Present Status of Natural Dyes

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Indian Journal of Fibre & Textile ResearchVol. 26, March-June 2001 , pp . 191-201

Present status of n tur l dyesM L Gulrajani

Department of Textile Technology Indian Institute of Technology New Delhi 11001 6, India

The present status of natural dyes with reference to the stake holders of natural dyes, est imates of dye requiremcnts,availability of natural dyes. technology for production, and some important natural dyes and mordants is critically discusscd.Application techniques and fastness properties of natural dyes arc also brieOy discussed. t is suggested that the natural dyesare not substitutes of synthetic dyes . Some of the limitations of natural dyes such as use of banned metal sa lts as mordants,poor fastne ss properties and use of agricultural land for growing natural dye plants can be overcome through research anddevelopment.Keywords: Environment protection, Mordants, Natural dyes

IntroductionNatural dyes find use in the colouration of textiles,

food, drugs and cosmetics. Small quantities of dyesare also used in colouration of paper, leather, shoepolish, wood, cane, candles , etc. In the beginning,there were dyes derived only from natural sources.Some processing was required but essentially the dyeitself was obtained from a plant, mineral or animal.After the accidental synthesis of mauveine by WilliamHenry Perkin in 1856 and its subsequentcommercial ization, heralding the advent of coal tardyes (now synthetic dyes), the use of natural dyesreceded.

The limitations of the natural dyes that wereresponsible for their decline are: Availability, Colour yield, Complexity of dyeing process, and Reproducibility of shade.

Besides these, there are the following perceivedtechnical drawbacks of natural dyes I 2: Limited number of suitable dyes. Allow only wool, natural silk, linen and cotton to

be dyed. Great difficulty in blending dyes. Non-standardized. Inadequate degree of fixation. Inadequate fastness properties. Phone: 6591404; Fax: 0091-11 -6514033 ;E-mail: ml [email protected]

Water pollution by heavy metals and largeamounts of organic substances.

The following properties are often considered to bethe advantages of natural dyes : They are obtained from renewable resources. No health hazards, sometimes they act as health

cure. Practically no or mild chemical reactions are

involved in there preparation No disposal problems. They are unsophisticated and harmonized with

nature. Lot of creativity is required to use these dyes

judiciously.According to Hi l 3, the research effort devoted to

natural dyes is negligible. If there had been significantresearch on the use of natural dyes it is probable thatthey would have already been much more widely usedthan they currently are. As there is much catching upto do after 150 years of neglect, there is plenty ofscope for rapid developments. This app lies to thetechniques of agricu ltural production, processing anddyeing.2 Stake Holders o Natural Dyes

The use of natural dyes has increased substantiallyduring the last couple of years. These dyes are beingmainly used by: Hobby groups, Designers ,


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192 INDIAN J . FIBRE TEXT. RES ., MARCH-JUN E 200 1

Traditional dyers and printers,Non-government organizations (NGO s),Museums,Academic institutes and researchassociations/laboratories, andIndustry.

The use of natural dyes, particularly by women as ahobby , has continued in spite of the advent ofsy nthetic dyes. Of late, this activity has increasedco nsiderably, particularly in US where many guildshave been formed to discuss about these dyes andorganize workshops and training programmes on aregul ar basis. A quarterly journal Turkey Red Journalcovers information about the workshops and theactivities of various hobby groups. The easyaccessibility of internet has also given fillip to thisactivity, where the various individua ls exchange notesalmost on daily basis. On e such popular site isNaturaIDyes@oneli st.com where one can get veryuse ful tips from the most profound use r Carolyn Leeand, of course, many other perso ns. Some sc hoolshave also introduced Natural Dyes as a co-curricularactivity. Many companies have come out with hobbykits for beginners. In India , Alps Industries have comeout with a large range of do-it-yourself kits (Table I).

