizedetermination of clays.Kelvin Equation. An equation useful insorption studies for the calculation of poresize and pore size distribution. It is:rRTln(p/po) = -2yV cos 0where p is the equilibrium vapour pressureof a curved surface (as in a capillary orpore) of radius r; po is the equilibriumpressure of the same liquid on a planesurface; R is the gas constant; T is theabsolute temperature; y is the surfacetension; V the molar volume; 9 the contactangle of the adsorbate. When the Kelvinequation is satisfied, vapour will condenseinto pores of radius r. (W.T. Thompson,Phil. Mag. 42,1871, p.448).Kelvin Temperature Scale (K). TheCentigrade scale displaced downwards so

that Absolute Zero (-273.16) is 0 K; 00C= 273.16 K; etc. Once known as theABSOLUTE TEMPERATURE,0AbS.KER System. A coding system fortechnical ceramics proposed by H. W.Hennicke, Keram Z 22, (9), 544,1970.Oxides are coded KER OX followed by anumber; silicon carbides are KER SIC, etc.Keradur. Tradename. A resin compositefor moulds. (H & E Borgardts,Germany).Keramzit. Trade-name: a Russianexpanded-clay aggregateKeraflamm. A process for flame glazingthe surface of lightweight concrete.(K. Bergmann, Ziegelindustrie (9), 330,1975).Keralloy. A glass-ceramic coated metalalloy, for use as a substrate for thick-filmcircuitry. (Ceramic Developments Ltd.,Nuneaton.).KeraLum. Trade-name. A range ofglasses, some of which are luminescent,others phosphorescent. (Degussa).Keram. Trade-name. A plaster made byH & E Borgardts, Germany.Keram'ik. Trade-name. Oxide basedtool-tips for metal cutting. (Raybestos-Manhatten Inc, USA).Keramiton. Trade-name. A ready-to-useceramic modelling material, which airdries, or may be fired. (Faber-CastellGmbH).Keratin. The protein in hair. An extractobtained by the treatment of hair withcaustic soda is used, under the namekeratin, as a retarder to control the rateof setting of plaster - in making potterymoulds for example.Kerb. See also curb bend. In the UKwall-tile industry the accepted spelling is'curb'. A kerb is a refractory course laidto protect a right-angled joint betweentwo materials.Kerlane. Trade-name. (French)Aluminosilicate ceramic fibres.

Kerner Equation. See THERMALEXPANSION OF COMPOSITES.Kerr Effect and Kerr Constant. Thebirefringence produced in glass, or otherisotropic material, by an electric field;the effect was discovered in 1875 by J.Kerr, a British physicist. The AbsoluteKerr Constant has been defined as thebirefringence produced by unit potentialdifference.Kervit Tiles. Trade-name derived from thewords 'Keramik ' and 'VitrunV, denotingthe mixed nature of the material which ismade by casting a ceramic slip containingabout 30% of ground glass. The slip ispoured on to a refractory former that iscoated with a separating material, e.g. amixture of bentonite and limestone; thetiles, while on the formers, are fired at950-10000C then trimmed. The processwas first used in Italy; it was introducedinto England in 1960. (M. Korach and DalBorgo, Brit. Pat., 468,010; 10/6/36.)Kessler Abrasion Tester. Apparatusdesigned by the National Bureau ofStandards, USA, for the determinationof the abrasion resistance of floor tilesand quarries. A notched steel wheel ismounted on an overhanging frame sothat a definite and constantweight bears on the test-piece as thewheel revolves; No. 60 artificialcorundum is fed at a specified ratebetween the wheel and the test-piece,which is mounted in an inclined position.(D. W. Kessler, Nat. Bur. Stand. Tech.News Bull, 34,159, 1950.)Ketteler-Helmholz Formula. A formulafor the optical dispersion of a glass:

rfi = nj+ T^MJP-VJr*where n is the refractive index of theglass for a wavelength X, H00 is the indexfor an infinitely long wavelength, and Xm

are the wavelengths of the absorptionbands for each of which there is anempirical constant Mnr

Kettle. (1) A heated iron or steel vesselin which gypsum is partially dehydratedto form plaster-of-paris.(2) A vessel for containing molten glass.Keuper Marl. A Triassic clay much usedfor brickmaking in the E. and W.Midlands, the W. of England, and theCardiff area. This type of brick-clayusually contains a considerable amountof lime and iron oxide; magnesiumcarbonate and gypsum may also bepresent in significant quantities. KeuperMarl is of variegated colour, hence thename, from German Koper (a spottedtype of fabric).Key Brick. A brick with opposite sidefaces inclined towards each other so that itfits the apex of an arch, see Fig. 1, p39. Infurnace construction such bricks are alsosometimes referred to as BULLHEADS,CUPOLA BRICKS Or CROWN BRICKS.Keybrick System. A system ofbricklaying in which plastic pins hold thebricks in place, while mortar is pouredaround them. The bricks are made toclose dimensional tolerances byrepressing extruded blanks.Key-in. To undercut all or part of thesurrounding sound refractory to providea physical key for the repair to amonolithic lining.Keying. Ensuring a tight fit in arch orring construction.Key-plates. Steel plates, 3mm thick inthe UK, driven into one or more radialjoints in a ring of bricks to tighten andsecure it.Key Zone. The final sector installed in aring of bricks, where fitting adjustmentsare made, using closure bricks and keyplates.KHN. KNOOP HARDNESS NUMBER (q.V.).Kibbler Rolls. Toothed steel rolls of atype frequently used in the crushing andgrinding of brick clays; from an old wordKibble - to grind.

Kick's Law. A law relating to the energyconsumed in the crushing and grindingof materials. The energy required toproduce identical changes ofconfiguration in geometrically similarparticles of the same composition variesas the reduction in the volume or weightof the particles. (F. Kick, Das Gesetz derProportionalen Widerstand und SeineAnwendung, Leipzig, 1885.)Kidney. See POTTER'S HORN.Kieselguhr. German name, formerlyused also in Britain but now obsolete,for DIATOMITE (q.V.).Killas. Term used in the Cornish china-clay mines for the altered schistose orhornfelsic rocks in contact with thegranite and often considerably modifiedby emanations from the latter.Kilmo. Computer software forcalculating heat flow through kiln walls,and heat flow and air flow in the kiln.(Donald Shelley, UK).Kiln. A high-temperature installationused for firing ceramic ware or forcalcining or sintering. Kilns for firingceramic ware are of three main types:INTERMITTENT, ANNULAR and TUNNEL;for calcining and sintering: SHAFT KILNS,ROTARY KILNS and MULTIPLE-HEARTHFURNACES are used (see entries undereach of these headings).Kiln Car. A car for the support of warein a tunnel kiln or bogie kiln; the car hasfour wheels and runs on rails. In a tunnelkiln, through which a number of thesecars are moved end-to-end, the metalundercarriages are protected from thehot kiln gases by continuous sand-seals.The car deck is constructed of refractoryand heat-insulating material.Kiln Furniture. General term for thepieces of refractory material used for thesupport of pottery-ware during kilnfiring; since the use of clean fuels andelectricity has made possible the

open-setting of ware, a multiplicity ofrefractory shapes has been introducedfor this purpose. For individual items seeCOVER, CRANK, DOT, DUMP, PILLAR,PIN, PIP, POST (or PROP), PRINTER'S BIT,RING, SADDLE, SAGGAR, SETTER, SPUR,STILT, THIMBLE; see also Fig. 4. As wellas fireclay refractory, recrystallizedsilicon carbide and nickel metal havebeen used.Kiln Scum or Kiln White. See SCUM.Kimmeridge Clay. A clay of the UpperJurassic system used as a raw materialfor building bricks in Dorset and Oxford;the lower beds often contain gypsum andlime, the upper beds are shaly andbituminous.King Closer. A brick cut diagonally, sothat one end is full-width, the other halfwidth (50cm).King's Blue. A blue pigment, beingmixed cobalt oxide and alumina.Kink. A type of WAVINESS (q.v.) whichintersects the edge of the wavy surface.(ASTM F109)Kiss Marks. Local term for discolouredareas on the faces of bricks thathave been in contact during the kilnfiring.Klebe Hammer. A device for thecompaction of test-pieces of cement ormortar prior to the determination ofmechanical strength; a weight fallingfrom a fixed height on the test-piecemould ensures compaction understandardized conditions.Klein Turbidimeter. Apparatus designedby A. Klein (Proc. A.S.T.M., 34, Pt. 2,303,1934) for the determination of thespecific surface of portland cement. Thesample is suspended in castor oil in adish and the turbidity is measuredphotoelectrically. Because of the highviscosity of the suspending liquid theparticles do not settle significantly. Thespecific surface is deduced from the

Fig. 4 See KILN FURNITURE(The relative sizes are not to scale)

turbidity by means of a calibrationcurve.Kling. A type of TRANSFER LADLE (q.v.)for the conveyance of molten iron.Klingenberg Clay. A refractory claycontaining (unfired) 32-37% Al2O3;PCE. 32-34. From Klingenberg-am-MainS.W. Germany.Klinker Brick. A type of building brick,which may be either of engineering-brickor facing-brick quality, made inGermany and Holland from clays thatgenerally have a long vitrification range.The bricks have low water absorptionand high crushing strength The colourmay be yellow, red or variegated.

Post or uprightCrank

CrankPin

Saddle Saddle Thimble

Stilt Spur

Klompje Brick. A miniature facing brickof a type used in S. Africa for decorativeconstruction.Knock-in Mould. A mould with a loosetop die, for hand or light machineforming.Knocking. The accidental removal,during the period between glazeapplication and the glost firing, of apatch of glaze from the surface ofceramic ware.Knockings. US term for the oversizematerial remaining after ceramic slip hasbeen screened; the UK word isKNOTTINGS.

Knock-out. See BUTTON.Knoop Hardness. A pyramidal-diamondindentation test. The result is expressedin kg/mm2, the applied load beingindicated, eg. Knoop 100 or KlOO; a USabbreviation is KHN(Knoop HardnessNumber) The test was introduced by F.Knoop, C G Peters and W. B. Emerson(/. Res. Nat. Bur. Stand., 23, 39,1939).ASTM C849 describes its application toceramic whitewares; C730 to glass.Knot. A fault, in glass, consisting of asmall inclusion of glass having a differentcomposition (and so revealed by itsdifferent refractive index) from that ofthe surrounding glass.Knottings. UK term for the oversizematerial remaining after a ceramic sliphas been screened; the US word isKNOCKINGS.

Knotts. Term sometimes applied to theLower Oxford Clay used forbrickmaking in the Peterboroughdistrict, England.Knuckling. Shaping a thrown pot withthe knuckles of the hand.Kohn Pipette. Apparatus for particle-size analysis by sedimentation; it hasbeen used more particularly in the studyof clay soils. (M. Kohn, Z. Pflanz. Dung.,All, 50,1928.)

Kolene Process. Trade-name: anelectrolytic salt-bath treatment of sheet-steel before it is enamelled; (KoleneCorp., Detroit, USA).Kopecky Elutriator. An elutriatorconsisting of three cylinders of differentdiameters, it has been used for theparticle-size analysis of clays. (Tonind.Ztg., 42, 629,1918.)Kopp's Rule. The SPECIFIC HEAT of acompound is approximately equal to thesum of the heat capacities of itsconstituent elements.Koranna Stone. Pyrophyllite (q.v.).Kovar. A FeNiCo alloy, whose thermalexpansion curve against temperatureintersects that of alumina at 6200C. If thedifferential stresses during cooling canbe withstood, a glass-metal seal made at6200C will be stress-free at roomtemperature. Kovar is thus valuable forglass-metal and alumina metal seals.Kozeny Equation. An equation relatingthe rate of flow (q) of a fluid of viscosityJLt through a packed bed of particles ofdepth L and area A, under a pressuredifference AP, the specific surface of theparticles being S and the voids per unitweight being V:q = K. AVAILS2. AP/LThis equation, due to J. Kozeny (Sitz.Akad. Wiss. Wien., Math., Naturw. Kl,136, 271, 1927) forms a basis for thedetermination of the specific surface of apowdered ceramic material by the gaspermeability method.Kramers-Kronig Dispersion Relations.Describe the scattering of light by smallparticles, based on fundamentalconsiderations of causality.Kreuger's Ratio. A ratio claimed by H.Kreuger (Trans. Roy. Swedish Inst., ScLRes. No. 24,1923) to be a criterion of thefrost resistance of clay building bricks; itis the ratio of the percentage waterabsorption after 4 days' immersion in

cold water to the total water absorptioncalculated from the specific gravity (cf.SATURATION COEFFICIENT).Kreutzer Roof. A design for a furnaceroof, particularly for open-hearth steelfurnaces. Its feature is the system oftransverse and longitudinal ribs, whichdivide the exterior of the roof into box-like compartments. The design waspatented by C Kreutzer in Germany in1948.Kronig-Penny Model. A simplified, one-dimensional model of the crystal lattice,giving the essentials of the behaviour ofelectrons in a periodic potential. See alsoCRYSTAL STRUCTURE, ELECTRICALCONDUCTIVITY.Krupp-Renn Process. A rotary-kilnprocess, developed at Essen, Germany,in 1932-33, for the direct extraction ofnodules (luppen) of iron from low-gradeores. Refractories in the 'luppen zone',nearest to the discharge end of the kilnare exposed to the most severeconditions: attack by a ferruginous slagat about 13000C. Dense siliceousfirebricks and high-alumina refractorieshave been used. The term derives fromthe German word Renn, meaning'direct'.Kryptol Furnace. The term used on theContinent and in Russia for a granular-carbon resistance furnace; the namederives from the German company,Kryptol Gesselschaft, that originally sup-plied the carbon granules.K-S Test. The Kolmogorov-Smirnovgoodness of fit test assesses the ability ofa probability distribution calculated fromWEiBULL STATISTICS (q.v.) to fit theexperimental data. It and the A-D(Anderson-Darling) test (which is moresensitive to discrepancies at low and highprobabilities of failure) are used as partof the CARES (q.v.) computer programfor failure prediction. For a discussion of

the K-S and A-D tests, see R.B.D'Agostino and M.A. Stephens,Goodness of Fit Techniques, Dekker1986, p97-193. An additional test ofgoodness of fit is given by the Kanofsky-Srinivasan 90% confidence bands.(Biometrika 59 (3) 1972 p623.).Kubelka-Munk Theory. This theorydescribes the diffusion of light through atranslucent medium in terms of ascattering coefficient S and an absorptioncoefficient K. Equations relate thesecoefficients to the measured values ofreflectance and transmission, suitablycorrected for internal and externalsurface reflections when applied toceramics. (P. Kubeika and F. Munk, Z.Techn. Physik 12, 593, 1931. applied toceramics by A. Dinsdale, Am.Ceram.Soc. Bull 55, 993,1976).Kuhl Cement. A hydraulic cementintroduced by H. Kuhl (Brit. Pat.,231,535; 31/3/25). It contains less SiO2

but more Al2O3 and Fe2O (about 7% ofeach) than does portland cement; itsstrength properties are similar to thoseof rapid-hardening portland cement.Also known as BAUXITLAND CEMENT.Kurlbaum Method. A method for thedetermination of flame temperature bymeans of an optical pyrometer (F.Kurlbaum, Phys. Z, 3,187,1902).Kyanite. A mineral having the samecomposition (Al2SiO5) as sillimanite andandalusite, but with different physicalproperties. The chief sources areVirginia and S Carolina (USA), andIndia. When fired, kyanite breaks downat 13000C into mullite and cristobalitewith a volume expansion of about 10%;it is therefore calcined before use.Calcined kyanite is used in makingaluminous refractories.Laboratory Glassware. Chemicalresistance tests are specified in B.S. 3473.There are other standards for particular

products (e.g. B.S. 2586 for pHelectrodes; B.S. 572 and 2761 for conicaland spherical joints.Laboratory Porcelain. Qualityrequirements and testing methods arelaid down in B.S 914.Labradorite. A lime-soda FELDSPAR(q.v.). A typical composition is (%):SiO2, 55; Al2O3, 30; CaO, 12; Na2O, 0.5;H2O etc, 2.5.Labyrinth Factor. A correction to beapplied in calculating the gaspermeability of a porous refractory, toallow for the diminished air flow becausepores are neither circular nor straight.The labyrinth factor is the ratio of thatpart of the total porosity whichcontributes to the air-flow, to the totalporosity.Laced Valley. A form of roof tilingdesigned to cover a re-entrant corner ofa roof. The courses of tiling meet andinterlace to provide efficient drainage.Lacustrine Clay. A clay that was formedby deposition on the bed of a lake; thelacustrine clays of the Vale of York,England for example, are used inbrickmakingLadd Circular Tunnel Kiln. A ROTARY-HEARTH KILN (q.v.) of a type introducedin 1941 by the Ladd Engineering Co.,USA (see Brick Clay Record, 99, No 2,42, 1941).Ladder. A horizontal support for glasstubing that is to be cut into lengths (seealso WASHBOARD).Ladle Brick. A refractory brick ofsuitable shape and properties for use inthe lining of a ladle; unless otherwisestated it is assumed that a ladle for thecasting of steel is implied. Ladle bricksare almost invariably made of groggedfireclay; the features required are goodshape, uniform size, low porosity and, ifpossible, a permanent expansion whenexposed to high temperature. In the

USA three qualities of ladle brick arespecified in ASTM-C435.Ladle Shroud. A refractory tubeattached to the teeming system of aladle, extending below the liquid surfacein the tundish, to protect the steel streamfrom the atmosphere.Ladling. An obsolescent term, describingthe hot repair of small diameter rotarykilns by pouring a clay-based sloppymortar onto the repair site from a ladleintroduced through the kiln hood.Lagoon, Lagoon Settling. A largeshallow pond into which suspendedsolids are allowed to settle after aprocess, for recovery of the waste, orprevention of discharge of harmfuleffluent.Laitance. The layer of water sometimesformed on the upper surface of freshlyplaced concrete as a result of theaggregate settling by sedimentation (seealso BLEEDING).Lambert's Law. For a TRANSLUCENT(q.v.) body, I=I0C-*1' where I is theintensity of the transmitted light; I0 theintensity of the incident light; JLL is aconstant, the linear absorptioncoefficient of the material and t is itsthickness.Laminate. A material in sheet formconsisting of several different layersunited by a ceramic bond. Ceramiclaminates have been made to providelightweight heat insulation. Refractorylaminates have been used as bats onwhich to fire electroceramics andferrites; these laminates consist of asilicon carbide core with outer layers ofalumina or mullite.Laminated Glass. Safety glass madefrom alternating and adherent layers ofglass and organic plastics, the glass layersbeing outermost; if broken, thefragments of glass are held in position bythe plastics interlayer. For some

purposes the interlayer may be made ofglass fibre. Other laminated glassware ismade by simultaneously forming twoglasses with similar viscosities at theforming temperature. Thermometers aremade by laminating a white OPAL GLASS(q.v.) stripe into a clear glass tube.Corning Glass developed a specialvertical turret machine which forms glasstableware with an outer skin of lowerthermal expansion, laminated to an innercore glass. When the ware cools, thesurface is placed in compression,improving strength and thermal shockresistance.Lamination. (1) Textural inhomogeneityin clayware resulting from the shapingprocess and particularly common inproducts that have been extruded. Instructural clay products, lamination is asource of mechanical weakness and acause of poor frost-resistance; inrefractory products lamination mayreduce resistance to slag attack and tothermal shock.(2) An elongated excrescence, or line ofsuch excrescences, in vitreousenamelware; the fault is usually amanifestation of swelling in the metal.Lamotte Comparator. A pH meter of atype recommended by the US PorcelainEnamel Institute for use in thedetermination of the acidity or alkalinityof PICKLING (q.v.) solutions. (LamotteChemical Products Co., Baltimore,USA.)Lamp-blown. Glass-ware shaped bymeans of an oxy-gas or air-gas burner;glass tubing or rod is the usual startingmaterial.Lancashire Kiln. A type of HOFFMANNKILN (q.v.) large wickets facilitate settingand drawing.Lancaster Mixer. Trade-name: Acounter-current pan-type mixer. (PoseyIron Works Inc., Lancaster, Pa., USA.)

Land-drain Pipe. See FIELD-DRAIN PIPE.Lander. See LAUNDER.Lance. (1) A refractory tube for theinjection of gases into a melt.(2) = STRIATiON (q.v.) in fractography.Langmuir's Adsorption Isotherm. SeeADSORPTION.

Lanthanum Boride. LaB6; m.p. 21000C;sp. gr. 4.7; thermal expansion (25-10000C), 5.7 x 1(HLanthanum Carbide. LaC2 exists invarious forms: the tetragonal room-temperature form changes to hexagonalat intermediate temperatures; at 17500C,through reaction with excess carbon, acubic phase is produced.Lanthanum Oxide. La2O3; m.p. approx.22000C; sp. gr. 6.51; thermal expansion(25-10000C) 12 x 10-6. A rare earthsometimes used in special optical glasses.Lanthanum Titanates. Two compoundshave been reported: LaTi2O3 andLa2Ti2O9; the former has a PEROVSKITE(q.v.) structure and can be synthesizedby heating a mixture of La2O3 and Ti2O3

at 12000C in a vacuum.Lanxide Process. The directed oxidationof molten metal precursors, injected intoa mass of filler. (Lanxide, Newark,Delaware, USA. See Ceram. Eng. ScLProc. 8 (7/8), 879, 1987).Lap. (1) A faulty surface on glass-warecaused by a fold in the glass.(2) A rotating disk, normally horizontal,carrying abrasive grain or powder andused for the finishing of work-pieces.(3) The amount by which a roofing tileoverlaps the course next but one below it.Laporite. Trade-name for synthetichectorite (q.v.) (originally made by theFuller's Earth Union, which became partof the Laporte Group.)Large Nine-inch Brick;. US term for abrick 9 x 6-3A x 3 in. or 9 x 6-3A x 21A in.Larnite. One of the crystalline forms ofCALCIUM ORTHOSILICATE (q.V.).

Laser. A device for producing lightamplification by stimulated emission ofradiation. The atoms of various materialswill absorb light and remain for quitelong periods in a metastable 'excitedstate'. The emission of a few photonswill 'stimulate' or induce the emission ofothers so that all the excited atomsreturn together to their ground stateenergy. The light may be emitted as avery short pulse (ruby laser) or as acontinuous beam (helium/neon ororganic excimer ultraviolet laser). Thisradiation is of high intensity, of veryspecific wavelength (monochromatic)and unlike ordinary light, very coherent- having a constant phase relation. Theseproperties allow lasers to be used totransmit information along OPTICALFIBRES (q.v.) to be used in measuringequipment based on interference anddiffraction effects, such as rangefindersand PARTICLE SIZE ANALYSIS; to heatmaterials to high temperatures in LASERABLATION, powder preparation or inLASER MACHINING.

Laser Ablation. The formation ofsamples of fine powders by burning themfrom a solid surface using a laser.Laser Beam Machining. A machiningprocess in which material is removed bymelting or vaporization with highenergy focussed LASER beams. Veryprecise localised heating is possible, bywhich means, for example, fine holesmay be drilled in highly refractorymaterials.Laser Decoration. Glass surfaces may beetched or engraved using a focussedLASER (q.v.) beam. The appropriatepattern may be produced by coveringareas with a metal mask; by a vectormethod, with linear movement of thebeam controlled by a computer program;by raster scanning. The beam must bemodulated to produce a series of points

rather than a continuous melted line,which would lead to cracking.Laser Particle Size Analysis. The preciseand constant wavelength and coherentphase relationships in LASER (q.v.)beams are valuable in particle-sizeanaylsis. Techniques include those basedon diffraction, and on laser Dopplereffect measurement of the velocities offalling particles, in which a system of'beats' is established between theunreflected beam and the beam reflectedfrom the falling particles, to measure thefrequency difference and hence theSEDIMENTATION (q.v.) velocity.Lateral Crack. A crack beneath andparallel to a glass surface, producedduring the unloading of contact with ahard, sharp object.Laterite. Material rich in alumina and/oriron oxide; it is formed by the tropicalweathering, in situ of appropriate silicaterocks. The most aluminous laterites areknown as BAUXITE (q.v.).Lath. See CLAY LATH.Lathe. A machine for turning unfiredhollow-ware, e.g. cups or vases.Latorex. A building material made ofLATERITE (q.v.) and a bond, withoutfiring.Lattice Brick. A hollow building brick,or block, in which the cells form apattern of open lozenges; such bricks areclaimed to have a high heat-insulatingvalue because of the extended path ofany heat flow through the solid material.Lattice Colour. Ceramic colours in whichthe CHROMOPHORE (q.v.) or colouringatom forms part of the crystal lattice.(Cf. ENCAPSULATED COLOURS).

Lattice Constant, Lattice Vector. SeeCRYSTAL STRUCTURE.

Launder or Lander. An inclined channel,lined with refractory material, for theconveyance of molten steel from thefurnace tap-hole to a ladle.

Lavaflame. A flame gunning system forthe repair of coke-oven walls (NipponSteel Corp., Japan.Lawn. Term used in the British potteryindustry for a fine-mesh screen or sieve.In the past, makers of these lawns' gavethem somewhat arbitrary numbers; theyare now largely replaced by meshesconforming to British Standards.Lazy Slurry. A dilatant body whichremains fluid when still or slowly stirred,but solidifies if stirred rapidly. Itcomprises about 100 parts of precipitatedcalcium carbonate (depending on theparticle size); 10 parts of 5% ZnNO3; 20parts 5% Calgon; 40 parts water.L-D Process. A process for theproduction of steel by the oxygen-blowing of molten iron held in a staticvertical vessel. The latter is lined withtarred or fired dolomite refractories;dead-burned magnesite is alsosometimes added to the batch. Theprocess was first used in 1952, at Linz,Austria, and 'L-D' stands for LinzerDusenverfahren, i.e. Linz Nozzle Process(not Linz-Donawitz, as is commonlybelieved).Lea and Nurse Permeability Apparatus.A device for the determination of thespecific surface of a powder bymeasurement of the permeability to airof a prepared bed of the sample; thecalculation is based on the CARMANEQUATION (q.v.). (F. M. Lea and R. W.Nurse, J. Soc. Chem. Ind., 58, 277, 1939.)Leaching. In particular the process ofremoving soluble constituents from heattreated glasses, using hot dilute acids, toproduce POROUS GLASS (q.v.),Lead Antimonate (Naples Yellow). Thiscompound, generally used in conjunctionwith tin oxide or zinc oxide, gives a goodonglaze yellow for pottery decoration; itis also used, with a lead borosilicate flux,as a vitreous enamel colour.

Lead Bisilicate. See LEAD SILICATE.Lead Chromate. The basic chromate,PbO. PbCrO4, is normally used inceramics. If the firing temperature is low,it can be used to produce coral reds inpottery glazes; in glassmaking itproduces a deep green.Lead Crystal Glass. A CRYSTAL GLASS(q.v.) specified in B.S. 3828 as containing>24% PbO; cf. FULL LEAD CRYSTALGLASS.

Lead Niobate. Pb(NbO3)2 a ferroelectriccompound having properties that makeit useful in high-temperature transducersand in sensing devices. The Curietemperature is 5700C.Lead Oxide. The more common leadoxides are litharge (PbO, m.p. 886°C)and red lead or minium (Pb3O4). Theseoxides are important constituents ofheavy glassware, enamels, and somepottery glazes; because the oxides arepoisonous, it is normal (in the UKcompulsory) to form an insoluble leadsilicate frit and to employ this non-toxicmaterial as a source of lead for ceramicglazes.Lead Poisoning. In the UK, leadpoisoning has been virtually eliminatedfrom the pottery, glass, and vitreous-enamel industries by successively morestringent factory regulations. The currentregulations for the UK pottery industryare the 'Control of Lead at WorkRegulations 1980' and the Totteries etc.(Modifications) Regulations'.Lead Silicate. A material obtained byfritting lead oxide with silica in variousratios. The usual ratio approximates toPbO.2SiO2 and a frit of this compositionis known as lead bisilicate; a specification(Trans. Brit. Ceram. Soc, 50, 255, 1951)is 63-66% PbO, 2-3.5% Al2O3, and PbO+ SiO2 + Al2O3 to exceed 98%. A LEADSOLUBILITY TEST (q.v.) is also specified.The bisilicate is used in pottery glazes,

enamels, etc. Tribasic lead silicate,3PbO-SiO2, finds some use in makinglead glasses. There is also a so-calledlead monosilicate with the approximateformula PbO.0.7SiO2.Lead Solubility Test. The (British)Tottery (Health and Welfare) SpecialRegulations, 1947 and 1950' defined thistest, as applied to the specification of aLow Solubility Glaze as follows: 'Aweighed quantity of the material whichhas been dried at 10O0C and thoroughlymixed is continuously shaken for 1 h, atthe common temperature, with 1000times its weight of an aqueous solutionof HCl containing 0.25% by wt of HCl.This solution is thereafter allowed tostand for 1 h and then filtered. The leadsalt contained in the clear filtrate is thenprecipitated as PbS and weighed asPbSO4.' The American test (ASTM -C555) exposes the glazed ware to aceticacid ( 1 : 20) at 600C for 30 min. (Seealso LOW-SOLUBILITY GLAZE).Lead Stannate. PbSnO3: up to 5% of thismaterial is sometimes added to bariumtitanate ceramics to reduce theirtendency to depolarize when used aspiezoelectrics.Lead Tantalate. PbTa2O6; a ferroelectriccompound of interest as an electro-ceramic. The Curie temperature is 2600C.Lead Titanate. PbTiO3: added in smallamounts to barium titanate ceramics toimprove their piezoelectric behaviour; acomplex lead titanate-zirconate body(P.Z.T.) finds use as a ceramiccomponent in piezoelectric transducers.The Curie temperature is 4900C.Lead Zirconate. PbZrO3; a ferroelectricmaterial. It is also used in lead titanate-zirconate (P.Z.T.) piezoelectric ceramics.Leaded Glass. Windows made fromsmall pieces of glass which are held inposition by strips of lead, H- orU-shaped in section.

Leadless Glaze. In the UK this is definedin the 'Potteries etc (Modifications)Regulations 1990 (S.I. 305)'. A glazewhich does not contain more than 1% ofits dry weight of a lead compoundcalculated as PbO. Under currentenvironmental pressures to reduce theuse of lead, bismuth glaze and colourflux systems are being actively studied.Lean Clay. A clay of low plasticity; theadjective 'lean' is also applied to a bodyof low plasticity.Lean Mix. (1) Fuel with a highproportion of combustion air.(2) Concrete with low cement content.Leather-hard. A term for clayware thathas been partially dried; at this stage ofdrying, the shrinkage has been largelycompleted.LECA. Abbreviation for LIGHTWEIGHT

EXPANDED CLAY AGGREGATE (q.V.).Le Chatelier Soundness Test. Aprocedure for assessing any expansion ofhydraulic cement caused by the presenceof excess lime, magnesia or sulphates.The gauged cement is put into a splitbrass cylinder 30 mm i.d., to which areattached two needles 156 mm long fromthe centre-line of the mould, one needleon each side of the split in the mould.The cement is allowed to set for 24 himmersed in water at 15-18°C; thedistance between the ends of the needlesis then measured. The mould is immersedin water and boiled for 1 h. When it hascooled, the distance between the ends ofthe needles is again measured. Thedifference between the first and secondreadings should not exceed 10 mm. Thetest is included in B.S. 12.Ledge Rock. US term for GANISTER(q.v.) occurring in solid rock formations,as distinct from FLOE ROCK (q.v.).Lee Board. See under HACK.Leer. The original form of the wordLEHR (q.V.).

Lehr. A heated chamber for annealingglass-ware; usually tunnel-shaped, theware passing through on a conveyor.The spelling lehr originated in USA atthe end of the 19th century; the olderform - leer - first appeared in anEnglish text of 1662. The origin of theword is obscure.Leighton Buzzard Sand. An importantsource of sand from the LowerGreensand deposits of Bedfordshire,England. The sand is high in silica andwell graded; it is used as a refractoryfoundry sand and as a standard sand formixing with portland cement for testingaccording to B.S. 12.Lens-fronted Tubing. Tubing for liquid-in-glass thermometers made in such away as to magnify the width of thecolumn of liquid.Lepidolite. A lithium mineral,approximating to LiKAlF2Si3O4; sp. gr.2.9; m.p. 11700C. The largest deposits arein Rhodesia but it also occurs in USA;the average Li2O content is about 4%.Lepidolite is a source of Li for specialglasses, pottery bodies and glazes, andvitreous enamels; account must be takenof its F content.Lepol Kiln. See ACL KILN.Leptize. To disintegrate a material, inthe dry state, into very fine particles byimpact, at least 50% of the product is<50[im and at least 1% is 2fxm. The termwas introduced by J. G. Bennett, M.Pirani, and M. W. Thring (Brit. Pat.549,142, 9/11/42); it has not beengenerally adopted.Lessing Rings. A particular shape forchemical stoneware tower fillings.Leucite. K2O.Al2O3.4SiO2; there are twoforms stable above and below 6200Crespectively; sometimes formed whenalkali attacks fireclay refractories, as in ablast furnace stack.Lew Board. See under HACK.

LG Process. The large grain process forseawater magnesia. Greater density andgrain size is achieved by using tube filterpresses to dewater the slurry to theoptimum 75% solids content. Theproduct can be directly dead-burned.(Refract J. May/June, 1976, pl3).Lias Clay. Clay of variable composition,usually calcareous occurring in theJurassic System. In Britain it is used to alimited extent in brickmaking, e.g. inNorthamptonshire.Libbey-Owens Process. See COLBURN

PROCESS.Libo. Trade-name; a lightweight buildingmaterial made from very fine sand andlime (Nederlands-BelgischeMaatschappij voor LichteBouwproducten, Gorinchem, Holland).Liesegang Rings. The stratification ofprecipitated material formed when onereactant diffuses into another. Liesegangrings can be seen in minerals such asagate.Lift. A fault in vitreous enamelware, arelatively large area of enamel comingfrom the metal; the fault is also knownas PEELING. The cause may beinadequate cleaning of the base metal ora defective ground-coat.Ligand Field Theory. A theory concernedwith the changes in electronic energylevels of ions, especially of transitionelement ions, which occur when otherions or polar groups (ligands) are broughtinto their immediate neighbourhood.Variations in the environment of the ion,e.g. in the nature of the ligands or thesymmetry of their arrangement, causevariations in the spacings of the energylevels. This forms the basis of the modernexplanation of the colours of crystals andof glasses.Light. (1) As applied to optical glass theterm means that the glass has a relativelylow refractive index.

(2) When applied to part of a glasscontainer this word means that that partis too thin; e.g. Light Shoulder.Light-extinction Method. SeeTURBIDIMETER.Light Magnesia. A form of magnesiumoxide normally made by extraction fromsea-water (see SEA-WATER MAGNESIA);the precipitated hydrate is subsequentlypurified by conversion to the carbonatewhich is then calcined at approx. 8000C.The bulk density is 0.1. On exposure tothe air it takes up water and CO2 toform a basic carbonate. Light magnesiafinds use as a heat insulator and as asource of magnesia in various chemicalprocesses.Lightweight Expanded Clay Aggregate.A bloated clay aggregate made by thesudden heating of suitable clays either ina rotary kiln (the original method usedin Denmark in 1939) or on a sinter-hearth. It is used as an aggregate formaking lightweight concrete. B.S. 3797specifies appropriate materials andproperties for lightweight aggregates,structural concrete and concrete blocks.The US specification is ASTM C331.Lignosulphonate. See SULPHITE LYE.Lime. CaO; m.p. 2615°C; sp. gr. 3.3;thermal expansion (0-10000C), 13.5 x10"6. Added as WHITING (q.v.) to somepottery bodies and glazes, and ascrushed limestone (CaCO3) ormagnesian limestone to most glassbatches. Limestone is a majorconstituent of the batch used to makePortland cement clinker.Lime Blowing. The falling away of smallpieces from the face of a clay buildingbrick as a result of the expansion(following hydration and carbonation bythe atmosphere) of nodules of limepresent in the fired brick. Some brick-clays contain nodules of calcite (CaCO3)which are converted into CaO during the

kiln firing; these nodules can berendered innocuous by fine grinding andharder firing. A cure that is more of anexpedient is DOCKING (q.v.).Lime Refractory. Because of itsabundance and high m.p.(2615°C), limewould be an attractive basic refractorybut for its ready hydration andcarbonation when exposed to the air.There has been much research onmethods of stabilization, but the onlyaccepted use of lime as a refractory hasbeen as a container material for themelting of the platinum metals.Lime Saturation Value. The ratio of theactual lime content of a hydrauliccement to that calculated from anequation deduced as representing theamount of lime combined as silicate,aluminate and ferrite. Several suchequations have been proposed; all areempirical.Lime-slag Cement. Alternative name forSLAG CEMENT (q.V.).Limestone. A hard rock consisting ofcalcium carbonate, CaCO3. It is used asa source of lime in cement manufactureand in glass-making; for the latter usesee B.S. 3108 'Limestone for colourlessglasses'.Limit State Design. Structures reachtheir limit state when they become unfitfor use, either by collapse or by reachingtheir serviceability limit. Attempts tocalculate load-bearing capacity andmaximum loads as precisely as possible,and then choose a safety factor in designso that the former is appreciably greaterthan the latter, are replaced in limit statedesign by a design philosophy in whichthe arbitrary safety factor is replaced byan estimate of the strength for which theprobability of failure does not exceedsome acceptably low value. Limit statedesign is now applicable to brickmasonry structures.

Linde Flame Plating. See FLAMEPLATING.Lindemann Glass. A lithium berylliumborate glass that is highly transparent toX-rays. It is made from a batch consistingof 10 parts Li2B2O7, 2 parts BeO and 3parts B2O This glass is difficult to shapeand is of low chemical durability. (C. L.Lindemann and F. A. Lindemann, Z.Roentgenkunde, 13,141,1911.)Lindemann-Danielson Test. SeeDANIELSON-LINDEMANN TEST.Line Defect. See CRYSTAL STRUCTURE.Line Reversal Method. See SODIUM-L I N E REVERSAL METHOD.Liner Plates. Vitrified clay units shapedin the arc of a circle, used as a protectiveinternal lining for pipes, culverts andother structures. They usually havetenon ribs on their backs to key themfirmly to the structure to be protected.ASTM C479 refers.Lining. See BANDING.Linhay. Cornish name for a storage shedfor china clay.Linseis Plastometer. A device designedby M. Linseis for the evaluation of theplasticity of clay on the basis of twoparameters: cohesion (measured astensile strength) and the capacity forrelative movement of the clay particleswithout rupture. The apparatus is madeby Netzsch Bros., SeIb, Germany.Lintel or Mantel. The metal supportingstructure that takes the weight of therefractories and casing of the stack of ablast furnace.Liparite. A term that has been used forrocks of various kinds but, in Europe, ithas usually referred to a volcanic rock ofthe rhyolite type. The name derives fromthe Lipari Islands, off the N. coast ofSicily, where the rock in questionconsists chiefly of feldspars and quartz.Italian and Japanese liparites have beenused as fluxes in porcelain manufacture.

Liquid Gold. See BRIGHT GOLD.Liquid-liquid Opals. See OPAL GLASS.Liquid-phase Sintering. A form ofSINTERING in which a liquid phase isformed, and viscous flow and particlesliding leads to initial shrinkage,followed by a stage in which capillaryforces draw the liquid to solid graincontact points which dissolve. Somematerial diffuses to free surfaces where itprecipitates, reducing the distancesbetween particle centres. If there isinsufficient liquid phase to fill the pores(cf VITRIFICATION), final shrinkage mustbe by solid-state processes. Additives areused to produce liquid phases incovalently bonded ceramics which areotherwise nearly impossible to sinter. Inmany electronic ceramics the controlledboundary phases liquefy during firing.Liquid Pressure Forming. Metal matrixcomposites are made by filling a cavitywith a fibre pre-form, evacuating andrefilling with molten metal underpressure. (Cray Advanced Materials,Yeovil. Engineering 222 (11) 643, 1987).Liquid Shear Plane. See ZETA POTENTIAL.Liquidus. The line on a binaryequilibrium diagram (e.g. Fig 5. p230)showing the temperature at which anymixture of the two components, whenunder conditions of chemicalequilibrium, becomes completely liquid:conversely, the liquidus shows thetemperature at which a liquid of a givencomposition begins to precipitate solidmaterial. In a ternary, i.e. three-component, system, the liquidus isrepresented by a curved surface.Lisicon. The compound Li14Zn(GeO4)4,a fast ion conductor (q.v.).Litharge. Lead monoxide, PbO. See

LEAD OXIDE.Lithium Carbonate. Li2CO3; used as asource of Li2O in vitreous enamel fritsand in glazes.

Lithium Minerals. See AMBLYGONITE,EUCRYPTITE, LEPIDOLITE, PETALITE,SPODUMENE.Lithium Niobate. LiNbO3; a ferroelectricelectroceramic having the ilmenitestructure.Lithium Silicate Glasses. Li2SiO3 can beprecipitated from lithium silicatephotosensitive glasses under the actionof light and heat. The precipitatedcrystals are much more soluble in 10%HCl than is the glass. After dissolvingout the Li2SiO3, X-ray or ultravioletirradiation, followed by heat treatment,produces a non-porous glass-ceramicwithout distortion, with 1% shrinkage,and with higher strength and electricalresistivity than the original glass, usefulfor high temperature (5000C) printedcircuit substrates and dielectrics.Lithium Tantalate. LiTaO3; aferroelectric compound of potentialvalue as a special electroceramic. TheCurie temperature is above 3500C.Lithium Titanate. A compoundsometimes used as a flux in titanatebodies and in white cover-coats invitreous enamelling. It is alsocharacterized by very high thermalexpansion: 19.5 x IQ-* (25-7000C).Lithium Zirconate. Sometimes used as aflux in more refractory zirconate bodiesof the type used as electroceramics.Lithographic Decal. A transfer whosedesign is applied by dusting pigments onto varnished areas of the backing paper.See DECAL.

Lithography (UK); Decalcomania(USA). A method used for thedecoration of pottery by means oftransfers. A special paper is used but theceramic colours cannot be printeddirectly and the actual printing is done invarnish and the colour then dusted on.The Litho or Decal (to use the commoncontractions of these words) is placed

coloured-side down on the sized ware,rubbed firmly on. and the paper thensponged off.Lithophane. A decorative type oftranslucent pottery which when viewedby transmitted light, exhibits a scene orportrait that is present in low relief onthe ware. The process originated atMeissen, Germany, in 1828; examples ofthe ware were also produced in Englandduring the 19th century.Litre-weight Test. A works' test for theroutine control of the firing of portlandcement clinker; it was introduced by W.Anselm (Zement, 25, 633,1936).Littler's Blue. A royal blue firstproduced in about 1750 by WilliamLittler of Longton Hall, Stoke-on-Trent,by staining white slip with cobalt oxide,applying the slip to pottery-ware, firing,and salt-glazing.Littleton Softening Point. SeeSOFTENING POINT.

Live-hole. A flue left in a CLAMP (q.v.)and filled with brushwood to start thefiring process.Liver. A vitreous enamel fault defined inASTM-C286 as: 'In dry-processenamelling, a defect characterized by awave-like form of abnormally thickenamel'.Liver Spotting. See MOTTLING (of silicarefractories).Livering. A general term coveringcurious faults in casting slip which maydevelop if the slip is allowed to stand;the cause is lack of control in theDEFLOCCULATION (q.V.)

Livesite. A disordered kaolinite,particularly as found in some micaceousfireclays. The term is now little used; itwas proposed by K. Carr, R. W.Grimshaw and A. L. Roberts (Trans.Brit Ceram. Soc, 51, 339, 1952).Load. The weight of glass produced by aglass-making furnace in a given time,

usually 24 h. Known in USA (and alsoless commonly in UK) as PULL; otheralternative terms are DRAW andOUTPUT.

Load-bearing Brickwork. Brick masonryof controlled construction and calculatedstrength, for high-rise buildings orengineered structures such as bridges.Load-bearing Tile. US term for a hollowfired-clay building block designed tocarry superimposed loads.Loading. Choking of the pores in theface of an abrasive wheel with debrisfrom the workpiece that is being ground.LOF-Colburn Process. (LOF = Libbey-Owens-Ford Glass Co. See underCOLBURN PROCESS.

L.O.I. Abbreviation sometimes used forLOSS ON IGNITION (q.V.).

London Clay. A tertiary clay used inmaking building bricks in Surrey,Berkshire, Essex, Suffolk, Dorset,Wiltshire, and Hampshire.London Sink. A domestic or industrialsink with no overflow; the top edge isplain (cf. BELFAST SINK and EDINBURGHSINK).London Stock Brick. See STOCK BRICK.Long Glass. Glass that is slow-setting.Longitudinal-arch Kiln. An ANNULARKILN (q.v.) in which the axis of thearched roof, on both sides of the centre-line of the kiln, is parallel to the lengthof the kiln (cf. TRANSVERSE-ARCHKILN). Kilns of this type were much usedin the firing of building bricks.Loo Board. See under HACK.Looping or Loops. See CURTAINS.Los Angeles Test. The HARDNESS andABRASION RESISTANCE of concreteaggregate is assessed by tumbling astandard sample in a standard ball-millfor a specified time.Loss on Ignition. The loss in weight of asample of material expressed as apercentage of its dry weight, when the

sample is heated under specifiedconditions. In the testing of clays andsimilar materials, the temperatureemployed is 1050 ± 500C, in the testingof frits, the temperature must be belowthe fusion point and below thetemperature at which there is loss byvolatilization*Lost-wax Process. See INVESTMENT

CASTING.

Low Cement Castable. Alumina andaluminosilicate castable refractoriescontaining hydraulic setting cement andwhich have a total lime (CaO) content ofgreater than 1.0 to 2.5% on a calcinedbasis. Ultra-low cement castables have alime content from 0.2 to 1.0% (ASTMC401-91).Low-duty Fireclay Brick. Defined inASTM - C27 as a fireclay refractoryhaving a P.C.E. 15 and a modulus ofrupture 600 p.s.i. (4.2 MNm-2)Low-frequency Induction Furnace. Seeunder ELECTRIC FURNACES FORMELTING AND REFINING METALS.

Low-heat Cement. Hydraulic cementcompounded so as to evolve less heatduring setting than does normal portlandcement. This feature is important whenlarge volumes of concrete are placed, asin dams. It is achieved by reducing theproportions of 3CaCSiO2 and 3CaO.Al2O3. For specification see B.S. 1370.Low-heat rejection diesel. SeeADIABATIC DIESEL.

Low-solubility Glaze. The Potteries etc(Modifications) Regulations 1990 (S.I.305) define this as a glaze which does notyield to dilute HCl more than 5% of itsdry weight of a soluble lead compound,when determined in accordance with anapproved method; see LEAD SOLUBILITYTEST (q.v.). for the original approvalmethod.Low Thermal Mass Kiln. A design ofkiln requiring relatively little heat input

per degree of temperature increase. Thedesign was made practical by replacingconventional refractories with ceramicfibre hot-face lining; one-high firingwhich reduced kiln dimensions, andgeneral lightweight (often prefabricated)construction. As well as general fueleconomy, such kilns are suited to rapidfiring and flexible production schedules.LO-X. Ceramics with negativecoefficients of thermal expansion,produced by Lockheed, California.(1970).L.P.G. Abbreviation for LiquefiedPetroleum Gas, (propane or butane).LSP. Liquid Stabilised Plasma torch forthermally sprayed coatings.LTM Kiln. See Low Thermal Mass Kiln.Lubber's Process. This early process forthe manufacture of sheet glassmechanized the hand cylinder methodfor BROAD GLASS (q.v.) A blow pipewith a large flanged metal disc, or 'bait',was lowered into a pool of molten glass.The bait was then raised and air blownthrough the pipe to blow a glass cylinderof the required length. This was severedat the bottom, turned sideways, split inhalf and flattened. Sheets 3ft x 30ft (1 x10m) long were acheived (The AmericanWindow Glass Co. 1903).Lucalox. Trade-name: a translucent,pure, polycrystalline alumina made byGeneral Electric Co., Cleveland, Ohio,USA. The translucency results from theabsence of micropores. Because thecrystals are directly bonded to oneanother, without either matrix or poresbetween the crystal boundaries, themechanical strength is very high:transverse strength, 350 MNm-2;modulus of elasticity, 400 GNm-2.Ludwig's Chart. A diagram proposed byT. Ludwig (Tonind. Ztg., 28, 773, 1904)to relate the refractoriness of a fireclayto its composition, which is first

recalculated to a molecular formula inwhich Al2O3 is unity, i.e.JtRO-Al2O3^SiO2. In the chart, x isplotted as ordinate and y as abscissa; aseries of diagonal lines indicatescompositions of equal refractoriness.The diagram is inevitably a roughapproximation only.Luerkens Equations. Equationsdeveloped by J.K. Beddow {Advances inCeramics VoI 21,1987) to describe theshapes of particles by Fourier analysis.Application of the calculus of variationsleads to a Fourier series in the1-dimensional case; and to Fourier seriesmultiplied by a Bessel function or by anAssociated Legendre Polynomial in the2- and 3- dimensional cases respectively.See also MORPHOLOGY; SHAPE FACTOR.Lug. See SPACER LUG.Liihr Filter. Dust-removal equipment inwhich the dusty air is drawn through acontinuously-moving belt of filter cloth(H. Ltihr, Stadthagen, Germany).Lumenized. Lenses coated with MgF2.(Trade-name - Kodak Ltd., Kingsway,London).Luminous Wall Firing. Term sometimesused in USA for kiln or furnace-firing bySURFACE COMBUSTION (q.V.)Lumnite Cement. Trade-name: a HIGH-ALUMINA CEMENT (q.v.) made byUniversal Atlas Cement Division of U.S.Steel Corp., New York.Lump. (I)A heap of unmelted batchfloating on the molten glass in a tankfurnace.(2) The most defective saleable pottery-ware remaining after the sorting process;Cf. FIRSTS, SECONDS.(3) A fault in vitreous enamelware in theform of a small excrescence, Vi-1A in.(12-3 mm) diam.; it is often caused bydripping of the spray gun.Lump Man. A workman in a glassworkswhose job is to observe and control any

lumps of floating batch in a glass-tankfurnace.Lunden Conductive Tile Flooring. Amethod of using ceramic tiles in an ANTI-STATIC (q.v.) floor: electrically-conducting'dots' of metal, or of special ceramicmaterial that has been made conductingby loading the body with carbon, areinterspersed among the normal tiles. Themethod was devised by S. E. Lunden, aCalifornian architect, in 1950.Lurgi Process (for CementManufacture). A method for theproduction of hydraulic cement bysintering the charge on a grate.Lustre. A form of metallic decoration onpottery or glass introduced in the MiddleEast before AD 900. Lustres for bothmaterials can be made from metallicresinates, e.g. of Cu, Mn, or Co, in asolvent. Lustres are formed underreducing conditions achieved by thepresence of reducing agents in the lustrecomposition and/or by adjustment of thekiln atmosphere. Lustre finishes can alsobe produced on vitreous enamelware,particularly cast iron ware for solid-fuelappliances; a metallic etching solution issprayed on the enamelled surface whileit is still red hot. See also BRIANCHON,

BURGOS, CANTHARIDES and FRANCHETLUSTRES.Luting. Joining two leatherhard ceramicsurfaces with slip, as in sticking handleson cups.Luting Cement. Refractory mortar forjointing spouts in glass forming, sealingcoke oven doors etc.L.W.F. Luminous Wall Firing (q.v.).Lynch Machine. A machine for themanufacture of glass bottles; it is basedon the original design introduced by J.Lynch in 1917 and operated on the'blow-and-blow' principle. Tress-and-blow' Lynch machines are also widelyused.

Lytag. Trade-name: a lightweightaggregate for concrete made by sinteringpulverized fuel ash (Lytag Ltd, BorehamWood, England).MA. See IL/MA.MacAdam System. A method of colournotation in which nonspherical regionsof equal perceptual differences areinscribed in the CIE (q.v.) space. (W. R.J. Brown and D. L. MacAdam, /. Opt.Soc. Amen, 33, 18, 1943.)Machineable Ceramics. All ceramics canbe machined in the green state, and in thefired state with diamond tooling.Machineable ceramics are those whichcan be shaped when fired, to engineeringtolerances with ordinary high speed metalcutting tools. See MACHINING, andPYROPHYLLITE, DICOR, MACOR, PHOTON.Machining. Shaping (usually to precisetolerances) by mechanical removal ofmaterial. There are three basic groups ofprocesses: grinding methods, in whichABRASIVES (q.v.) bonded into thegrinding wheels, burrs or other tools arethe usual and most versatile methods;free abrasive methods use abrasivepowders for lapping, honing, polishing,ULTRASONIC MACHINING and ABRASIVEJET MACHINING (q.v.); non abrasivemachining techniques include LASER-B E A M MACHINING, ELECTRICALDISCHARGE MACHINING, ION-BEAM andELECTRON BEAM MACHINING, andCHEMICAL and ELECTROCHEMICALMACHINING (q.v.) See also TOOL(CERAMIC) for machining metals.Machlan Diagram. A diagram giving ingeneral terms the liquidus lines in aternary system of acidic oxide, alkalineoxide, and an alkaline earth oxide.Mackensen Blower. An apparatus todetermine the variation of hardness andinhomogeneity of structure acrossceramic surfaces. A probe is zeroedagainst a scale, lifted from the surface

and abrasive powder blown on to thesurface at a pressure of 1.5 kg/cm2. Thedisplacement of the probe thereafter is ameasure of the hardness of the surface.Macor. Tradename. A machineableglass-ceramic based on fluormica crystalsdispersed in a glass matrix. The tiny micaflakes break away during machiningprocesses. (Corning Glass Co, USA. BrPat 1345294 and 1365435,1974)Mack's Cement. A quick-setting plastermade by adding Na2SO4 or K2SO4 toplaster of Paris.Mackenzie-Shuttleworth Equation.Relates to the progress of shrinkage, ordensification, during the sintering of acompact, the latter being considered as acontinuous matrix containing uniformlydistributed spherical pores:

*? = (1 - a)2/3 (4.57ryna)1/3/r|dta is the relative density, t the time inseconds, y the surface tension, r\ theviscosity in poises and n the number ofpores per cm3 of real material. (J. K.Mackenzie and R. Shuttleworth, Proc.Phys. Soc. B, 62, 833, 1949.)Mackler's Glaze. A type of AVENTURINEGLAZE (q.v.); (H. Mackler, Tonind. Zeil,20,207,219,1896).MacMichael Viscometer. A rotation-type viscometer designed for the testingof clay slips. (R. F. MacMichael, Trans.Amer. Ceram. Soc. 17, 639, 1915.)Macrodefect-free cement The flexuralstrength of cements can be increasedfourfold to c. 70 MPa, if all defects>100mm can be removed. This isachieved by rheological control andcareful mixing of fine powder. (J. D.Birchall et al, Nature 289, 388,1981)Macro Process. Tungsten carbidepowder is made direct from the oneconcentrate by an exothermic reactioncausing simultaneous reduction andcarburization.

Maerz-Boelens Furnace. A type of open-hearth steel furnace with back and frontwalls sloping inwards, thus reducing thespan of the roof; the design wasintroduced by E. Boelens, in Belgium, in1952. (Also known as a PORK-PIEFurnace.)Mafic Minerals. Magnesium, iron (Fe)and calcium silicates, cheap mineralssometimes substituted for feldspars.Magdolo. Trade-name: a half-wayproduct in the extraction of magnesiafrom sea-water, used in Japan as arefractory material for the L-D PROCESS(q.v.). It contains 55-62%, MgO and 30-35%, CaO, together with minor amountsof SiO2, Al2O3 and Fe2O3.Magneli Phase. A series of structurallyrelated compounds with regularlyincremented oxygen contents. Thetitanium suboxides TinO2n-1 with n=4 to8 form a series of materials whoseelectrical conductivity falls rapidly from3xlO5 ohm.cm to a very small value.Magnesia; Magnesium Oxide. A highlyrefractory oxide, MgO; MgO can besintered to a dense engineering ceramic,and is also incorporated into otherengineering ceramics as a sintering aid.For properties see under HEAVY

MAGNESIA, LIGHT MAGNESIA andPERICLASE.Magnesio-chromite. SeePICROCHROMITE.Magnesio-ferrite. MgFe2O4; m.p.17500C; sp. gr. 4.20; thermal expansion

Madelung Constant. An importantconstant for calculating the lattice energyof an ionic crystalline solid. If thedistance between nearest adjacent ions isR, and the distance of the jth ion from a(negative) reference ion is rj (alwaystaken as positive), then the Madelungconstant

(0-12000C) 13.5 x 10-6. This spinel isformed in some basic refractories byreaction between the periclase (MgO)and the iron oxide present.Magnesite. Magnesium carbonate,MgCO3; the natural mineral often containssome FeCO3 (if more than 5%, themineral is known as breunnerite). Themain sources are Russia, Austria,Manchuria, USA, Greece and India. Afterit has been dead-burned at 1600-17000C,magnesite is used as raw material for themanufacture of basic refractories (see alsoSE A-W ATER MAGNESIA).

Magnesite Refractory. A refractorymaterial, fired or chemically-bonded,consisting essentially of dead-burnedmagnesite so that the MgO contentexceeds 80%. ASTM C-455 specifies anominal MgO contents of 90, 95 and98%, with the first having a minimumMgO content of 86%, below which therefractory is classified as MAGNESITE-CHROME (q.v.). Such refractories areused in the hearths and walls of basicsteel furnaces, mixer furnaces andcement kilns, for example.Magnesite-chrome Refractory. Arefractory material made from dead-burned magnesite and chrome ore, themagnesite being present in the greaterproportion so that the fired productcontains 55-80% MgO. Such refractoriesmay either be fired or chemically bondedand are used principally in the steelindustry. A typical chemical analysis is(per cent): SiO2, 3-4; Fe2O3, 4-6; Al2O3,4-6: Cr2O3, 8-10; CaO, 1-2; MgO, 70-75.ASTM C455 specifies 6 grades ofchrome-magnesite and magnesitechrome refractories; with nominal MgOcontents of 30 to 80% , with theminimum allowable being 5% less ineach case.Magnesium Aluminate. MgAl2O4; m.p.2135°C; sp. gr. 3.6: thermal expansion

(0-12000C), 9.3 x 10-6. This compound isthe type mineral of the SPINEL (q.v.)group.Magnesium Chromite. SeePICROCHROMITE.

Magnesium Fluoride. MgF2; m.p.1255°C. Hot-pressed (200 MNm-2 at6500C) compacts had the followingproperties: sp. gr. 3.185; hardness,Knoop 585, Rockwell C52; YoungsModulus, 75 GNm-2; thermalexpansion, 11.5 x 10-6 (20-5000C). Thehot-pressed material is suitable for usein infra-red components operatingunder severe conditions.Magnesium Oxide. See MAGNESIA.Magnesium Oxychloride. See SORELCEMENT.

Magnesium Stannate. MgSnO3; whenadded to titanate electroceramic bodies,the dielectric constant is usuallysomewhat increased up to the Curiepoint.Magnesium Sulphate. MgSO4JH2O;Epsom salt; used in the vitreous-enamelindustry to improve the suspension ofthe enamel slip.Magnesium Titanates. Three compoundsexist. Mg2TiO4, m.p. 17300C; this has aspinel structure and has been proposedfor use as a resistor. MgTiO3, m.p.16300C; ilmenite structure. MgTi2O5,m.p. 16500C; has a low dielectricconstant and has been added to othertitanate bodies to reduce their dielectricconstants.Magnesium Zirconate. MgZrO3; m.p.21500C. This compound is sometimesadded in small amounts (up to 5%) toother electroceramic bodies to lowertheir dielectric constant at the Curiepoint.Magnet Thickness Gauge. A non-destructive device for determiningthe thickness of a coating ofvitreous enamel; it depends on the

principle that the force required to pulla permanent magnet off the surface ofenamelware is inversely proportional tothe thickness of the non-magneticenamel layer on the magnetic basemetal.Magnetic Ceramics. See FERRITES.Magnetic Separator. Equipment forremoving iron particles from clay orother ceramic material; in the designcommonly used in the pottery industry,the prepared body is allowed to flow as afluid slip over a series of permanentmagnets, which are periodically removedand cleaned.Magnetite. Fe3O4; a spinel; m.p. 15900C;sp. gr. 5 .14; thermal expansion(0-10000C) 15 x 10^6, This magnetic ironoxide is present in many ferruginousslags and in their reaction products withrefractory materials.Magnetoplumbite Structure. Ceramicswith the general formula M0.6Fe2O3,where M is usually Ba, Sr or Pb, have ahexagonal crystal structure with a unique'c' axis. These are FERRITES (q.v.) andmore complex structures withinterlayered spinels are possible.Magnit. Trade-name: A tarredmagnesitic-dolomite refractory made byVereinigte Osterreichische Eisen undStahlwerke, Linz, Austria, and used bythem in the L-D PROCESS (q.v.) ofsteelmaking. The composition of thecalcined raw material varies as follows:65-80° MgO, 10-25% CaO, 2-5% SiO2,1% Al2O3, 4-6% Fe2O3, Loss onignition, 0.5-2%.Magnum. A 2-quart wine bottle.Main Arch. (1) The refractory blocksforming the part of a horizontal gas-retort comprising the DIVISION WALLS(q.v.) and the roof that covers the retortsand the recuperators.(2) General term for the central part of afurnace roof, particularly used as a

synonym of the crown of a glass-tankfurnace.Maiolica; Majolica. Originally a poroustype of pottery, with a glaze opacifiedwith tin oxide, from the island ofMajorca; this pottery was first made inthe 16th century under the combinedinfluence of Hispano-Moresque andNear Eastern wares; it was essentiallysimilar, technically, to delft-ware andthe original faience. As applied topresent-day pottery, the term signifies adecorated type of earthenware havingan opaque glaze, usually fired at acomparatively low temperature(900-10500C). The term has also beenapplied to vitreous enamels that aretransparent, but that contain colouringoxides; they are used over ground-coatsand allow the latter to show wherethere is any relief.Malachite Green. CuO-CO3-Cu(OH)2.A dye, used to test absorption of bodies,and to colour stoneware.Malm. ( I)A synonym of Marl in itsoriginal sense of a calcareous clay.(2) The best quality of clamp-firedLondon Stock Bricks.Manchester Kiln. A type of longitudinal-arch kiln that was introduced in theManchester district of England for thefiring of building bricks. It is top-fired. Adistinctive feature is the flue system, withhorizontal damper-plates, in the outsidewall. The Manchester kiln usually has ahot-air system.Mandrel. ( I)A former used in theproduction of blown glassware fromtubing or of precision tubing.(2) A refractory tube used in theproduction of glass tubing or rod.(3) A central core in ISOSTATIC PRESSTOOLING (q.v.) to enable hollow articlesto be formed.Mangalore Tile. A clay roofing tile of theinterlocking type as made in the

Mangalore district of India. See IndianStandard 654.Manganese-Alumina Pink. A ceramicstain, particularly for the colouring ofpottery bodies; it is produced bycalcination of a mixture of MnCO3,hydrated alumina and borax. This stainwill produce a strong, clean colour overa wide firing range but the glaze must berich in Al2O3; this requirement makes itdifficult to produce a smooth glaze.Manganese Oxides. There are severalmanganese oxides, the commonest beingMnO2 (pyrolusite); other oxides areMnO (m.p. approx. 17800C) and Mn3O4

(m.p. 15700C). MnO2 is used as acolouring oxide (red or purple); mixedwith the oxides of Co, Cr, Fe, it producesa black. This oxide is also used to colourfacing bricks, and to promote adherenceof ground-coat vitreous enamels to thebase-metal. When added in smallamounts to glasses (particularly leadglasses) during pot melting, MnO2 actsas a decolorizer.Mangle. A type of dryer used in thetableware section of the pottery industry.The ware, while still in the plastermould, is placed on trays suspendedbetween two endless chains that passover wheels above and below theworking opening in the dryer; by meansof these chains the trays, when filled, aremoved vertically through the hot aircurrent in the dryer until they arrive at asecond opening where the moulds anddried ware are removed.Mansard Roof. A tiled roof having asteeper pitch towards the eaves thantowards the ridge; the term is alsoapplied to a flat-topped roof withsteeply-pitched tiling towards the eaves.(F. Mansard, 17th century Frencharchitect.)Manson Effect. The BOILING (q.v.) ofvitreous enamel that occurs when heated

cast-iron is DREDGED (q.v.) with only athin coating of enamel, which is allowedto fuse before a further coating ofenamel has been applied. The effect wasfirst observed by M. E. Manson (Bull.Amer. Ceram. Soc, 11, 204,1932).Mantel. See LINTEL.Mantle Block. ( I)A refractory block foruse in the gable wall of a glass-tankfurnace above the DOG-HOUSE (q.v.).(2) The upper course of refractoryblocks, in a sheet-glass furnace, enclosingthe Fourcault drawing pit.Manx Stone. See CHINA STONE.Marbleized. A vitreous-enamel finishresembling marble; it can be obtained byan offset process from natural marble.Marbling. A procedure sometimes usedby the studio potter: the marble effect isobtained by covering the piece ofpreviously dried ware with coloured slipsand then shaking the ware (while theslips are still wet) to make the coloursrun into one another.Map Cracking. Random surface cracksin concrete, due to surface shrinkage orinterior expansion.Marcasite. A form of iron sulphide,FeS2, sometimes found as particles ornodules in clays, forming dark spotswhen the clay is fired.Margin. See GAUGE.Mariotte Tube. An orifice-typeviscometer designed by E. Mariotte(Paris, 1700). One such instrument witha tube diameter of 54 mm and a 3 mmorifice has been used for the assessmentof the fluidity of clay slips (/. Amer.Ceram. Soc, 27, 99,1944).Marl. Strictly, an impure, calcareousclay; the word is used in N. Staffordshire,England, to denote a low-grade fireclay,e.g. saggar-marl. See also ETRURIA

MARL, KEUPER MARL.Marlow Kiln. A tunnel kiln fired withproducer gas and preheated air; it was

first used, in Stoke-on-Trent, England,for the biscuit- and glost-firing of walltiles (J. H. Marlow, Trans. Brit. Ceram.Soc, 21,153,1922).Marquardt Porcelain. A mullitic (65%Al2O3) porcelain introduced early in thepresent century by the State PorcelainFactory, Berlin, chiefly for pyrometersheaths and furnace tubes.Mars Pigments, PIGMENTS (q.v.)produced by calcining the precipitateresulting from mixing solutions offerrous sulphate and calcium hydroxide.The calcination temperature determinesthe colour: yellow, orange, brown, red orviolet.Marseilles Tile. A clay roofing tile of theinterlocking type, particularly of thepattern made in the Marseilles district ofFrance. These tiles are made in aREVOLVER PRESS (q.V.).Martensitic Transformation. A solid-state transformation between two phaseswith the same chemical composition,with a characteristic shape change in thetransforming region. Any originally flatsurface in the transformed regionremains flat, but is tilted about its line ofintersection with a definite habit plane(the interface common to the parent andproduct phases). Planes and straightlines in the parent phase are transformedinto planes and straight lines in theproduct phase. Elastic and plasticdeformation in the surrounding matrixaccommodates the distortion due to thetilting. Martensitic transformations areusually athermal and diffusionless. Theyare usually associated with rapid cooling,but can lead to both equilibrium ormetastable final phases. They areimportant in ceramics, contributing toTRANSFORMATION TOUGHENING. Theirname derives from the transformationwhich forms martensite - a hardmetastable phase developed in Fe -C

alloys when they are quenched tostrengthen them. See also BAINDEFORMATION.Martin's Cement. A quick-setting plastermade by adding K2CO3 to plaster ofParis.Marumerizer. A machine for producingspherical granulate from cylindricalextrudate. The granules, 0.5 to 15mmdiameter, are made by allowing shortsections of extruded material to fall onto a rotating plate at the bottom of acylindrical bowl. This breaks theextrudate into pellets about 1 diameterlong. Collisions with the wall, the frictionplate and other particles graduallyproduce spherical granules in a fluidizedring of particles slowly rotating againstthe wall of the Marumerizer. Themachine is Japanese, licensed to RussellFinex, London)Marver. A small metal or stone table onwhich a gather of glass is rolled orshaped by hand.Mason's Ironstone China. A vitrifiedtype of earthenware introduced by C. J.Mason, Stoke-on-Trent, England.According to his patent (Brit. Pat. 3724,1813) the batch composition was: 4 pts.china clay, 4 pts. china stone, 4 pts. flint,3 pts. prepared ironstone, and a trace ofcobalt oxide. It is now known that thebody did not contain ironstone, thename merely being a highly successfulmethod of indicating to the public thatthe ware was very strong.Masonry. Bricks (or other structuralunits of a similar type) bonded togetherand depending for their structuralstability mainly on the strength of thebricks and of the mortar, but also on thebonding and weight. See alsoPREFABRICATED MASONRY;REINFORCED BRICKWORK. B.S. 8000 Pt3 is a code of practice for siteworkmanship for masonry. B.S. 5628 is a

code of practice for the structural use ofmasonry, including reinforced andprestressed masonry. B.S. 5080 andASTM E488 give tests for tensile loadingand shear for anchors in masonry. B.S.6270 specifies techniques for cleaningand repairing the surfaces of stone,calcium silicate and clay brick masonry.ASTM E518 specifies two test methods(uniform and 3-point loading) for theflexural bond strength of masonry.ASTM E519 specifies a shear strengthtest in which a 1.2m masonry square isloaded across its diagonal. Cl 196 andCl 197 are test methods for in situcompressive strength and deformabilityof masonry. The construction of dry-stacked surface bonded walls, in whichwalls of concrete blocks, laid closetogether without mortar are coated withmortar on both sides, is specified inASTM C946.Master Mould. See under MOULD.Mat. See GLASS FIBRE.Match Mark. See JOINT LINE.Matching Piece. A short refractorychannel between the spout of a glass-tank furnace and the pot spout for arevolving pot; also known as anINTERMEDIATE PIECE.Matrix. That part of a ceramic rawmaterial or product in which the largercrystals or aggregates are embedded. Afired silica refractory, for example,consists of crystalline silica (quartz,cristobalite and tridymite) set in a glassymatrix; a fireclay refractory may consistof quartz and mullitic GROG (q.v.) set ina largely amorphous matrix. (Alsosometimes known as the GROUND-MASS.)Matt Blue. A colour for potterydecoration depending on the formationof cobalt aluminate; zinc oxide is usuallyadded, a quoted recipe being 60%Al2O3, 20% CoO, 20% ZnO.

Matt Glaze. A ceramic glaze that haspartially devitrified; the effect isdeliberately achieved, for example, onsome types of glazed wall tile. The glazesused for the purpose are usually leadlessand devitrification is encouraged by theintroduction, into the glaze batch, ofsuch oxides as TiO2, CaO or ZnO.Maturing Temperature or MaturingRange. (1) The firing temperature atwhich a ceramic body develops arequired degree of vitrification.(2) The firing temperature at which theconstituents of a glaze have reacted toform a glass that, when the ware hasbeen cooled, appears to the eye to behomogeneous and free from bubbles.Maximum Exposure Limit. Themaximum concentration of an airbornesubstance, (averaged over a referenceperiod) to which employees may beexposed by inhalation under anycircumstances. Cf OCCUPATIONAL

EXPOSURE STANDARD.Maxitherm. A brick with verticalperforations, and slots in the side intowhich expanded polystyrene claddingcan be dovetailed.Mazarine Blue or Royal Blue. A ceramiccolou$ for on-glaze or under-glaze,based on the use of cobalt oxide (40-60%) together with a flux.MBI Methylene Blue IndexMCC Test. (Metodo Centro Ceramica) isa test for the surface abrasion resistanceof glazed tiles, specified in BS 6431 Pt 20.It uses a dry abrasive, in contrast to thePEI TEST (q.v.) which is also specified.MCC - IP. Static Leach Test.Speciments of known geometric surfaceare immersed in selected leachants,without agitation, for defined timeintervals at defined temperatures. Thetest has been applied to dental ceramics,with leach periods of 1, 7, 14 and 28 daysat 900C, with leachants chosen to

simulate saliva. (MCC = MaterialsCharacterization Center).MCVD (Modified Chemical VapourDeposition). See OPTICAL FIBRES.MDF Cement - Macrodefect-freeCement, (q.v.)MDHS Methods for the Determination ofHazardous Substances are published bythe (UK) Health and Safety Executive.MDHS 6,7,8 relate to lead and leadcompounds;MDHS 10,11 to cadmium and itscompounds;MDHS 14 to respirable dust;MDHS 29 to beryllium and itscompounds;MDHS 37,38,51 to quartz in respirabledust;MDHS 39 to asbestos fibresMDHS 59 to man-made mineral fibres;MDHS 61 to hexavalent chromiumcompounds;Measles. Unbroken bubbles that havepenetrated the groundcoat into thecover-coat of vitreous enamels.Mechanical Analysis. A term sometimesused as a synonym of PARTICLE-SIZEANALYSIS (q.v.).Mechanical Boy. A device used forcontrolling the mould during the hand-blowing of glass-ware.Mechanical Press. A press in whichbricks (building or refractory) areshaped in a mould by pressure appliedmechanically, e.g. by a togglemechanism, as distinct from theprocedure in a hydraulic press.Median Crack. A crack in glassperpendicular to the surface, caused by ahard, sharp object.Mediceram. Biocompatible calciumphosphate glass-ceramics developed inEast Germany, (lnterceram 37, (3), 34,1988)Mechanical Shovel. The original formof excavator, still much used in the

getting of brick-clays. It consists of abucket (or 'dipper') on the end of anarm pivoted to a boom; the bucketscoops upwards, the excavatoroperating below the clay face.Mechanical Spalling. SPALLING (q.v.) ofa refractory brick or block caused bystresses resulting from pressure orimpact.Mechanical Water or Mechanically-heldWater. The water that is present in moistclay and is not chemically combined.When the clay is heated, themechanically-held water is virtually allremoved by the time that thetemperature has reached 1500C.Medina Quartzite. A quartzite fromMedina, Pennsylvania, USA, used as araw material for silica refractories. Aquoted chemical analysis is (per cent):SiO2, 97.8; Al2O3, 0.9; Fe2O3,0.85;alkalis, 0.4.Medium-duty Fireclay Brick. Defined inASTM - C27 as a fireclay refractoryhaving a P.C.E. 29 and a modulus ofrupture 500 p.s.i. (3.5 MNm-2).Meissner Effect. The expulsion of amagnetic field from a SUPERCONDUCTOR(q.v.) when the temperature is loweredbelow the critical temperature Tc atwhich the material becomessuperconducting.MEL. Maximum Exposure LimitMeldon Stone. A CHINA STONE (q.v.) oflow quality from Cornwall, England. Aquoted analysis is (per cent): SiO2, 70;Al2O3, 18; Fe2O3, 0.4; CaO, 0.6; Na2O, 4;K2O, 4.5; loss on ignition, 2.5.Melting. See CONGRUENT MELTING;iNCONGRUENT MELTING. For meltingpoints of various compounds andminerals, see under name of compoundor mineral.Melt Blowing. The production ofrefractory fibre by blowing a melt withsteam or compressed air.

