Finish, Culet Size, and GirdleThickness: … Finish, Culet Size, and GirdleThickness: Categories of...

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Finish, Culet Size,and Girdle Thickness:Categories of the GIADiamond Cut Grading System

This booklet summarizes the relationship of Finish, Culet Size, and Girdle Thickness tothe GIA Cut Grading System for round brilliant diamonds. It is intended to help members ofthe jewelry trade better understand the attributes of diamond appearance, and how those attributesare evaluated within the GIA Cut Grading System.

In the GIA Cut Grading System for standard round brilliantdiamonds, finish (for Polish and Symmetry features) isfactored into the final overall cut grade as follows:

• To qualify for an Excellent cut grade, polish andsymmetry must be Very Good or Excellent.

• To qualify for a Very Good cut grade, both polishand symmetry must be at least Good.

• To qualify for a Good cut grade, both polish andsymmetry must be at least Fair.

• To qualify for a Fair cut grade, both polish andsymmetry must be at least Fair.

• A Poor cut grade is assigned when either polish orsymmetry is Poor.

To determine the relationship between finish and overallcut quality, GIA conducted extensive observation testingof numerous diamonds using standardized lighting andviewing conditions. Observations of diamonds withcomparable proportions, but differing in their polish andsymmetry categories, were analyzed to determine theeffects of finish on overall cut appearance. In this way,GIA found that a one grade difference between the otheraspects of a diamond’s cut grade and its polish andsymmetry assessments did not significantly lower atrained observer’s assessment of face-up appearance, andcould not be discerned reliably with the unaided eye—e.g., polish and/or symmetry descriptions of Very Gooddid not cause observers to lower their assessment of adiamond that would otherwise receive an overall cutgrade of Excellent.

©2009 The Gemological Institute of America. All rights reserved. The Gemological Institute of America (GIA) grants you a one-time, non-exclusive license toreproduce in print form this booklet solely for non-commercial, private use to reference the GIA Diamond Cut Grading System within an individual organization.This booklet may also be reproduced and used electronically in circumstances where such use is limited to the private, internal business use by the individualor firm to whom GIA provides the material. The material may not be modified in any way. GIA retains all rights to the material, and all other use is prohibitedwithout the express, written permission of GIA.

Contributors: T. Blodgett, R. Geurts, A. Gilbertson, A. Lucas, D. Pay, I. Reinitz, J. Shigley, K. Yantzer, C. ZinkEditor: Brooke Goedert Design and layout: Richard Canedo, Al Gilbertson

Finish—Polish and Symmetry

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Categories of the GIA Diamond Cut Grading System

In the GIA Cut Grading System “polish” refers to thequality of a diamond’s surface condition as a result of thepolishing process or to blemishes created after the cuttingprocess, often referred to as “wear and tear.” Polish featuresare located on the surface and do not visibly penetrate intothe diamond as seen at 10X magnification. Polish isassessed on a scale consisting of Excellent, Very Good,Good, Fair, and Poor. A number of features are consideredin the evaluation of polish. GIA Laboratory gradersconsider the amount and visibility of the polish featurespresent. The general appearances of GIA’s five polishcategories and various polish features are described below.

As with all other aspects of diamond grading, standardmethodology and a controlled environment are used toevaluate polish consistently. The following steps are

performed at 10X magnification with either a fully correctedloupe or a gemological microscope under darkfield illumina-tion to assess polish (the final result in the GIA Laboratoryis an objective consensus of independent grader opinions):(1) The diamond is first examined face-up, girdle-to-girdleto gain an initial impression of the polish; (2) The diamondis then examined one section at a time, through both thecrown and pavilion, to locate and identify the specificpolish features present; (3) The diamond is again examinedface-up, girdle-to-girdle, and this time viewed in at leastfour different positions with a loupe; some features may bemore or less apparent depending on the orientation of thediamond; (4) A verbal polish description is assigned thatconsiders the diamond’s overall face-up appearance as wellas polish features seen in any view. Emphasis is placed onthe diamond’s face-up appearance as seen with a 10X loupe.