Des igners have very effecti ve ly utili zed naturaldyes as a design tool. The non-reproducibility andnon-uniformity of shades make each creation a uniquepiece. Various kinds of design production methods,such as tie-and-dye or stitching (shibori), resistprinting, stencilling, batik, Indian Ajrakh, Kalamkari,Ikal, etc. are being practised by the designers to createunique products. Weavers Studio, Calcutta(www.weaversstudio.com) is one unique set-up whereDarshan Shah has very effectively combined manytechniques to create visually attractive products.Jagada Rajapa is a weaver-designer who has beenworking with weavers in remote villages and helpingth em to look at their traditional designs and select

Table I- US companies selling natura l dyes through inte rn ctJane s Fiber Works, hllp:llgrecnc.x tn .ne lf- fibre/dyes. htmlThc Mannings Catalog, hllp:llth e- mannings.colllCarol Leigh s Hillcreek Fiber Studio, hllp :llwww.hillcreek.comLouet Sales, hllp:llwww.cybe rtap .colllMawia Hand prints, hllp:llwww .lllaiwa .comLa Lana Wools, hllp:llwww.taaosfiber.comMisty Mountain Farm, hllp:llwww .mistymountainfarm.comThe Spinnery, hllp:llwww.thespinnery.comAlps Industries, hllp://www.alpind .co lllAlexa ndria Textiles, hllp:llwww.alex tex.comEanh Guild, hllp:llwww.eanhguild.colll

pleasing colour co mbinations. She has also beenconducting workshops in natural dyeing and try in g torebuild the sk ills long lost (www.icr.com.au). WhileHim ani Kapila is actively trying to pro mote the use oflac dye in Bihar, designing with indigo has bee n themain activity of Padmini Balaram. There are manymore such creative designers in India and abroad .National Institute of Des ign is creating a data onnatural dyes and products.

Kim Ji-hee of Catholic Universi ty in Taeg u, apartfrom conducting research on traditi onal dyes, is alsoan accomplished textile artist. She uses traditionalKorean dyes and textile product ion methods toproduce contemporary artworks. In many of herworks, she imitates the pojagi or traditional Korea nwrapping cloth by piecing together natural dyed fabricusing a traditional Korean stitchin g method. She th enforms a collage by assembling these fabrics w ithhandmade Korean mulberry paper, go ld foil , stitcheryand traditional folding tec hniques.

The handicraft industry in many countries hasevolved around local talent in th e art and craft ofdyeing yarn with natural dyes and wea ves th e m toproduce speciality fabrics. Printing of natural dyes bydirect, resist or dyed style is the special ity of printersof Rajasthan while Kalamkari with natural dyes ispractised in Shi Kal ahasti , Andhra Pradesh(www.icr.com.au).

Fine Turki sh ca rpets recognized for th eir va lue andbeauty are mad e with natural dyes obtai ned fro mplants, berries and trees (www .about-turkey.com).Perhaps, one of th e most successful natural dyesproject is the DOBAG (Dogal Boy a Arastirma veGelistirme Proj es i of Anatol ia (Turkey). Th eDOBAG projec t go t underway in the autumn of 1981in the di strict of Ayvacik. There are now twoDOBAG co-operatives - one in th e Ayvacik regionwith 220 families as members and other in theYuntdag region with 130 members. Serife Atlihanfrom Marmara University , Istanbul , lives mai nl y inthe DOBAG village and helps the weavers and doesquality control on each carpet (www.dobag.com.au).

In India, we have ARANYA, a natural dyes projectsupported by Tata Tea and loca ted in Pri stine hill s ofMunnar in Kerala. It gives employment to th ephysica lly handicapped and fam ily members of theemployees of Tata Tea .

Another interesti ng project is the Akha J im (AsianTribal Handicrafts) . Under this project , Akha tribes ofNorthern Thailand produce bedspreads, wall hangingsand tribal jackets from hand-spun and hand-wo vcn


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GULRAJANI: PRESENT STATUS OF NATURAL DYES 19

cotton dyed with natural dyes. The production issupervised by American Jim Godman(www.bangkokneLcom/Goodman .html) . Thailand isalso the home of Mat i Ikat mad e form natural dyedyed yarns.

The Mexican Indians, also know n as ZapotecIndians, living in the Central Valley of the state ofOaxaca have evo lved their wool-weaving art,adapting and absorbing the ideas from other culturesthrough hi story . The Zapotecs use sheep s wool andnatural dyes derived from the plants and insec ts ofthis rich reg ion. Designs are varied. Some aretraditional Zapotec designs while ot hers are adoptedfrom the Mayan and Aztec art (www .Southwestfurn ishings.com). Natural dyes are also exclusive lyused for dyeing Porcupine quills by nat ive Americans.