Melting End. The part of a glass-tankfurnace where the batch is melted andthe glass is refined.Melt Infiltration. Production of a metal-ceramic composite by a controlledreaction between a ceramic preform anda liquid metal which pentrates its pores.Melt Spinning. Ceramic fibres areproduced from low viscosity metal melts,from which a molten jet is drawn andchemically stablilized to form the fibre.Melting Temperature. For a glass, theASTM definition is: The range offurnace temperatures within whichmelting takes place at a commerciallydesirable rate, and at which the resultingglass generally has a viscosity of 101-5 to102 5 poises; for purposes of comparingglasses, it is assumed that the glass atmelting temperature has a viscosity of102 poises'.Meltspinning. The production of ductileribbons of active metal brazing materialsby rapid quenching from the liquid stateto form a glassy metal.Membrane Curing. Spraying abituminous seal on the surface of freshconcrete, to prevent moisture loss.Membrane Filter. See DUST SAMPLING,FILTERS.Membrane Theory of Plasticity.Attributes the plasticity of clay to thecompressive action of a postulatedsurface envelope of water around theclay particles. (F. H. Norton, J. Amer.Ceram. Soc, 31, 236,1948).Mendheim Kiln. A gas-fired chamberkiln designed by G. Mendheim, ofMunich, in about 1910 for the firing ofrefractories at high temperature. The gasenters at the four corners of eachchamber, and burns within BAG WALLS(q.v.) which direct the hot products ofcombustion towards the roof; they thenpass downward through the setting andare exhausted through the chamberfloor.

Menhaden Fish Oil. A dispersant used inTAPE CASTING (q.V.)Menstruum Process. An alternativename for the Auxiliary Metal BathProcess (q.v.)Merapon. Metal-complex solutionsabsorbed by unglazed ware, which thendevelop colour on firing. (BenckiserKanpsack GmbH. Sprechsaal (10) 922,1986)Merch Bricks. Term sometimes used inUSA for building bricks that come fromthe kiln discoloured, warped or off-sized.Mercury Penetration Method. Aprocedure for the determination of therange of pore sizes in a ceramic material.It depends on the fact that the volume ofmercury that will enter a porous body ata pressure of P dynes /cm2 is a measureof the volume of pores larger than aradius r cm where r - -2a cosO/P, abeing the surface tension of mercury indynes/cm and 0 being the contact anglebetween mercury and the ceramic. Adevelopment of the method has beendescribed by R. D. Hill (Trans. Brit.Ceram. Soc, 59, 198, 1960).Mereses. The ribs found on the stems ofsome wine-glasses.Merriman Test or Sugar Test. A qualitytest (now discarded) for hydrauliccement. The sample is shaken with asolution of cane sugar and the amount ofcement dissolved is determined by titra-tion with HCI (T. Merriman, J. BostonSoc. Civil Eng., 26, (1), 1939, p.l).Merwinite. 3CaO. MgO. SiO2; meltsincongruently at 1575C; thermalexpansion (0-12000C) 13.4 x 1(H\ It mayoccur in, or be formed during service in,dolomite refractories.MetahaIIoysite. A clay mineral of thekaolinite group and of the sameapproximate composition as kaolinite -Al2O3.2SiO2.2H2O. It is formed by thepartial dehydration of HALLOYSITE (q.v.).

Metakaolin. An intermediate productformed when kaolinite is heated attemperatures between about 500° and8500C; the layer structure of the parentkaolinite persists in modified form butcollapse of the layers destroys anyperiodicity normal to the layers. Athigher temperatures (925°C) metakaolintransforms to a cubic phase with aspinel-type structure; at 1050-11000Cmullite is formed.Metal. In the glass industry, the moltenglass is called 'metal'.Metal Blister. A defect that may occur invitreous enamelware if there is any gastrapped in a fault in the base metal.Metal-cased Refractory. A basicrefractory with a thin sheetmetal casingon three or four sides, leaving the endsof the brick exposed; the refractorymaterial itself (generally magnesite orchrome-magnesite) is usually chemicallybonded. Such bricks are used chiefly insteel furnaces; during use, the metal caseat the hot end of the brick oxidizes and'knits' each brick to its neighbours.There are many variants of this type ofbasic refractory but all derive from thesteel tubes packed with magnesite aspatented in 1916 by N. E. MacCallum ofthe Phoenix Iron Co., USA.Metal Line. See FLUX LINE.Metal-marking. See SILVER MARKING.Metal Oxide Chemical VapourDeposition. A process in which metaloxides are deposited from the vapours oforganic compounds of the relevantmaterial.Metal Protection (at high temperature).Metals can be protected from oxidationat high temperature by various types ofceramic coating, the commonest beingflame-sprayed alumina and refractoryenamels. Such coatings have foundparticular use on the exhaust systems ofaircraft.

Metal Release. The action of foods, or oftest solutions of acids, may leach toxicmetals from the glaze or decoration ofceramic whitewares. Propensity to metalrelease may depend on complexinteractions between glaze, decorationand kiln atmosphere. The usual tests arefor Pb, often Cd, and sometimes forother metals. The usual test solution is4% acetic acid, sometimes hot if cookingware is being tested. There are variedbut strict limits in the amounts (in thep.p.m. range) of metal leached into thetest solutions. These limits vary fromcountry to country, and are enforced bylegislation. British Ceramic ResearchLtd Special Publication 136,1993 gives adetailed summary of tests and limits inover 40 countries. The most importantare US FDA Compliance Policy Guide7117.06 and 7117.07 for cadmium andlead; European EC Directive 84/500/EEC 1984 and GB Ceramic Ware(Safety) Regulations SI 1647,1988. Thetest methods for ceramic tableware andcooking ware and vitreous enamelwarehave been unified in Britain in BS6748;1986. In USA, ASTM C738, C895,Cl 035 give test methods for glazedceramics, ceramic tile and cookware.C927 is a test for the tip and rim areas ofglass tumblers.Metallic Glasses. Electrically conductingglasses can be prepared fromcombinations of predominantly metallicelements by rapid cooling or vapourdeposition. Their magnetic propertiesmake them suitable for low-losstransformer cures, and their mechanicalstrengths approach theoretical fracturestrength, as local dislocation fracturemechanisms do not operate.Metallizing. Electroceramics aremetallized when it is required to join theceramic to a metal or form a seal. Analumina ceramic, for example, can be

metallized by painting it with apowdered mixture of Mo and Fe andfiring it in a protective atmosphere tobond the metals to the surface; themetallized area is then plated with Cu orNi. This two-stage procedure is known asthe TELEFUNKEN PROCESS (TelefunkenG.m.b.H., Berlin). Single stagemetallizing is possible if the hydride ofTi or Zr is used, together with a hardsolder: this is sometimes known as theBONDLEY PROCESS (R. J. Bondley,Electronics, 20, (7), 97, 1947).Metalloceramic. One of the old, nowobsolete, names of CERMET (q.v.).Metal Strain. Lines, often parallel, ofsmall blisters in vitreous enamelware;they may be the result of severe stress inthe metal or they may be caused bydamage to the fired ground-coat beforethe cover-coat is added.Metameric Colours. Colours that appearto be the same under one type ofilluminant but, because they have differentspectral reflectivity curves, will not matchunder a different illuminant. Two whitevitreous enamels may be metameric, forexample, if one is opacified with titania inthe anatase form whereas the othercontains titania in the form of rutile.Methuselah. A 9-quart wine bottle.Methylene Blue Index A simpleapproximate method for assessing thesurface area of a clay. 0.01M methyleneblue dye is added to aqueous suspensionof clay, in successive small amounts, todetermine the least amount of dyerequired to impart colour to the watersuspending the clay. Dye up to thisamount is absorbed by the clay, so thatthis is a measure of the clay's cationexchange capacity (see IONICEXCHANGE). For most pottery clays thisis proportional to the surface area to agood approximation. ASTM C837specifies a test for clays.

Methyltrichlorosilane. A gaseousPRECURSOR, whose breakdown leads tovapour-deposited silicon nitride.Mettlach Tile. A vitreous floor tile(especially of the multicoloured type) asfirst made by Villeroy and Boch atMettlach, in the Saar. The term (oftenmis-spelt 'Metlach') is now commonlyused on the Continent and in Russia forany vitreous floor tile.MEXE Method. A calculation methodfor determining the permissible loadingof brick and masonry arches. For acritique and development of this methodoriginally due to Pippard, see R.P.Walklate and J.W. Mann, Proc. Inst.Civil Engrs. Pt. 2 75 (Dec) 585,1983, anddiscussion Pt. 2 77 (Sept). 401,1984.MEXE is the Military EngineeringExperimental Establishment.Mexim. A glass-ceramic joiningcompound for metals (English Electric,Stafford) cf MEXIMS.Mexims. Matched Expansion Insulator/Metal Systems. These are ceramic-to-metal seals. (Trade-name: EnglishElectric Co., Stafford, England).MG-Block, MG-plank. Perforatedbuilding units, 9in x 4Vi x 9in (228 x 114 x228 mm) (block) or storey-height (plank),made from fired clay. Developed by theMellor Green Laboratories of BritishCeramic Research Ltd.Mg Point. See TRANSFORMATION POINTS.MHD Magnetohydrodynamics. Thestudy of the motion of an electrically-conducting fluid (which may be aplasma) in a magnetic field. Ceramics areused to contain the fluid in directelectricity generation by this process.Mica Convention. See under RATIONAL

ANALYSIS.Mica (Glass-bonded). An electroceramicmade by the bonding of mica (natural orsynthetic) with a glass of high softeningpoint. Some products of this type can be

used up to 5000C. They have gooddielectric properties. Transversestrength, 90-105 MNm-2 Thermalexpansion 11 x ICh6 . Sp. gr. 3.0.Mica (Natural). Group name for a seriesof silicates, the most important of which,to the ceramist, is MUSCOVITE (q.v.). acommon impurity in clays.Micas Hydrated aluminium silicates withsheet-type crystal structures which allowcleavage into thin plates. Their generalformula is M[Al2(OH)2][Si3Al)O10]where M is K (MUSCOVITE q.v) or Na.The Al may be substituted by Mg or Ca.Micas crystallize in the monoclinicsystem as Al2(OH)2 sandwichedbetween two Si1.5 Al05O5 sheets. Theyare excellent electrical insulators.Michigan Slip Clay. A clay occurring inOntonagon County Michigan; it issimilar to ALBANY CLAY (q.v.).Micoquille. Thin glass similar toCOQUiLLE (q.v.) but with a radius ofcurvature of 180 mm.Microballoons. Hollow glass spheres20-300jLim diameter, with wallthicknesses of a few microns, made byintroducing particles comprising amixture of glass-forming componentsand a blowing agent (e.g.urea) into thefuel supply of a burner. The particlesmelt to form glassy spheres which areblown into microballoons by gaseousdecomposition products of the blowingagent.Microcharacter Hardness. A scratchhardness test in which a loaded diamondis used; it has been applied to the testingof glazes. The 'Microcharacter'instrument was developed by C. H.Bierbaum (Trans. Amer. Soc. Mech.Engrs., p. 1099,1920; p. 1273, 1921).Microcline. See FELDSPAR.Microcracking See FRACTURE, CRACKNUCLEATION; CRACK PROPAGATION;TOUGHNESS.

Microcracks (sub-micron fractures)are the origin of weaknesses inBRITTLE ceramics. However, regionscontaining extensive pre-existingmicrocracking can inhibit the growth ofa larger crack by blunting the crack tipand reducing the stress concentration.See STRAIN HARDENING; CRACK

BRANCHING.

Micro-glass. Thin glass for making cover-slips for use in microscopy.Microlite (1) An expanded volcanicmineral, white spheroidal granules of ametastable amorphous aluminiumsilicate with a honeycomb, microcellularstructure.(2) Trade-name: a dense corundum,consisting of uniform micro-crystals(l-3um), introduced in 1951 by theMoscow Hard-Alloy Combine. Itcontains 99% Al2O3 and a small amountof MgO to inhibit crystal growth; theprimary use is in tool tips.Micromeritics. The science of smallparticles. This term, which has notachieved popularity, was proposed by M.J. DallaValle in his book Micromeritics(Pitman, 1943).Micromerograph. Trade-name: aninstrument for particle-size analysisdepending on the rate of fall of particlesin air; it is suitable for use in the rangel-250um. (Sharpies Corp. ResearchLabs., Bridgeport, Pa., USA.)Micron. One-thousandth of a millimetre;symbol um.Micronizer. A type of fluid-energy millused for very fine grinding, e.g. talc to5um. (This term was originally a trade-name registered by The BuellCombustion Co. Ltd., London).Microscopy. The classic books on the useof the microscope in ceramics are: Thin-Section Mineralogy of Ceramic Materialsby G. R. Rigby. (British CeramicResearch Assoc, 2nd Ed., 1953) and

Microscopy of Ceramics and Cements byH. Insley and D. Frechette (AcademicPress, New York, 1955).Microstructure. The arrangement ofgrains, pores and cracks and mineralspecies on the scale of approximately 1micron. The microstructure of ceramics,and its wideranging importance, wasextensively reviewed by R. Rice (inTreatise on Materials Science andTechnology, VoI II, Academic Press1977, pp 199-381.Microwave Heating. Materials absorbenergy from radiation when thefrequency of that radiation correspondsto the natural or resonant frequency ofan interatomic bond in the material.Typically microwave energy is absorbedby the OH bond stretching frequencyand so can be used for drying or firing ofceramics. As heating is uniformthroughout the body, there are technicaladvantages, but also economiclimitations to the processes.Midfeather. A dividing wall between twoflues, in a gas retort or glass-tank furnacefor example; in the latter, the wall mayalso be called a TONGUE.Midland Impact Test. A test for theABRASION RESISTANCE (q.V.) of PAVERS(q.v.), which is a modified version of B.S.368,1965. The surface is abraded by ballbearings, and the volume removed iscalculated from the measured loss inmass.Midrex Process. In this process for thedirect reduction of iron, iron ore isreduced in a shaft furnace by H2 and COat up to 7600C. (/. lnsL Refract. Engrs.Winter 1980, pl7)Mie Scattering. Detailed calculationsbased on the full electromagnetic theoryof light are required to explain lightscattering by particles of sizescomparable to the wavelength of light.(G. Mie Ann Phys 25, 1908, 377). Such

scattering by colloidal particles isresponsible for the red colour of gold-ruby glasses.Migeon Kiln. A zig-zag brick and tilekiln, but with a single gallery. (Br. Pat701337, 23/12/53. QRE Migeon, France.Mil. One-thousandth of an inch.Milford-Astor Machine. A simpleprinting machine that has been used forthe small-scale production of transfersfor the decoration of pottery. (BrittainsLtd., Stoke-on-Trent, England.)Milk Glass. Alumina and fluorspar isadded to soda-lime glass to produce anopaque white glass, (cf OPAL GLASS;

ALABASTER GLASS).Mill Addition. Any of the materials,other than the frit, charged to the ballmill during the preparation of a vitreousenamel slip. Such materials include clay,opacifier, colouring oxide and settingupagent.Millefiori. Decorative glassware,particularly paperweights, made bysetting multi-coloured glass cane to forma design within a clear glass matrix. Thistype of glass-ware originated in Italy andderives its name from Italian wordsmeaning 'A Thousand Flowers'.Mineral Dressing. A term formerly usedin UK instead of the now more commonU.S. term BENEFICIATION (q.v.)Mineral Wool or Rock Wool. There arethree main types of mineral wool: RockWool, made from natural rocks or amixture of these; Slag Wool made frommetallurgical slag; Glass Wool, madefrom scrap glass or from a glass batch.All three varieties are used as heat-insulating materials. B.S. 3958 deals withthe properties of mineral fibre thermalinsulation. US Dept. CommerceStandard CS 117-49 defines 5 classes ofmineral wool having the following max.temperature limits of use: Class A -6000F; Class B - 10000F; Class C -

12000F; Class D - 16000F; Class E -18000F.Mineralizer. A substance that, eventhough present in only a small amount,assists the formation and/orcrystallization of other compoundsduring firing. A small amount of alkali,for example, mineralizes the conversionof quartz to cristobalite; boric oxide actsas a mineralizer in the synthesis of spinel(MgAl2O4); the presence of ironcompounds facilitates the growth ofmullite crystals.Minium. Red lead, Pb3O4. See LEADOXIDE.Minter System. A method ofinterconnecting periodic brick kilns by aflue system that permits the withdrawalof hot gases from one kiln and theirtransfer to another kiln in the system.(M. M. Minter, Clayworker, 70, 332,1918).Minton Oven. A down-draught type ofpottery BOTTLE OVEN (q.v.) patented byT. W. Minton (Brit. Pat. 1709, 10th May1873).Mirac Process. Trade-name: a processfor the treatment of steel claimed topermit one-coat enamelling; (PemcoCorp., Baltimore, Md., USA).Miraceram Barium titanate ceramicswith positive temperature coefficientof resistance, used to make heatingelements for domestic appliances,which then need no separateoverheating cutout. The heaters aremade as honeycomb with high specificsurface.Miraware Disposable 'china' containing50% vermiculite developed by theAmerican Can Co. U.S. Pat. 3689611,5/9/72; Ceram Ind 97 (1) 28 1971MISIA An automatic loading/unloadingsystem for bricks and blocks. The blocksare loaded on trays, which aretransported on special cars (in tunnel

dryers) or moved by fork-lift truck (ontochamber dryers). (Ennepi NosenzoPoggi SpA, Italy).Mismatch. If the properties, particularlythe thermal expansion, of thecomponents of a heterogeneous solid aremutually incompatible, there is said tobe 'mismatch'. A typical example is thecase of a ceramic material consisting ofcrystals set in a glassy matrix; it may beimportant that there is no mismatchbetween these two components.Mistron Vapour. Talc, marketed byUnited Sierra, USA.Mitographic Decal A transfer whosedesign is applied by silk-screen printing.Mitre Seam. See JOINT LINE.Mix. A BATCH (q.v.) after it has beenmixed.Mixer. In the clay industries the usualtypes of mixer are:(1) Batch-type Mixer, operates byrotating arms.(2) Shaft Mixer, a continuous mixer forwet or plastic material which is fed intoan open trough along which it ispropelled and mixed by one or tworotating shafts carrying blades.(3) Pug Mill; a shaft mixer with a closedbarrel instead of an open trough; theterm PUG MILL should not be confusedwith PUG (q.v.)Mixer Furnace. See HOT-METAL MIXER.MMC Metal matrix composite - seeCOMPOSITES.

Mobilometer. See GARDNERMOBILOMETER.Mocca or Mocha Ware. A type ofpottery having a brown moss-like ordendritic decoration similar inappearance to the Mocha, or Mecca,stones (brown agates) used in Arabia forbrooches. The effect is produced byallowing differently coloured slips toflow over the surface of the ware.Mock Acid Gold. See ACID GOLD.

MOCVD The Metal Oxide ChemicalVapour Deposition process (q.v.).Modified Chemical Vapour Deposition(MCVD). See OPTICAL FIBRES.Modular Co-ordination; Module. Asystem for the standardization of thedimensions of building components onthe basis of multiples of one or moremodules, i.e. basic units of length. TheBritish Standards Institution has issuedB.S. 6649 specifying a 200 x 100 x 75 mmformat for clay and calcium silicatebricks, giving a work size of 190 x 90 x65 mm. ISO 1006/1 specifies a 100 mmmodule for tiles and other buildingproducts. ASTM C909 specifies sizes forrefractory bricks and shapes based on a38 mm module. E835 specifies a metric100 mm module for clay and concretebuilding units. See also PREFERRED

INCREMENT.Modulus of Elasticity. The ratio of stressto strain within the elastic range. SeeYOUNG'S MODULUS.Modulus of Rigidity. The MODULUS OFELASTICITY (q.v.) in shear.Modulus of Rupture. The maximumtransverse breaking stress applied underspecified conditions, that a material willwithstand before fracture. The modulusof rupture, M, of a test piece ofrectangular cross-section is given by: M= 3Wl/2bd2, where W is the breakingload, / the distance between the knife-edges in the transverse-strength test, bthe breadth of the test piece and d itsdepth. For a cylindical test-piece ofdiameter d, the equation is : M =8W1/7WP. B.S. 1902 Pts 4.4 and 4.5 specifythe test methods for refractories atambient and at elevated temperatures.Pt 7.6 specifies the test for castablerefractories. ASTM C133 and C93specify tests for refractories and forinsulating firebricks; C583 specifies a testfor refractories at high temperatures;

C491 a test for air-setting plasticrefractories. C-1099 for carboncontaining refractories. ASTM Cl 161specifies a test for advanced ceramics atambient temperature, C1211 at elevatedtemperature, F417 a test for electronicgrade ceramics. C689 is a test for unfiredclays; for C648 test for tiles; C674 forwhitewares; C158 for glass.Mogensen Sizer. A classifer consisting ofa system of cascading screens (FredrikMogensen AB, Sweden).Mohammedan Blue. See CHINESE BLUE.Mohr-Coulomb Failure Law. Predictsthe shear stress which a powder compactwill support before particlerearrangement or flow begins.xf = C + af tan §where xf is the shear stress required toproduce flow; C is a constant; af is theapplied axial load, ty is the angle ofinternal friction, a material constant,depending on the mechanical andmorphological properties and surfacechemistry of the powder, ty gives ameasure of the fluidity of the powder;low values indicate that the powder iseasy to shear.Mohs' Hardness. A scale of scratchhardness based on a series of minerals inascending order of hardness. Theoriginal scale, due to Mohs, in the early19th century, is still used, with minorchanges, but an extended scale takesaccount of the need for greaterdifferentation between hard materials.See APPENDIX C.Moil. The excess glass remaining on ashaping tool or in a glass-makingmachine; it is re-used as CULLET (q.v.).Moistorer. Japanese (ShinegawaRefractories) equipment for preventingthe slaking of dolomite bricks.Moisture Content. In chemical analysisthe moisture content is determined bydrying the sample at 1100C until the

weight is constant. For works control ofthe moisture content of a powder or ofclay, instruments are available based onmeasurement of the pressure developedby the evolution of acetylene from amixture of the sample with calciumcarbide. Methods depending on thevariations of the electrical properties of amaterial with changes in its moisturecontent are not applicable to clays owingto the great influence of exchangeablebases and soluble salts. The neutronabsorption method is more promising.Moisture Expansion. See ADSORPTION.Molecular Sieve. The crystal structuresof some compounds (e.g. ZEOLITES, q.v.)contain holes or tunnels which permitthe passage of certain other molecules ifsmall enough.Moler. A deposit of DIATOMITE (q.v.) ofmarine origin occurring on the island ofMors, Denmark; it has been workedsince 1912 for use as a heat-insulatingmaterial, as a constituent of specialcements and for other purposes.Moller and Pfeiffer Dryer. A multi-tracktunnel dryer with concurrent air flow andheat recuperation from the hot air at theexit end. This design of dryer is wellsuited to heavy clay products requiringgentle initial drying.Molochite. Trade-name: a pre-fired chinaclay. Composition (per cent): SiO2 54-55; Al2O3 42-43; Fe2O3 0.7; Alkalis 1.5-2.0. P.C.E. 17700C. Thermal expanson4.7 x 10-6 (0°-1000°C). It is used as aCHAMOTTE (q.v.) in blast-furnace stackrefractories, kiln furniture, refractorycements, etc. (English Clays LoveringPochin & Co. Ltd, St. Austell, England).Molten-cast Refractory. A refractorymade by FUSION CASTING (q.v.); also,and in the UK more commonly, knownas a FUSION-CAST REFRACTORY.Molybdenum Borides. Five compoundshave been reported: Mo2B; m.p. 21200C;

sp. gr. 9.3. Mo3B2, dissociates at 19000C.MoB exists in two crystalline forms -a-MoB, m.p. 23500C sp. gr. 8.8; p-MoB,m.p. 21800C, sp. gr. 8.4. Mo2B5

dissociates at approx. 16000C; sp. gr,. 7.5.MoB2; m.p. 21000C; sp. gr., 7.8; thermalexpansion, 7.7 x Ky-6.Molybdenum Carbides. MoC; m.p.27000C; sp. gr. 8 .; thermal expansion(20-10000C) 5.7 x 10 ̂ 6, (20-20000C)11.5 x 10-6. Mo2C; m.p. 2685C; sp. gr.8.9; thermal expansion (20-10000C) 6.2 x10-6.Molybdenum Disilicide. SeeMOLYBEDENUM SILICIDES.Molybdenum Enamel ('MoIy' Enamel).A vitreous enamel containing about7.5% molybdic oxide, which improvesthe adherence and acid resistance.Molybdenum Nitrides. MoN and Mo2N;both compounds are unstable aboveabout 7000C.Molybdenum Silicides. There are at leastthree compounds: MoSi2, Mo5Si3 andMo3Si. The most important is thedisilicide MoSi2 m.p. 19800C (dissociatesinto Mo5Si3); hardness 80-87 RockwellA; thermal expansion (20-10000C) 8 x10~6, This special refractory materialresists oxidation up to 17000C. Becauseof its relatively high electricalconductivity, it has found some use as amaterial for furnace heating elements.Moly-manganese Process. The mostwidely-used BRAZING (q.v.) process foralumina ceramics. A slurry of powders ofMn, Mo or their oxides, with glass-forming compounds, is painted on theceramic and fired in wet hydrogen at15000C. Glassy material from theceramic bonds the Mo constituent to itssurface. Braze metals may then be used,which wet this metallized interface,though not the original ceramic.Monazite. Strictly, the mineral(La,Ce)PO4; the term is commonly used

for the naturally occurring sands rich inrare earths.Monel. Trade name: Henry Wiggin &Co. Ltd., Birmingham, England. Anickel-copper alloy having goodresistance to acids and therefore used forequipment in the PICKLING (q.v.) processin the vitreous-enamel industry.Monitor. Equipment for directing a high-pressure (2 MPa) jet of water against aclay face in the hydraulic process ofwinning china clay.Monk-and-Nun Tile. German name forSPANISH TILE (q.V.).Monk Bond. A method of laying bricksin a wall; each course is laid as twostretchers followed by one header; theheaders in alternate courses coververtical joints, those in the intermediatecourses are set in the middle of astretcher. Also known as flying bond it isa modified FLEMISH BOND (q.v.).Monnier Kiln. A tunnel kiln designed forthe firing of building bricks; it ismechanically fired from the top withcoal, which burns among the bricks as ina HOFFMANN KILN (q.v.). Although thedesign is of French origin (Patented by J.B. Monnier) the first such kiln was builtin Kent, England, in 1979.Monocottura. The process of single firingof glazed tiles, and the resulting product,of particular properties.Monofire. Tradename. A tile setter forsingle-fired glazed tiles. Ferro Corp.lntercemm (2) pl47, 1978.Monolithic. Literally, 'single stone'. Theolder meaning was attached to furnacelinings made by casting, ramming orgunning rather than by bonding togetherbricks or shapes. The newer meaningrelates to ceramics made from a singlematerial, as opposed to composites.Monometer Furnace. Trade-name:Monometer Mfg. Co. Ltd, London. Anoil-fired rotary furnace, particularly for

the melting of cast iron; a rammedrefractory lining is used, generallysimilar to that in a CUPOLA (q.v.).Monticellite. The complex orthosilicateCaO.MgO.SiO2; dissociates at 1485°Cwith the formation of a liquid phase, sp.gr. 3.2; thermal expansion (0-12000C)12.8 x ICh6. Monticellite is formed inbasic refractories when appreciableamounts of lime and silica are present; itis for this reason that specifications forchrome ore and dead-burned magnesiteusually stipulate low maxima for theSiO2 and CaO contents.Montmorillonite. A magnesian claymineral approximating in composition to5Al2O3.2MgO.24SiO2.6H2O; some ofthe H+ groups are usually replaced byNa+ or by Ca2+. Montmorillonite is theprincipal constituent of bentonite; Na-bentonite is characterized byconsiderable swelling when it takes upwater, whereas little, if any, swellingoccurs with Ca-bentonite. The mineralwas originally found (1847) atMontmorillon, France.Moonstone Glass. A type of OPAL GLASS(q.v.) resembling moonstone (a whitish,pearly feldspar).Moore Bin Discharger. Trade-name: asystem of vibrating fins arranged to assistthe discharge of clay, or other 'sticky'material, from a storage bin. (Conveyors(Ready Built) Ltd,, Stroud, Glos.,England.)Moore-Campbell Kiln. An early type ofelectric tunnel kiln; its principal featurewas the free suspension of the heatingelements on refractory knife-edges. (B.J. Moore and A. J. Campbell, Brit. Pat.270 035, 5/5/27.)Morehouse Mill. A mill of the attritiontype consisting essentially of avertically-driven shaft, with horizontalmilling elements, made of sinteredalumina. It has been used for the

preparation of vitreous-enamel slipsand ceramic glazes.Morgan-Marshall Test. A sand-blast testdeveloped by Morgan Refractories Ltd.,and Thos. Marshall & Co. Ltd., England,for the evaluation of the abrasionresistance of refractory bricks. In the UKthe original apparatus (Trans. BritCeram. Soc, 54, 239,1955), modified in afew details, has been generally adoptedby the refractories industry. See B.S.1902 Pt 4.7, which test is obsolete,though still listed. Some typical ranges ofresults of this test are given in thefollowing table:Material Abradability IndexMild Steel 5Silicon carbide refractory 15-120Floor quarry 30-50Blue engineering brick 50-80Plate glass 65-70Fireclay refractory 70-300High-alumina refractory 40-300Carbon refractory 130-160Magnesite refractory 160-300Silica refractory 200-300Morphology. The study of size, shapeand texture of particles and particlecompacts. B.S. 2455,1958 defines avariety of particle shapes:Spherical - globule shaped,

approximately sphericalNodular - rounded irregularGranular - approximately equi-

dimensional, but irregularIrregular - lacking all symmetryCrystalline - geometric, as freely

developed crystals in a fluidDendritic - branched crystallineAcicular - needle shapedAngular - sharp-edged, polyhedralFlaky - plate-likeFibrous - threadlikeMortar. Material for the joining ofstructural brickwork. B.S. 4551 includestests for sampling, chemical analysis,

consistency, flow properties, stiffeningrate and strength of mortars. It givescompositions, methods for theircalculation, and tables of mixproportions.. See also REFRACTORY

MORTAR, and B.S. 1902 Pt 11. The usualtypes of building mortars, and theproportions (by vol.) recommended inB.S. 5628 Pt 3, are:

Type of Cement Lime FineMortar Aggre-

gateCement 1 0-1A 3MortarCement-Lime 1 1 5-6MortarCement-Lime 1 2 8-9MortarCement-Lime 1 3 10-12MortarLime Mortar - 1 2-3

ASTM standards for mortar includeC270; Cl 142 for ready-mixed mortar;C780 for evaluation of mortars. Nineother ASTM standards specifyaggregates, grouts and special tests. Seealso ACID RESISTANT CEMENTS.Morted Ware. A fault in pottery-wareresulting from a small localconcentration of soluble salts forming onthe surface of the green ware or thebiscuit ware. In the green state the faultmay result from a drop of water fallingon the ware, during fettling for example.In the biscuit state, the fault arises frommoisture condensing on the ware duringthe early stages of firing.Mosaic. Small pieces of coloured glass orclay tile arranged to form a pattern orpicture and cemented to a wall or floor.(The word is cognate with Muse, aGreek goddess of the arts.) In the USAthe largest facial area for a ceramicmosaic tile is 6 in2 (3750 mm2).

Mottling. ( I )A form of decorationapplied to vitreous enamelware, toglazed ceramic tiles, and to some studiopottery. For tiles the effect is producedby hand, with a sponge, or by a rubberroller.(2) The staining that sometimes developsduring the firing of silica refractories; thestains are irregular in shape and varyfrom red to brown. The cause isprecipitation of Fe2O3 from solution inthe matrix of the brick. These stains arealso sometimes referred to as LIVERSPOTTING Or FLOWERS.Mould (for the Shaping of Pottery). Theplaster moulds used for the casting,jiggering and jolleying of pottery-ware aremade as follows. Stage 1, Model: theprototype of the piece of ware that is to bemade is usually shaped of clay,occasionally of wood or plaster. Stage 2,Master Mould: plaster is cast round themodel: depending on the shape of thelatter, the mould, when set, may need tobe cut into several pieces. Stage 3, CaseMould: a replica of the original model,usually made by casting plaster in themaster mould, which is first coated with aseparating agent, e.g. soft soap. Morerecently, organic plastics have been used inthe making of case moulds; they are costlybut, owing to their hardness, have a longlife. Stage 4, Working Mould: as manymoulds as may be required are made bycasting plaster around the case mould.Mouldable. A mixture, containinggraded refractory aggregate and otherplasticizing and/or bonding materials,which will harden when heated, by theformation of a chemical and/or a ceramicbond. Such a mixture is supplied mixedwith an appropriate addition of water orother liquids, and in a workablecondition ready for installation by handor pneumatic ramming. (Mouidables aredistinguised from RAMMING MIXES (q.v.)

by having a WORKABILITY (BS 1902 Pt7.2) greater than 15%.Mould Brick. A fireclay brick, or a heat-insulating brick shaped to fit in the topof an ingot mould to help to maintainthe steel at the top of an ingot moltenuntil the main part of the ingot hassolidified.Mould Mark. A fault on glass-warecaused by an uneven mould surface, or,in the case of curved glass sheets, by thedies or frame used in its shaping (seealso JOINT LINE).Mould Plug. A piece of refractorymaterial, or metal, for sealing the bottomof an ingot mould in the casting of steel.(See also PLUG.)Mould Release. After casting orpressing, the ceramic shape must beremoved from the mould withoutdamage or distortion. Such mould releasedepends partly on good mould design,but can be aided by lubricating themould surface prior to use with a mouldrelease agent. Mould release from metalmoulds can be achieved electrically. Anapplied potential causes water in theceramic compact to migrate to the mouldsurface, there providing lubrication.Mould Runner. A man or youth who, inold pottery factories, carried filledmoulds from the making department tothe drying room and empty moulds backagain to the maker; this work has nowbeen eliminated by the introduction ofdryers of various types placed adjacentto the making machines.Mouldable Refractory. A mixture ofgraded refractory aggregate (oraggregates) and a plasticizer, usuallyclay, supplied mixed with water so that itis already workable; chemical bondingagents may also be incorporated; theworkability is such that the material canreadily be placed by hand malleting.Also known as a PLASTIC REFRACTORY.

Mounted Point. A small abrasive unit,variously shaped, permanently mountedon a spindle.Mouth (of a Converter). See NOSE.Mouthpiece. There is a difference inusage of this term as applied to a PUG(q.v.) or AUGER (q.v.): more commonlyit refers to the die only, but sometimesto the die-plus-spacer.Move. In the hand-made glass industry, astipulated output per CHAIR (q.v.) for anagreed rate of pay.Moving-fire Kiln. See ANNULAR KILN.Mud Hog. A US machine for thedisintegration of dry or moist plasticclay. It consists of a rotating swinghammer operating close to a series ofanvils linked together to form a steeplyinclined slat conveyor.Muff. A blown cylinder of glass, cut andflattened while plastic, to make smallpieces of flat glass.Muffle. A refractory internal shell,forming a permanent part of some fuel-fired kilns. Ware placed in a muffle isprotected against contact with thecombustion gases. In small laboratorykilns the muffle is usually a singlerefractory shape; in industrial kilns themuffle is built up with refractorybrickwork. In a SEMI-MUFFLE therefractory protection acts only as a shieldagainst direct flame impingement, thecombustion gases subsequently beingfree to pass through the setting.Mulberry. A cobalt stain modified to apurple colour by the addition ofmanganese dioxide.Muller Mixer. A WET PAN (q.v.) inwhich the mullers are suspended out ofcontact with the pan bottom. Thus thematerial charged to the pan is mixedwithout further grinding taking place.Mullet. A knife-shaped piece of ironused in severing a handmade glass bottlefrom the blow-pipe.

Mullite. The only compound of aluminaand silica that is stable at hightemperatures (m.p. 18500C). Thecomposition is 3Al2O3.2SiO2 but it cantake Al2O3 into solid solution. Mullite isformed when any refractory clay is firedand is an important constituent ofaluminosilicate refractories, aluminousporcelains, etc. In USA, mulliterefractories are defined (ASTM - C467)as containing 56-79% Al2O3.Multi-bucket Excavator. A type ofmechanical excavator sometimes used inthe getting of brick-clays. Buckets arecarried by endless chains round a steelboom (known as a 'ladder') and as theytravel they scoop up clay. This type ofexcavator normally gets clay from belowthe level on which the truck of themachine is standing.Mul-T-Cote. Tradename, A coatingmachine for glass containers particularlybottles. A single polyurethane-basedcoating can be applied for decoration, ora double coating with a second 'highmodulus' polyurethane to provideresistance to shock, scratches chemicalattack, and to ultraviolet light. Coating isby dipping and drying. (Moon-Star,Japan and Smit Oven, Neths).Multiflies. A tiling system in which tentiles may be fixed simulaneously on to areinforced screed covered with a contactslip. Various joint patterns can be made,with exact bond widths. (Fliessen Flatten37 (3) 64 1987).Multiform Process. Dry-milled glasspowder is mixed with an organic binderand a fluid vehicle, spray-dried and theagglomerates pressed, to form smallarticles of complex shape such as threadguides and television tube electron gunmounts.Multijet Kiln. Outside fresh air is fedthrough the roof to the top of the kiln,so that convection automatically

establishes an even temperaturedistribution. (Solaquaire Corp. USA).Multi-passage Kiln. A kiln consisting ofa number of adjacent tunnels, each ofsmall cross-section, through which theware is pushed on refractory bats. Thesekilns may be electric or gas-fired. Thetypical electric multi-passage kiln has 24passages arranged 4 across and 6 high;the ware is pushed in opposite directionsin adjacent passages. Gas-fired multi-passage kilns usually have only 4passages and the ware is pushed in thesame direction in each passage.Multiple-hearth Furnace. A furnacedesigned primarily for the roasting ofores in the non-ferrous metal industry,but which has more recently beenadapted to the calcination of fireclay toproduce CHAMOTTE (q.v.). The furnaceis in the form of a large, squat, verticalcylinder and consists of several hearthsaround a central shaft on which rabblearms are mounted. The material to becalcined is charged to the top hearth andslowly descends, hearth by hearth, to thebottom, where it is discharged.Munsell System. A method of colournotation based on evaluation of threeparameters: lightness, hue andsaturation. (A. H. Munsell, A ColourNotation, Munsell Color Co., Inc.,Baltimore, USA.)Munter Wheel. A rotary air/air heatexchanger, fitted between the exhaustand supply air ductwork of kilns anddryers. The device was originallydeveloped in Scandinavia for theprinting trade, in which additionaleconomies were achieved by therecovery of condensed solvents.Murgatroyd Belt. That part of the sidewall of a glass container in which stressesare concentrated following thermalshock; the belt normally extends fromthe base to about three-quarters of the

height of the wall. (J. B. Murgatroyd, /.Soc. Glass Tech., 27, 77, 1943)Murray-Curvex Machine. A device foroff-set printing from an engraved copperplate on to pottery flatware by means ofa solid convex pad of gelatine. Cold-printing colours are used, the mediumbeing formulated from synthetic resinsand oils. Output is about 1200 pieces/day. (G. L. Murray, Brit. Pat., 735 637,24/8/55; 736 312, 7/9/55.) In modernembodiments of this machine, siliconerubber replaces the gelatine pad, toobtain greater dimensional stabilitywhen temperature and humidity vary;inks need to be compatible with thesilicone; the engraved copper plate maybe replaced by a PHOTOPOLYMER PLATE(q.v.) for quicker and cheaperproduction of designs. See also TOTAL

TRANSFER PRINTING.Muscovite. A mica approximating incomposition to (Na, K)2O.3Al2O3.6SiO2.2H2O; it is in this formthat most of the alkali is present in manyclays. Thermal expansion (20-8000C) 9.6x 10-6. When heated, mica begins to losewater at about 2500C but, at normalrates of heating, dehydration is notcomplete until about 11000C; theproduct is a glass containing mullite andsome free Al2O3.Musgrave-Harner Turbidimeter. Aninstrument developed in 1947 by J. R.Musgrave and H. R. Harner of theEagle-Picher Co., Missouri, USA: it hasbeen used for the particle-size analysis ofclays and other ceramic raw materials inthe range 0.25-60jim.Mussel Gold. An old form of preparedgold for use in the decoration of pottery.It was made by rubbing together goldleaf, sugar (or honey) and salt; the pastewas then washed free from solublematerial and, traditionally, stored inmussel shells.

Mycalex. Trade-name: a particular typeof MICA (GLASSBONDED) (q.v.). Mycalexand T.I.M. Ltd., Cirencester, England).Mylius Test. See IODOEOSIN TEST.n, nD, etc. Symbol for refractive index,the subscript indicates the spectral lineto which the quoted value refers, e.g. nD

= the refractive index for a wavelengthequivalent to the sodium D line.v-value. Alternative name for ABBEVALUE (q.v.).Nabarro-Herring Creep, CREEP (q.v.)controlled by the diffusion of vacanciesthrough the lattice (bulk diffusion). Thecreep rate is proportional to the squareof the grain size. (F.R. Nabarro,Conference on the strength of solids,Bristol University 1947, and C. HerringJ. AppL Phys 21,1950, p437).Nacrite. Al2O3.2SiO2.2H2O. A rare,exceptionally well crystallized, claymineral of the kaolinite group.Naftoflex. Trade-name. A range of fluidpolymers, which can be cured with ahardener to form rubber-like or hardplastics at room temperature. They areused to make case moulds.(Metalgesellschaft AG, Frankfurt/Main.Nalfloc. Trade-name. Colloidal silica.(Nalfloc, Northwich, 1970).Nanoperm. See PERM.Nanostructure. Particle size, porosity andother structural features of ceramics onthe scale of approximately lnm (Kh9

metre) of microstructure.Naples Yellow. See LEAD ANTIMONATE.Napoleon Green. A ceramic colour thatcan be fired-on at temperatures up to10000C. It consists of (%): CoO, 30;Cr2O3. 45; hydrated Al2O3,15; ZnO, 10.Nasicon. The compound Na3Zr2PSi2O12

is a superionic conductor withapplication as a solid electrolyte.Natch. The key (a hemispherical hollowand complementary protrusion) in a two-or multi-part plaster mould for pottery

making; the purpose is to ensure that theparts fit correctly. Occasionally known asa JOGGLE.Natural Clay Tile. US term defined(ASTM - C242) as a tile made by eitherthe dust-pressed method or the plasticmethod from clays that produce a densebody having a distinctive, slightlytextured, appearance.Natural Gas. Gas from large naturalunderground deposits (in Britain, chieflybelow the North Sea). The gas is chieflymethane, and has provided a readilycontrollable, clean burning, sulphur freefuel for the ceramics industry since the1970's. Cf. LPG.Navvy. Old name for a MECHANICALSHOVEL (q.v.) - from its original use incanal ('Navigation') excavation.NDE. Non-Destructive Evaluation(q.v.).NDT. Non-Destructive Testing (q.v.)Neapolitan Yellow. See LEADANTIMONATE.

Neat Work. In a brick structure, thebrickwork set out at the base of a wall.Near-net shaping. Shaping methods forgreen ceramics which provide a closeapproximation to the final fired shape,minimising the need for expensivediamond grinding of the fired shape toachieve the required shapes and sizetolerances. This is particularly importantwhen making complex shapes to closetolerances from hard, wear resistantengineering ceramics.Nebuchadnezzar. A 20-quart wine bottle(the largest size).Neck. (1) That part of a bottle betweenthe FINISH (q.v.) and the shoulder.(2) A stack of unfired bricks as set in aCLAMP (q.v.).Neck Brick. US term for FEATHER-END(q.v.).Neck Mould or Neck Ring. The mouldthat shapes the neck of a glass bottle.

(Also known as a FINISH MOULD orRING MOULD.)Needle or Plunger. A refractory part ofa feeder in a glassmaking machine; itforces glass through the orifice and thenpulls it upwards after the shearingoperation.Needling. A process for bondingrefractory fibres into a blanket.Negative thixotropy. A phenomenon,displayed by suspensions of some clayminerals, in which fluidity increases withresting time, and the hysteresis loops areclockwise.Nelson Stud. A proprietory form of stud,fusion welded in place.Neo-Ceramic Glass. A term proposed byB. V. Jana Kiramarao Glass Tech., 5, (2).67, 1964) for DEVITRIFIED GLASS (q.v.).In defining the term, absence ofnucleation after 4 h heating at thedeformation temperature is taken as anarbitrary criterion for distinguishingbetween neo-ceramic glasses and stableglasses.Neodymium Oxide. Nd2O3; m.p. 22700C;thermal expansion (25-10000C) 11.4 x10"6. This oxide imparts a violet colourto glass.Neophane Glass. A yellow glass forautomobile sunroofs, sunglasses, etc.tinted with neodymium oxide to reduceglare.Nepheline Syenite. An igneous rockcomposed principally of nepheline(K2O.3Na2O.4Al2O3.8SiO2) andfeldspar. There are large deposits inOntario (Canada), and Stjernoy(Norway). It is used as a flux inwhiteware bodies, and as a constituent ofsome glasses and enamels.Nernst Body. A sintered mixture ofthoria, zirconia and yttria together withsmall amounts of other rare-earthoxides. After it has been preheated toabout 20000C this body becomes

sufficiently electrically conducting foruse as a resistor in high temperaturelaboratory furnaces. (W. Nernst, Brit.Pat. 6135,12/3/1898.)Network-forming Ion. One of the ions ina glass that form the network in the glassstructure as postulated by Zachariasen(see under GLASS). The ratio of the ionicradius of the network-forming ion to thatof the oxygen ion must lie between 0.155and 0.225 for triangular co-ordination, orbetween 0.225 and 0.414 for tetrahedralco-ordination; such ions include B3+,Al3+, Si4+ and P5+.Network-modifying Ion. One of the ionsin a glass which, according toZachariasen's theory (see under GLASS),do not participate in the network. Theymust have a rather large radius and alow valency, e.g. the alkali metals andthe alkaline earths.Neuberg Blue. A pigment comprisingcopper carbonate, and iron ferrocyanideand sulphate.Neumann - Kopp Rule. The heatcapacity of a compound is equal to thesum of those of its components in thesame standard state at the sametemperature. This implies that there isno change in heat capacity on formationof the compound, and so the entropy offormation is zero - an assumption morelikely to be valid for non-ioniccompounds.Neutral Glass. A name sometimesapplied to glass that is resistant tochemical attack; such glasses commonlycontain 8-10% B2O3. (cf. NEUTRAL-TINTED GLASS).Neutral Refractory. A refractorymaterial such as chrome ore that ischemically neutral at high temperaturesand so does not react with either silica orbasic refractories.Neutral-tinted Glass. A grey glass,usually of the borosilicate type; these

glasses are used in light filters to reducethe transmission without (as far aspossible) selective absorption ofparticular wavelengths (cf. NEUTRALGLASS).Neutralizer. A dilute solution of alkali orof sodium cyanide used in the treatmentof the base-metal for vitreous enamellingafter the PICKLING (q.v.) process. AlkaliNeutralizer consists of a warm (65-700C)solution of soda ash, borax or trisodiumphosphate, the strength being equivalentto 0.3-0.4% Na2O. Cyanide Neutralizeris a 0.10-0.15% solution of sodiumcyanide: other ingredients may bepresent to neutralize the hardness of thewater.Neutron-absorbing Glass. For thermalneutron-absorption a glass must containcadmium, which is the only commonglass constituent having a high neutron-capture cross-section; it is used to form acadmium borate glass, which is mademore chemically durable by the additionof TiO2 and ZrO2.New Mine Fireclay. A fireclay (there arefive seams) occurring below the OLDMINE FIRECLAY (q.v.) in the Stourbridgedistrict. England.Newcastle Kiln. A type of intermittentkiln formerly popular in the Newcastle-on-Tyne area. In its original form it is arectangular kiln with two or threefireboxes at one end and openings forthe exhaustion of waste gases at the baseof the other end-wall, which incorporatesa chimney. In a later design the kiln is ofdouble length, there are fireboxes ateach end, and the waste gases areremoved from the centre of the kiln.Such kilns found particular use in thefiring of refractories and salt-glazedware.Newtonian Fluid. A fluid for which theratio of the shear stress to the shear rateis constant; this constant is the viscosity.

Ceramic slips approach Newtonianbehaviour when completelydeflocculated. (cf. BINGHAM BODY;DILATANCY; RHEOPEXY; THIXOTROPY)Nextel. Trade-name. 3M Corp. Mullitefibres.Nib. (I)A protrusion at one end of aroofing tile serving to hook the tile onthe laths in the roof.(2) A fault in flat glass, in the form of aprotrusion at one corner, caused duringcutting.Nibbed Saggar. A SAGGAR (q.v.) withinternal protrusions to support a bat(thus permitting the placing of twoseparate layers of ware) or to allow acover to be placed inside the top of thesaggar.Nibber. A US term for the squeegeeblade in SCREEN PRINTING (q.v.)Nicalon. Silicon carbide yarn (i.e. acontinuous thread, not simply discretefibres) made by Nippon Carbon Co.Nickel Dip. Also sometimes known asNICKEL FLASHING Or NICKEL PICKLING.A process for the treatment (afterPICKLING (q.v.)) of base-metal forvitreous enamelling to improveadherence and reduce the likelihood ofCOPPERHEADS (q.v.) and FISH-SCALING(q.v.). A solution of a nickel salt, e.g. thesulphate or double ammonium sulphate,is used; boric acid and ammoniumcarbonate are also added in smallamounts to give the correct pH. In analternative process the nickel isdeposited on the metal by the additionof a hypophosphite solutionNickel Oxide. There are two commonoxides: grey, NiO, m.p. 19800C; black,Ni2O3. They are used (about 0.5% ofeither type) in ground-coat enamels forsheet steel to promote adherence, and inferromagnetic ferrites.Niobates. Compounds of metals withNb2O3, usually made by firing the oxides

or their precursors together. Best knownare lithium niobate (LiNbO3) and leadniobate (PbNb2O6). They have astructure similar to, but of lowersymmetry than the PEROVSKITES, (seeTUNGSTEN BRONZE) and have highpolarizability, and so are piezoelectric,pyroelectric or ferroelectric compounds.Lithium niobate is used in laser andmicrowave electronics applications. Leadniobate is used for high-temperaturepiezoelectric transducers. Some niobatesare RELAXOR (q.v.) ferroelectrics. PNN,PZN, PFN, PMN are lead niobates withnickel, zinc, iron and magnesiumrespectively.Niobium Borides. Several compoundshave been reported, including NbB2;decomposes at 29000C; sp. gr. 7.0:thermal expansion, 5.9 x 10-6 parallel toa and 8.4 x 10-6 parallel to c. NbB; m.p.23000C; sp. gr., 7.6. Nb3B4; meltsincongruently at 27000C, sp. gr. 7.3.Niobium Carbide. NbC; m.p. 35000C; sp.gr. (theoretical), 7.8 g/ml; modulus ofrupture (25°C), 25 MNm-2; thermalexpansion (25-15000C) 7.5 x 10-6.Niobium Nitrides. Three nitrides havebeen reported: NbN, Nb2N and Nb4N3.During reaction between Nb and N2 at800-15000C the product generallyconsists of more than one compound.Most of the phases are stable at least to15000C.Niobium Oxide. The commonest oxide isNb2O5; m.p. 1485°C; sp.gr.4.6.Niopside. The nickel analogue,CaO.NiO.2SiO2, of diopside.Nip. A small glass bottle for mineralwater.Nitre. See POTASSIUM NITRATE.Nitrides. A group of special ceramicmaterials: see under the nitrides ofthe following elements: Al, Be, Cr,Ga, Hf, Mo, Nb, Si, Ta, Th, Ti, U, V,W, Zr.

Nitriding. The production of nitridesfrom a porous metal shape, by directreaction with nitrogen gas infiltrating thepores.Nitrogen Ceramics. The nitrides,oxynitrides, sialons and relatedcompounds containing nitrogen.Nitty Enamel. Vitreous enamelcontaining almost imperceptible smallsurface pits.Nobel Elutriator. An early type ofmultiple-vessel elutriator for particle-sizeanalysis; it is described in Z. AnalChem., 3, 85,1864.Noborigama. A step kiln invented inChina c. 400 B.C. and introduced intoJapan c. 1300 A.D. It comprisessuccessive chambers built into the side ofa hill, and will fire pottery to 13000C.(Keram Z. 35 (3) 149 1983).No-Cement Castable. Alumina andaluminosilicate castable refractorieswhich do not contain hydraulic settingcement and in which the bonding agentscontribute no significant amount of lime(CaO). The product might contain up to0-2% total lime (CaO) on a calcinedbasis as contributed by the aggregate.(ASTM C401-91).Nodular, see MORPHOLOGY.Nodular Fireclay. An argillaceous rockcontaining aluminous and/or ferruginousnodules.No-fines Concrete. Concrete made withaggregate from which all the finematerial, i.e. less than 9 mm, has beenremoved; the proportion of cement toaggregate varies from 1:8 to 1:12 (vol.).The strength is low (7-8.5 MNm-2) butso too are heat and moisture transfer.Nominal Dimension. As applied tohollow clay building blocks this term isdefined in the USA (ASTM - C43) as: Adimension that may be greater than thespecified masonry dimension by thethickness of a mortar joint.

Nomogram or Nomograph. Two or morescales drawn as graphs and arranged sothat a calculation involving quantitiesrepresented by the scales can be reducedto a reading from the diagram. Examplesof the use of nomograms in ceramicsinclude the determination of porosity,the solids concentration in slips, thedrying and firing shrinkage of clay pipes.Non-Destructive Evaluation, Non-Destructive Testing. Methods ofmeasuring the properties of materialswhich preserve the items tested; e.g.strength measurements relying onmeasuring elastic propertiesultrasonically, rather than by breakingrods. Such techniques are of greaterimportance in the testing of expensiveengineering ceramics, especially when itis desirable to evaluate the properties ofshaped and fired components. ASTMCl 175 specifies test methods andstandards for the non-destructive testingof advanced ceramics, largely ultrasonicand radiographic techniques.Non-load Bearing Tile. US term for ahollow fired-clay building block for usein masonry carrying no superimposedload.Non-metallic Inclusion. A non-metallicparticle that has become embedded insteel during its processing. Tests,particularly those employing radioactivetracers, have shown that (contrary toearlier belief) these inclusions rarelyoriginate from the refractory materials ofthe furnace, ladle or casting-pit.Non-Oxide Ceramics. A useful generalterm for ceramics (such as borides,carbides, nitrides) in whose structureoxygen plays no role.Non-Plastics. (1) Those components ofa TRIAXIAL WHITEWARE BODY (q.V.)having no inherent plasticity of theirown. (2) Ceramic materials (e.g.alumina) with no inherent plasticity,

requiring the addition of a PLASTICIZER(q.v.) to allow them to be shapedsatisfactorily.Non-stoichiometric. A chemicalcompound is said to be nonstoichiometricif the ratio of its constituents differs fromthat demanded by the chemical formula.This may happen with oxides that arereadily reducible, or with compoundscontaining an element of variablevalency, or when interstitial atoms arepresent in the lattice. Some non-stoichiometric ceramics are of interest asbeing semi-conducting.Non-vitreous or Non-vitrified. Thesesynonymous terms are defined in USA(ASTM-C242) in terms of water-absorption: the term non-vitreousgenerally implies that the ceramicmaterial has a water absorption above10% except for floor tiles and wall tileswhich are considered to be non-vitreousif the water absorption exceeds 7%.Norfloat, Norflot. A Norwegian feldspar(the latter is the German spelling).Normal Spinel. See SPINEL.Norman Brick. A long brick, 2%rds x 4 x12 in. (68 x 102 x 305 mm).Norman Slabs. A type of glass forstained windows; it is made by blowingbottles of square section and cuttingslabs of glass from the four sides.Normative Analysis. The CALCULATED

MINERALOGY (q.V.)Nose or Mouth. The constricted circularopening at the top of the refractorylining of a CONVERTER (q.v.); throughthis opening molten pig-iron is chargedand steel is subsequently poured.Nose-ring Block. A block of refractorymaterial specially shaped for buildinginto the discharge end of a rotary cementkiln; also known as a DISCHARGE-ENDBLOCK.

Nose-ring Dam. A deep dam, or (bandof thicker refractory) at the discharge

end of a rotary kiln, to ensure anextended soaking period for the charge.Nostril. The term used for the refractorygas- or air-port in a gas retort.Nostril Blocks. See RIDER BRICKS.Notch. See SLAG NOTCH.Notch Test. A test proposed by R. Roseand R. S. Bradley (/. Amer. Ceram. Soc,32, 360,1949) for the assessment of thelow-temperature spalling tendency offireclay refractories. A notch is made ina transverse-strength test-piece and theeffect of this on the strength at 8000C isdetermined; if the transverse strength isbut little reduced by the notch, the low-temperature spalling resistance of thefireclay refractory will be good.Novamur. See HELTON.Novorotor. A double-rotor hammer millfor clay preparation. (Hazemag,Germany cf UNIROTOR).NOx. A general (punning) term for theoxides of nitrogen, now subject to emissionlimitation rules for noxious gases.Nozzle. A cylindrical fireclay shapetraversed by a central hole of uniformdiameter; the top of the nozzle iscontoured to form a seating for aSTOPPER (q.v.). Nozzles are fitted in thebottom of ladles used in the teeming ofsteel. In the USA, three qualities arespecified in ASTM - C435.NSC Clay. A blended clay withcontrolled casting concentration, tailoredto casting sanitaryware (English Clays,St Austell, Cornwall).NTC. New Tundish Coating. Theautomatic spraying of a tundish withrefractory, 75-90% MgO. (Foseco,Japan).Nucerite. Trade-name. A glass-ceramiccoating for metal (Pfaudler Permutit Inc,New York, 1966; Pfaudler Balfour,Leven, Scotland, 1990).Numerical Aperture (NA). The sine ofthe maximum launch angle (the

acceptance angle) that allows totalinternal reflection and hencetransmission of a signal down an opticalfibre. Optical fibres usually have a coreglass of refractive index nt, surroundedby a cladding glass of refractive index n2.(NA)2 = Ti1

2 - n22.

Nu-Value. See ABBE VALUE.Nuclear Reactor Ceramics. These specialceramics include: fuel elements - UO2,UC and UC2; control materials - rare-earth oxides and B4C; moderators - BeOand C.Nucleation; Nucleating Agent.Nucleation is the process of initiation ofa phase change by the provision ofpoints of thermodynamic non-equilibrium; the points are provided by'seeding', i.e. the introduction of finely-dispersed nucleating agents. The processhas become of great interest to theceramist since DEVITRIFIED GLASS (q.v.)became a commercial product.NZP. Sodium Zirconium Phosphate.Materials of this structural group havevery low and highly anistropiccoefficients of thermal expansion. Thestructure consists of PO4 tetrahedra andZrO6 octohedra linked by shared oxygenatoms at the corners. Each member ofthe alkali zirconium phosphate familycan be derived from this structure byrotating the polyhedra in the network.Obsidian. A natural glass. A darktransparent, siliceous igneous materialwhose composition is similar to granite.Obscure Glass. Glass designed or surfacetreated to diffuse the light it transmits, toprevent objects behind it being seenclearly.Occlusion. Trapping of gas or liquidwithin a solid.Occupational Exposure Standard. Theconcentration of an airborne substance,(averaged over a reference period) atwhich according to current knowledge,

there is no evidence that it is likely to beinjurious to employees if they areexposed by inhalation day after day tothat concentration. Control of exposureis considered adequate if the OES is notexceeded, or if it is exceeded, theemployer has identified the reason and istaking appropriate steps to comply withthe OES as soon as is reasonablypracticable. See Occupational ExposureLimits, Criteria Document Summaries.HSE, London HMSO 1993.Ochre. Impure hydrated iron oxide usedto a limited extent as a colouringmaterial for coarse pottery and structuralclayware.Ocrate Process. The treatment ofconcrete with gaseous SiF4 to transformany free CaO into CaF2. The treatedconcrete has improved resistance tochemicals and to abrasion. (Ocriet-fabriek NV, Baarn, Holland.)Octa-comb System. This system forinstalling ceramic fibre panels requiresno pre-anchoring plan, but uses stud-welding of octagonal packs.Octahedrite. See ANATASE.Octopus. A system of firing intermittentkilns with gas or pulverised fuel, so-called from the spoke-like arrangementof burners across the kiln roof. Thesystem was developed by National CoalBoard and Gibbons Bros (see e.g.Clayworker 83, (983), 16, 1974)Oddments or Fittings. Special glazedclayware shapes used in conjunction withglazed pipes. These shapes includeBends, Junctions, Tapers, Channels,Street Gullies, Syphons, Interceptors andYard Gullies; the first five of these aremade partly by machine and partly byhand, the last three items have to beentirely hand-moulded. For dimensionssee B.S. 539.Oden Balance. Apparatus for particle-size analysis; one of the pans of a

delicate balance is immersed in thesettling suspension and the change inweight as particles settle on the pan ismeasured. (S. Oden, Internal Mitt.Bodenk., 5, 257, 1915)OES Occupational Exposure Standard.Off Gases. The exhaust or stack gasesfrom a kiln firing ceramics, particularlythose that originate from the body beingfired or the burnout of binders.Off-hand. Hand-made glass-wareproduced without the aid of a mould.Off-hand Grinding. See FREEHAND

GRINDING.

Offset. A recessional set-back ofbrickwork, e.g. in a domestic chimney.Offset Finish. See FINISH.Offset Printing. A process of decorationas applied, for example, in the MURRAY-CURVEX MACHINE (q.V.).

Offset Punt. Term applied to the bottomof a bottle if it is asymmetric to the axis.OH Furnace. See OPEN-HEARTHFURNACE.

Oil Spot. A surface fault, seen as amottled circle, on electric lamp bulbs orvalves; it is caused by carbonization of acontaminating drop of oil.Old Mine Fireclay. A fireclay occurringin the Brierley Hill district, nearStourbridge (England); it usuallycontains 56-64% SiO2, 25-30% Al2O3

and > 2.5% Fe2O3. A smooth plasticfireclay formerly much used for makingglass-pots, but now largely workedout.Old Roman Tile. Roofing tiles designedfor use in pairs: a flat under-tile (theTegula) is laid adjacent to a roundedover-tile (the Imbrex), cf. ROMAN TILE;

SPANISH TILE.

Olivine. A mineral consisting principallyof a solid solution of FORSTERITE (q.v.)and FAYALiTE (q.v.). Rocks rich inolivine find some use as a raw materialfor the manufacture of forsterite

refractories and, when crushed, as afoundry sand.Omnicon. A linescan computerisedimage analyser for measuring particlesize and shape. (Trade-name, Bausch &Lomb Corp.).Once-fired Ware (UK) or Single-firedWare (USA). Ceramic whiteware towhich a glaze is applied before the wareis fired, the biscuit firing and glost firingthen being combined in a singleoperation. Because the glaze mustmature at a relatively high temperature,it is usually of the leadless type.Sanitary-ware is the principal type ofware made in this way.One-Coat ware. Articles with a singlecoat of vitreous enamel, though the termis sometimes used as a contraction ofone-cover coat ware, in which case asingle cover coat is applied over aground coat.One-fire Finish. US term for vitreousenamelware produced by a single firing.One-high firing. The American term forSINGLE LAYER SETTING (q.V.).O'Neill Machine. A machine for makingglass bottles originally designed byF. O'Neill in 1915; it was based on the useof blank moulds and blow-moulds. Theprinciple in modern O'Neill machines isthe same; they are electrically operatedand are capable of high outputs.On-glaze Decoration. Decoration appliedto pottery after it has been glazed; theware is again fired and the colours fuseinto the glaze, the decoration thusbecoming durable. Because thedecorating fire can be at a lowertemperature with on-glaze decoration, amore varied palette of colours is availablethan with under-glaze decoration. A testfor the resistance to detergents isprovided in ASTM - C556.Ooms-Ittner Kiln. An annular,longitudinal-arch kiln divided into

chambers by permanent walls and with aflue system designed for the salt-glazingof clay pipes; the fuel can be coal, gas oroil. Ooms-Ittner Co., Braunsfeld,Cologne, Germany.)Opacifier. A material added to a batchto produce opal glass, or to a glaze orenamel to render it opaque. Glass isusually opacified by the addition of afluoride, e.g. fluorspar or cryolite; forglazes and enamels the oxides of tin,zirconium or titanium are commonlyused.Opacity. Defined in ASTM - C286 as:The property of reflecting light diffuselyand non-selectively. For a definitionrelating specifically to vitreous enamelSee CONTRAST RATIO.Opal. Non-crystalline hydrated silica.Opal Glass. A translucent to opaqueglass with a 'fiery' appearance. (Cf.ALABASTER GLASS). Opal glasses aremade by phase-separation processeswhich produce dispersed crystals in theglass. In crystalline opals these crystalsform spontaneously during cooling fromthe melt or later heat treatment duringmanufacture. NaF or CaF2 crystals arecommonest. Liquid - liquid opals areformed by separation of the glass intotwo distinct glassy phases while it is stillsoft. Reheat or restrike opals are clearafter forming, and are reheated toproduce the phase separation. Theiropacity is due to light scattering, anddepends on the difference in refractiveindex between the phases, the degree ofphase separation and the sizedistribution of the dispersed secondphase. Opal glasses are usually madecreamy white, and used for dinnerware.Liquid-liquid opal is more expensive tomake, but process control is better.Opalizer. A substance (usually afluoride) which will produce opalescence(iridescent reflection) in glass.

Opaque Ceramic Glazed Tile. US term(ASTM - C43) for a hollow clay facingblock the surface faces of which arecovered by an opaque ceramic glazewhich is coloured and which has a brightsatin or gloss finish.Opatowski Process. A process for theextraction of BeO from siliceous ores.The ground ore is mixed with NH4HSO4

and water and heated to 95°C todissolve metal salts. Mn is oxidised usingNH4S2O8, and ammonia treatmentprecipitates the metals as hydroxides.After separation, treatment with NaOHdissolves the beryllia as Na2BeO2, whichis hydrolized to Be(OH), which onheating to 2500C, decomposes toberyllia, BeO. The process is effectivefor concentrations of BeO in the ore of51%, and the (NH4)2SO4 formed isrecycleable. (J. Opatowski, CanadianPat. 663 776 1962).Open Flame kiln. A kiln in which theware being fired is exposed directly tothe burning gases of the flame.Open Handle. A cup handle of the typethat is attached to the cup at the top andbottom only, the side of the cup itselfforming part of the finger-opening (cf.BLOCK HANDLE).Open-hearth Furnace. A largerectangular furnace in which steel,covered with a layer of slag, is refined ona refractory hearth; it is heated by gas oroil, and operates on the regenerativeprinciple which was first applied to thistype of furnace by Sir Wm. Siemens in1867 (hence the earlier name SIEMENSFURNACE). The type of refractory liningdepends on the particular steelmakingprocess used: see ACID OPEN-HEARTH

FURNACE, BASIC OPEN-HEARTHFURNACE and ALL-BASIC FURNACE. Theprocess is now obsolete.Opening Material. Term occasionallyused for a non-plastic that is added to a

clay to decrease the shrinkage andincrease the porosity; such materialsinclude grog, chamotte, sand andpitchers.Op-po Mill. Tradename. A mill for thevibratory grinding of fine powders.Podmore & Sons, Stoke-on-Trent.Optical Blank. A piece of optical glassthat has been pressed to approximate tothe shape finally required; also called aPRESSING.Optical Crown Glass. Any glass of lowdispersion used for optical equipment(cf. flint glass). There are many varieties,their names indicating theircharacteristic composition, e.g. bariumcrown, borosilicate crown, fluor-crown,phosphate crown, zinc crown.Optical Fibres. Fine glass fibres alongwhich information can be transmitted bytotal internal reflection of coherent lightsignals. One fibre may be several kmlong and carry as much information ascan several thousand telephone wires.Glasses in the GeO2-SiO2 system areusually used, with additions of P2O5 toease fabrication and of chlorides toadjust the resultant refractive index tothat of silica. The fibres are made by oneof several vapour-phase techniques.Volatile halides (SiCl4, GeCl4 andPOCl4) and high purity gases (Cl2, O2,C2Cl2F2 etc) deposit glass onto a suitablesubstrate after a high temperatureoxidation or hydrolysis reaction. Theresulting preform is drawn into fibreswith appropriate variations incompostion across their cross-section. InMCVD (modified chemical vapourdeposition) the vapour stream reactsinside a rotating silica tube heated by anoxyhydrogen torch. A white soot isdeposited downstream of the torch, andsintered into an internal glassy layer bymoving the torch downstream. The tubeis collapsed into a solid preform rod by

increasing the flame temperature. InOVPO (outside vapour-phaseoxidation) and VAD (vapour-phaseaxial deposition) the hydrolyzedreactants are deposited on the side of arotating starting rod (OVPO) or on theend of a rotating rod which is graduallyraised from the flame as the depositgrows (VAD). Heating may also be byplasma oxidation at RF- or microwavefrequencies, with higher reactionefficiencies. Optical fibres arecharacterized by high strength (severalGPa) due to careful surface treatmenteliminating flaws from whichmicrocracks can develop.Optical Flint Glass. See under FLINT

GLASS.Optical Glass Classification. A system bywhich an optical glass is classifiedaccording to its refractive index, nD andits Abbe Value, \). Standard borosilicatecrown glass, for example, has nD = 1.510and v = 64.4; its classification by thissystem is 510644 or 510/644. Furtheridentification is often provided by letters,preceding the number; e.g. BSC = Boro-Silicate Crown; LF = Light Flint, etc.Optical Pyrometer. A device for themeasurement of high temperaturesdepending ultimately on visual matching.The type most used in the ceramicindustry is the DISAPPEARING FILAMENTPYROMETER (q.v.); a less accurate type isthe WEDGE PYROMETER (q.V.).Optimat. A de-airing extruder designedon the basis of model experiments andtheoretical studies of the plastic flow ofclays. (Rieterwerke, Germany ZI Int 32,(5) 1980, p267).Optoelectronics. The study andapplication of the variation of the opticalproperties of materials with appliedelectric fields. See FERPICS.Orange Peel. A surface blemish,adequately described by its name,

sometimes occurring on vitreousenamelware, glass-ware and glazedceramics. In vitreous enamelling, thefault can usually be prevented by analteration in the spraying process and/orin the specific gravity of the enamel slip.Orbit Kiln. A continuous kiln for firingtableware. Each item is fired separately,and is mounted on an alloy support,coated with alumina, which rotates theware on its own axis as it passes throughthe kiln, thus ensuring uniformtemperature distribution. There is noother kiln furniture, and the ware can beloaded and unloaded automatically.(Kerabedarf, Germany).Organic Bond. (1) A material such asgum or starch paste that can beincorporated in a ceramic batch to give itdry-strength; the organic bond burnsaway during the firing process, whichdevelops a ceramic bond or causessintering.(2) Some abrasive wheels have anorganic bond such as synthetic resin,rubber or shellac, and are not fired.Organotin Compounds. Chemicalcompounds in which the element Sn iscombined with organic radicals.Organotin compounds can catalyse thehydrolysis of ETHYL SILICATE (q.v.) to agel, or mineralise MULLITE formation.Orifice Ring. See under BUSHING.Ormosil. Organically-modified silicates.Ornamental Ware. Decorative itemssuch as statuettes, figures, flowers andornamental plates. The COMBINEDNOMENCLATURE (q.v.) regards a plate asornamental if it has on its face anobviously decorative design; is not partof a table service; has a pierced rim forhanging, or other integral stand, and/oris generally unsuitable for culinarypurposes because of shape, weight,material, decoration or difficulty incleaning its non-smooth surface. The

distinction is significant becauseornamental plates do not usually need tomeet METAL RELEASE (q.v.) regulations.Orthoclase. See FELDSPAR.

Orthosilicates. See SILICATE STRUCTURES.

Orton Cones, PYROMETRIC CONES (q.v.)made by the Edward Orton Jr. CeramicFoundation, Columbus, Ohio. They aremade in two sizes: 2Vi in. (63.5 mm) highfor industrial kiln control, and 1 l/8th in.(29 mm) high for P.C.E. testing. Fornominal equivalent softeningtemperatures see Appendix 2.Osborn-Shaw Process. See SHAW PROCESS.

Osmosis. See ELECTRO-OSMOSIS.

Ostwald Ripening. Grain growth due todifferential dissolution between particlesof different sizes and shapes. Solutedissolves at sharp corners, or from smallparticles, and tends to reprecipitate oncoarser, larger or rounder particles, whichgrow at the expense of fine particles.Osumilite - see BARIUM OSUMILITE.

Outside Vapour - phase Oxidation(MCVD, OVPO and VAD). SeeOPTICAL FIBRES.

Oven. Obsolete term for a kiln, moreparticularly the old type of BOTTLE-

OVEN (q.v.).Ovenware. Ceramic whiteware orglassware (casseroles etc) of good thermalshock resistance for use in cooking.Overalls. Workers overalls in thepottery industry are designed withoutlapels, pockets and other dust traps.They are made from terylene, a smoothfibre which does not retain DUST (q.v.).Overarching. A progressive departure ofcircumferential joints in arches or ringsfrom the required radial alignment.Sometimes due to the use of too manysharply tapered bricks.Overburden. The soil and other unwantedmaterial that has to be removed before theunderlying clay or rock can be worked bythe open-cast method.

Overflow Process. A DOWNDRAW

PROCESS (q.v.) for special glasses, rangingfrom soft photochromic glasses to hardchemically strengthened aluminosilicateautomobile glass. Molten glass flows into atrough, then overflows and runs downeither side of a pipe, fuses together at theroot, and is drawn downward until cool.The thickness of the sheet depends on thevelocity of pulling. Sheets 0.4mm up tolcm can be drawn, with both surfaces fire-polished and comparable to float glass.The process is higher viscosity than theFLOAT GLASS PROCESS (q.v.) with ratherlower production rates. (Corning GlassWorks, USA).Overflush. A fault in glass-ware causedby the flow of too much glass along theline of a joint (cf. FIN).Over-glaze Decoration. See ON-GLAZE

DECORATION.

Over-glazed. Pottery-ware having toothick a glaze layer, particularly on thebottom; this thick glaze is likely to becrazed. Causes of this fault are incorrectdipping, the use of slop glaze of too higha density, or biscuit ware that is tooporous, i.e. underfired.Over-pickling, PICKLING (q.v.) for toolong a period or in too strong a solution;this causes blisters in vitreousenamelware.Overpress. A fault, in glass-ware, in theform of an inside FIN (q.v.).Oversailing. A projection in brickwork,e.g. in a domestic chimney.Overspray. (1) In the application, byspraying, of enamel slip to base-metal orof slop glaze to ceramic whiteware, thatproportion of slip or glaze that is notdeposited on the ware; it is normallycollected for re-use.(2) In vitreous enamelling, theapplication of a second (usually thinner)coat of enamel slip over a previous layerof enamel that has not yet been fired.