Polish

CATEGORIESExcellent: ranges from no polish features to a few minute features that can be viewedface-up with difficulty at 10X magnification.

Some typical features that would be allowed in the Excellent category include a few pits ornicks, a small area with faint transparent polish lines, or negligible scratches or abrasion.

* Although a diamond with a few minute polish features might qualify for the Excellent polishcategory, the same diamond could not qualify for a Flawless clarity grade. Only diamondswith no polish features visible at 10X magnification qualify for a Flawless clarity grade.

Very Good: minor polish features are seen face-up at 10X magnification.

Some typical features that would establish a Very Good category include several pits or nicks,a few small areas of abrasion, a limited extent of moderate transparent polish lines, a smallarea with faint white polish lines, several faint scratches or a few heavier white scratches, faintlizard skin, or a small area of very faint burn marking.

Good: noticeable polish features are seen face-up at 10X magnification. The luster of thediamond may be affected when viewed with the unaided eye.

Some typical features that would establish a Good category include moderate to heavy trans-parent polish lines, white polish lines, many heavy scratches, lizard skin or burn marks.

Fair: obvious heavy polish features are seen face-up at 10X magnification. The luster of thediamond is affected when viewed with the unaided eye.

Some typical features that would establish a Fair category include heavy white polish lines orburned facets over most of the crown or pavilion.

Poor: prominent heavy polish features are seen face-up at 10X magnification. The luster ofthe diamond is significantly affected when viewed with the unaided eye.

Some typical features that would establish a Poor category include heavy white polish lines orburned facets over most of the crown and pavilion.

scratch

transparentpolishlines

whitepolishlines

most ofpavilionburned

entire crownand pavilionburned

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Finish, Culet Size, and Girdle Thickness

FEATURES

AAbbrraassiioonn:: area of minute scratches or pits along a facetedge producing a fuzzy white line instead of a sharp facetjunction.

LLiizzaarrdd sskkiinn:: transparent uneven texture confined to onefacet; caused by polishing a facet off-grain, at the hardestdirection near a cleavage plane.

PPiitt:: tiny opening appearing as a white dot.

RRoouugghh ggiirrddllee:: irregular pitted or granular surface of a brutedgirdle due to pits and nicks.

BBuurrnn mmaarrkk oorr bbuurrnneedd ffaacceett:: whitish haze across a facet ora concentrated area caused by excessive heat duringpolishing or occasionally by a jeweler's torch.

NNiicckk:: small notch on a facet junction, usually along thegirdle or culet; minute chip with no visible depth at 10Xmagnification.

PPoolliisshh lliinneess:: parallel lines left by the polishing process; mayappear white or transparent.

SSccrraattcchh:: surface mark normally seen as a fine white line,curved or straight.

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In the GIA Cut Grading System, “symmetry” refers tothe exactness of the shape of a diamond and the sym-metrical arrangement and even placement of the facets.As with polish, a number of features are considered inthe evaluation of symmetry; these are defined andillustrated below.

Symmetry features can be subdivided into two types:proportion-related and facet-related. Due to a polisheddiamond’s three-dimensional nature, the presence of onesymmetry feature may be linked to others. GIALaboratory graders consider the extent and visual appear-ance of any symmetry features present.

The general appearances of GIA’s five symmetrycategories are described below. The following steps areperformed at 10X magnification with either a fullycorrected loupe or gemological microscope underdarkfield illumination to determine the symmetry of apolished diamond (the final result is an objectiveconsensus of independent grader opinions): (1) Thediamond is first examined face-up, girdle-to-girdle inorder to gain an initial impression of the symmetry; (2)The diamond is then rotated in profile view to reveal anysymmetry features that are best seen in this position —such as non-pointing, misalignment, wavy girdle, girdlethickness variation, table and girdle not parallel, crown

Symmetry

CATEGORIES

Excellent: ranges from no symmetry features to minute symmetry features that can beviewed face-up with difficulty at 10X magnification.

Some typical features that would be allowed in the Excellent category include misaligned,misshapen, non-pointed, or extra facets that are barely visible.

Very Good: minor symmetry features are seen face-up at 10X magnification.