Ann Svenson has described the art of production ofKuba textiles4 The Kub a people of Zaire, formerly theBelgian Congo, live in the fertile lands of equatorialAfrica between Kansai and Sankuru Rivers. Kubacloth is woven from the fibres of the Raphia ViniferaPalm. Production of these textiles is a multiple - stageprocess that involves the participation of children,men and women of the same cla n. The processincludes ga th ering and preparing the raffia fibres forweaving and embroidery , weaving the basic clothunit, dyeing the embroidery fibres, and embelli shingthe woven cloth with embro idery, applique andpatchwork .

The township of Momostenango in Guatemala isknown for its natural dye rugs. The rugs are producedfrom both cotton and wool. Solola is the on ly town inGuatemala where women wear natural dyed qui lip(woman s shirt) . Of course, Mayan wo men wear trajea natural Mayan clothing.

Non-government organizations (NGOs) are alsoextensive ly engaged in promoting natural dyes inrural areas. Presently , Punjab Durrie Weavers (anNGO) is implementing a major project on theDevelopment and Use of Natural Dyes in Textiles in

India. This two-ycar 453,000 UNDP-funded projecthas very ambitious objectives of (a) establishment ofa database of dye-yielding pl ants and traditionaldyeing methods. (b) establishment of a bank of dyeyielding plant materials from Western India, (c)compilation of a short-list of plants with appropriatedye properties and sui table growth characteristics, (d)establishment of the veracity of tradit ional dyeingmethods with regard to the dye-fast ness withtraditional dyeing methods, (e) economical product ionof high-quality indigo, f) economic cultivation of dye

plants and cotton without the use of syntheticchemicals, and (g) evaluation of the potential ofmicrobial pigments as textile dyes. The project isbeing co-ordinated by a textile histOlian, AnnShankar The main beneficiaries of this project shallbe members of rural co-operatives and rural folk dueto the equitable distribution of income by increasedrural employment and increased crop variety .

A similar project funded by CEC on Cultivationand Extraction of Natural Dyes for Industrial Use inNatural Textiles Production , completed in 1997 bythe collaborators from Jena, Germany (TLL), Wieren(L1VOS), Univers ity of Bristol, and IAC R LongAshton Research Station (GB) , has led to theconclusion that natural dyes can provide a viablealternative to sy nthe ti c dyes in an industrial context(www.nf-200.org). Thi s project studied the agronomy,biochemistry and dye production capacity of severalspec ies of dye plants. The projec t scientists wereDavid Cooke (dave.cooke@bbsrc. ac. uk) , David Hilland KelTY Stokers ([email protected]).

As a consequence of thi s initial work, a three-yearmajor projec t has been initiated through a LINKprogramme between the academic partners(U niversity of Bristol and Silsoe Research Institute)and industry by the MAFF who have contributedalmost 300,000, which has been matched by 400,000 from the private sector, viz. WilletInternational Ltd, Gortham and Bateson (Agriculture)Ltd, Express Separations Ltd and Agrifusion Ltd. Theobjectives of the work are to grow woad on anagricultural scale, using modern forming techniques,co upled to a breeding programme aimed at producinga greater yielding, stable variety of the crop. Thewoad will be harves ted using the specially designedharvesters and the indigo precursor will be extractedusing a process which will take 12 min to produce thedye against the old 12-week long process. At theinstigation of the industry involved and based on th edemands of the co nsumers for more environmentfr iendly materials, the end product will be used in themanufacture of water-based, ink-jet inks forcomputers (www.lars.bbrsc.ac.uk/plantsciJindink2.htm).A project for the cultivation and extraction of indigofrom woad is in operation in southwest of France.This project, started in 1995, is being funded byOffice National Interprofessionnel des PlantesaParfum, Aromatique et Medicinales Midi-Pyre neesRegional Council. The project is being implementedby Laboratoire de Chimie Agro-Industrielle/Centred Application et de Yraitement des Agroressources.


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\94 INDIAN J. FIBRE TEXT. RES . MARCH JUNE 2001

Other major European projects are: (a) Oro BluProject (Italy), and (b) Flax company project.

A process for better way of extracting andproducing powdered form of natural indigo has alsobeen developed by Guinean scientists working at theQuebec Centre for Textile Technology. As per thisprocess, the leaves are fermented anaerobically forfew hours, after which the liquor is filtered, decantedand dried in the sun to produce the powdered form ofthe dye (www.idrc.calaventure/eteintur.html).