Overswing. See TORSION VISCOMETER.OVPO (Outside Vapour - PhaseOxidation). See OPTICAL FIBRES.Owens Machine. A suction-type machinefor making glass bottles; the originalmachine was designed by M. J. Owensbetween 1897 and 1904. Since then, therehave been many improvements but thebasic principle remains the same.Ox Gall. This material (an indefinitemixture of fats, glycocholates andtaurocholates) has been added to glazesuspensions to prevent crawling.Oxford Clay. A clay of the UpperJurassic system providing raw materialfor 30% of the building bricks made inthe UK; the Fletton brick industry of thePeterborough area is based on this clay,which contains so much carbonaceousmaterial that the drypressed bricks canbe fired with very little additional fuel.Oxford Feldspar. A ceramic grade offeldspar occurring in Maine, USA. Aquoted analysis is (%) SiO2, 69; Al9O3,17; Fe2O3, 0.1; CaO, 0.4; K2O, 7.9; Na2O,3.2; Loss, 0.3.Oxidation Period. The stage in the firingof clayware during which anycarbonaceous matter is burned out, i.e.the temperature range 400-8500C. It isimportant that all the carbon is removedbefore the next stage of the firingprocess (the vitrification period) begins,otherwise a black core may result.Oxide Ceramics. Special ceramics madefrom substantially pure oxides, usuallyby dry-pressing or slip-casting followedby sintering at high temperature. Themost common oxide ceramics are Al2O3,BeO, MgO, ThO2, and ZrO2.Oxygen Sensor. An application forceramics whose electrical conductivity issensitive to changes in the oxygen partialpressure of the surrounding atmosphere.Zirconia is a potentiometric sensormaterial, whose conductivity is based on a

solid-state ionic transfer process. Titaniais a conductimetric sensor dependentupon semiconduction processes.Oxynitride Glasses, GLASS FORMINGSYSTEMS (q.v.) are found amoung thesilicon and aluminium oxynitrides, as wellas among the silicates. Such oxynitrideglasses have increased resistance todevitrification, higher refractive index,higher dielectric constant and greaterviscosity and glass-transition temperatures.They are more difficult to prepare thansilicate glasses, needing highertemperatures and an atmosphere with alow oxygen content. Crystallisationprocesses in them yield polycrystallinenitride ceramics with good high-temperature properties. (The strength andcreep-resistance of nitrogen ceramicsdepend markedly on the amount andproperties of the intergranular glasses).Silicon oxynitride surface coatings on silicaoptical fibres greatly enhance theirmechanical strength.Packing Density. The BULK DENSITY (q.v.)of a granular material, e.g. grog or crushedquartzite, when packed under specifiedconditions. A common method of test,particularly for foundry sands, involves theuse of a SAND RAMMER (q.v.).Packing Factor. The ratio of the TRUEVOLUME (q.v.) to the BULK VOLUME(q.v.).Pad. The refractory brickwork below themolten iron at the base of a blast furnace.Pad Printing. Printing ceramicdecoration using silicone pads. SeeMURRAY-CURVEX process.Paddling. The process of preliminaryshaping of a piece of glass, while it is in afurnace and soft, prior to the pressing ofblanks of optical glass.Padmos Method. A comparative methodfor the determination of the coefficientof thermal expansion of a glass; the glassbeing tested is fused to a glass of known

expansion and similar transformationtemperature. From the birefringenceresulting from the consequent stress atthe junction of the two glasses, thedifference in expansion can becalculated. (A. A. Padmos, Philips Res.Repts., 1, 321,1946.)Paillons. Small pieces of vitreousenamelled metal foil, for jewelry orartware.Pale Glass. Glass of a pale green colour.Palissy Ware. Fine earthenware with abrightly coloured tin glaze.PaIl Ring. A type of ceramic filling fortowers in the chemical industry - the'ring' is a small hollow cylinder with slotsin the sides and projections in the core.The design was introduced by BadischeAnilin und Soda Fabrik - see Industr.Chemist, 35, 36, 1959.Pallet. A board, small platform orpackaging unit sometimes used, forexample, in the transport of refractoriesor building bricks; cf. STILLAGE.Pallette. See BATTLEDORE.Palmqvist Cracks. Short cracks, semi-circular in a section perpendicular to thesurface, which form at the corners of theindentation made by the diamondpyramid in a VICKERS HARDNESS (q.v.)test. S. Palmqvist (Jernkontorets Ann.141,1957, p300; Arch. Eisenhiittenwesen33, (6), 1962, p.629) first suggested, byempirical reasoning, that the indentationhardness test could also be used as aFRACTURE TOUGHNESS TEST (q.V.).Palygorskite. A fibrous, hydratedmagnesium aluminium silicate.Structurally, this mineral is the same asATTAPULGITE (q v.). There is a depositof economic size at Cherkassy, Russia.PAM. Pneumatically Applied Mortar.PAMM. British Ceramic Plant andMachinery Manufacturer's Association.PO Box 28, Biddulph, Stoke-on-TrentST8 7AZ.

Pan Mill. Term sometimes applied to anEDGE-RUNNER MILL (q.v.) but moreproperly reserved for the old type of mill(also known as a BLOCK MILL) forgrinding flint for the pottery industry. Itconsists of a circular metal pan pavedwith chert stones over which are movedheavy blocks of chert (RUNNERS)chained to paddle arms.Pandermite. A hydrated calcium boratethat has been used as a component ofglazes.Panel Brick. A special, long, rectangulartongued and grooved refractory brick,laid stretcher-fashion in the wall of acoke-oven.Panel Spalling Test. A test for the spallingresistance of refractories that was firststandardized in 1936, in USA. A panel ofthe bricks to be tested is subjected to asequence of heating and cooling cycles andthe loss in weight due to the spalling awayof fragments is reported. General detailsof the apparatus and test are given inASTM - C38. ASTM C107 givesprocedures for High-duty FireclayRefractory, ASTM - C122 for Super-dutyFireclay Refractory. B.S. 1902 Pt 5.11specifies a panel test for refractories. Seealso THERMAL SHOCK TESTS.Paper Resist. See FRISKET.Pannetier's Reds. Brilliant on-glazeceramic colours, based on iron oxide,developed in the early 19th century byPannetier in Paris.Pantile. A single-lap roofing tile having aflat S-shape in horizontal section. Detailsof clay pantiles are specified in B.S.1424;the minimum pitch recommended is 35°.Parallel-plate Plastometer. SeeWILLIAMS' PLASTOMETER.Parge, Parget, Pargeting. The coating ofthe surface of brickwork, as with plaster.The term 'pargeting' is used in thebuilding trade, e.g. for the internalcoating of chimney flues with lime

mortar. In the refractories industry theterm 'parging' is more common, e.g. forcoating or patching a furnace lining.Parian. A white, vitreous, type of potterymade from china clay and feldspar (inthe proportion of about 1:2); somerecipes specify the addition of CULLET(q.v.). Parian ware is generally in theform of figures - hence the name, fromParos, the Aegian island from whichwhite marble was quarried for sculpturein Classical Greece. Parian was createdby the firm of Spode, England: it wassubsequently made by several otherfirms and was popular between about1840 and 1860. (PARIAN CEMENT orPLASTER is an alternative name forKEENE'S CEMENT (q.v.).)Paris Green. A ceramic colour suitablefor firing up to about 10500C andconsisting of (%) Cr2O3, 25; CoO, 4;ZnO, 8; whiting, 12; borax, 8; flint, 43.Paris White. See WHITING.Parison. A piece of glass that has beengiven an approximate shape in a pre-liminary forming process ready for itsfinal shaping. (From the French paraison,derived from purer - to prepare.)Parker Pre-namel. A process for thetreatment of steel prior to enamelling(US Pat., 2 809 907,15/10/57).Partially Stabilized Zirconia. SeeZIRCONIA.Particle Shape. See MORPHOLOGY.Particle Size or (preferably) ParticleMean Size. A concept used in the studyof powders and defined as: 'Thedimensions of a hypothetical particlesuch that, if a material were whollycomposed of such particles, it wouldhave the same value as the actualmaterial in respect of some statedproperty1 (cf. EQUIVALENT PARTICLEDIAMETER).Particle-size Analysis. The process ofdetermining the proportions of particles

of defined size fractions in a granular orpowdered sample; the term also refers tothe result of the analysis. The methodsof determination available include:ADSORPTION, in which the particle size isassessed on the basis of surface area; theDIVER METHOD; the use of a CENTRI-FUGE; COULTER COUNTER; ELUTRIA-TION; TURBIDIMETER; the ANDREASENPIPETTE; and, for coarser particles, aSIEVE. (For further details see undereach heading.) Automatic operation,electronic analysis of results, imageanalysis of direct microscopicobservation, and laser techniques havebeen added to the range of techniquesavailable. ASTM C678, 690, 721, 775,958,1070 and 1182 specify varioustechniques for measuring particle sizedistributions of clays, alumina andquartz.Particle Size Distribution. The graph ofthe number of particles in a given sizerange, against the size of the particles,measured in some consistent fashion(e.g. by diameter, mass, volume, etc.).Parting Agent. A MOULD RELEASE(q.v.) agent.Parting Line. See JOINT LINE.Parting Powder. Refractory powderspread between brick courses to preventthem sticking together when fired.Parting Strength. The tensile strenth of aceramic fibre product. Test methods arespecified by B.S. 1902 Pt. 6, Section 9.Parting Wheel. See CUTTING-OFF WHEEL.Partition Tile. US term for a hollowfired-clay building block for use in theconstruction of interior partitions but notcarrying any superimposed load.Paste. A literal translation of the Frenchword Pate in the sense of ceramic body;see HARD PASTE and SOFT PASTE.Paste Mould. A metal mould lined withcarbon and used wet in the blowing ofglass-ware.

Pat Test. A qualitative method forassessing the soundness of hydrauliccement. Pats of cement are made about3 in. (75 mm) dia., Vi in. (12.5 mm) thickat the centre but with a thincircumference. They are immersed incold water for 28 days or in boiling wateror steam for 3-5 hours. Unsoundness isrevealed by distortion or cracking.Patch. A repair to a brick lining,especially to one in which therefractories are bricked in rings, and nowhole ring is replaced.Pate Dure, Pate Tendre. HARD FIREDand SOFT FIRED (i.e. too high or lowtemperature) whitewares respectively.Pate-sur-Pate. A method of potterydecoration in which a bas-relief is builtup by hand-painting with clay slip as thepaint. The method is more particularlysuited to the decoration of vases in theclassical style; fine examples were madeby M. L. Solon at Mintons Ltd.,England, in the late 19th century.Pattern Cracking. See MAP CRACKING.Paul Floe Test or Paul Water Test. SeeFLOC TEST.Paver. Dense, well vitrified bricks ofnormal size or of lesser thickness for useas a material for walkways and paths. B.S.6677 Pt. 1 specifies materials, sizes,strengths and skid resistance of clay andcalcium silicate pavers. (Pts 2 and 3specify design practice and method ofconstruction of pavements). In the USA apaver may be a dust-pressed, unglazedrelatively thick floor tile with a superficialarea of at least 6in2 (3871mm2). ASTMC-902 is the US standard for pavingbricks for light traffic areas.Paving Brick. ASTM C410 specifies fourgrades of industrial floor bricks, type 'T'resistant to thermal and mechanicalshock; type 'H' resistant to chemicalsand thermal shock; type 'M' with lowabsorption (usually highly abrasion

resistant) and type 'L' with lowabsorption, high chemical resistance andhigh abrasion resistance, thoughnormally low resistance to thermal andmechanical shocks.Paviour. A term applied to clamp-firedSTOCK BRICKS (q.v.) that are not of firstquality but are nevertheless hard, well-shaped and of good colour.PBNT. Lead Barium NeodymiumTitanate has very low dielectric loss andits high frequency permittivity is stableover a wide temperature range, and so itis used in microwave resonators andfilters.PCE. Abbreviation for PYROMETRICCONE EQUIVALENT (q.V.).PDZ. Plasma Dissociated Zircon.Peach. A term used by Cornish miners,originally for chlorite, but latterlyapplied to veins of quartz and schorlforming part of the waste from china-clay pits.Peach Bloom. A glaze effect on potteryproduced by the Chinese andcharacterized by its soft pink colour withpatches of deeper red. It is achieved bythe addition of copper oxide to a high-alkali glaze but requires very carefulcontrol of the kiln atmosphere; the'bloom' results from incipientdevitrification of the glaze surface.Peacock Blue. A ceramic colour madefrom a batch such as 33% Cobalt oxide,7% STANDARD BLACK (q.v.), 45% ChinaStone, 15% Flint.Peacocking. An iridescent discolouration(predominantly purple and blue) on bluebricks exposed to rain and the prevailingwinds. A film of silica forms on thesurface of the brick, thin enough to showlight interference effects.Peak Lopping. Electricity from thenational grid supply is supplemented byon-site generation at periods of peakdemand, so that the load on the grid is

kept to lower values which attractpreferential tariffs.Pearl-ash. Potassium carbonate, K2CO3;sometimes used in glass and glaze batches.Pearlite. A lamellar aggregate of ironand cementite (Fe3C) found in carbonsteels.Pearson Air Elutriator. A down-blasttype of ELUTRIATOR (q.v.) designed byJ. C. Pearson (US Bur. Stand. Tech.Paper No. 48,1915) and used fordetermining the fineness of portlandcement.Pearson Distribution. A skew statisticaldistribution applied to find theappropriate sample size in metal releasetesting. (F. Moore. Trans J. Brit Ceram.Soc. 76 (3) 52 1977 where the equationand properties of the distribution arediscussed).Pebble Heater. A heat exchanger inwhich refractory 'pebbles' (which may bemade of mullite, alumina, zircon orzirconia) are used as heat carriers. Onetype of pebble heater consists of tworefractory-lined chambers joinedvertically by a throat; both chambers arefilled with 'pebbles', which descend at asteady rate, being discharged from thebottom of the lower chamber andreturned to the top of the upperchamber. In the latter they are heated bya countercurrent of hot gases; in thelower chamber they give up this heat toa second stream of gas or air.Pebble Mill. A BALL-MILL (q.v.) inwhich flint pebbles are used as grindingmedia.Peck. A unit of volume (16 pints)sometimes used in the pottery industryin the wet process of body preparation.See also SLOP PECK and STANDARD SLOPPECK.

Pedersen Process. A process devised in1944 by H. Pedersen, a Norwegian, forthe extraction of alumina from siliceous

bauxite; the bauxite is first melted in anelectric furnace with limestone and coke,the reaction product then being leachedwith NaOH.Peeling or Shivering. (1) The breakingaway of glaze from ceramic ware inconsequence of too high a compressionin the glaze layer; this is caused by theglaze being of such a composition that itsexpansion coefficient is too low to matchthat of the body (a certain degree ofcompression in the glaze is desirable,however).(2) A similar effect sometimes occurs onthe slagged face of a refractory.(3) A fault in vitreous enamelling that isalso known as LIFT (q.v,).Pegasus. A precision grinder, with theworkpiece fed normal to a metal or resinbonded diamond cupwheel, forsuperfinishing ultrahard surfaces.Pegmatite. A coarsely crystalline rockoccurring as veins, which may be severalhundred feet thick. Feldspars are acommon constituent of pegmatites,which are of ceramic interest for thisreason.PEL Porcelain Enamel Institute,Washington D.C., USA.PEI Test. An abrasive charge consistingof steel balls, alumina grit and deionizedor distilled water is rotated on thesurface whose ABRASION RESISTANCE isto be assessed. An abraded circle 80mmdiameter is produced. Glazed tiles thustested lose only little material, and theirabrasion resistance is assessed by a visualestimate of gloss and colour understandard lighting conditions after 150,600 and 1600 revolutions. (The test isspecified in ASTM C1027 and B.S. 6431Pt. 20, which also specifies a dry method,the Mcc TEST).

Pelletized Clay. Ball clays, especially forsanitaryware production, which havebeen extruded and the rods cut into

short lengths for easier handling anddispersion in water.Pencil Edging. The process of roundingthe edges of flat glass.Pencil Ganister. A GANISTER (q.v.) withblack markings, as though pencilled,formed by decomposition of the rootletsthat were present in the original seat-earth from which the ganister wasformed.Pencil Stone. Term sometimes applied toPYROPHYLLITE (q.V.).Pendulum Test. See TRRL PENDULUMTEST (for slip resistance of floors) andIMPACT RESISTANCE.Penlee Stone. Stone from PenleeQuarries, Penzance, comprising 53%silica, and used as a road stone.Pennvernon Process. See PITTSBURGHPROCESS.Pentacalcium Trialuminate.5CaO.3Al2O3; orthorhombic; sp. gr.3.03-3.06.Peptize. Term used in colloid chemistryfor the process in ceramic technologyknown as DEFLOCCULATION (q.v.).Percussion Cone. A circular or semi-circular crack on a surface subjected toimpact damage, which propagates intothe body of the material as a spreadingcone.Perfluent Sintering. Lightweight clayblocks are made by a process in whichcombustion gases stream through thepores of a partially expanded pelletizedclay contained in a sagger.Perforated Brick. A building brick madelighter in weight by its being piercedwith numerous, relatively small (6-12mm dia.) holes, usually in the directionof one of the two short axes. In the UK aperforated brick is defined (B.S. 3921) asone in which has holes not exceeding25% of the volume of the brick with theholes so disposed that solid material isnever less than 30% of the width of the

brick; in USA it is normally also over2 5 % (cf. HOLLOW CLAY BLOCKS).Periclase. Crystalline magnesium oxide,MgO; m.p. 28500C: sp. gr. 3.6; thermalexpansion (20-10000C), 13.8 x 10"6.Periclase, generally with a little FeO insolid solution, is the main constituent ofmagnesite refractories, SEA-WATERMAGNESIA (q.v.) can be produced as anearly-pure periclase. Large singlecrystals of periclase have measurableductility which may reveal the factorsdetermining ductility and how thisproperty might be achieved in ceramicproducts.Periodic Kiln. See INTERMITTENT KILN.Peripheral Speed. The rate of movementof a point on the edge of a rotating diskor cylinder: it is the product of thecircumference and the rate of revolution.The peripheral speed is of importance,for example, in the operation of abrasivewheels and ball mills.Perish. To disintegrate as a result of slowhydration on exposure to moist air;calcined dolomite disintegrates in thismanner if stored for more than a shortperiod.Perkiewicz Method for Preventing KilnScum. A process in which clay bricks,prior to their being set in the kiln, arecoated with a combustible, e.g. tar or amixture of gelatine and flour; shouldsulphur compounds condense on thebricks during the early stages of firing,the deposit will fall away when thecombustible coating subsequently burnsoff. (M. Perkiewicz, Brit. Pat. 3760,15/2/04).Perlite. A rock of the rhyolite type thatis of interest on account of itsintumescence when suddenly heated to atemperature of about 10000C.Composition (%): SiO2, 70-75; Al2O3,12-14; Alkalis, 6-8; Loss-on-ignition,3.5-6. Perlite occurs in economic

quantity in USA, Hungary, Turkey andNew Zealand. The expanded producthas a bulk density of 0.1-0.2 g/ml and isused as a heat-insulating material.Perm, (Pm). A c.g.s. unit of gaspermeability expressed in [(cm3/sec.) cm.Poise]/[cm.2(Dyne/cm.2)]. As this unit isvery large, the Nanoperm is used whenc.g.s. units are applied to thepermeability of ceramic materials;1 Nanoperm (nPm) = 10~9 Perm;1 Perm = 0.9871 x 10~18

DARCY.Permanent Linear Change. A preferredterm including the two terms AFTERCONTRACTION (q.v.) and AFTER-EXPANSION (q.v.). ASTM Cl 13, C210and C179 are the American tests forrefractory bricks, insulating firebrick andrefractory plastic and ramming mixes,respectively. ASTM C605 describes thedetermination of permanent volumechange for fireclay nozzles and sleeves,from which the PLC can be calculated.BS 1902 specifies PLC for shapedinsulating products (Pt. 5.9); for denserefractories (Pt. 5.10); for unshapedrefractories (Pt. 7.6); while Pt.6 Section 5specifies a SHRINKAGE test for refractoryfibre products.Permeability. The rate of flow of a fluid(usually air) through a porous ceramicmaterial per unit area and unit pressuregradient. This property gives some ideaof the size of the pores in a body -whereas the measurement of POROSITY(q.v.) evaluates only the total porevolume. From the permeability of acompacted powder the SPECIFICSURFACE (q.v.) of the powder can bededuced. B.S. 1902 Pt. 3.9 describes a gaspermeability test applicable to refractorymaterials, as does ASTM C577. TheASTM C866 test for the filtration rate ofwhiteware clays depends on their waterpermeability. See BLAINE TEST; CARMANEQUATION; LEA AND NURSE

PERMEABILITY APPARATUS; PERM;RIGDEN'S APPARATUS.Pernetti. (1) Small iron PINS or spurs forsetting ware in the kiln.(2) marks on the ware caused by stickingto the pins.Perovskite. CaTiO3; m.p. 1915°C; sp. gr.4.10. This mineral gives its name to agroup of compounds of similar structure,these forming the basis of the titanate,stannate and zirconate dielectrics.Extensive solid solution is possible so thatthe potential range of compositions andferroelectric properties is very great. R. S.Roth (J. Res. Nat. Bur. Stand., 58, 75,1957) has classified the perovskites on thebasis of ionic radii of the constituent ions;a graph of this type can be divided intoorthorhombic, pseudocubic and cubicfields with an area of ferroelectric andantiferroelectric compounds superimposedon the cubic field. In a development of thisclassification a three dimensional graphincludes the polarizability of the ions asthe third dimension.Perpend. An alignment of crossjoints inbrickwork.Perrit. A support, made of heat-resistingalloy, designed to carry vitreous enamel-ware through an enamelling furnace.Persian Blue. See EGYPTIAN BLUE.Persian Red. Pigments of ferric oxideand basic lead chromate.Perthite. A mineral consisting of alamellar intergrowth of feldspars,especially of albite and orthoclase.PESTS. Porcelain Enamel SteelSubstrates for screen printed or hybridcircuitry.Petalite. A lithium mineral,Li2O.Al2O3.8SiO2; sp. gr. 2.45; m.p.13500C. The chief sources are Rhodesiaand S. W. Africa. Normally it is a lesseconomical source of Li2O than isSPODUMENE (q.v.) but it is usually freefrom iron compounds. A major use is in

low-expansion bodies resistant tothermal shock.Petersen Air Elutriator. An up-blastELUTRIATOR (q.v.) that has found someuse in determining the fineness ofportland cement.Petrography, Petrology. The description,classification and study of minerals, theircompositions and structure.Petuntse, Petunze. The Chinese name ofCHINA STONE (q.V.).PFA. Abbreviation for PULVERIZEDFUEL ASH (q.v.).Pfefferkorn Test. K. Pfefferkorn(Sprechsaal, 57, 297,1924) suggested thatthe plasticity of a clay could be assessedby determining the amount of water thatmust be added to produce a standarddeformation when a test-piece of theclay is subjected to a standard impact.The test-piece used was a cylinder 40mm high and 33 mm diam.; the impactwas that given by a disk weighing 1.2 kgfalling through 14.6 cm; the standarddeformation was 33%. The test involvesplotting a graph relating water content todeformation; from this graph the watercontent for 66% deformation is read.PFN. Lead iron niobate.PFW. Lead iron tungstate (from thechemical symbols Pb, Fe, W).pH. Symbol for the acidity or alkalinityof a solution; it is a number equivalent tothe logarithm, to the base 10, of thereciprocal of the concentration ofhydrogen ions in an aqueous solution.The point of neutrality is pH7; a solutionwith a pH below 7 is acid, above 7 isalkaline. The pH of a casting slip is ofpractical importance in determining itsrheological properties.Phase Diagram. Equilibrium diagrams ofinterest to the ceramist representcrystallographic changes and the melting(or conversely the solidification)behaviour of compounds, mixtures, and

solid solutions) under conditions ofchemical equilibrium. As an example, theAlO-SiO equilibrium diagram, one of themost important for the ceramist, is shownin Fig. 5. Items of interest are:(1) The melting points of threecompounds are shown, namely those ofsilica (1723°C), mullite (18500C) andalumina (20500C).(2) There are two EUTECTICS (q.v.) thatbetween silica and mullite melting at1595°C, and that between alumina andmullite melting at 18400C.(3) The ability of mullite to take a smallamount of alumina into SOLID SOLUTION(q.v.). For a useful discussion ofequilibrium diagrams from the standpointof the ceramist, and a verycomprehensive collection of suchdiagrams, see E. M. Levin, C. R. Robbinsand H. F. McMurdie, 'Phase Diagramsfor Ceramists' (Amer. Ceram. Soc. 1964).This publication has now reached Vol.VIII; VoIs VI to VIII being published bythe ACS jointly with the US NationalInstitute of Standards and Technology.There are regular bibliographical updates,and prototype computer databases for anon-line service.Phase Rule. The number of degrees offreedom of a system at equilibrium plus

Al2O3 (wt%)

Temper

ature C

C)

LiquidLiquidus Corundum+liquid

Corundummullite-SS

Mullite-SS

Mulliteliquid

SiO2 + liquid

'Eutectic SolidusSiO2 + mullite

AI2O3 (mol%)AI2O3SiO2

Fig. 5 The Alumina-Silica Phase Diagram.

the number of phases, is equal to thenumber of components plus 2.Phase Separation. If a homogeneousliquid mixture is cooled below a criticalimmiscibility temperature, two liquid (orglass) phases may form, initiated byhomogeneous nucleation. Usually onephase has a higher surface tension andforms droplets in the other. Glassceramics may be formed in this way.Phlogopite. A magnesium MICA (q.v.)containing little iron, but otherwisesimilar to BIOTITE (q.v.) Phlogopitemicas are excellent electrical insulators,and form the basis of some machineableglass-ceramics.Phosphate Bond. Cold-setting bonds forrefractories can be formed by reactionsbetween oxides and phosphoric acid,phosphate-phosphoric acid reactions orthe direct use of liquid phosphate bonds.The bond is due to the formation of anacid phosphate, with weakly basic oramphoteric oxides.Phosphate Glasses. These are lowdurability glasses with structures basedon an oxygen-phosphorus tetrahedron.Iron-containing phosphate glasses aretransparent to visible light, but absorbheat in the infra-red range. They aremore resistant to fluorides than silicateglasses. Fluorphosphate glasses havevery low optical dispersion (ABB£NUMBERS (q.v.) of 70 to 80).Phosphides. Phosphide ceramics includeAlP, BP, Be3P2, InP and TiP. Some ofthese compounds have potential use assemiconductors.Phosphor. A fluorescent material ofthe type used, for example, in thecoating of the screen of a cathode-raytube. Ceramic phosphors have beenmade from Ca silicate, stannate orphosphate activated with Sn, Mn or Bi;some of the Ca can be replaced by Sr,Zn or Cd.

Phosphoric Acid. A syrupy liquid ofvariable composition sometimes used asa binder for refractories (seeALUMINIUM PHOSPHATE).Photochromic Glass. Glass whosetransmission of visible light decreaseswhen exposed to ultraviolet or visiblelight, and increases again when thatexposure ceases. Commercialphotochromic glasses contain silverhalide crystallites about 10 nmdiameter, dispersed about 100 nm apart.These are precipitated thermallywithout exposure to radiation (cf.PHOTOSENSITIVE GLASS). When lightshines on the glass, small amounts ofmetallic silver form on these silverhalide crystals, darkening the glassmuch as a photographic image isformed. The glass traps the reactionproducts close to each other. When theglass is no longer exposed to the light,the reaction reverses and the silver isre-absorbed. Darkening times rangefrom seconds upwards, while someglasses are stable for days in their darkstate. The glasses darken less and fademore quickly at higher temperatures.Applications are to sun glasses,opthalmic lenses, automobile sunroofsand architectural sheet glass.Photoelectric Pyrometer. A device formeasuring high temperatures on thebasis of the electric current generated bya photoelectric cell when it receivesfocused radiation from a furnace orother hot body. Instruments have beendesigned for the measurement oftemperatures exceeding 20000C, butothers are available for use at lowertemperatures, e.g. for checking thetemperature of the molten glass used inlamp-bulb manufacture.Photon. Trade-name. A machineableceramic made by Photon Ceramics Ltd,Tokyo.

Photopolymer Plate. A substitute for theengraved metal plate in the MURRAY-CURVEX process. A complex design isdeveloped photographically on apolymer sheet.Photosensitive Glass. A glass containingsmall amounts (< 0.1 %) of gold, silveror copper, which render the glasssensitive to light in a manner similar tophotographic films; the image isdeveloped by heat treatment. Such glassundergoes a change in some property,usually optical absorption, on exposureto light and simultaneous or subsequentheat treatment. There are three types:direct in which absorption develops atthe time of the exposure to light;developed in which later heat treatmentchanges the property; nucleated in whichthe heat treatment produces nucleationand growth of a second phase. In thefirst type, absorption is byphotoelectrons and holes trapped in thelattice. In the others, metal particles areproduced by chemical reduction, andthese absorb the light. See alsoPHOTOCHROMIC GLASS;POLYCHROMATIC GLASS.Photovoltaic Materials. Materials whichgenerate an electric potential whenexposed to light. CuS, CdS, GaAs and Siare such materials, which findapplications in photocells for thegeneration of solar power.Photozone Stream Counter. Particle sizecharacteristics are deduced from themagnitude and spatial distribution ofreflected light signals from the particlesto be measured.Piano-wire Screen. A screen formed bypiano wires stretched tightly, lengthwise,on a frame 2-3 ft (0.6-1 m) wide and 4-8ft (1.3-2.6 m) high. The screen is set upat an angle of about 45° and crushedmaterial is fed to it from above. Themesh size varies from about 4 to 16.

Because there are no cross-wires, andbecause the taut wires can vibrate, thereis less tendency for 'blinding', but someelongated particles inevitably pass thescreen.Pick-up. The amount of vitreous enamelslip (expressed in terms of dry weightper unit area) after the dipping anddraining process. For ground-coats, thepick-up is usually 350^450 g.nrr2.Pickings. Term applied to clamp-firedSTOCK BRICKS (q.v.) that are soft thoughof good shape.Pickle Basket. A container for vitreousenamelware during PICKLING (q.v.); thebasket is made from a corrosion-resistantmetal, e.g. Monel.Pickle Pills. Capsules, containingNa2CO3 and an indicator such as methylorange, for use in works tests of thestrength of the PICKLING (q.v.) bathemployed in vitreous enamelling.Pickling. The chemical treatment of thebase metal used in vitreous enamellingto ensure a satisfactory bond betweenthe enamel and metal. The variousmethods that have been used may beclassified as follows: (1) the use ofreducing acids, e.g. H2O4. HCl and acidsalts; (2) the sulphur compounds, H2Sand Na2S2O3; (3) metal coatings, e.g. Ni,As and Sb; (4) oxidizing acids and salts,e.g. H3PO4, HNO3, solutions of ferricsalts in acids, or NaNO3^H2SO4.Method 2 is no longer used; metalcoating with Ni (Method 3) is notregarded as pickling in the UK.Picotite. A complex spinel of generalformula (Fe,Mg)O.(Al,Cr)2O3; theproportion of Al exceeds that of Cr andthe Fe:Mg ratio is from 3 to 1. Picotitemay occur in slagged basic refractories.Picrochromite. Magnesium chromite,MgO-Cr2O3; m.p. 22500C: sp. gr. 4.41;thermal expansion (0-12000C) 8.2 x 10"6,This spinel can be synthesized by heating

a mixture of the two oxides at 16000C; itis formed (usually with other spinels insolid solution) in fired chrome-magnesiterefractories. Picrochromite is highlyrefractory but when heated at 20000Cthe Cr2O3 slowly volatilizes.Piezoelectric. A material is stated to be'piezoelectric' when an applied stressresults in the setting up of an electriccharge on its surface; conversely, if thematerial is subjected to an electric field,it will expand in one direction andcontract in another direction. Typicalpiezoelectric materials are the titanateand zirconate ceramics.Pigeonholes, basket-weave checkers(q.v.)Pigment. Pigments are solid particles ofcolour, which are suspended in glass toform ceramic colours. Ceramic pigments,as well as having good colouringproperties, must be able to withstandfiring temperatures of at least 7500C, andpossibly up to 14000C, in contact withfluxes and glazes. They must bechemically inert and colour stable, non-toxic (meeting METAL RELEASE (q.v.)regulations) and alkali-stable towithstand machine dishwashingdetergents. See also ENCAPSULATEDCOLOURS; FRIT; DRY COLOURMANUFACTURERS' ASSOCIATION (Abrief list of ceramic colours is to befound (by colour) in P.Rado.Introduction to the Technology ofPottery, Inst. of Ceramics, 1988 p 154.Pigskin. A defect in the surface textureof vitreous enamelware and of glazedsewer-pipes; it is caused by variations inthe thickness of the enamel or glaze.Pilkington Twin Process. A continuousprocess for the production of polishedplate glass; a continuous ribbon of glassis rolled, annealed and thensimultaneously ground on both faces.The process was introduced by

Pilkington Bros. Ltd., England, in 1937.(For a more recent process introducedby this firm see FLOAT GLASS PROCESS.)Pill Test. See SLAG ATTACK TESTS.Pillar. (1) A column of brickwork; forexample the refractory brickworkbetween the doors of an open-hearthsteel furnace.(2) An item of KILN FURNITURE (q.v.)forming one of the upright parts of aCRANK (q.v.); cf. POST.Pillared Clays. Monmorillonite clays, inwhich the interlayer spacing is widenedby intercalation of complex aluminiumhydroxide ions.PIM. Powder INJECTION MOULDING(q.v.).Pin. An item of KILN FURNITURE (q.v.);it is a small refractory SADDLE (q.v.) foruse in conjunction with a CRANK (q.v.).See Fig. 4, pl77.Pin Beater Mill. A type of HAMMERMILL (q.v.).Pin Disk Mill. A type of rotarydisintegrator sometimes used (moreparticularly on the Continent and inUSA) for the size reduction of clay.Pin-hole. ( I )A fault in vitreousenamelware. It is commonly the resultof a blister that has burst and partiallyhealed; the usual sources of the gas thatgave rise to the blister are a hole in thebase-metal or a speck of combustibleforeign matter in the cover-coat. Pin-holes can also occur on castings atpoints where there is extra metalthickness (lugs, etc). At such points theenamel is apt to be underfired andunmatured.(2) Pin-holes in glazes also result fromburst bubbles; here, most of the gasoriginates from air trapped between theparticles of powdered glaze as the glazebegins to mature.(3) A frequent source of pin-holes inpottery biscuit-ware, and in subsequent

stages of processing, is air occluded inthe clay during its preparation.(4) Pin-holes in plaster moulds originatein air attached to the particles of plasterduring blending; this can be eliminatedby blending the plaster in a vacuum.Pin Mark or Point Mark. A fault invitreous enamelware caused by theimprint of the supports used during thefiring process.Pin-on-Disc Test. A method formeasuring the coefficient of frictionbetween two materials in which onmaterial forms the pin, and is pressedagainst the other material, which forms arotating disc.Pinch Effect. Term applied by J. W.Mellor (Trans. Brit. Ceram. Soc, 31, 129,1932) to the crazing of wall tiles as aresult of contraction of the cement usedto fix the tiles on a wall, while it issetting.Pinch Spalling. Mechanical damage tothe hot face of a refractory arch or ring,indicating excessive compression. It maydevelop radially or axially.Pining Rod. A metal rod used tomeasure the contraction of a setting ofbricks in a kiln; from colloquial use ofthe word 'pine' in the sense of 'shrink.'Pinite. A rock consisting largely ofsericite. The composition is (per cent):SiO2, 46-50; Al2O3, 35-37; K2O, 8-10;loss on ignition, 4-6. A deposit inNevada, USA, was worked from 1933-1948 as a raw material for making denserefractories for rotary frit kilns and forthe cooler parts of cement kilns wherehigh abrasion-resistance is requiredPinning. The process of fixing PINS (q.v.)in kiln furniture.Pint Weight. The weight in oz of 1 pintof a suspension of clay, flint etc., inwater. (One of the last quantities to holdout against metrication, where slipdensity is expressed in kg/litre.

Pip. An item of KILN FURNITURE (q.v.).A pip is a small refractory button with apoint on its top surface; ware issupported on the point.Pipe. (1) See FIELD-DRAIN PIPE; SEWERPIPE, CONCRETE PIPES, PIPECLAY.

(2) A cavity at the top of a fusion-castrefractory resulting from the contractionof the molten material as it cools.Pipe Blister. A large bubble sometimesproduced on the inside of hand-madeglass-ware by impurities or scale on theblow-pipe.Pipeclay. A white-firing, siliceous, clay ofa type originally used for makingtobacco pipes.Pipette Method. A method for thedetermination of particle size: seeANDREASEN PIPETTE.

Pistol Brick. Brick slips cut intoL-shapes, to achieve decorative patterns.Piston Extruder. See STUPID.Pit. A fault in vitreous enamelwaresimilar to, but smaller than, a DIMPLE(q.v.).Pitch. The slope of a tiled roof. For clayroofing tiles the common pitch, measuredinternally at the ridge between the twosides of the roof, is 105°. Less common arethe SQUARE PITCH (90°), GOTHIC PITCH

(75°) and SHARP PITCH (60°).Pitch-bonded Refractory. See TAR-B O N D E D REFRACTORY.Pitch-impregnated Refractory. See TARIMPREGNATED REFRACTORY.

Pitch Polishing. The polishing of glasswith a polishing agent supported onpitch instead of the more usual felt.Pitchers. Pottery that has been broken inthe course of manufacture. Biscuitpitchers are crushed, ground and re-used, either in the same factory orelsewhere; the crushed material is alsoused in other industries as an inert filler.Because of the adhering glaze, glostpitchers find less use.

Pittsburgh Process. A process for thevertical drawing of sheet glass inventedby the Pittsburgh Plate Glass Co. in1921. The sheet is drawn from the freesurface of the molten glass, the drawingslot being completely submerged; theedges of the sheet are formed by rollers.(This process has also been referred toas the PENNVERNON PROCESS.)Place Brick. A clamp-fired STOCK BRICK(q.v.) of very poor quality - of use onlyfor temporary erections. The term wentout of use before 1940.Placing. For the purposes of COSHH(q.v.), the approved code of practicedefines Glost Placing to include placingware coated with unfired glaze onto kilncars; removal of such items from kilncars except in tunnel kilns.Placer. A man who sets pottery-ware inSAGGARS (q.v.) or with KILN FURNITURE(q.v.) ready for firing in a kiln. The manin charge of a team of placers was knownin the N. Staffordshire potteries as a CODPLACER.Placing Sand. Fine, clean silica sand usedin the placing of earthenware inSAGGARS (q.v.); calcined alumina is usedfor this purpose in the bedding of bonechina. With the increased use of opensetting in tunnel kilns and top-hat kilns,placing sand is less used than formerly.Plagioclase. See FELDSPAR.Plain Tile. See under ROOFING TILE,WALL TILE (Fig. 7, p350).Plaining (of Glass). See REFINING.Planches. Supports for firing enamelartware.Planiceram. Large thin tongue andgroove blocks with mortar-free internalwalls.Plaque. A flat refractory slab, often withtriangular indentations, to supportPYROMETRIC CONES (q.V.)Plascast. A clay-bonded castablerefractory which is claimed to combine

the advantages of mouldables andcastables, being more resilient and stableat high temperatures than castables, butmore difficult to install. (MorganRefractories. Steel Times 216, (3) 1988pl55).Plasma Activated Sintering. A plasma isgenerated among powder particles byapplying a high power electric pulse.This cleans the particles of surfaceoxides and entrapped gases. The powderis then resistance heated and uniaxialpressure applied. A brief application(minutes) causes sufficient material flowfor rapid consolidation with minimummicrostructural change.Plasma-dissociated Zircon. Zircon(ZrSiO4) can be dissociated into zirconiaand silica in a plasma at > 18000C, withrapid cooling to prevent reassociation.The free silica is removed by dissolvingin sodium hydroxide, leaving purezirconia powder.Plasma Spraying. The process of coatinga surface (of metal or of a refractory) byspraying it with particles of oxides,carbides, silicides or nitrides that havebeen made molten by passage throughthe constricted electric arc of a PLASMAGUN; the temperature of the plasma arc'flame' can be as high as 30 0000C. Anarc is struck between a thoriatedtungsten cone (the cathode) and ananode nozzle. As the plasma leaves thenozzle, it entrains a large quantity ofexternal air (APS - air plasma spraying)at velocities of 1000 m/s. The powder isinjected into the plasma orthogonally tothe jet axis. The outside gas may beargon (IPS - inert plasma spraying) orwith a suitably redesigned gun, VPS,vacuum plasma spraying may be used tospray carbides or cermets withoutoxidation. The usual purpose of arefractory coating applied in this way isto protect a material, e.g. Mo or C, from

oxidation when used at hightemperature.Plaster of Paris. Calcium sulphatehemihydrate, CaSO4-V^H2O; prepared byheating GYPSUM (q.v.) at 150-1600C.There are two forms: a, produced bydehydrating gypsum in water orsaturated steam; (3, produced in anunsaturated atmosphere. Plaster usuallycontains both forms. It is used formaking MOULDS (q.v.) in the potteryindustry.Plaster-base Finish Tile. US term(ASTM - C43) for a hollow clay buildingblock the surfaces of which are intendedfor the direct application of plaster; thesurface may be smooth, scored, combedor roughened.Plastic Cracking. Cracking in concretebefore it has set and hardened. Its causemay be differential settlement, orshrinkage.Plastic Deformation. Deformation dueto the movement of dislocation in thecrystal lattice. In ceramics it is themechanism for the initial formation ofnew cracks. See CRYSTAL STRUCTURE;CRACK NUCLEATION.Plastic Forming. All processes of shapingceramics in the plastic condition:extrusion, plastic pressing, injectionmoulding, roller-head shaping, jiggering,jolleying, throwing.Plastic Making, PLASTIC FORMING (q.v.)Plastic Pressing. The shaping of ceramicware in a die from a plastic body bydirect pressure.Plastic Refractory. ASTM C71 definesthis as a refractory material, temperedwith water, that can be extruded andthat has suitable workability to bepounded into place to form a monolithicstructure. See FIRECLAY PLASTICREFRACTORY, MOULDABLEREFRACTORY.Plastic Shaping. See PLASTIC MAKING.

Plasticity. The characteristic property ofmoist clay that permits it to be deformedwithout cracking and to retain its newshape when the deforming stress isremoved. Plasticity is associated with thesheet structure of the clay minerals andwith the manner in which water films areheld by the clay particles.Plasticizer. A material, usually organic,which is added to non-plastic ceramicmaterials such as oxide powders, to forma dough-like plastic mass more readilyshaped by pressing or moulding.Plastometer. An instrument for theevaluation of plasticity, see, for example,BINGHAM PLASTOMETER, LINSEISPLASTOMETER, PFEFFERCORN TEST;WILLIAMS PLASTOMETER.Plat. Cornish term for the overburden ofa china-clay mine.Plate Glass. Flat, transparent, glass bothsurfaces of which have been ground andpolished so that they give undistortedvision. Plate glass is used, for example, inshop windows.Platting. See under SCOVE.Plauson Mill. The original 'colloid mill'designed by H. Plauson in Germany, andcovered by a series of patents beginningwith Brit. Pat. 155 836, 24/12/20. Thenovel feature was the high speed ofoperation (up to 30 m/s) and theconcentration of the grinding pressure ata small number of points.P.L.C. Abbreviation for PERMANENTLINEAR CHANGE (q.V.).Plique-a-Jour. One type of vitreous-enamel artware: a pattern is first made ofmetal strips, and coloured enamels arefused into the partitions thus formed;after the object has been polished onboth sides, it can be held to the light togive a stained-glass window effect.(French words: 'open-work plait'.)Pluck, Plucking. (1) A surface blemishsometimes found on pottery where the

glaze has been removed by the pointedsupports for the ware used in the firingprocess.(2) A surface fault on rolled glass arisingif the glass sticks to the rollers.Plug. Part of a glass-blowing machine forhollow-ware; it moves in a blank-mouldwith a reciprocating action, forming acavity for blowing; this part is sometimesreferred to as a PLUNGER. (See alsoMOULD PLUG.)

Plugging Compound. See FILLER.Plumbago. A refractory materialcomposed of a mixture of fireclay andgraphite; some silicon carbide may alsobe included. It finds considerable use asa crucible material for foundries. InUSA refractories of this type are termedCARBON CERAMIC REFRACTORIES.

Plunger. See NEEDLE; PLUG.Ply Glass. Glass-ware, particularly forlamp shades and globes, made bycovering opal glass (usually on bothsides) with transparent glass of matchedthermal expansion (cf. CASED GLASS).PLZT. Lead lanthanum zirconatetitanate. PLZT is an OPTOELECTRONICmaterial (q.v.).PMN. Lead Magnesium Niobate is auseful capacitor material, with highpermittivity and high breakdownvoltage.Pneumatolysis. The breakdown of theminerals in a rock by the action of thevolatile constituents of a magma, themain body of the magma having alreadybecome solid. The china clays ofCornwall, England, were formed by thepneumatolysis of the feldspar present inthe parent granite.Pneumoconiosis. Disability causedby the inhalation, over a long period,of various dusts; the form of thedisease encountered most commonlyin the ceramic industry is SILICOSIS(q.v.).

PNN. Lead nickel niobate.PNZT. Lead niobium zirconatetitanate.Pocket Clay. A highly siliceous claysometimes found in large pockets inCarboniferous Limestone. In England itis found, typically, in Derbyshire and isworked as a refractory raw material atFriden, about 10 miles S.W. of Bakewell;a quoted composition is (per cent): SiO2

78; Al2O3 ,13.5; Fe2O3, 2.0; TiO2, 0.7;CaO, 0.2; MgO, 0.3; K2O, 1.6; Na2O, 0.1;loss on ignition, 3.9.Pocket Setting. See BOXING-IN.Podmore Factor. A factor proposed byH. L. Podmore (Pottery Gazette, 73, 130,1948) to indicate the intrinsic solubilityof a frit:Podmore factor = (solubility x 100) -s-(specific surface). The solubility of anygiven frit is approximately proportionalto the surface area of frit exposed to thesolvent, i.e. to the fineness of grinding;the Podmore factor is independent ofthis fineness.Poge. A tool formerly used for lifting the'balls' of ball-clay.Point. (1) Fill and neaten masonry jointswith mortar.(2) See MOUNTED POINT.Point Bar. One type of support forvitreous enamelware used during thefiring process.Point Defect. See CRYSTAL STRUCTURE.Point Mark. See PIN MARK.Poise. A unit of viscosity, of 10-1 Nm~2s,named after Poiseuille. The viscosity ofwater is about 1 cP.Poisson's Ratio. The ratio of the lateralcontraction per unit breadth to thelongitudinal extension per unit length,when material is stretched. Its value isnormally between 0.25 and 0.4. Young'smodulus (E) and the modulus ofrigidity G are related to Poisson'sratio

ASTM Cl 198 specifies a sonic resonancetest for E and hence <;, for advancedceramics.Poke Hole. An opening'in a refractorylining for compressed air lances or steelrods to free blockages.Polcal Process. This system for thecontinuous calcining of powders hasthree pre-heating cyclones (or onepreheating cyclone and a flash dryer); acalciner with a separating cyclone; acooling stage with one or more cyclones.It has been applied to calcining naturalmagnesite to caustic MgO. (KruppPolysius AG, Germany).Poling. ( I)A method of removingbubbles from molten glass in a pot; theglass is stirred with a wooden pole, gasessweep through the molten glass andremove the smaller bubbles, whichwould otherwise rise to the surface onlysluggishly. If a block of wood is used, theprocess is called BLOCKING.(2) The alignment with an externalelectric field of the electrostatic chargedomains in ferroelectric ceramics.Polished Section. A section of materialthat has been ground and plane-polishedon one face for examination, under amicroscope, by reflected light (cf. THINSECTION).

Polishing. (1) A finishing process forplate glass and optical glass. Plate glass ispolished by a series of rotating felt diskswith rouge (very fine hydrated iron oxide)as the polishing medium. For thepolishing of optical glass cerium oxide,rouge or (less commonly) zircon are used.(2) The grinding away of small surfaceblemishes from the face of glazedpottery-ware.Polychromatic Glass. A specialPHOTOSENSITIVE GLASS (q.V.) whichwhen activated by ultraviolet light andheat, can produce within the same glass,in 2 and 3 dimensions, patterns of white

or coloured opacity, or transparentcolours of all hues. Permanent full-colour 3-d photographic images can beproduced. The mechanism is theformation of metallic silver on aprecipitated sodium halidemicrocrystalline phase, each formed byseparate photosensitive processes.Polyphant Stone. An impure SOAPSTONE(q.v.) from the village of Polyphant, nearLaunceston, Cornwall, England.Composition (per cent): SiO2, 78-36;Al2O3, 6-9; FeOn-Fe2O3, 10-12; CaO 4-5, MgO, 23-27; loss on ignition, 10-12.The m.p. is 1300-14000C. Blocks of thisstone are used as a refractory material inalkali furnaces.Polytypes. Crystal structures, modifiedby stacking faults, but too near the idealto classify as separate structures.Polytypoids. Mixed POLYTYPES (q.v.)Two phase solid solutions with minorvariations in crystal structure.Aluminium nitride polytypoids arephases in the Si-Al-O-N system withconstanct (Si+Al):(O+N) ratio, whosestructures can be classified by RAMSDELLNUMBERS (q.v.).Pontesa Ironstone. Earthenware madeby Alfares de Pontesampayo, Vigo,Spain.Pontil. See PUNTY.Pooles Tile. An interlocking clay roofingtile of a design specified in B.S. 1424.Pop off or Popper. A fault sometimesoccurring during vitreous enamelling onsheet steel, small disks of ground-coatbecoming detached and rising into thefirst cover-coat. The fault may be causedby poor metal surface.Popout. A fault in concrete. A conicalpiece is pushed out from the surface bythe expansion of an aggregate particle atits apex.Popping. Term sometimes used for (1)LIME BLOWING (q.V.)

(2) the heat treatment of PERLITE (q.v.)to cause expansion.Porcelain. One type of vitreous ceramicwhiteware. The COMBINEDNOMENCLATURE (q.v.) defines this as:completely vitrified, hard, impermeable(even before glazing), white orartificially coloured, translucent (exceptwhen of considerable thickness) andresonant. In the UK the term is definedon the basis of composition: a vitreouswhite-ware made from a feldspathicbody (typified by the porcelain tablewaremade in Western Europe and containing40-50% kaolin, 15-25% quartz and 20-30% feldspar). In the USA the term isdefined on the basis of use: a glazed orunglazed vitreous ceramic white-wareused for technical purposes, e.g.electrical porcelain, chemical porcelain,etc. Note, however, that the termelectrical porcelain is also used in theUK. The firing of porcelain differs fromthat of earthenware in that the first firingis at a low temperature (900-10000C),the body and the feldspathic glaze beingsubsequently matured together in asecond firing at about 1350-14000C.Tensile strength 140 MPa; Young'smodulus 200 GPA; Poisson's Ratio c.0.25. See also HARD PORCELAIN, SOFT

PORCELAIN, SEMI-PORCELAIN, CHINA,BONE CHINA, STONEWARE.Porcelain Enamel. The term used inUSA for VITREOUS ENAMEL (q.v.) anddefined in ASTM - C286 as: Asubstantially vitreous or glassy inorganiccoating bonded to metal by fusion at atemperature above 8000F (427°C).Porcelain Tile. US term defined (ASTM- C242) as a ceramic mosaic tile orPAVER (q.v.) that is generally made bydust-pressing and of a compositionyielding a tile that is dense, fine-grained, and smooth, with sharply-formed face, usually impervious. The

colours of such tiles are generally clearand bright.Porcelainite. MULLITE, (q.v.) The usageis obsolete.Porcelit. A non-vitreous porcelain-typebody fired at C.1250°C to produce a typeof ware between earthenware andstoneware. Made in Poland at Pruszkow.(Tableware Int. 4, (10) 84, 1974).Pore-size Distribution. The range ofsizes of pores in a ceramic product andthe relative abundance of these sizes.This property is usually expressed as agraph relating the percentage volumeporosity to the pore diameter in microns.Pore-size distribution is difficult todetermine, the most generallysatisfactory methods are the MERCURYPENETRATION METHOD (q.v.) and theBUBBLE PRESSURE METHOD (q.V.). B.S.1902 Pt. 3.16 specifies the mercurypenetration method for refractories.Poriso. A fine-pored brick made fromcolliery washings, shale, sawdust and fly-ash, requiring no fuel for firing otherthan the combustible body compenents.(Hendrik Steenfabrick, Netherlands; ZIInt. 33, (1), 30 1981).Pork-pie Furnace. See MAERZ-BOELENSFURNACE.Porodur. A plastics material for mouldsfor plastic shaping of tableware. (SklarKeram 28 (3), 76,1978).Porosimeter. A term variously applied toapparatus for the measurement ofPOROSITY (q.v.) or of PORE-SIZEDISTRIBUTION (q.V.)Porosity. A measure of the proportionof pores in a ceramic material, definedas:Apparent Porosity. The ratio of the openpores to the BULK VOLUME (q.v.),expressed as a percentage. ASTM C830specifies a vacuum pressure test forrefractories; ASTM C20 a boiling watertest.

Fractional Porosity. A porosity valueexpressed as a decimal instead of as apercentage, e.g. 0.25 rather than 25%.Sealed Porosity or Closed Porosity. Theratio of the volume of the sealed poresto the bulk volume, expressed as apercentage.True Porosity. The ratio of the totalvolume of the open and sealed pores tothe bulk volume, expressed as apercentage.B.S. 1902 Pt. 3.8/ISO 5017 specifies animmersion test. Closed pores are thenthose which are not penetrated in thistest: open pores are those that are.ASTM C373 specifies tests for porosityand related products of whitewares.C949 specifies a dye penetration test.Poroton. Insulating bricks in whichfoamed polystyrene beads are mixedwith the clay as a combustiblecomponent, leaving a porous structure.(J Brit. Ceram Soc. 7, (1) 3, 1970.)Porous Glass. An alkali borosilicateglass is made, which solidifies in twophases, one soluble in dilute acid. This isleached out, leaving a porous glass witha nearly pure silica skeleton. Suchporous glasses can be consolidated bycareful heat treatment at c. 12000C tosinter them into an impervious clear highsilica glass. Volume shrinkage is then c.35%. The affinity of porous glass formoisture makes it a useful non-dustingdrying agent, used in various shapes inscientific instruments.Porous Plug. See GAS BUBBLING BRICK.Port. An opening through which fuel gasor oil, or air for combustion, passes intoa furnace; ports are usually formed ofrefractory blocks or monolithic material.Portakiln. Trade-name. A low thermalmass prefabricated brick kiln. (Bricesco,Euroclay (3), 12, 1979).Port Walker. A workman who observesthe sheet of glass issuing from a

FOURCAULT (q.v.) tank-furnace andgives warning of faults.Portland Blast-furnace Cement. Ahydraulic cement made by mixingPortland cement clinker with up to 65%blast-furnace slag and grinding themtogether (see B.S. 146 and cf. SLAGCEMENT).Portland Cement. A hydraulic cementproduced by firing (usually in a rotarykiln) a mixture of limestone, or chalk,and clay at a temperature sufficientlyhigh to cause reaction and the formationof calcium silicates and aluminates; theproportion of 3CaCSiO2 is about 45%,and that of 2CaCSiO2 about 25%, theother major constituents being3CaO-Al2O3 and 4CaCAl2O3. Fe2O3.The chemical composition is (per cent):SiO2,17-24; Al2O3, 3-7; Fe2O3,1-5;CaO, 60-65; MgO, 1-5; alkalis, 1; SO3.1-3. Properties are specified in B.S. 12and ASTM-C150. The name was givento this cement by its inventor, JosephAspdin (Brit Pat. 5022, 1824) on accountof the resemblance of the colour of theset cement to that of the well-knownbuilding stone from Portland, England.Post. (1) The gather of glass after it hasreceived preliminary shaping and isready to be hand-drawn into tube or rod.(2) An item of KILN FURNITURE (q.v.).Posts, also known as PROPS orUPRIGHTS, support the horizontal batson which ware is set on a tunnel-kiln car.(See Fig. 4, pl77.)(3) A discrete portion of bond betweenabrasive grains in a grinding wheel orother abrasive article. When the abrasivegrain held by a post has become worn,the post should break to release theworn grain so that a fresh abrasive grainwill became exposed.Post Clay. A term sometimes used inN.E. England for an impure siliceousfireclay.

Post-sintering. To produce denseengineering ceramics, a forming methodwhich leads to a porous fired componentis followed by sintering in a controlledatmosphere to densify the compact withminimum shrinkage. Complex near netshapes can be produced. For example,injection moulded silicon nitridecomponents were sintered in nitrogenafter forming, with shrinkage of only6%. (UK Pat. 2010913A and 2010915A,FIAT SpA).Post-tensioned Brickwork. Steel barspass through the brickwork in alignedperforations or pockets in the bonding.The bars are anchored top and bottomand tightened mechanically afterconstruction, to place the brickwork incompression. See REINFORCEDBRICKWORK.Pot. A large fireclay crucible used formelting and refining special types of glass.A pot may either be open (the surface ofthe glass being exposed to the furnacegases) or closed by an integrally mouldedroof, a mouth being left for charging andgathering; a CLOSED POT is also known asa COVERED Or HOODED POT.Pot Arch. A furnace for preheating thePOTS (q.v.) used in one method of glass-making.Pot Bank. Obsolete term in N.Staffordshire for a pottery factory.Pot Clay. A somewhat siliceous fireclaythat is used in the manufacture of glass-pots or crucibles for use in melting steel;the term is also applied to a mixture ofsuch a clay with grog, so that it is readyfor use.Pot Furnace. A furnace in which glass ismelted and refined in POTS (q.v.), or inwhich a frit is melted for use in a glazeor in a vitreous enamel.Pot Ring. See RING.Pot Spout. A refractory block used inthe glass industry to connect the working

end of a glass-tank furnace to a revolvingpot.Potassium cyanide. KCN; used as aneutralizer in vitreous enamelling.Potassium Niobate. KNbO3; aferroelectric compound having aperovskite structure at roomtemperature. The Curie temperature is4200C.Potassium Nitrate. KNO3; used to someextent as an oxidizing agent in glass-making. The old name was NITRE.Potassium Tantalate. KTaO3; aferroelectric material having a dielectricconstant exceeding 4000 at the Curietemperature (-2600C).Potassium Titanate. This compound,which approximates in composition toK2Ti6O13 and melts at 13700C, can bemade into fibres for use as a heat-insulating material.Potette. A refractory shape used in theglass industry; it is partly immersed inthe molten glass and protects thegathering point from the furnace gasesand from any scum that is floating on theglass.Potsherd. A piece of broken pottery.The word is not now used in theindustry; the N. Staffs, dialect word is'shord'.Potter's Horn or Kidney. A thin kidney-shaped piece of horn or metal used, untilthe early 20th century, by potterypressers. To make dishes, a bat ofprepared body was placed on a plastermould and hand-pressed to shape with apiece of fired ware; the horn was usedfor final smoothing of the surface.Potter's Red Cement. A POZZOLANA(q.v.) type of cement consisting ofcrushed fired clay mixed with portlandcement; (C. J. Potter, /. Soc. Chem. Ind.,28, 6,1909).Potter's Shop. 4COSHH in Production ofPottery, Approved Code of Practice'

1990 defines a potter's shop to include allplaces where pottery is formed bycasting, pressing or any other processand all places where shaping, fettling orother treatment of pottery prior toplacing for biscuit fire is carried on.Pottery. This term is generallyunderstood to mean domestic ceramicware, i.e. tableware, kitchenware andsanitaryware, but the pottery industryalso embraces the manufacture of wall-and floor-tiles, electroceramics andchemical stoneware. There aresubdivisions within these main groups ofpottery-ware, e.g. tableware may beearthenware, bone china or porcelain;similarly, sanitaryware may be sanitaryfireclay, sanitary earthenware or vitreouschina sanitaryware. 4COSHH in theProduction of Pottery, Approved Codeof Practice' 1990 defines POTTERY toinclude china, earthenware and anyarticle made from clay or from a mixturecontaining clay and other materials. Seealso COMMON POTTERY, FINE POTTERY.In USA the term WHITEWARE (q.v.) isused. A pottery is also general usage forthe factory where pottery is made.Potting Material. A material for theprotection of electrical components, e.g.transformers. The use for this purpose ofsintered alumina powder, withinhermetically sealed cans, has provedsuccessful.Pour. To place concrete. A pour is asingle such placement.Pour Point. The optimum temperaturefor pouring a molten batch.Pourbaix Diagrams. Plots of equilibriumpH vs electrochemical potential Edescribe the effects of aqueous corrosionon borosilicate and silicate glasses. Theyare applicable to weathering studies andto ground water attack on nuclear wasteglasses. The diagrams display anyimmune zone between active corrosion

and passivation due to the formation of asurface layer. M. Pourbaix, Atlas ofElectrochemical Equilibria in AqueousSolutions (translation) Nat. Assoc.Corrosion Engs. Houston, Texas, 1974.Pouring-pit Refractories. Alternativeterm (particularly in USA) for CASTING

PIT REFRACTORIES (q.V.).Powder Blue. See SMALT.Powder Density. See TRUE DENSITY.Powdering. A process sometimes usedfor the on-glaze decoration of the moreexpensive types of pottery-ware. Colourmixed with an oil medium is firstbrushed on the ware, dry powderedcolour then being applied to achieve astippled effect.Pozzolana. A material that, whenground and mixed with lime and water,will react with the former to producecompounds having hydraulic properties.There are both natural and artificialpozzolanas. The original NaturalPozzolana was a volcanic tuff worked atPozzoli (or Pozzuoli), Italy, in Romantimes. One of the principal types ofArtificial Pozzolanas is produced byfiring clay or shale at 600-10000C.PPG Delivery System. See FLOAT GLASSPROCESS.

PPG Ring-roll Process. PPG =Pittsburgh Plate Glass Co.; see RING-ROLL PROCESS.Prague Red. Red iron oxide pigment.Prall Mill. An impact mill consisting ofan impeller rotating clockwise at 1000rev/min, a baffle plate moving anti-clockwise at 1500 rev/min, and a secondbaffle plate that is stationary.Praseodymium Oxides. There are atleast two oxides: Pr2O3, and PrO2.Praseodymium Yellow. A ceramiccolour made by calcining astoichiometric mixture of ZrO2 and SiO2

with about 5% PrO2 or Pr2O3. Thisclean, bright yellow can be used in glazes

firing from about 1100-13000C; thezirconium silicate acts as a stabilizer.PRE. (Produits Refractaires Europeen)Federation Europeanne des Fabricantsde Produits Refractaires. (EuropeanFederation of Refractories Producers)Via Corridoni 3, Milan, Italy. The PRERefractory Materials Recommendations1978 comprised over 40 recommendedtest methods and classifications ofvarious types of refractory materials.The PRE Glossary listed refractoriesterminology in French, German, Italianand English. (See Appendix B) SIPRE(Siderugie et PRE) was a body whosemembers were drawn from PRE and theEuropean iron and steel industry.Precipitation Hardening. SeeDISPERSION STRENGTHENING.Precision-bore Tubing. Special glasstubing made by heating ordinary glasstubing until it is soft and then shrinkingit on to a steel mandrel.Precursor. Precursors are materialswhich can be converted into ceramicmaterials by suitable heat or chemicaltreatment. The properties of theprecursor may make it possible toachieve e.g. finer powders with greateruniformity by precipitation fromsolution, the ceramic being insoluble.Prefabricated Masonry. Panels or beamsof specially designed hollow clay blocksformed by the insertion of metal rein-forcing wires through a number of theblocks, laid side by side, followed byinfilling with cement. Many designs of suchprefabricated panels and sections havebeen developed to accelerate buildingconstruction. ASTM C901 is a specifi-cation for prefabricated masonry panels.Preferred Increment. In the buildingindustry this term is defined as: 'thesmallest interval between twoconsecutive sizes in any range ofpreferred dimensions for spaces or

components.' The (UK) Ministry ofPublic Buildings and Works, in itsDimensional Co-ordination forIndustrialized Building (Feb. 1963),recommended preferred increments of 1,4 and 12 in.; these are nominaldimensions. See also MODULAR CO-ORDINATION.

Preform. (1) Term used in the glassindustry, and particularly in the makingof glass-to-metal seals, for a compact ofpowdered glass that has been fired to anon-porous state.(2) A shaped powder compact which isto be further processed (e.g. by post-sintering, reaction bonding, isostaticpressing, machining) to form the finalshape, particularly of an engineeringceramic component.Prepared Body. Instead of individualwhiteware producers themselves mixingthe raw materials, the body is preparedcentrally by a specialist supplier. At thecost of variety, body may be preparedunder better control, and using processes(e.g. spray drying) which to beeconomically viable require a scale ofproduction greater than that needed byan individual manufacturer, who mayalso avoid waste by buying the requiredamount of body appropriately groundand packaged.President Press. Trade-name: a dry-pressbrickmaking machine of a type that givestwo pressings on both the top andbottom of the mould, a short pausebetween the pressings allowing anytrapped air to escape. (W. Johnson &Son (Leeds) Ltd., England.)Press-and-Blow Process. A method ofshaping glass-ware, the PARISON (q.v.) ispressed and then blown to the finalshape of the ware.Press Cloth. See FILTER CLOTH.Pressing. In the pottery industry,pressing was an old method of shaping

ware by hand-pressing a prepared pieceof body between two halves of a mould.See also DRY PRESSING; DUST PRESSING;isosTATic PRESSING; HOT PRESSING;PLASTIC PRESSING; RAM PRESSING.Glassware, such as dinnerware, lensesand other flat shapes, is pressed betweena plunger and a mould, usually in anautomatic rotary press. See OPTICALBLANK.

Pressure Casting. Hydraulic pressure isapplied to the slip in SLIP CASTING, toincrease the casting rate. The techniquewas first applied particularly tosanitaryware, as a high pressure process,or latterly to speed up BATTERYCASTING. More recently it has beenapplied to tableware shaping, where it isbecoming more widespread. The higherstresses on the moulds led to studies ofsand-resin, plastics or even porous metalmould systems, but these require longproduction runs to make them economic,and they have by no means oustedstrong plaster moulds.Pressure Check. A crack in a glassarticle caused by too high a formingpressure.Pressure Cracking. Cracking of thecompacted semi-dry powder immediatelyafter it has been shaped in a dry-press;the cause is sudden expansion of air thathas been trapped and compressed in thepores of the compact. The fault has beenlargely eliminated by designing pressesso that the plunger descends twice to itslowest level, the trapped air having timeto escape between the first and secondpressings.Pressure Sintering. This term has thesame meaning as HOT PRESSING (q.v.).Pressureless Sintering. Sintering atatmospheric pressure.Prestocal. A machine for applying HEAT

ACTIVATED DECALS ( q.V.).

(Commercial Decal Inc, USA).

Preston Density Comparator. Aninstrument designed in 1950 at thePreston Laboratories, USA, for use inthe routine quality control of glass onthe basis of an observed relationship, forany specific glass, between any change incomposition and the associated changein density; the sink-float method isemployed.Preton. A brick panel system (KellerAG, Germany).Primary Air. The air that mingles withthe fuel and effects the initial stages ofits combustion. In a ceramic kiln of atype fired by solid fuel on a grate, theprimary air passes through the grate andthe fuel bed (cf. SECONDARY AIR andTERTIARY AIR).

Primary Boiling. Gas evolution duringthe initial firing of vitreous enamel; thismay result in faults in the ware.Primary Clay or Residual Clay. A claystill remaining in the geographicallocation where it was formed; in the UKsuch a clay is typified by the CHINACLAY (q.v.) of Cornwall (cf.SEDIMENTARY CLAY).

Primary Colours. See TRI-STIMULUSVALUES.

Primary Crusher. A heavy crusher suitablefor the first stage in a process of sizereduction, the product being about 25-75mm in size. Gyratory and jaw crushers,and Kibbler rolls, fall into this class.Primary Phase. The first crystallinephase to appear when a liquid is cooled.For example, in the Al2O3-SiO2 system(see Fig. 5, p230), if a liquid is formedcontaining 40% Al2O3, and if this liquidis then cooled, the primary phase, whensolidification begins, will be mullite; ifthe liquid contains 80% Al2O3, however,it can be seen that the primary phase willbe corundum.Prince Rupert's Drops. Drops of glassthat have been highly stressed by

quenching; when the 'tail' of one ofthese drops is broken the glass explodesto dust, but the drop itself is immenselystrong. These drops were first made byPrince Rupert, nephew of King Charles Iof England.Printer's Bit. An item of KILNFURNITURE (q.v.). It is a small piece ofrefractory material for use as a distance-piece in the stacking of decoratedpottery-ware before and during firing.Prism Test. See THERMAL SHOCK TESTS.Prismatic Glass. Glass that has beenpressed or rolled to produce a pattern ofprisms; these refract light passingthrough the glass. (The term is alsosometimes, erroneously, applied to LENS

FRONTED TUBING (q.V.)

Prismo. Trade-name. Ceramic fibremodules for lining and lids of ladles andreheating furnaces (Lafarge AluminousCement Co).Proarcus. A range of partly curved walltiles, to provide smooth transitionbetween wall and floor surfaces in wetrooms, shower trays, etc (KorziliusGmbH, Fliessen Flatten 37, (6), 52,1987).Process Fish-scaling. A fault in vitreousenamelling, FISHSCALING (q.v.)occurring during the drying or firing ofthe covercoat.Proctor Dryer. The original 'ProctorDryer' of the early 1920s was a tunneldryer for heavy-clay and refractorybricks; drying was achieved by airrecirculating over heated steam coils, orover pipes carrying hot waste gases.Proctor dryers operating on the sameprinciple were subsequently made in avariety of types suitable for all kinds ofceramic product. The name derives fromthe manufacturers: Proctor andSchwartz, Philadelphia, USA.Profile Setter. A SETTER (q.v.) whoseshape matches that of the article to besupported for firing.

Progression China. Tableware with acordierite body, made by Noritaki,Japan.Prokaolin. A term that has been appliedto an amorphous intermediate product inthe process of KAOLINIZATION (q.v.).Prop. See POST.Proppants. Millimetre-sized ceramicparticles, forced with hydraulic fluidsinto fractures in oil and gas wells, tokeep them open. The productivity of thewells is thus enhanced.Prosper Stone. A form of CORNISHSTONE (q.v.).Prostheses. Artificial functionalreplacements for body parts, especiallybones and joints. Ceramic materials forthe latter are usually alumina, apatite orhydroxyapatite, and some glass-ceramics.Carbon composites have been used forheart valves. B.S. 7253 Pt. 2 specifiesalumina bone substitutes. SeeBIOCERAMICS.

Proto-Enstatite. See ENSTATITE.Prouty Kiln. A tunnel kiln of smallcross-section suitable for rapid firing ofpottery-ware, which is carried throughthe kiln on bats. (T. C. and W. O.Prouty, US Pat., 1 676 799,10/7/28.)Proximate Analysis. See RATIONALANALYSIS.

Prunt. A crest, or other device, that hasbeen fused on glassware subsequent tothe general shaping process.Prussian Blue. An iron-ferrocyanideblue pigment.Prussian Red. Potassium ferrocyanidered pigments.PSD. Abbreviation for PORE SIZEDISTRIBUTION (q.V.).

Pseudo-wollastonite. See underWOLLASTONITE.

p.s.i. Abbreviation for pounds per squareinch. (Obsolete. 1 p.s.i. = 7 kNnrr2).Psychrometric Chart. A graphicalrepresentation of the relationship

between the relative humidity, specificvolume, weight ratio of moisture to air,dry-bulb temperature, vapour pressure,total heat, and dew-point of moist air.The chart finds use in the ceramicindustry, particularly in the control ofdryers.PSZ. Partially Stabilized Zirconia. SeeZirconia.PT. Lead Titanate.PTCR. Positive temperature coefficientof resistance. Ceramics with PTCR'sinclude barium titanates.Pucella. A tool for widening the top of awine glass in the handmaking process;from Italian word meaning a virgin.Puddling Clay. Clay used to produce animpervious layer to line a pool orreservoir. The term relates to theapplication, not to the composition ofthe clay.Puesta. An Italian vitreous enamellingprocess using electrostatic powdercoating.Puff-and-blow Process. A modifiedBLOW AND BLOW (q.v.) technique usedto make thin-walled hollow glassware.The first use of compressed air (puff)produces a hollow PARISON (q.v.) whichis shaped in a rotating paste mould, bythe second blow. Light bulbs, flash bulbsand Christmas tree ornaments are madefrom a continuous ribbon of glass(Corning ribbon machine) while largerarticles are made by the turret-chainmachine which uses individual glass gobsand produces less cullet.Pug. A machine for consolidating plasticclay or body into a firm column. Itconsists of a steel cylinder ('barrel')which tapers at one end to a die, throughwhich the clay or body is forced byknives mounted on a shaft which rotatescentrally to the barrel (cf. AUGER andMIXER).Pug Mill. See MIXER.

Pull. See LOAD.Pulled Stem. See STEMWARE.Pullout. See FIBRE PULLOUT;TOUGHNESS.Pulpstone. Sandstone used as a grindingwheel.Pulsed Laser Deposition. A pulsed laser(e.g. a Kr-F excimer laser) is used tovaporise material from a target, anddeposit it to form a coating on asubstrate. The technique is particularlyapplicable to the production ofelectronic devices using hightemperature superconductors.Pulverized Fuel Ash. Finely divided ashcarried over from coalfired power-stationboilers. It has found some use in themanufacture of building materials, e.g.THERMALITE YTONG (q.V.), LYTAG(q.v.), and to a less extent in claybuilding bricks. The composition of theash is (per cent): SiO2 43-50; Al2O3, 24-28; Fe2O3, 6-12; CaO, 2-4; MgO, 2-3;alkalis, 3-5; loss on ignition, 2-10. In theUK, the Central Electricity GeneratingBoard Specification is: > 35% SiO2; <4% MgO; < 3% SO3; > 12% loss onignition.Pulverizer. See FINE GRINDER.Pump Casting. A process in whichcastable refractories are pumped throughpipes to their point of application.Punch Test. A simple test to determinewhether the glaze on a piece of firedpottery is in tension or compression. Asteel centrepunch with a blunt end 0.8-1.6 mm dia. is placed on the glazedsurface and hit sufficiently hard with ahammer to break the glaze. If the latterwas in tension, one or more cracks willbe found to have radiated from the pointof impact; if the glaze was incompression a circular crack will haveformed round the punch mark or aconical piece of glaze will have becomedetached.

Punch Ware. US term for thin hand-blown glass tumblers, etc.Punt. The bottom of a glass container.Punt Code. A mark of identification onthe base of a glass bottle.Punty. An iron rod used in the hand-making of glass-ware to hold the base ofthe ware during its manipulation; fromLatin puntellum, the word used in 16thcentury manuscripts on glassmaking.Pup. A brick (particularly a refractorybrick) of a shape and size based on thatof a standard square but with the endfaces square (or nearly square). Thisshape of brick is also known as a SOAPor CLOSER. See Fig. 1, p39.Purcell Method. Name sometimes giventO the MERCURY PENETRATION METHOD(q.v.) for determining pore-sizedistribution (W. R. Purcell, /. PetroleumTech., 1, (2), 39, 1949).Purple of Cassius. Colouring materialproduced by adding a mixture of tinchlorides to a dilute solution of goldchloride; the latter is reduced to the metaland hydrated stannic oxide isprecipitated, the colour resulting from thefinely-divided gold on the SnO2 particles.Purpling. A fault liable to occur withCHROME-TIN PINK (q.v.) ceramic colourif the amount of alkali and borax is toohigh and the amount of lime too low.Push-down Cullet. A fault occasionallyfound in sheet glass as a result of thepresence of CULLET (q.v.) in the zone ofthe furnace from which the glass wasdrawn.Push-up. Alternative name for PUSHEDPUNT (q.v.).Pushed-bat Kiln or Sliding-bat Kiln. Atunnel kiln, of small cross-section,through which the ware is conveyed onsliding bats instead of on the usual cars;when there are a number of such tunnelsin a single kiln, it is known as a MULTI-PASSAGE KILN (q.v.).