Some typical features that would establish a Very Good category include slight table or culetoff-center, a slightly out-of-round outline, and/or minor misshapen, non-pointed or extra facets.

Good: noticeable symmetry features are seen face-up at 10X magnification. The diamond’soverall appearance may be affected when viewed with the unaided eye.

Typical features that would establish a Good category include any proportion feature that isnoticeable: table or culet off-center, out-of-round outline, wavy girdle, table and girdle notparallel, girdle thickness variation, crown or pavilion angle variation, and/or many noticeablemisshapen, misaligned, non-pointed, or extra facets.

Fair: obvious symmetry features are seen face-up at 10X magnification. The diamond’soverall appearance is often affected when viewed with the unaided eye.

Typical features that would establish a Fair category include any proportion feature that isobvious: table or culet off-center, out-of-round outline, wavy girdle, girdle thickness variation,crown or pavilion angle variation, many obvious misshapen or extra facets, misalignment ornon-pointing on most of the facets, and/or an obvious missing facet such as a bezel or main.

Poor: prominent symmetry features are seen face-up at 10X magnification. The diamond’soverall appearance is significantly affected when viewed with the unaided eye.

Typical features that would establish a Poor category include any proportion feature that isprominent: table or culet off-center, out-of-round outline, wavy girdle, girdle thickness variation,crown or pavilion angle variation, or prominent faceting distortion.

misalignment

misshapenmains

out-of-roundand prominentfacetingdistortions

misalignment

culetoff-center

misshapen andshort mains

misshapenbezels andstars

non-octagonaltable

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angle variation and pavilion angle variation; (3) Thediamond is again examined face-up, girdle-to-girdle, andthis time viewed in at least four different positions with aloupe; some features may be more or less apparentdepending on the orientation of the diamond; (4) Thegrader checks the values of the optically measuredsymmetry features to evaluate the degree of misalignment,especially culet off-center, table off-center, and out-of-round; (5) A verbal symmetry description is assigned thatconsiders the diamond’s face-up appearance as well assymmetry features seen in profile view. Emphasis isplaced on the diamond’s face-up appearance as seenwith a 10X loupe.

While this chart focuses on symmetry evaluation as partof the GIA Cut Grading System for standard roundbrilliant diamonds, most of the criteria apply similarly tofancy shapes with the addition of some specific guidelinesin regard to shape and lines of symmetry.

Variations in crown height and/or pavilion depth resultfrom one or more of the following deviations: wavygirdle, table and girdle not parallel, crown angle varia-tion, pavilion angle variation, and/or girdle thicknessvariation.

Crown anglevariation

all eight crown anglesare not equal; typicallyrelated to table off-center.

Pavilion anglevariation

all eight pavilion anglesare not equal; typicallyrelated to culet off-center.

Table and girdlenot parallel

the girdle plane is notparallel to the table.

Culet off-center

deviation of the culet from the centralposition on the pavilion; results in thecross-line formed by lower half facetjunctions to be bowed or bent. Whenviewed through the table, more of thepavilion is seen to one side of the culetthan the other.

culetoff-center

Out-of-round

deviation from the circular shape of around diamond; a flattened area suchas that created by a natural or extrafacet also constitutes out-of-round.Comparison of the minimum andmaximum diameters can help assessroundness.

Table off-center

deviation of the table from the centralposition on the crown; results inopposing bezels of differing sizes.When viewed through the table, moreof the pavilion is seen to one side ofthe culet than the other.

flattenedarea

Girdle thicknessvariation:

variations of the girdlethickness at “valley” and“hill” positions.

tableoff-center

Table/culetalignment

displacement ofthe table facet andculet in oppositedirections.

Wavy girdle

undulating girdle.

PROPORTION-RELATED SYMMETRY FEATURES

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Extra facet

additional facet placedwithout regard for symmetryand not part of the standardcutting style; typicallycauses an out-of-roundoutline, short facets ormisshapen facets.

Misalignment

displacement of thecrown and pavilionfacets in relation toeach other.