There are many more examples of gainfulcollaboration between research institutes and use rindustries. For example, the DOBAG projec tmentioned above is administered by the Dean of thefaculty of Fine Arts of Marmara University, Istanbul.Similarly in India, there is the Alps IndustriesTIFAC-IIT (Delhi) project, being guided by theauthor and discussed elsewhere in thi s paper.

The agronomical research at the Department ofAgronomy of Pisa University is aimed at th efollowing issues of the production industrial chain(from raw material production to quality control) ofReseda luteola Anthemis lincloria Anlhemislinctoria Genisla tinctoria Rubia lincloria /salislinCloria and Polygonum linClorium.: (a) germplasmcollection of several dye species and evaluation oftheir agronomic potential, (b) agronomic aspects ofcultivation of madder, woad and weld, (c) seedproduction of madder, weld and woad, (d) chemicaleva luation of pigments by HPLC, and (e) dye in gproperties of natural dyes, colour measurement, andlight and wash fastness.

Resea rch work on the extraction , puri fication andcharacterization of the natural dyes by sophisticatedtechniques such as TLC, HPLC, UV-VIS and IRspectroscopy , mass spectroscopy and NMR is beingcarried out in many academic institutes a ll over theworld. There are others working on the theory ofdyeing by natural dyes and developing newer andeasier methods of application as well as developingpretreatments to improve dye uptake and aftertreatments to improve the fastness properties.Research on the analysis and radiocarbon dating ofthe historical tex tiles is of interest to museums.Laboratory for Hi storical Colorants, housed in theIn stitute of Geophysics and Planetary Physics atUCLA, set up in 1974 is engaged in the analysis ofhistoric and ethnographic colorants. It has analyzedsamples for the Museum of Internation al Folk Art, theKunsthistoricshe Museum in Vienna, the School ofAmerican Research in Santa Fe, the Natural History

Museum of Los Angeles, etc. as well as for privatecollectors and dealers. In India, Kharbade of NationalResea rch Laboratory for Conservation of CulturalProperty, Lucknow, is actively engaged in theanalysis and characterization of natural dyes inhistoric textiles.3 Estimates of Dye Requirements

The consumption of synthetic dyes has beenestimated to be close to one million tonnes per year.As per the report of the German Ministry of Food andAgriculture and Forestry, about 90 ,000 tonnes ofnatural dyes can be produced every yearS

The production of natural dyes requ ires agriculturalland. It is estimated that about 250-500 million acresof land will be req uired to produce about 100 milliontonnes of plant material needed to produce onemillion tonnes of natural dyes. Thi s land requirementcorresponds to 10-20% of the area cultivated for grainthroughout the world.

A market and technical survey on natural dyes hasbee n conducted recentll. USA is one of the majorimporters of natural dyes. The total imports of thesedyes which is about 3500 tonnes per yea r works out tobe 0.4% of the sy nthet ic dyes 7. In terms of value, theUS import market reached 41 million in 1998 whichwas an increase of 70 % from 1994 and an increase of22% from 1997. Imports of natural dyes by EUcountries were 5538 tonnes for the year 1998. Thisaccounts for 0 .55 % of the synthet ic dyes 8. The EUimports market for natural dyes reachedapproximately 63 million ECUs (US 70 million) in1998, which was an increase of 46 % from 1994 and10% from 1997. The primary importers in Europe fornatural dyes and colourants are Germany (32 %),France (17%), Italy (14%) and the UK (10 % . Besidesthis, in many countries the dyes are produced forlocal consumption which may al so be about 1000tonnes.

t is apparent from above that the presentrequirement of natural dyes is about 10,000 tonneswhich is equivalent to 1% of the world synthetic dyesconsumption.4 Availability of Natural Dyes

From the information available on the internet, it isobserved that th ere are over a dozen companiesoffering natural dyes, mostly in small packing. List ofso me of these companies is given in Table l Mostlywomen dominate this activity. Some of the prominentamon g them are Michelle Wipl in ge r, Carol Todd ,Carol Leigh and Trudy Van Stralen.


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GULRAJANI: PRESENT STATUS OFNATURAL DYES 195

Alps Industries is one major natural dye producingcompany. The company has a production capacity ofaround 300 tonnes per year. Other Indian companiesare: Satal Katha, Sam Ram, Amma Herbal, D.Manohar Lal, etc.