Pushed Punt. The concave bottom of aglass wine-bottle or other container.Putnam Clay. A fine-grained, plastic,Florida kaolin; it fires to a good whitecolour.Puzzuolana. Obsolete spelling ofpozzoLANA (q.v.).PVA. Polyvinyl alcohol, frequently usedas a binder and plasticizer.PVD. Physical Vapour Deposition.Vapour is created by evaporation orsputtering and transported along a line-of-sight path to the substrate to becoated (normally in vacuum) seeSPUTTERING, ION-PLATING.Pycnometer. A small bottle having anaccurately-ground glass stopper piercedwith a capillary. The bottle is of knownvolume and is used for the accuratedetermination of the specific gravity of amaterial.Pyrex. Trade name. A borosilicate glassintroduced by the Corning Glass Co.,USA in 1915 and made in England by J.A. Jobling & Co. Ltd., since 1922. Thisglass has high thermal endurance and ismuch used for making chemical ware.Pyrite, Pyrites. Iron sulphide, FeS2:sometimes present in clays causingslaggy spots on the fired product.Pyroceram. Trade-name (Corning GlassWorks, USA) for the originalcommercially available GLASS-CERAMIC(q.v.); the equivalent material made inthe UK under licence is known asPYROSiL (q.v.)

Pyro-clad. Trade-name. A process fordepositing multilayer coatings of metals andceramics. (Aremco Products Inc. USA).Pyroelectric Materials. Pyroelectricsdevelop an observable spontaneouselectric moment only when heated. CfFERROELECTRics. Pyroelectric ceramicsinclude some niobate-zirconate systems,barium titanate modified with zirconiaand hafnia, and lanthanum-modified lead

titanate. Applications are to infra-reddetectors and other electronic devices.Pyrofix. Trade-name. (1) A highlysiliceous sleeve brick. HarimaRefractories, Japan.(2) A refractory concrete anchoringsystem based on a ribbed steel bar. Theribs eliminate the need to bend the barinto complex shapes. (George Clark,(Sheffield) Ltd. Refract J. May/June1976, pl8)Pyroflam. Trade-name. Glass-ceramiccooking ware marketed in the UK asPYROSiL (q.v.) (Corning NederlandeFabricken).Pyrogel. Trade-name. Mixed oxidecompositions made by SOL-GELprocessing (UKAEA, Harwell).Pyrolite. Trade-name. A lithium-aluminium-silicon oxide ceramic. (KrohnCeramic Corp, USA).Pyrolusite. MnO2; see MANGANESEOXIDE.

Pyrolytic Coatings. Pyrolysis is thedecomposition of a material by heat. Apyrolytic coating is a thin coatingproduced by the breakdown of a volatilecompound on a hot surface. Some typesof resistor are made by the pyrolyticcoating of an electroceramic rod withcarbon. Pyrolytic coatings of BN, SiC,and Si3N4 have been applied tocomponents for their protection duringexposure to high temperatures.Pyron. Trade-name. A range of coloursfor articles, including glazed ceramics,glass as well as wood or plastics, whichare not to be subsequently fired. (CMSColours Ltd, UK).Pyrometer. A device for themeasurement of high temperature, e.g. athermocouple or a radiation pyrometer.B.S. 1041 deals with temperaturemeasurement and various pyrometers.Pyrometric Cone. A pyramid with atriangular base and of a defined shape

and size; the 'cone' is shaped from acarefully proportioned and uniformlymixed batch of ceramic materials so that,when it is heated under statedconditions, it will bend due to softening,the tip of the cone becoming level withthe base at a definite temperature.Pyrometric cones are made in series, thetemperature interval between successivecones usually being 200C. The bestknown series are Seger Cones(Germany), Orton Cones (USA),Staffordshire Cones (UK); for nominaltemperature equivalents see Appendix D.Pyrometric Cone Equivalent. A measureof refractoriness: the identificationnumber of the standard pyrometric conethat bends at the temperature nearest tothat at which the test-cone bends underthe standardized conditions of test.These conditions are specified in thefollowing national standards: Britain,B.S. 1902 Pt. 5.1 specifies pyrometriccones, and Pt. 5.2 the determination ofPCE (refractoriness); USA, ASTM -C24 specifies the determination of PCEfor firebrick and high aluminarefractories; France, B49-102; Germany,DIN 51 063.Pyrophyllite. A natural hydratedaluminium silicate, Al2O3.4SiO2.H2O. Itoccurs in N. Carolina, Newfoundland,Japan, and S. Africa, and finds some usein whiteware bodies. The massivematerial can be turned on a lathe andthen fired at 1000-12000C with noappreciable change in dimensions.Pyroplastic Deformation. Theirreversible deformation suffered bymany ceramic materials when heavilystressed at high temperatures. The termhas been applied more particularly to theslow deformation of fireclay refractorieswhen loaded at high temperatures.Pyroscope. A device that, by a change inshape or size, indicates the temperature

or, more correctly, the combined effectof time and temperature (which has beencalled HEAT-WORK). The best-knownpyroscopes are PYROMETRIC CONES(q.V.), BULLERS RINGS (q.V.)HOLDCROFT BARS (q.V.); and WATKINHEAT RECORDERS (q.V.).Pyrosil. (1) Glass-ceramic cooking ware.See PYROFLAM, PYROCERAM.(2) Kiln car tops containingPYROPHYLLITE (q.v.) (South Yarra FireBrick Co Pty, Australia).Pyrotenax. Mineral insulated cables orthermocouple probes, made by BICCPyrotenax Ltd, Hebburn. Used inelectrical power distribution in ships, andwhere there is a high fire risk.Pyroxenes. See SILICATE STRUCTURES.Pythagoras Ware. Trade-name:W. Haldenwanger, Berlin Spandau.A gas-tight mullitic porcelain that canbe used at temperatures above 14000C.P.C.E. 1825°C. Thermal expansion(20-10000C), 5.7 x 1(H, Tensilestrength, 50 MNm-2; crushing strength,700 MNm-2.PZN. Lead Zinc Niobate.PZP. A zircon refractory ramming mixmade by Savoie Refractaire, France.PZT. Lead zirconate-titanate,Pb(Zr5Ti)O3; used as a ceramiccomponent in piezoelectric transducers.Trade-name of Vernitron Ltd.Quality Assurance. An organisedprogramme which specifies tests, andresponsibilities for testing and therecording of results. It is designed toensure that a claimed quality of productor service is consistently delivered, andthe origin of any shortfall identified. Thestandards for such quality systems areB.S. 5750 and ISO 9000.Quality Control. A system of regulartests to ensure that products attain therequired standards of performance. Seealso ACTION LIMIT.

Quantimet Image Analyser. A methodof analysing the image in microscopy, bydisplaying it on a television screenscanned at 720 lines, which allows areasof interest to be scanned at 625 lineswith 800 image points, or 500,000observable dots. Grain size and shapecan be studied, and phases identified bydistinguishing black, grey and whiteareas.Quarl Block. A refractory shape formingthe whole, or a segment, of a gas- or oil-fired burner, particularly in a boilerfurnace or glass-tank furnace.Quarl Throat. An opening in the wall of aboiler furnace, into which a burner is set.Quarry. (1) An open-cast working ofrock.(2) See FLOOR QUARRY.Quartz. The common form of silica,SiO2. Quartz is the principal constituentof silica sand, quartzite and ganister, andit occurs as an impurity in most clays.The room-temperature form, a-quartz(sp. gr. 2.65) undergoes a reversiblecrystalline change to p-quartz at 573°C;this inversion is accompanied by a linearexpansion of 0.45 %. At 8700C quartzceases to be stable but, in the absence offluxes, does not alter until a much highertemperature is reached, when it isconverted into cristobalite and/ortridymite, depending on the temperatureand nature of the fluxes present.Quartz Glass. This term is derived fromthe German Quarzglas and as such refersto Transparent Vitreous Silica; the termis not recommended. For definitions ofthe types of VITREOUS SILICA see underthat term.Quartzel. 99.99% SiO2 silica yarn whichcan be woven into textiles.Quartzite. A silica rock of a type inwhich the quartz grains as originallydeposited, have grown at the expense ofthe siliceous cement. Its principal use in

the ceramics industry is as raw materialfor the manufacture of silica refractories.For this purpose the quartzite shouldcontain as little alkali and aluminacompounds as possible; the porosityshould be low (< 3%) and the rockshould consist of small quartz grains setin a chalcedonic or opaline matrix.Quartzite for silica refractories is workedin Britain in N. and S. Wales, theSheffield area and the N. Pennines (cf.GANISTER; SILCRETE).Quasi-brittle fracture. See FRACTURE.Quasi-brittle fracture is characterized bysome toughening mechanism whichincreases the fracture energy to a rangefrom 0.1 kJirr2 (in concrete) to severalkJm-2 in fibre-reinforced materials.There is usually a CRACK BRIDGINGZONE just behind the crack tip, with asmall (sub-millimetre) microcrack regionat the crack tip, and the cracking processzone extends over several mm. This isthe cracking mechanism in some large-grained ceramics, and in whiskerreinforced ceramics. See CRACKBRIDGING; TOUGHNESS.Quasi-isostatic Pressing. A variant ofisosTATic PRESSING, in which rubber orsynthetic elastomer, rather than a fluid,is used as the pressure transmittingmedium. It is claimed to be of value forlarge products. In the Dorst press formaking tableware plates, the lowerplunger is a hollow membranepressurized from within with oil. (Dorst-Keramikmachinenbau, Br.Pat 1589666and UK Pat 2060470A, 1981).Quebracho Extract. An extract of tanninfrom the S. American tree QuebrachoColorado. It has found some use,particularly as sodium tannate, as adeflocculant for pottery slips.Queen Closer. A brick cut longitudinallyto half width (50cm), used to maintainthe bond.

Queen's Ware. The name given byQueen Charlotte, wife of George III, tothe fine white earthenware introduced byJosiah Wedgwood in 1763.Quench Tests. See THERMAL SHOCK TESTS.Quenching of Frit. Molten glaze-frit orenamel-frit is quenched to break it up,thus making it easier to grind. Thesimplest method is to allow the stream ofmolten frit to fall into water, but thisdoes not give uniform quenching andfracture. Better methods are to exposethe stream of molten frit to a blast of airand water, or to pass the stream betweenwater-cooled rolls; the latter processgives a flaky product.Quetta Bond. A brickwork bond whichprovides vertical channels the height ofthe wall, into which reinforcement canbe placed. The walls are usually lx/2bricks thick. Named after the town ofQuetta, in Pakistan, where the bond wasintroduced after an earthquake, toprovide reinforced structures capable ofwithstanding seismic damage. SeeREINFORCED BRICKWORK.

Quick Clay. A term in soil mechanics fora clay that, when undisturbed, has acertain shear strength and can beregarded as a solid body but which,when remoulded, can be regarded as aliquid (cf. THIXOTROPY).Quickfire Kiln. An experimental lowcross-section low thermal mass tunnelkiln for tableware, designed for shortfiring cycles of ware set one-high,enabling flexible operation, with thefiring schedule matched to daily shifts, orreadily changed between small batchesof different ware. The kiln was designedby British Ceramic ResearchAssociation, and a very similar kilnmarketed as the FIREPOWER (q.v.).Quintus Press. Trade-name. An isostaticpress made by Asea, Sweden.Quoin. An external corner of brickwork.

R-Curve. R is the crack resistance force,which for many ceramics increases as thecrack propagates. This is termed 'R-curve behaviour,1 but the shape of thecurve R vs a/W is not a characteristic ofthe material, but depends also on thetest conditions. a/W is the crack length a,normalized for a specimen height W.The crack resistance force R is given by:R = (P2/2b). d/da (d/P) where P is theload, d the deflection and b is thespecimen width. See CRACK BRIDGING.R-value. The partial dispersion ratio of aglass expressed as (nD-nc)(nF-nc)-1

where nc, nD and nF are the refractiveindices at wavelengths equivalent to thespectral lines C, D and F. (cf. ABBENUMBER.)

Rack Mark. A surface blemish on rolledglass resulting from a mechanical defectin the drive actuating the forming roller.Radial Crack. A semi-elliptical crackperpendicular to a surface damaged bypressing on to it a hard, sharp object.Radial Brick. A brick with the two endfaces curved to form parts of concentriccylinders (cf. CIRCLE BRICK and seeFig. 1. p39)Radio-frequency Heating. See underINDUCTION HEATING.

Radome. A protective cone for the radarequipment in the nose of an aircraft,rocket or space vehicle. At high speedsthe skin temperature may exceed 5000Cand ceramic radomes become necessary;alumina and glass-ceramics have beenused.Rain Penetration. The degree to whichrain penetrates brickwork greatly affectsthe thermal insulation value and theresistance to frost damage. It depends onthe integrity of the structure, theworkmanship, as well as the porosity ofthe bricks and mortar. It is influenced bywind conditions and site exposure todriving rain. Test cabinets with water

sprays to simulate real conditions havebeen devised. B.S. 8104 recommends twomethods for assessing the exposure ofwalls to driving rain. ASTM E514 is apanel test to assess water penetration ofbrickwork. In Britain, the BritishCeramic Research panel test is used.Other ASTM tests (E331, E5467, E1105)relate to windows, curtain walls anddoors.Rain Spalling. Severe mechanicaldamage to the refractory lining of arotary kiln, indistinguishable fromCHEVRONiNG (q.v.), but sometimes dueto sudden contraction of exposed partsof the kiln in heavy rain.Rain Spot. A dark circular mark, oftensurrounded by a halo, on vitreousenamelware; the fault arises if a dirtydrop of water falls on the biscuit ware.Rake, CULLET CUT (q.v.).Rake-out Slots. Gaps left in a kiln cardeck for the removal of debris.Raking Stretcher Bond. A method oflaying bricks in a wall, all the coursesbeing stretchers and all vertical jointsbeing broken by the length of a quarterof a brick.Raku Ware. A type of pottery used inJapan for the Tea Ceremony. The wareis thick-walled, is covered with a verysoft lead borosilicate glaze, and is once-fired at about 7500C.RAL Colour Register. (ReichsAusschusz fur Lieferbedingungen -(German) National Board forConditions of Delivery). This register isa collection of samples of those colourspredominantly used in industry. (Cf. B.S.5252 1976). Every named colour in theregister is placed in the RAL ColourList, a set of cards with the originalcolour shade on their left-hand side. Thecolour register makes possiblerationalisation and standardization indealing with colours in all parts of

industry. It is relevant to ceramic tilesand sanitaryware. It is not a coloursystem based on a strict scientific colourmeasurement, but has been developedempirically to classify colours used inpractice.Ram Pressing. A process for the plasticshaping of tableware and sanitarywareby pressing a bat of the prepared bodybetween two porous plates or mouldunits; after the pressing operation, air isblown through the porous mould parts torelease the shaped ware. The processwas patented in 1952 by RamIncorporated (US Pats, 2 584 109 & 10).Ramming. The forming of refractoryshapes or monolithic linings by means ofa portable device (usually pneumatic) bywhich the material is compressed byrepeated impact from a blunt ended tool(cf. TAMPING).

Ramming Material. Graded refractoryaggregate, or a mixture of aggregates,with or without the addition of aplasticizer; ramming materials areusually supplied at a consistency thatrequires a mechanical method ofapplication; chemical bond(s) may beincorporated. The rammed massbecomes strong and monolithic byvitrification or sintering in situ.Ramming Mix. A mixture containinggraded refractory aggregate and otherbonding materials which will hardenwhen heated, by the formation of achemical and/or ceramic bond. Such amixture may be supplied either dry ormixed with water or other liquids and, ineither case, requires to be installed bythe use of mechanical or pneumatic toolsor vibration. (B.S. 1902 Pt. 7). ASTMCIl defines a ramming mix as arefractory material, usually temperedwith water, that cannot be extruded, butcan be rammed in place to form amonolithic structure.

Ramonite. A material developed forinvestment casting and lost-wax casting,from a mixture of enriched raw materialscontaining up to 52% alumina.Ramp. That part of the roof of an open-hearth steel furnace that rises from theend of the main roof to the top of theend wall; as the furnace is symmetrical,there is a ramp at each end.Ramsdell Numbers. A shorthandnotation for labelling POLYTYPES (q.v.)of crystal structures The numbers are ofthe form /?R or nli were n is the numberof layers in the UNIT CELL (q.v.)necessary for the arrangement of thelayers to repeat itself. R, H stand forrhombohedral or hexagonal crystal formrespectively. Originally devised toclassify silicon carbide polytypes, thesystem has been applied to othercarbides and nitrides. (L.S. Ramsdell,Amer. Miner 32, 147, p64).Randalusite. ANDALUSITE (q.v.) fromthe Transvaal.Rankine Temperature Scale. TheFahrenheit scale displaced downwards sothat Absolute Zero (-4920F) is 0°Rankine: 32°F = 492° Rankine; etc.Rankinite. 3CaO.2SiO2; meltsincongruently at 1464°C to formdicalcium silicate and a liquid; thermalexpansion (20-10000C) 13 x 10"6. It isnot found in portland cement.Rapid Firing. Reducing the conventionalfiring schedules for traditional ceramicsfrom days to hours, or less, by methodssuch as SINGLE LAYER SETTING, radiantheating, LOW THERMAL MASS KILNS andimproved body and glaze formulations.Rapid-hardening Portland Cement. TheUK equivalent of the US term HIGH

EARLY-STRENGTH CEMENT. It is morefinely ground than ordinary portlandcement; B.S. 12 stipulates a specificsurface 3250 cm2/g compared with 2250cm2/g for ordinary cement. This extra

fineness results in the 1-day strengthbeing as high as the 3-day strength ofordinary cement.'Rapid9 Method of Silicate Analysis.Analysis of clays and ceramics, usingselected reagents and spectrophotometryto complete an analysis in about 8 hours,instead of several days by the 'standard'wet chemical technique. Moderninstrumental techniques such as X-rayfluorescence can produce completeanalysis in minutes.Rapid Omnidirectional Compaction.This method for shaping mixed ceramicand metal powders combines highpressure and short compaction time withdensification by plastic deformation toachieve near net shape forming (CeramEng ScL Proc. 9, (7/8), 965, 1988).Rapidor Mill. A ball mill with a rapidly-rotating vertical barrel. Tradename WmBoulton Ltd., Stoke-on-Trent.Rare Earths. Oxides of the rare earthelements of Group III in the PeriodicSystem. Those used in ceramics are theoxides of LANTHANUM, CERIUM,

PRASEODYMIUM, NEODYMIUM, andYTTRIUM (q.V.).Raschig Ring. A thin-walled hollowcylinder made of chemical stoneware,glass, carbon or metal, for the packing ofabsorption towers. These rings are madein various sizes from about 12.5 x 12.5mm (300000/m3) to 50x50 mm (5000/m3)and even up to 200x200 mm. (F. Raschig,German Pat, 286 122.)Rasorite. Natural BORAX (q.v.).Rat Hole. A hole eroded through therefractory structure, especially thecrown, of a glass tank.Rate-controlled Sintering. Densificationrate (the slope of the density/time curve)is used as the independent variable inthe control of the sintering process(instead of the temperature, as is usual).Densification is made to proceed at the

lowest temperatures which will maintainthe desired density-time curve. Thepower input to the furnace is varied byfeedback from continuous dilatometry ofthe sintering sample. (The resultingtemperature-time curve will be quitenon-linear, and may include periods ofcooling).Rational Analysis. The mineralogicalcomposition of a material as deducedfrom the chemical analysis. Withmaterials whose general mineralogicalcomposition is not already known, thecalculation is made only after micro-and/or X-ray examination has shownwhat minerals are present and theirapproximate proportions. With potteryclays the calculation is made withoutsuch guidance, either on the FELDSPAR

CONVENTION Or the MICA CONVENTION.The former is the older procedure andassumes that the minerals present arekaolinite, feldspar and quartz. It is nowknown, however, that the alkali impurityin English pottery clays is present asmica and according to the micaconvention the rational analysis iscalculated on the basis of kaolinite, micaand quartz. (The term PROXIMATEANALYSIS is sometimes applied to therational analysis of clays.)Rattler Test. A test introduced in 1913by ASTM, as a method for evaluatingthe resistance of paving bricks to impactand abrasion; it is now a standard test(ASTM - C7). A sample of 10 bricksis subjected to the action of 10 cast-iron balls 3.75 in. (47.5 mm) dia. and245-260 balls 1.875 in. (95 mm) dia.in a drum (28 in. dia; 20 in. long(0.7 m x 0.5 m)) rotating at 30 rev/minfor 1 h. The severity of abrasion andimpact is reported as a percentage lossin weight.Raw Glaze. A glaze in which none of theconstituents has been previously fritted.

RBAO. Reaction Bonded AluminiumOxide.RBM. REINFORCED BRICK MASONRY(q.v.)RBSC. Reaction-bonded SiliconCarbide. See SILICON CARBIDE.RBSN. Reaction bonded silicon nitride.See SILICON NITRIDE.RCVD. Reactive Chemical VapourDeposition (q.v).RE, REL, REO, REOL, RER, RES,REX, REXH, REXR. Symbols forvarious shapes of ceramic wall tiles andfittings (see Fig. 7, p350).Reaction-bonding. The formation of apolycrystalline ceramic by a chemicalreaction between the powder and a gasor a liquid. Cf. REACTION SINTERINGand see SILICON NITRIDE, SILICONCARBIDE.Reaction-sintering, SINTERING (q.v.) of atwo-component powder, in which achemical reaction also takes place toproduce a dense single phase or amultiphase material. Ceramic-ceramiccomposites may be thus produced - e.g.dense mullite zirconia composites fromzircon and alumina. See also REACTIVE

HOT-PRESSING.Reaction-sintered Silicon Carbide. Amisnomer, for reaction bonded siliconcarbide. See SILICON CARBIDE.Reactive Chemical Vapour Deposition.(RCVD). A variant of CVD, in whichmore than one material is deposited atthe same time, to optimise the desiredproperties of the composite coating.RESA (Reactive Electrode SubmergedArc Technique). Fine (10-1000nmanhydrous oxide powders are made assols by striking an arc between two metalelectrodes submerged in a dielectricliquid, typically water. (A. Kumar and R.Roy J Mater Res 3 (6), 1988 p. 1373).Reactive Hot-Pressing. A term proposedby A. C. D. Chaklader (Nature, 206, 392,

1965) for the special case in which thematerial being pressed decomposes, e.g.by losing H2O or CO2, at thetemperature employed; increasedstrength and decreased porosity can beachieved in this way.Reactive Spraying. A mixture of metal,metal oxide and a peroxide is sprayed onto a surface pre-heated to 1200-150O0C(e.g. a hot refractory lining in need ofrepair). A monolithic ceramic layer isformed in situ.Reactolite. Trade-name, PHOTOCHROMICGLASS (q.v.) used particularly forspectacles. (Chance-Pillington).Ready-mixed Concrete. See SHRINK-MIXED and TRANSFER-MIXED.Real Brick. Thin brick slips are cut fromgreen bricks and fired alongside thenormal products. They are intended asdo-it-yourself facings. (Michegan BrickCo. Brick Clay Rec 168, (2) 23, 1976).Ream. A fault in flat glass resulting fromthe presence of a heterogeneous layer,or layers, within the glass. The fault isseen as a series of parallel lines when theglass is viewed through an edge; theappearance is similar to a pile of paper,hence the name.Rearing. The setting of pottery flatwareon edge for the firing process (cf.DOTTLING).Reaumur Porcelain. A fritted porcelain('soft paste') made from 75% frit, 17%chalk and 8% clay; the frit contained60% SiO2 the remainder being K2O,Na2O, Al2O3 and CaO. It was first madeby a Frenchman, R. A. Reaumur (1683-1757).Reaumur Temperature Scale. A little-used scale in which the temperatureinterval between the freezing point andboiling point of water is divided into 80degrees.Reboil. The appearance of bubbles inglass or vitreous enamel during

manufacture. Molten glass may reboilafter it has apparently freed itself fromgases; in vitreous enamelling, bubblesmay appear on the surface of sheet-steelground-coats during the second or thirdfiring process.Recessed Wheel. An abrasive wheelhaving a contoured central recess in oneor both sides.Recesso. Ceramic bathroom fittings, e.g.recessed soap-trays. (Trade-mark,Richards Tiles Ltd., England.)Reciprocal Lattice. A mathematicalconstruct to express elegantly theconditions for an X-ray beam to bediffracted by a crystal lattice. If thedirections of the crystal lattice are givenby vectors a, b and c, then the reciprocallattice vectors a*, b* and c* are such thata* is perpendicular to the plane of b andc, and a*.a = 1, etc. Then a vector r*from the origin to a point (h, k, 1) of thereciprocal lattice is perpendicular to theplane (h, k, 1) of the crystal lattice, andits length is the reciprocal of the spacingof the (h, k, 1) planes of the crystallattice. Every point in the reciprocallattice corresponds to a possible X-rayreflection from the crystal lattice. Seealso X-RAY CRYSTALLOGRAPHY.Reckna Clay Beams. Prefabricatedbeams made of specially designed hollowclay building blocks reinforced with steelrods; the load-bearing capacity is about40MNm"2. The design originated inGermany (Ziegelindustrie, 3, 60, 1950).Reclaim. Overspray (enamel or glaze)that, after it has been reconditioned, issuitable for re-use. In vitreousenamelling, reclaim is generally usedonly in first-coats.Reconstructed Glass, POROUS GLASS(q.v.) can be impregnated with aqueoussolutions of nitrates or chlorides ofcolouring ions. The impregnated glass iswashed and CONSOLIDATED in air or

oxygen, to form heat-resistant colouredglasses. Black glasses of variouselectrical resistivities can be made byimpregnating with furfuryl alcohol,which polymerises to a resin. This ispyrolyzed to an amorphous carbon phasein the pores, and the glass consolidated.Recrystallization. The process ofproducing strain-free grains in aplastically deformed matrix. One crystalspecies grows at the expense of other(s)of the same substance which are smaller.Primary recrystallization is by nucleationand growth of new strain-free grains inthe plastically deformed matrix. Insecondary recrystallization large grainsgrow at the expense of a fine-grainedstrain-free matrix. There is a thresholdtemperature below whichrecrystallization does not take place.ALUMINA and SILICON CARBIDE are themost common materials available inrecrystallized form.Rectangular Kiln. An intermittent kiln,rectangular in plan, with fireboxes atintervals along the two long sides. Suchkilns find limited use in the heavy-clayand refractories industries.Recuperator. A continuous heatexchanger in which heat from furnacegases is transferred to incoming air orgas through walls (usually tubes) ofmetal or refractory material.Red Clay. A term applied in thepottery industry to any of theferruginous clays used for making tea-pots, floor tiles and plant pots; inEngland these clays are typified by theETRURIA MARLS (q.V.)Red Edge. A fault in plate glasscharacterized by numerous smallcavities, containing rouge from thepolishing, around the edges.Red Lead. Pb3O4; see LEAD OXIDE.Red Mud. The residue from themanufacture of alumina by the Bayer

process. Red mud has been used tomake building bricks.Red Ware. See ROCKINGHAM WARE.Redwood Cup. An orifice-typeviscoMETER. See FLOW CUP.Redston-Stanworth Annealing Schedule.A procedure for determining theoptimum conditions for annealing smallglass articles; it is based on the Maxwellmodel of stress release, modified to takeaccount of the variation of viscosity withtime. (G. D. Redston and J. E. Stanworth,/. Soc. Glass Tech., 32, 32,1948.)Reel Cutter. A type of CUTTING-OFFTABLE (q.v.) in which the wires arestretched within a large circular frame,the axis of which is slightly above theline of the extruding clay column. Thistype of cutter can operate on a stiff clayand, if powered and automatic, has ahigh output.Rees-Hugill Flask. A 250 ml flask, with aneck graduated directly in specificgravity units, designed expressly for thedetermination of the specific gravity ofsilica and other refractories. It wasintroduced by W. Hugill and W. J. Rees(Trans. Brit. Ceram. Soc, 24, 70, 1925)and has since become the subject of aBritish Standard (B.S. 2701).REFEL. Registered tradename (ReactorFuel Element Laboratory) of theUKAEA Springfields laboratory, forREACTION BONDED SILICON CARBIDEdeveloped there on the basis of P.Popper's original work at BritishCeramic R.A. (Power Jets (R&D) Ltd,Br. Pat. 866,813, 3/5/61).Refining. The process in glass-makingduring which the molten glass becomesvirtually free from bubbles; this iseffected in the REFINING ZONE of aglass-tank furnace, or in a pot.Retire Opal. See OPAL GLASS.Retiring. A second firing given to articlesof ceramic sanitaryware or vitreous

enamel, which fires a partial glaze orenamel coating applied to repair orfurther decorate the piece.Reflectance. This term is defined inASTM-C286 as: The fraction of incidentlight that is diffusely reflected, measuredrelative to magnesium oxide understandard conditions.'Reflectivity. As applied to vitreousenamel, this term is defined in ASTM-C286 as: 'The REFLECTANCE (q.v.) of acoating so thick that additional thicknessdoes not change the reflectance. Themethod of test is given in ASTM -C347.' See also GLOSS.Reflex Glass. Glass strip, for use invessels containing liquids, made withprismatic grooves to facilitate thereading of the liquid level.Reformulation. If one raw material issubstituted for another nominally similarin a ceramic body, significant changes inbehaviour can result, which may beovercome by the stepwise replacementof other ingredients. Reformulationtechnology replaces this experimentationby numerical calculation techniquesbased on measurements of a smallnumber of characterizing features of thebody. (G.W. Phelps,, Am. Ceram. Soc.Bull. 55, (5) 1976 p.528 - R. L. Lehman,Ceram Eng. ScL Proc. 13 (1/2) 1992 p.321).Refractoriness. The ability of a materialto withstand high temperatures; it isevaluated in terms of the PYROMETRIC

CONE EQUIVALENT (q.V.).Refractoriness-under-Load. The abilityof a material to withstand specifiedconditions of load, temperature andtime. Details of variations in this test willbe found in the following nationalstandards: Britain-B.S. 1902; USA-ASTM-C16; Germany-DIN 51064;France-AFNOR B49-105. B.S. 1902specifies a dilatometer method (Pt. 4.8)

and a differential method (Pt. 4.9). It isusual to show the result of this test as acurve (Fig. 5) relating the expansion/contraction to the temperature. In theASTM method the test-piece is twowhole bricks; unless the brick fails byshear, the subsidence caused by the testis determined by direct measurement ofthe brick after it has cooled to roomtemperature. The German procedurereports two temperatures: ta at which thecurve has fallen 3 mm from its highestpoint, and either te, (10mm subsidencefrom its highest point) or tb (thetemperature at which the test-piececompletely collapses).Refractory Cement. A finely-groundrefractory material, or mixture, used forthe jointing of furnace brickwork. Theterm is often used to denote all types ofsuch cement but should more properlybe reserved for materials that hardenonly as a result of ceramic bonding athigh temperature.Refractory Coating. A refractorymaterial for the protection of the surfaceof refractory brickwork or of metals (e.g.pyrometer sheaths or aircraft exhaustsystems). Examples of such coatingsinclude Al2O3, ZrSiO4, MoSi2 and (forthe protection of metals) refractoryenamels. Refractory coatings for furnace

brickwork are sometimes known asWASHES.Refractory Concrete. A concrete madefrom a graded aggregate of crushedrefractory material together with high-alumina hydraulic cement, e.g. CimentFondu or Lumnite. The concrete may becast in position in a furnace lining or itcan be made into blocks and specialshapes. With an aggregate of crushed40%-Al2O3 firebrick, such a concretecan be used up to about 13000C.Insulating concrete can be made for useup to 9000C; its thermal conductivity isabout 0.25-0.35 W/mK.Refractory Material. Also known asREFRACTORY PRODUCT, or simplyREFRACTORY. Typical refractorymaterials are fireclay, silica, magnesite,chrome-magnesite, sillimanite; dolomiteand carbon. They are materials used inlarge quantities to withstand hightemperatures, in furnace linings andsimilar industrial applications. B.S. 3446Pt. 1,1990 defines a REFRACTORYMATERIAL as a non-metallic materialor product (but not excluding thosecontaining a proportion of metal)having heat resisting properties,usually measured by classes inPYROMETRIC CONE EQUIVALENT andselected according to the operating

Contr

action

(%)

Expa

nsion

(%) 3mm inDIN test

10mm inDIN test

Temperature CC!

Fig. 6 REFRACTORINESS-UNDER-LOAD

temperature and the level of protectionrequired.Refractory Mortar. Jointing material forfurnace brickwork. (B.S. 1902 Pt.llwhich specifies properties and tests)ASTM C71 defines refractory mortar asa finely ground preparation whichbecomes trowelable and plastic whentempered with water, and is suitable forlaying and bonding refractory brickwork.A heat-setting mortar is defined as arefractory mortar whose potentialstrength is dependent on use at furnaceor process temperature. ASTM C198specifies a cold bonding strength test;C199 a test for their refractoriness, inwhich a brick pier laid with the testmortar is heated in prescribed manner tosee if the mortar flows from the joints.Refractory Putty. A MOULD ABLE withmaximum grain size of 0.5mm, for small-scale sealing, patching and coating. SeeB.S. 3446 and B.S. 1902 Pt. 11, whichspecifies properties and tests.Refrasil. Fused silica fibre. (Trade-nameof Chemical & Insulating Co.,Darlington).Refrax. Trade-name. A silicon carbide/silicon nitride composite, used for specialrefractory shapes and tiles. The siliconnitride bond is formed in-situ betweenthe grains of silicon carbide, imparting afiner crystal structure to the refractory,so improving strength and refractoriness,to 18000C. (Refrax S.I is silicon nitride).Regenerator. A periodic heat exchangerin which refractory checker bricksalternately receive heat from furnacegases and give up heat to incoming air orgas; this is achieved by reversing thedirection of gas flow.Reheat Test. The prescribed heattreatment of a fired refractory todetermine its dimensional stability whenreheated to a second temperature higherthan the temperature to which it was first

subjected. ASTM Cl 13 specifies eightheat treatment schedules which can beused for various types of refractories.See PERMANENT LINEAR CHANGE.Rehoboam. A 6-quart wine bottle.Reinforced Brickwork or ReinforcedMasonry. Brickwork that is reinforcedby steel rods or wires inserted intocontinuous cavities through thebrickwork, the space between steel andbrick then being filled with pouredconcrete. Such brickwork can withstandtensile, as well as the usual compressive,stresses. Rules for the design of suchbrickwork are included in B.S.5628 Pt2.Reintjes Bricking Rig. A scaffoldingsystem for lining cylindrical furnaces,cement kilns in particular. When thelower part of the lining has been laid, therig is assembled and further bricks arelaid over the top of the rig by bricklayersworking from a scaffold integral withand moving with the rig as it advancesupwards course by course. The rig allowsindividual rings of bricks to be tightenedusing hydraulic jacks, with shims fromthe side, rather than by applying forcesto the hot-face.Relaxors. FERROELECTRIC (q.v.)ceramics in which the ferroelectric-paraelectric phase transition takes placeover a range, rather than at a well-defined CURIE TEMPERATURE (q.V.).The relaxation (or exponential decay) ofthe dielectric constant takes place over arange of temperature. One explanationOf this DIFFUSE PHASE TRANSITION ISthat the materials have a structurecomprising an assembly of microregions,each with its own Curie temperature, butthere is a distribution of Curietemperatures from different individualmicrovolumes. Thus the transition fromferroelectric to paraelectric behaviourtakes place over a wide temperaturerange, within which some of the

microregions are paraelectric, while theothers are still ferroelectric. Ceramicrelaxors include some PLZT ceramicsand some niobates. Their properties arealso frequency dependent.Relict. A porous AGGLOMERATE ofoxide particles, formed by calcination ofsalt particles with the same size andgrouping as the resulting agglomerate.Relicts have ultrafine porosity and aregood thermal insulators and barriers togas diffusion.Relieving Arch. An arch built intostructural or refractory brickwork totake from that part of the wall below thearch the weight of brickwork above thearch.Rendering. A coating of mortar orplaster on brickwork or the process offorming such a coating.Renn Press. See KRUPP-RENN PROCESS.Repressing. A second pressingsometimes given to bricks (both buildingand refractory) to improve their finalshape; with building bricks the purposecan also be to provide some specialsurface effect.Repetitive Strain Injury (RSI). Injurydue to overstressing by constantrepetition of a movement, or prolongedholding of a limb in an unnaturalposition. Chronic pain or loss of mobilitymay result.Replicast CS Process. In this metalcasting process, a refractory coating isapplied to high quality expandedpolystyrene, which replaces the wax inmanufacture by ceramic shell moulding.Relatively large components with goodsurface finish can be produced. Theprocess was developed by SCRATA,Sheffield, using coatings developed byFoseco International.Replication. The technique ofreproducing the topology of a polishedsection or a fracture surface by applying

to it a thin film such as a softened plastictype or a rapidly polymerizing liquidsilicone rubber. The topology may thenbe examined by microscopy, using thereplica, while the original is available forother tests.Re-setting (of Portland Cement). Theproperty of portland cement, after it hasbeen mixed with water and allowed toset, to set for a second time (althoughgiving a great reduced strength) if it isagain finely ground. The effect is due tothe fact that the hydration causingsetting is confined to the surface (10mm)of the cement particles, some of whichare as large as 100mm.Residual Clay. See PRIMARY CLAY.Resinous Cement. A term used inchemical engineering for an acid-proofcement, based on synthetic resin, forjointing chemical stoneware or acid-resisting bricks. The cement, when set, isimpervious and very hard.Resist. (1) A fluoride-resisting layer usedduring acid etching to protect those partsof glass or ceramic ware not required tobe etched. Wax, asphalt, resin, etc.,dissolved in turpentine are suitable forthis purpose.(2) A method for the on-glazedecoration of pottery, particularly foruse with lustres. The decoration ispainted on the ware with glycerine, orother resist; the ware is then coated withthe lustre solution, dried, the paintedarea washed clear with water, re-driedand fired. Alternatively, an infusibleresist can be used, e.g. china clay, andthe ware can be fired before the resist isgently rubbed away with a soft abrasivepowder.Respirable Dust. For dust to penetrateto the lungs, it must be less than 10mmdiameter. Maximum deposition in thelungs occurs for particles below 5mm,with a peak at 1 to 2mm. For the

purposes of estimating airborne dust inrelation to pneumoconiosis, samplesshould represent only the respirablefraction. This is defined in terms of thefree-falling speed of the particles. C/Co =l-f/fc where C and C0 are theconcentrations of particles of fallingspeed/in the respirable fraction and thewhole sample, while /c is a constant:twice the falling speed in air of a sphereof unit density and 5mm diameter.Residual Carbon. The amount of carbonretained in test-pieces of pitch-bonded,resin-bonded or -impregnated refractoryafter carbonization. The carbonized test-piece is ignited in an oxidisingatmosphere at a specified temperaturefor a specified time. The weight lossexpressed as a percentage of the weightof the original uncarbonized test-piece, isthe carbon yield, or amount of residualcarbon present. ASTM C831 specifies atest for residual carbon and carbon yieldin coked bricks and shapes.Resilience. The resilience of ceramicfibre is the percentage increase inthickness of a test-piece after 5 min,following removal of the pressurerequired to compress the fibre to 50% ofits original thickness. Cf.COMPRESSIBILITY. B.S.1902 Pt.6 Section8 specifies tests for refractory fibres.Resistazone Stream Counter. Particlesize analyzers based on the change inelectrical resistance of a well-definedcylinder of conducting fluid, due to thepresence of fine particles. The particlesare suspended in an electrolyte, and thevoltage pulses generated when they passbetween measurement electrodes arerecorded and analysed electronically.RESS - Rapid Expansion ofSupercritical Solutions. A jet of densegas is expanded through a jet. Solidmaterial dissolved in the gas at hightemperature and high pressure is then

precipitated as a powder from aconcentrated solution, or deposited as afilm from a dilute solution using a shortnozzle. (D.W. Matson et al, J. Mater Sci22, (6) 1987, p.1919).Restrike Opal. See OPAL GLASS.Retarder. (1) A material, such as sodiumcitrate or keratin, that can be added toplaster to retard setting.(2) Retarders for the setting of portlandcement generally consist of cellulosederivatives (e.g. carboxymethyl-cellulose), starches or sugars; these areadditional to the 1-3% of gypsum addedto all ordinary portland cements toretard the setting time to withinconvenient limits (see INITIAL SET andFINAL SET).

Retort. A structure, generally built ofrefractory material, into which rawmaterials are charged to be decomposedby heat, e.g. a zinc retort or gas retort.Retouch Enamel. To cover or protectimperfections in vitreous enamel, using afine overspray or brushed-on coating.Retroflex Curves. Solubility curves forsubstances whose solubility decreaseswith increasing temperature.Revergen Kiln. Trade-mark: See DAVIS

REVERGEN KILN.Reverse Cam Spalling. PINCH SPALLING(q.v.) of refractory brick CAMS (q.v.) andtheir loss by SLABBING (q.v.). Theintervening thinner refractory is usuallyundamaged, with the recessed sites ofthe lost cams between.Revolver Press. A type of press for theshaping of clay roofing tiles. It consists ofa pentagonal or hexagonal drum,mounted on a horizontal shaft andcarrying bottom press-moulds on eachflat surface. As the drum rotates,discontinuously, each mould in turn isbrought beneath a vertical plunger whichconsolidates a clot of clay in the mould.While the drum is stationary (during

pressing) a clot of clay is fed to themould next due to arrive beneath theplunger.Revolving Pot. A shallow refractory pot,which is slowly rotated and from whichmolten glass is gathered by a suctionmachine.Revolving Screen or Trommel. Acylindrical screen, usually of theperforated-plate type, set at an inclinedangle and made to rotate about its axis.RF. Radio-frequency, as in RF-heating,RF sputtering.RH-degassing. The Rheinstahl-HeraeusProcess for SECONDARY STEELMAKING.By introducing a gas stream (argon) intothe steelmaking vessel through a snorkel,the steel is sucked into a vacuum chamber.After degassing, the steel (now in acolumn of greater than barometric height)flows down again, continuously. As thesteel enters the vacuum chamber, therelease of argon and the evolution of COproduces a large surface area in the formof droplets, ensuring rapid degassing.Rheology. The science of thedeformation and flow of materials, e.g.the study of the viscosity of a glass, glazeor enamel; the study of the plasticity ofclay.Rheopexy. The complex behaviour ofsome materials, including a few ceramicbodies, which show DILATANCY (q.v.)under a small shearing stress followed byTHixoTROPY (q.v) under higher stress.Rhythmical Firing. The original namefor the SWEEP-FIRE system (q.v.)Rib. A wooden or metal tool forsmoothing the outside of a vase or bowlwhile it is being thrown.Rib Marks. The marks found on thesurface of broken glass; they are in theform of raised arcs perpendicular to thedirection in which fracture occurred,usually convex in the direction of crackpropagation. See HACKLE MARKS.

Ribbed Roof. A furnace roof(particularly of an open-hearth steelfurnace) in which some of the refractorybricks, while conforming with thesmooth internal surface of the roof,project outwards to form continuous ribsacross the furnace; these ribs, becausethey remain cool, confer strength on theroof even when it has worn thin.Ribbon. An ornamental course of tileson a roof (cf. RIBBON COURSES).Ribbon Courses. Successive courses ofroofing tiles laid to alternately greaterand lesser exposures.Ribbon Machine. See PUFF-AND-BLOW

PROCESS.

Ribbon Process. A glass-making processin which the glass, after it has beenmelted and refined, is delivered as acontinuous ribbon.Ribbon Test. See THERMAL SHOCKTESTS.Rice Hulls or Rice Husks. The wastehusks from rice consist when calcined, ofabout 96 5% SiO2 2 2% CaO and minoramounts of other oxides. Because thiscomposition is highly refractory, andbecause the porosity of the calcinedmaterial is nearly 80%, this wasteproduct has been used, particularly inItaly where rice is an important crop, asa raw material for the manufacture ofinsulating refractories.Riddle-tile Hearth. Passages beneath akiln for the removal of waste gases.Rider Bricks. Refractory bricks, whichmay be solid, perforated or arched, usedin the base of a regenerator chamber toform a support for the checker bricks; ina coke-oven regenerator, also known asSOLE-FLUE PORT BRICKS Or NOSTRIL

BLOCKS; in a glass tank regenerator, alsoknown as the RIDER ARCH, BEARERARCH Or SADDLE ARCH.

Ridge Tile. A special fired-clay orconcrete shape for use along the ridge of

a pitched roof. There are a number ofvarieties, e.g. SEGMENTAL, HOG'S BACK,WIND RIDGE, etc.Riffling. Dividing a stream of particles intorepresentative samples, using a mechanicaldevice. E.g. a spin-riffler is an annular setof sieves which is rotated under a streamof powder, so that each in turn receives arandom sample of the stream.Rigden's Apparatus. An air-permeabilityapparatus for the determination of thespecific surface of a powder; air is forcedthrough a bed of the powder by thepressure of oil displaced fromequilibrium in a U-tube. (P. J. Rigden, /.Soc. Chem. Ind., 62, 1, 1943.) Theapparatus is essentially the same as thatused in the BLAINE TEST (q.v.).Rigidizer. A liquid binder for renderingceramic fibre products hard and erosionresistant.RILEM. Reunion Internationale desLaboratoires d'Essais et de Recherchessur les Materiaux et les Constructions.This body is the author of various testmethods and standards relevant toconstructional ceramics.Ring. (I)A free-standing, selfsupporting annular structure formed oftapered refractory brick, used for theconstruction of cylindrical and conicalsections of furnaces, vessels and ducts.Design is flexible. The sizes and numbersof bricks to make different sizes of ringsare variable. Axial and radial tightnessdepends on the area of application, theproperties of the refractory and theseverity of the process. VariousBRICKING RIGS have been designed foreasier and/or faster construction of rings.(2) A refractory ring that floats on themolten glass in a pot to keep any scumfrom the gathering area within the ring(cf. FLOATER).(3) The part of the mould that forms therim of pressed glassware.

(4) A SAGGAR (q.v.) without a bottom,also sometimes known as a RINGER.Ring Mould. See NECK MOULD.Ring-roll Crusher. A grinding unitconsisting, typically, of a steel casing inwhich is housed a free-running grindingring, within which revolve three crushingrolls; the top roll is mounted on thedriving shaft while the two lower rollsare carried on floating shafts supportedby springs. The three rolls are pressedagainst the inner surface of the ring bythese springs and material is ground as itpasses between the ring and the rolls.This type of crusher has been usedsuccessfully with ceramic raw materialssuch as bauxite.Ring-roll Process. A method for theproduction of blanks for plate-glassmanufacture. Molten glass passesbetween a heated 'ring-roll' castingtable, of large diameter, and a smallerforming roll.Ring Setter. A SETTER designed toprevent or correct warping of tablewareduring firing. Cf STRAIGHTENING RING.Ring Test. (1) GLAZE FIT: a test first usedby H. G. Schurecht and G. R. Pole (J.Amer. Ceram. Soc, 13, 369,1930). Thetestpieces are hollow cylindrical rings 2 in.(50 mm) dia. glazed on the outside onlyusing the glaze to be tested. The glazedring is fired and two grooves or holes arethen cut in one edge of the ring, approx. 2in. (50 mm) apart and large enough tohold glass capillary tubes l/6th in. (4 mm)long and 1/32 in. (0.8 mm) dia.; thesecapillaries provide sharp reference marks,the distance between which is measuredwith a micrometer microscope. The ring isthen cut open with a diamond saw and thedistance between the reference marks isagain measured. Similar measurements aremade on ungiazed rings so that the trueexpansion or contraction caused bypartially releasing the stress between glaze

and body can be determined. If the glazeis in tension the ring will expand when cutopen; if in compression it will contract.(2) A THERMAL-SHOCK test proposed byW. R. Buessem and E. A. Bush (J.Amer. Ceram. Soc, 38, 27,1955). Astack of ceramic rings, each 2 in. (50mm) o.d. and 1 in. (25 mm) Ld., and Viin. (12.5 mm) long, are heated from theinside by a heating element and cooledfrom the outside by a calorimetricchamber. Both thermal conductivity andthermal-shock resistance can beevaluated (cf. BRITTLE-RING TEST).Ring Wall. See SHELL WALL.Ringed Roof. A furnace roof consistingof arches of bricks unbonded withadjacent arches (cf. BONDED ROOF).Ringelmann Chart. A chart divided intofive (Nos. §-A) shades of darknessintroduced in the late 19th century byProfessor Ringelmann, of Paris, as ameans of designating the blackness ofsmoke emitted from industrial chimneys.The charts have been standardized (B.S.2742) and are used in the ceramicindustry in compliance with the CleanAir Act in which dark smoke is definedas equal to, or denser than, Shade 2 onthe Ringelmann Chart.Ringer. See RING (4).Rinman's Green. A colouring materialconsisting of a solid solution of CoO inZnO; it finds limited use as a ceramiccolour. (S. Rinman, Kong. Vet. Akad.HandL, p. 163, 1780.)Ripple. See ORANGE PEEL.Ripple Mark. = WALLNER LINE (q.v.).Rippled. See DRAGGED.Rise. (1) In a sprung arch, the verticaldistance between the level of thespringer and the highest point of thearch at its inner surface.(2) The vertical distance though whichthe centre of the sprung roof of afurnace rises as a result of expansion

when the furnace is heated to itsoperating temperature.Riser Brick or End Runner. A RUNNERBRICK (q.v.) with a hole near one end ofits upper face and (generally) a shorttubular projection from this hole to leadmolten steel into the bottom of an ingotmould.Rittinger's Law. A law relating to thetheoretical amount of energy required incrushing or grinding: the energynecessary for the size-reduction of amaterial is directly proportional to theincrease in total surface area. (P.R. vonRittinger, Berlin, 1867).River marks. Cleavage steps onindividual grains of a polycrystallinematerial, or on a single crystal, spreadingfrom the point of origin. A special caseOf TWIST HACKLE (q.V.).RO Fusion-cast Refractory. A fusion-cast refractory made in an inclinedmould designed to concentrate theshrinkage cavity in one corner of theblock: such blocks are made in France(RO = Retassure Orientee, i.e. orientedcavity; cf. DCL, RT and SR).Robertson Kiln. Several types of tunnelkiln were designed by H.M. Robertsonbut that most commonly associated withhis name was a tunnel kiln for salt-glazing; the salt was introduced viafireboxes in the side walls and the fumesextracted in the cooling zone. (Brit Pats.,331 224 and 331 225, 9/5/28.).Robinson Trolley. A circular trolley,weighing 68.1 ± 2.3 kg with threeequally-spaced wheels, which can befitted with various types of rim or tyre. Itis rotated over a 4ft x 4ft (1.23 x 1.23 m)test panel of floor tiles to assessresistance to wear or damage by small-wheeled vehicles such as fork-lift trucks,(ASTM C627-76).Robey Oven. A down-draught type ofpottery BOTTLE OVEN (q.v.) patented by

C. Robey (Brit. Pat. 970,17th March,1873).Rocaille Flue. An alternative (now lesscommon) name for STRASS (q.v.).ROC Technique. Rapid OmnidirectionalCompaction (q.v.).Rock Cement. US term for ROMANCEMENT (q.v.).Rock Crystal. Large, naturally occurring,transparent crystals of quartz. In USAthe term is also used for CRYSTAL GLASS(q.v.)Rock Wool. Trade-name. A form ofMINERAL WOOL (q.V.).Rocker. A glass bottle that has a faulty,convex, bottom.Rocket Nozzle. The flame temperaturein a rocket nozzle exceeds 25000C; inaddition, thermal shock is very severe.Special refractory materials that havebeen used in rocket nozzles includesilicon carbide (usually with graphiteadditions), silicon nitride, boron nitride,beryllia and various refractory carbides.Rockingham Ware. The term originallyreferred to the ornate porcelain made ata pottery at Swinton, Yorkshire,England, on the estate of the Marquis ofRockingham during the years 1826-1842.Ware with a brown manganese glaze wasalso produced and it is this type of glaze,which in the UK is usually applied toteapots made from red clay, to which theterm Rockingham Ware now refers. Inthe USA, Rockingham Ware was madeat Bennington.Rockwell Hardness. Symbol HR. Acriterion of hardness based onindentatiion, either by a steel ball or by adiamond cone. Details are given in B.S.891. It has been but little used in theceramic industry, except in relation tosome special ceramics.Rod Cover or Sleeve. A cylindricalfireclay shape having an axial hole andterminating in a spigot at one end and a

socket at the other. These refractorysleeves are used to protect the metalstopper-rod in a steel casting ladle. Inthe UK six sizes of rod cover arestandardized in B.S. 2496. In the USAthree qualities are specified in ASTM-C435.Rod Mill. A steel cylinder into which ischarged material that is to be finelyground together with metal rods asgrinding media. This type of mill willreduce material from 1 in. (25 mm) to 10mesh in one stage and the product tendsto be granular. Rod mills are employedfor the preparation of the materials usedin the manufacture of sand-lime bricks.Rokide Process. Trade-name: (NortonCompany, USA): a process for theproduction of a refractory coating, onmetal or on ceramic, by atomizingdirectly from the fused end of a rod ofthe coating material, e.g. Al2O3 or ZrO2;the molten particles are blown againstthe cool surface that is to be coated. Theoriginal patent was granted to W.M.Wheildon (US Pat. 2 707 691, 3/5/55).Rolands9 Cement. Trade-name: a HIGH-ALUMINA CEMENT (q.v.) made byRolandshiitte A.G., Lubeck, Germany.Roll Back, CRAWLING (q.v.) of vitreousenamel. The coating pulls away or rollsup at the edges of the metal, or overareas of dirt.Roll Quenching. See under QUENCHINGOF FRIT.Rolled Edge. The edge of a plate orsaucer is said to be 'rolled' if its diameteris greater than the general thickness ofthe rim of the ware.Rolled Glass. (1) Flat glass that has beenrolled so that one surface is patterned ortextured; also known as Rough Cast. (2)In USA the term is also applied tooptical glass that has been rolled intoplates at the time of manufacture, asdistinct from TRANSFER GLASS (q.v.).

Roller-bat Machine. A machine formaking, from stiff-plastic clay, bats for afinal pressing process in one method ofroofing-tile manufacture.Roller Elutriator. An air-type elutriatordesigned for the determination offineness of portland cement. (P. S.Roller, Proc. ASTM, 32, Pt. 2, 607,1932.)Roller's Equation. A relationshipbetween the percentage weight and thesize of powders: w - cr\d. exp(-b/d),where w is the weight percent of allmaterial having diameters less than dy

and a and b are constants. Otherequations were deduced relating tospecific surface and to the number ofparticles per gram or powder. (P. S.Roller, /. Franklin Inst., 223, 609,1937.)Roller's Plasticity Test. A method forthe assessment of plasticity on the basisof the stress/deformation relationshipwhen clay cylinders are loaded. (P. S.Roller, Chem Industries, 43, No. 4, 398,1938.)Roller-head Machine. A machine for theshaping of pottery flatware on a rotatingmould, as in a JIGGER (q.v.), but with arotary shaping tool instead of a fixedprofile. The rotary tool is in the form ofa shallow cone of the same diameter asthe ware and shaped to produce the backof the article being made. The ware iscompletely shaped, by relativelyunskilled labour, in one operation at arate (depending on the size of the ware)of about 12 pieces per minute. Themachine, developed from earlierattempts to improve on the use of a fixedtool, was patented by T. G. Green & Co.and H. J. Smith (Brit. Pat., 621 712,14/4/49) with subsequent improvementsby J. A. Johnson (Brit. Pat., 765 097,2/1/57; 895 988, 9/5/62). It is made byService (Engineers) Ltd., Stoke-on-Trent, England.

Roller-hearth Kiln. A tunnel kilnthrough which the ware, placed on bats,is carried on rollers. Tiles may be carrieddirectly, without bats.Roller Mark or Roller Scratch. A surfaceblemish on vertically drawn sheet glasscaused by contact with the rollers.Rolling (of Glaze). A term sometimesused instead of CRAWLING (q.v.).Rolling-out Limit. The lower limitingwater content in the ATTERBERG TEST(q.v.).Roll Mark. A machine for applyingtransfers, especially to tiles. (MeyercordCo. USA).Rollrod Kiln. A roller-hearth kiln for therapid firing of tiles. The tiles rest onsupporting rods which themselves glideon the kiln rollers at right angles tothem. (Agrob Ab).Rolls. See CRUSHING ROLLS.Roman Brick. US term for a buildingbrick of nominal size 12 x 4 x 2 in. (305 x102 x 50 mm).Roman Cement. The misleading namegiven in the early 19th century to anaturally-occurring mixture of clay andlimestone after its calcination; theproduct had hydraulic properties andwas the forerunner of PORTLANDCEMENT (q.v.). A small quantity ofRoman Cement is still made. In USA itis known as ROCK CEMENT.Roman Tile. A type of roofing tile madein the Bridgwater area of England anddeveloped from the OLD ROMAN TILE(q.v.). There are two varieties: SingleRoman and Double Roman. SingleRoman is a flat tile with an upturnededge along one side and a roil at theother which, in use, covers the upturnededge of the adjacent tile; Double Romanis larger and has an additional rollmoulded on the centre line of the tile.Roofing Tile. A tile for the covering of apitched roof. The terminology of the

many designs of roofing tile is confused:it is particularly difficult to equate theterms used in different languages. Fordefinitions of British terms see: DOUBLEROLL VERGE TILE; INTERLOCKING TILE;ITALIAN TILE; MARSEILLES TILE; OLDROMAN TILE; PANTILE; POOLES TILE;ROMAN TILE; SINGLE-LAP ROOFINGTILE; SPANISH TILE. Most of the roofingtiles now being made in England areconcrete; these must meet therequirements of B.S.473, 550 ConcreteRoofing Tiles and Fittings. Clay roofingtiles are dealt with in B.S. 402. B.S. 5534is a code of practice for slating and tilingwith cross-reference to B.S. 8000 Pt. 6.Pt.2 provides design charts for fixing rooftiles against wind uplift. The ASTMspecification for clay roof tiles is Cl 167.Rosekl. A Japanese rock, which ismainly pyrophyllite. With smalladditions of kaolin and diaspore it iscommonly used to make glass-meltingcrucibles, and has also been usedexperimentally in pottery bodies. Rosekiis also the name of an 80% silicaramming material, made byHiroshimaken, Japan.Rosin-Ramniler Equation. An equationrelating to fine grinding: for mostpowders that have been prepared bygrinding, the relationship between R, theresidue remaining on any particularsieve, and the grain-size in microns (x) isexponential:R = 100 exp (-bxn)where b and n are constants. (P. Rosin,E. Rammler and K. Sperling, Ber. C52Reichs-Kohlenstaubs, Berlin, 1933.)Rosso Antico. A red unglazed stonewaremade in the 18th century by JosiahWedgwood; it was a refinement of thered ware previously made in NorthStaffordshire by the Elers.Rotablock. A system of furnaceconstruction in which the refractory

blocks are suspended on metal hangers,which hook on to an external suspensionbar. Individual blocks can be pulled backfrom the lining by rotating the hangerabout the bar. (Foseco Trading AG Br.Pat 1534914,1978).Rotap. Testing sieve shaking equipment(C-E Tyler Co, Mentor, Ohio).Rotocast System. A system forinstalling castable refractories incylindrical kilns, particularly cementkilns. Anchors and ties are welded tothe shell, and formwork fitted aroundthe circumference. Concrete is placedand vibrated behind the formwork.As work progresses the kiln isprogressively turned, and the formworkmoved on.Rotary Disk Feeder. See DISK FEEDER.Rotary Drum Test. See SLAG ATTACKTESTS.Rotary-hearth Kiln. A circular tunnelwith a slowly rotating platform forconveyance of the ware through the kiln.An early example was the WOODHALL-DUCKHAM KILN (Brit. Pat. 212 58523/2/23). The principle has since beenadapted in the CLARK CIRCLE SYSTEM ofbrickmaking introduced in Australia in1953 and in some modern pottery-decorating kilns. (This type of kiln issometimes also known as a ROTATING-

PLATFORM KILN.)Rotary Kiln. A kiln in the form of along cylinder, usually inclined, andslowly rotated about its axis; the kiln isfired by a burner set axially at its lowerend. Such kilns are used in themanufacture of portland cement and inthe dead-burning of magnesite,calcination of fireclay, etc.Rotary Smelter. A batch-type cylindricalfurnace which can be rotated about itshorizontal axis while frit is being meltedin it; when the process of melting iscomplete the furnace is tilted so that the

molten frit runs out. Such furnaces arefired by gas or oil and their capacityvaries from about 0 05 - 05 tonne.Rotary Vane Feeder. See VANE FEEDER.Rotating-platform Kiln. See ROTARY-HEARTH KILN.Rotolec. Trade-name: a circular electricdecorating kiln for pottery-ware.(Gibbons Bros. Ltd, Dudley, England.)Rotomixair. Trade-name: a reciprocatingairjet system of drying bricks and tiles;the system originated in Italy in 1958.(W. G. Cannon & Sons Ltd., LondonS.W.19.)Rotor Process. A process for theproduction of steel by the oxygen-blowing of molten iron held in ahorizontal, rotating vessel. This is usuallylined with tarred dolomite refractories,but tarred magnesite refractories havealso been used.Rouge. Very fine (<lfxm) ferric oxideused for polishing glass. Rouge pits areresidual imperfections in the glasssurface, containing traces of rouge.Rouge Flambe. (1) As applied to oldChinese porcelain this term means aSANG DE BOEUF (q.v.) glaze that hasstreaks of purple or blue to give a flame-like (French, flambe) appearance.(2) As applied to modern pottery theterm refers to a reduced copper glazeproduced by an on-glaze process (cf.SANG DE BOEUF); although the colour isproduced by on-glaze treatment, micro-examination shows that the layer ofcolloidal copper occurs within the glazelayer.Rough-cast. See ROLLED GLASS.Round Edge Tile. For the various typesof wall tiles with round edges see Fig. 7,p350.Round Kiln or Beehive Kiln. Anintermittent kiln, circular in plan, withfireboxes arranged around thecircumference. Such kilns find use in the

firing of blue engineering bricks, pipes,some refractory bricks, etc.Rouse-Shearer Plastometer. See R & SPLASTOMETER.Rowlock. A form of brickwork whichincludes courses of HEADERS (q.v.) laidon edge.Royal Blue. See MAZARINE BLUE.RPS. Reinforced Porcelain System.Porcelain dental crowns are reinforcedwith thimble couplings with metalextensions in the form of shelves, beltsor blades. (J Prosthetic Dentistry 50, (4),489,1983)RSBN. Reaction sintered boron nitride.RSI. Repetitive Strain Injury (q.v.).R & S Plastometer. A device for theassessment of the rheological propertiesof a clay slip in terms of the time takenfor a given volume of the slip to flowthrough a tube of known diameter; itwas designed by Rouse and Shearer Inc.,a firm of ceramic consultants in Trenton,NJ., USA. (J. Amer. Ceram. Soc, 15,622,1932.)RT Fusion-cast Refractory. A refractorymade by a process devised by L'Electro-Refractaire, Paris, for ensuring freedomfrom large cavities in fusion-cast blocks,RT = Remplissage Totale (cf. DCL, ROand SR).RTS System. Radial TrockenStrangpresse. In this DRY BAGisosTATic PRESS (q.v.) for thecontinuous production of ceramic tubes,a length of tube is isostatically pressed ina vertical cavity between pressure tubeand mandrel. The top of the tube iswidened into a short cone. The formedtube length is then extruded downwards,leaving the cone at the bottom of themould. A second length of tube is thenisostatically pressed above the first, andthe cone closes over its lower end toform a continuous tube. The processmay be repeated to make tubes of any

desired length. (H. Ittner, HandleGmbH, Germany. Ceram. Eng. ScLProc. 7 (11/12) 1391,1986).Ruabon Kiln. A CHAMBER KILN (q.v.) inwhich the hot gases entering a chamberare deflected by a BAG-WALL (q.v.) tothe roof before descending through thesetting. The design originated atRuabon, N. Wales.Rubber. A building brick made from asandy clay and lightly fired so that it canbe readily rubbed to shape for use ingauged work. The crushing strength ofsuch a brick is about 7MNm-2

Rubbing Block. A shaped block ofabrasive material used in the grinding ofblocks of marble or other natural stones.Rubbing Stone. A block of fine-grainedabrasive, e.g. corundum, for the STONING(q.v.) of vitreous enamel.Rubbing Up. When flatware is placed ina bung for biscuit firing, the spacesbetween the rims of the ware are filledwith sand (if the ware is earthenware) orcalcined alumina (if the ware is bonechina); this is done by taking handfuls ofsand, or alumina, from a heap aroundthe bung and allowing it to fall betweenthe rims of the ware. The process isknown in N. Staffordshire as 'rubbingup'.Ruby Glass. Glass having a characteristicred colour resulting from the presence ofcolloidal gold, copper or selenium. Toproduce GOLD RUBY a batch containinga small quantity of gold is first meltedand cooled; at this stage it is colourless,but when gently heated it develops a redcolour as colloidal gold is formed. ForCOPPER RUBY, produced in the samemanner but with copper substituted forthe gold, the batch must contain zinc andmust be smelted in a non-oxidizingatmosphere. The most common rubyglass today is SELENIUM RUBY; arecommended batch contains 2% Se, 1%

CdS, 1% As2O3 and 0.5% C; the furnaceatmosphere must be reducing. Thecolour is due to MIE SCATTERING (q.v.)of light by the colloidal particles.Ruby laser, (see also LASER) consists ofsingle-crystal alumina with some Alreplaced by Cr. The Cr electrons can be'pumped' to higher energy levels; a beamof light making repeated passes alongthe crystal will trigger the Cr electronsback to their ground state and will itselfgain in energy. The resultant laser beamoffers a ready means of heating smallsamples to very high temperatures; it willdrill holes in ceramics.Ruckling. See CRAWLING.RuL. Abbreviation for REFRACTORINESS

UNDER LOAD (q.V.).Rumbling. See SCOURING.Run or Run-down. A fault in vitreousenamelling resulting from an excessiveamount of cover-coat becomingconcentrated in one area of the ware.Runner. (1) The channel in whichmolten iron or slag flows from a blastfurnace when it is tapped. The runner isusually lined with fireclay refractorieswhich are then covered with a layer ofrefractory ramming material, e.g. amixture of fireclay, grog and carbon.Refractory concrete has also been usedto line runners.(2) A large block of chert as used in aPAN MILL (q.v.).Runner Brick. A fireclay shape, squarein section and about 30 cm long, with ahole about 25 mm dia. along its lengthand terminating in a spigot at one endand a socket at the other end. A numberof such refractory pieces, when placedtogether, form a passage through which,during the bottom-pouring of steel, themolten metal can pass from the CENTREBRICK (q.v.) to the base of the ingotmould. Two standard sizes are specifiedin B.S. 2496.

Running-out Machine. Name sometimesapplied to a batchtype extrusion machineof the type more commonly called aSTUPID (q.v.).Rust-spotting. A fault in vitreousenamelling: the appearance of rust-coloured spots in ground-coat enamelsduring drying. The fault is most frequentwith ground-coats of high Na2OiB2O3

ratio; it can often be cured by theaddition of 0.05-0.10% of sodium nitriteto the enamel slip.Rustic Brick. A fired clay facing brickwith a rough textured surface; this effectcan be obtained by stretching a wireacross the top of the die so that itremoves a thin slice of clay from themoving column.Rusticating. A mechanical process forthe roughening of the facing surface of aclay building brick, while it is still moist,to give it a 'rustic' appearance whenfired; wire combs or brushes, orroughened rollers are used.Rutile. The most common form ofTITANIUM OXIDE (q.v.) sp. gr. 4.26. Itoccurs in the beach sands of Australia,Florida and elsewhere; used as anopacifying agent in enamels and glazes.Rutile is also used in the production oftitania and titanate dielectrics; purerutile has a dielectric constant of 89perpendicular to the principal axisand 173 parallel to this axis; the valuefor a polycrystalline body is 85-95 at200C.Rutile Break. A crystalline effect inpottery (particularly tile) glazes,obtained by the addition of rutile to asuitable basic glaze composition.Ryolex. A volcanic aluminosilicate usedas lightweight thermal insulation.S-Brick. Bricks of S shape, into whosebends polystyrene sheet is placed asthermal insulation and to align the nextcourse of bricks.

S-crack. Lamination, in the form of aletter 'S', in a clay column from a pughaving a poorly designed mouthpiece.The crack develops from the central holein the clay column formed at the end ofthe shaft in the pug, the hole beingdeformed to an 'S' in the rectangularmouthpiece.S-Glass (Strength). A low alkali glasscomposition for glass fibres, used forspecialised applications in which itshigher (than 'E' glass) strength andelastic modulus are important.Sacrificial Red. Old Chinese namefor the ceramic colours known asROUGE FLAMB£ and SANG DE BOEUF(q.v.).Saddle. (1) An item of KILN FURNITURE(q.v.). It is a piece of refractory materialin the form of a bar of triangular cross-section. See Fig. 4, pl77.(2) The upper part of a two-piece low-tension porcelain insulator of theCallender-Brown type.Saddle Arch. See RIDER BRICKS.Sadler Clay. An ALBANY CLAY (q.v.).Safety. See HEALTH AND SAFETY.Safety Glass. See LAMINATED GLASS;

TOUGHENED GLASS; WIRED GLASS. B.S.6206 is an impact resistance test for flatsafety glass. B.S. AU178 and B.S. 857specify safety glasses for road andrailway vehicles.Safiil. Trade-name. Alumina, andsometimes zirconia, fibres manufacturedby ICI pic.Saggar. A fireclay box, usually oval (0.6x 0.45 m), in which pottery-ware can beset in a kiln. The object is to protect theware from contamination by the kilngases and the name is generally thoughtto be a corruption of the word 'safe-guard'. Since the bottle-oven has becomeobsolete as a kiln for the firing of potteryand since clean fuels and electricity havebecome increasingly used in the industry,

the use of saggars has been largelydisplaced by the setting of ware onlighter pieces of KILN FURNITURE (q.v.)though special saggars are still used invery specialised applications in whichprotection from kiln atmosphere is vital(eg some electronic ceramics).Saggar-maker's Bottom-knocker. Theman whose job it was to beat out, bymeans of a heavy wooden tool, a wad ofgrogged fireclay to form a bottom for aSAGGAR (q.v.). To the regret offolklorists, the species is now virtuallyextinct.Sagging. (1) The permanent distortionby downward bending of vitreousenamelware that is inadequatelysupported during firing(2) The flow of enamel on verticalsurfaces of vitreous enamelware while itis being fired; the fault is visible asroughly horizontal lines or waves and iscaused by the enamel being too fluid, byoverfiring, or by the enamel layer beingtoo thick.(3) A method of shaping glass-ware byheating the glass above a mould andallowing it to sag into the contours of themould.(4) The dropping away from the casingof a ring or series of rings in a rotary kilnlining.Salamander. The mass of iron which, asa result of wear of the refractorybrickwork or blocks in the hearthbottom of a blast furnace, slowlyreplaces much of the refractory materialsin this location.Salmanazar. A 12-quart wine bottle.Salmon. Salmon Brick. US term for anunderfired building brick (in allusion toits colour). See CHUFF BRICK.Salt Cake. Commercial grade sodiumsulphate, Na2SO4; it is added to glassbatches, together with carbon, to preventscumming - particularly in flat-glass

manufacture; it is also added to facilitatemelting and refining but to a less extentthan formerly.Salt Expansion. Irreversible expansionthat may occur in a porous ceramicproduct containing SOLUBLE SALTS (q.v)if it becomes moist and is then dried; it isgenerally believed that the expansion isassociated with crystallization of thesalts.Salt Glaze. In the 17th century and 18thcentury salt-glazing was used in themanufacture of domestic pottery. Now,except for its use by some studio potters,the process is obsolete. Before its demisein the face of environmental clean airrestrictions, it was last used in theproduction of salt-glazed sewer-pipes.The pipes (made from a siliceous clay toensure a good glaze) were fired in theusual way up to 1100-1200C and saltthen thrown on the fire, where itvolatilizes; the salt vapour passesthrough the setting of pipes and reactswith the clay to form a sodiumaluminosilicate glaze. Borax wassometimes added with the salt in theratio of about 1:4. (See also SEWERPIPE.)

Saltpetre. See SODIUM NITRATE.Samel. An underfired brick from theouter part of a CLAMP (q.v.).Samarium Oxide. Sm2O3; m.p. approx.23000C; sp. gr. 7.4; thermal expansion(20-10000C) 10 x 10-6.Samian Ware. See TERRA SIGILLATA.Sampling. The choice of procedure forthe obtaining of a representative sampleof a consignment of ceramic rawmaterial or product prior to testing, is ofgreat importance. In USA a procedurefor the sampling of clays is laid down inASTM - C322; in the UK, B.S. 812 dealswith the sampling of mineral aggregatesand sands, and B.S. 3406 (Pt. 1) dealswith the sampling of powders for

particle-size analysis. B.S. 6065 specifiessampling and acceptance testing ofshaped refractories and B.S. 6434 is aguide to its use. Details of the number ofbricks that should be taken as a samplefor testing are given in B.S. 1902 (Pts. 3,4and 5) (Refractories) and B.S. 3921(Building Bricks). B.S. 1902 Pt.7.1 givesguidance on taking samples fromunshaped refractories. In a slightlydifferent sense, ASTM C1190 describeshow test samples should be cut from tar-bonded and burned basic refractorybricks. In his book 'Particle SizeMeasurement/ (3rd Ed 1981) T. Aliengave a 'golden rule' for powder samplingfor size distribution measurements that asample should be taken from a movingstream, and all of the stream caught for ashort time.Sand. Typically, sand consists of discreteparticles of quartz: some beach sandscontain a concentration of heavyminerals, e.g. rutile, ilmenite and zircon.Silica sand occurs widely and is used as amajor constituent of glass, as a refractorymaterial for furnace hearths and foundrymoulds, and for mixing with portlandcement to make cement mortar andconcrete. The purest sands are used forglassmaking; B.S. 2975 deals with theirsampling and analysis. For specificationsfor building sands see B.S. 812; B.S. 1199and 1200; B.S. 4550 Pt. 5 and Pt. 6.Sand-creased. A texture produced on thesurface of clay facing bricks. In the hand-made process the clot of clay is firstsprinkled with, or rolled in, sand; wherethe sand keeps the clay away from themould a crease is produced. Animitation of this texture can be achievedin machine-made bricks by impressingthe surface of the green bricks with atooled steel plate.Sand-faced. A clay building brick thathas been blasted with sand while in the

GREEN (q.v.) state; alternatively, withextruded bricks, the sand-facing can beapplied by gravity to the column of clay.A wide range of surface textures can beobtained by sandfacing.Sand-gritting. The process ofroughening those parts of the glaze ofan electrical porcelain insulator wherecement will be applied in the finalassembly. The 'sand' (a specially-prepared mixture of coarse-gradedporcelain together with powderedglaze) is applied to areas of the glazedinsulator before it is fired.Sand Holes. Small fractures in glasssurfaces produced during rough grindingand not completely removed bypolishing.Sand-lime Brick. See CALCIUM SILICATEBRICK.Sand Rammer. The standard rammer formaking test-pieces allows a 14 Ib (6.25kg) weight to fall 50 mm on sandcontained in a 50 mm diam. mould; threeblows from the rammer are used inmaking a standard test-piece. Its use incompaction and workability tests forunshaped refractories is specified in B.S.1902 Pt. 7.2.Sand resin moulds. Moulds for pressure-cast sanitaryware have been made fromcured organic resins with a graded sandfiller. The material has controlledporosity and is stronger and moreabrasion resistant than plaster.Sand Seal. A device for preventing hotgases from reaching the undercarriage ofthe cars in a tunnel kiln. It consists oftwo troughs running parallel to theinternal walls of the kiln and filled withsand; into this sand dip vertical metalplates (APRONS) which are fixed to thesides of each kiln car.Sand SIinger. A rotating head whichprojects refractory powder on to theinner wall of a circular ladle or furnace.