Misshapen facet

difference in shape or sizebetween one facet andanother of the same type;or distortion of a givenfacet.

extrafacet onpavilion

misshapenstars andbezels

misshapenmainsMissing facet

asymmetrically missingor deleted facet.

missingmain

Natural

part of the originaldiamond crystal’ssurface that remainson the polisheddiamond; typicallycauses an out-of-round girdle outline,short facets ormisshapen facets.

flattened area created bya natural Non-octagonal

table

the table is not aregular octagon;results in mis-shapen star andbezel facets.

Non-pointing

facet that does notreach its prescribedlocation (short facet) oris incompletely finished(open facet), resulting inadjoining facets notmeeting at precisepoints.

shortmain

openbezel

FACET-RELATED SYMMETRY FEATURES

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The culet is a polished facet placed parallel to the table, thepurpose of which is to prevent damage to the point. Culetsize is an important element in GIA’s Cut Grading System,as it can affect evaluations of the face-up appearance.

To determine the significance of culet size, GIAresearchers used computer modeling and visual obser-vations to examine the effects of these proportions onface-up appearance — for example, eye-visible culetsthat may disrupt the face-up pattern.

In the GIA Laboratory, graders first assess culet size face-up, looking through the table facet at 10X magnification.In GIA’s International Diamond Grading System™, culetsize is described as None, Very Small, Small, Medium,Slightly Large, Large, Very Large, or Extremely Large. Ifthere is no culet facet the size is reported as None. Whenall eight mains meet each other, it may be referred to as“pointed.” If the culet is at more than a slight angle to thetable facet, the size is also reported as None, as it is nolonger considered a culet but an extra facet.

Culet size can be measured through the use of a non-contact optical measuring device or with the GIAMulti-Purpose Gemological Reticule and a standardgemological microscope. These measurements can beexpressed as a percentage relative to the averagediameter of the diamond, which graders may use as aguide when making visual assessments. Becausemeasured results are susceptible to the variabilityinherent in measurement device tolerances and claritycharacteristics as well as irregularities in shape or angle,the final call is determined by visual observation. Tosupport their visual assessment of culet size, GIALaboratory graders use photographic references. Theaccompanying chart provides definitions and typicalexamples for each description and their relationship tothe calculated culet-size percentages.

Culet Size

None VerySmall

Small Medium

SlightlyLarge

Large VeryLarge

ExtremelyLarge

≈≈ 1.5% ≈≈ 3%

≈≈ 5% ≈≈ 7% ≈≈ 11% ≈≈ 15%

Culet size percentages shown here represent typical values (not the highest or lowest point) for culets that are octagonal in shape. None,Very Small, and Small are best evaluated visually since these fine measurements are more susceptible to measurement tolerances and thepresence of clarity characteristics. For these same reasons, in addition to the fact that the culet may be irregular or not parallel to the table,all assessments must be verified visually.

The culet is a facet placed at the tip of the pavilion where the mains meet toreduce the risk of damage on loose diamonds. Although the definition ofculet is limited to the facet located at the bottom of the pavilion, this term iscommonly used to refer to this area in general.culet culet size

Culet Size % =culet size (mm)

X 100average diameter

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The girdle is a narrow section separating the crown fromthe pavilion and functions as the diamond’s setting edge,reducing the risk of damage when sufficiently thick. Thegirdle of a standard round brilliant diamond is scallopedand consists of 16 “valley” and 16 “hill” positions createdby the final brillianteering (cutting). Both the averagegirdle thickness percentage and the minimum/maximumverbal descriptions are important elements in the GIA CutGrading System. A thick girdle can contribute toward aheavier diamond than its face-up appearance warrants, anda thin girdle can increase the risk of damage such aschipping. GIA Laboratory graders visually assess girdlethickness at 10X magnification with the diamond in profileview, and consider each of the 16 valley positions and theirthicknesses relative to the diameter of the diamond.