Water extracts of natural dyes such as weld,chlorophyll, logwood and cochineal are also beingproduced by De la Robbia (Milan) since 1992. Thedyes are sold in bulk as powders ready for use 4

Livos Pflanzenchemic Forschungs-undEntevicklung GmbH has developed natural dyes inGermany. They are also marketing kits for use in adomestic washing machine to dye cloth 4 . Apart fromthese companies there are a large number of othermanufacturers. Many of them produce only singledyes, namely indigo, lac, cochineal, catch, etc.5 Technology for Production of Natural Dyes andColourants

Technology for production could vary from simpleaqueous to complicated solvent system tosophisticated supercritical fluid extraction techniquesdepending on the product and the purity beingachieved. Purification may entail filtration or reverseosmosis or preparatory HPLC and drying of theproduct may be by spray or under vacuum or by afreeze drying technique. Analysis and characterizationis another area of fundamental research, not only toidentify new molecules of interest but also toauthenticate valuable museum pieces. One canharness the catalytic ability of enzymes to hydrolyzethe dye-cellulose bonds as is the case in theproduction of indigo, use microbes to generateanthraquinone-based colourants the way LusijferLaeea produces the lac dye or use biotechnological methods to increase the yield of colorants inplants.6 Some Important Natural Dyes

Colouring matter could be obtained from all almostall vegetable matter. However, only a few of thesesources yield colourants which can be extracted andwork out to be commercially viable. Similar is thecase of colourants obtained from animal origin.Basically, three primary colours are required to getany given hue (or colour). This type of approach hasbeen worked out for synthetic dyes. However, in thecase of natural dyes, the dyeing procedures aredifferent for different dyes and they cannot beblended to get the required colour easily. Never-theless, while looking for different colours, it is better to

have a limited number of dyes with good fastnessproperties rather than having too many colours(sources) with limited fastness properties.

While selecting the proper palette of colours, onewould like to have atleast one blue, one red and ayellow to start with. Due to the limited number ofnatural dyes available, the correct choice of the dyesis very important. Information on some importantnatural dyes is given bellow.6.1 Blue DyesThe Colour Index lists only three natural blue dyes;

namely Natural Indigo, sulphonated Natural Indigoand the flowers of the Japanese Tsuykusa usedmainly for making awobana paper.The only viable choice among the blue natural dyes

is indigo. Natural indigo is obtained by fermenting theleaves of various species of Indigofera, running offthe liquor and oxidizing it to precipitate the dye.Woad lsatis tinetoria L. is another important sourceof indigo. The plant is grown mostly in NorthernEurope and the British Isles.

Until 1887, indigo was derived exclusively fromplants. In that year more than 7,00,000 hectares ofland in Bengal was cultivated with the indigo plantlndigofera tinetoria). The annual production of pure

dye was around 8,000 tonnes worth 100 millionMarks (Rs. 240 crores, taking current value of DM =Rs. 24.00). Bengal produced 80% of the worldproduction. Other growing regions were Java andCentral America 9.

With the synthesis of indigo in 1880 and itssuccessful commercial exploitation in 1897 by BASF,the production of natural indigo decreased. The kingof natural dyes went into oblivion. There are somesigns of its revival.The current demand of indigo in the country is

estimated to be around 800 tonnes per year, priced ataround 20 million. This is equivalent to about 111the production of natural indigo in the country in1897.The main ingredients of natural indigo are indigotin(I) and indirubin (II).

{Ju


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196 INDIAN J. FIBRE TEXT. RES., MARCH-JUNE 2001

The same dyeing process is carried out with naturalindigo as that used for the synthetic indigo. However,natural indigo has higher affinity and the dyed fabricshave better fastness.

6.2 Red DyesThe Colour Index lists 32 red natural dyes. Theprominent among them are madder Rubia tinctorumL.), Manjeet Rubia cordifolia L.), Brazilwood/Sappan wood Caesalpina sappan L.), AI orMorinda Morinda citrifolia L.), Cochineal Coccuscacti L.) and Lac dye Coccus laccae). All these dyesare based on anthraquinone molecule except Braziland Sappan wood based dyes . These dyes are prone tooxidation and hence are not suitable.