Sanding. (1) The sprinkling of sand orfinely crushed brick between courses ofbricks as they are being set in a kiln; theobject is to make even any irregularity inlevel and to prevent sticking.(2) The treatment with sand, duringmanufacture, of the surface of facingbrick to give it a pleasing texture andcolour.(3) The BEDDING (q.v.) of earthenwarein sand.Sandstock Bricks. Made in Australiasince 1788, these are handmade brickswith a distinctive appearance due to theuse of sand as the mould release agent.This appearance is simulated in modernbricks by replacing the sand by colouredbrick frit or flake.Sandstone. A sedimentary rock whichmay be of several types, e.g. siliceous,calcareous, argillaceous, depending onwhether the grains of silica in the rockare bonded with secondary silica, withlime or with clay. Siliceous andargillaceous sandstones both find someuse in the refractories industry; crushedsandstone is used as a source of silica inglass manufacture.Sandstorm Kiln. A system of coal-firingfor kilns for earthenware tiles, in whichan alternating arrangement of grates andsecondary air flues was claimed toprovide a more even distribution of hotgases over the fired ware. (G.H.Downingand H.R.Holding Br. Pat 391 175, 1933and 464 128,1937).Sandstruck Brick. A brick (hand)moulded at 20 to 30% moisture, in amould coated with sand to preventsticking.Sandwich Kiln. A tunnel kiln designed forrapid firing; the height of the setting issmall compared with the width and thefiring is from above and below the setting.Sang de boeuf. A blood-red in-glaze effect(cf. ROUGE FLAMB£) achieved by the

Chinese potters by adding a very smallamount of copper oxide to the glaze batchand firing under reducing conditions toform colloidal copper; the glaze alsousually contained some tin oxide.Sangrind Pantograph. A device for thesurface grinding of sanitaryware. (W.S.Industrial Designs Ltd.).Sanitary Earthenware. A type ofsanitaryware made from white-firingclays but often covered with a colouredglaze; the body itself has a waterabsorption of 6-8% (cf. VITREOUS-CHINA SANITARYWARE). The body ismade from a batch containing 22-24%ball clay, 24-26% china clay, 15-18%china stone and 33-35% flint; it may beonce- or twice fired, the firingtemperature being about 11200C.Sanitary Fireclay. A type of sanitarywaremade from a grogged fireclay body, whichis covered with a white ENGOBE (q.v.),which in turn is covered with a glaze. Atypical body composition is 60-80%fireclay, 20-40% grog. The engobecontains 5-15% ball clay, 30-50% chinaclay, 15-30% flint, 20-35% china stone,0-10% feldspar; the proportions of chinastone and feldspar vary inversely as oneanother.Sanitaryware. The various types include:SANITARY EARTHENWARE (q.V.);VITREOUS CHINA SANITARYWARE (q.V.);SANITARY FIRECLAY (q.V.); VITREOUS-ENAMEL SANITARYWARE, e.g. baths. B.S.1125 and B.S. 1188 specify W.C flushingcisterns and ceramic wash basins andpedestals respectively. B.S. 5503 and B.S.5504 specify materials, dimensions andquality of vitreous china washdownW.C.'s and wall hung W.C.'s respectively.B.S. 5627 specifies plastics connectors forvitreous china W.C. pans. B.S. 5505 is aspecification for bidets; B.S. 5506 forpedestal and wall hung wash basins;B.S. 5520 for vitreous china bowl urinals;

B.S. 6340 specifies shower trays (Pt. 6 -vitreous enamelled cast iron; Pt. 7vitreous enamelled sheet steel; Pt. 8glazed ceramic). B.S. 6465 specifies therequired scale of sanitary wareinstallation. B.S. 3402 specifies the qualityof vitreous china sanitary ware. B.S. 8000Pt. 13 specifies site workmanship.Santorin Earth. A POZZOLANA (q.v.) fromthe Grecian island, Santorin. A quotedcomposition is (per cent): SiO2, 64; Al2O3,13; Fe2O3, 5.5; TiO2,1; CaO, 3.5; MgO, 2;alkalis, 6.5; loss on ignition, 4.Saphiber. 99% alumina fibres, a trade-name of Alcoa, USA.Saphikon. Trade-name. Single-crystalsapphire filaments. Tyco Laboratories,Waltham, Mass. USA.Sapphire. Single-crystal alumina;sapphire boules can be made by theVERNEUiL PROCESS (q.v.) and find use asbearings and thread guides.Sardamag. Trade-name. Sardinianseawater magnesia.Sarking. A layer of insulating materialunder the main roof covering. InScotland the term has the specialmeaning of sawn roof boarding usually15 mm thick (cf. TORCHING).Satin Glaze, Satin-vellum Glaze orVellum Glaze. A semi-matt glaze,particularly for wall tiles, with acharacteristic satin appearance. Suchglazes are generally of the tin-zinc-titanium type.Satin Gold. Bright gold applied over afinely etched or satin finish decorationon glassware.Saturation Coefficient. The ratio of theamount of water taken up by a porousbuilding material after it has beenimmersed in cold water for an arbitraryperiod (e.g. 24 h) to its water absorption,normally determined by boiling in waterfor 5 h; the ratio is usually expressed as adecimal fraction, e.g. 0.85. A low

saturation coefficient generally indicatesgood frost resistance but the correlationis far from perfect.Saucer Wheel. An abrasive wheelshaped like a saucer.Saxon Slabs. A less common name forNORMAN SLABS (q.V.).Saybolt Cup. An orifice type viscometer.See FLOW CUP.SBPM. Sonon-based particle model, inwhich ultrasonic properties are modelledby particle interactions, and related tosintering and processing in space underzero gravity.Scab. ( I)A fault in the base-metal forvitreous enamelling; the 'scab' is apartially detached piece of metal (whichmay subsequently have been rolled intothe metal surface) and is liable to causefaults in the applied enamel coating.(2) A fault in glass caused by anundissolved inclusion of sodiumsulphate; also known as SULPHATE SCABand as WHITEWASH.SCACB. Strengthening by ChemicalActivation of Chemical Bonds. Unfiredcompacts of fused silica and sand werestrengthened by treatment at roomtemperature and above (includinghydrothermal treatment) with sodiumsilicate solution.Scalding. A term that has been used todescribe the fault in the glost firing ofpottery when glaze falls off the warebefore it has fused; a cause is too great adifference between dimensional changesof body and applied glaze.Scale. A fault, in glass or vitreous enamel-ware, in the form of an embedded particleof metal oxide or carbon.Scaling. Preparation of the base-metal forvitreous enamelling by heating it (often inan atmosphere of acid fumes or ofsulphur gases) to form a surface coatingof oxide - 'scale' - which is subsequentlyremoved by PICKLING (q.v.).

Scallop. (1) The rims and edges ofpottery-ware are sometimes trimmed togive a scalloped effect, i.e. smallsegments are symmetrically removedfrom the edges before the ware is fired.Until 1955, when a scalloping machinewas introduced, the process had alwaysbeen carried out by hand.(2) Term sometimes used in theStaffordshire potteries for a dish.Scandium Oxide. Sc2O3; m.p. >2400°C;sp. gr. 3.86.Scanning Acoustic Microscopy. The useof high frequency (100-200 MHz)ultrasound to detect surface defects bygenerating surface waves on the samplewith a wide-angle acoustic lens.Scanning Electron Microscopy. SeeELECTRON MICROSCOPY.Scanning Laser Acoustic Microscopy.SLAM. A transducer beneath thesample produces a collimated ultrasonicbeam which is altered by voids, cracks orinclusions in its path. The resultantupper surface displacement pattern ofripples is scanned by a laser beam andconverted into a magnified visual image.SCARE. See CARES.Scarp. See INTERSECTION SCARP,TRANSITION SCARP.Scatter Coefficient. See COEFFICIENT OFSCATTER.SCC Test. The test for the ABRASIONRESISTANCE (q.v.) of PAVERS (q.v.) usedby Sydney City Council. It involves ballbearings both rotating on and impactingthe surface.Scheidhauer and Giessing Process. SeeS.U.G. PROCESS.Schellbach Tubing. A type of ENAMEL-BACK TUBING (q.v.) with a central blueline.Schenck Porosimeter. Apparatus for thedetermination of PORE SIZEDISTRIBUTION (q.v.) by the MERCURYPENETRATION METHOD (q.V.); it has

been applied to the study of refractories.(H. Schenck and J. Cloth, ArchEisenhiittenw. 27, 421 1956.)Schlenkermann's Stone. A GermanFIRESTONE (q.v.); it contains about 90%SiO2.Schmidt Hammer. A device for the non-destructive testing of set concrete; it isbased on the principle that the reboundof a steel hammer, after impact againstthe concrete, is proportional to thecompressive strength of the concrete. (E.Schmidt. Schweiz. Bauzeitung. 15/7/50).It is also used to test for the adherenceof tiles to their substrates. Adherencemarkedly affects the measuredcoefficient of restitution, and the impactresistance of tiles.Schnitzler's Gold Purple. A tin-goldcolour, produced by a wet method: it hasbeen used for the decoration of porcelain.Schone's Apparatus. An elutriatorconsisting of a tall glass vessel taperingtowards the bottom, where water entersat a constant rate. Schone's formula is: V= 104.7(5 - I)157Z)157 where V is thevelocity of water (mm/s) required tocarry away particles of diameter D andsp. gr. S. (E. Schone, UberSchlammanalyse und einen neuenSchlammapparat, Berlin, 1867.)Schottky Defect. See CRYSTAL

STRUCTURE.Schugi Mixer. A continuous mixer forpowders or for powders and liquids(Schurmans & Van Ginneken).Schuhmann Equation. An equation forthe particle-size distribution resultingfrom a crushing process: y = 100(x/K)a,where y is the cumulative percentagefiner than x, a is the distributionmodulus, and K is the size modulus: aand K are both constants. (R.Schuhmann, Amer. lnst. Min. Engrs.,Tech. Paper, 1189,1940) cf. GAUDIN'SEQUATION).

Schuller Process. See UP-DRAWPROCESS.Schulze Elutriator. The original type ofwater elutriator, it has since beenimproved by H. Harkort (Ber. Deut.Keram. Ges.y 8, 6,1927).Schurecht Ratio. A term that has beenused for SATURATION COEFFICIENT(q.v.); named from H. G. Schurecht(USA) who introduced this coefficient inhis research on frost-resistance of terracotta carried out at the National Bureauof Standards in 1926 but neverpublished; the term 'Schurecht Ratio'was first applied by J. W. McBurney.Scleroscope. An instrument fordetermining the relative hardness ofmaterials by a rebound method.Scone. See SPLIT.

Scotch Block. One form of gas port in anopen-hearth steel furnace, thedistinguishing feature is that it ismonolithic, being made by rammingsuitably graded refactory materialaround a metal template.Scotch Kiln. See SCOVE.Scouring. The cleaning and smoothing ofbiscuit-fired ceramic ware by placing theware in a revolving drum together withcoarse abrasive material, e.g. PITCHERS(q.v.). This process is used in the makingof bone china and of some other types ofvitreous tableware (in USA); whenapplied in the manufacture of electricalporcelain, the process is known (in UK)as RUMBLING.Scouring Block. An abrasive block ofceramically bonded SiC or Al2O3 used inthe grinding of steel rolls. Such a block is125-150 mm long and 50-75 mm 'square'(the actual section may be trapezoidal,roughly semicircular or of other specialshape).Scove or Scotch Kiln. An early type ofup-draught intermittent kiln for thefiring of bricks, etc. It was rectangular

and consisted of side-walls and end-wallsonly, with fire holes in each side-wall andWICKETS (q.v.) in each end wall. The topof the setting was covered with aPLATTING consisting of a layer of firedbricks, with ashes or earth above.SCR Brick. A perforated clay buildingbrick introduced in 1952 by theStructural Clay Products ResearchInstitute, USA, whence its name. Thebrick is IIV2 x 5Vi x 2Vi6th in., with 10holes l3/8ths in. dia. and a 3A in. squarejamb-slot in one end. The weight is 8 Ib:(292 x 140 x 52 mm, with 10 holes 34mm dia, and a 19 mm slot. The weight is3.6 kg)Scrapings, OVERSPRAY (q.v.) removedfrom the sides and bottom of a spray-booth in vitreous enamelling; it is re-milled and used as a first coat.Scrapping. The removal of excess bodyfrom a shaped piece of pottery-warewhile the latter is still in or on themould; (cf. FETTLING).Scraps. Excess body removed during theshaping of potteryware, together withany broken, unfired, pieces. Scraps areusually returned to the blunger for re-use.Screed. A layer of mortar or othermaterial applied to a sub-floor andbrought to a defined level. (B.S. 6100Pt.6). A fine-grained mix is used toprovide a level surface for TILE FIXING(q.v.).Screeding Board. See TRAVERSING

RULE.Screen. An industrial-scale unit for sizeclassification (a SIEVE (q.v.) is forlaboratory use). A screen consists of awire mesh or a perforated metal plate:the usual types are REVOLVING SCREENS(q.v.) and VIBRATING SCREENS (q.v.).Screen Printing. A decorating methodthat can be applied to pottery, glasswareor vitreous enamelware. The simplest

silkscreen equipment consists of a frameover which is stretched silk bolting cloth,or fine wire gauze, of 50-60 meshes percm. A stencil is then placed on the frameand varnish is applied to fill in thoseparts of the screen not covered by thedesign. Colour, dispersed in a suitableoil, is pressed through the open parts ofthe screen by means of a roller and thepattern of the stencil thus reproduced onthe ware. The stencil can be madephotographically, and the whole processmechanised. A further development wasthe screen printed collodion filmtransfer, which has itself been improvedto give screen-printed cover-coattransfers. Screen-printing is particularlyapplied to the decoration of wall-tiles.Screw Press. See FRICTION PRESS.Scrub Marks. A surface blemish on glassbottles; see BRUSH MARKS.Scuffing. The dull mark that sometimesresults from abrasion of a glazed ceramicsurface or of glass-ware.Scull. See SKULL.

Scum; Scumming. (1) A surface depositsometimes formed on clay buildingbricks. The deposit may be of solublesalts present in the clay and carried tothe surface of the bricks by the water asit escapes during drying: it is then knownas DRYER SCUM. The deposit may alsobe formed during kiln firing, either fromsoluble salts in the clay or by reactionbetween the sulphur gases in the kilnatmosphere and minerals in the claybricks; it is then known as KILN SCUM(cf. EFFLORESCENCE).

(2) Undissolved batch constituentsfloating as a layer above the molten glassin a pot or tank furnace.(3) Areas of poor gloss on a vitreousenamel: the fault may be due to theaction of furnace gases, to a non-uniformfiring temperature, or to a film of clayarising from faulty enamel suspension.

Scurf. A hard deposit, mainly ofcrystalline carbon, formed by thethermal cracking of crude coal gas on therefractory walls of gas retorts and cokeovens. When the scurf is periodicallyremoved, by burning off, there is adanger that the refractory brickwork ofthe retort or oven may be damaged byoverheating.Scutch. US term for a hand tool fortrimming bricks.Sea-water Magnesia. Sea-water containsapprox. 0.14% Mg. It can be extractedby treatment with slaked lime or withlightly calcined dolomite:MgCl2 + Ca(OH)2 -> Mg(OH)2 + CaCl2

MgSO4 + Ca(OH)2 -> Mg(OH)2 + CaSO4

When calcined dolomite is used asprecipitant, the yield is almost doubledbecause the MgO in the calcineddolomite is also largely recovered. Theprecipitated Mg(OH)2 is settled in tanks,filtered, and then calcined or dead-burned to produce MgO. The first small-scale plant was put into operation inCalifornia in 1935. The first large-scaleproduction was at West Hartlepool,England, in 1938; most of the magnesianeeded for the production of basicrefractories in Britain has since beenderived from the sea; typical analysis %:SiO2, 2; Al2O3 0.5; Fe2O3,1.5; CaO, 2;MgO, 93.Seailles Process. For the simultaneousproduction of alumina and portlandcement from siliceous bauxite, or froman aluminous slag or clay. Anappropriately proportioned batch is firedin a rotary kiln to give 5CaO. 3Al2O3

and 2CaO-SiO2; leaching of this productyields alumina and reburning of theresidue with more lime yields a cementclinker. The process was introduced in1928 by J. S. Seailles who later worked incollaboration with W. R. G. Dyckerhoff(whence the alternative name Seailles-

Dyckerhoff Process), see their jointBritish Patent 545 149, 2/8/38.Seal. See CERAMIC TO METAL SEAL;GLASS-TO-METAL SEAL; METALLIZING;SEALING GLASS.Sealed Porosity. See under POROSITY.Sealing Glass. A glass that is suitable foruse in sealing a glass envelope of anelectronic valve, for example, to metal.The usual basis for the selection of sucha glass is matching its thermal expansionand contraction with that of the metalover the range of temperature from thatat which the seal is made to roomtemperature; however, a glass that issufficiently soft (e.g. a lead glass) canaccommodate considerable stress at aglass-metal seal by slowly yielding. Somesealing glasses are crystallized duringprocessing to form glass-ceramics withimproved properties. ASTM F79specifies sealing glasses.Seam. See JOINT LINE.Seat. A place prepared on the SIEGE(q.v.) of a glass-pot furnace for thesupport of a pot.Seat Earth or Underclay. The materialimmediately beneath a coal seam,normally a fireclay but in some cases asilica rock (GANISTER, q.v.).Seating Block. A block of fireclayrefractory, shaped to support a boiler.Secar. Trade-name: a pure calciumaluminate cement, suitable for use inmaking special refractory castables orshapes, made by Lafarge AluminousCement Co. Ltd. It is available in twogrades; the purer (Secar 250) contains70-72% Al2O3, 26-29% CaO, 1% SiO2

and 1% Fe2O3.Secondary Air. Air that is admitted to akiln (that is being fired under oxidizingconditions) in an amount and in asuitable location to complete thecombustion of the fuel initiated by thePRIMARY AIR (q.v.). In a kiln fired by

solid fuel on a grate, the secondary airpasses over the fuel bed and burns thecombustible gases arising therefrom.Secondary Clay. See SEDIMENTARYCLAY.Secondary Crusher. A machine for thesize-reduction of a feed up to 25 mm to aproduct passing about 8 mesh. Thisgroup of machines includes the finertypes of jaw crusher and gyratorycrusher, and also crushing rolls, hammermills and edge-runner mills.Secondary Steelmaking. The treatmentof steel in the ladle (e.g. by vacuumdegassing) to improve cleaness,composition control and steelplantproductivity. See Appendix B.I.Seconds. Pottery-ware with small, notreadily noticeable, blemishes (cf. FIRSTS,LUMP).

Sedigraph. Trade-name. A particle sizeanalyzer based on the differentSEDIMENTATION (q.v.) rates of differentsizes of particles, which provides anautomatic graphical printout of thePARTICLE SIZE DISTRIBUTION.Sedimentary Clay or Secondary Clay. Aclay that has been geologicallytransported from the site of its formationand redeposited elsewhere. The Englishball clays, for example, are secondarykaolins (cf. PRIMARY CLAYS).Sedimentation. The settling out of solidparticles from a liquid. Some deposits ofclay, sand etc, have been formed bysedimentation from lakes, estuaries andthe sea. Sedimentation is used as amethod of purifying clays, heavyimpurities (e.g. iron compounds) settlingout more quickly than the lighterparticles of clay. Sedimentation is also amethod for determining the particle sizeof clays and powders (cf. ELUTRIATION).Sedimentation Volume. The volumeoccupied by solid particles after they havesettled from suspension in a liquid. With

most clays, the sedimentation volumedepends on the degree of flocculation ordeflocculation. Determination of thesedimentation volume of brick claysprovides some indication of the finenessof the clay, its working moisture content,and drying shrinkage.Seed. A fault, in the form of smallbubbles, in glass. When near the surfaceof plate glass they sometimes becomeexposed, as minute depressions, duringthe polishing process; they are thenknown as BROKEN SEED.Seekers. Mechanisms for the location ofkiln cars.Seger Cone. The first series ofPYROMETRic CONES (q.v.) was that of H.A. Seger (Tonind. Zeit., 10, 135, 168, 229,1886); the standard cones of Germanyare still known by his name. For table ofequivalent temperatures see Appendix 2.Seger Formula. A procedure introducedby H. A. Seger (Collected Writings, Vol.2. p. 557), and still commonly used, forthe representation of the composition ofa ceramic glaze. The chemicalcomposition is recalculated to molecularfractions and the constituent oxides arethen arranged in three groups: the bases,which are made equal to unity; R2O3;RO2. Example: (0.3 Na2O. 0.2 CaO. 0.5PbO). 0.2 Al2O3. (3.0 SiO2.0.7 SnO2).Seger's Green. A ceramic colour thatcan be fired up to about 10500C and thatconsists of (%): K2Cr2O7, 36; CaCl2, 12;whiting, 20; CaF2,10; flint, 20.Seger's Porcelain. A German porcelainintroduced in 1886 by H.A. Seger: 30%feldspar, 35-40% quartz, 30-35% kaolin.It is covered with a glaze prepared from83.5 parts feldspar, 26 parts kaolin, 35parts whiting, 54 parts flint. It is biscuitfired at a low temperature and glost firedat Cone 9.Seger's Rules. A series of empirical rulesput forward by the German ceramist H

A. Seger (Collected Writings, Vol. 2. p.577) for the prevention of crazing andpeeling. To prevent crazing, the bodyshould be adjusted as follows: decreasethe clay, increase the free silica (e.g. flint;replace some of the plastic clay bykaolin; decrease the feldspar; grind theflint more finely; biscuit fire at highertemperature. Alternatively, the glaze canbe adjusted: increase silica and/ordecrease fluxes; replace some SiO2 byB2O3; replace fluxes of high equivalentweight by fluxes of lower equivalentweight. To prevent peeling, the body orglaze should be adjusted in the reversedirection.Seger's Solution. A solution for testingthe acid resistance of ceramics(Portuguese Stand. P.144,1956) 262 mlof sulphuric acid (s.g. 1.84) and 108 ml ofnitric acid (s.g. 1.42) are added to 1 litreof distilled water.Seggars. A N.E. England dialect term formixed fireclay and coal, used as a blast-furnace tap hole clay.Segmental Arch. A sprung arch havingthe contour of a segment of a circle.Segmental Tile. See RIDGE TILE.Segmental Wheel. An abrasive wheelthat has been built up from speciallymade segments of bonded abrasive;wheels up to 1.5 m dia. can be made inthis way.Segregation. Partial re-separation of apreviously mixed batch of material intoits constituents; this can occur either as aresult of differences in particle size or indensity. Segregation is liable to occur instorage bins, on conveyors and in feedersduring the dry or semi-dry processing ofceramic materials.Seignette-electric. Seignette salt is thealternative name for Rochelle salt (Na-Ktartrate). Crystals of this composition aremarkedly piezo-electric and were used,for this property, before titanate

ceramics were introduced. The term'seignette-electric' is still sometimes usedin Western Europe and Russia to signifyferroelectric.Selenium. Compounds of Se are used fordecolourising glass in the tank-meltingprocess; under other conditions thiselement will produce red coloured glass(see RUBY GLASS), pottery, or vitreousenamel.Self-bonded Silicon Carbide. SeeREACTION BONDED SILICON CARBIDE.Self-cleaning Enamel. Vitreous enamelswhich contain components designed topromote oxidation of grease and ovenspills during use.Self-glazing Tiles. Russian pressed floortiles, based on volcanic glasses, culletand ceramic scrap, are dried byradiation, which causes alkalis to migrateto the upper surface as the waterevaporates. There they act as a fluxduring firing, increasing vitrification andforming a glazed surface.Self-propagating High TemperatureSynthesis. Self-sustaining highlyexothermic solid state reactions result ina combustion wave which converts thereactants to the desired product as itpropagates through a compacted mixtureof the reactant powders.Self-slip. A term introduced byarcheologists to describe the fine surfacelayer on pottery vessels, produced bywet-surface smoothing.Selfstak. A system of handling bricks fordelivery to sites. The bricks are stackedin cubes, on pallets or shrink-wrapped,about Im side. The cubes are lifted by asmall crane mounted on the deliverylorry. The system originated in Canada,but was developed by the London BrickCo., whose fletton bricks are deliverednationwide.Self-reinforced Ceramic. A ceramicreinforced by in-situ growth of whisker-

like elongated grains of the samematerial as the bulk ceramic.Selvedge. The formed edge of a ribbonof rolled glass.SEM. Scanning Electron Microscopy.Semi-conducting Glaze. Porcelaininsulators that are covered with a normalglaze are liable, particularly if thesurface gets dirty, to surface dischargeswhich cause radio interference and maylead to complete flashover andinterruption of the power supply. Thiscan be largely prevented if the glaze issemi-conducting as a result of theincorporation of metal oxides such asFe2O3, Fe3O4, MnO2, Cr2O3, Co3O4,CuO or TiO2; SiC and C have also beenused as semi-conducting constituents.Semi-conductor. A material with modestELECTRICAL CONDUCTIVITY (q.V.) whichincreases with temperature. Semi-conducting ceramics include siliconcarbide (used in heating elements), othercarbides, oxides of variable valencymetals (e.g. ZnO) and specializedelectronic ceramics such as GaAs. (Mostceramics become semi-conducting athigh temperatures.)Semi-continuous Kiln. A TRANSVERSE-ARCH KILN (q.v.) having only a singleline of chambers, so that when the firingzone reaches one end of the kiln theprocess of fire travel must be re-startedat the other end. Kilns of this type werenever common.Semi-dry Mortar, MORTAR (q.v.) whichis mixed using just sufficient water tomake a mix which coheres in the hand(much less than in a conventional mix).This leads to lower shrinkage, anadvantage in TILE-FIXING, (q.v.).Semi-dry Pressing. See DRY PRESSING.Semi-muffle. See under MUFFLE.Semi-porcelain. A trade term sometimesapplied, both in the UK and the USA, tosemi-vitreous tableware. The term is

confusing but is nevertheless included inthe COMBINED NOMENCLATURE (q.V.)and defined as ware 'prepared,decorated and glazed to give thecommercial appearance of porcelain.Without being really opaque likeearthenware, or truly translucent likeporcelain, these products may be slightlytranslucent in the thinner parts such asthe bottoms of cups. These materials can,however, be distinguished from realporcelain because their fracture is rough-grained, dull and non-vitrified. They aretherefore porous beneath the glaze andthe fracture clings to the tongue. Theyare easily scratched with a steel knife,and are not considered as porcelain orchina.'Semi-silica Refractory; Semi-siliceousRefractory. See SILICEOUSREFRACTORY; note, however, thatASTM-C27 defines a semi-silicarefractory as containing 72% SiO2. Atentative ISO recommendation defines asemi-siliceous refractory as containing85-93% SiO2.Semi-universal Bricking. See SPIRAL

BRICKING (q.V.)Semi-vitreous or Semi-vitrified. Thesesynonymous terms are defined in theUSA (ASTM - C242) as signifying aceramic whiteware having a waterabsorption between 0.5% and 10%,except for floor tiles and wall tiles whichare deemed to be semi-vitreous when thewater absorption is between 3% and 7%.S.E.N. Submerged Entry Nozzle.S.E.N.B. Single Edge Notched Beam.See FRACTURE TOUGHNESS TESTS.Sensitizing Compound. A substancewhich, in solution, can be applied to aceramic surface to facilitate silvering orplating. Salts of Al, Ti, Fe or certainother metals can be used.Sentinel Pyrometers. Small cylindersmade from blended chemical compounds

(non-ceramic) and so proportioned thatthey melt at stated temperatures withinthe range 220-10500C, used principallyin controlling the heat treatment ofmetals.S.E.P.B. Single Edge Precracked Beam.See FRACTURE TOUGHNESS TESTS.Sepiolite. 3MgO.4SiO2.5H2O; themagnesian end-member of the series ofclay minerals known as PALYGORSKITES(q.v.); it has been found in some of theKeuper Marls used for brickmaking inCentral England.Sepulchre Kiln. A shaft kiln used for thecalcination of dolomite and othermaterials. (F. Sepulchre, Soc. Anon, deMarche-les-Dames, Namur, Belgium.)Serpentine. A naturally occurringhydrated magnesium silicate, 3MgO.2SiO2 .2H2O; some of the Mg iscommonly replaced by Fe. Serpentine isa common gangue mineral associatedwith chrome ore. Some types ofserpentine are used as raw materials(together with dead-burned magnesite)for the manufacture of forsteriterefractories.Serrated Saddle. A refractory supportfor pottery-ware during kiln firing; thisparticular item is a rod of triangularsection, its upper edge being serrated tofacilitate the REARING (q.v.) of theware.S.E.S. Submerged Entry Shroud.SESCI Furnace. A rotary furnace,designed to burn low-volatile coal, andused for the melting of cast iron. Arammed siliceous refractory is generallyused as lining material. The namederives from the initials of the Frenchmakers: Societe des EntreprisesSpeciales de Chauffage Industriel.Sessile Drop Test. A method for themeasurement of SURFACE TENSION y.If the drop, resting on a horizontalsurface, is so large that the curvature at

the top is negligible y - l/2h2gd where h isthe height of the drop and d its density.If not, y = V2h2gd(l + 0.609Vr) where r isthe drop radius and h is the distancefrom the top of the drop to its greatesthorizontal diameter.Sessile drops can be measured at hightemperature using a travelling telescopethrough a furnace window. ASTM C813specifies a test for the 'HydrophobicContamination of Glass by ContactAngle Measurement'. The angle ofcontact is measured by a comparatormicroscope, or with a protractor on aphotograph of the drop.Set. The general flow behaviour ofvitreous enamel slip determining the rateof draining, residual thickness, anduniformity of coating.Setter. (1) A man who sets bricks or tilesin a kiln; (the man who sets pottery-wareis known as a PLACER).(2) An item of KILN FURNITURE (q.v.); itis a piece of fired refractory materialshaped so that its upper surfaceconforms to the lower surface of thepiece of ware that it is designed tosupport during kiln firing.Setting. (1) The arrangement of ware ina kiln. With pottery-ware, the settinggenerally consists of the individual piecestogether with the kiln furniture thatsupports them; a setting of buildingbricks or refractories consists merely ofthe bricks themselves.(2) A group of gas retorts or chamberswithin a bench, the group being heatedindependently of other groups ofretorts in the same bench; also knownas a BED.

(3) The process of hardening of a cement(see INITIAL SET and FINAL SET) or of aplaster.Setting Density. The fired weight perunit volume of ceramic ware set in a kilnfor the firing process; it is usually

expressed in kgnrr3 (or lb/ft3. In BritishStandard Test Codes for ceramic kilns(BS 1081 and 1388, now withdrawn) twosetting densities were defined: theOverall Setting Density is the fired weightdivided by the overall setting volume;the Actual Setting Density is the firedweight divided by the actual settingvolume. The Overall Setting Densityindicates the effectiveness of filling theavailable kiln volume; the Actual SettingDensity excludes the spaces in the kilnthat are not utilized and thus gives abetter indication of the closeness ofpacking of the ware within the settingitself.Setting Rate. The time taken for a glassto cool over its WORKING RANGE (q.v.).Setting-up Agent. An electrolyte, e.g.K2CO3, MgSO4, etc., added to a vitreousenamel slip or to slop glaze to flocculatethe clay particles and thus to hold thecoarser and heavier frit particles insuspension.Settle Blow. The stage in the BLOW-AND-BLOW (q.v.) glass-making processwhen glass is forced into a finish or ringmould by air pressure.Settle Mark. Any slight variation in thewall thickness of a glass container;sometimes called a SETTLE WAVE.Settlement. Movement of a kiln settingduring firing, due to dimensionalchanges.7.6 Temperature. See SOFTENING POINT.Sewer Brick. A specification for claybricks intended for this use is given inASTM-C32.Sewer Pipe. An impervious clay pipe(usually glazed) for sewerage and trade-effluent disposal. Relevant BritishStandards are: B.S. 65, and B.S. 8000 Pt.14 (a code of practice for below-grounddrainage) Relevant US specificationsare: ASTM-C12, C-301, C-425, C700,C-828, C-1091, C-1208 which specify

installing clay pipe lines, the pipes andjoints and air tests on the lines. See alsoCONCRETE PIPES.Sgraffito. A mode of decorationsometimes used by the studio potter: acoloured ENGOBE (q.v.) is applied tothe dried ware and a pattern is thenformed by scratching through theengobe to expose the differentlycoloured body. (From Italian graffito, toscratch.)Shadow Wall. A refractory wall in aglass-tank furnace erected on the bridgecover; it may be solid or may haveopenings, its purpose being to screen theworking end from excessive heatradiation. It is also sometimes known asa BAFFLE WALL Or CURTAIN WALL butthe latter term is by some authoritiesreserved for a suspended wall serving thesame purpose.Shaft. See STACK.Shaft Kiln. A vertical kiln charged at thetop and discharged at the bottom. Ifsolid fuel is used it is fed in with thecharge, but shaft kilns can also be firedwith gas or oil by burners placed nearerto the bottom of the shaft. Such kilnsare used for the calcination of flint,dolomite, fireclay, etc.Shaft Mixer. See MIXER.Shaker Table. A slightly tilted vibratingtable, sometimes with a riffled surface.Particles poured on it are separated, thelarger and denser reaching the bottomfirst.Shaking Gold, BURNISH GOLD (q.v.)suspensions, which require vigorousshaking to disperse settled particles, (aUS term.)Shale. A hard, laminated, generallycarbonaceous, clay. Colliery shales arefrequently used as raw materials forbuilding brick production.Shale Cutter or Shale Planer. Amechanical excavator sometimes used

for getting clay from deposits that areboth hard and friable, and that willmaintain a steep clay face. The mainfeature of the machine is an endlesschain that carries a series of cutterswhich bear downwards on the clay,removing a layer about 18 mm thick.The machine makes semi-circular sweepsinto the clay face before being movedforward or sideways.Shaling. A fault in vitreous enamelware;also known as SPALLING (q.v.).Shape Factors. Ratios of characteristiclengths or areas of particles (e.g. theratio of the longest to the shortestdimensions) to give a dimensionlessnumerical assessment of the geometricalappearance of the particle. See alsoFRACTAL.Shaping Block. A piece of wood for thepreliminary shaping of glass on theblowing-iron before it is blown in amould.Shark's Teeth. A STRIATION (q.v.) ofdagger-like step fractures from thescored edge to the compression edge(the region in which the brittle materialis subject to compressive stress).Sharon Quartzite. A quartzite occurringin Ohio, USA, and used in themanufacture of silica refractories. Aquoted analysis is (per cent): SiO2, 98.7;Al2O3 0.3; Fe2O3. 0.3; alkalis, 0.3.Sharp. The bricks with larger radialtaper in a two-taper system of arch orring construction. The opposite of SLOW.Sharp Finish. See FINISH.Sharp Fire. Combustion with excess airand short, hot flame.Sharp Pitch. See under PITCH.Shatterbox. Trade-name. A laboratorygrinder producing 1 to 300 mesh powder.(Glen Creston Co., Middx.).Shaw Kiln. A gas-fired chamber kiln;one feature is that some of the hot gasespass beneath the kiln floor to diminish

the temperature difference from top tobottom of the setting. The kiln wasdesigned by Shaw's Gas Kiln Co. Ltd., inabout 1925.Shaw Process. A process for theprecision casting of small metalcomponents; its main feature is the useof silicon ester as the bond for therefractory powder, e.g. sillimanite. fromwhich the mould is made. (N. Shaw,Brit. Pat., 716 394, 6/10/54 and laterpatents.)S.H.C.C. Strain Hardening CementitiousComposite. See STRAIN HARDENING.Shear-cake. A counterbalancedrefractory slab acting as the door of asmall furnace. (USA).Shear Fire. A thin flame, used to sever aglass article from the tool after shaping.Shear Hackle. A HACKLE MARKgenerated by interaction of a shearcomponent with the principal tensiondriving the crack.Shearicon. See TIMBRELL-COULTER

SHEARICON.

Shear Marks on glassware are caused bythe cooling action of the cutting offshears on the hot but solid glass.Shearer Plastometer. See R & SPLASTOMETER.

Sheet Glass. Flat, transparent glass madeby drawing or blowing.Sheet Silicates. See SILICATE STRUCTURES.Shell. (1) The falling away of a 25-50mm internal layer of refractory from theroof of an all-basic open-hearth steelfurnace; the probable cause is thecombined effect of flux migration,temperature gradient and stress. Thisform of wear is also known as SLABBING.(2) A flake of glass chipped from theedge of glass-ware, or the hollow left bysuch a flake.(3) The 'shell' of a hollow clay buildingblock refers to the outer walls of theblock.

Shell Moulding. A method for theprecision casting of metal in refractorymoulds made from silica sand bondedwith synthetic resin, sodium silicate orsilicon ester; alumina and crushed high-silica (96% SiO2) glass have also beenused as the refractory component ofthese moulds.Shell Wall or Ring Wall. The wall offireclay refractories that protects theouter steel casing of a HOT-BLAST STOVE(q.v.).Shellback, Shellbacked. An erroneousvariant of SCHELLBACH.Shelling. See SHELL.Shell-stone. A CHINA STONE (q.v.) fromCornwall containing too much iron (asbrown mica) for use as a flux in potteryglazes but of potential value in sewer-pipe glazes.Shelving. The effect produced in therefractory lining of a glass-tank furnaceby severe erosion of the horizontal jointsbetween the tank blocks.Sherd, POTSHERD (q.v.) Sometimesspelled SHARD.Shetty's Criteria. The critical crack sizerelative to the size of the stress-concentrating defect is the keyparameter determining the effect ofstress-state on flaw severity. The relativecritical crack size is a parameter of thematerial. In commercial aluminas it is 2to 3 times the pore size. In RBSN it ismuch smaller. (D.K. Shetty et al, inFracture Mechanics of Ceramics 5, Bradtet al, Plenum 1983, p 531). SeeFRACTURE, FRACTURE MECHANICS.

Shetty's Mixed Mode Equation.K1ZK1C + (KS/CKIC)2 = 1where K1 is the STRESS INTENSITYFACTOR (q.v.) for Mode 1 loading (stressperpendicular to the crack plane); KIC isthe critical stress intensity; Ks is thestress intensity for Mode II or Mode IIIloading (parallel to the crack plane)

whichever is dominant. C is a constantwhich is adjusted to best fit the data, andis usually in the range 0.8<C<2.0 forlarge flaws. As C increases, the materialbecomes less sensitive to shear. SeeFRACTURE; FRACTURE MODES.Shielding Glass. A protective glass foruse in nuclear engineering; although it istransparent to visible light, it absorbshigh-energy electromagnetic radiation.Such glasses contain a maximumproportion of oxides of heavy elements,e.g. PbO, Ta2O5, Nb2O3, WO3.Shillet. Local term for the Devonianslates used for brick-making in thePlymouth and Torquay areas ofEngland; the word is a dialect form of'shale'.Shiners or Shiner Scale. Minute FISHSCALES (q.v.) that sparkle in reflectedlight; they are liable to occur in vitreousenamelware if the ground-coat isoverfired.Ship-and-Galley Tile. US term for aspecial FLOOR QUARRY (q.v.) with anindented anti-slip pattern on its face.Shivering. See PEELING.Shoe. A hollow refractory shape that isplaced in the mouth of a glass pot andused for heating the BLOWING IRONS(q.v.).Shop. (1) A department or room in apottery, etc.(2) A team of men operating a blowingor pressing process in a glass-works.Shore Hardness Tester or Scleroscope.A procedure for the determination ofthe hardness of a surface by dropping aball from a fixed height above thesurface and noting the height ofrebound. This technique was firstproposed by A. F. Shore, an American,in 1906. Although primarily for thetesting of the hardness of metals, it hasalso been applied to a limited extent inthe testing of ceramics.

Shore-lines. A fault in vitreousenamelware similar in appearance to themarks left on a shore by receding water.The basic cause is the drying out of solublesalts. The cure is adjustment of the milladditions and of the drying process.Short. Term applied to a clay body thathas little workability or to a glass thatquickly sets.Short Glazed. See STARVED GLAZE.Shot. Non-fiberized material, appearingas small spherical particles, in ceramic,glass or mineral wool fibres. It impairsthermal insulation. B.S. 1902 Pt. 6section 7 describes a test for the shotcontent of refractory fibres. See SLUG.Shotcrete. A mixture of sand, cementand water applied by a compressed airhose to surface concrete. Cf. GUNCRETE.Shoulder Angle. A special shape ofceramic wall tile (see Fig. 7, p350).Shouldering. The splay at the top right-hand and bottom lefthand corners of asingle-lap roofing tile.Shraff. N. Staffordshire word for thewaste (e.g. broken fired ware, brokensaggars, old plaster moulds) from apottery.Shredder. See CLAY SHREDDER.Shrend. US term for the process ofmaking CULLET (q.v.) by running moltenglass into water (cf. DRAG-LADLE).Shrinkage. Reduction in dimensions.Ceramic fibre products shrink whenheated. A test is described in B.S. 1902Pt. 6 section 5. See also DRYINGSHRINKAGE; PERMANENT LINEAR

CHANGE.Shrinkage Cracking. Cracking due toexcessively rapid evaporation ofmoisture from (e.g.) concrete, mortar ora drying ceramic. It can be reduced byAIR ENTRAINING (q.V.)Shrink-mixed Concrete. Concrete whosemixing is completed in the mixer lorryon the way to the site.

Shrink-wrapping. A packagingtechnique, used for pottery and forbricks. The ware is covered with a thickpolymer sheet, which is sealed andshrunk onto the ware by hot air.SHS. Self-propagating High-temperatureSynthesis (q.v.)Shuff. A clamp-fired STOCK BRICK (q.v.)that is of too poor a quality for use.Specifically, it is a Stock Brick from thetop of a CLAMP (q.v.) that has beensubjected to heavy rain while under fullfire, the thermal shock resulting in ashattered texture and no 'ring'.Shuttle Kiln. An intermittent bogiekiln consisting of a box-like structurewith doors at each end andaccommodating kiln cars (usuallytwo in number). Pottery-ware is seton the refractory decks of the carswhich are then pushed along railsinto the kiln, displacing two other carsof fired ware from the kiln. The firedware is taken from the displaced carswhich are then re-set with more ware tobe fired. The shuttle movement of thekiln cars is is then repeated (cf. BOGIEKILN).

Shuttle Press. A press with two mouldcavities to be used alternately.S.I. (Systeme International). Theinternationally accepted system of units.ISO 1000 1992; B.S. 5555,1993. For adescription of this system, see S.I. TheInternational System of Units. Approvedtranslation of the International Bureau ofWeights and Measures publication 'LeSysteme International d'Unites (SI)'.National Physical Laboratory, London,HMSO, 1986. ASTM C899 describes thereporting of properties of refractories inmetric units.Sial. A borosilicate glass, of highchemical resistance and thermalendurance, made by the KavalierGlassworks, Sazava, Czechoslovakia.

Sialcor. A double layer nozzle for steelcasting. A 42% alumina outer shell islined with 90% alumina. (SavoieRefractaire, France.)Sialons. Materials in the Si-Al-O-N andrelated systems, originally made by hot-pressing alumina and silicon nitridemixtures K.H. Jack and W.I. Wilson,Nature Phys. ScL 238, (80), 1972, p 28).Si is partly substituted by Al, and N byO, in an expanded p silicon nitridelattice, to form p1 sialon. fP-sialon is asilicon oxynitride solid solutioncontaining Al, with a mullite-likestructure, o^-sialon (harder than (51) is anexpanded structure based on a-siliconnitride in with Si4+ is substituted by Al3+

with charges balanced by interstitial Y3+,Ca2+ or Li+ or rare earths. Aluminiumnitride POLYTYPOIDS (q.v.) (Si-Al-O-Nphases with constant (Si+A1):(O+N)ratio) with AlN structure are mixed withOC-Si3N4 (with its SiO2 surface film) andY2O3 as a sintering aid, and pressed andsintered in nitrogen under a BNprotective powder bed, to form P^sialon.Residual yttria forms a grain-boundaryglass or yttrium aluminium garnet phasewhich controls the high temperatureproperties. Sialons are used as enginecomponents, seals, bearings, wear partsand cutting tools. GC1JJ1 compositesperform better in the last two applications.Similar systems are possible with oxidesother than alumina. See SIMONS.Sibeon. A solid solution between(J-silicon nitride and beryllia, developedas a crucible material for molten silicon.Side Arch. A brick with the two largestfaces symmetrically inclined towardseach other, see Fig. 1, p39.Side-blown Converter. See CONVERTER.Side-construction Tile. A US term for ahollow block designed to undergocompression at right angles to the axis ofthe perforations.

Side Feather. See FEATHER BRICK.Side Lap. The distance by which the sideof a roofing tile overlaps the joint in thecourse of tiles next below.Side Pocket. Alternative name for SLAGPOCKET (q.v.) as applied to glass-tankfurnaces.Side Skew. A brick with one of the sidefaces completely bevelled at an angle of60°. An arch can be sprung from such abrick. See Fig. 1, p39.Siderite. Natural ferrous carbonate.FeCO3, found as an impurity in someclays.Siege. The refractory floor of a glassfurnace, particularly of a pot furnace:from French siege, a seat).Siemens or Siemens-Martin Furnace. SeeOPEN-HEARTH FURNACE.

Sieve. This term is generally reserved fortesting equipment: the correspondingindustrial equipment is generally called aSCREEN (q.v.). Automated sievingequipment has been developed, (seeAUTOSIEVE; SORSI). ASTM C285specifies Methods of Test for SieveAnalysis of Wet Milled and Dry-MilledPorcelain. B.S. 1902 Pt. 3.3 specifies thesieve analysis of refractory materials, asdoes ASTM C92. ASTM C325 specifieswet sieve analysis of whiteware clays.C371 and C925 are methods for non-plastic ceramic powders, using wire-clothsieves and wet sieving using precisionelectroformed sieves respectively. Thereare several standard series of test sieves;those most frequently met with in theceramic industry are:British Standard sieves (conforming toB.S. 410)USA Standard sieves (conforming toNational Bureau of Standards LC-584;or ASTM - Ell)French Standard sieves (AFNOR NF11-501)German Standard sieves (DIN 4188)

Tyler sieves, in which the ratio betweenthe mesh sizes of successive sieves in theseries is 2; thus the areas of the openingsof each sieve are double those of thenext finer sieve.Institution of Mining and Metallurgy,London (I.M.M. Sieves).(For a comparison of these series seeAppendix E.) All now follow the ISOsieve sizes. (ISO 2591, 3310)SIFCA. Slurry Infiltrated FibrousCastable (q.v.)Sigma Cement. Trade-name: a hydrauliccement made by mixing portland cementconsisting only of particles <30|im with16-50% of an inert extender, e.g.limestone, basalt or flint, the particle sizeof which is 30-200jLim. (S. Gottlieb, Brit.Pat., 580 291,26/6/44.)Signal Glass. Coloured glass for lightsignals on railways, roads, airfields and atsea; the glass must conform to a closespecification (B.S. 1376).Silazanes. Organic compounds in whichthe SiNH2 group is substituted for ahydrogen atom. They are pyrolysed toform silicon nitride films.Silcomp. A composite made byinfiltration of molten silicon into fibrousgraphite above 1450C.Silcrete. A type of quartzite that is eithercryptocrystalline or chalcedonic. Itoccurs, typically, at Albertinia, MosselBay, S. Africa; the porosity is low andthe Al2O3 content is less than 0.5%.Silex. A name sometimes applied toCHERT (q.v.), particularly to the trimmedblocks of this material, from Belgium,used in the lining of ball mills. For themilling of vitreous-enamel frits, silexblocks are used more in mills for ground-coats than for covercoats.Silica. Silicon dioxide, SiO2. For thevarious forms in which silica occurs seeCHALCEDONY, CHERT, COESITE,

CRISTOBALITE, FLINT, KEATITE,

QUARTZ, SAND, TRIDYMITE and

VITREOUS SILICA.

Silica Fireclay. A US term defined as: Arefractory mortar consisting of a finelyground mixture of quartzite, silica brickand fireclay.Silica Gel. A form of silica produced bytreatment of a solution of sodium silicatewith acid and/or other precipitant. Thedried gel is highly porous. It has foundlittle use in the ceramic industry.Silica Glass. This term is notrecommended; see VITREOUS SILICA.Silica Modulus. The ratio of SiO2:(Al2O3 + Fe2O3) in a hydraulic cement.In portland cement this modulus usuallylies between 2 and 3. A cement with alow silica modulus can be expected tohave high early strength, but if thismodulus is high the final strength will bethe greater.Silica Refractory. Defined in B.S. 1902Pt. 2 as a refractory material that, in thefired state, contains not less than 92%SiO2. Refractories of this type were firstmade in 1822, by W. W. Young, from thequartzite of Dinas, S. Wales, and are stilloften referred to as Dinas bricks inGermany and Russia. They arecharacterized by high RuL (q.v.) but aresensitive to thermal shock attemperatures up to 600C. Their principaluse is in steel furnaces, coke-ovens, gas-retorts and glass-tank furnaces. B.S. 4966specifies the properties required of silicarefractories for coke-ovens; they mustcontain at least 93% SiO2. In the USAsilica refractories are defined (ASTMC416) as containing < 1.50% Al2O3. <0.20% TiO2; < 2,5% Fe2O3: < 4% CaO;they are classified on the basis of a 'fluxfactor' equal to the percentage Al2O3

plus twice the total percentage of alkalis;Type A has a flux factor of 0.50 or less,Type B includes ail other silicarefractories meeting the general part of

the specification. (See also SUPER DUTYSILICA REFRACTORY.)

Silica Sol. Colloidal silica in the form ofa dispersion in water. The modernmethod of manufacture involves thepassage of sodium silicate solutionthrough an ion-exchanger. As made, thesols contain about 3% SiO2 but theconcentration can be increased to 20%by evaporation; to give stability, aconcentrated sol must have a largerparticle size or a stabilizer, e.g. NaOH,must be added. In the ceramic industry,silica sol has been used to a small extentas a bond.Silicate Bond. (1) As applied to ceramicsother than abrasives, this term meansthat the fired material consists of largergrains set in a matrix of a complex,usually glassy, silicate.(2) In the abrasives industry this termmeans a bond consisting essentially ofsodium silicate, the abrasive wheels sobonded being baked at about 2500C.Silicate Cement. As used in chemicalengineering, this term denotes an acid-proof cement, consisting of an inertpowder bonded with silica gel that hasbeen precipitated in situ from Na- orK-silicate (usually in the presence ofsodium silicofluoride), or from siliconester.Silicate Structures. Silicates have avariety of crystal structures, based on thesilica tetrahedron comprising a silicon ionwith four oxygen ions surrounding itsymmetrically. In island structures thetetrahedra are linked to each otherthrough additional non-silicon cations -the ORTHOSiLiCATES, which includezircon and the aluminosilicates. Inisolated group structures two or moretetrahedra are linked by commoncorners. This results in (Si2O7)

6- groups,or in ring structures, which includeZEOLITES. Chain structures form when

two oxygen ions in every tetrahedron areshared, with general formula /2(SiO3)

2".The charge balance is maintained byadjacent foreign cations which link thechains in three dimensions. SuchPYROXENES include enstatite (MgSiO3),wollastonite (CaSiO3) and spodumeneLiAl(SiO3)2. In the AMPHIBOLES, thechains are linked by shared oxygen ions.If three oxygen ions are shared, sheetstructures are formed, the layers havingthe general formula «2(Si2O5)

2-. Mostclay minerals have this structure, whichimparts plasticity and determines theirbehaviour in slips. In framework silicatesall four oxygen atoms are shared. Aswell as the various crystal forms ofSILICA (SiO2) itself, some silicon atomsmay be replaced by Al, with alkali oralkaline earth atoms then incorporatedto maintain charge balance, as in theFELDSPARS. See R.W. Grimshaw. TheChemistry and Physics of Clays andAllied Ceramic Materials, Ch HI 4th EdLondon, Ernest Benn, 1971.Siliceous Refractory. Defined in B.S.3446 as a refractory material that, in thefired state, contains 85-93% SiO2 theremainder being essentially Al2O3: anISO standard stipulates 85-93% SiO2.SEMI-SILICA and SEMI-SILICEOUSrefractories also fall within thisdefinition. The specification forrefractory materials for the gas andcoking industries laid down by the GasCouncil in collaboration with the Societyof British Gas Industries and the BritishCoking Industry Association subdividessiliceous refractories into three groups:Clay-bonded Siliceous 'B', with <88%SiO2; Clay-bonded Siliceous 'C\ with<85% SiO2; Semi-siliceous Firebrick,with 78-85% SiO2.The PRE definition of a siliceousrefractory is that the SiO2 contentshall not exceed 93%, a further

quality specification being according touse.Silicides. A group of special ceramicmaterials: see under the silicides of Cr,Mo, Ti, W, Zr.Silicon Borides. Several compounds havebeen reported. SiB4, oxidation-resistantto 13700C; thermal expansion (20-100O0C) 58 x 1(H; thermal conductivity(700C); 0.023c.g.s.; microhardness, 2100kg/mm2 (KHN-100). SiB6, m.p. 19500C;thermal expansion (20-10000C) 5.1 xICh6 ; thermal conductivity (700C), 0.023c.g.s.; microhardness, 2350 kg/mm2

(KHN-100). A special refractory hasbeen made by reacting Si and B in air,the product containing SiB4 and Si in aborosilicate matrix; it is stable in air to atleast 15500C and has good thermal-shockresistance. Other compounds reportedare SiB3 and SiB12.Silicon Carbide. SiC. A non-oxideceramic with a wide range of types anduses which depend on the method ofproduction, the resulting microstructureand purity, and the grain size.SiC dissociates at approx. 22500C.Density 3.2 kg; thermal expansion (25-14000C) 5 x 10-8 ; thermal conductivityusually below 100 W/m.K. The value isgreatly dependent on the type of bond,as is the electrical conductivity. SiC is asemiconductor.The uses of SiC are very varied, anddepend on the method of production,the resulting microstructure and purity,and the grain size. SiC resists oxidationbetter than most carbides, due to theformation of a protective surface film ofsilica. ASTM C863 evaluates theoxidation resistance of SiC. p-SiC is acubic crystal, stable above 2000C,produced by vapour phase reactions.a-SiC is rhombohedral or (usually)hexagonal, and is the low temperatureform. There are many POLYTYPES (q.v.)

of oc-SiC, giving rise to a specialclassifying notation (see RAMSDELLNUMBERS. oc-SiC is made by reducingsilica sand with carbon in an arc furnace.The resulting grain is used as anABRASIVE (q.v.) or to manufacturerefractory shapes. The abrasive productsmay be resin or glass bonded.Clay-bonded Silicon Carbide is made bymixing coarse SiC grain with up to 50%clay and shaping and firing to form aporous thermal-shock resistantrefractory.Recrystallized Silicon Carbide is asingle-phase material with a fairly coarsegrain size and a highly faceted surfacestructure. A bimodal oc-SiC grain sizedistribution is shaped (usually slip-cast)and sintered without additives in an inertgas at 2200C. The product is used fortubes, other refractory shapes, kilnfurniture and heating elements. Thereare strong intergranular bonds and highporosity. There is no shrinkage, andRECRYSTALLiZATiON (q.v.) takes placeby a complex evaporation/condensationmechanism. SiC in the fine-grained halfof the bimodal distribution reacts withthe silica surface layer always adheringto SiC particles. The reactionSiC + SiO2 -> Si + CO + Vi O2 proceedsin the opposite direction to producecoarse particles. In CRYSTAR (q.v.)electronic grade silicon is incorporatedto promote this reverse reaction.Silicon Carbide Heating Elements makeuse of SiCs semiconducting properties.They are made by proprietary methods,either from pressed or tamped oc-SiCfired at 22000C, or from (3-SiC at a lowertemperature. The objective is to form acentral zone of high electrical resistancein a rod or tube, e.g. by using capillarysuction to infiltrate the tube ends withmolten silicon metal. The result is acoarse crystal structure cross-section

with an oc-SiC 'recrystallized' facetedsurface.Reaction-bonded silicon carbide. Finersilicon carbide grains are shaped withgraphite and a binder into a porouscompact. The binder carbonizes in thepores. The compact is heated further incontact with molten silicon, which isdrawn into the pores by capillary action.In self-bonded silicon carbide the siliconreacts with the carbon, depositingfurther silicon carbide epitaxially on theoriginal grains. All the carbon isconverted, strengthening and densifyingthe compact, while excess silicon fills theremaining interconnected pores. Thismaterial, originally developed as acladding for nuclear fuel elements (seeREFEL) is used for many engineeringapplications including bearings, enginecomponents and seals. It is sometimes(inappropriately) known as reactionsintered silicon carbide.Nitride bonded silicon carbide is formedsimilarly, with less graphite and moresilicon. The latter may be incorporatedas a powder in the original mix. It reactswith nitrogen in the atmosphere to forman intergranular bond with a highproportion of Si2N2O. Engineeringceramics of almost zero porosity can bemade. Sintered SiC uses B4C as asintering aid. Hot-pressed SiC has about2% alumina added as a densification aid.Sintered SiC is less oxidation resistantthan reaction-bonded SiC.SiC films can be made by pyrolysis ofchlorinated silanes, as can SiC fibressome 0.1mm diameter. Finer continuousfibres are made from C-Si polymerfibres. SiC whiskers (q.v.) are much usedin fibre-reinforced composites.Typical values of Young's modulus forvarious forms of SiC illustrate thedependence of mechanical properties onmicrostructure and production method:

sublimed SiC 460-470 GPa; CVD 440-470 GPa; hot-pressed (2% Al2O3) 415-445 GPa; sintered a-SiC 410 GPa;reaction-bonded 380-390 GPa;recrystallized 145 GPa.Silicon Monoxide. SiO deposited byCVD and PVD methods to formdielectrics and insulating layers inintegrated circuits, and as a protectivecoating.Silicon Nitride. Si3N4 There are twoforms, both hexagonal, a (Si12N16)changes irreversibly to (3 (Si6N8) atapprox. 17000C, above whichtemperature decomposition sets in.Silicon nitride powder is mainly a form.It can be made by nitriding siliconpowder, by the carbothermal reductionof silica in nitrogen, or by reactingsilicon tetrachloride with ammonia.Dense engineering ceramics can be madeby most of the advanced ceramicforming processes, including:Reaction Bonded Silicon Nitride - aporous silicon compact is made (e.g. byisostatic pressing) and heated in nitrogenat 1100 to 14500C. The silicon (solid,liquid or vapour depending on thetemperature) reacts with the nitrogen toform sub-micron grains of a - and (3 -silicon nitride, which fill up the porespace of the original silicon compact,without shrinkage. The porosity is 15-30%, with some large pores (50um) dueto the melting of impurity particles fromthe silicon. Compacts can be partiallynitrided to sufficient strength but lowenough hardness for machining to finalsize and shape with normal machinetools. Nitriding is then continued.Engineering components of complexgeometry can be made, as can pouringtubes and nozzles for molten aluminium.Sintered Silicon Nitride. Denseengineering ceramics can be made byusing MgO, Y2O3 or other oxides as

SINTERING AIDS for oc-silicon nitridepowder (which usually has a surfacelayer of silica). The powder mixture isshaped and fired in nitrogen, protectedby a bed of boron nitride powder. Anoxynitride liquid is formed, whichdissolves OC-Si3N4 which then precipitatesas acicular (J-Si3N4, densifying andstrengthening the compact. Dependingon the oxide additive the liquid cools toan amorphous or crystalline grainboundary phase, which controls the hightemperature properties of the ceramic.Hot pressed Silicon Nitride is similar tosintered silicon nitride, but uniaxiallypressed in an induction heated graphitedie at 1700-18500C. See also SIALONS.Pyrolytic Silicon Nitride. Tubes andprotective coatings for engineeringcomponents are made by chemicalvapour deposition from chlorosilane orsilane-ammonia-hydrogen mixtures.CVD and physical vapour depositionprocesses, and the resulting crystalstructures, have been much studied andused to deposit silicon nitride films andgrow epitaxial layers as electricalinsulators and as masks for thedeposition of other materials inelectronic integrated circuitry.Silicon Oxynitride. Si2N2O,orthorhombric crystals made byreaction-bonding or by crystallizationfrom OXYNITRIDE GLASSES (q.V.).Density is 1.9 to 2.3 kg/1 and flexuralstrength 30 to 90 mPa. Silicon oxynitrideis used as a lining for cells for theelectrolysis of AlCl3 to Al and ZnCl2 toZn, and as crucibles and tubes formolten salts. It occurs as a constituent ofnitride bonds (see SILICON NITRIDE,SILICON CARBIDE) and has been used tostrengthen silica optical fibres by surfacecoating.Silicone. Organo-silicon polymers someof which can be used up to a temperature

of 3000C or even higher. Silicones havebeen used in the ceramic industry asmould-release agents, for the coating ofglass-ware to increase its strength andchemical durability; a specification forsilicone for spraying on brick-work togive it water-repellancy is provided inB.S. 6477 Water Repellants for MasonrySurfaces.Silicosis. A lung disease caused byinhalation, over a long period, ofsiliceous dusts, particularly thosecontaining a high proportion of freesilica of a size between 1 and 2|im. SeeDUST; HEALTH & SAFETY.

Silit. Trade-mark: a heating elementconsisting principally of SiC; to maintaina constant resistance for a long period, Siis included in the batch and the shapedrods are fired in a controlled atmosphereto cause some nitridation and/orcarbonation. (Siemens-PlaniawerkeA.G., Germany.)Silk. See GLASS FIBRE.

Silk-screen Process. See SCREEN

PRINTING.Sill. A horizontal course of brickwork, ora precast slab of concrete, under anopening e.g. a window in a house or adoor or port in a furnace wall. Sizes,materials (stone, concrete or clayware),workmanship and jointing and water-proofing of sills are specified in B.S. 5641PtI .Sillimanite. A mineral having the samecomposition (Al2SiO5) as kyanite andandalusite but with different physicalproperties. The chief sources are S. Africaand India. Sillimanite changes into amixture of mullite and cristobalite whenfired at a high temperature (15500C); thischange occurs without any significantalteration in volume (cf. KYANITE). Themineral is used as a refractory.Sillimanite Refractory. A refractorymaterial made from any of the

SILLIMANITE (q.v.) group of minerals.Such refractories generally contain about60% Al2O3; they have a high RuL (q.v.)and good spalling resistance. Sillimaniterefractories are much used in glass-tankand frit-melting furnaces, electric steel-furnace roofs, rotary kilns and in kilnfurniture for use in the firing of pottery-ware.Silver Lustre. Because silver itself tendsto tarnish, 'silver lustre' is, in fact, madefrom platinum, with or without theaddition of gold.Silver-marking of Glazes. Silver cutlery, orother relatively soft metal, will leave a verythin smear of metal on pottery-ware if theglaze is minutely pitted. A glaze may havethis defective surface as it leaves the glostkiln, or it may subsequently develop sucha surface as a result of inadequatechemical durability. The fault is alsoknown as CUTLERY MARKING.

Silvering. The formation of a thin film ofsilver on glass; such a film can beproduced by treatment of the glasssurface with an ammoniacal solution ofAgNO3: together with a reducing agent.A trace of copper is also often included.Simax A glass, of very high thermalendurance and good chemical resistancemade by the Kavaiier Glassworks,Sazava, Czechoslovakia .Simplex Kiln. A type of annular kiln inwhich two barrel-arch galleries are eachdivided by transverse walls into eight ornine chambers, each of which has gratesat the corners for the handfiring of solidfuel. This kiln can be used for the firingof facing bricks, roofing tiles, firebricksor (because the flue system permits eachchamber to be isolated) blue engineeringbricks.SiMONs. A more general term forSiALONS (q.v.) M is 'metal' substituted inthe silicon nitride structure. The term isnot widely used.

Sindanyo. An asbestos-free heatresistant board (Tenmat Ltd,Manchester).Singer's Test. A rough test for glaze-fitproposed by F. Singer (Sprechsaal, 50,779,1917); the glaze is placed in a dish ofthe biscuit ware and fired to its normalmaturing temperature; when cold, theglazed dish is examined for faults.Single-bucket Excavator. There are twoprincipal types of this machine: theMECHANICAL SHOVEL (q.v.) and theDRAG-LINE (q.V.).Single Crystal. See CRYSTALSTRUCTURE.Single Edge Notched Beam. SeeFRACTURE TOUGHNESS TESTS.Single Edge Precracked Beam. SeeFRACTURE TOUGHNESS TESTS.Single-fired Ware. See ONCE-FIREDWARE.Single-lap Roofing Tile. This term, asdefined in B.S. 1424 'Clay Single-lapRoofing Tiles and Fittings' includespantiles, double Roman tiles, flatinterlocking tiles and Pooles tiles.Single Layer Setting. Ware is placed inthe kiln in a single layer, to facilite rapidfiring. Such setting is also conducive tomechanical handling or to automatedsetting and dehacking.Single Roman Tile. See under ROMAN

TILE.Single-screened Ground RefractoryMaterial. A US term defined (ASTM-C71) as: A refractory material thatcontains its original gradation of particlesizes resulting from crushing, grinding, orboth, and from which particles coarserthan a specified size have been removedby screening (cf. DOUBLE-SCREENED).Single-taper Construction. Making brickarches or rings, using only one size oftaper brick.Single-toggle Jaw Crusher. A jawcrusher with one jaw fixed, the other jaw

oscillating through an eccentric mountednear its top. This type of jaw crusher hasa relatively high output and the productis of fairly uniform size.Sinter. As a verb, see SINTERING. AS anoun, a porous compact formed byheating a powder so that the contactpoints of the grains fuse together at atemperature below the melting point ofthe material.Sinter-active Powders. See ULTRAFINEPOWDERS.Sinter-Canning. An ENCAPSULATED-HIP(q.v.) technique, SOL-GEL (q.v.)technology is used to coat (e.g.) siliconnitride with alumina or zirconia gel,which is dried and sintered, to form adense layer of oxide, encapsulating thepreform before HIPing.Sinter-forging. See HOT FORGING.Sinter-HIP. Also known as CLADLESSHOT ISOSTATIC PRESSING. A form ofHiping in which gas pressures of 70 to200 MPa are applied direct to the surfaceof the compact, which has previouslybeen sintered to that density (92-96%theoretical) at which all the remainingpores are closed pores. The gas must bechosen to inhibit dissociation of thesintered material. The technique isuseful for large parts.Sintered Filter. A filter made fromsintered glass, sintered silica or unglazedceramic. B.S. 1752 refers to sintered diskfilters for laboratory use varying inmaximum pore size from Grade 00(250-500|im) to Grade 5 (<2|im). (cf.CERAMIC FILTER.)Sintered Glass. Glass-ware of controlledporosity used for filtration, aeration, etc.;it is made by carefully heating powderedglass so that the surfaces of the particlesbegin to melt and adhere to one another.Sintering. The general term for theDENSiFiCATiON by heat of a powdercompact to produce a polycrystalline

body. Densification may be by theformation of liquid phases which fillpores; by solid state diffusion or othermechanisms which also reduce surfaceenergy. The term was originallyrestricted to what is now known asSOLID-STATE SINTERING (q.v.) See alsoVITRIFICATION; LIQUID PHASE

SINTERING; OSTWALD RIPENING.

Sintering Aid. A material, typically anoxide, which reacts with the material tobe sintered to form small quantities of aliquid phase. See LIQUID PHASE

SINTERING.

Siporex. Trade-name: A lightweight (0.5kg/1) pre-cast concrete made fromPortland cement, fine sand, Al powderand water. The set aerated blocks areautoclaved. (Costain Concrete Co. Ltd.,London.)SIPRE. (S/derurgie et PRE) see PRE.Shall. Russian term for GLASS CERAMIC

(q.v.).Sitter-up. An assistant TEASER (q.v.) in aglass-works.Size. A solution used to treat the surfaceof pottery ware or of plaster moulds.Mould-makers' size is commonly asolution of soft soap. Decorators' size istraditionally based on boiled linseed oil;after its application, and after it hasbecome tacky, the lithograph is appliedand brushed down.SK Porosity Test. A method for thedetermination of the porosity ofaggregates; the principle is to fill thevoids in turn with mercury, air andwater. The method, primarily developedfor the testing of iron ores, was proposedby H. L. Saunders and H. J. Tress atSouth Kensington, hence the name 4SK';(J. Iron Steel Inst, 152, No. 2, 291P,1945).Skewback. A refractory block having aninclined face, or a course of such blocksforming the top of a wall, from which an

arch or furnace roof may be sprung; alsoknown as SPRINGER.

Skids. Refractory skids for use in pusher-type reheating furnaces in the steelindustry have been made from sinteredor fused alumina; they have a longservice life and permit more uniformheating of the ingots or billets than dowater-cooled metal skids.Skimmer. A single-bucket excavator inwhich the bucket travels along the boom,which is kept almost horizontal duringoperation. This machine is sometimesused for removing OVERBURDEN (q.v.).Skimmer Block, Skimmer-dam. Aspecial refractory block that is partlyimmersed in the molten glass in a tankfurnace to prevent impurities fromentering the feeder channel.Skimming Pocket. One of the smallrecesses, on the sides of a tank furnacefor the production of flat glass, by meansof which impurities on the surface of themolten glass can be removed. Theskimming pockets are usually located ashort distance before the FLOATERS

(q.v.).Skintling. The setting of bricks in a kilnso that courses of bricks lie obliquely tothe courses above and below.Skittle Pot. A small POT (q.v.) for glassmelting.Skiving. US term for a finishing process,on a lathe, of partially dried ceramicware such as H.T. insulators, ribbedformers or sparking-plug insulators.Skull. Metal remaining in a steel-castingladle at the end of teeming; its removaloften causes damage to the refractorylining of the ladle. The same term is usedfor the glass left in a ladle after most ofthe molten glass has been poured inglass-making; in the glass industry theusual spelling is SCULL.

Skull Melting. The refractory material tobe melted is contained in a water-cooled

crucible. The melt forms inside asintered shell (or skull) of the samecomposition, eliminating reaction with orcontamination by the crucible material.(Intermat Corp., Cambridge, Mass. BrickClay Rec. 168 (3) 1976 p24.Sky Firing. Burning wood slivers in thetop of an updraft biscuit kiln, to increasethe draught at the finish of the firing. AnAmerican craft pottery term.Skylight. A plate glass of low quality.Slab Glass. A block of optical glassresulting from preliminary shaping ofCHUNK GLASS (q.V.).Slabbing. (1) The fixing of ceramic tilesto fireplace surrounds, etc., to produce aprefabricated unit.(2) A form of failure of refractories, alsoknown as SHELLING. See SHELL.Slag. (1) The non-metallic fusion thatfloats on a metal during its extraction orrefining.(2) The product of reaction betweenfluxing materials and a refractoryfurnace lining.Slag Attack Tests. Refractories areattacked by the corrosive slags formedduring metallurgical processes. Varioussimulative tests have been devised toassess the resistance of refractories toslag attack.In the Crucible Test a well, drilled ormoulded in a block of the refractory tobe tested is filled with the selected slagand the block heated to the requiredtemperature, for a specified time. Theblock is then removed, cooled, sectionedand the slag/refractory interfaceexamined. The test is simple, but isstatic, and does not allow a temperaturegradient to be studied. The reactionlayer built up at the interface mayproduce erroneous results. The Pill Testis similar - a pellet of slag can bemeasured. In the Drip Test a stream ofslag pellets falls on to a refractory block

maintained at high temperature in afurnace. The test is dynamic, maintainingslag/refractory interaction, but heating isuniform and the interface forexamination is small. (ASTM C768specifies a drip test). The Rotary Drumtests are dynamic and a temperaturegradient can be maintained through thetest-piece. Test bars or a test panel ofrefractories are mounted in a rotatingfurnace into which slag pellets areintroduced, to pour down the test panel.B.S. 1902 Pt. 5.13 and ASTM C-874specify tests of this type. In the FingerDip test a bar of refractory material isimmersed in molten slag, or several barsmounted on a rotating disc to provide adynamic test. Slag chemistry is difficultto maintain and there is little or notemperature gradient across the testpieces, but the effects of slag and moltenmetal simultaneously can be assessed.Induction Melting provides erosive wearand dynamic slag conditions by theinduction stirring effect, maintains slagchemistry and can provide a controlledtemperature gradient across a test piece.(Cf. ASTM C621 and C622 which specifytests for the resistance of refractories tomolten glass; C987 which specifies a testfor vapour attack on refractories forfurnace superstructures; C288 whichspecifies a test for carbon monoxideattack on refractories; C454 whichdescribes the disintegration of carbonrefractories by alkali. B.S. 1902 Pts 3.10and 7.6 specify tests for the resistance ofrefractory materials and unshapedrefractories to carbon monoxide.Slag Cement. A mixture of granulatedblast-furnace slag and lime, togetherwith an ACCELERATOR (q.v.); very littleis now made (cf. PORTLAND BLAST-FURNACE CEMENT).Slag Line. The normal level of the slag/metal interface in the working chamber

of a metallurgical furnace. Therefractory lining of the furnace is liableto be severely eroded at this level owingto the improbability of chemicalequilibrium between slag metal andrefractory.Slag Notch. The hole in the refractorybrickwork of the wall of the hearth of ablast furnace permitting molten slag toflow from the furnace as and whennecessary. It is also sometimes known asthe CINDER NOTCH.Slag Pocket. A refractory-lined chamberat the bottom of the downtake of anopen-hearth steel furnace, or of a glass-tank furnace, designed to trap slag anddust from the waste gases before theyenter the regenerator.Slagsitalls. Glass ceramics made inEastern Europe from glasses from blast-furnace and other slags. They are used tomake durable building products, such astiles.SLAM. Scanning Laser AcousticMicroscopy (q.v.)Slant Mill. This type of BALL MILLconsists of an inclined cylinder whichrotates around a central horizontal axis,causing the charge of balls and feed toroll from one end of the mill to theother. The charge does not lift, the millhas no critical speeds, and less power isrequired for its operation compared to anormal ball mill. (H. E. Vivian lndustr.Ceram. 727,1979 p.265).Sled(ge) Kiln. See PUSHED BAT KILN.Sleek. A fine, scratchlike mark, withsmooth boundaries, made on glass by aforeign particle during polishing.Sleeper Block. See THROAT.Sleeper Wall. In structural brickwork, alow wall (generally built with openingscheckerwise) built to carry floor joists.Sleeve. See ROD COVER. Sleeve Bricksare refractory tubes used to line slagvents.