The average girdle thickness is measured strictly by anoptical device and its percentage calculated using theprovided formula. In contrast, the minimum andmaximum verbal descriptions rely on the judgment ofGIA Laboratory graders at 10X magnification. Girdlethickness is assessed as a range from the thinnest tothickest valley positions; these valley positions – or thinareas – are located where the upper and lower half facetscome closest to meeting. Girdle thickness is verballydescribed as Extremely Thin, Very Thin, Thin, Medium,Slightly Thick, Thick, Very Thick, and Extremely Thick.

Minimum and maximum girdle thickness can bemeasured through the use of a non-contact opticalmeasuring device or with the GIA Multi-PurposeGemological Reticule and a standard gemological micro-scope. These measurements can be expressed as apercentage relative to the average diameter of thediamond, which graders may use as a guide when makingvisual assessments. Girdle thickness assessments (min.and max.) must continue to rely on visual observations

because measured results are susceptible to the variabilityinherent in measurement device tolerances and claritycharacteristics, as well as irregularities in shape or angle.This is especially true when distinguishing betweenextremely thin and very thin girdles.

An extra facet, natural, chip, cavity, or indented naturallocated at the girdle edge can narrow the girdle, in whichcase the remaining area is considered in the thicknessassessment. If a “knife-edge” is created, the girdle thick-ness is reported as Extremely Thin. When a chip, cavity,or indented natural breaks through the girdle onto thecrown and pavilion, the effect on the girdle thickness isnot considered in the assessment.To support their visualassessment of girdle thickness, GIA Laboratory gradersuse photographic references as well as the girdle thick-ness percentages of the “valley” positions. A descriptionof the girdle thickness is assigned based on the visualappearance at 10X magnification. When both the thinnestand thickest results fall in the same category, a singledescription is reported, such as Very Thin. More often,however, thickness is reported as a range from thethinnest to thickest valley areas, e.g., Very Thin toMedium. Variation in girdle thickness is also accountedfor in the assessment of the diamond’s symmetry or inevaluation of painting or digging out (see below). Thegirdle’s condition may be bruted — the surface producedby the process used to shape the round diamond — or itmay be polished or faceted. The girdle’s thickness isassessed the same, regardless of its condition. Theexamples shown illustrate approximate sizes for visualcomparison and are not boundaries.

Girdle Thickness

Girdle Thickness % =girdle thickness (mm)

X 100average diameter

Girdle thickness — as described by the GIA Laboratory — represents the thinnest and thickest “valley” positions on the girdle of the roundbrilliant — i.e., thin areas located where the upper and lower half facets meet — relative to the average diameter of the diamond.

girdlethickness

girdle

hill position atbezel/main

hill positionat upper/lower half

valleyposition

hill

valley

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ExtremelyThin

VeryThin

Thin

(≈≈ 2.9% hill)

≈≈ 1.2% valley

Medium

(≈≈ 3.5% hill)

≈≈ 1.8% valley

SlightlyThick

(≈≈ 4.2% hill)

≈≈ 2.5% valley

Thick

(≈≈ 5.2% hill)

≈≈ 3.5% valley

VeryThick

(≈≈ 6.7% hill)

≈≈ 5.0% valley

ExtremelyThick

(≈≈ 9.2% hill)

≈≈ 7.5% valley

Crown andpavilion meetwith no girdle inbetween, creatinga sharp edge; may bereferred to as a “knife-edge.”

Girdle thickness percentages shown here represent typical values (not the highest or lowest point) for symmetrical diamonds with evenlyscalloped girdles. Extremely Thin and Very Thin are best evaluated visually since these fine measurements are more susceptible tomeasurement tolerances in the presence of clarity characteristics. For these same reasons, in addition to the fact that the girdle may beirregular or not perpendicular to the table, all assessments must be verified visually.

An extra facet on the pavilion side of this diamondnarrows the girdle at a “hill” position. The girdle thicknessin this example would be reported as a range from Thin —at the location of the extra facet — to Slightly Thick — thethickest “valley” position present.

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Painting and Digging Out: A Type of Girdle Thickness Variation

Understanding Painting and Digging Out

While we illustrate here how to observe this visually,GIA calculates the extent of painting and digging outfrom the three-dimensional model produced by the non-contact measuring systems used to find a diamond’sproportions and angles.