The most important colourants in madder are theanthraquinones, alizarin III) , purpuroxanthin (IV),rubiadin (V), manjistin (VI), purpurin VII) andpseudopurpurin VIII) .

Madder has atleast six identifiable components, allhaving different absorption maxima (i.e. differentcolour). Hence, the colour obtained from a givenmadder dye is the composite colour of all thesecompounds. Therefore, for getting consistent shade,dye should always be reformulated after extraction,purification, etc.

Madder has been used for many centuries and thecotton textiles dyed with it around 3000 BC areknown from the Indus Civilisation . In the middleages, madder became of great importance in Europeand was grown extensively in France and Germany .Between the sixteenth and eighteenth centuries, itsproduction had become almost a Dutch monopoly andit was even exported to India for the expanding cottonindustry'o.

The strong and almost fadeless cotton dye knownas turkey red was developed in Ind ia and spread fromthere to Turkey. It involved about twenty separateprocesses using wood, oil and rancid fat, charcoal,cow/sheep/dog dung, and liquid contents of animalstomach. Only the dyers and their families notsurprisingly, occupied villages where the process wascarried out. The use of madder declined abruptlyfoIlowing the development of synthetic alizarin in1869.

Today, in India, most of the so called vegetable dyeprinted clothes of Rajasthan are printed with syntheticalizar in . Madder dye powder being produced in Indiacosts about Rs 5000/kg. Good quality madderwood/root is priced at Rs 100 - 200/kg. It has about 3-4% dye, all of which is not recoverable.

Manjeet or Indian madder is another anthraquinonebased red dye. The main colouring component ofManjeet is manjistin (VI). Other minor componentsfound in Manjeet are purpurin VII) , pseudopupurinVIII) and pupuroxanthin (IV) .

Manjeet was an important dye for the Asian cottonindustry as the use of native plant was obviouslymuch more economical than imported products. It isstill used in Nepal in areas where interest in use ofnative dyes is being promoted. The whole plant, notjust the roots, is dried and used to dye various fibresred and pinks.

Brazilin (e.1. Natural Red 24) is the main colouringcomponent of Ceasalpinia echinata Lam (Brazi lwood) and Ceasalpinia Sappan L. (Sappan wood) .Brazilin IX) gets oxidised to form the red BrasileinX).

Ill)

o OcCc CHJ' I h Oo(V)o Of

O

o(IX)

(VII)

o O

O o


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alum, copper and chromium to give crimson blackand purple shades respectively. These colours havepoor light fastness.

The most important red dyes of antiquity were allobtained from animal sources. Lac is perhaps one ofthe oldest of all known red dyes. However, cochinealand kermes were widely used in the western world forthe production of bright purple and red colours.

The lac dye is extracted from lac, the resinousprotective secretion of tiny insect, Luccifer Lacca,which is a pest on a number of plants, both wild andcultivated. The secretions of the insect contain 1-2dye.

There are four colouring compounds in lac,designated as laccaic acids A, B, C and 0 (XI, XII).Laccaic acid A is the most abundant. Laccaic acid isalso called xanthokermesic acid and it closelyresembles kermesic acid in structure.

e CH1CHI NH11 eOOH'B' CH1CH1 1i4 H1 (H 1NH QCH)

OH eH)~ O O HH O ~ O Ho(XII)

Lac dye being an acid dye can be directly dyed onprotein fibres such as wool and silk. It also producesvery dark shades on nylon. The hues can be modifiedby post-mordanting treatment with metal salts. Thedye has very good light and washing fastness.

Cochineal is another important natural red dyeproduced mostly as a food colour in Mexico and Peruwww.cochineal.c1/ingles.html).AnInternational

Congress on Cochineal and Natural Colours was heldin Oaxaca, Mexico, last year to discuss theagronomical aspects, industrialization and uses, etc.(Source: IALC Online Newsletter).6.3 Yellow Dyes

Yellow is the most common colour in the naturaldyes. However, most of the yellow colourants arefugitive. The Colour Index lists 28 yellow dyes. Someof the important yellow dyes are obtained fromBarberry Berberis aristata), Tesu flowers Buteafrondosa. monosperma) and Kamala Mallotusphilippensis).

Other sources of yellow dyes are Black oakQuercus veLutina), Turmeric Curcuma Longa), WeldReseda luteoLa) and Himalayan rhubarb Rheum

emodi).