Slenderness Ratio. The ratio betweenheight and thickness of a wall.Slick. (1) To move a smooth metal blade,or piece of wood, over the surface ofplastic clay; the combined action ofpressure and movement tends to bringwater, soluble salts and fine clay particlesto the surface. If slicking occurs as aresult of movement of the knives orscrew in a pug, it causes lamination asthe affected clay surfaces do not readilyknit together again.(2) In USA a ceramic raw material issaid to be 'slick' if it is greasy to thetouch but is not plastic; such a material istalc or pyrophyllite .Slide-gate Valve. A device forcontrolling the flow of molten metal incasting. Two refractory plates slidelaterally or rotate against one another,so that the solid plate opens or closes thehole in the other plate.Slide-off Decal. The cover-coat andpattern layer are attached to the backinglayer with a water soluble adhesive, suchas dextrin. Also known as a water-slidetransfer.Slide-off Transfer. A type of transfer forthe decoration of pottery. The pattern isSILK SCREEN (q.v.) printed on lithopaper and then covered with a suitableplastic medium. Prior to use. the transferis soaked in water so that the pattern,still firmly fixed to the plastic, can be slidoff the paper and applied to the ware.During the subsequent decorating fire,the plastic coating burns away.Sliding. The faulty draining of wet-processenamel by the slipping downwards ofpatches of enamel; one cause isoverflocculation of the enamel slip.Sliding-bat Kiln. See PUSHED-BAT KILN.Sliding-gate Valve. See SLIDE-GATE

VALVE.SLIM. Single Leaf Insulated Masonry. Athin brick external wall is restrained by

brick partition walls and the roof. Anarrow cavity separates the brick wallfrom 50mm thick expanded polystyreneinsulation, lined internally with 10mm-thick plasterboard. The system andguidelines for architectural design detailsfor its use, were developed by BritishCeramic Research Ltd., Stoke-on-Trent.Slinger Process. A method used in USAfor the moulding of insulatingrefractories; the wet batch is thrown onto pallets by rotary machine -a 'slinger' -to form a column on a belt conveyor; thecolumn is then cut to shape, dried andfired.Slip. (1) The mechanism by which shearstress causes plastic deformation, bydriving lines of dislocation across certaincrystal planes, the slip or glide planes.See CRYSTAL STRUCTURE; FRACTURE.(2) A suspension in water of clay and/orother ceramic materials; normally aDEFLOCCULANT (q.v.) is added todisperse the particles and to preventtheir settling out. In the whitewareindustry, a slip is made either as a meansof mixing the constituents of a body (inwhich case it is subsequently dewatered,e.g. by filter-pressing) or preparatory toCASTING (q.v ). In vitreous enamelling, aslip is used for application of the enamelto the ware by spraying or dipping.(Cf. BRICK SLIP).Slip Casting. See CASTING.Slip Clay. A fusible clay (because offluxing impurities) with a fine-grainedstructure and low firing shrinkage. Itfires at a low temperature, producing anatural glaze.Slip Decoration. Application of acontrasting layer of slip (of a bodycomposition, rather than a glaze) todecorate ware. It may be appliedthrough a RESIST (q.v.) See SLIPWARE.Slip Glaze. US term for a glaze madeessentially from a fusible clay.

Sliphouse. Defined by COSHH in the'Production of Pottery, Approved Codeof Practice' 1990 to 'include any placewhere machinery is used for mixing clayand/or other materials to form slip.'Slip Kiln. A heat resistant trough placedover a heated flue; water can beevaporated from slip placed on thetrough. This method of dewatering wasreplaced by filter-pressing.Slip Plane. See SLIP (1).Slip Resistance. An important propertyof floors and tiled surrounds toswimming pools. It is measured byinstruments such as the TORTUS (q.v.)and the TRRL PENDULUM (q.v.) whichtake account of (deliberate) macroscopicirregularities in tiles and tiled surfaces,as well as measuring the (microscopicallydetermined) friction between them andtypical footwear materials.Slip Trailing. See TRAILING.Slipware. An early type of pottery(revived by studio potters) usuallyhaving a red body and a lead glaze,decorated with white or coloured slip bydipping, trailing or sgraffito. Englishslipware was made in the 17th and early18th century, the chief centres beingStaffordshire, Kent, Sussex and the WestCountry.Slit Kiln. A fast-fire kiln, usually a roller-hearth kiln, whose width is much greaterthan its height. The ware, usually tiles, isfired one-high.Slop Glaze. A suspension of glaze-forming materials prepared forapplication to ceramic ware, usually bydipping or spraying. The materials arekept in suspension by the presence ofdispersed clay and by the highconcentration of solids. A small amount(about 0.02%) of calcium chloride is alsoadded to prevent the glaze from settingin the glaze tub and to act as athickening agent.

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Slop Moulding. The hand-moulding ofbuilding bricks by a process in which theclay is first prepared at a water-contentvarying from 20 to 30% depending onthe clay. The wet clay is thrown into awooden mould, pressed into the corners,and the top surface is finally strucksmooth with a wet wooden stick. Thefilled mould is set on a drying floor untilthe clay has dried sufficiently tomaintain its shape; the mould is thenremoved and the drying process iscompleted.Slop Peck. The volume of slip thatcontains 20 Ib of dry material. See alsoSTANDARD SLOP PECK.

Slop Weight. The weight (oz) per pint ofa suspension of clay flint, etc., in water.See PINT WEIGHT.Slotting Wheel. A thin abrasive wheelused for cutting slots or grooves; suchwheels are usually made with an organicbond.Slow. The bricks with smaller radialtaper in a two-taper system of arch orring construction. The opposite ofSHARP.

Slow Crack Growth, CRACKPROPAGATION (q.v.) can occur inceramics at values of STRESS INTENSITYFACTOR (q.v.) much below the criticalvalue KIC needed to initiate BRITTLEFRACTURE (q.v.). The susceptibility tocracking of glasses and many oxideceramics is greatly increased by chemicalreaction between stressed cracks,especially small surface cracks, andenvironmental agents, especially water.Under these conditions there are threeregions of crack growth. The third isgoverned by the intrinsic properties ofthe material. The second (a plateau)occurs when the crack growth rate islimited by non-availability of reactant.The first is most important. In it, stressesare usually well below the critical stress

intensity, and the crack growth iscontrolled by the reaction rate. Suchslow crack growth is also termed stresscorrosion, and may be more rapid athigher temperatures. The crack velocity\) is related to the stress intensity K1 bythe power law x> = AK/1 where A is aconstant and n is the slow-crack growthexponent. A low value of n indicatesthat the material is susceptible to slowcrack growth over a broad range ofstresses. A high value of n meanssusceptibility over a narrow stressrange. Constant load stress-rupture tests(static FATIGUE (q.v.) tests) plot thestress against time to failure onlogarithimic axes and have a slope of-XIn. Strength plots against loading rate,again on logarithmic axes, have a slopeof 1/(1 + n). (Dynamic FATIGUE tests.).Grain boundary sliding, diffusion andother intrinsic deformation processeslead to CRACK NUCLEATION (q.v.),CRACK PROPAGATION (q.v.) andcoalescence. At moderate, rather thanhigh, temperatures, these processes mayonly be effective in causing crackgrowth in the already highly-stressedregion near the tip of an existing crack.This is also known as slow crack growth.At high temperatures, these processescause CREEP (q.v.) fracture, and arethose same atomic mobility processesactive in SINTERING (q.v.).Slug. (I)A rough piece of prepared claybody sufficient for making one piece ofware, by throwing or by jiggering forexample.(2) A fault in a glass-fibre productresulting from the presence of non-fibrous glass; also called SHOT.Slugged Bottom. A fault in a glasscontainer characterized by the bottombeing thick on one side and thin on theother; also called a WEDGED BOTTOMand (in USA) HEEL TAP.

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Slum. A US term for fireclay containinga high concentration of fine coalparticles.Slumping. Serious deformation of a brickor column setting of bricks under its ownweight.Slump Test. (1) A rough test for theconsistency of freshly mixed concrete interms of the subsidence of a truncatedcone of concrete when upturned from abucket; ASTM - C143 and B.S. 1881.(2) A works' test for the consistency ofvitreous enamel slip; for details seeIRWIN SLUMP TEST.Slurry. A suspension with high solidscontent.Slurry infiltrated fibrous castable(SIFCA). A refractory castablecontaining up to 16% steel fibres. Thefibres are filled into the mould first,followed by a fine-grained castable, thisapproach overcoming previousdifficulties of mixing and placing whichlimited the fibre content to c. 2 vol%(US Pat. 4266255).Slurry process The production ofrefractory fibres by extruding asuspension as a filament, drying andcalcining.Slushing. A method for the applicationof vitreous-enamel slip to ware,particularly to small awkwardly-shapeditems. The slip is applied by dashing iton the ware to cover all its parts, excessthen being removed by shaking the ware.A slip of 'thicker' consistency thannormal is required for this process.Smalt or Powder Blue. A fused mixtureof cobalt oxide, sand and a flux, e.g.potash. It is sometimes used as a bluepigment for the decoration of pottery orfor the colouring of glass or vitreousenamel (cf. ZAFFRE).Smear. In the glass industry the word hasthe special meaning of a surface crack inthe neck of a glass bottle (cf. CHECK).

Smectite. Obsolete name for the claymineral HALLOYSITE (q.v.).Smock, Potter's Smock, OVERALLS (q.v.)worn by (male) operatives in the potteryindustry, which are designed withoutlapels, pockets and other stitchedfeatures; which have short sleeves; andwhich are made from the smoothartificial fibre, terylene. They are thusfree of dust traps. See also DUST,RESPIRABLE DUST, HEALTH ANDSAFETY.Smoked. Glass or glaze discoloured by areducing flame.Snagging. Rough grinding with anabrasive wheel to remove large surfacedefects; wheels with an organic bond aregenerally used.Snaking. (1) Progressive longitudinalcracking in continuous flat glassproduction.(2) Variation in the width of the sheet inglass drawing.Snakeskin Glaze. A decorative effectobtainable on potteryware by theapplication of a glaze of high surfacetension, e.g. 320 dynes/cm. A quotedglaze formula for the production of asnakeskin glaze maturing at 11400C is:(0.3 PbO; 0.3 MgO; 0.2 CaO; 0.2 ZnO).1.5 SiO2. 0.2 Al2O3.Snap. A device for gripping formed glassduring polishing.Snap-header. See HALF-BAT.Soaking. As applied to the firing ofceramic ware this term signifies themaintenance of the maximumtemperature for a period to effect adesired degree of vitrification, chemicalreaction and/or recrystallizationSoaking Area. The part of a cross-firedglass-tank furnace between the GABLEWALL (q.v.) and the first pair of ports;also known as the FRITTING ZONE.Soaking Pit. In the steel industry, arefractory-lined furnace for the reheating

of ingots. In the glass industry, a furnacefor bringing pots of glass to a uniformtemperature.Soap. See PUP.Soapstone. A popular name forSTEATITE (q.V.).Socket, (of sewer pipe) see BELL.Soda Ash. Anhydrous sodium carbonate,Na2CO3. A major constituent of mostglass batches. Together with sodiumsilicate it is used to deflocculate clayslips.Sodium Aluminate. An electrolyte usedas a mill addition in the preparation ofacid-resisting vitreous enamel slips; 0.10-0.25% is generally sufficient.Sodium Antimonate. Na2O-Sb2O5.

1/^H2O An opacifier for dry-processenamel frits for cast-iron enamel-wareand for some acid-resistant frits for sheetsteel enamels. It is also a source ofantimony for yellow ceramic colours.Sodium Carboxymethylcellulose. SeeCARBOXYMETHYLCELLULOSE.Sodium Cyanide. NaCN; used as aneutralizer in vitreous enamelling.Sodium Fluorsilicate. See SODIUMSILICOFLUORIDE.Sodium-line Reversal Method. Atechnique for the measurement of flametemperatures. If a black-body is viewed,by means of a spectroscope, through aflame that has been coloured by sodium,there will be some temperature of theblack-body at which its brightness in thespectral region of the NaD line will equalthe brightness of the light transmitted inthis region through the flame, plus thebrightness of the NaD lines from theflame itself. At this temperature thespectrum of the black-body as seen inthe spectroscope is continuous; there is areversal in contrast above or below thistemperature. The method was firstdescribed by C. Fery (Compt. Rend.y 137,909,1903).

Sodium Niobate. NaNbO3; a compoundbelieved to be ferroelectric and havingpotential use as a special electroceramic.The Curie temperature is 3600C.Sodium Nitrate. NaNO3; used as anoxidizing agent in some glass batchesand enamel frits. The old name wasSaltpetre.Sodium Nitrite. NaNO2; added in smallquantities to vitreous enamels to toprevent rust-spotting and tearing;0.1-0.25% is usually sufficient.Sodium Phosphate. The hexa-metaphosphate (generally underthe proprietary name CALGON) is usedto control the viscosity of slips inthe pottery and vitreous enamelindustries.Sodium Silicate. Name given to fusedmixtures in which the Na2OiSiO2 rationormally varies from about 1:2 to 1:3.5;care should be taken in selecting thegrade best suited to the purpose in view,e.g. as a deflocculant or as an air-settingbond for refractory cements, etc. Morealkaline silicates are used for cleaningmetal, prior to enamelling for example.A classification of sodium silicates isgiven in B.S. 3984.Sodium Silicofluoride. Na2SiF6; used tosome extent as a flux in vitreous enamelsand as a constituent of acid-resistingsilicate cements.Sodium Sulphate. See SALT CAKE.Sodium Sulphate Test. A test claimed toindicate the resistance of a clay buildingmaterial to frost action. The test-piece issoaked in a saturated solution of sodiumsulphate and is then drained and dried;the cycle is repeated and the test-piece isexamined for cracks after each drying.The principle underlying the test is thatthe stresses caused by the expansion ofsodium sulphate as it crystallizes are, tosome extent, similar to the stressescaused by water as it freezes. The test

has also been used to reveal laminationspresent in bricks.Sodium Tannate. Sometimes used as adeflocculant for clay slips; the effect ismarked, only a small proportion beingrequired. The material used for thispurpose is generally prepared fromNaOH and tannic acid; the formershould be in excess and the pH shouldbe about 8-9.Sodium Tantalate. NaTaO3; aferroelectric compound having theilmenite structure at room temperature;the Curie temperature is approx. 475°C.Of potential interest as a specialelectroceramic.Sodium Uranate. Na2O.2UO3.nH2O; hasbeen used as a source of uranium forcoloured glazes; the colour can varyfrom ivory through yellow and orange todeep red depending on the glazecomposition.Sodium Vanadate. NaVO3; aferroelectric compound having potentialuse as a special electroceramic. TheCurie temperature is approx. 3300C.Sofim-Fichter Kiln. A gas-fired open-flame tunnel kiln; its novel feature, whenintroduced in about 1935, was the designof the pre-mix burners. The namederives from the initial letters of Societedes Fours Industriels et Metallurgiques,the designers of the original kiln, andFichter (of Sarreguemines) who designedthe burners.Soft. As applied to a glass or glaze,this word means that the softeningtemperature is low; such a glass orglaze, when cold, is also likely to berelatively soft, i.e. of lower than averagehardness, in the normal sense.Soft Ferrite. FERRITE (q.v.) materialswhose magnetization is easily lost inthe absence of an applied field.Soft Fire. A cool flame, deficient inair.

Soft-mud Process. A process for theshaping of building bricks from clay at awater content of about 35%. Theprepared wet clay is fed into sandedmoulds which are then shaken or jolteduntil the clay fills the mould; because ofits THixoTROPY (q.v.), after the joltingceases the clay stiffens sufficiently for thebricks to maintain their shape. Theprocess can form the basis of hand-making or, more commonly, it can bemechanized as in the BERRY MACHINE(Berry & Son, Southend-on-Sea,England) or in the ABERSON MACHINE(Aberson, Olst. Holland).Soft-paste or Fritted Porcelain. A typeof porcelain made from a soft bodycontaining a glassy frit and fired at acomparatively low temperature(110O0C). The most famous soft-pasteware was that produced in the 18thcentury at the Sevres factory in France,and at Chelsea, Derby, Bow, Worcesterand Longton Hall in England. TheCOMBINED NOMENCLATURE (q.V.) Statesthat soft porcelain contains less aluminabut more silica and fluxes than hardporcelain. See PORCELAIN.Softening Point. Generally, the indefinitetemperature at which a ceramic materialbegins to melt. The term has a definitemeaning however, when referring toglass of density near 2.5 namely thetemperature at which the viscosity is107 6 poises; this viscosity corresponds tothe temperature at which tubes, forexample, can be conveniently bent andwas first proposed as a basis fordefinition by J. T. Littleton (/. Soc. GlassTech. 24.176, 1940). Also known as the7.6 TEMPERATURE Or the LITTLETONSOFTENING POINT.Solar Furnace. A particular type ofIMAGE FURNACE (q.v.) in which thesun's rays are focussed to provide theheat.

Solarization. An effect of strong sunlight(or artificial ultraviolet radiation) onsome glasses, causing a change in theirtransparency. Glasses free from arsenicand of low soda and potash contents areless prone to this defect.Solder Glass. The glass powder used inmaking GLASS-TO-METAL SEALS (q.v.) isessentially lead borate.Soldier Blocks. Refractory blocks set onend. In the glass industry the term isparticularly applied to blocks that extendmore than the depth of the glass in afurnace.Sole. The refractory brickwork formingthe floor of a coke oven; as the charge ofcoal-which is subsequently transformedinto coke-rests on this brickwork, and asthe coke is pushed out of the oven bymeans of a mechanical ram, the sole issubjected to severe abrasion.Sole-flue Port Brick. See RIDER BRICKS.Sol-gel Process. Ceramic mixed oxidesare prepared by co-precipitating thecomponent metal oxides or precursors asgels from an aqueous mixture ofcomponents. The gelled particles areseparated and sintered. Close control ofchemical composition is possible(UKAEA, Br. Pat. 1253807, 1971 andother later patents).Solid Brick or Block. Defined in BS.3921 as a brick or block in which holespassing through, or nearly through, thebrick (or block) do not exceed 25% of itsvolume, and frogs do not exceed 20% ofits volume' (cf. SOLID MASONRY UNIT).Solid Casting. See under CASTING.Solid Electrolyte. A ceramic capable ofconducting electricity which acts as theelectrolyte in batteries, fuel cells oroxygen sensors. Electricity is conductedby the movement of electrons, holes orcharged ions.Solid Masonry Unit. Defined in ASTM -C43 as: 4A unit whose net cross-sectional

area in every plane parallel to thebearing surface is 75% or more of itsgross cross-sectional area measured inthe same plane' (cf. SOLID BRICK).Solid Solution. A crystalline phase, thecomposition of which can, within limits,be varied without the appearance of anadditional phase. In Fig. 5 (p230), a solidsolution of mullite is shown to existranging in composition from that of puremullite (60 mol% Al2O3) to 63 mol%Al2O3. A complete series of solidsolutions exists between forsterite(Mg2SiO4) and fayalite (Fe2SiO4); thesesolid solutions occur naturally as themineral olivine and are important in thetechnology of forsterite refratories.Solid-state Sintering. Densification ofpowder compacts by heat, below theirmelting points. Initially the compactshrinks because of material transport byviscous or plastic flow, and volumediffusion. Evaporation-condensation andsurface diffusion change the shapes ofthe pores, so that the original particulatestructure is replaced by a polycrystallinebody containing a network of pores.Grain growth then occurs by grainboundary migration, producing closedpores which gradually shrink asvacancies diffuse to the surface. Allprocesses take place in the solid state.Solidus. In a binary equilibrium diagramwithout solid solution (see left-hand sideof Fig. 5, p230, representing the binarybetween silica and mullite), the solidus isthe line showing the temperature belowwhich a given composition, when inchemical equilibrium, is completely solid.At temperatures between the solidusand the LIQUIDUS (q.v.) a compositionwill contain both solid and liquidmaterial. In a ternary system withoutsolid solutions, the solidus is a plane.Soluble Salts. Salts, particularlysulphates or carbonates of Ca, Mg and

Na, present in some clays used inceramic manufacture or subsequentlyentering the fired product from othersources. If present in the clay, these saltstend to migrate to the surface duringdrying. In the pottery industry this cancause trouble during glazing; in the wetprocess of body preparation however,these salts are mostly eliminated duringfilter-pressing. If present in firedproducts (particularly bricks or glazedtiles) or if entering these products frommortar, cement or other sources, solublesalts may cause EFFLORESCENCE (q.v.),SCUMMING (q.V.), Or SALT EXPANSION(q.v.). B.S. 3921 specifies a method fordetermining soluble salts in bricks.Bricks with low (L) salt contentclassification have Ca 0.3%; Mg, K, Na0.03% each; SO4 0.5%. ASTM C867specifies a photometric method fordetermining soluble sulphates inwhitewares.Solution Ceramics. A type of ceramiccoating introduced by Armour ResearchFoundation, USA. In the originalprocess (Brit. Pat., 776 443, 5/6/57) asolution containing a decomposablemetal salt is sprayed on the hot surfacethat is to be coated. A subsequentdevelopment (Brit. Pat., 807 302,14/1/59)refers to the application of a coating ofvitreous enamel or thermoplastic resin tothe surface that has been flame-sprayedwith the solution; this is claimed to resultin a vitreous-enamelled surface havingimproved resistance to thermal shock.Sorel Cement. A cement, usedparticularly in monolithic flooringcompositions, first made by StanislausSorel (Comp. Rend., 65, 102, 1867).Calcined magnesia is mixed with a 20%solution of MgCl2, interaction forming astrong bond of Mg oxychloride,Mg3(OH)2CUH2O. In flooringcompositions, various fillers are used,

e.g. sawdust, silica, asbestos, talc;colouring agents are also added. Therelevant British specification is B.S. 776,there are ASTM specifications forsampling and testing the constituentmaterials.SORSI (Self Organised Sieving System).An icosahedral sieving chamber can berotated on two great circular supports.Ten triangular surface elements betweenthese can carry several sieving surfaces.The system operates in continuous or inbatch mode, the latter being preferablefor powder characterization. The residueon the sieve after a prolonged period canbe calculated.Sorting. The removal, from potterytaken from the glost kiln, of adheringbedding material and/or particles thathave become detached from the kilnfurniture. Sorting is usually done with asmall pneumatic tool.Soundness. As applied to portlandcement, this term refers to its volumestability after it has set (cf.UNSOUNDNESS).Souring. (1) An alternative term forAGEING (q.v.).(2) The storage for a short while of themoistened batch for making basicrefractories; some magnesium hydroxideis formed and this acts as a temporarybond after the bricks have been shapedand dried. If souring is allowed toproceed too far, cracking of the bricks islikely during drying and the initial stagesof firing. The high pressure exerted bymodern brick presses generally givessufficient dry-strength without the bricksbeing soured, and this process istherefore now generally omitted.Space Group. The 3-dimensionalsymmetry of a CRYSTAL STRUCTURE(q.v.) which is developed by applyingsymmetry operations (translation,rotation, reflection) to the 14 BRAVAIS

LATTICES (q.v.). It is the group of 230such operations which leave the infinitelyextended regularly repeating pattern of acrystal unchanged.Space Lattice. See CRYSTALSTRUCTURE; also RECIPROCAL LATTICE.Spacer. The tapered section of a pugjoining the barrel to the die; in thissection beyond the shaft carrying thescrew or blades the clay is compressedbefore it issues through the die.Spacer Lug. One of the projections onthe edge of a glazed ceramic tile orpaving brick ensuring correct width ofjoint; for sizes see BS 6431 and ASTM -C7, respectively.Spalling. (1) The cracking of a refractoryproduct or, in severe cases, the breakingaway of corners or faces. The principalcauses are: thermal shock, crystallineinversion, a steep temperature gradient,slag absorption at the working face witha consequent change in properties, orpinching due to inadequate expansionallowance (see also HOT-PLATESPALLING TEST; PANEL SPALLING TEST).(2) The chipping of vitreous enamelwarein consequence of internal stress.Spaltplatten. See SPLIT TILES.Spandrel Glass, ARCHITECTURAL GLASSused in external cladding and curtainwalls.Spanish Tile. A fired clay roofing tilethat, in section, is a segment of a circle;the tile tapers along its length so that thelower end of one tile will fit over theupper end of the tile below (cf. ITALIANTILES).Spark Plug; Sparking Plug (UK,obsolete). The older type of ceramiccore for spark plugs was made ofELECTRICAL PORCELAIN (q.V.); themodern type is sintered alumina. Thecores, formerly shaped by pressing,rotary tamping or injection moulding,are made by automated dry-bay isostatic

pressing: they are fired at 1600-1650C.The standard size is 14 mm.Spark Test. A method for the detectionof pin-holes in a vitreous enamel surfaceby the discharge of an electric spark.Sparrow-pecked. See STIPPLED.Spathic Iron. Ferrous carbonate FeCO3,used as the basis of many ceramicpigments.Spatterware. A type of mottled ceramicartware; a white or coloured glaze isspattered irregularly over the dippedglaze before the glost firing.Special Ceramics. A generic term fornon-clay ceramics for electronic andengineering applications, more usedwhen such materials were novel.Special Oxides. See OXIDE CERAMICS.Specific Gravity. See APPARENTSPECIFIC GRAVITY; BULK SPECIFICGRAVITY; TRUE SPECIFIC GRAVITY.When the term is used withoutqualification it may be assumed that truespecific gravity is meant.Specific Heat. The mean specific heat ofmost traditional ceramics lies between0.22 and 0.26 (20-5000C); 0.23-0.28 (20-10000C). The principal exception iszircon: 0.17 (20-5000C) and 0.18 (20-10000C).Specific Surface. The total surface areaper unit weight of a powder or poroussolid; in the latter case the area of theinternal surfaces of the pores is included.The usual units are m2/g. Methods ofdetermination include GAS ADSORPTION(q.v.) and PERMEABILITY (q.v.). See alsoSURFACE FACTOR.Speckled Ware. Vitreous enamelwarehaving small particles of one colouruniformly scattered in an enamelbackground of a different colour.Spectroscopy. A great variety ofspectroscopic techniques has beenapplied to elucidating the structure andproperties of ceramics. Details must be

sought in general texts on physical andchemical techniques. Some of the morecommon are listed by theirabbreviations.Specular Gloss (45°). An operationaldefinition of this property, relevant inthe surface evaluation of glazed orenamelled surfaces is as follows (ASTM-C346): 'The ratio of reflected to incidentlight, times 1000, for specified aperturesof illumination and reception when theaxis of reception coincides with themirror image of the axis of illumination'.A test for 60° Specular Gloss is given inASTM - C584.'Speedy' Moisture Meter. The apparatusmeasures the acetylene evolved whenthe moisture in the test sample is reactedwith calcium carbide.Speedycal. A process and equipment forthe rapid application of decorativetransfers, developed by Matthey PrintedProducts and F. Malkin & Co.Speeton Clay. A clay occurring in theLower Cretaceous strata; the name wasfirst applied to a blue clay outcrops atSpeeton, between Bridlington and Filey(Yorkshire, England).Spengler Press. Trade-name: (Spengler-Maschinenbau G.m.b.H., Berlin.) Acam-operated automatic rotary table drypress for bricks and tiles.Spew. See DUST.Sphalerite. Zinc Blende, (Zn,Fe)S, amineral with a cubic structure. BN canalso assume this structure.Sphene (or Titanite). CaO-SiO2TiO2;m.p. 1386°C. This mineral has beenfound in the ceramic colour known asCHROME-TIN PINK (q.V.).Spherical. See MORPHOLOGY.Spheroidizing. The production ofspherical particles, e.g. by calcininggelled particles produced from dropletsof pre-determined size, comprisingpolymer and refractory precursor.

Spider. ( I)A metal unit with two ormore radial arms; for example, a spideris used in the mouthpiece of a pug tohold a core or to break up laminations.(2) The term is sometimes used as analternative to CENTRE BRICK (q.v.).(3) A star-shaped fracture in a vitreousenamelled surface.(4) A multi-legged refractory brick archcapped with refractory castable, used insome vertical shaft preheaters in cementmanufacture.Spigot. The part of a sewer pipe jointwhich is overlapped by the socket of thenext pipe.Spike Ramming, Spiking. Theinstallation of a refractory lining,particularly in an induction furnace, bycompacting successive layers of dryaggregate with a spiked steel shaft,ensuring that each layer is bonded withthe previous one.Spiked Bottom. One form of bottom fora CONVERTER (q.v.); it is of monolithicrefractory material, air passages beingformed by spikes which pierce thebottom while the refractory material isbeing rammed into place (cf. TUYERE

BLOCK BOTTOM and TUBE BOTTOM).Spinel. A group of isometric mineralshaving the same general structure andformula - R2+O-R2

3+O3, where R2+ is adivalent metal (Mg, Fe2+, Zn, Co, Ni,etc.) and R3+ is a trivalent metal (Fe2+,Cr, Al). In a normal spinel all thedivalent cations occupy tetrahedral siteswhile the trivalent cations occupyocathedral sites; in an inverse spinel thedivalent cations occupy octahedral siteswhile the trivalent cations occupy bothtetra- and octahedral sites. The typemineral, to which the term 'spinel' refersif not qualified, is magnesium aluminate,MgO-Al2O3; this mineral is sometimessynthesized, by firing a mixture of theconstituent oxides at a high temperature,

for use as a refractory material. Anotherimportant group of spinels, knowncollectively as FERRITES (q.v.), are usedas FERROMAGNETICS (q.v.). For otherspinels see CHROMITE, HERCYNITE,

PICROCHROMITE, MAGNESIOFERRITE.Spin-Flash Drying. This process is inessence fluidized-bed drying. Filter cakeis introduced into the chamber by ascrew feeder and drops to the bottom. Astirrer breaks up the particles until theyare small enough to be carried up by hotair to a cyclone via a central constrictionof variable diameter which acts as aclassifier. The dried powder does nothave the good flow properties requiredfor automatic pressing.Spinodal Decomposition. A diffusionlimited process of phase separationwhich takes place in thermodynamicallyunstable multicomponent (solid)solutions. A spinode on an equilibriumdiagram is a cusp, a point at which thereare two real tangents.Spiral Bricking. A method of bricking aLADLE (q.v.) in which the first course ofthe sidewall comprises special shapesforming an incline. The spiral iscompleted with standard (semi-universal) bricks. Closure bricks are notneeded. The brickwork is a continuousspiral, instead of separate rings. B.S.3056 Pt. 8 gives further details.Spiralling. Circumferential movement ofbrick rings relative to the casing of acylindrical kiln and to each other. Someaxial movement may also take place.The effect may take years to becomeapparent, or may swiftly affect refractorystability and wear.Spiratron. In this fettling machine biscuittableware traverses a spiral path througha chamber, in which it is smoothed bytumbling hardwood blocks. (CentralCeramic Services Ltd. Ceramics 20, (242)13,1969).

Spissograph. An automatic machine forchecking the time of set of cement ormortar. (BuIlASTM, No. 170, 79,1950.)Spit-out. Pin-holes or craters sometimesoccurring in glazed non-vitreousceramics while they are in the decoratingkiln. The cause of this defect is theevolution of water vapour, adsorbed bythe porous body, during the periodbetween the glost firing and thedecorating firing, via minute cracks inthe glaze.Split. (1) A brick of the shape of aSTANDARD SQUARE (q.V.) Split down itslength, see Fig. 1, p39; commonly a9 x AVi in. (228 x 114 mm) brick with athickness of IV4, Wi or 2 in. (31.5, 37 or51 mm) (Also known as a SCONE.)

(2) A glass bottle containing 6Vi fl. oz(200 ml) (for mineral water).(3) A crack that penetrates glass-ware,as distinct from a CHECK or VENT (q.v.).Split Rock. US term for the grade ofFIRESTONE (q.v.) that is most suitablefor use as a refractory.Split Tiles. These tiles are formed doubleand separated after firing, to obtainsingle tiles. They have characteristicridges on their backs, and may be glazedor not. The German word is Spaltplatten,which has gained some currency as animport.Splitter. A refractory restriction in aduct, to change the gas flow pattern.Spluttering. Glaze fragments from theware fusing to the setters and shelves.Spodumene. A lithium alumino-silicate,Li2O.Al2O3.4SiO2; it occurs in Rhodesia,Canada, USA and Brazil, and thecommercial product usually containsabout 6.5% Li2O. The a form changesirreversibly at approx. 9000C to the pform with a considerable expansion; theP form is a constituent of some specialceramic bodies of zero thermalexpansion.

Sponge, Sponging. The smoothing out,with a moistened sponge, of slightsurface blemishes on pottery-warebefore it is dried.Spongy Enamel. Vitreous enamelwarethat is faulty because of local highconcentrations of bubbles.Spoon Proof. A specimen of moltenglass for analysis. These are taken atvarious stages of melting.Spout. A refractory block shaped tocarry molten glass, usually to a formingmachine; see also FEEDER SPOUT andPOT SPOUT.Sprag. See TWIG.Spray Drying. The process of dewateringa suspension, e.g. clay slip, by sprayingthe suspension into a heated chamber,the dried powder being removed fromthe bottom of the chamber. Spray dryingis particularly used to prepare granulatefor pressing tiles and tableware. Thegranulate comprises free-flowing roundor toroidal particles.Spray Frost. A ceramic or organicmaterial, sprayed onto a glass surfaceand fired, to simulate acid-etching.Spray - ICP. See INDUCTIVELY

COUPLED PLASMA.Spray Sagging. The appearance of wavylines on the vertical surface of vitreousenamelware after it has been sprayedand before the slip coating is dried. Thefault is caused by incorrect adjustmentof the fluidity and thixotropy of theslip.Spray Welding. A process for thelocalized repair of cracks in therefractory brickwork of a gas retort orcoke oven; a refractory powder is carriedby a stream of oxygen into an oxy/coal-gas flame so that the powder fuses on thebrickwork to seal the selected damagedarea on which it is projected. Thistechnique was first used by T. F. E.Rhead, City of Birmingham Gas Dept.

(Trans. Inst. Gas Engrs., 81, 403, 1931)(cf. AIR-BORNE SEALING).Spreader Block. See DEFLECTINGBLOCK.Sprigging. The decoration of potteryvases, etc., by affixing clay figures(frequently classical) or other motifs toform a bas-relief. The figures are pressedin a biscuit pottery mould separatelyfrom the ware and are made to adhere tothe ware by means of clay slip (cf.EMBOSSING).Springback. The expansion of a compactafter dry-pressing, when the pressure isremoved and the compact is ejectedfrom the die. Springback is greater athigher compaction pressures. It may beprevented by applying axial pressure{hold-down) to the compact duringejection.Springer. See SKEWBACK.Springing. The radially outwardmovement or thrust of brick arches orrings when being constructed orremoved, a problem if axial restraint islacking.Sprue. In vitreous enamelling this term issometimes applied to the frit that buildsup at the tap-hole of a frit-kiln. Fromtime to time pieces fall into thequenched frit and cause trouble inmilling because of their hardness.Sprung Arch; Sprung Roof. An arch, orfurnace roof, the brickwork of which issupported solely by SKEWBACKS (q.v.);(cf. SUSPENDED ARCH Or ROOF).Spur. An item of KILN FURNITURE (q.v.)in the form of a tetrahedron withconcave faces and sharp points on whichthe ware is set; see Fig. 4, pl77.Sputtering. A DC or RF voltage isapplied to ionize argon gas. Theaccelerated Ar ions hit a solid target, sothat the material of the target is'sputtered' on to the article to be coated.Targets of complex composition can be

used, and higher plating productivity isachieved at lower temperatures thanwith other methods.Square. (1) See STANDARD SQUARE.(2) A SQUARE of roofing tiles is 100 ft2

(c.9m2) as laid.Square Pitch. See under PITCH.Squatting, SLUMPING (q.v.), thoughslumping is used to refer to the mostsevere cases.Squeegee Process. See SCREENPRINTING. The term SQUEEGEE OIL isused, particularly in the US industry, forthe mixture of oils used to suspend aceramic or enamel colour for silk-screenprinting. Similarly, the term SQUEEGEEPASTE is used for the mixture of oils,colours and flux used in this process ofdecoration.Squeeze Casting. A hybrid metal-forming process, combines casting andforging, applying a high pressure (70N/m2) as the liquid metal solidifies. Theprocess has been applied to producemetal-matrix composites.Squint. A building brick with one endchamfered on both edges so that thebrick can be used at an oblique quoin.SRBSN. Sintered Reaction-BondedSilicon Nitride.SR Fusion-cast Refractory. A Frenchfusion-cast refractory, e.g. glass-tankblock, made by a process that largelyeliminates the cavities that occur as aresult of shrinkage while the block coolsfrom the molten state. The block is madeby a so-called high-filling process (SR =Sur-Remplis) and is then heat-treated,(cf. DCL, RO and RT).SRA Load Test. Automaticallycontrolled RuL (q.v.) equipmentdesigned by the Special RefractoriesAssociation, USA (Bull. Amer. Ceram.Soc, 42, (12), 741, 1963).SSN. Sintered Silicon Nitride.Stabilized Zirconia. See ZIRCONIA.

Stack or Shaft. The upper part of a blastfurnace, widening from the THROAT(q.v.) at the top to the LINTEL (q.v.) atthe bottom. This part of the furnace islined with refractories selected for theirresistance to abrasion and to thedisintegrating action of the carbonmonoxide present in the stackatmosphere.Stacked Fibre, Stacking. Ceramic fibreblanket aligned with the planeorientation normal to the lining.Stack Kiln. An old type of up-draughtintermittent kiln for the firing ofbricks. It was usually round, the featureof the kiln being the brick cone builton top of the kiln; waste gases passedinto this cone, and thence to theatmosphere, through openings in thekiln crown.Staffordshire Blues. See underENGINEERING BRICKS.

Staffordshire Cones, PYROMETRICCONES (q.v.) made by Harrison MayerLtd., Stoke-on-Trent, England. Forsquatting temperatures see Appendix 2.Staffordshire Kiln. A particular design oftransverse-arch kiln: it is fired from thetop into combustion spaces in thesetting. Such kilns were used for firingbuilding bricks. The original design waspatented by Dean, Hetherington & CO.in 1904.Stahlton System. Prefabricated buildingelements made from hollow clay blocks,a row of which is united by prestressedwires and cement filling; each reinforcingwire is pre-stressed individually andanchored singly. The elements are usedin floors and ceilings. The name derivesfrom the German words Stahl (steel) andton (clay).Stain. (I)A coloured imperfection onthe surface of ceramic ware.(2) An inorganic colouring material usedin the preparation of under-glaze and

on-glaze pottery colours, for colouringpottery bodies and glazes, or fordecorating the surface of glassware.(3) To produce yellow, amber or redcolours in glass by applying to its surfacecompounds of Cu and/or Ag as apowder, the latter usually being 'diluted'with an inert material, e.g. sillimanite.(4) An organic colorant (which burnsout during firing) used to identifybatches of different slips.Stamping. A process for the application,by hand or by machine, of decoration topottery-ware; a rubber stamp with asponge backing is used. Stamping isparticularly suitable for the applicationof BACK STAMPS (q.v.) and for someforms of gold decoration.Standard Black. A ceramic colour; aquoted composition is 30 parts Co2O3

56 parts Fe2O3, 48 parts Cr2O3, 8 partsNiO and 31 parts Al2O3.Standard Slop Peck. The volume of apottery slip that, at 32 oz/pint, contains201b of dry material of sp. gr. 2.5. Seealso SLOP PECK.

Standard Square. In the UK this termrefers to bricks of the following sizes:(1) Common Clay Building Bricks (B.S.3921): 8 5/8ths x 4 l/8th x 2 5/8ths in.(219 x 105 x 67mm)(2) Refractory Bricks (B.S. 3056): 9 x AVix 3 in. and 9 x AVi x 2Vi in. (229 x 114 x76 or 64 mm); the ISO recommendedsize is 230 x 114 x 64 mm.Standard Surface Factor. See SURFACEFACTOR.

Stanford Joint. A joint, for sewer-pipes,consisting of tar, sulphur and groundbrick or sand; the proportions varyaccording to the nature of the tar, whichshould contain sufficient pitch to ensurethat the joint will set (W. H. C. Stanford.Brit. Pat 1873).Stannic Oxide. See TIN OXIDE.Staple Fibre. See GLASS FIBRE.

Star Dresser. A tool for the DRESSING(q.v.) of abrasive wheels; it consists of aseries of star-shaped metal cuttersseparated by washers, freely mounted onthe spindle of a holder. Also known as aHUNTINGTON DRESSER.

Star Mark. A defect (star-shapedfracture) liable to occur in vitreous-enamel cover-coats if the ware is roughlyhandled as it is being placed on thepointed supports used in the firingprocess; the fault may also occur if thesesupports are either too cold or too hot.The marks result from fracture of theenamel coating.Starred Glaze. Term sometimes appliedto a glaze that has partially devitrified,star-shaped crystals appearing on thesurface; the cause may be SULPHURING(q.v.).Starved. (1) The poor quality of theglazed surface of ceramic ware ifinsufficient glaze has been applied; alsosometimes called SHORT GLAZED.(2) A blue brick is said to be 'starved' ifthere is an orange colour or dappledgrey-brown colour over the blue.Static Leach Test. See MCC-IP STATIC

LEACH TEST.

STD Method. See SUMITOMO-TSURUMIDRY FORMING METHOD.

Steam Blowing Process. The processused to make most GLASS FIBRE (q.v.)for glass wool. Glass is poured throughslots in a platinum rhodium bushing, andfiberized by a steam blower just below.Steam Curing. The rapid CURING (q.v.)of pre-cast concrete units; this can bedone at high pressure in an AUTOCLAVE(q.v.) or at atmospheric pressure inchambers or tunnels.Steam Pressing. US term forREPRESSING (q.V.).

Steam Shovel. See MECHANICAL SHOVEL.Steam Tempering. The treatment of clay(particularly brick clay) with steam to

develop its plasticity for the shapingprocess: with hollow blocks an additionaladvantage is to reduce the time requiredto dry the shaped blocks. The claygenerally reaches a temperature of 70-800C. (Also known as HOTPREPARATION; cf. HOT EXTRUSION).Steam Test. See under AUTOCLAVE.Stearates. Organic compounds used as alubricant in the dry pressing of ceramics;the stearates used are those of Al, Ca,Mg and Zn.Steatite. Massive form of the mineraltalc, Mg3Si4O10(OH)2. The chief sourcesare in USA, France, Italy, India, Austriaand Norway. The natural rock can bemachined and the shaped parts fired foruse as electroceramics. A far greaterproportion is ground and shaped in theusual way with a clay bond to producelow-loss electroceramics; thermalexpansion (20-5000C) 7-9 x Kh6; volumeresistivity (3000C) 108 - 1011 ohm-cm.;dielectric constant (1 MHz) 5.5-6.5;power factor (IMHz) 5 - 25 x Kh4.Steatite is also used as a raw material forcordierite electroceramics and forrefractories containing cordierite.Steelite. A high strength hotelware body,presumed to contain alumina, firstintroduced by Ridge way Potteries, 1967.Now the name of a hotelware company,Steelite International Ltd, Stoke-on-Trent.Steger's Crazing Test. A method for theassessment of the 'fit' between a ceramicbody and a glaze by measuring anydeformation, on cooling, of a thin barglazed on one side only. (W. Steger, Ber.Deut. Keram. Ges., 9, 203,1928; moreprecise details were given in a laterpaper-ibid., 11,124,1930.)Steinbuhl Yellow. Barium Chromate.Stemware. A general term for wineglasses, etc., having stems. The stem maybe pulled or drawn from the bowl

(PULLED STEM or DRAWN STEM), or itmay be made separately (STUCKSHANK).Stent. Cornish term for the mixture ofsand and stone occurring with china clayin the china-clay rock.Step Fracture. See STRIATION.Stepping. The undesirable projection onone or other contact face of adjacentbricks in a ring or arch.Steric Hindrance. See SURFACTANT.Stern Plane. See ZETA POTENTIAL.Sticking Up. The process of joiningtogether, by means of SLIP (q.v.), thevarious parts of items of pottery-warethat cannot readily be made in onepiece, e.g. putting the knob on a tureencover, or spouts on teapots.Stiff-mud Process. The equivalent USterm for the WIRE-CUT PROCESS (q.v.).Stiff-plastic Process. A process ofbrickmaking by mechanical presses; theclay is prepared to a moisture content ofabout 12% and the shaped bricks can beset direct in the kiln without preliminarydrying. This is particularly common inbrickworks sited on the clays and shalesof the Coal Measures.Stikons. Trade-name for surfacethermocouple sensors, made by RDFCorp., New Hampshire, USA.Stillage. A small platform on whichshaped clayware may be placed tofacilitate its handling within the factoryto and from a dryer, for example (cf.PALLET).

Stilt or Wedge-stilt. An item of KILNFURNITURE (q.v.) in the form of a three-pointed star; the three arms are SADDLES(q.v.) with points. See Fig. 4, pl77.Stippled. ( I)A surface texture on a clayfacing brick produced by the rapidimpingement on the green brick of ahead, carried on a reciprocating arm,fitted with steel spikes; this texture isalso called SPARROW-PECKED.

(2) A mottled decoration on pottery-ware or on vitreous enamelware,produced by applying colour with asponge, brush, steel wool or speciallyprepared pad.Stishovite. A high-pressure modificationof SiO2: sp. gr. 4.28; a = 0.417nm; c =0.268nm (S. M. Stischow and S. V.Popova, Geokhimiya, 10, 837,1961).Stockbarger Method. A technique forgrowing single crystals in a temperature-gradient furnace (D. C. Stockbarger,Rev. ScL Instr., 7, 133, 1936; 10, 205,1939).Stock Brick. Originally a term localizedto S.E. England and meaning a claybuilding brick made by hand on a'stock', i.e. the block of wood thatdefined the position of the mould on themoulding table. Stock bricks are nowmachine-made. The London Stock Brickis a yellow brick of rough texture. Theterm 'stock' in the sense of 'usual', issometimes applied to bricks of otherareas, however, e.g. a Lincoln Stock is asemi-dry-pressed brick from the Lias. ABelfast Stock is a pink wire-cut brickfrom the Keuper Marl.Stockholm Black. An underglazeceramic colour. A stated composition is37.7 g. CuSO4.5H2O, 39.6 g.MnSO4.4H2O, 22.7 g. CoSO4, 7H2O;these are dissolved in boiling water andthe solution is made slightly alkaline byadding Na2CO3. The solution is boiledand filtered; the residue is then washedto remove sulphates and calcined atabout 6000C.Stoichiometric. A chemical compound,or a batch for synthesis, is said to bestoichiometric when the ratio of itsconstituents is exactly that demandedby the chemical formula. Of someinterest in the field of special ceramicsare NON-STOICHIOMETRIC (q.v.)compounds.

Stoker. A mechanical device for feedingsolid fuel into a kiln firebox or throughthe roof of a Hoffmann-type kiln.Stokes. A unit of kinematic viscosity:1 Stokes = 1 poise -s- (density of thefluid).Stokes's Law. The force required tomove a sphere of radius r at uniformvelocity \) through a medium of viscosityT] is equal to 67rn\)r. This law is appliedin the determination of particle size bysedimentation, elutriation orcentrifugation. For a particle of densitydx settling in a medium of density d^ gbeing the acceleration due to gravity,when equilibrium is reached thefollowing equation applies:r?= [9vyV2(drd2)g]Stone. A crystalline inclusion present asa fault in glass; stones may result fromincomplete reaction of particles of batchor from the pick-up of small fragmentsof the refractory lining of the pot orfurnace in which the glass is melted. Themost common constituents of stones arecarnegieite, corundum, cristobalite,mullite, nephelite, tridymite andzirconia. See also CHINA STONE.Stone China. A US term for IRONSTONEWARE (q.v.).Stoner. A workman in a glass-workswhose job is to smooth the rims of theware; also called a FLATTER.Stoneware. The COMBINEDNOMENCLATURE (q.v.) is: 'Stoneware,which, though dense, impermeable andhard enough to resist scratching by asteel point, differs from porcelainbecause it is more opaque, and normallyonly partially vitrified. It may be vitreousor semi-vitreous. It is usually colouredgrey or brownish because of impuritiesin the clay used for its manufacture, andis normally glazed'. A TRANSLUCENCY(q.v.) test is specified. Water absorptionis to be 3 wt %. The body consists either

of a naturally vitrifying clay (a stonewareclay) or of a mixture of suitable ballclays, filler and flux. Stoneware may beonce-fired or it may be biscuit fired atabout 9000C followed by glost-firing at1200-12500C. At the present daystoneware is produced on a commercialscale chiefly as kitchen-ware andtableware, for which purposes its highstrength and freedom from crazing arevaluable; on a smaller scale, stoneware ismuch favoured by studio potters. Seealso CHEMICAL STONEWARE.Stoning. The removal, by means of aRUBBING STONE (q.v.), of excrescencesfrom enamelware during the stages ofmanufacture. The need for stoning mayarise as a result of splashes of enamelslip from the spray-gun, or of non-uniform draining of the slip.Stopper. (1) The round-ended refractory(fireclay or graphite) shape thatterminates the stopper-rod assembly in asteel-casting ladle and controls the rateof flow of metal through the nozzle.(2) A movable refractory shape for thecontrol of the flow of glass in the channelleading from a glass-tank furnace to arevolving pot of a suction machine.(3) A refractory closure for the mouth ofa covered glass-pot or for the working-hole outside an open pot.An alternative term with meanings (2)and (3) is GATE.Stopping. The filling up of any cracks inbiscuit pottery-ware prior to the glostfiring.Storage Heater. A type of electric spaceheater in which a refractory block isheated at night and transmits its heat tothe room as it cools during the day.Storage heater refractories need highdensity and high specific heat.Storey-height Panel. A hollow clayblock, whose cross section is usually thesize of a normal brick, of sufficient

length (c. 2.5m) to form the whole of awall in a dwelling when used vertically.Such blocks are usually extruded, andare difficult to dry and fire withoutdistortion.Stormer Viscometer. A rotating cylinderviscometer of a type that has foundconsiderable use in USA for thedetermination of the viscosity andthixotropy of clay slips. (Industr. Engng.Chem., 1, 317, 1909.)Stove. See HOT-BLAST STOVE.Stove Clay. A little used American termfor FIRECLAY.Stove Fillings. The special fireclayrefractory shapes used as checker bricksin a HOT-BLAST STOVE (q.v.). Normally,these stoves operate at a max.temperature (at the top of the stove) ofabout 12000C; the top 5m or so of fillingsare therefore built with 40-42% Al2O3

refractories, with 35-37% Al2O3

refractories below. At higher hot-blasttemperatures 50-65% Al2O3 stovefillings for the upper courses have beenintroduced.St.P. Abbreviation for STRAIN POINT

(q.v.).Straightening Kilns. Electric intermittentkilns have been used specifically forstraightening distorted ware, especiallyearthenware.Straightening Ring. A SETTER (q.v.)designed to correct the shape ofdistorted flatware.Strain Disk. A glass disk internallystressed to give a calibrated amount ofbirefringence; the disk is used as acomparative measure of the degree ofannealing of glass-ware. The discs areair-quenched to produce a strain of 22x8nm. each. The discs are piled up on topof the glass whose degree of strain is tobe measured, until the total disc strainpattern matches the strain pattern of theglass.

Strain Hardening. Under concentratedstrains, such as at crack tips, stressredistribution occurs so that localizedfracture is delayed. A zone ofmicrocracking extends around the cracktip, over a diffuse region much greaterthan the normal volume of microcracksaround a crack tip. This expanded zonecan be created by stress transfer byreinforcing fibres. It producesconsiderable energy absorption awayfrom the plane of the crack. This off-plane inelastic absorption of energy givesrise to a ductile type fracture behaviour,and has developed strain capacities over100 times those of the matrix incementitious composites reinforced withpolyethylene fibres.Strain-line. Alternative term for thevitreous-enamel fault more generallyknown as HAIR-LINE (q.v.).Strain Point. The temperaturecorresponding to the lower end of theannealing range and defined in USA(ASTM- C336) as: the temperaturecorresponding to a rate of elongation of0.00043 cm/min when measured by theprescribed method. At this temperaturethe viscosity of a glass is approx. 1014-5

poises. Abbreviated to St.P.Strainer Core. A porous refractory shapefor use in foundries to control the flow ofmetal and to keep slag and sandinclusions out of the casting. Highthermal-shock resistance is required.Strand Count. The thickness of a strandof glass fibres expressed as the numberof 100 yd lengths per pound weight.Strapping. (1) the methods of fastening(loadbearing) brickwork to floors androof.

(2) fastening conveniently-sized loads ofbricks on pallets or into cubes, fortransport, using steel or nylon bands.Strass. A glass of high lead content andgreat brilliancy used for artificial jewelry;

named from its 18th century Germaninventor, Josef Strasser.Straw Stem. The slender hollow stem ofa wine-glass.Stress Corrosion. The susceptibility ofglasses and many oxide ceramics toSLOW CRACK GROWTH (q.v.) due tointeraction between stressed cracks andenvironmental agents.Stress intensity factor, K1. For a crack oflength C, and an applied stress a, thestress intensity K1 is given by K1 =yaC/1/2where y is a dimensionlessconstant depending on the specimengeometry and the crack shape.The critical stress intensity KIC is the valueof K1 at the critical stress ac at which thecrack propagates destructively. See alsoFRACTURE, CRACK PROPAGATION.

Stretched-membrane Theory. SeeMEMBRANE THEORY OF PLASTICITY.

Stretcher. A brick with its length parallelto that of the wall in which it has beenlaid (cf. HEADER).Stretcher Bond. A brick wall in which allthe courses are stretchers, the verticaljoints in alternate courses being in line.Striae. A fault, in glass, in the form offine CORDS (q.v.); also known as VEIN.Striation. The separation of theadvancing crack front into separatefracture planes, giving a series of stepfractures.Striker Pad. An area of increased liningthickness or higher quality refractorywhich accepts the initial impact of hotmetal into a ladle.Striking. (1) The development of opacityor colour in glassware by a heat-treatment process, e.g. by the formationof a colloidal dispersion, within the glass,of a small amount of Cu, Ag or Au.(2) The smoothing of the wet claysurface in a mould by means of awooden or metal rod, as in the hand-moulding of special clay building bricks.

(3) A fault sometimes encountered withenamel colours on pottery-ware, thecolour becoming detached from the wareduring firing; a common cause is lack ofcontrol during HARDENING-ON (q.v.).(4) Setting out the first mould and theprofile tool for the shaping of ware on aJIGGER (q.v.).String. A fault in glass with theappearance of a straight or curled line;the usual cause is slow solution of a largesand grain or other coarse material.String Course. A distinctive, usuallyprojecting, course in a brick wall; itspurpose is aesthetic.String Dryer. A tunnel-type dryer,particularly for building bricks, that isoperated intermittently; in the earlystages of drying, the exits and exhaustducts are closed so that a high humidityis built up. This type of dryer has beenused particularly in Texas, USA.Stripper. A person employed in thepottery industry to remove the driedware from the plaster moulds.Stronbal Glass. Name for StrontiumZ?oro-v4/uminate glass proposed byM. Monneraye, J. Serindat and C.Jouwersma (Glass Techn., 6, (4), 132,1965).Strontium Boride. SrB6; m.p. 2235°C; sp.gr., 3.42.Strontium Oxide. SrO; m.p. 24200C; sp.gr. 4.7; thermal expansion (20-12000C)13.9 x 10-6.Strontium Stannate. SrSnO3; sometimesused as an additive to titanate bodies,one result being a decrease in the Curietemperature.Strontium Titanate. SrTiO3; used aloneor in combination with BaTiO3 as aceramic dielectric. The power factor atlow frequency is high. The Curietemperature is approx. 2600C. Thedielectric constant is 230-250.Strontium Zirconate. SrZrO3; m.p.

27000C; sp. gr. 5.48. Sometimes used insmall amounts (3-5%) in ceramicdielectric bodies, one effect being tolower the Curie temperature.Structon. A unit of atomic structure inan amorphous solid, such as glass,proposed by M. L. Huggins (/. Phys.Chern., 58,1141,1954) and defined as 'Asingle atom (or ion or molecule)surrounded in a specified manner byothers'; examples for a sodium silicateglass would be Si(40), O(2Si,Na), etc.The concept aimed to reconcile therandomness of the long-range structureof a glass with the relative regularity inthe short-range structure. The term hasnot achieved popularity (see VITRON).Structural Ceramics. In Britain, ceramicsfor civil engineering structures. In theUSA the term is so used, but also usedfor ceramics for mechanical engineeringapplications such as automotive engineparts.Structural Clay Tile. In USA this term isdefined (ASTM - C43) as a hollowburned-clay masonry building unit withparallel cells or cores or both; theequivalent term in the UK is 'HollowClay Block'.Structural Spalling. A form of SPALLING(q.v.) defined in USA as: The spalling ofa refractory unit caused by stressesresulting from differential changes in thestructure of the unit.Structure. As applied to abrasive wheels,this term refers to the proportion anddistribution of the abrasive grains inrelation to the bond. In USA the termGRAIN SPACING is also used.Stub. An abrasive wheel that has beenused until its diameter has been so muchreduced by wear that it is no longerserviceable.Stuck Shank. See STEMWARE.Stuck Ware. Pottery-ware that has stuckto the kiln furniture during the glost

firing and is therefore waste. The faultmay be caused by careless placing, bythe presence on the ware of too muchglaze, or by firing at a temperature thatis too high for the glaze being used,which therefore becomes too fluid.Stud. A round piece of steel, weldedinside a steel enclosure to retain arefractory lining.Stupid. An extrusion machine in whichclay is forced through the die by of apiston; such machines are now rare.Submerged Entry Nozzle. A refractorycomponent acting as both tundish nozzleand SUBMERGED ENTRY SHROUD (q.V.).Submerged Entry Shroud. A LADLESHROUD (q.v.) which may incorporatespecially designed exit ports and facilitiesfor gas injection.Submerged Wall. A wall of refractorymaterial below the level of the moltenglass in a tank furnace and separatingthe melting zone from the refining zone.Sub-porcelain. A class of WHITEWAREdefined (Tariff Schedules of the UnitedStates, 1976) to be: fine grained ceramicware (other than stoneware) whether ornot glazed or decorated, having a firedbody which is white (unless artificiallycoloured) and will absorb more than0.5% but not more than 3% of its weightof water.Subsolidus. That region of the phasediagram in which the only stable phasesare solids.Substance. In the glass industry thisword means the thickness of glass sheetsin oz/ft2.Substrate. The base on which a thinlayer of different composition isdeposited; an electroceramic, forexample, can serve as the substrate of athin-film resistor or of a printed circuit.ASTM F865 specifies the camber orcurvature of substrates; F394 theirstrength (modulus of rupture).

Substitutional Defect. See CRYSTALSTRUCTURE.Suck-and-Blow-Process. A method ofshaping glass-ware, the PARISON (q.v.) ismade by sucking molten glass into amould, the final shape beingsubsequently produced in a BLOW-MOULD (q.v). The process is known inU S A as VACUUM-AND-BLOW.Sucking. Loss of volatile oxides,particularly lead oxide, from a glaze byvolatilization during glost firing inunglazed saggars or adjacent to non-vitreous kiln furniture. The vapour being'sucked' into the porous refractory. Thefault is prevented by washing the insidesof saggars with glaze or, in saggarlessfiring, by the use of kiln furniture of lowporosity.Suction Pyrometer or High VelocityThermocouple. An instrument for thedetermination of the temperature ofmoving gases when it differsconsiderably from that of theirsurroundings: the hot gases are drawnrapidly past the junction of a fine-wirenoble-metal thermocouple. Such aninstrument is used, for example, in thedetermination of the temperature of hotkiln gases passing through a setting ofrelatively cool bricks.Suffolk Brick. A white or pale yellowbuilding brick made from the limy claysof Suffolk, England.Suffolk Kiln. An early type ofrectangular up-draught intermittent kiln.The fireboxes were below the kiln floorwhich was perforated for the upwardpassage of the hot gases: the waste gasesescaped through openings in the kilncrown.S.u.G Process. A German method forthe shaping of highly grogged fireclayrefractories; the bond-clay is added as aslip and shaping is by a compressed-airrammer. The name derives from the

originators: Scheidhauer und GiessingA.G. (Brit. Pat., 262 383, 24/6/26).Sugar. A fault on lead crystal glassresulting from inadequate control duringacid polishing and revealed as crystalliteson the surface of the glass.Sugar Test. A quality test for cement;See MERRIMAN TEST.Sugary Cut. Undue roughness of theedge of flat glass resulting from faultycutting.Sullivan Process. A process for thetreatment of sheet steel prior to vitreousenamelling; it is based on the spraying ofa suspension of NiO on the metal to givea deposit of about 0.01 - 0.1 g/m2. (J. D.Sullivan, US Pat., 2 940 865. 14/6/60).Sulmag Process. Registered tradenameof Sulzer Bros. Ltd. Precalcinedmagnesite is dissolved by reaction withCaCl2 and CO2 to form MgCl2 andCaCO3. The solution is made alkalinewith ammonia, and further CO2

precipitates MgCO3.3H2O. Theprecipitate has excellent filtration andwashing characteristics, and decomposesat low temperatures to reactive MgOwith density 3.35-3.40 g/ml and over99% purity.Sulphate-resisting Cement. A portlandcement specially made to resist exposureto water containing dissolved sulphates.The chief difference between this cementand ordinary portland cement is that theformer has a low tricalcium aluminatecontent; B.S. 4027 stipulates 3.5 % (Seealso SUPERSULPHATED CEMENT).Sulphate Scab. See SCAB.Sulphides. Compounds of metals withthe element sulphur. Some melt above20000C, though some decompose atmuch lower temperatures. Applicationsare as electroceramics, in solar cells andother energy conversion applications.Cadmium sulphide is a pigment, thoriumsulphide a crucible material for cerium.

Sulphide Stain. Discolouration of enameldecoration by exposure to sulphidecompounds, commonly by too longstorage in corrugated packaging.Sulphite Lye. A by-product of the paperindustry used as a cheap temporarybond, e.g. for silica refractories; it hasalso been used as a plasticizer in makingbuilding bricks. It generally contains 50-70% of the ligno-sulphonate of Na, Caor NH4, together with 15-30% of amixture of sugars; the ash content of theNH4 type is very low but that of the Caor Na types may amount to 30%.Sulpho-aluminate Cement. A hydrauliccement made by grinding a mixture ofhigh-alumina cement and gypsum (oranhydrite) (Lafarge, Brit. Pat., 317 783,29/7/29).Sulphuring. A surface bloom or dullingof glazed ceramic ware resulting fromattack by SO3 in the kiln, and moreparticularly by sulphuric acid condensedon the ware in cooler parts of the kiln inthe early stages of firing. The sulphurcompounds may originate in the fuel orin traces of sulphur compounds (e.g.pyrite) present in the ware itself. Thefault is most common in glazescontaining calcium or barium; glazescontaining lead are usually more fluidand, although they may absorb moresulphur as sulphate, this may not resultin a visible fault.Sumitomo-Tsurumi Dry FormingMethod. Blast furnace troughs are linedwith a dry material (Al2O3-SiC withwater content 0.5%), densely packedusing pressure and vibration. Uniformpacking is achieved, though unlimitedrepair by patching is possible, with shortcuring times.Sump Throat. See THROAT.Sunburner. A faulty piece of hand-blownglass-ware characterized by excessivelocal thickness.

Sunderland Splatter. A characteristiceffect found on some of the old lustrepottery made in Sunderland, England;after the lustre had been applied it was'splattered' with a second medium whichcaused the formation of irregular patcheson the base lustre.Superceram. Tableware containing addedalumina, made by Hall China, USA.Superconductor. A material withvirtually no resistance to the passage ofelectric current.Superconductivity is a quantummechanical effect observed at lowtemperature. Roughly speaking, due tointeractions with the crystal lattice, theconduction electrons in superconductorstend to form weakly bound pairs.Thermal vibration disrupts these pairs atother than very low temperatures, but atsuch temperatures the 'electron pairs' actas though they were single particles,subject to 'Bose statistics' - that is, theyall tend to congregate in the lowestenergy state In normal conduction, theelectrons have a range of energies and itis relatively easy for successive electronsto be 'knocked out' of the regular flowby interaction with the crystal lattice. Inthe superconducting state, the electrons'stick together' in the lowest energy stateand maintain the current.Superconductors also show the Meissnereffect, expelling a magnetic field fromwithin themselves if cooled below Tc ,the critical temperature below whichthey exhibit superconductivity.Superconductive behaviour is lost if thematerial is heated above T c and also ifthe current density in the material isabove a critical value Jc. Most metalsshow superconducting behaviour, butonly at temperatures of a few degrees K.Some metal alloys have T c s of some3OK, but ceramic superconductors existwith Tc 's as high as 90-11OK. The

objectives of superconductordevelopment are to have T c and J c ashigh as possible, with initially T c abovethe temperature of liquid nitrogen.Ceramic superconductors are usuallyoxygen-deficient materials with distortedPEROVSKITE (q.v.) crystal lattices. Twosystems have been particularly studied:the 1:2:3 or YBa2Cu3O7.x system (inwhich other rare earths may besubstituted for Y) and the lead/bismuth -rare earth-copper oxide systems.Ceramic superconductors are made bythe powder forming technique now usualfor technical ceramics, but requireextremely careful control ofmicrostructure and chemical purity. Inpractical devices, ceramic-metal joiningtechniques are also of great importance.Supercritical Solvents. Supercriticalfluids are fluids above their critical pointsi.e. in the P-T region where the vapourcannot be condensed by pressure alone,but must also be cooled. They have highdissolving power, good diffusionalproperties, high density and lowviscosity. Expansion of solutions basedon supercritical fluids leads to rapidnucleation and precipitation of solidsolute particles. Submicron mixed oxideand spinel powders can be made bydecomposition of organometalliccompounds in supercritical fluids such asethanol. See RESS PROCESS.Super-duty Fireclay Refractory. Definedin ASTM - C27 as a fireclay brick havinga P.CE. 33 and an after-contraction 1%when tested at 16000C. There are threetypes: Regular, Spall Resistant, SlagResistant. Limits are set for panelspalling loss, modulus of rupture andbulk density. ASTM C-673 specifies asuper-duty plastic refractory with P.C.E.321A

Super-duty Silica Refractory. In the UKthe National Silica Brickmakers'

Association has defined this type ofrefractory as SILICA REFRACTORY (q.v.)containing not more than 0.5% Al 2O3

and with a total of Al2O3 plus alkalis notexceeding 0.7%.Superheater. A refractory-lined chamberin a water-gas plant. It is filled withcheckers and ensures completion of thedecomposition of the oil vapours begunin the CARBURETTOR (q.v.).Superlattice. The regular, orderedstructure of the atoms of two elements inthe crystal lattice of a SOLID SOLUTION.Superplasticity. The ability of someceramics to demonstrate large strains ordeformation without cracking. Suchceramics usually have ultrafine(nanometre) grain size and have highstrength across grain boundaries, so thatcavities do not form. The phenomenon isrelated to diffusional creep, in whichstrain rate is inversely related to thecube of grain size, and has beenreviewed by Y. Maehara and T.G.Langdon (/ Mater. Sci 25,1990 p 2275-2286).Super Staffordshire Kiln. ASTAFFORDSHIRE KILN (q.v.) modified indesign so that the fuel is charged on to agrate instead of within the setting ofbricks. Kilns of this type can be used fortemperatures up to about 12000C.Supersulphated Cement. A hydrauliccement made by finely grinding amixture of 80-85% granulated blastfurnace slag 10-15% calcined gypsumand 5% portland cement (or lime). Itsprincipal feature is resistance to attackby water containing dissolved sulphates.(See also SULPHATE-RESISTINGCEMENT).

Surface Combustion. That fuel gasesburn more readily when brought intocontact with a hot surface was firstdemonstrated by W. A. Bone and R. V.Wheeler (Phil Trans, A, 206, 1, 1906).

where G is the specific gravity of thepowder; W 1? W2 etc., are the fractionalweights of material whose averagediameters are d1? d2. etc.; W1-I-W2 +... = 1.Surface Tension. The effect of internalmolecular attraction acting at the surfaceof a liquid to cause the surface to behaveas though it were a tense skin. Somesurface tension values are (dynes/cm):paraffin (kerosene), about 20 at 200C;water, 74.2 at 100C; glasses in theirworking temperature range, 200-300.See SESSILE DROP TEST.Surfactant. A surface active agent; achemical which reduces the surfacetension of a liquid, and so improves thewetting of a surface. They are useful indispersing powders, when surfactantsadsorbed on particle surfaces producerepulsive forces between the particleswhen the adsorbed layers overlap (sterichindrance.)Surkhi. Indian term for clay that hasbeen lightly fired to give it some of theproperties of POZZOLANA (q.v.).Suspended Arch, Roof or Wall. An arch,furnace roof, or wall, in which some orall of the bricks are suspended by metalhangers from a steel framework. In anarch or roof, the object is to relieve thebricks from the mechanical stressresulting from the thrust of the arch; in a

The principle has been applied tofurnace design, combustion taking placeon the incandescent surface of refractorymaterial; in one surface-combustiondevice, the fuel gas is passed through aporous refractory burner, 'flamelesscombustion' occurring over the surfaceof the refractory.Surface Factor. A factor used in theceramic industry to indicate the finenessof a powder. It is calculated from theequation:

suspended furnace wall, the usualpurpose is to permit refractorybrickwork to be inclined inwards withoutdanger of it falling into the furnace.Suspending Agent. A material, such asclay, used to keep a vitreous enamel orglaze in suspension so that it can beconveniently used for application to theware by dipping or spraying.Svedala Kiln. A chamber kiln with adryer built above it; designed inScandinavia for use in the building brickindustry.Swab Test. An electrical test, carried outwith low voltage, for exploration of suchdefects in vitreous enamelware as pin-holes or other discontinuities.Sweep-fire System. In this system for firingstoneware pipes in periodic kilns, burnersare arranged in opposed pairs, and thepower to opposite burners is variedrhythmically. The system was developedby Paul Schneider & Co, and licensed toBickley Co., in USA and W.Germany (seeZL Int. 40, (12) 629 1987).Sweep-gas System. As binder is burnedout, a carrier gas is passed over the partsto entrain the binder vapour. This can becarried out at low pressures (a few Torr)instead of at atmospheric pressure, ifbinder is removed from the body undervacuum. (Ind. Heating 53 (4) 1986, p 28)Sweet. A term applied to glass that iseasy to shape.Swept Valley. A form of roof tilingdesigned to cover a re-entrant corner ofa roof without any sharp valley; carefulcutting of the roofing tiles is necessary toensure a symmetrical finish.Swindell-Dressier Kiln. See DRESSLER

KILN.

Swinger. The Pereco SW-850 rockingfurnace for drying and calcining powder.(Interceram 24 (4) 261 1975).Swing Press. A hand-operated screwpress sometimes used, for example, in

the shaping of a small quantity ofspecial-shaped wall or floor tiles.Swirlamiser. A design of oil and gasburner which replaces the fuel/airmissing tube with a short choke venturimixing port. The port is a refractoryquad to sustain high temperature andpromote rapid and stable combustion.(Autocombustions, Telford).Sworl. The marks made on the bottomof a thrown pot when it is cut from thewheel.Syalon. Trade-name, for SIALON (q.v.)materials manufactured by Lucas,Cookson Syalon, UK. They haveparticular application in cutting tools (inwhich yttria is incorporated, but this isperhaps fortuitous).Syndite. Trade-name. An abrasive-sintered diamond with a cobalt bond (Cfhard metals). De Beers Co., South Africa.Syneresis. The phenomenon of theseparation of liquid from a gel after thecorresponding sol has set; the liquidexpressed is termed the 'Syneretic liquid'(J. Ferguson and M. P. Appleby, Trans.Farad. Soc, 26, 642, 1930).Synroc Process. High level radioactivewaste from reprocessed nuclear fuel isimmobilised in a synthetic mineralformed from a mixture of oxides,principally TiO2, BaO, ZrO2, Al2O3 andCaO. SYNROC-B contains the threephases barium holiandite (BaAl2Ti6O16);perovskite (CaTiO3) and zirconolite(CaZrTi2O7) chosen for theirparticularly great geochemical stabilityand for their ability to take into solidsolution, as titanates, all the importantelements in radioactive wastes.(Australian Ceram, Soc. 16, (1) 10, 1980)Synthetic Vitreous Silica. See underVITREOUS SILICA.

Syphon. A special type of refractoryblock for the bath of a glass-tankfurnace.

'TV Glass. A glass composition formaking glass fibre. T 1 ' glass, with 10%Na2O, replaced the 'A' glass initiallyused, giving increased chemicaldurability and better fibre-formingproperties. T2'-type glasses (15% Na2O)replaced T1'-type with the introductionof modern rotary-spinner productiontechnology.Ta and Tb. See under REFRACTORINESS-

UNDER-LOAD.T c - Critical Temperature, below whicha superconducting material is aSUPERCONDUCTOR.Te. (1) The temperature at which theelectrical resistivity is 1 megohm.cm. TheTe value of some ceramics is: porcelain,3500C, cordierite, 7800C; steatite, 8400C;zircon, 8700C, forsterite, 10400C;alumina, 10700C.(2) A temperature associated withREFRACTORINESS-UNDER LOAD (q.V.)TA-Luft. The Federal Geraman CleanAir Guide of 1986, which sets emissionlimits for fluorides and the oxides ofsulphur and nitrogen.Taber Abraser. A device for assessingthe abrasion resistance of a surface; theprinciple is contact with loaded abrasivewheels which are rotated against thesurface to be tested. It is used for testingfloor-tiles, see ASTM - C501. (TaberInstrument Corp. I l l Goundry St. NorthTonawanda, NY, USA).Tabular Alumina. See ALUMINA(TABULAR).

Tailings. The oversize material retainedon a screen; normally the tailings arereturned to the grinding plant for furthergrinding but in some cases the tailingscontain a concentration of impurities andare discarded.Talc. See STEATITE.Talwalker-Parmelee Plasticity Index.This index, based on the results of testson a clay in shear with a specially

designed apparatus, is the ratio of thetotal deformation at fracture to theaverage stress beyond the proportionallimit. (T. W. Talwalker and C. W.Parmelee, /. Amer. Ceram. Soc, 10,670, 1927.)Tammann Furnace. An electric high-temperature furnace having a carbontube as resistor; it is used without aprotective atmosphere but is sealed toprevent ingress of air (G. Tammann; seepaper by E. Lowenstein. Z. Anorg.Chem., 154, 173, 1926.).Tammann Temperature. Thetemperature at which reaction betweentwo solids (or sintering within powdercomposed of a single solid) becomesappreciable. As originally defined byG. Tammann (Z. angew. Chem., 39, 869,1926) this temperature lies between thetwo values obtained by multiplying them.p. (K) of each reactant by 0.57. Thetemperature is only approximate anddifferent multiplying factors have beenproposed.Tamping. The shaping of a semi-drypowder, e.g. of refractory material, in amould by repeated blows deliveredmechanically on the top mould-plate (cf.JOLT MOULDING and RAMMING).Tank Block. A refractory block used inthe lower part of a glass-tank furnace.These blocks are normally made ofsillimanite, mullite or corundum; theyare frequently made by electrofusion ofthe refractory, which is then cast in amould to form a highly crystalline,virtually non-porous, block. See T. S.Busby, Tank Blocks for Glass Furnaces(Sheffield: Soc. Glass Tech., 1966).Tank Furnace. A furnace for thecontinuous process of glass melting andrefining; it is usually gas-fired andregenerative. The glass is melted in thebath of the furnace, which is lined withrefractory blocks.