Visual Cues at the GirdleIn a diamond with a normal girdle, the girdle thickness atthe points where the bezel facets meet the pavilion mainsis roughly equal to the girdle thickness at the pointswhere the center junctions of the upper half facets meetthe center junctions of the lower half facets. With all ofthese hill positions being relatively equal, there’s fairlyeven scalloping of the girdle all around the diamond.

During fashioning, the polisher uses techniques called“painting” and “digging out” to change the relativepositions of the upper and/or lower half facets. As aresult, the girdle edge at the half-facet junctions canbecome thicker or thinner relative to the girdle edge atthe bezel-main junctions and their relative angles change.

Both techniques can be used to maximize weight yield,especially if a small difference can lift a diamond beyondan important weight threshold, such as the half-carat,one-carat or two-carat levels. Digging is also used toremove clarity characteristics located near the girdle.Moderate to strong painting or digging out will changethe face-up appearance of a diamond, even if all of thefacets are arranged symmetrically and the proportions fallwithin traditional ranges for better looking diamonds.

PaintingWhen painting, the cutter tilts the upper or lower halffacets toward the bezel facets or pavilion mains. In adiamond with a painted girdle, the thickness of the pointswhere the upper half facet junctions meet the lower halffacet junctions is greater than the girdle thickness wherethe bezel facets meet the pavilion main facets.

Digging OutDigging out is the opposite of painting. When diggingout, the cutter tilts the upper and/or lower half facets,away from the bezel or pavilion main facets and towardeach other. In a round brilliant with dug-out facets, the

girdle thickness at the points where the upper half facetjunctions meet the lower half facet junctions is less thanthe girdle thickness at the points where the bezel facetsmeet the pavilion main facets.

Impact of Painting/Digging Out in theGIA Cut Grading System

The visual impact of painting and digging out varies withthe combination of diamond proportions in a complexway. Among diamonds of typical proportions, GIA hasfound that most people prefer diamonds that are neitherpainted nor dug out beyond minimal thresholds. GIAcalculates the extent of painting or digging out from thethree-dimensional model produced by the non-contactmeasuring systems used to find a diamond’s proportionsand angles. This calculation is not yet available throughFacetware. These charts are merely a guide to show theslight difference in girdle appearance, and how theseslight differences in painting or digging out create differ-ences in face-up appearance, affecting the final GIA cutgrade accordingly.

For typical proportion combinations, observation testingconfirmed that diamonds with painting and/or digging outbeyond a certain degree were less preferred thandiamonds of similar proportions with standardbrillianteering. In agreement with these observations, theGIA Cut Grading System will take into account variousextents and combinations of painting or digging out.

When a diamond is painted, face-up appearance is morestrongly affected through painting of the pavilion than thecrown. As pavilion painting increases, a diamond beginsto look like a single-cut diamond (a round diamond withfewer facets) with strong wide areas of darkness in thepattern. In combination with crown painting, the effect ofa dark and bright banded pattern is accentuated.

Face-up appearance is more sensitive to digging out.Strong digging out on the crown causes upper half facetsto darken, blending with the bezel facets, which alsodarken. Digging out on the pavilion can cause the entirestone to have an interrupted pattern that takes on a stronggray appearance, lacking in contrast. Digging out on boththe crown and pavilion causes the most extreme differ-ences in appearance, darkening the center with unusualbands of dark and light in the reflection pattern.

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Normal Girdle Painted Girdle

Crown Painting Only

Dug Out Girdle

bezel facet upper half facet

pavilion main lower half facet

A B





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FEATURES OF PAINTING

Moderate CrownPainting

Significant PavilionPainting

Significant Pavilionand Crown Painting

Crown Only Crown and PavilionPavilion Only

Negligible(Excellent)

Moderate(Very Good)

Significant(Good)

Severe(Fair)

FEATURES OF DIGGING OUT

Significant CrownDigging Out

Significant PavilionDigging Out

Significant Pavilion andCrown Digging Out

Crown Only Crown and PavilionPavilion Only

Negligible(Excellent)

Moderate(Very Good)

Significant(Good)

Severe(Fair)

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