As a dye, barberry has been mentioned since the4th century in the records of Christian monasteries.

One of the most ancient centres of its use was theMediterranean basin of North Africa and Turkeywhere this dye was used to dye carpets, tents, etc.

Wool and silk are kept, without boiling, in a dyebath composed of a decoction of the mashed plantuntil the desired intensity of colours is obtained. Itturns brownish yellow on exposure to light. The roots,barks and stems are rich in alkaloids, essentiallyberberine XIII)-the main colouring matter,accompanied by hydroxylated derivatives (XIV).

The main colouring pigment in Tessu flowersButea monosperma) is butein (XV), a calcone of

orangish red colour. The dye from the flowers isextracted by boiling with dilute hydrochloric acid.The solution is then neutralized by sodium carbonate.To make colours more lively and fast, a decoction oflodh SympLocos racemosa) or fruit of myrobolansTerminaLia chebula), both quite rich in tannins, is

added to the dye bath by traditional dyers. Coloursobtained range from orangish-yellow, ochre to browndepending on the mordant used. Colours have goodfastness to washing and fair fastness to light.

Kamala Mallotus phillipinensis) is a sm llevergreen tree belonging to the Euphorbiaceae family ,flowering in the forests of tropical Asia from India toMalaysia and Phillipines, China and Australia. Thetree bears fruits in the form of pods. The dye is anorange-red powder, which occurs as a glandularpubescence on these pods and is gathered by shakingthe ripe capsules harvested in February - March.

The colouring matter of Kamala comprises severalchalcones, such as rottlerin (XVI) and isorottlerin .The traditional method for dyeing with Kamalacomprises single bath for mordanting and dyeing. Thecolour obtained is fast to soap, alkalis and acids butshows poor fastness to light. In combination with saltsof tin, iron and copper, it gives a range of colours l2

Another yellow natural dye of great importance isweld. It is grown throughout Europe, West Asia,North Africa and United States; however, it is notgrown in India. The main colouring component ofweld is luteolin (XVII). The yellow and olivesproduced by weld are light fast. In England, it wasused with woad or indigo to produce the colourknown as Lincoln or Kendal green. Weld has beengradually superseded by black oak which, weight forweight, produces a greater strength of colour.

An important anthraquinone-based yellow dye isextracted from Himalayan rhubarb Rheum emodi). It


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198 INDIAN J. FIBRE TEXT. RES ., MARCH-JUNE 2 1

is a stout herb, grown mainly in the Himalayas fromKashmir to Sikkim. About 11,000 kg of rhizomes arecollected annually from Kullu and Kangra valley ofHimachal Pradesh. Rhizomes and roots are dug up inSeptember from 3-10 year old plants, washed, cut intosmall pieces, dried and stored in airtight containers.Roots contain a number of anthraquinone derivativesthe most prominent among them is chrysophanic acidXVIII), the main source of the natural dye.

XIII)OHO ~ O ~

=/ OH

j 0 M OHHO'CXOH , I I I OH

>-.. c CHIIo

XV)W ~ O OHO,;/ ' 0 -' I I,OH 0(XVID

XIV)

(XVI)

~ H JoXVIJI)

Wool and silk can be easily dyed in a range ofcolours with this dye. The colours obtained are yellowwithout any mordant, brown Cu), olive green Fe),red-violet Cr) and bright yellow Sn) . Colours arevery fast to light and washing.7 Tannins

Tannins are the most important ingredients in thedyeing with natural dyes producing yellow, brown,grey and black colours. They also modify the affinityof fibres towards different dyes. A back tanningprocess improves the wash fastness of some dyes.However, the treatment with tannins makes dyeingsdull.

Tannins are naturally occurring compounds of highmolecular weight about 500 - 3000) containingphenolic hydroxyl groups 1-2 per 100 Mw) to enablethem to form effective crosslinks between proteinsand other macromolecules. The term tannins wasintroduced by Seguin in 1796 to describe thesubstances present in number of vegetable extracts

which are responsible for converting puterescibleanimal skins into the stable product leather by tanningprocess.

In the dyeing of textiles, tannins form the basis ofso called natural mordant. As stated above, tannins

are phenolic compounds, and those tannins, whichhave o dihydroxy catechol) groups, can form metalchelates, giving different colour with different metals .An after-treatment with metal salts not only alters thelight sorption characteristics of tannins but also makesthem insoluble in water. Hence, they are fixed on thetextile substrate, giving good washing fastness .