Tannin. A complex organic compound ofC, H and O produced by metabolism intrees and plants. Sodium tannate is usedto some extent as a deflocculant for clayslips.Tantalum Borides. Several borides areknown, including: TaB2; m.p. 30000C; sp.gr. 12.5; thermal expansion, 5.5 x 10"6.TaB; m.p. 24000C; sp. gr. 14.3. Ta3B4 :melts incongruently at 26500C; sp. gr.13.6.Tantalum Carbides. Two carbides exist;TaC, m.p. 3800C; Ta2C, m.p.3400°C. Themonocarbide has the followingproperties: sp. gr. (theoretical), 14.5 g/ml;hardness, 850 (KlOO); modulus ofrupture, 200 MNm-2 at 25°C and120MNm-2 20000C; thermal expansion(25-20000C) 8.4 x 1(H\Tantalum Nitrides. Two nitrides areknown: TaN, m.p. 30000C; Ta2N, whichloses nitrogen at 19000C.Tantalum Oxide. Ta2O5; m.p. 18700C;sp. gr. 8.7. Transition temp, from lowform (b) to the high (a) form is approx.13400C. The sintered oxide can be usedas a special dielectric material; OC-Ta2O5

ceramics exhibit large migrational losses,similar to those found in glasses, causedby migration of Ta5+.Tap Density. The density of a powderwhich has been tapped in a containerunder specified conditions, e.g. until thevolume of powder does not decreasefurther (ISO 3953, 1977)Tapered Cantilever Beam. SeeFRACTURE TOUGHNESS TESTS.Tape Casting. A ceramic slip, containingsuitable plasticizers if required, is filteredthrough a slot on to a moving continuousband. A gate or blade controls thethickness of the resultant cast tape, orsheet, which may be cut into appropriatethin shapes. The band is of plastics orother non-porous material, and removalof the liquid carrier medium, which is

usually organic, is by evaporation. Gooddispersion of the powder in the carrierliquid is essential before adding bindersand plasticizers. Fatty acids, their esters,or synthetic polymer dispersants anddeflocculants have been used.Tapered Wheel. An abrasive wheel thatis thicker at the hub than at thecircumference.Tapestry Brick. A US term for a brickwith a rough textured surface.Taphole. A small passage through therefractory lining of the hearth-wall of ametallurgical furnace, e.g. a blast furnaceor open-hearth steel furnace.Taphole Clay. The plastic refractorymaterial used to plug the tap-hole of ablast furnace generally consists of amixture of fireclay and grog togetherwith carbon in the form of coal or coke(in USA pitch is also sometimes used).The range of chemical composition of anumber of British taphole clays is (percent): SiO2, 40-60; Al2O3, 22-27; loss onignition, 8-18. The material is adjustedto have a moisture content of 15-18%and is forced into the taphole by meansof a 'gun'.Taphole Gun. A gun-shaped device usedto force TAPHOLE CLAY (q.v.) into theTAPHOLE (q.v.) of a blast furnace after ithas been tapped.Tapped Wirecut. This term has beenused in the Ibstock (England) area for awire-cut facing brick; these bricks weremade on a side-cutting table and as thepallets were lifted from the table theywere given a gentle tap to fettle theedges where the wires had emerged fromthe clay column.Tapping Cone. A protective refractoryfibre cone for the end of a tapping bar,used to seal a furnace TAPHOLE.Tappit Hen. A 3-quart wine bottle.Tar-bonded Refractory. Tar or pitch isadded (4 to 6%) as a binder to a graded

dolomite or magnesite refractory grain ina heated mixer. The mixed batch isstored at about 1000C and shaped byhydraulic or vibratory pressing. Theresultant blocks may be 'tempered' at250-3500C to improve hydrationresistance and carbon retention. Thefinished blocks are sprayed with tar andwrapped in plastics to prevent moistureabsorption. The blocks are used to linefurnaces, particularly basic oxygensteelmaking furnaces, being heated in-situ, during which process the tar orpitch forms carbon and the refractory isfired, bonding the grains. (For relevantproperties of tars and pitches, see W.D.Betts, Trans. J. Br. Ceram. Soc. 74 (3),85,1975).Tar-impregnated Refractory. A firedrefractory, particularly one subject tohydration, such as dolomite ormagnesite, whose pores have been filledwith tar by autoclaving at c. 2000C,evacuating and pouring in tar. Tarimpregnated refractories are used to linebasic oxygen furnaces.Tarras Cement, TRASS (q.v.).TCB. Tapered Cantilever Beam. SeeFRACTURE TOUGHNESS TESTS.TD Diffusion Coating. Carbides arecoated on to iron and steel by dipping ina molten salt bath for 1-10 hours. Thebath is mainly borax added to low costcarbide precursors. Coatings 5 to 15mmthick are deposited, and cooled in air orby quenching in oil or water to obtainoptimum mechanical properties. (ToyotaR & D Laboratories, Japan. Engrs. Dig.36, (7), 1975, p27).Tea-dust Glaze. An opaque stonewareglaze, greenish in colour from reducediron compounds, sometimes used bystudio potters.Teapot Ladle. A ladle, lined withrefractory material and used in foundriesfor the transfer of molten iron or steel;

its distinctive feature is the refractorydam below which the metal passes toreach the ladle spout; the refractory damprevents the outflow of slag.Tear. (1) An open crack in glass-ware(cf. CHECK). (2) An excess spot ofenamel on the edge of a vitreous-enamelsheet caused by too thick a coating or byfiring at too high a temperature.Tearing. Cracks (usually partiallyhealed) in the cover-coat of vitreousenamelware. The cause is high dryingshrinkage resulting, most commonly,from too-fine grinding, too wet a slip, ortoo heavy an application of slip. Theamount of electrolyte in the slip isimportant; the presence of sodium nitriteis beneficial.Teaser. A glass-worker who controls thetemperature of a pot or tank-furnace tothat required for feeding the batch; alsocalled FOUNDER.Tecalemit System. Trade-name: animpulse system for the oil-firing (fromthe top or side) of ceramic kilns; theimpulses are controlled by a compressed-air device (Tecalemit Engineering Ltd.,London).Technate. A less common name forDiDYMiuM (q.v.).Technical Ceramics. As well as modernENGINEERING CERAMICS, this term alsoincludes more traditional electricalporcelains, steatites etc.Teem. To pour molten metal (or glass)from a ladle (or pot).Tegula. See ITALIAN TILES.Telefunken Process. See underMETALLIZING.Tellus System. A system for bricklayersworking inside steel converters. Ahorizontal working platform ishydraulically raised or lowered by acentral column, around which isprovided a spiral automatic feed systemto deliver bricks to the bricklayers.

TEM. Transmission ElectronMicroscopy.Temmoku. See TENMOKU.Temper. The residual stress in annealedglass-ware as measured by comparisonwith STRAIN DISKS (q.v.). See alsoTEMPERING.Temperature. For conversion fromFAHRENHEIT to CENTIGRADE, and VlCeversa, see these entries.7.6 Temperature. See SOFTENING POINT.13.0 Temperature. See ANNEALINGPOINT.Temperature Gradient Furnace. Anelectric-resistance furnace in which theheating element is wound round thefurnace tube in such a manner that thereis a steady temperature gradient alongthe axis of the furnace. Such a furnace isuseful in the ceramic laboratory in that itwill expose a long test-piece placedwithin the furnace to differenttemperatures at different points, so thatthe effect of various firing temperaturescan be studied in a single operation.Temperature Indicating Crayons orPaints. The marks made by such paintsor crayons change colour at a range ofpredetermined temperatures, up toseveral hundred 0C.Tempered Dolomite Block. A tarreddolomite block that has been preheatedat about 400-5000C to eliminate volatilematerial from the tar; this prevents theblocks from slumping while they arebeing heated up to the operatingtemperature of the furnace or steelconverter in which they are being used.The process is also claimed to improvethe hydration resistance.Tempered Glass. See TOUGHENEDGLASS.

Tempering. The mechanical treatment ofmoistened clay, or body, to disperse thewater more uniformly and so to improvethe plasticity; tempering is usually done

in a solid-bottom edge-runner mill withthe mullers raised slightly above the panbottom.Tempering Tub. A combined pan andvertical pug mill for the preparation ofclay for brickmaking. The mixing pan isabout 2m dia., a central vertical shaftcarrying the mixing blades; the shaftcontinues downward as the shaft of thepug mill. In some districts of Englandthis equipment is known as a SLUDGEPAN,

Tenmoku. A glaze containing ironcompounds sometimes used by studiopotters; it is lustrous black exceptwhere it is thinner and has oxidised to ared colour. A quoted composition is(%): feldspar, 50; quartz, 23; whiting,10.9; kaolin, 5.9; magnesite, 2.3; ironoxide, 7.6.Tensile Strength. The force required tobreak a specimen, when applied to pullapart the material. Direct tensilestrength tests for ceramics havenotorious difficulties in aligning the testpieces and gripping them properlywithout introducing bending forces.Indirect tensile tests such as theBRAZILIAN TEST (q.v.) and othersinvolving splitting rings or cylinders havebeen adopted. ASTM C1006 is a splittingtest for the tensile strength of masonry.Terminology. See Appendix A, B.Terra Alba. Pure white uncalcinedgypsum.Terra Cotta. Unglazed fired clay buildingblocks and moulded ornamental buildingcomponents. In England, the use ofarchitectural terra cotta reached its peakin the 19th century (cf. FAIENCE).Terra Rosa. Haematite used as a redglaze pigment.Terra Sigillata. A type of pottery having afine-textured red body and a glossysurface, usually with a raised decoration.The Latin name derives from the pastilles

made from certain clay deposits inLemnos and Samos (hence the alternativename Samian ware) and impressed withthe sacred symbol of Diana; thesepastilles were used medicinally.Tertiary Air. Preheated air introducedinto the waste-gas flue of a kiln firingunder reducing conditions, e.g. a blue-brick kiln; its purpose is to burn thecombustible matter in the gases leavingthe kiln chamber, thus helping tominimize smoke emission from the stack(Cf. PRIMARY AIR and SECONDARY AIR).Tessara(e). The small rectangular tile(s)used in mosaics.Tessha. A version of the TENMOKU (q.v.)glaze; it is described by Bernard Leach{A Potter's Book, (Faber) London, 1945)as 'more metallic and broken thanTenmoku'.Test Cone. A test-piece cut or mouldedfrom a sample of refractory material thatis to be tested for refractoriness orP.C.E. (q.v.). The shape is that of apyramid on a triangular base; thedimensions vary according to whichnational specification is being followed.Tetracalcium Aluminoferrite. SeeBROWNMILLERITE.Tetrahedron. See SILICATE STRUCTURES.Textile Ceramics. The achievement ofartistic effects with combinations oftextiles and ceramics, in particular byusing viscose-silica fibre, a cellulose fibrecontaining up to 33% silica, used for fire-resistant clothing and upholstery. Bowls,wall hangings and other ornaments ofdelicate texture can be produced.Texture. (1) The physical property of aceramic product determined by theshapes and sizes of the pores and thegrading of the solid constituents. Thetexture can to some extent be evaluatedin terms of porosity and permeability;additional information is provided bypore size measurement and the total

internal surface area (as measured by gasadsorption, for example).(2) The general surface appearance of aclay facing brick.Tg Point. See TRANSFORMATIONPOINTS.Thenard's Blue. A dark blue colour foruse under-glaze in pottery decoration; itconsists of approx. four parts cobaltoxide to five parts alumina.Theoretical Density. The density of amaterial, assuming 100% purity and zeroporosity.Therm. A unit of heat equivalent to 100000 Btu. (lBtu = 1.055 kJ)Thermal Analysis. A group oftechniques in which a physical propertyof a substance is measured as a functionof temperature, whilst the substance issubjected to a controlled temperatureprogramme. The NomenclatureCommittee of the InternationalCommittee on Thermal Analysis (ICTA)defines a wide range of techniques andtheir abbreviations, these beingincorporated in ASTM E473-85. Thosecommon in ceramics are (q.v.)DIFFERENTIAL THERMAL ANALYSIS(DTA) ; DIFFERENTIAL THERMO-GRAVIMETRY (DTG); DIFFERENTIALSCANNING CALORIMETRY (DSC).Thermal Barrier. The zone where thetemperature is highest in the melting endof a glass-tank furnace.Thermal Checking. Thermal checkingof a glass container occurs when largeamounts of heat are transferred from itssurface very rapidly, and the resultingstresses exceed the strength of theglass.Thermal Conductivity. The quantity ofheat transmitted through a material inunit time, per unit temperature gradientalong the direction of flow, and per unitof cross-sectional area. The thermalconductivity of crystalline ceramics of

low porosity decreases with increasingtemperature; that of porous ceramicshaving a glassy bond generally increaseswith temperature. Some typical room-temperature values are: Silicon carbide,14; magnesite, 4.5; chrome-magnesite,2.2; fireclay refractory, 1.2; insulatingrefractory, 0.4 W/m.K.Thermal Conductivity Tests. There aretwo main classes: Direct Tests. Aconstant, measured thermal gradient isestablished in a test-piece. The heatinput required to maintain it ismeasured. The test-pieces are usuallyrectangular prisms or cylinders, with'guards' to ensure that a uniformtemperature is maintained up to theedges. Tests of this type are B.S. 1902: Pt5.5 Method 1902-505; B.S. 1902 Pt. 6, forceramic fibre products up to 13000C, andASTM C201 and C202, the latter being amodification of the former for lowerconductivity materials (up to 28.8W/m.K). These ASTM tests forrefractories have special procedures forunfired monolithic refractories (C417);insulating firebrick (C182) and carbonrefractories (C767).In Comparative Tests the same constantheat flow is established through thespecimen to be measured, and astandard sample of known conductivity.The different temperature gradientsacross the two samples are compared.(B.S. 1902 Pt. 5.8 specifies a test of thistype for refractories, Pt.6 Section 6 aguarded hot-plate test up to 12000C forceramic fibre products; ASTM C408 onefor ceramic whitewares, using a copperstandard from 40 to 1500C.For a more rapid method see HOT-WIREMETHOD; for rapid, transient heat flowmethods see THERMAL DIFFUSIVITY.Thermal Cycling Test. Refractories subjectto repeated changes in temperature(thermal cycling) lose strength. ASTM

Cl 171 evaluates this effect by using sonictechniques to measure modulus ofelasticity, or by measuring cold modulus ofrupture, before and after specified cyclicthermal treatment.Thermal Diffusivity. A measure of therate of change of temperature at a pointin a material when heat is applied orremoved at another point, e.g. the rateof rise of temperature at the centre of afurnace wall when the furnace is heated.The thermal diffusivity is the ratio of thethermal conductivity of the material tothe product of the bulk density and thespecific heat. Two methods ofmeasurement used for ceramics are theAngstrom Method, in which a sinusoidalvariation in temperature is applied toone face of a specimen, and the changesin amplitude and phase of thetemperature wave are measured on theopposite (parallel) face; and the FlashMethod, in which a short duration heatpulse (from a flash tube or laser) isapplied to one face, and the temperaturerise on the opposite face is recordedelectronically as a function of time.(ASTM E1461-92). Both methodsare rapid and suitable for relativelysmall samples, which may be heated ina small furnace to measure the variationof thermal diffusivity with temperature.Thermal Endurance. The ability of apiece of glass-ware to resist thermalshock. An attempt to assess this in termsof the physical properties of the glass isoffered by the WINKELMANN AND

SCHOTT EQUATION (q.V.).Thermal Expansion. The reversibleincrease in dimensions of a materialwhen it is heated. Normally, the linearexpansion is quoted, either as apercentage or as a coefficient, in eithercase over a stated temperature range; forexample, the thermal expansion of asilica refractory may be quoted as 12%

or as 12 x Kh6 (per 0C, implied),between 0 and 100O0C B.S. 1902describes a horizontal linear method (Pt.5.3) for use up to 11000C, and acomparative method for large testpieces, suitable up to 16000C to providedata for furnace design calculations (B.S.1902 Pt. 5.4) Pt. 5.14 describes horizontaland vertical dilatometer methodssuitable up to 15000C. ASTM has twotests, interferometric (C539) and adilatometer method (C372) for vitreousenamel, glaze frits and fired whitewares.B.S. 7030 specifies a method for glass.Thermal Expansion of Composites.Kerner derived an equationincorporating shear effect, to predict thethermal expansion of a two phasecomposite. Without shear, a simplerexpression due to Turner can be used,(see W.D. Kingery, H.K. Bowen andD.R. Uhlman, Introduction to Ceramics,Wiley 1976, p 307).Thermal Expansion Factors for Glass.Factors that have been proposed fromtime to time for the calculation of thecoefficient of linear thermal expansion ofa glass on the assumption that this is anadditive property. The factors areinserted in the equation X(= 108Al/lAT)= ^1P1 + a2p2 + ... anpn where P1, etc., arethe percentages of the oxides and a1? etc.,are the factors in the following table:

1. A. Winkelmann and O. Schott, Ann.Physik., 51,135,1894.2. S. English and W. E. S. Turner, /.Amer. Ceram. Soc. 10, 551,1927;ibid., 12, 760,1929.3. P. Gilard and L. Dubrul, VerresSilicates Ind. 5,122,141,1934.4. F. P. Hall, /. Amer. Ceram. Soc. 13,182,1930.Thermal Shock. Sudden heating orcooling: the stresses set up by thedifferential expansion or contractionbetween the outside and inside of athermally-shocked ceramic may cause itto crack.Thermal Shock Tests. Panel Test.(ASTM C38-89 and B.S. 1902 Pt.5.11)Panels of refractory bricks are heated tothe test temperature, cooled by waterspray and the weight loss andappearance after a predeterminednumber of such cycles are observed. SeePANEL SPALLING TEST.

Cylinder Test (Water Quench). (PRE/R5Part 1) the number of cycles required torupture a hollow cylinder 50mmdiameter 50mm high by cycling betweena furnace at 9500C and running water at10/200C is recorded. The test is severe;for types of refractory unsuited to it,there is:Prism Test (Air Quench) (PRE/R5 Part2), test pieces 114 x 64 x 64 mm arecycled between 9500C and a cold airblast for 5 min. followed by a bend testunder a load of 0-3MN/m2. The cycle isrepeated to rupture, or for 30 cycles.Small Prism Test (B.S. 1902 S.5.11 1986Method 1902-511. The test pieces are 75x 50 x 50 mm and subjected to 10 min.cycles between cold and 1000-12000C,and subjected to an equal stress in eachcycle. Testing is to rupture.Water-Quench Test (for unshapedrefractories) B.S. 1902 Pt.7.6. The test isa water quench cycle from 12000C to

SiO2

B2O3

Na2OK2OMgOCaOZnOBaOPbOAl2O3

Winkel-mann &Schott(1)2.670.33

33.3328.33

0.3316.676.0

10.010.016.67

English&

Turner(2)0.50

-6.5341.639.04.5

16.37.0

14.010.61.4

Gilard &Dubrul

(3)0.4

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07.5+0.35p7.75-O.25p9.1+0.14p

U.5-O.05p2

Hall

(4)

2.038.030.02.0

15.010.012.07.55.0

cold running water, for 20 cycles or until10% of the specimen weight has beenlost. The test conditions are specificallydesigned for samples cast frommonolithic insulating refractories.Ribbon Test (B.S. 1902 Pt.5.12) Thelower faces of a series of bricks areheated by a linear burner 1.52m long at9800C for 15min. The bricks are thencooled to 2000C. The reduction inmodulus of elasticity (using a non-destructive ultrasonic method) after 5-10cycles provides a measure of themalshock resistance. ASTM CIlOO alsospecifies a ribbon test.ASTM C484 is a test for ceramic tiles,which are removed from an oven at145°C and placed on a sheet ofaluminium at room temperature. C149 isa test for glass containers involvingtransfer from hot to cold water. C600 is awater-quench test for glass pipes.Thermal Spalling. SPALLING (q.v.)caused by stresses resulting from non-uniform dimensional changes of a brickor block produced by a difference intemperature.Thermal Transmittance. (U-value). Theheat flux density through a givenstructure divided by the difference inenvironmental temperatures on eitherside of the structure under steady-stateconditions. The units are W/m2K. BS 874Pt3 describes a calculated hot-boxmethod for its determination for largestructural elements.Thermal Wheel. See Munter Wheel.Thermalite Ytong. Trade-name: Alightweight concrete made from portlandcement, sand, and pulverized fuel ash;these are well mixed with water and asmall proportion of aluminium powder isthen added. This causes gas bubbles toform. Blocks of the cellulated materialare then autoclaved. The material is adevelopment of the Swedish material

YTONG (q.v.). (Thermalite Ytong Ltd,Lea Marston, Sutton Coldfield,England.)Thermistor. A material having a hightemperature coefficient of electricalresistance. Ceramic thermistors having anegative temperature coefficient (theusual type) are made from mixtures ofthe oxides of Mn, Fe, Ni, Co, Cu and U;the batch is shaped and fired to lowporosity. The electrical resistance ofBaTiO3 to which rare earths, Bi or Thhave been added has a high positivetemperature coefficient. The propertiesof thermistors make them useful invarious instruments and controllers.Thermocouple. A device for themeasurement of temperature on thebasis of the electric current generatedwhen the junction between twodissimilar conductors is heated. Thecommon types of thermocouple, withtheir maximum temperature of use(when protected) are: Copper/Constantan, 4000C; Iron-Constantan,10000C; Chromel/Alumel, 12000C;Platinum Platinum-Rhodium, 17000C.Thermocouples with Tungsten/Iridium,or with Silicon-Carbide/Carbon,elements have been used for specialpurposes at 20000C. B.S. 1041 Pt. 4 givesguidance on the choice and use of anappropriate thermocouple.Thermocromaticity. The phenomena ofcolour value readings changing as thetemperature of the object being measuredvaries (R.L. Weintraub, Ceram. Eng. SciProc. 13, (1/2), 1992, p 385.Thermodyne Test. A test to determinethe durability of optical glass in contactwith moist air. Freshly broken or opticallypolished surfaces, sealed off in a flasktogether with a quantity of water, aresubjected to a series of temperaturecycles, each of 2 h duration, from 15 to600C in air saturated with water vapour

for a period of 12 days. (W. M. Hampton,Proc. Physical Soc, 54, 391,1942.)Thermography. The observation of thetemperature distribution across buildingsor objects by infra-red photography.Photographic prints, or computer-processed images, show regions invarious colours, corresponding to theirtemperatures.Thermoluminescence. Emission of lightby heated ceramics. The energy resultingfrom radioactive decay of smallconcentrations of radioactive materialsin ceramic raw materials is stored in thecrystal lattices by electron trapping incrystal flaws such as lattice vacancies andimpurity sites. Some of these bonds arestable at room temperature, butdisturbed by temperatures abovec.300°C, when the energy is emitted aslight. Firing would have released anyprior trapped electrons, so the degree ofthermoluminescence of fired potterywhen it is re-heated gives someindication of the time since it was fired,(i.e. an estimate of the age of ancientpottery), when compared to thethermoluminescence produced by aknown dose of radiation in thelaboratory. Aitken Tite & Reid, Nature202, (4936), 1032, 1964.Thermoplastic Decoration. Colours aredispersed in a thermoplastic medium(one which softens when heated andhardens when cooled, without changingother properties). They are then appliedthrough a hot screen (see SCREENPRINTING) on to cold ware, whichhardens the design.Tbermoscope. See PYROSCOPE.Thick-bed. Mortar or adhesive layers forTILE-FIXING (q.v.) greater than 6mmthick.

Thick-film Electronics. Electroniccircuitry produced by printing circuitcomponents on to a substrate.

Thimble. (1) An item of kiln furniture,Fig. 4, pl77; it is conical, hollow, andwith a projection at the base to supportthe pottery-ware being fired; thimblesare inserted into one another so that abung of ware can be built up.(2) A refractory shape, usuallyresembling the letter L, used to stiroptical glass in a pot.Thimble-Bat. A refractory BAT (q.v.) ofa type used in the firing of pottery; it isperforated to hold the ends of THIMBLES(q.v.).Thin Bed. Mortar or adhesive layers forTILE-FIXING (q.v.) up to about 3mmthick.Thin-film Electronics. Electroniccircuitry produced by depositing circuitcomponents of microscopic dimensionsby CVD, vacuum and sputteringtechniques.Thin Section. A section of material thathas been prepared, by grinding toextreme thinness (about 30jnm), forexamination by transmitted light under apolarizing microscope. For details of thetechnique see such books as Thin SectionMineralogy of Ceramic Materials by G.R. Rigby, 2nd Ed. 1953, and Microscopyof Ceramics and Cements by H. Insleyand D. Frechette, 1955.Thirsty Glass, POROUS GLASS (q.v.), so-called because of its affinity for moisture.Thirting. Cutting ball clay into blocksabout 0.25m cube.Thivier Earth. A siliceous hydrated ironoxide from Thivier, 19 miles N.E. ofPerigueux, France. A quotedcomposition is: 83% SiO2,10% Fe2O3,2% Al2O3, 1% CaO, 1% alkalis, 3% losson ignition. It has been used as a redcolour for pottery decoration.Thixotropy. The property, exhibited bymany clay slips for example, of becomingmore viscous when left undisturbed butmore fluid when stirred. The name was

first proposed by T. Peterfi (Arch.Entwicklungsmech. 112, 689,1927).Thoria. See THORIUM OXIDE.Thorium Borides. At least two boridesare known: ThB4 (grey) and ThB6 (deepred). The more attention has been paidto the tetraboride, the properties ofwhich are: m.p., 22000C (but oxidizesslowly above 10000C); thermalexpansion, 5.9 x 1(H (20-10000C); sp. gr.8.45 g/ml; modulus of rupture (200C),140 MNm-2. Some properties of ThB6

are: m.p. 22000C; sp. gr. 6.1.Thorium Carbides. Two carbides areknown: ThC, m.p. 2625°C; ThC2, m.p.27000C. Monoclinic ThC2 inverts to thetetragonal form at 1410 + 200C and fromtetragonal to cubic at 1500° -^200C.These special carbides are of potentialinterest in nuclear engineering.Thorium Nitride. Three nitrides havebeen reported: ThN, m.p. 26500C;Th2N3, decomposes at 17500C; Th3N4.Thorium Oxide or Thoria. ThO2; m.p.approx. 32200C; sp. gr. 9.8. Thermalexpansion (20-10000C) 9.3 x 1(H; (20-2500°C)10.9 x 1(H-Thoria has been used for crucibles forthe melting of refractory metals but ithas poor thermal-shock resistance.Thorium Sulphides. Three sulphideshave been reported: Th4S7, Th2S3 andThS. Crucibles made of these sulphideshave been used as containers for moltenCe.Thorpe's Ratio. A formula suggested byProf. T. E. Thorpe in 1901 for assessingthe probable solubility of a lead frit: thesum of the bases expressed as PbOdivided by the sum of the acid oxidesexpressed as SiO2 should not exceed 2.Thread Guide. Porcelain thread guidesare satisfactory for use with cotton, wool,or silk; man-made fibres, e.g. rayon andnylon, are more abrasive and sinteredalumina or synthetic sapphire thread

guides are used. Thread guides havebeen made from or coated with titaniumdioxide heated in hydrogen. The whiteTiO2 insulator turns black, and becomesconducting (see MAGNELI PHASE) whichprevents the frictional build-up of staticelectricity on the guides.Three-edge Bearing Method. Inmeasuring the load-carrying capacity ofconcrete pipes, the load is applied at thecentre of the pipe, resting on two outsideedges.Theshold Limit Value (TLV). Thatconcentration of (possiblity harmful)substance to which it is believed nearly allworkers may be exposed day after daywithout adverse effect. The values aretime-weighted average concentrations fora 7 or 8 hour day and a 40 hour week.Throat. (1) The part of a blast furnace atthe top of the stack.(2) The zone of decreased cross-sectionfound between the port area and thefurnace chamber in some designs ofopen-hearth steel furnace.(3) The submerged passage connectingthe melting end to the working end of aglass-tank furnace; the refractory blocksforming the sides of the throat areknown as THROAT CHEEKS, SLEEPERBLOCKS or DICE BLOCKS, the refractoriesfor the top are the THROAT COVER. Athroat below the bottom of the melter isknown variously as a submerged,submarine or sump throat.Throwing. The method of shapingpottery hollow-ware in which a ball ofthe prepared body is thrown on arevolving potter's wheel, where it iscentred and then worked into shape withthe hands. The process is now chieflyused by studio potters, although a smallamount of high-class commercial potteryis still made in this way.Thwacking. The process by which claypantiles are given their final curved

shape. When partially dry, the tiles areplaced on a wooden block of the correctcurvature and beaten to that contour bymeans of a bevelled block of wood(hence the alternative name BLOCKING).Any distortion of the tile caused byunequal shrinkage during thepreliminary drying is thus corrected.Tickell Roundness Number. An index ofthe shape of a particle in terms of theratio of the actual area of the projectionof the grain to the area of the smallestcircumscribing circle; (F. G. Tickell, TheExamination of Fragmental Rocks 1931).Tiering. See TORCHING.Tiger Eye. A particular type ofAVENTURINE (q.v.) glaze.Tiger Skin. A decorative SALT GLAZE(q.v.), in which CRAWLING gives astriped or mottled appearance.Tile. See FLOOR TILE, ROOFING TILE,WALL TILE. In Europe, the chiefdistinction is between glazed andunglazed tiles, rather than between floortiles and wall tiles; a given range of tilesmay be supplied for either application.B.S. 6431 Pt.l classifies tiles according tomethod of manufacture (extruded, dust-pressed or cast) and their waterabsorption (group I low 3%; medium 3-10, subdivided Ha 3-6, Hb 6-10;highlO%, Group III). Other parts of thestandard specify a wide range ofrequirements and test methods.Standards for glazed wall and floor tilesin the USA deal separately withindividual properties and test methods.See ASTM C482, C483, C484, C485,C499, C501, C502, C609, C627, C648,C650, C895, C1026, C1027, C1028. In theUSA the word 'tile' also denotes hollowclay building blocks, in such self-evidentcombinations as 'load bearing tile,''partition tile;' DRAIN TILES and

AGRICULTURAL TILES are FIELD DRAINPIPES. The following ASTM standards

relate to structural clay tile: C212, facingtile; C34 load-bearing wall tile; C56 non-loadbearing screen tile.Tile Bridging. Shrinkage of the base onwhich tiles are laid leads to compressionof the tiling, and the formation of a gapbehind the tile(s), which arch clear of thebase. (New concrete floors can undergosubstantial shrinkage.)Tilebacker. Extruded polystyrene foam,reinforced with glass-fibre mat, andplastic modified mortar used as anunderlay for tiles.Tile Fillet. Roofing tiles cut and fitted toform a fillet as an alternative to flashings.See FLASH (2).Tile Hanging. The process of fixingroofing tiles (as distinct from wall tiles)on a vertical outside wall.Tile Listing. Roofing tiles used to form asplayed fillet at abutments.Tilemaster. An electronic system, basedon an array of 512 x 512 light-emittingdiodes, used to measure length, widthand rectangularity of tiles, and to detectdamaged edges and corners.Tiling. The fixing of tiles to walls andfloors is governed by several BritishStandards, B.S. 5383 is a code of practicefor the design and installation of internaltiles and mosaics for walls and floors.B.S. 8000 specifies workmanship onbuilding sites. Pt. 11 specifying a code ofpractice for ceramic, terrazzo, mosaicand natural stone tiles. Pt.9 specifiesfloor screeds; Pt.6 slating and tiling ofroofs. B.S. 5980 is the specification forwall tile adhesives. Proper specificationof appropriate adhesives and fixingmethods, and a high standard ofworkmanship are essential to the successof tiling.Till. Older name for BOULDER CLAY

(q.v.).TI-LOC Process. Trade-name: a processfor the treatment of steel prior to

enamelling, it is claimed to improveadherence and to eliminate the need fora ground-coat. (Strong Mfg. Co.,Sebring, Ohio, USA.)Timbrell-Coulter Shearicon. Semi-automatic image-shearing equipment tosize particles or features observed byoptical microscopy, or of images fromoptical or electron photomicrographs, ora television picture. (J.Powder BulkSolids Technol. 3 (1), 26, 1979).Tin Ashes. Mixed oxides of tin and leadformerly used as a constituent of someglazes; the metals were mixed in a ratiothat would produce SnO2 and PbO in therequired proportions when the alloy wasoxidized in a preliminary calcination.Tin Oil. A mixture of SnCl2, SnCl4, Sand oils; it is used in the preparation ofsome types of LUSTRE (q.v.).Tin Oxide. Two oxides exist but themore common is stannic oxide, SnO2,m.p. approx. 16300C; sp. gr. 7.0. It isused as an opacifier and in thepreparation of colours, e.g. CHROME-TINPINK (q.v.). Properties making this oxideof some interest as a special ceramic areits high thermal conductivity and lowthermal expansion (20-10000C) 4 x 10"6;it is sensitive to reducing atmospheres.Tin oxide has been used for makingrefractory feeders for high-lead glasses.Tin-Vanadium Yellow. See VANADIUM

YELLOW.Tinsel. Very thin glass that has beencrushed and silvered for use as adecorative material (cf. GLASS FROST).Tirschenreuther Pegmatite. A by-product of china-clay washing,comprising quartz and feldspar, used inporcelain bodies and in spray-driedprepared bodies. (Hutschenreuther AG,Germany).Tit. A small imperfection on glassware.Titanate Ceramics. A group of electro-ceramic materials generally based on the

compound BARIUM TITANATE (q.v.) butoften with the addition of other titanates,zirconates, stannates or niobates. Theseceramics are notable for their highdielectric constant (up to, and evenexceeding, 10 000 compared with a valueof 5-10 for the more common ceramicmaterials); because of this property theyfind use in capacitors. Titanate ceramicsare also used where piezoelectricproperties are needed, i.e. in transducers.Titania. See TITANIUM OXIDE.Titanising. Trade-name (United GlassLtd., England). A process for thestrengthening of glassware by applyingliquid titanium compounds to the glasssurface while it is still hot; the glassthereby acquires a small amount ofmetal oxide in the surface layer, and thisenables the article to retain a greaterproportion of its strength when in use.Titanite. See SPHENE.Titanium Borides. The most important isTiB2; m.p. 29200C with excellentoxidation-resistance up to 10000C; sp. gr.(theoretical). 4-5, Knoop hardness(KlOO), 2710; thermal expansion,9.7 x 10-6 (200-18000C). Modulus ofelasticity (GNm-2) of material ofdensity 4.21: 43.5 (200C), 42 (10000C), 30(20000C). Transverse strength MNm-2 at25°C is greatly dependent on crystal size:20mm, 300; 35mm, 200; 100mm, 105.Thermal conductivity 0.10 c.g.s. (1000-14000C). Electrical resistivity (200C) 20ma-cm increasing to 80 at 12000C. Inertto molten Al and Zn but not to ferrousalloys. It has been used in rocket nozzles,as a constituent of cermets, and for boatsfor the evaporation of Al (for thin-filmcoatings). Other compounds that havebeen reported include TiB, Ti2B andTi2B5, but these are stable only in theabsence of carbon.

Titanium Carbide. TiC; m.p. 31500C; sp.gr. 4.9, thermal expansion (25-10000C)

8 x 1(H (25-20000C) 9 x 1(H. A hardrefractory compound; it has found use asthe ceramic component of some cermets.Titanium Dioxide. See TITANIUMOXIDES.Titanium Nitride. TiN; a specialrefractory material; m.p. approx. 30000C;thermal expansion (25-14000C) 9 x 10"6.It can readily be produced from TiCl4

and NH3. TiN coatings on metal cuttingtools act as a diffusion barrier toimpurities. They have higher electricalconductivity and better adhesion thanalumina, and are used as an undercoatfor Al2O3 coatings on tungsten carbide.Thin TiN films show iridescentinterference effects, and are used asdecorative hard surfacing for watchesand jewelry.Titanium Oxides. The common oxide isTiO2; m.p. approx. 18500C. Used as anopacifier, particularly in vitreousenamels, and as a constituent of someceramic colours. Titania and titanateelectroceramics, for use in the radio-frequency field, are based on this oxideand its compounds. Titania occurs inthree crystalline forms: ANATASE,BROOKiTE and RUTILE (see under eachmineral name). Ti2O, TiO, Ti2O3 andTi3O5 also exist.Titanium Silicides. Several compoundsexist. Ti5Si3; m.p. 2120°C; sp. gr. 4.3; hasgood resistance to high-temperatureoxidation but not to thermal shock.Titanium Suboxides. See MAGNELIPHASE.Titanizing. See TITANISING.Titzicon. Na08+x Zr1..55SixP^xO11 seeNASiCON, of which titzicon is amodification usually with enhancedamount (30%) of glassy phase.TLV. Threshold Limit Value.Tobermorite. A hydrated calcium silicateapproximating in composition to5CaO.6SiO2.5H2O. Tobermorite gel is

the principal cementing compound inhardened portland cement.Toggle Press. See MECHANICAL PRESS.Toki. Japanese hard-fired eathenware. Aquoted body recipe is: 70% clay, 10%pegmatite, 20% ground pitchers.Tomography. Investigation of theinternal structure of an article based onthe detection of emissions fromradioactive elements distributed withinthe item. A 3-dimensional representationof the internal structure is built up bycomputerised reconstruction from asuccession of 2-dimensional cross-sections. Resolutions of 10|im can beachieved.Tong Outcrop Clay. A fireclayassociated with the Better Bed coal,Yorkshire, England. The raw claycontains about 65% SiO2, 22% Al2O3,1.5% Fe2O3 and 1.6% alkalis.Tongue. See MIDFEATHER.Tonstein. A hard kaolinitic depositsometimes found as thin bands in theCoal Measures. The kaolinite crystalsare large but are not orientated, havingapparently been formed in situ from agel. Tonstein differs from FLINT CLAY(q.v.) in that it is not a LATERITE (q.v.).Tonsteins were first observed inGermany; the name means 'Clay Stone'.Tool (Ceramic). Ceramic tools for themachining of metals retain strength,hardness and wear-resistance at hightemperatures, giving long life and cleancutting at high cutting speeds>vMaterialsused are Sialons, boron carbide, cubicboron nitride, hard metals especially Co-bonded tungsten carbide, cementedoxide (alumina bonded with a transitionmetal) and pure alumina (to which asmall amount of MgO is added to inhibitcrystal growth to lOjLim).Tooling. The rubber or plastic bag usedin isosTATic PRESSING (q.v.); the termmay also include the rigid core or former

needed for the pressing of ware that ishollow or recessed.Toothing. In structural brickwork, bricksleft projecting at the temporarytermination of a wall so that futureextensions can be bonded in.Top-Blown Converter. See CONVERTER.Top-fired Kiln. A kiln with the burnersin the roof, rather than in the walls, orfired by feeding coal or oil throughapertures in the roof. The typical kiln ofthis type is the Hoffmann annular kiln,but the Monnier kiln provides anexample of a topfired car-tunnel kiln.Top-hat Kiln. An intermittent kiln of atype sometimes used in the firing ofpottery. The ware is set on a refractoryhearth, or plinth, over which a box-shaped cover is then lowered.Top-Jet Firing System. For morecomplete utilisation of the firing space ina tunnel kiln, the flue-gas passage underthe setting is omitted. High velocityburners, staggered longitudinally, areinstalled vertically in the sidewalls abovethe usable firing space. The burners aredirected downwards and the combustiongases directly led into the car loadingabove the setting level. The system wasintroduced by Riedhammer (Germany)(Ceram Forum Int/DKG (6), 466, 1981).Topping Material. Refractory above themetal level in an induction furnace.Top Pouring. See DIRECT TEEMING.Topaz. Al2SiO4(OH5F)2. Occurs ineconomic quantities in Australia, Brazil,Nigeria and USA. After it has beencalcined, the material has a compositionsimilar to that of mullite and it has beenused to a small extent, either alone ormixed with calcined kyanite, for makinghigh-alumina refractories.Torbed Process. A toroidal, rotating,fluidized bed of particulate feed some20-50mm deep is established by a fanwhich directs a flow of air through a

series of rotating apertures in a steel orceramic ring. High specific throughputsare achievable from a compact plant,easily dust-sealed. The system can beused for continuous calcining, expansion,exfoliation, flash drying, combustion orliquid coating of particles, up to 13600C.Torching. The pointing, with cement ormortar, of the underside of a tiled roof;also sometimes known as TIERING (cf.SARKING) .

Torkret Process. German process forspraying refractory patching material onthe walls of steel-furnace ladles.Tornebohm's Minerals. See ALITE;BELITE; CELITE; and FELITE.Torsion Viscometer. An instrumentmuch used for works' control of theviscosity and thixotropy of clay slips. Itconsists of two concentric cylinders, theslip occupying the space between them;the inner cylinder is suspended from atorsion wire and is released from aposition equivalent to a 360° twist in thewire. The overs wing (past zero) gives ameasure of viscosity; comparison of thisdegree of overswing with that after aspecified lapse of time provides ameasure of the thixotropy of the slip.Tortoiseshell. A decorative effectproduced on a lead glaze by dustingmetal oxides (MnO2, CoO or CuO) overthe surface and firing.Tortus. A floor friction test machine. Atracked trolley, about 30 cm long, dragsa spring-loaded probe about lcmdiameter across the floor to be tested.Various materials (e.g. leather, rubber)are used to tip the probe. A continuousreading of the frictional force betweenthe probe and floor is obtained. Themethod was devised by British CeramicResearch Ltd, and the machine made bySevern Science (Instruments) Ltd,Bristol.Toseki. Japanese china stone (q.v.).

Total Energy System. The use of e.g.diesel generators to produce mechanicalpower, heat and electricity on-site.Total Transfer Printing. A developmentfrom the MURRAY-CURVEX MACHINE(q.v.) in which the whole of the design istransferred from design plate to ware.This enables multicoloured printing bysuccessive operations of the samemachine. The design is prepared on aheated metal screen, and squeegeed onto a warmed silicone rubber substrate,from which it is picked up by a siliconepad, and transferred to cold ceramicware. The key to the total transfer is thatas the medium of the colour cools, itbecomes more tacky, and carefuldevelopment of the inks and pads, withproper combination of surfaceproperties, allows complete transfer ofthe design. (British Ceramic ResearchLtd, UK Pat 2118900 A, 1983incorporated into a commercial machineby Service Engineers pic).Totanin. Trade-name: an ammonium-based SYLPHiTE LYE (q.v.) (Lambethand Co. Ltd., Liverpool).Toughened Glass. Glass that has beenrapidly cooled so that the surface layersare in compression; the thermal andmechanical endurance are increased and,if the glass does break, it will shatter intosmall, granular, fragments rather thaninto large and dangerously jagged pieces.Toughness. The ability of a material toresist FRACTURE (q.v.). Variousmechanisms exist which absorb the energyrequired to form new fracture surfaces.These increase the toughness of theceramic and may act concurrently, toenhance the toughening effect. See also

FRACTURE TOUGHNESS; STRESSINTENSITY FACTOR; CRACK BRIDGING;QUASI-BRITTLE FRACTURE; STRAINHARDENING; CRACK BRANCHING; CRACKDEFLECTION; TRANSFORMATION

TOUGHENING; WHISKER REINFORCEMENT;FIBRE REINFORCEMENT; MULTIPLECRACKING; DISPERSION STRENGTHENING.Tourmaline. A complex alumino-borosilicate that will often contain smallamounts of iron and alkalis. Whenheated, tourmaline loses water at 150-7500C; B2O3 is evolved at 950-9700C.Tourmaline is an accessory mineral inthe granite from which the Cornish chinaclays are derived.Tower Packing. Increased surface areafor the reaction, and longer durations,are provided for chemical reactions if theliquid reagents are allowed to trickledown a tower filled with inert shapes ofhigh surface area. Chemical porcelain orother ceramics are frequently used. Suchtower packings may also act asCATALYST CARRIERS (q.v.). The ASTMStandard is C515.Towing. The smoothing, generally on apowered wheel, of the outer edge ofdried pottery flatware before it is fired.Tow is commonly used for the purpose,but sandpaper or a profile scraper arealso sometimes used.Trace Flue or Trace Hole. A smallhorizontal passage or flue left in a settingof bricks in a kiln to facilitate themovement of hot gases.Trailing. A method of slip decorationsometimes used by the studio potter: apattern is formed on the ware by meansof a viscous slip squeezed through a fineorifice, e.g. a quill.Tramp Iron. Accidental metalliccontamination during manufacture.Transducer. A device for the directtransformation of electrical energy intomechanical energy, PIEZOELECTRIC(q.v.) ceramics are used for this purpose.Transfer. See DECAL.Transfer Glass. US term for optical glassthat has been cooled in the pot in whichit was melted (cf. ROLLED GLASS).

Transfer Ladle or Hot-metal Ladle. Alarge ladle lined with refractory material(usually fireclay bricks) for the transportof molten pig-iron from a blast furnaceto a hot-metal mixer or to a steelmakingfurnace.Transfer Printing. An intaglio process ofdecoration, particularly applicable topottery-ware; a single-coloured pattern istransferred directly from a printing plateor roller by means of thin paper. Thecolour used is generally dispersed inlinseed oil; soft-soap is the traditionalsize for the transfer paper but varioussynthetics have also been used (cf.LITHOGRAPHY).

Transfer Ring. See HOLDING RING.Transformation Points. Temperatures atwhich the coefficient of thermalexpansion of a glass changes. For anyone glass, there are normally two suchpoints known respectively as the Tgpoint and the Mg point: the Tg point isthe first temperature at which there is asudden change in expansion when theglass is heated at 4°C/min; the Mg pointis the temperature at which the thermalexpansion curve reaches a maximum andis usually equal to the softeningtemperature.Transformation Toughening. Increasingthe TOUGHNESS (q.v.) of a ceramic orcomposite by using a change in CRYSTALSTRUCTURE to absorb energy and inhibitFRACTURE (q.v.). The method isparticularly applicable to ZIRCONIA(q.v.). Tetragonal zirconia crystalspresent in bulk zirconias are stable,except in highly stressed areas near cracktips. There, they undergo aMARTENSITIC TRANSFORMATION (q.V.)to monoclinic zirconia, absorbing energyand inhibiting CRACK PROPAGATION(q.v.). This toughening mechanism iseffective in fine-grained single-phasetetragonal zirconia; in two-phase zirconia

ceramics containing precipitatedtetragonal zirconia; in two-phasealumina or silicon nitride containing adispersed phase of tetragonal zirconia.Transit-mixed Concrete. Concretewholly mixed in the mixer lorry on theway to the site. (cf. SHRINK-MIXEDCONCRETE).Transition Aluminas. Metastablecrystalline aluminas (there are severalseries) which contain minor amounts ofOH- ions. They are usually produced bygradual heating of alumina hydrates.Transition Scarp. A RIB MARK when acrack changes from one mode of growthto another.Translucency. Bodies are translucent ifthey transmit light, though notTRANSPARENT, (q.v.). Translucency is animportant attribute, enhancing theappearance of certain types of highquality tableware. It agrees reasonablywell with LAMBERT'S LAW (q.v.). B.S.5416 1990 'China Tableware' includes asimple test for translucency, measuringthe percentage of white light transmittedthrough a 2mm thick sample. TheCOMBINED NOMENCLATURE of the E C(q.v.) also includes a (different) test fortranslucency, based on the outline of anobject being visible through ware 2 to4mm thick, illuminated by a standardsource.Translucent Vitreous Silica. See underVITREOUS SILICA.Transmission Electron Microscopy. SeeELECTRON MICROSCOPY.Transmutation Glaze. A term that hasbeen applied to a glaze such as ROUGEFLAMB£ (q.v.) or SANG DE BOEUF (q.v.).Transparent Ceramics. Bodies aretransparent if they transmit light withoutscattering or diffusion, so that objects ontheir far side can be seen clearly. Forceramics to be transparent, their crystalstructure must not be disrupted by

impurities, and careful sintering isrequired to remove any residual closedpores which might act as light scatteringcentres.Transparent Vitreous Silica. See underVITREOUS SILICA.Transverse-arch Kiln. An ANNULARKILN (q.v.) that is divided into a series ofchambers by fixed walls (hence thealternative name CONTINUOUSCHAMBER KILN). The axis of the archedroof of each chamber is transverse to thelength of the kiln. This type of kiln findsuse in the heavy-clay industry.Transverse Strength. See MODULUS OFRUPTURE.

Trass. A product of the partialdecomposition of volcanic ash; it is oftenconsolidated as a result of infiltration ofcalcareous or siliceous solutions. Trass isused in POZZOLANA (q.v.).Travelling Thermocouple. A continuousrecord of the temperature applied toware in a (tunnel) kiln is obtained from athermocouple arranged to travel with theware through the kiln.Traversing Rule. A wooden straight-edge used for floating a plane surface, bymoving it, with a sawing motion, with itsends resting on screed battens or guidesat the correct thickness. (B.S. 6100 Pt.6).Trebuchon-Kieffer Annealing Schedule.A procedure for annealing the glasscomponents of electron tubes; it is basedon annealing at the transformationtemperature for 20 min followed bycooling at a rate dependent on thenature of the glass and its thickness (G.Trebuchon and J. Kieffer, VerresRefract., 4, 230,1950; Glass Industry, 32,240, 1951.)Trefoil. A refractory structure in thepreheaters of some rotary kilns, dividingthe kiln into three channels to improvecontact between the hot gases and theburden.

Tremolite. 2CaO.5MgO.8SiO2.H2O.Tremolite is sometimes present insteatite rocks, rendering them unsuitablefor use as a ceramic raw material.Triangle Bar. One type of metal supportfor vitreous enamelware during firing.Triaxial Test. A method of testing clay inwhich the test-piece, in a plastic state, isenclosed in a rubber envelope and is thensubjected to uniform hydrostatic pressurewhile it is also being loaded axially. Astress/deformation diagram is plotted.Triaxial Whiteware Body. One based ona three-component system of clay, fillerand flux. Most traditional pottery bodiesfall into this class. The filler is usuallyquartz, but may be alumina. Fluxes areusually feldspathic materials. Higher claycontent improves unfired workability;higher flux content increases fusibility;the filler content affects thermalexpansion and so glaze-body fit. In thetriaxial quartz-feldspar-clay system, onlya relatively small range of compositionsare suitable for pottery bodies. (See ADinsdale. Pottery Science, Ellis HorwoodLtd. 1986 for a concise discussion).Tribomet Process. Trade-name. Anelectrodeposition process for theproduction of wear-resistant orlubricating coatings. Theelectrodeposited particles are metalparticles. The composite particles mayincorporate hard borides, oxides, nitridesor carbides; or molybdenium disulphideor other solid lubricant. (Bristol Aerojet.Br.Pats 1220078 and 1220331,1971).Tricalcium Aluminate. 3CaO-Al2O3;melts incongruently at 1539 ± 5°C;thermal expansion (0-12000C) 10 5 x10-6 This compound is present inPortland cement.

Tricalcium Disilicate. 3CaO.2SiO2 (seeRANKINITE).Tricalcium Pentaluminate. A compound,3CaO.5Al2O3, formerly believed to be

present in high-alumina hydrauliccement. It is now known that a melt ofthis composition consists of a mixture ofCaO.2Al2O3 and CaO-Al2O3, the lattercompound being responsible for thehydraulic properties.Tricalcium Silicate. 3CaCSiO2

undergoes the following transformations:Triclinic I 62Q \ Triclinic II 920°cTriclinicIII 95Q 0C Monoclinic ?90X^Orthorhombic 1QQ5Q 0^ Hexagonal.Dissociates at approx. 19000C to formCaO and 2CaO-SiO2; thermal expansion(0-100O0C) 12.9 x 10-6. This compound isthe principal cementing constituent ofPortland cement, small quantities of MgOand Al2O3 usually being present in solidsolution. Tricalcium silicate is also presentin some stabilized dolomite refractories.Trichromatic Printing. The system ofprinting used to print coloured pictureson paper. The image is made up of tinydots of three primary colours, present insuch numbers as to give the impressionof the desired colour by mixing. A fourthblack pigment is usually added, to ensuredense blacks.Tridymite. SiO2; sp. gr. 2.28. Accordingto the classical research of C. N. Fenner(Amer. J. ScL, 36, 331,1913) tridymite isthe form of silica that is stable between870 and 14700C; he considered that thereare three crystalline varieties changingreversibly, one into another, as follows:oc-tridymite (117°C) prtridymite (163°C)P2-tridymite.More recent research has indicated afurther inversion at about 2500C and hassuggested that tridymite can be producedonly in the presence of foreign ions,which enter the crystal lattice and causedisorder in the structure.Trief Process. A process for makingconcrete with PORTLAND BLAST-FURNACE CEMENT (q.v.) first proposedby a Belgian, V. Trief (Brit. Pat., 673

866,11/6/52; 674913, 2/7/52). The slag iswet ground and fed as a slurry to aconcrete mixer together with portlandcement and aggregate.Trimmers. See FITTINGS.Triple Brick. A brick 5Vz x 4 x 12 in (135x 102 x 305mm)Triple Round Edge. A type of wall tile(see Fig. 7, p350).Tripoli. A sedimentary rock consistingessentially of silica and having a porousand friable texture. A principal use is asan abrasive.Tri-stimulus Values. A set of threechosen primary colours. All colours thatcan be made by additive mixtures ofthese three primaries are known as thegamut of the chosen primaries. Theobjective for TRICHROMATIC PRINTING(q.v.) is to find three primaries whosegamut covers the whole range of colours.The ClE (Commission Internationald'Eclairage) specified three colourwavelengths which when mixed give anequal-energy White: Red 700nm; Green546.lnm; Blue 435.8nm. See COLOUR.Triton. (I)A rotary pulveriser and mixerused to prepare clay slip (A. Faure &Co., Limoges).(2) Trade-name, Wheatley & Co, Staffs,for FLOOR QUARRIES.(3) Trade-name, under which KAOWOOLwas originally sold in UK.The tradename has also been used for awetting agent, and, as Triton Milan, forroofing tiles.Trommel. See REVOLVING SCREEN.Trompe I9OeM. Decoration, mainlyapplied as transfers, which deceives theeye to simulate e.g. bas-reliefs, or lustresto simulate silver or marble.Tropenas Converter. See CONVERTER.TRRL Pendulum Test. A test for theSLIP RESISTANCE of floor tiles andpavers, (originally developed by theTransport and Road Research

Laboratory to measure the skidresistance of road surfaces. Road Note27,1960). A weighted pendulum isadjusted to carry a rubber slider along a5 inch (127mm) length of the surface tobe tested. The pendulum is releasedfrom a horizontal position, carrying withit a pointer which records the upswingon the other side of the vertical. Thegreater the upswing, the lower the skidresistance of the surface (though thescale is marked in reverse to give lowreadings for low skid resistance).Truck Chamber Kiln. See BOGIE KILN.True Density. A term used whenconsidering the density of a porous solid,e.g. a silica refractory. It is denned as theratio of the mass of the material to itsTRUE VOLUME (q.v.). (Sometimesreferred to as POWDER DENSITY, thoughif the grains contain imprenetrablepores, the true density will be greaterthan the powder density, which isassessed by grinding the material topowder form. B.S. 1902 Pt. 3.4 specifies aPYCNOMETER (q.v.) method forrefractories and Pt. 3.5 the REES-HUGILLFLASK method for powder density.True Porcelain, HARD PORCELAIN (q.v.).True Porosity. See under POROSITY.True Specific Gravity. The ratio of themass of a material to the mass of aquantity of water that, at 4°C, has avolume equal to the TRUE SOLIDVOLUME of the material at thetemperature of measurement. ASTMC604 specifies a gas-comparisonpycnometer test, and C135 a waterimmersion test for refractories.True Volume. A term used in relation tothe density and volume of a porous solid,e.g. a brick. It is defined as the volume ofthe solid material only, the volume ofany pores being neglected.Trumpet or Bell. A fireclay refractoryfunnel placed at the top of the assembly

of GUIDE TUBES (q.v.) to receive moltenmetal from the nozzle of a ladle in theBOTTOM POURING (q.v.) of steel.Trutile. A plastics grid to aid tile-fixing.The grid is fixed to the base to be tiled,using a little tile adhesive. Its voids arefilled with tiles, which are groutedwithout removing the grid.T-T-T Curve. Time-temperature-transformation curves describingmineralogical changes.TTZ. Transformation ToughenedZirconia (see ZIRCONIA andTRANSFORMATION TOUGHENING).Tube Bottom. One form of bottom for aCONVERTER (q.v.); it is made ofmonolithic refractory material, the airpassages being lined with copper tubes(Cf. SPIKED BOTTOM and TUYERE BLOCKBOTTOM).Tube Furnace. A type of furnace,particularly for vitreous enamelling,heated by tubes of heat-resisting metal inwhich gas is burned.Tube Mill. A ball mill having a cylinderlonger than usual, this usually being sub-divided internally so that the material tobe ground passes from one compartmentto the next, the grinding media insuccessive compartments beingappropriately smaller than in precedingcompartments.Tube Press. A high pressure tubular filterpress. The filter cake forms on the outsideof a hollow perforated steel tube, aroundwhich the filter cloths are wrapped.Hydraulic pressure forces the liquid to theinside of the tube. (English Clays LoveringPochin: various British Patents.Tubelining. A process of decoration,particularly for wall tiles requiring 'one-off designs. Lines of coloured slip areadded to the tile by squeezing slip from arubber bag through a narrow tube. Thetile is then fired and the pattern betweenthe raised lines is filled-in with various

colours and retired; alternatively, thecolours can be applied to the unfired tileand the once-fired process used.Tuckstone; Tuckwall. A shapedrefractory block fitting above the tankblocks of a glass furnace. The generalpurpose of the tuckstones is to protectthe top of the tank blocks from thefurnace gases and, in some types of tankfurnace, to act as a seal between the tankblocks and the side- and end-walls. Thecourse of tuckstones is sometimes calledthe TUCKWALL.

Tumbler. A refractory (or heat-resistantsteel) projection inside a rotary kiln, toimprove heat transfer and stir the feed.Tumblers can be arranged in series invarious axial rows, to form tumblingledges.Tumbling, BARRELLING (q.v.).Tundish. A rectangular trough lined withfireclay refractories and with one ormore refractory nozzles in its base.Tundishes are sometimes used betweenthe ladle and the ingot moulds in theteeming of steel.Tungsten Borides. Data have beenreported on five compounds. W2B; m.p.approx. 27000C; sp. gr. 16.7. WB exists intwo crystalline forms: a-WB, sp. gr. 16.0;p-WB, sp. gr. 15.7 (both forms melt atapprox. 29000C). W2B5 m.p. 22000C; sp.gr.13.1. WB2 m.p. 29000C. WB6, m.p.29200C.Tungsten-bronze Structure. This crystalstructure is typified by certain alkali metalcompounds of tungstic oxide. It is that ofseveral niobate electroceramics. Thestructure is that of MO6 groups(M=W,Ta,Ti,Nb etc) with spacesbetween, forming tunnels in the structure.These A-site tunnels are perpendicular tothe c-plane, in which their section issurrounded by 3(A3) 4(Al) or 5(A2)oxygen atoms. Lower valency cations arelocated in these tunnels above and below

the c-plane oxygen atom network. TheMO6 groups provide two distinguishableB sites. The general formula is[(Al)2(A2)4A3][(Bl)2(B2)8]O30.Inferroelectric tungsten bronzes, the polaraxes are usually parallel to the A-sitetunnels.Tungsten Carbides. WC; m.p. 2865°C;hardness, 1880 (KlOO); sp. gr., 15.7;modulus of rupture. 350-550 MNm-2 at25°C, thermal expansion (25-10000C) 5 x10"6. The principal use of this carbide isin cutting tools. There is also aditungsten carbide: W2C; m.p. 2855°C;sp. gr. 17.2; hardness 2150 (KlOO);thermal expansion (25-10000C) 4 x 10-6

Tungsten Nitride. W2N; exists in at leasttwo crystalline forms.Tungsten Oxide. The most commonoxide is WO3: m.p. 14700C; inversiontemp, approx. 3000C. Thermal expansion13.5 x 10-6 (20-3000C); 11 x Kh6 (300-7000C).Tungsten Silicides. There are least atthree compounds. WSi m.p. 21500C;WSi2 m.p. 21600C; sp. gr. 9.3; hardness(KlOO), 1090 kg/mm2; thermal expansion(20-10000C) 8.25 x Kh6; W3Si2 m.p.23400C; sp. gr. 12.2; hardness (KlOO) 770kg/mm2.Tuning-fork Test (for Glaze-Fit). A test-piece is made by joining, with clay slip,two bars of the extruded pottery body toa short piece of the same material. Thetest-piece is biscuit fired and the outerfaces are then glazed. The test-piece isplaced in a furnace and fired so that theglaze matures; it is then allowed to cool,while still in the furnace, and anyrelative movement of the two ends of the'tuning fork' is measured by amicrometer telescope. From thismeasurement the magnitude of anystress in the glaze can be calculated. Thetest was devised by A. M. Blakely (/.Amer. Ceram. Soc, 21, 243, 1938).

Tunnel Dryer. A continuous dryerthrough which shaped clayware can betransported on cars; it is controlled sothat the humidity is high at the entranceand low at the exit.Tunnel Kiln. A continuous kiln of thetype in which ware passes through astationary firing zone near the centre ofthe kiln. In the most common type oftunnel kiln the ware is placed on therefractory-lined deck of a car, acontinuous series of loaded cars beingslowly pushed through a long, straight,tunnel.Turbidimeter. An instrument fordetermining the concentration ofparticles in a suspension in terms of theproportion of light absorbed from atransmitted beam. An instrument of thistype designed for particle-size analysis isthe WAGNER TURBIDIMETER (q.V.)Turbine Blades. See GAS TURBINE.Turbostratic. A layered structure inwhich successive layers are oriented atrandom with respect to each other. Oneform of boron nitride has this structure.(US Pat 3,241,919 22/03/1966; E.I duPont de Nemours & Co).Turret Chain Machine. See PUFF ANDBLOW PROCESS.Tuscan Red. An iron oxide glazepigment.Tuscarora Quartzite. An importantsource of raw material for silicarefractories occurring in Pennsylvania,USA. A typical analysis is (per cent):SiO2, 97.8; Al2O3, 0.9; Fe2O3, 0.7;alkalis, 0-4.Tuyere. A tube or opening in ametallurgical furnace through which airis blown as part of the extraction orrefining process. In a blast furnace thetuyeres are water-cooled metal tubeswhich pass through the refractory liningof the BOSH (q.v.) (French wordmeaning 'a tube'). Tuyere bricks are

refractory bricks containing holes to actas tuyeres.Tuyere Block Bottom. One form ofbottom for a CONVERTER (q.v.). Thepassages for the air blast are separatepre-formed tuyeres each having severalholes; these tuyere blocks areinterspersed with solid refractory blocks,the whole bottom then being finished byramming refractory material into anyspaces.Twaddell Degrees (° Tw). A system fordenoting the specific gravity of a liquid:Degrees Twaddell = (sp. gr. - 1) x 200The specific gravity of solutions ofsodium silicate, for example, is oftenquoted in this form; each Twaddelldegree corresponds to a sp. gr. intervalof 0.005. This scale is named afterWilliam Twaddell who, in Glasgow in1809, made a hydrometer with this scaleto the design of Charles Macintosh (ofrainwear fame).Tweel Block. A type of refractoryblock used in the glass industry forsuch purposes as protection of a newly-set pot, the construction of a furnacedoor or damper, or control of the flowof molten glass. (From French tuile atile.)12.0 Temperature. See ANNEALING

POINT.Twin-plate Process.Twig. A small metal anchor forunshaped linings, usually V-shaped.Twinning. Intergrowth of two (or more)crystals of near-symmetry, with a definiterelation between their crystalorientations.Twin-plate Process. A process for thesimultaneous grinding and polishing ofboth faces of a continuously-producedribbon of glass; the complete flow-line isover 400m long. The process wasintroduced by Pilkington Bros. Ltd,England, in 1952.

Twist Hackle. A HACKLE MARK thatseparates portions of the crack surface,each of which has rotated from theoriginal crack plane due to rotation ofthe axis of principal tension.Tyler Sieve. See under SIEVE; for meshsizes see Appendix E.Tyndall Beam Lighting. A technique ofindirect lighting used to reveal normallyinvisible dust particles by sidewaysscattering of the light, as dust motes arerevealed by a shaft of sunlight.Tyranno. Trade-name. Ceramic fibres inthe Si-Ti-C-O system.TZP. Tetragonal Zirconia Polycrystals.See ZIRCONIA.

U-type Furnace or Hair-pin Furnace. Afurnace for the firing of vitreousenamelware, which is carried along aU-shaped path so that ware enters andleaves the furnace at adjacent points.U-value. See THERMAL TRANSMITTANCE.Udden Grade Scale. A scale of sievesizes introduced by J. A. Udden(Augustana Library Pub. No. 1, 1898).The basic opening is 1 mm, the scaleabove and below being a geometricalseries with a ratio of 2 (above 1 mm) andVi (below 1 mm).Ulexite. A boron mineral approximatingin composition toNa2O.2CaO.5B2O3.16H2O. Ulexite occursin Chile and Argentina. Trials have beenmade with this mineral as a flux in ceramicglazes.Ultimate Analysis. The chemical analysisreported in terms of constituent oxides,as distinct from the RATIONAL ANALYSIS(q.v.), which is in terms of the mineralsactually present.Ultimate Compressive Strength. Thecompressive strength of a test piece withload bearing surface ground flat andsmooth, and tested without packingmaterials. B.S. 1902 Pt. 4.2 specifies thetest for dense refractory materials.

UItrafine Powders. Powders in the sizerange 10-100nm have high surface areasand so enhanced reactivity in sintering.Additives are required to maintain goodflow properties in this size range.Ultragres. A floor tile comprising twoinseperable layers, the upper being hardand impermeable to moisture. (MosaBV, Holland).Ultrasonic Equipment. The word'ultrasonic' signifies vibration at afrequency greater than the maximumaudible frequency, and should not beconfused with 'supersonic', which signifiesa velocity greater than that of sound.Ultrasonic vibrations can be generated bypiezoelectric ceramics, by magnetostrictivedevices, or by 'whistles' in which there is asteel blade vibrated by a high-pressure jetof fluid. Ultrasonic equipment has beenused in the ceramic industry for thedispersion of clay slips, for metal cleaningprior to vitreous enamelling, and for flawdetection, particularly in large electricalporcelain insulators.Ultrasonic Machining. A speciallydesigned tool is vibrated at lowamplitude (c. 25jim) but at highfrequency (20 kHz). This tool combineswith abrasive slurry to microscopicallygrind the workpiece.Ultra-violet Absorbing Glass. Glassescan be made to absorb U.V. light, whiletransmitting visible light, by the inclusionof CeO2 in the batch. Other elementsabsorbing U.V. light include Cr, Co, Cu,Fe, Pb, Mn, Nd, Ni, Ti, U and V.Ultra-violet Transmitting Glass. For hightransmittance of U.V. light, a glass must befree from Fe, Ti and S. Phosphate glassesand some borosilicate glasses have goodU.V. transmittance. Uses include specialwindows and germicidal lamps.Umber. A naturally-occurring hydratediron oxide occasionally used as acolouring agent for pottery decoration.

Unaker. An old American Indian(Cherokee) term for clay from whichsand and mica had been removed bywashing.Underarching. Underadjustment of thecircumferential joints from true radialalignment in brick arches or rings. It maybe due to the use of too many slow taperbricks.Underclay. See SEAT EARTH.Undercloak. A layer, of plain clay tilesfor example, between the laths and theroof tiling proper at the VERGE (q.v.) ofa tiled roof.Undercutting. Faulty cutting of flat glassresulting in an edge that is oblique to thesurface of the glass.Under-glaze Decoration. Decorationapplied to pottery before it has beenglazed. Because it is finally covered bythe glaze, such decoration is completelydurable, but because the subsequentglost firing is at a high temperature therange of available colours for under-glaze decoration is limited.Underloading. Having insufficient chargein a ball mill for proper grinding; or,deliberately reducing the charge to speedgrinding.Under-ridge Tile. A roofing tile for useat the top of a tiled roof. Such tiles areshorter than standard roofing tiles andare used to complete the roof along theridge beneath the RIDGE TILES (q.v.).UNI. Prefix to specifications of theItalian Standards Association: EnteNazionale Itaiiano di Unificazione,Piazza Diaz, Milano, Italy.Uni Process. A vitreous enamellingprocess which requires no pickling ornickel deposition prior to enamelling.Described in Vitreous Enameller 28, (3),48, 1977 and 30, (2), 39,1979.Uniflame Process. The TRANSFER (q.v.)design layer contains a solid resin whichdiffers in polarity from the resin in the

covercoat, which protects the design instorage but may be removed manually orby air pressure after the transfer isapplied to the ware, but before firing.This eliminates the need for twoseparate firings of transfer and glaze forunderglaze transfers (Commercial DecalInc., USA).Unirotor Mill. Trade-name. A hammermill for clay preparation. The singlerotor is reversible to even out wear.(Hazemag, Germany).Unit Cell. See CRYSTAL STRUCTURE.Univertrave. A machine forprefabricating clay beams for roofs andfloors. Pairs of hollow blocks are fedalong the steel reinforcing rods set infeeder channels where mortar is vibratedinto the joints between the blocks. Awalking beam carries the blocks forwarduntil the desired length of beam hasbeen built up. (Univertex, Milan).Unshaped Refractory. A mixture ofrefractory materials, that may contain aproportion of metallic constituents,supplied in granular or pliable formsuitable for the construction ofmonolithic structures which will besubjected to elevated temperature. Itmay be placed in-situ by one or more ofthe pour casting, pumping, vibrationcasting, tamping, ramming or pneumaticgunning installation techniques, but notby trowelling or brushing. B.S. 1982 Pt. 7defines various classes of unshapedrefractories, and specifies test methodsfor their properties, and the preparationof test samples. ASTM Standards C973,C974, C975 describe preparing testspecimens from basic gunningrefractories (by pressing), from basiccastables (casting) and from basicramming mixes (pressing). C862describes casting refractory concretespecimens, C903 their preparation bycold gunning; C865 their firing. C1054

describes pressing and drying plasticrefractory and ramming mix specimens.Unsoundness. As applied to portlandcement, this term refers to slowexpansion after the cement has set. Theprincipal causes of this fault are thepresence of free CaO, excess MgO, orexcess sulphates.Up-cast. Local term in England forpositive pressure in the atmosphere ofsome zones of an annular kiln; the termis applied to the hot products ofcombustion that escape through anyopen feed caps in these zones.Up-draught Kiln. An intermittent kiln inwhich the combustion gases pass fromthe fireboxes through the setting andthence through one or more chimneys inthe roof. Such kilns are inefficient andare now obsolete.Up-draw Process. The continuous verticaldrawing of glass rod or tubing from anorifice; to produce tubing, the rod is drawnaround a refractory cone. (This processhas also been called the SCHULLERPROCESS, or WOOD'S PROCESS.)UPEC Classification System. In thisFrench system, floor tiles are assigned tovarious classes according to tests relatingto four criteria: U {mure) wear due towalking; P (poingonnemeni) marking dueto fixed or moving furniture; E (eau)behaviour in water; C (chimique) resis-tance to chemicals and domestic staining.(Industr. Ceramique (746), 1981, p68).Uphill Teeming. See BOTTOM POURING.Upright. See POST.

Uprisings. Scraps recovered for re-use.Uptake. See DOWNTAKE.Upward Drilling. Wear on horizontalfaces in glass-tank refractories, below theglass level, due to trapped gas bubbles.Uranium Borides. Three borides areknown: UB2, UB4 and UB12. The mostattention has been paid to thetetraboride, the properties of which are:

m.p. > 21000C (but oxidises rapidlyabove 6000C); sp. gr. 9-38 g/ml; thermalexpansion, 7.1 x 10-6 (20-10000C);modulus of rupture (200C), 400 MNm"2;electrical resistivity, 3 x 10~5 ohm.cm.Uranium Carbides. Three carbides exist.UC: m.p. approx. 25000C; sp. gr. 13.6;thermal expansion (25-10000C) H xIO-6. UC2: m.p. approx. 24000C; sp. gr.11.7; thermal expansion (25-10000C) 9.5x 10-6. U2C3: m.p. approx. 24000C; sp.gr. 12.9; thermal expansion (25-10000C)9 x 10-6. The powdered carbides can bemade, by ceramic processes, into nuclearfuel elements.Uranium Nitrides. UN decomposes at28000C at a N2 pressure of 1 atm.; underthe same conditions U2N3 decomposesat 1345°C. UN2 also exists.Uranium Oxides. The important oxidesof uranium are UO2, U3O8 and UO3.The dioxide (m.p. 288O0C; theoreticaldensity 10.96) is used as a, nuclear fuelelement. Uranium oxide has been usedto produce red and yellow glazes andceramic colours.Uranium Red. A ceramic stain forcoloured glazes suitable for firingtemperatures up to 10000C. Increasingthe uranium oxide content strengthensthe colour from orange, through red totomato red. The glaze should be basic,preferably 0.5 mol SiO2, 0.1-0.2 molAl2O3, 0.1 mol K2O and the remainingbases chiefly PbO; B2O3 should not bepresent in significant quantity.Uranium Silicides. Several compoundshave been reported; the most interesthas been shown in USi2.Uvaroite. 3CaO.Cr2O3.3SiO2; thecolouring agent in VICTORIA GREEN (q.v.).UV-Curing. Rapid curing of organicmaterials by exposure to ultra-violetradiation. The process has been appliedto the covercoats and decorative designsof ceramic transfers.

Uviol Glass. Glass highly transparent toultraviolet wavelengths.V-bricks. A series of perforated claybuilding bricks designed by the BuildingResearch Station, England, in 1959-60;the name derives from the fact that theperforations are Vertical.V-draining. See DOUBLE-DRAINING.V-Stud. A V-shaped STUD or ANCHORfor a refractory lining.Vacancy, See CRYSTAL STRUCTURE.Vacuity. The expansion space left abovethe liquid in a closed glass container.Vacupress. A continuous machine whichincreases the bulk density of powders bydeaeration and pre-compaction.Vacuum-and-BIow Process. See SUCK-

AND-BLOW PROCESS.Vacuum Casting. A SLIP CASTING (q.v.)process in which the casting rate isincreased by applying a vacuum to theoutside of a porous mould. Cf. PRESSURECASTING.Vacuum Degassing. A SECONDARYSTEELMAKING PROCESS in which thebath of molten steel in the ladle, or thestream of molten steel from it, isexposed to a vacuum to accelerate theremoval of hydrogen from the steel.Vacuum Drying. Reducing the airpressure over ware being dried speedsup moisture removal.Vacuum Firing. A process for the firingof special types of ceramic either toprevent oxidation of the ware or toreduce its porosity. Vacuum firing isused, for example, in the firing of dentalporcelain to produce teeth of almostzero porosity.Vacuum Forming. A sheet of material isplaced over a porous mould, heated ifnecessary, and the air between the sheetand the mould is pumped out throughthe mould, forcing the sheet to conformto its shape. A variety of rigid shapesare made from ceramic fibre blankets

with suitable binders, using thistechnique.Vacuum Mixer. A machine for thesimultaneous de-airing and moistening ofdry, prepared clay as it is fed to a pug. Inthe original design (L. Walker, Claycraft,25, 76,1951) the clay fell as a powderthrough a vertical de-airing chamberwhere water was added as a fine spray;from the bottom of the de-airingchamber the moist, de-aired, clay passedinto a pug. There have been severaldevelopments of this principle.Vacuum Pug. A PUG (q.v.) with avacuum chamber in which the clay is de-aired before it passes into the extrusionchamber.VAD (vapour-phase axial deposition).See OPTICAL FIBRES.Valiela Process. A decorating processfor tableware. A table has a recess toreceive the article to be decorated,alongside a silk-screen stencil which canslide into a predetermined positionabove a rubber sheet. This is on a panelhinged to superimpose it on to thecurved surface of the ware, where it isforced down by compressed air totransfer the decoration. (J. Valiela andInterpace Corp, USA, Br. Pat. 746,1001956).Vallendar Clay. A clay fromWesterwald, Germany. The best knowngrade is that used in the vitreous enamelindustry; a quoted analysis is (%): SiO2,54; Al2O3, 35; Fe2O3, 0.8; alkalis, 1.8;loss-on-ignition, 8.3.Valley Tiles. Specially-shaped roofingtiles for use in the 'valley' where tworoof slopes meet; these tiles are made tofit into the angle. They lap and course inwith the normal tiling.VAMAS Programme. The VersaillesProject on Advanced Materials andStandards is a European Communityinititative to develop standard test

methods for the evaluation of advancedceramics.Vanadium Borides. Several borides havebeen reported, including the following:VB2; m.p. 21000C; sp. gr. 5.0; the thermalexpansion is highly anisotropic. VB; m.p.22500C; sp. gr. 5.3. V3B4; meltsincongruently at 23000C; sp. gr. 5.5.Vanadium Carbide. VC, m.p. 28300C; sp.gr. 5.8.Vanadium Nitrides VN, m.p. approx.23000C; sp. gr. 6.1. V3N is relativelyunstable.Vanadium Oxide. The common oxide isV2O5; m.p. 675°C.Vanadium Yellow or Vanadium-TinYellow. A ceramic colour produced bythe calcination, at about 10000C, of amixture of 10-20% V2O5 (as ammoniummetavanadate) and 80-90% SnO2. Astronger yellow results if a small amountof TiO2 is added. These colours can beused in most glazes and either SnO2 orzircon can be used as opacifier.Vanadium-Zirconium Blue (orTurquoise). See ZIRCONIUM-VANADIUMBLUE.

Vanal. Trade-name: Hagenberger-Schwalb A.G., Hettenleidelheim/Pfalz,Germany. A coating for the protectionof refractories against slag attackdeveloped by A. Staerker (Ber. Deu.Keram. Ges., 28, 390, 1951; 29, 122,1952). It contains vanadium and isclaimed to prevent slags wetting therefractory.Van der Waal's Forces. Electrostaticforces between polarized molecules orgroups of atoms, which are considerablyweaker than the normal interatomicbonding forces giving rise to solid crystalstructures. They are important inproducing aggregates of particles indense suspensions, and spontaneousagglomeration in dry powders of verysmall (sub-micron) particle sizes.

Vane Feeder. A device for feeding dryground clay from a hopper to atempering machine or mixer, forexample. Vanes fixed to a horizontalshaft at the base of the hopper rotate todischarge the material.VAR. Vacuum Arc Refining. SeeSECONDARY STEELMAKING.Varistor. A material having an electricalresistance that is sensitive to changes inapplied voltage. A typical example is thevaristor made from a batch consisting ofgranular silicon carbide, mixed withcarbon, clay and water; the shapedcomponents are fired at 1100-12500C inH2 or N2.Varved Clay. A clay deposited in layers,some coarse, others fine and silty.VAS. Vacuum Arc Spraying. Athermally sprayed coating process.VE. Abbreviation for VITREOUSENAMEL (q.v.).Vebe Apparatus. A device developed bythe Swedish Cement Association for themeasurement of the consistency ofconcrete. It is a slump test in which theconsistency is expressed in degrees, thevalue being obtained by multiplying theratio of the volume of the test-piece aftervibration to that before vibration by thenumber of vibrations required to causethe test-piece to settle.Vegard's Law. States that in a binarysystem forming a continuous series ofsolid solutions, the lattice parametersare linearly related to the atomicpercentage of one of the components.This law has been applied, for example,in the study of mixed spinels of the typeformed in chrome-magnesiterefractories. (L. Vegard, Z. Physik, 5,17, 1921.)Veiling. A US term for gold and organiccolours sprayed on glass in a thread-liketexture.Vein. See STRIAE.

Vein Quartz. An irregular deposit ofquartz, often of high purity, intrudedinto other rocks. In consequence of itsmode of formation, vein quartz usuallycontains occluded gas bubbles and isunsuitable as a raw material for silicarefractories.Velio Process. A method for theproduction of glass tubing; molten glassflows vertically through an annularorifice; the central refractory pipe withinthe orifice is hollow and rotates. Theprocess will produce up to 1 tonne/h oftubing, 1.5-75mm dia. cf. DANNER

PROCESS.

Vellum Glaze. See SATIN GLAZE.

Velvet Finish. An embossed appearanceformed on glass by acid treatment whichobscures transmission of light.Veneered Wall. A wall having a facing(of faience panels, for example) which isattached to the backing but not in a wayto transmit a full share of any imposedload; the veneer and the backing do notexert a common action under load (cf.FACED WALL).

Venetian Red. A colour consistingchiefly of ferric oxide.Vent. See CHECK.

Verge. The gable edge of a tiled roof. Atthe verge the roofing tiles are edge-bedded, preferably on a single or doubleundercloak of plain tiles. This form ofundercloak gives a neat appearance tothe verge and slightly inclines the vergetiles so that rainwater is turned back onto the main roof.Vermiculite. A group name for certainbiotite micas that have been alteredhydrothermally. When rapidly heated to800-9500C vermiculite exfoliates as thecombined water is expelled; the volumeincrease is about 15%. Large deposits ofvermiculite occur in USA, Transvaal,Uganda, Australia and the UralMountains of Russia. The exfoliated

material is used as loose-fill insulationand in the manufacture of vermiculiteinsulating bricks. Standards for theloose-fill are laid down in US Govt. Fed.Spec. HH-I-00585. Vermiculite bricksare made by bonding the gradedmaterial with about 30% of clay,shaping, and firing at 10000C. The bulkdensity of such bricks is 500-600kg.m~3;thermal conductivity 0.2-0.25W/mK.They can be used up to 10000C.Verneuil Process. A method for theproduction of ceramic BOULES (q.v.) byfeeding powdered material, e.g. Al2O3,into an oxy-hydrogen flame. (A.Verneuil, Ann. Chim. Phys., 3, 20, 1904.)Versatran. A programmable machine forpositioning, transfer and handling orobjects, suitable for bricks. (Licensedfrom the American Machine & FoundryCo).Vesicular. A solid is said to be vesicularif it contains a lot of small bubbles; abloated clay may be vesicular, forexample.Verson System. A continuous mouldingprocess for clayware, particularlysanitaryware. A thin mould liner issupported by a rigid female mould. Aforming die gives preliminarycompaction to the charge of plastic claybetween it and the liner. The liner andcharge can then be moved on to asecond (and subsequent) female mould,the last of which imparts the finishedshape. (Verson Manufacturing Co, USABr. Pat. 1004 540,1964).Vibrating Ball Mill; A BALL MILL (q.v.)

supported on springs so that an out-of-balance mechanism can impart vibrationto the mill, usually in the vertical planeand typically at about 25 Hz. The feedshould not be coarser than 100 mesh; thecharge should be at least 85% of the millvolume. It is particularly suitable forgrinding to less than 40|xm. Advantages

over the ordinary ball mill are increasedrate of grinding (particularly with veryhard materials), lower energyconsumption per ton of product, and lesswear.Vibrating Screen. A screen, set at anangle of 25-35° to the horizontal, andvibrated by an eccentric, a cam orhammer, an out-of-balance pulley, or anelectro-magnet. When operating with 10-mesh cloth on damp clay, such a screenshould have an output of about 5 ton/h/m2. The screening efficiency isgenerally 80-85%.Vibrating Table. A table which oscillatesrapidly to remove air and compact arefractory castable placed on it.Vibro-casting. Pouring concrete into amould, and densifying by vibration.Large concrete pipes can be vibrocast.Vibro-compaction. Vibration andpressure are applied simultaneously, todensify powder mixtures. The usualtechniques produce particle accelerationsof some 50g, and require an appropriateparticle size distribution to obtain densecompaction. To densify mixed powderswhose components differ greatly indensity, very strong vibrations(accelerations c. 20 00Og) have beenstudied.Vibro-energy Mill. Trade-name: aVIBRATING BALL MILL (q.v.) designed tooscillate both horizontally and vertically,the vertical motion being of small butsufficient amplitude to prevent thecharge from becoming tightly packed.(W. Podmore Ltd., and W. Bouiton Ltd.,Stoke-on-Trent, England.)Vicat Needle. An instrument forevaluating the consistency of cement interms of the depth of penetration of a'needle' of standard shape and under astandard load; it was designed by L. J.Vicat, a Frenchman, in the early 19thcentury. Details of dimensions and

method of use are given in B.S. 12 andits application to refractory mortars inB.S. 1902 Pt. 11. (Cf. GILLMORENEEDLE).

Vickers Hardness. An indentation test inwhich a diamond pyramid is used. Thediamond is loaded mechanically by alever, the application of the load beinghydraulically controlled to give thecorrect duration. The symbol is HV; itshould be supplemented by a numberindicating the load used. The VickersHardness of most pottery glazes liesbetween 570 and 630 kg/mm2; that ofvitreous enamels is approx. 500 kg/mm2.See also FRACTURE TOUGHNESS TESTS.

Victoria Green. A bright green ceramiccolour. A quoted batch composition is:38% K2Cr2O7, 20% CaCO3, 22% CaFz2,20% SiO2. This batch is calcined, washedfree from soluble chromates, andground. The colouring agent is stated tobe uvarovite (3CaO.Cr2O3.3SiO2).Vignetting. The decoration of a glasssurface by firing-on a metal or othersuitable powder; the surface is firstcoated with sodium silicate solution andthe powder is then dusted on and thearticle fired.Vinsol Resin. Trade-name: athermoplastic powder used as an AIR-ENTRAINING (q.v.) agent in the mixingof concrete. (Hercules Powder Co. Ltd.,London.)Vise 2B. This viscosity meter suited todetermine the flow properties of enamelsuspensions measures the dependence ofthe deformation speed gradient as afunction of sliding tension measured byturning a roller in the enamel suspension.Vit Enameller 29 (1) 5 1978).Viscometer. The commonest types ofviscometer, as used in the ceramicindustry, depend on measurement of theflow of the test liquid through an orificeor of the drag on one of a pair of

concentric cylinders when the other isrotated, the test-liquid occupying thespace between the cylinders. B.S. 7034specifies tests for viscosity andviscometric fixed points for glasses. Seealso FLOW CUP, TORSION VISCOMETER.Viscone. Trade-name. Silicone rubberfor pads and membranes for ceramicprinting, supplied by Blythe Colours Ltd,Stoke on Trent.Viscosity. The viscosity of a true('Newtonian') liquid is the ratio of theshearing stress to the rate of shear, ofwhich the viscosity itself is independent;this is not generally true of clay slips,vitreous-enamel slips, or glazesuspensions, all of which exhibitTHIXOTROPY (q.V.).Viscous Plastic Processing (VPP). Agreen forming technique for advancedceramics which minimises the size andnumber of flaws by avoidingagglomeration of the starting powdersthrough high-shear mixing and carefulchoice of binder. Articles are thenshaped by plastic forming. The processwas developed from MDF CEMENT (q.v.)technology by British Ceramic ResearchLtd.Visil. Trade-name. A viscose silica fibre- a cellulose fibre containing up to 33%silica. Kemira Oy, Finland.Vitramic Ware. A vitrified red-brownbody, oven and freezer proof, chip-resistant and dishwasher proof, wasmade by Hornsea Pottery (Lancaster) toa basically earthenware recipe. CeramInd. J. 84 (1991) 20 1975.Vitreous. This term, meaning 'glassy', isapplied to ceramic ware that, as a resultof a high degree of vitrification (asdistinct from sintering) has an extremelylow porosity. In the USA the term isdefined (ASTM - C242) as generallysignifying that the ware has a waterabsorption below 0.5%, except for floor

tiles, wall tiles and low-tension electricalporcelain which are considered to bevitreous provided that the waterabsorption does not exceed 3%.Vitreous Carbon. See GLASS-LIKECARBON.Vitreous-china Sanitaryware. Defined inB.S. 3402 as: 'A strong high-gradeceramic ware used for sanitaryappliances and made from a mixture ofwhite-burning clays and finely groundminerals. After it has been fired at a hightemperature the ware will not, evenwhen unglazed, have a mean value ofwater absorption greater than 0.5% ofthe ware when dry. It is coated on allexposed surfaces with an imperviousnon-crazing vitreous glaze giving a whiteor coloured finish.' A typical batch forthis type of body is: 20-30% ball clay,20-30% china clay, 10-20% feldspar, 30-40% flint, 0-3% talc; sometimesnepheline syenite is used instead offeldspar. B. S. 3402 also includes tests forchemical resistance to various acids,alkalis and detergents, (the visualassessment of reflectivity to beunchanged by the chemical treatment);an autoclave test for crazing resistance,and definitions of various blemishes andfaults affecting sanitaryware.Vitreous Enamel. Defined in B.S. 1344as: 'An inorganic glass which is fused onto a metal article in the form of arelatively thin coating and providesprotection against corrosion. A glazedsurface finish produced by theapplication of a powdered inorganicglass, dry or suspended in water, tometal parts, and its subsequent fusion.'Iron is the usual metal so treated, butaluminium, copper and other metals canbe enamelled with glasses withappropriate properties. The equivalentUS term is PORCELAIN ENAMEL (q.v.).B.S. 1344 also specifies various tests for

chemical resistance; fluidity behaviour, alow voltage electrical test for defects incoatings on metal, and a high voltagetest for use when the enamelled articleswill face severe conditions.Vitreous Silica. The glassy (vitreous)form of silica. There are two majorcommercial forms: TRANSLUCENTVITREOUS SILICA (which has often beenreferred to as Fused Silica) andTRANSPARENT VITREOUS SILICA (oftenreferred to as Fused Quartz).Translucent Vitreous Silica is made bythe fusion of quartz sand in a furnaceopen to the atmosphere; it is translucent,i.e. not fully transparent, because of thenumerous small bubbles that it contains.Transparent Vitreous Silica is made bythe fusion (frequently under vacuum) ofquartz crystal, or by the hydrolysis oroxidation of a volatile silicon compoundand subsequent fusion of the silica soformed; the product of the latter processis known as Synthetic Vitreous Silica.Vitreous Slip. A US term defined(ASTM - C242) as a slip coatingmatured on a ceramic body to produce avitrified surface.Vitriam. A type of sanitary earthenware,made by Societe Amandinoise deFaiencerie et de Produits Refractaires etSanitaires S.a.r.l.Vitrification. The progressive partial fusionof a clay, or of a body, as a result of afiring process or, in the case of a refractorymaterial, of the conditions of use in afurnace lining. As vitrification proceeds theproportion of glassy bond increases andthe apparent porosity of the fired productbecomes progressively lower. The body issaid to be completely vitrified if the glassfills all the pores, and forms a bondbetween the grains at the grainboundaries. The VITRIFICATION RANGE isthe temperature interval between thebeginning of vitrification of a ceramic body

and the temperature at which the bodybegins to become deformed.Vitrified. See VITREOUS.Vitrified Wheel. An abrasive wheelmade from a batch consisting of abrasivegrains and a ceramic bond formed bykiln firing at 1200-13000C. Over half theabrasive wheels currently produced areof this type.Vitrite. The black glass used in the capsof electric lamps.Vitroceramic. One of several termsproposed for the type of ceramic productformed by the controlled devitrificationof a glass; see GLASS CERAMIC.Vitroderm. Sections of glazed wareprepared for microscopic examination,by grinding away the body from belowthe glaze. The term, which means 'glassskin' was coined by F. Smithson {Trans.Br. Ceram. Soc. 47,191,1948).Vitron. A unit of atomic structure,particularly in silica glass, proposed byL. W. Tilton (J. Res. Nat. Bur. Stand. 59,139, 1957). Its basis is a pentagonal ringof five SiO4 tetrahedra; these rings canbe built up into three-dimensionalclusters but only to a limited extentbecause of increasing distortional stress;a cluster of the pentagonal SiO4 rings isa VITRON. Its most important property,as a basis for the understanding of theproperties of glass, is its fivefoldsymmetry which precludes the formationof crystals, (cf. STRUCTON).VogePs Red. A pure ferric oxideproduced by precipitating ferrousoxalate which is then calcined. It hasbeen used as a basis for some 'iron'colours on porcelain.Void. (1) The spaces between grains, orother cavities in shaped, especiallypressed, ware.(2) A porous or hollowed-out region,representing the last area ofsolidification of a fusion cast refractory.

Volclay. A sodium bentonite fromWyoming, USA. (Tradename.)Voluphant. A derivative of theELEPHANT (q.v.) electrophoretic castingmachine, to make large pieces of ware,such as sanitaryware. The anodes formthe upper and lower dies of a pressmoulding. The cathode is shaped to fitbetween them and build up the castbefore it is removed and the press dieclosed to shape the article. (IndustrieCeram (718) 423 1978)Von Kobells' Scale. An empirical scaleof fusibility for minerals, based on theflames required to fuse the solid. It is1. Stibnite (candle flame); 2. Natrolite(luminous Bunsen); 3. Garnet(Blowpipe, readily); 4. Hornblende(Blowpipe, readily at edges);5. Orthoclase (Blowpipe, edges fuse withdifficulty); 6. Bronzite (Blowpipe, onlythin particles fused); 7. Infusible.VOR. Vacuum oxygen refining. SeeSECONDARY STEELMAKING.VPB Kiln. A kiln for the firing ofbuilding bricks; it consists of two groupsof chambers in which the fire travelfollows a zig-zag course. The bricks areset on refractory bats and are put into,and subsequently drawn from, the kilnwithout the workmen having to enter thehot chambers. The name is from theinitials of the inventor, V. P. Bodin(French PaL, 1 156 918, 22/5/58).VPS. Vacuum plasma spraying. SeePLASMA SPRAYING.Vycor. Trade-name. A POROUS GLASS(q.v.), made by a process patented byH.P. Hood and M.E Nordberg, CorningGlass (US Pat. 2106744,1938). Vycor isalmost pure vitreous silica. Aborosilicate glass is first made and thissolidifies in two phases, one of which issoluble in dilute acid and is thusremoved, leaving a highly siliceousskeleton. The porous ware is then heated

at about 10000C; it shrinks considerablyand non-porous high-silica glass (96%SiO2) is produced. This trade-name isderived from Viking and Corning.Wad. An extruded strip or rod of fireclay(with or without the addition of finegrog) used in the firing of pottery to sealthe joints between saggars, or to levelthe supporting surfaces of saggars in abung.Wad Box. A simple hand-extrusiondevice for producing cylindrical fireclayWADS (q.v.) for use during the setting ofbungs of saggars. A wad box was alsoused in the old method of pressinghandles and similar shapes of potteryware; used for this purpose, the devicewas sometimes called a DOD BOX.Wadhurst Clay. A Cretaceous clay usedfor brickmaking in parts of Kent andSussex, England.Waechter's Gold Purple. A colour, ofvarious shades, that has been used in thedecoration of porcelain.Waelz Furnace. A rotary furnace usedparticularly for the calcination of non-ferrous ores; chrome-magnesite liningshave been used in Waelz furnacesproducing ZnO.Wafers. Small sheets of electroceramicmaterial (e.g. BaTiO3, 0.025-0.25 mmthick for use in electronic equipment,particularly in miniature capacitors,transistors, resistors and other circuitcomponents.Wagner Turbidimeter. Apparatus for thedetermination of the fineness of apowder by measurement of the turbidity,at a specified level and after the lapse ofa specified time, of a suspension ofparticles that are settling by gravityaccording to Stokes' Law. The methodwas proposed by L. A. Wagner (Proc.ASTM, 33, Pt. 2, 553,1933).Waist. See BELLY.Wake Hackle. See GULL WINGS.

Fig. 7 Wall Tile Shapes.

Walker Vacuum Mixer. See VACUUMMIXER.

Walking-beam Kiln. A tunnel kiln ofunusual type, the ware (set on bats)being moved through the kiln in steps bya mechanism that alternately lifts thebats and sets them down further alongthe kiln.Wallner Line. Wavelike lines on theFRACTURE SURFACE (q.v.) caused bydisturbance of the fracture front by sonicwaves. The Wallner line is the locus ofinterception of the spreading elasticpulse with successive points along thepropagating crack front.Wall Tie. A metal wire, or sometimesplastics, shape used to link together

the inner and outer leaves of a cavitywall.Wall Tiles and Fittings. Glazed walltiles (which are also used in fireplacesurrounds) are made by a highlymechanized dust pressing process fromwhite or buff bodies; to reduce thefiring contraction and MOISTUREEXPANSION (q.v.) these bodies oftencontain lime compounds. Wall tiles aremade in a wide variety of colours andglazes; a satin or matt glaze is oftenused. Some of the shapes of tiles andfittings are shown in Fig. 7; for standardsizes and other properties see B.S. 6431;for fixing procedures see B.S. 5385. SeeTILE and TILING.Wall White. See EFFLORESCENCE.Warm Block. A building block of goodthermal and accoustic insulation andhigh heat capacity. It is perforated by aseries of narrow slits arranged in close-spaced lines parallel to the faces of theblock. Trade-name WienerbergerBaustoffindustrie AG, Austria.Warning Limit. See ACTION LIMIT.Warpage. A test for warpage (departurefrom flatness) of vitreous-enamelledflatware is given in ASTM-C314; a test forthe warpage of refractories is included inB.S. 1902, Pt. IA. ASTM C485 is a test forwarpage of ceramic tiles.Wash. See REFRACTORY COATING.Wash-back. See under WASH-MILL.Washbanding. A form of potterydecoration, usually on-glaze in which athin layer of colour is applied over alarge surface of the ware by means of abrush.

Washboard. Unintentional waviness onthe surface of glassware; also known asLADDERS.

Wash-gate. See under WASH-MILL.Washing Off. Removing printing paperfrom pottery ware that has beendecorated by the transfer process.

ExternalcoconutpieceInternalshoulderangle

Cove skirtingExternal angle tocove skirting

Internal angle tocove skirting

InternalcoconutpieceExternalshoulderangle

Round edgeexternal reveal,curb corner,(REXR)Curb bend Internalanglebead

ExternalanglebeadInternalbird'sbeak

Externalbird'sbeak

Round edgeexternal corner,left hand (HREX)Round edgeexternal corner,right hand (REXH)

Round edge opposites,long sides (REOL)Round edge tile,short side (RES)

Round edgeopposite (REO)Round edge externalreveal (REXR)Triple roundedge (TRE) Round edge tile,long side (RED

Plain tile Round edgetile (RE) Round edge externalcorner (REX) Round edgereveal (RER)

Wash-mill. A large tank fitted withstirrers (known as HARROWS or WASH-GATES) for the cleaning of the impuresurface clays used in the manufacture ofSTOCK BRICKS (q.v.). From the wash-millthe clay slurry, together with a slurry ofany lime or chalk that is to be added, ispumped into a settling tank known as aWASHBACK.

Waste-heat Dryer. A dryer for claywarethat derives its heat from the coolingware in the kilns. Such dryers arecommon in the brick industry and, eventhough the fuel consumption in the kilnsmay be slightly increased, this method ofheat utilization results in an overalleconomy in fuel. Hot-floors, chamberdryers or tunnel dryers can be operatedon this principle and the necessary heatcan be derived from intermittent,annular or tunnel kilns.Waster. A brick, structural or refractory,that is defective as drawn from the kiln;wasters in the refractories industry werecrushed and re-used as GROG (q.v.).Water Absorption. The weight of waterabsorbed by a porous ceramic material,under specified conditions, expressed asa percentage of the weight of the drymaterial. This property is much quotedwhen referring to structural clayproducts. B.S. 3921 specifies a testmethod and limits for ENGINEERINGBRICKS and for bricks for DAMP-PROOFCOURSES. B.S. 6431 classifies TILES(q.v.) on the basis of their waterabsorption. Limits for water absorptionare also specified for vitreous chinasanitaryware (B.S. 3402); vitrifiedhotelware (B.S. 4034); china andporcelain tableware (B.S. 5416). TheUS tests for refractories are ASTM C20(a boiling water test) and ASTM C830(A VACUUM PRESSURE TEST); theapparent porosity is more commonlyquoted for refractories and whitewares.

The two properties are related by theequation:Apparent Porosity = Water Absorption

x Bulk Density(Note: In the USA, the term'Absorption' is preferred to 'WaterAbsorption').Water Gain. See BLEEDING.Water Glass. Popular name for solublegrades of SODIUM SILICATE (q.v.).Water Mark or Water Spot. (1) Ashallow depressed spot sometimesappearing as a defect in vitreousenamelware.(2) During transfer-printing on pottery, awater-mark may form if a drop of waterdries on the ware, leaving a deposit ofsoluble salts.Water Streak. A fault in vitreousenamelware arising from drops of waterrunning down the ware, while it is beingdried, and partially removing the enamelcoating. The obvious cause is the use ofa slip that is too wet, when water-streaksare liable to occur in any sharp angle ofthe ware; condensation of drops of wateron parts of the ware during the dryingprocess is another cause.Water Test. See FLOC TEST.Waterfall Process. A method for theapplication of glaze materials to aceramic body by mechanically conveyingthe ware through a continuously flowing(recirculated) vertical stream of the glazesuspension. The process is used in theglazing of wall tiles.Wateriord Glass. Cut or gilded glassmade in the Waterford district of Irelandand characterized by a slight bluenessresulting from the presence of a trace ofcobalt.Waterjet Cutting. See ABRASIVE JET

MACHINING.

Water-line. A defect in vitreousenamelware in the form of a linemarking the limit of water penetration

from wet beading enamel into theunfired enamel coating.Waterproofing, (1) Concrete can bemade more waterproof by surfacetreatment of the set concrete or by theaddition of an integral waterproofer. Forsurface treatment a solution of sodiumsilicate or of a silicofluoride may beused; silicones, drying oils and mineraloils are also sometimes employed.Integral waterproofers include calciumchloride solution and/or variousstearates.(2) Water repellants for above-groundbrickwork are recommended in B.S.6477.Water-slide Transfer = SLIDE OFF DECAL

(q.v.).Water-smoking Period. The stage in thefiring of heavyclayware and of fireclayrefractories when the mechanically-heldwater in the clay is being evolved, i.e. thetemperature range 100-2500C. Thetemperature distribution in the settingshould be such as to preventcondensation of any of this watervapour, and the temperature should notbe raised further until all the water hasbeen evolved.Waterstruck Brick. A soft-mud brickmade in a damp mould to preventsticking.Watkin Heat Recorders. Cylindricalpellets (9mm high, 6mm dia.) made of ablend of ceramic materials and fluxes soproportioned that, when heated undersuitable conditions, they will fuse atstated temperatures. They arenumbered from 1(6000C) to 59 (20000C)and were introduced by H. Watkin(Stoke-on-Trent, England) in 1899 andsupplied by Harrison Mayer, Ltd,Stoke-on-Trent.Wauk. A US term for a plastic clay bodyrolled and beaten to the rough shape ofthe mould, before hand moulding.

Wave. An optical defect in glass causedby uneven glass distribution or bySTRIAE (q.v.).Waviness. Long range departure fromflatness, on a scale greater than aspecified surface finish. See also KINK.(ASTM F109).Weald Clay. A Cretaceous clay, oftenvariable in composition even within thesame clay-pit, used for brickmaking inparts of Surrey, Kent and Sussex,England.Wear diagram. A 3-co-ordinaterepresentation of the dependence ofwear on the applied pressure and thesliding velocity.Weathering. (1) The preparation,particularly of clay, by exposure to theweather for a long period. This helps tooxidize any pyrite present, rendering itsoluble, so that this and other solubleimpurities are to some extent leachedout; the water content also becomesmore uniform and agglomerates of clayare broken down with a consequentincrease in plasticity.(2) The attack of glass or other ceramicsby the atmosphere.(3) An inclined surface that facilitatesthe running-off of rainwater frombrickwork.Web. One of the clay partitions dividinga hollow building block into cells.Webb Effect. The increase in volume ofa pottery slip as deflocculation proceeds.(H. W. Webb, Trans. Brit. Ceram. Soc,33,129,1934.) After a detailedexperimental study, P. H. Dal and W. J.H. Berden {Science of Ceramics, G. H.Stewart (Ed.) 2, 59,1965) concluded thatthis effect is non-existent.Wedge Brick. US term for KEY BRICK(q.v.).Wedge Pyrometer. An instrument forthe approximate measurement of hightemperatures. It depends on a wedge of

coloured glass, the position of which isadjusted until the source of heat is nolonger visible when viewed through theglass; movement of the wedge operates ascale calibrated in temperatures.Wedge-stilt. See STILT.Wedged Bottom. See SLUGGEDBOTTOM.Wedging. (1) A procedure for preparingclay or a clay body by hand: the lump ofclay is repeatedly thrown down on aworkbench; between each operation thelump is turned and sometimes cutthrough and rejoined in a differentorientation. The object is to disperse thewater more uniformly, to removelamination and to remove air.(2) A fault in dust-pressed tiles if thepowder is not charged to a uniformdepth in the die. In ASTM C502,wedging refers to finished tiles in whichtiles, not uniformly pressed and fired, areout-of-square. The standard specifies aprocedure to measure wedging.Wedgwood Pyrometer. A device for thedetermination of high temperatures onthe basis of the approximate relationshipbetween the contraction of clay test-pieces and the temperature to whichthey have been exposed; this pyrometerwas introduced by Josiah Wedgwood{Phil. Trans., 72, 305,1782) and nowforms the basis of the BULLERS' RING(q.v.).Weibull Distribution. This empiricalstatistical distribution function describesthe scatter in strength values of brittlematerials. It is used to assign mechanicalproperties to brittle materials inprobabilistic terms, and to define designrequirements in terms of strength andreliability. If p (ac) is the probability thatthe material will fail at a measuredcritical stress ac then In In [1 - p (G0)]-

1

= M In (ac) + C where M is the WeibullModulus. High values of M correspond

to little scatter in the test data. Metalstypically have values of M -100, whiletraditional ceramics have values ~5 andengineering ceramics are in the range10-25. The goodness-of-fit of Weibullstatistics to experimental data can beassessed by the K-S TEST (q.v.) andothers. See also CARES program.Weibull's Theory. A statistical theory ofthe strength of materials proposed by W.Weibull (/ng. Vetenskaps Akad. Hand.,No. 151, 1939); its basic postulate is thatthe probability of fracture of a solidbody depends on the volume understress and on the stress distribution. Thistheory has been applied in studies of thestrength of ceramic materials and theirresistance to the stresses induced bythermal shock.Weissenberg Camera. A camera forX-ray diffraction analysis of crystalstructures. The crystal is rotated, in theX-ray beam. The film is rotated andmoved parallel to the axis of rotation.Weissenberg Rheogoniometer. In essencea CONE AND PLATE VISCOMETER (q.V.),but with accessories and control systemsto allow it to measure, as well as viscosity,elasticity and a wide range of flowproperties such as dilatancy, thixotrophy,relaxation phenomena, etc in steadyrotation or in torsional oscillation, overwide but controlled ranges oftemperature and shear.Weiss Field and Curie-Weiss Law. SeeCURIE LAW.Weld Mark. A deep groove or fissure (inglass or whiteware) formed byincomplete union of two or moreparticles or streams of material flowingtogether. (ASTM F109).Well. The term sometimes used for thelowest part of a blast furnace, i.e. thepart in which molten iron collects.Well-hole Pipe. One of the short fireclaypipes that were used to carry the flame

upwards from the well-hole in thebottom of a BOTTLE OVEN (q.v.).Wentworth Grade Scale. An extensionof the UDDEN (q.v.) scale of sieveopenings proposed by C. K. Wentworth(/. Geol, 30, 377,1922).Westerwald Clay. A refractory clayoccurring in an area east of the Rhinebetween Coblenz and Marburg. Theseclays are of Oligocene origin and varywidely in composition from highlysiliceous to clays that contain (raw) over35% Al2O3.Westlake Process. An automatic methodfor making glass-ware in paste moulds;the process closely imitates hand-makingand was invented in 1916 by theWestlake European Machine Co.,Toledo, USA.Wet Bag Process. See ISOSTATICPRESSING.Wet Felt. Flexile ceramic fibreinsulation, impregnated with organicliquid binder which dries to a strongrigid lightweight shape.Wet Pan. An EDGE-RUNNER MILL (q.v.)used for grinding relatively wet materialin the refractories and structural clay-wares industries. The bottom has slottedgrids with a proportion of solid plates onwhich the mullers can grind.Wet Pressing. Alternative term in USAfor PLASTIC PRESSING (q.V.).Wet Process. (1) The method ofblending the constituents of a whitewarebody in the form of SLIPS (q.v.).(2) The process of portland cementmanufacture in which the limestone (orchalk) and clay are fed to the kiln as aslurry.(3) The method of applying vitreousenamel as a slip, usually by spraying.Wet-rubbing Test. A test to determinethe degree of attack of a vitreous-enamelled surface after an acid-resistance test; (see ASTM - C282).

Wetting Off. The severing of a hand-made glass bottle from the blow-pipe bymeans of a fine jet of water.Whales. See DRAIN LINES.Wheelabrator. A shot-blasting machineof a type used for cleaning castings priorto vitreous enamelling. This equipmenthas also been adapted to the testing ofrefractory bricks for abrasion resistance(see Trans. Brit. Ceram. Soc, 50, 145,1951).Whelp. A refractory brick of the samethickness and breadth as a standardsquare but of greater length, e.g. 12 x AVix 3 in. (305 x 114 x 76 mm) (see Fig. 1,p39).Whirler. (1) A piece of tableware thathas warped slightly during drying and/orfiring; in consequence, such ware will'whirl' on its foot if spun on a flatsurface.(2) A turntable used for checking thesymmetry of a model in pottery making,or for the hand-making of a SAGGAR(q.v.).Whirlering. The plaster moulds for bone-china hollow-ware are often revolved ona turntable while they are being filledwith slip; this is known as 'whirlering'.The object is to prevent WREATHING(q.v.).Whisker. A hair-like single crystal; thethickness can vary considerably but istypically l-2um; the length can attainseveral cm. The most important propertyof ceramic whiskers is high strength, e.g.alumina whiskers have been made with atensile strength of 14000 MNm-2.Ceramic whiskers have been dispersed inmetals to increase their strength,particularly at high temperatures (cf.FIBRE (CERAMIC) and FILAMENT).Whisker Reinforcement. The addition ofceramic WHISKERS (q.v.) to metals orceramics increases their strength andTOUGHNESS (q.v.) by several possible

mechanisms. The whiskers arethemselves strong, and may inhibitcracking by STRAIN HARDENING (q.v.)or CRACK BRIDGING (q.v.) mechanisms.Whiskers = STRIATION (q.v.)White Acid. An etchant for glass, beinga mixture of HF and ammoniumbifluoride.White Alumina. A recrystallized aluminaabrasive.White Cement. Portland cement madefrom non-ferruginous raw materials, i.e.chalk (or low-iron limestone) and chinaclay. The Fe2O3 content is <1%.White Dirt. A fault sometimes occurringduring the manufacture of tableware as aresult of the protrusion of white particlesthrough the glaze; usually, if the glazelayer is adequately thick, any such 'dirt'is hidden. Sources include the beddingmedium (alumina or sand), fragments ofthe body itself, and scale derived fromhard water.White Firing. A clay of low iron contentwhich produces a white biscuit ware onfiring.White Flint. See FLINT GLASS.White Glass. Glass that has a uniformlow absorption coefficient over thewhole visible spectral range; forcontainers and for flat glass this isusually achieved by the addition tothe glass batch of a DECOLORIZER(q.v.).White Granite Ware. A US term forIRONSTONE WARE (q.V.).White Ground-coat. Term sometimesused for a white vitreous enamel of highopacity used for one-coat application.White Hard. Clay from which surfacewater has evaporated.White Lead. Basic lead carbonate,2PbCO3-Pb(OH)2. Used to some extentin USA as a glaze constituent.White Spot. A fault sometimes occurringin pottery colours, e.g. in chrome-tin

pink and in manganese colours. It iscaused by evolution of gas during firing,the glaze subsequently flowing over thecrater left by the gas bubble withoutcarrying with it sufficient colour to matchthe surrounding area.White's Test. A method for thedetection of free lime, for example inPortland cement or dolomiterefractories. A few mg of the powderedsample is placed on a glass microscope-slide and wetted with a solution of 5gphenol dissolved in 5 ml nitrobenzenewith the addition of two drops of water.Micro-examination ( x 80) will reveal theformation of long birefringent needles iffree CaO is present. (A. H. White,Industr. Engng. Chem. 1, 5, 1909.)Whiteware. A general term for all thosevarieties of pottery that usually have awhite body, e.g. tableware, sanitary wareand wall tiles. See also CERAMICWHITEWARE, which has an ASTMdefinition.Whitewash. (1) Local term forEFFLORESCENCE (q.V.) Or SCUM (q. V.)on bricks.(2) A fault in glass; see SCAB.Whiting. Finely-ground Cretaceouschalk, CaCO3. British whiting is 97-98%pure and practically all finer than 25 Jim.It is used as a source of lime in potterybodies and glazes, and to a small extentin glasses and vitreous enamels.Wicket. A wall built of refractories toclose an opening into a kiln or furnace; itis of a temporary nature, serving as adoor, for example, in intermittent orannular kilns.Wiegner Sedimentation Tube.Apparatus for particle-size analysis bysedimentation from a suspension in atube (or cylinder) of relatively largediameter; the rate of sedimentation isindicated by the movement of themeniscus in a narrow side-tube, joined

to the large tube near the base of thelatter and itself containing thedispersing liquid free from solidparticles. It was designed by G. Wiegner(Landw. Vers.-Stat, 91, 41, 1918); alater development was the KELLYSEDIMENTATION TUBE (q.V.).Wilkinite. A particular type of bentoniticclay; it has been used as a suspendingagent for glazes.Wilkinson Oven. A pottery BOTTLEOVEN (q.v.) designed so that the hotgases rise through the bag-walls and thecentral well-hole, and descend betweenthe saggars to leave the kiln through flueopenings in the floor mid-way alongradii. (A. J. Wilkinson, Brit. Pat. 4356,20/3/1890.)Willemite. Zn2SiO4; formed incrystalline glazes that are loaded withZnO.Williams' Plastometer. A parallel-platecompression apparatus designed by I.Williams (Industr. Eng. Chem., 16, 362,1924) for the testing of rubber; it hassince been used quite considerably in thetesting of clay.Williamson Kiln. A tunnel kiln of thecombined direct-flame and muffle typedesigned by J. Williamson {Trans. Brit.Ceram. Soc, 27, 290,1928) and firstused, in England, for the firing of wall-tiles and sewer-pipes. This kiln differedfrom earlier tunnel kilns in that the hotcombustion gases passed across, ratherthan along, the kiln.Willow Blue. Cobalt blue diluted withwhite ingredients such as ground silica; aquoted recipe is 40% cobalt oxide, 40%feldspar and 20% flint.Willow Pattern. This well-knownpseudo-Chinese scene was first engraved,in 1780, for the decoration of potteryware, by Thomas Minton for ThomasTurner of the Caughley Pottery,Shropshire, England.

Wimet. Trade-name. Cemented tungstencarbide tool metal. Wickman Wimet Ltd,Coventry.Winchester. A straight-sided glass bottleof the type used for transportinglaboratory liquids; the two BritishStandard Winchesters have volumes of80 and 90 fl. oz respectively, i.e. approx.21A and 2Vi litres. (B.S. 830.)Winchester Cutting. A method of splay-cutting roofing tiles for the top course(s)in the vertical tiling of exterior walls, sothat the final course of tiles isperpendicular to the overhanging verge.Wind Loading. Lateral loads exerted on(brick) structures by the wind.Wind Ridge. A type of RIDGE TILE (q.v.).Wing Walls. Narrow refractory walls in agasifier, built radially to form severalvertical chambers.Winkelmann and Schott Equation. Anequation proposed by A. Winkelmannand O. Schott {Ann. Phys. Chem., 51,697, 730, 735, 1894) for assessing thethermal endurance (F) of glass-ware onthe basis of the tensile strength (P),modulus of elasticity (ZT), coefficient oflinear thermal expansion (a), thermalconductivity (K), specific heat (C) andspecific gravity (S): F= (P^K)IaE-J(SC)See also THERMAL EXPANSION FACTORS

FOR GLASS.Winning. The combined process ofgetting (i.e. excavating) and transportinga raw material such as clay to abrickworks or stockpile.Winnofos. Aluminium phosphate, usedas a binder for refractories, made by ICI,Runcorn until 1976.Wire-cut Process (UK); Stiff-mudProcess (USA). The shaping of bricks byextruding a column of clay through a die,the column being subsequently cut to thesize of bricks by means of taut wires.The bricks are usually end cut, but sidecut bricks are also made.

Wired Glass. Flat glass that has beenreinforced by the incorporation of wiremesh. One use is as a 'fire-stop':whereas, in a fire, ordinary windowpanes crack, fall out and allow flames tospread, wired glass will crack but holdtogether.WIST. A porous cold-setting resin formouldmaking, which hardens by reactionwith water. It is much lighter (70-80%)than plaster. The name is an acronym ofthe German for the formation of anintermediate structure with water (. . .die mil HiIfe von Wasser eineYntermedidrstructur bildet) (Keram Z. 37,(12), 1985, p 683).Witenite. Trade-name. Slip resistantfloor tiles for wet situations. (Certels,UK).Withe. A partition between adjacentflues in a domestic chimney; also knownas a MIDFEATHER (q.V.).Witherite. Natural BARIUM CARBONATE

(q.v.).Wohl Block. A hollow clay buildingblock designed for the construction ofwalls of various thicknesses and for usein ceilings. (E. Wohl, Ziegelindustrie, 2,99, 1949.)Wollanite. A material claimed toincrease the hardness and strength ofearthenware, and to comprise crystals ofwollastonite and cristoballite sinteredtogether, (Oreste Bitossi, Livorno, Italy.)Wollastonite. Calcium metasilicate,CaSiO3; m.p. 1544°C; There are twoprincipal forms: the natural, p, form sp.gr. 2.92; thermal expansion (0-10000C),11 x 10-6; the synthetic, a, form which isalso known as pseudo-wollastonite sp. gr.2.91; thermal expansion (0-10000C), 6 xIO-6. The a form is slowly producedwhen the p form is heated above 12000C.There are economic deposits in NewYork State, Finland and USSR.Wollastonite has been used in some

pottery bodies (particularly wall tiles), inglazes and in special low-losselectroceramics.Wonderstone. A popular name(particularly in S. Africa) forPYROPHYLLITE (q.V.).Wood's Glass. A special glass thattransmits ultra-violet but is almost opaqueto visible light; such a glass was first madeby Prof. R. W. Wood, John HopkinsUniversity, USA, and was used forinvisible signalling during World War 1.Woods Hole Sediment Analyser. Amethod of particle-size analysis based onmeasurement of pressure changesresulting from sedimentation in asuspension of the particles in water. It isapplicable to coarse silts and fine gravels,and permits 150 tests to be made in aday. The instrument was designed byWoods Hole Oceanographic Institution(/. Sed. Petrology, 30, 490,1960).Wood's Process. See UP-DRAW PROCESS.Woodhall-Duckham Kiln. See ROTARY-HEARTH KILN.Wool. See GLASS FIBRE; MINERAL

WOOL.Wool-drag. A fault in GROUND LAYING(q.v.) resulting from accidental smearingof the colour.Worcester Shape. A tea- or coffee-cuphaving the general shape of a plaincylinder, rounded sharply near thebottom, which has a broad but shallowfoot. For specification see B.S. 3542.Work-board. A board, about 6 ft longand 9 in. wide, on which pottery-waremay be placed and carried from oneprocess to the next.Work Size. See CO-ORDINATING SIZE.Work Speed. A term relating to theprocess of grinding with abrasive wheels.In surface grinding, the work speed isthe rate of table traverse, usuallyexpressed in m/s. In centreless,cylindrical and internal grinding, the

work speed is the rate at which theobject being ground (the 'work')revolves; this may be expressed either inrev/min or in m/s.Workability. A measure of the ease ofdeformation of dough-like pastes. A testfor the workability of unshapedrefractories, involving measurement ofthe percentage change in the height of aprepared cylinder subjected to specifiedblows, is described in BS 1902 Pt. 7.2.ASTM C181 specifies a similar test forthe workability index of fireclay andhigh-alumina plastic refractories.Working End. Part of a glass-tankfurnace: (1) in such a furnace as used forcontainer glass, the term signifies thecompartment following the melting endand separated from it by the bridge;(2) the end from which the glass iswithdrawn in a glasstank furnace thathas no bridge.Working Mould. See under MOULD.Working Range. The temperature rangewithin which glass is amenable toshaping; at higher temperatures the glassis too fluid (viscosity less than about 103

poises) and at lower temperatures toorigid (viscosity above 107 poises). Forcomparative purposes, the WorkingRange is equated to a viscosity rangefrom 104 to 107 6 poises (see SOFTENINGPOINT).

Wreathing. ( I)A fault that sometimesoccurs on the inside of cast whiteware asa slightly raised crescent or snake-likearea; it is probably a result of orientationof the plate-shaped clay particles and canusually be prevented by increasing theviscosity and the thixotropy of thecasting slip.(2) Wreathing can also occur in a glaze:(a) as a result of the presence of solublesalts which can segregate as the glazedries; (b) as a result of the glaze notbeing applied uniformly to the ware.

Wyko Trace. A surface profile contourtrace.Wythe. A continuous vertical section ofmasonry one unit thick. Also thethickness of masonry separating flues ina chimney.Xerography. A method of copyingdesigns. An image is projected on to acharged metallic plate coated withphotoconductive material (usuallyselenium). A pigment powder isdispersed over the plate. It adheres morethickly in proportion to the charge onthe plate, which is turn depends on thedarkness of the image. The image is thentransferred electrostatically to paper andfused by heat. It has been applied in theproduction of transfers for thedecoration of glass and ceramic ware.Xonolite. A hydrated calcium silicatewith better thermal stability than othercalcium silicates. Large panels can befabricated for use up to 8000C.X-Ray Crystallography. Because thewavelength of X-rays is comparable tothe separations between atoms in theirregular arrangement which makes up aCRYSTAL STRUCTURE (q.v.), the X-raysare diffracted. That is, a pattern ofinterference is produced between theoriginal X-ray beam, and the parts of itscattered by the atoms in the crystal. Thepattern produced is characteristic of thearrangement of atoms, which can bededuced from it. (See RECIPROCALLATTICE). Strong diffracted beams areproduced at an angle 6 to the incidentbeam when 2d sin 0 = nd, where d is thedistance between planes of atoms, A, isthe X-ray wavelength and n is a wholenumber. (Bragg's Law). Varioustechniques have been used. The Debye-Sherrer or powder technique surrounds asample of crystalline powder (randomly-oriented crystals) with a circularphotographic film, and illuminates the

powder with X-rays of a singlewavelength.XRD X-ray Diffraction. See X-RAYCRYSTALLOGRAPHY.XRF - X-Ray Fluorescence Spectro-metry. A now standard method forchemical analysis, dependent on thecharacteristic X-ray spectra emitted bymaterials subjected to a beam of X-rays.YAG. Yttrium Aluminium Garnet (q.v.).YBCO. Yttrium-barium-copper oxideSUPERCONDUCTORS.Yellow Ware. US term for CANE WARE

(q.v.)-YIG. Abbreviation for YTTRIUM-IRONGARNET (q.v.).Young's Modulus. The MODULUS OFELASTICITY (q.v.) in tension orcompression; named from T. Young, anEnglish physicist (1773-1829). Sometypical values for this property are:earthenware, 40 kNm~2.; electricalporcelain, 80kNnrr2; sintered alumina,300 kNm-2. B.S. 1902 Pt. 4.11 specifiesthe test for refractories. ASTM C885specifies a sonic resonance test forrefractories; C848 is a sonic resonancetest for whitewares, and Cl 198 a sonicresonance test for advanced ceramics;these also measure SHEAR MODULUSAND POISSON'S RATIO. C623 is a similartest for glass and glass-ceramics.Y-Stud. A piece of round or rectangularsection metal, Y-shaped, used to anchora refractory lining.YSZ. Yttria stablised ZIRCONIA.Ytong. A cellular (lightweight) concretemade in block form from shale and lime,and subsequently hardened by autoclavetreatment. It was first produced in 1918,by A. Eriksson in Sweden, (cf.THERMALITE YTONG).Yttralox. Transparent yttria.Yttria. YTTRIUM OXIDE Y2O3 (q.v.).Yttrium Aluminium Garnet. Y3Al5O12

YAG occurs as a grain-boundary phase

in [3-sialon ceramics used as cutting tools.Doped with Nd3+ it is a laser material.Yttrium Iron Garnet. A ferromagnetic.A well-vitrified special ceramic can beproduced by firing the compacted oxideat 18000C, up to which temperature thecubic form is stable.Yttrium Oxide. Y2O3; m.p. approx.24500C; sp. gr. 4.84; thermal expansion(25-15000C) 9 x 10-6. An oxide extractedfrom MONAZiTE (q.v.) though not itself,strictly, a rare earth. An infra-red trans-mitter in the wavelength range 1 to 8 jam.ZAC Block. A zirconia alumina fusion-cast refractory, resistant to corrosion inglass tanks.Zachariasen's Theory. See under GLASS.Zaffre. A roasted mixture of cobalt oreand sand, formerly used as a bluecolouring material for pottery and glass(cf. SMALT).Zahn Cup. An orifice-type viscometer; ithas been used for the determination of theviscosity of glaze suspensions. (E. A. Zahn,Chem. Industries, 51, (2), 220,1942.)ZAN. A form of pressure-sinteredsilicon nitride using ZrN and AlNpowders as sintering aids, (referred to asAZ powders).ZAS Refractory. See AZS.ZCG. Zirconia-lime-graphiterefractories.Zebra Roof. A type of roof for basicOpen Hearth steel furnaces, the featurebeing alternate rings of chrome-magnesite and of silica refractories,hence the name from the dark and lightstripes across the roof. The Zebra Roofwas introduced in 1947 with a view tocombining the merits of the two types ofrefractory. By 1952 there were 300 suchroofs in service in USA alone, but theZebra Roof was later displaced by theall-basic roof.Zeissig Green. An underglaze colourthat has been used for pottery

decoration. It is made by calcining amixture of 10 parts barium chromate, 8parts whiting and 5 parts boric acid.Zeolites. A group of aluminosilicates ofalkali or alkaline earth metals with ringstructures (see SILICATE STRUCTURES).Water or other substances can enter thecavities within the structure. Zeolitesoccur naturally, or can be made by sol-gel processes. They are used asmolecular sieves, catalyst carriers and inion exchange.Zerodur. Trade-name. A transparentglass-ceramic with very low thermalexpansion. (Jenaer Glaswerk Schott u.Gen, Mainz).Zeta Potential. The electrical potential £set up by the double layer of chargedions in a colloidal solution (such as a clayslip) where it is close to a solid surface:C = Aned/Dwhere e - density of charge on thesurface of the particles; d = thickness ofthe double layer; D = dielectric constantof the liquid medium. It is the potentialat the limit of the rigidly-held layer ofpolarized water molecules adjacent tothe particle surface - the liquid shearplane or Stern plane. If the zeta potentialfalls below a critical value, particlesagglomerate and settle out. Control ofthe zeta potential is important formaintaining stable suspensions forcasting slips.Zettlitz Kaolin. A Czechoslovakiankaolin; a quoted analysis of the standardgrade is (%):SiO2 46.9; Al2O3 38.0;Fe2O3, 0.9; TiO2, 0.25; CaO 0.65; MgO0.15; alkalis 0.4; loss-on-ignition 12.6.Zig-zag Kiln. A TRANSVERSE-ARCHKILN (q.v.) with staggered dividing walls,the fire-travel thus being forced to followa zig-zag path. Such kilns find use in thefiring of structural clay products.Zinc Aluminate (Gahnite). ZnAl2O4;m.p. 19500C. This spinel, when made

from industrial-grade oxides, has aP.C.R> 19000C and RuL > 17000C.Russian experiments indicate that it canbe used as a refractory lining for electricfurnaces melting Al, Zn, Pb or Sn. It israpidly attacked by alkalis.Zinc Flash. Yellow to green coloursformed on the surface of red bricks bythe deposition of zinc vapour from zinccompounds introduced into the kiln atthe end of firing, (see FLASHING).Zinc Oxide. ZnO; sp. gr. 5.65: m.pt.19700C; thermal expansion (20-10000C)6.7 x 10"6. Used in glasses, glazes,enamels, and more recently in specialferromagnetic ceramics and varistors.Zircon. Zirconium orthosilicate.ZrO2-SiO2; sp. gr. 4.56. The principalsource is along the most easterly part ofthe coast of Australia, on both sides ofthe border between Queensland andNew South Wales, where it occursabundantly as beach sands. Whenheated, zircon dissociates at 1600-18000C into SiO2 and ZrO2; it isnevertheless used as a refractory, in thelining of aluminium-melting furnaces andnozzles for the continuous casting ofsteel, for example. Two types of zirconrefractory are defined in ASTM - C545,Type A with bulk density < 3.84 g/cm3

and Type B > 3.84 g/cm3. Zircon is alsoused as an opacifier in vitreous enamelsand glazes, and as a constituent ofspecial electrical porcelains.Zircon Colours. The ZrSiO4 lattice isextremely stable, and lends itself to theproduction of ceramic colours, bothLATTICE COLOURS (q.v.) andENCAPSULATED COLOURS (q.v.). See

also PIGMENT.Zircon Porcelain. An electroceramic madefrom a batch consisting of 60-70% zircon,20-30% flux and 10-20% clay; the fluxmay be a complex Ca-Mg-Ba-Zr silicate orother alkaline-earth composition. Zircon

porcelain has high mechanical strength(Young's Modulus) and good thermal-shock resistance over a wide temperaturerange. Electrical properties are: volumeresistivity (3000C) 1010-1012 ohm-cm.;dielectric constant (1 MHz) 8.5-9.5: powerfactor (1 MHz) 10-15 x 1(H.Zirconia. Zirconium Oxide, ZrO2;M.pt.approx. 27000C; density 5.6 kg.m-3.The high temperature crystal form iscubic with a fluorite structure. Below23700C this transforms to a tetragonalform, which undergoes a MARTENSITIC

TRANSFORMATION (q.V.) to the lowtemperature monoclinic phase. Thereis a 3% volume change at thistransformation, causing cracking in purezirconia. Heating zirconia with smallamounts of cubic oxides (CaO, MgO)produces solid solutions with the ZrO2

which is stabilized in the cubic structure.Fully-stabilized zirconia (with c. 15 mole% CaO) has the cubic fluorite structureat room temperature.Partially-stabilized zirconia(v/\th c. 8%MgO) has a cubic structure containing afine dispersed precipitate of c. 0.1 umtetragonal (and/or monoclinic) zirconiacrystals.Tetragonal zirconia poly crystals comprisec. O.lum crystals of wholly tetragonalcrystal structure, made by the controlledsintering of very fine starting powderswith c. 3% Y2 O3 sintering aid. Intetragonal zirconia, toughening is by theMartensitic transformation to monocliniczirconia. This absorbs energy and sets upcompressive stresses around the cracktip, inhibiting further crack growth. Withsufficient microclinic zirconia present,the resulting microcracking throughoutthe structure causes CRACK BRANCHING,absorbing crack propagation energy,when the dispersed particles are largeenough. Zirconia is used as a secondphase, usually in its tetragonal form, in

dispersed-phase ceramic-ceramiccomposites such as zirconia-toughenedalumina and silicon nitride. About 20%ZrO2 is usual. Zirconia is of particularinterest as an engineering ceramic, as itsthermal expansion coefficientapproximates that of cast iron,simplifying ceramic-metal joining.Fused zirconia is used as kiln furniturefor titanates.Zirconium Borides. ZrB, m.p. 29500C;sp. gr. 6.7. ZrB2, m.p. approx. 30500C;sp. gr. 6.1. A hard, refractory, chemicallyresistant material. When shaped byceramic processes it may find use inrocket nozzles, in the casting of alloys,and for thermocouple sheaths. It has ahigh electrical conductivity; the thermalexpansion is approx. (25-10000C) 6.0 x10^5. A less well-known compound isZrB12; m.p. 26800C; sp. gr. 3.6.Zirconium Carbide. ZrC; m.p. 35300C;sp. gr. 6.7; thermal expansion (25-20000C) 7.5 x 1(H. The face-centredcubic form is stable at least up to26500C. This special refractory materialhas been used in the manufacture of aflame deflector operating at very hightemperatures.Zirconium-Iron Pink. A ceramic stainsuitable for the colouring of a variety ofglazes maturing at 1220-12800C. Thisfiring range is greater than thatpermissible with chrome-tin pink or withchrome-alumina pink.Zirconium Nitride. ZrN; m.p. 2980 ±500C; sp. gr. 7.3; thermal expansion (25-14000C) 8 x 1(H. A brown compoundZr3N4, sp. gr. 5.9, has also been reported.Zirconium Oxide. See ZIRCONIA.Zirconium Phosphate. Normal zirconiumphosphate, ZrP2O7, has a reversibleinversion at 3000C and at 15500Cdissociates into zirconyl phosphate,(ZrO)2P2O7, with loss of P2O5 asvapour. Zirconyl phosphate is stable up

to about 16000C and has a very lowthermal expansion (20-10000C) 1 x 10"6.Zirconium Silicate. See ZIRCON.Zirconium Silicides. Eight compoundshave been reported; the following appearto be the most important. ZrSi, m.p.>2000°C, sp. gr. 5.5, hardness (KlOO) 1030kg/mm2. ZrSi2, decomposes >1500°C, sp.gr. 4.9, hardness (KlOO) 1030 kg/mm2.Zr5Si3, m.p. 22500C, sp. gr. 5.9.Zirconium-Vanadium Blue (orTurquoise). A pigment, for use inceramic glazes, introduced by HarshawChemical Co. (US Pat., 2 441 447,11/5/48; Brit. Pat. 625 448, 28/6/49). Thecomposition is (parts by wt): ZrO2, 60-70; SiO2, 26-36; V2O5, 3-5. Alkali mustalso be present, e.g. 0.5-5% Na2O. Inthe absence of alkali a green colour isproduced.Zirkite. A term used in the mineral tradefor the natural, impure, zirconia ore(baddeleyite) that occurs in Brazil.

Zirlane. Trade-name. Ceramic fibrescontaining zirconia (Kerlane, France).Zone Melting. A heat treatmentcontrolled in such a way as to cause ashort molten zone to travel slowlythrough a relatively long solid charge ofcrystalline material, gathering upimpurities more soluble in the liquidphase as it goes. The process wasintroduced by W. G. Pfann {Trans.A1M.E., 194,747,1952).ZTA. Zirconia Toughened Alumina. SeeZIRCONIA.

ZTS. Zirconium Titanium Stannate hastemperature-stable high-frequencypermittivity and very low dieectriclosses, and is used in microwaveresonators and filters.Zytan Block. Lightweight clay blocks ofprecise dimensions. See PERFLUENTSINTERING.

Zyttrite. Translucent yttria-stabilizedzirconia.

Appendix AThe Definition of 'Ceramics'

The definition of ceramics has provedperennially difficult. Scientific ortechnological definitions have attemptedto be accurate and exhaustive, whetherbased on the type of material or whetheroperational definitions based on theprocesses used to make ceramics.

Definitions for commercial purposes(usually the collection of tariffs, orrestriction of imports) have concentratedon precision at the expense of scientificaccuracy or generality.

Dictionary definitions must reflect theactual use of words, without straying toofar from what is precisely and technicallycorrect.

Historically, usage has broadened from'largely crystalline products made of firedclay' to include non-clay materialsavailable as articles, or as coatings orpowders. This extension of meaningbegan in 1822 when silica refractorieswere first made by the normal ceramicprocess of shaping, drying and firing. Ithas gathered pace in the last half centuryto encompass many novel materialsshaped by new processes. In 1920 theAmerican Ceramic Society extended thescope of the word ceramics to include allthe silicate industries, bringing in glass,vitreous enamel and hydraulic cement.The problem today is to provide adefinition which is sufficiently broad,without including a whole range ofnaturally occurring materials such asrocks, ores and minerals. (One of thelatest general compendiums ofinformation on ceramics - the EngineeredMaterials Handbook VoI 4 - seeAppendix B - abandons this struggle andregards 'ceramics' as a synonym for all'non-metallic, inorganic materials.')

The 'everyday' definition from theConcise Oxford Dictionary is: 'Of (theart of) pottery; of (substances producedby) process of strong heating of clay etc.materials. An article made of pottery;substance made by firing clay etc.minerals at high temperatures.'

The Illustrated Dictionary ofCeramics for collectors of antiques andconnoisseurs, says that ceramics is 'thebroad term for all objects made of firedclay' (further subdivided intoearthenware, stoneware and porcelainon the basis of firing temperature).

In British Standards, definitionsusually relate to the content of aparticular standard. BS 5416 definesceramics as 'materials generally madefrom a mixture of clays and othermaterials, distinguished from glass andglass ceramics by the fact that they arefirst shaped and then renderedpermanent by firing at a temperaturegenerally well in excess of 10000C(This definition, framed in the context ofdefining china tableware for mainlycommercial purposes, is not notable forgenerality, accuracy or precision).

The American Society for Testing andMaterials adopts an operationalapproach, in terms of a 'ceramicprocess.' (ASTM C-242)

Ceramics - a general term applied tothe art or technique of producing articlesby a ceramic process, or to the articles soproduced.

Ceramic Process - the production ofarticles or coatings from essentiallyinorganic, nonmetallic materials, thearticle or coating being made permanentand suitable for utilitarian anddecorative purposes by the action of heat

at temperatures sufficient to causesintering, solid-state reactions, bonding,or conversion partially or wholly to theglassy state.

Ceramic Article — an article having aglazed or unglazed body or crystalline orpartly crystalline structure, or of glass,which body is produced from essentiallyinorganic, non-metallic substances andeither is formed from a molten masswhich solidifies on cooling, or is formedand simultaneously or subsequentlymatured by the action of the heat.

Definitions for commercial purposesinclude those of the EC Combined(Tariff) Nomenclature, and the TariffSchedules of the United States(Annotated Schedule 5 - Non-metallicMinerals and Products, Pt 2, CeramicProducts, Headnotes, 1976). TheEINECS definition, aiming at definingexisting substances in contrast to 'new'ones, adopts an 'exhaustive listing'approach.Combined NomenclatureCeramic Product - products obtained byagglomerating (by firing) earths or othermaterials with a high melting pointgenerally mixed with binders, all ofwhich materials have been previouslyreduced to powders or, from rock firedafter shaping. (The explanatory notesdescribe body preparation, shaping,drying, firing and finishing). Firing, aftershaping, is the essential distinctionbetween ceramic products and mineralor stone articles, which are generally notfired, and glass articles in which theverifiable compound has undergonecomplete fusion.US Tariff SchedulesCeramic Article - a shaped article havinga glazed or unglazed body of crystallineor substantially crystalline structure,which body is composed essentially ofinorganic non-metallic substances and

either is formed from a molten masswhich solidifies on cooling, or is formedand subsequently hardened by such heattreatment that the body, if reheated topyrometric cone 020, would not becomemore dense, harder, or less porous, butdoes not include any glass article.EINECSCeramic Materials and Wares,Chemicals - this category encompassesthe various chemical substancesmanufactured in the production ofceramics. For purposes of this category,a ceramic is defined as a crystalline orpartially crystalline, inorganic, non-metallic, usually opaque substanceconsisting principally of combinations ofinorganic oxides of aluminium, orzirconium which conventionally isformed first by fusion or sintering at veryhigh temperatures, then by cooling,generally resulting in a rigid, brittlemonophase or multiphase structure.(Those ceramics which are produced byheating inorganic glass, thereby changingits physical structure from amorphous tocrystalline but not its chemical identityare not included n this definition.) Thiscategory consists of chemical substancesother than by-products of variousceramics and concurrently incorporatedinto a ceramic mixture. Its compositionmay contain any one or a combination ofthese substances. Trace amounts ofoxides and other substances may bepresent. The following representativeelements are principally present asoxides but may also be present asborides, carbides, chlorides, fluorides,nitrides, silicides, or sulfides in multipleoxidation states, or in more complexcompounds:

Al, B, Ba, Be, C, Ca, Cd, Ce, Co, Cr, Cs,Cu, Fe, Hf, K, Li, Mg, Mn, Na, P, Si, Sn,Th, Ti, U, Y, Zn, Zr.

Appendix BOther Sources ofInformation

These documents are grouped underthree headings.

BJ Works which provide additionaltechnical information, either over awider range of topics (eg Chambers) orin greater depth and detail.

B.2 Standard glossaries, in which thedefinitions of terms may differ fromthose given in this dictionary (havingbeen developed in a different context)and in which a wider range of relatedterms may also be defined.

BJ Some specialised multilingualdictionaries and glossaries of ceramicterms.

BJ

Chambers Science and TechnologyDictionary.Ed. P.M.B. Walker, Chambers,Edinburgh, 1991.Provides brief definitions over the wholerange of science and technology, (c. 1000 pp).

Engineered Materials Handbook, VoI 4,Ceramics and Glasses.Ed. SJ. Schneider, ASM International,Materials Information Society, 1991.Provides short technical descriptions (up to afew pages) of ceramics materials andprocesses (1 VoI, c. 1200 pp A4).

Encyclopaedia of Materials Science andEngineering.Ed. M.B. Bever, Pergamon, 1986 (8 VoIs).Similar brief technical descriptions, over awider field of materials technology.

An Illustrated Dictionary of Ceramics.G. Savage and H. Newman, Thames andHudson, London, 1974.Definitions from the viewpoint of the artist,collector and connoisseur.

Ceramics Handbook.Cookson Ceramics Ltd, Stoke-on-Trent,1990.A brief compendium of useful factual datarelating to ceramics.

Technological and Economic Trends inthe Steel Industries.B. Wiishire, D. Horner, N.L. Cooke,Pineridge Press, Swansea, 1983.Useful background information on theprincipal uses of refractories. Appendix Dcontains an extensive list of abbreviations forsteelmaking processes.

B.2

BS 3130 Glossary of packaging terms.Pt 3 Glass containers and closures.

BS 3447 Glossary of terms used in theglass industry.

ISO R836 1968 Vocabulary for theRefractory Industry (Eng. Fr.Russian).

BS 6711 Vocabulary relating tolaboratory apparatus made essentiallyfrom glass, porcelain or vitreous silica.Pt. 1. Names for items of apparatus.

BS 6045 Ceramic and Glass InsulatingMaterials. Pt. 1. Definitions andclassifications.

BS 3402 'Quality of Vitreous ChinaSanitaryware', contains definitions ofvarious blemishes and faults.

BS 6100 - 1992 ff. Glossary of buildingand civil engineering terms.

UDC 1000 BS 1000 [666] 1984. UniversalDecimal Classifications. GlassIndustry, Ceramics, Cement andConcrete.

BS 4642 1984 Industrial Furnace Terms.ASTM D2946, Cl 154 and 460 give

terminology for asbestos, asbestos and

fibre cement and asbestos-cementrespectively.

ASTM C-904 Terminology relating tochamical-resistant non-metallicmaterials.

ASTM C-1180 Terminology for mortarsfor unit masonry.

ASTM C-896 Terminology relating toclay products.

ASTM C-43 Terminology relating tostructural clay products.

ASTM C-162 Terminology relating glassand glass products.

ASTM C-242 Terminology relating toceramic whiteware and relatedproducts.

ASTM C-1209 Terminology of concretemasonry units.

Terminology - B. 3

Glossaire PRE - Refractories. (E, F, G,It.)

Federation Europeenne des Fabricant deProduits Refractaires, Case Postale 3361,Lowenstrasse 31, CH 8023, Zurich, 1973.

CEC Ceramic Tile Dictionary. (E, F, G,Sp, It, Sw.)

Conseil Europeenne de Ceramique, 1970.

Vilmy Montanari, Collection of CeramicTechnical Words (tiles). (E, It.)

Casella Postale 8, 42013 Casalgrande Alto,Italy, 1989.

Terminologia Alafar. Refractories. (E,Sp, Port, F.)

Asociacion Latinoamericana de Fabricants deRefractarios.

Glossaire Feugres: Ceramic Sewer Pipes.(G, F, E, It.)

Europaische Vereinigung derSteinzeugrohrenindustrie, Zurich, 1962.

ICG Dictionary of Glassmaking. (E, F, G.)Sub-Committee A-I, InternationalCommission on Glass, Elsevier, 1983.

European Ceramics Glossary. (E, F, G,Sp, It, Sw)

Gruppo Editoriale Faenza Editrice, s.p.A.,1992 48018 Faenza, Italy.

Appendix CHardness of materials

Hardness tests are at best semi-empirical, and comparisons betweendifferent scales unreliable, as the testconditions differ. Some indications ofcomparative values for materials ofceramic interest can be gleaned from thefollowing tables. The Mohs referenceminerals are in bold type.

APPROXIMATE CONVERSION OF HARDNESSVALUES

SINTERED CARBIDES

Vickers diamondhardness, 50 kg

load

1750170016501600155015(X)1450140013501300125012001150110010501000950900850

Rockwell A scale60 kg load:

diamond cone

92.492.091.791.390.990.590.189.789.388.988.588.187.687.086.485.785.084.082.8

Rockwell C scale150 kg load:

diamond cone

80.579.879.278.477.777.076.275.474.673.873.072.271.370.469.468.266.664.6

Substance

TalcRock saltor GypsumKaoliniteMicaCalciteMarbleDolomiteFluoriteGlassAsbestosApatiteSoda-lime glassPumiceFeldspar(orthoclase)AgateSteelVitreous SilicaQuartz(or Stellite)ZirconiaBerylliaTopazGarnetFused ZirconiaCo-bonded WCZirconium BorideCorundumTitanium NitrideTungsten CarbideTantalum CarbideZirconiumCarbideFused AluminiaBeryllium CarbideTitanium CarbideSilicon CarbideAluminium BorideBoron CarbideDiamond

MohsHardness

No.(Original

scale)

122

(2-2.5)(2.5-3)

3(3-4)

(3.5-4)4

(4.5-6)(5)5

(5.5)(6)6

(6-7)(5-8.5)

7

(7)(7)8

(8)(8)

(8-9)(8)9

(9)(9)(9)(9)

10

MohsHardness

No.(Extended

scale)

1

2

3

4

5

6

788

91011

12

13

1415

KnoopHardness

32

135

163

370

560

820

1160

1250

1400-18001550

1800188020002100

2100241024702480250027507000

Reference: In Butterworths Metal Handbook VoI 3.

Appendix DNominal Temperature (0C) Equivalents of Pyrometric ConesCONENo.

022022A021020019018017016015015A014014A013013A012012AOilOHA010010A0909A0808A0707A0606A0505A0404A0303A0202A0101A1IA22A33A44A55A66A77A88A8B99A1010A11

BRITISH(Staffordshire)

4°C/min

600625650670690710730750790

815

835

855

880

900

920

94095096097098099010001010102010301040105010601070108010901100111011201130114011501160117011801190120012151230124012501260127012801290130013101320

GERMAN(Seger)

600

650670690710730750

790

815

835

855

880

900

920

940

960

980

1000

1020

1040

1060

1080

1100

1120

1140

1160

1180

12001230

1250

1280

1300

1320

AMERICAN(Orion)

LargerC/min

585

602625668696727767790

834

869

866

886

887

915

945

973

991

1031

1050

1086

1101

1117

1136

1142

1152

1168

1177

1201

1215

1236

1260

1285

1294

Large21A0CZmIn

600

614635683717747792804

838

852

884

894

894

923

955

984

999

1046

1060

1101

1120

1137

1154

1162

1168

1186

1196

1222

1240

1263

1280

1305

1315

Small5°C/min

630

643666723752784825843

870

880

900

915

919

955

983

1008

1023

1062

1098

1131

1148

1178

1179

1179

1196

1209

1221

1255

1264

1300

1317

1330

1336

CONENo.

1213141516171819202326272829303131V*3232V233343536373839404142

* 10°C/min

BRITISH(Staffordshire)

4°C/min

135013801410143514601480150015201530

158016101630165016701690

1710

1730175017701790182518501880192019602000

GERMAN(Seger)

135013801410143514601480150015201530

158016101630165016701690

1710

1730175017701790182518501880192019602000

AMERICAN(Orion)

Largel°C/min

13061321138814241455147715001520154215861589161416141624163616611685170617181732175717841798

Large2Vz0CZmIn

13261346136614311473148515061528154915901605162716331645165416791700171717301741175917841796

RCE.Cones

21A0CZmIn

1337134913981430149115121522154115641605162116401646165916651683169917171724174317631785180418201835*1865*1885*1970*2015*

Appendix EComparison Table for Sieve SizesISO/(USA)

Size

125106(100)9075

6353(50)4537.5

31.526.5(25.0)22.419.0

16.013.2(12.5)11.2

9.58.06.7(6.3)

5.6

4.754.003.35

2.802.362.001.70

1.401.181.00

.850

.710

.600

.500

.425

.355

.300

.250

.212

.180

ASTM

No

3!/2

456

78

1012

14

161820

25

3035

40

45

50

6070

80

Size

5"4.24"4"31A"3"

2Vi"2.12"2"WA"

VA"

VA"1.06"1"

VA"

Vs".530"Vz"1At"

WVlt".265"VA"

4.76

3.36

2.832.38

1.41

1.19

0.84

.707

.595

.354

.297

All

BRITISH

No

5

678

10

12

141618

22

2530

36

44

52

6072

85

Size

3.35

2.802.402.001.68

1.40

1.201.00.850

.710

.600

.500

.420

.355

.300

.250

.210

.180

IMM

No

5

8

10

12

16

20

30

40

50

607080

Size

2.54

1.57

1.27

1.06

.792

.635

.422

.317

.254

.211

.157

TYLER

No

21A

3

3XA

4

5

6

7

8

9

10

12

14

16

20

24

28

32

35

42

48

6065

80

Size

1.05"

.883"

.742"

.624"

.525"

.441"

.371"

4.73.963.33

2.792.361.981.65

1.17.99.83

.701

.589

.495

.417

.351

.295

.246

.208

.175

FRENCH

No

38

37

36

353433

32

31

30

29

28

27

26

25

24

23

Size

5.000

4.000

3.150

2.5002.0001.600

1.250

1.000

.800

.630

.500

.400

.315

.250

.200

.160

GER-MAN

Size

25.0

20.0

18.016.0

12.5

10.0

8.0

6.3

5.0

4.0

3.15

2.52.01.6

1.25

1.0

.800

.630

.500

.400

.315

.250

.200

.160

CANADIAN

metric

Size

26.9

22.619.0

16.013.5

11.2

9.518.006.73

5.66

4.764.003.36

2.832.382.001.68

1.41

1.191.00.841

.707

.595

.500

.420

.354

.297

.250

.210

.177

No

3V2

456

78

1012

14

161820

25

3035

40

45

50

6070

80

imperial

Size

1.06"

Vs"VA"

W.530"

7/l6"

3/8H

5/l6"

.265"

ISO/(USA)

Size

.150

.125

.106

.090

.075

.063

.053

.045

.038

.032(.025)(.020)

ASTM

No

100120140

170

200

230

270

325

400

Size

.149

.088

.074

BRITISH

No

100120150

170

200

240

300

350

Size

.150

.125

.105

.090

.075

.063

.053

.045

IMM

No

90100120

150

200

Size

.139

.127

.107

.084

.063

ITLER

No

100115150

170

200

250

270

325

400

Size

.147

.124

.104

.088

.074

.061

.043

.038

FRENCH

No

22

21

20

19

18

17

Size

.125

.100

.080

.063

.050

.040

GER-MAN

Size

.125

.100

.090

.080

.071

.063

.056

.050

.045

.040

CANADIAN

metric

Size

.149

.125

.105

.088

.074

.063

.053

.044

.037

No

100120140

170

200

230

270

325

400

imperial

Size

ISO/(USA) ISO 3310/ASTM E-Il metric*

BRITISH BS 410IMM Institution of Mining & Metallurgy, LondonFRENCH AFNOR X-11-501GERMAN DIN 4188ASTM ASTM E-Il (USA)TYLER Tyler Sieve Sizes (USA)CANADIAN Standard sieve series 8-GP-lb

*NB ISO Standard Sieve Sizes are now in general use, and national standards conform to them. The figures in the left-hand column arethe ISO sizes, plus a few additional sizes (bracketed) retained in the metric version of ASTM El l on grounds of extensive use. Theremaining columns give designations and actual aperture sizes (in mm unless inches (") are specifically noted) of older sieve serieslikely to be found in the literature.

Dictionary of Ceramics_A.Dodd-1994

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