Besides these reactions, it is postulated that tanninsform following three types of bonds with proteinse.g. wool and silk) and cellulose e.g. cotton and

viscose rayon):Hydrogen bonds between the phenolic hydroxylgroups of tannins and both the free amino andamido groups of protein, or the hydroxyl andcarboxyl groups of other polymers.Ionic bonds between the sui tably chargedanionic groups on tannin and cationic groups onprotein.Covalent bonds formed by the interaction of anyquinone or semiquinone groups that may bepresent in the tannins and any other suitablereactive groups in the protein or other polymer.

The stability of the tannin-fibre bond depends onthe pH, ionic strength and metal chelators.The vegetable tannins may be divided structurally

into two distinct classes depending on the type ofphenolic nuclei involved and the way they are joinedtogether.7.1 Hydrolyzable Tannins

Tannins of this class are characterized by having asa core a polyhydric alcohol, such as glucose, thehydroxy l groups of which are esterified eitherpartially or wholly by gallic acid or its congeners.Tannins having this structure can be readilyhydrolyzed by acids, bases or enzymes to yield thecarbohydrate and a number of isolable crystallinephenolic acids. Thus, they are called hydrolyzabletannins.

The other acid isolated from hydrolyzable tanninsis ellagic acid. Therefore, sometimes the hydrolyzabletannins of vegetable origin are divided into twogroups, namely gallotannins and ellagitannins. Someof the important raw materials for these tannins are:Myrobolan fruit Terminalia chebula), Oak bark and


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200 INDIAN J. FIBRE TEXT. RES., MARCH-JUNE 2001common natural dyes is given in Table 2. It isapparent from the table that some of the dyes can beplaced in more than one dye class.

The procedures of application of these dyes aresimilar to those followed in the case of synthetic dyes.For example, the natural indigo is dyed by the sameprocedure as the synthetic indigo. Both are vat dyes.

Madder, being a mordant dye for cotton, requirescreation of dye-sites in the fibre before the dyeing iscarried out. Conventionally, this was being done byfirst applying a water-soluble aluminium salt such asalum and then converting it into an insoluble salt bytreating it with calcium hydroxide. The aluminiumcalcium salts precipitated into the fibre acted as sitesfor the madder dye. This formed the basis of thefamous Turkey Red colour.

The process at some stage got modified wherein thematerial was first treated with tannin-containing plantmaterial which provided sites for aluminium to formcomplex as described above. Thus, the tannin-alumtreated cotton became the base material for the dyeingof madder and other such dyes.

Since wool, silk and nylon have cationic groups inthe form of protonated amino groups, these fibres canbe dyed with natural acid dyes such as lac underacidic pH in the same manner as synthetic acid dyes.Lac can be post-mordanted to give dye-metalcomplexes. Hence, it is not only an acid dye but also amordant dye like chrome-mordant dyes among thesynthetic dyes).The chemical structures of many natural dyes aresimilar to those of synthetic disperse dyes in the sensethat they do not have solubilizing groups and are onlysparingly soluble in water. Hence, they can be dyedon hydrophobic fibres such as polyester and nylon.Table 2 Classification of natural dyes on the basis of application

propertiesBotanical Common name Dye classname/sourceIndigofera tinctoria Indigo VatRubia tinctorum Madder MordantlDisperseRubia cardifolia Manjeet AcidlMordantlDisperseCeasalpinia sappan Sappanwood MordantlDisperse

ccifer lacca Lac dye Acid/MordantBerberis aritata Berberine BasicButea frondosa Tesu MordantlDispersemonospermaMallotus philippensis Kamala MordantlDisperseRheum emodi Dolu MordantlDisperseQuercus infectoria Gall nuts Acid/MordantAcacia catechu Cutch Acid/Mordantl

Disperse

Furthermore, these dyes can be directly dyed on wooland silk since these dyes also have some limitedaffinity for these fibres. However, these dyes can befixed onto the fibres by post-mordanting treatmentwith metal salts.

For getting the compound shade wherein more thanone dye is required to be used, the same principle asadopted for synthetic dyes works. That is thenatural dyes, which can be dyed under identicalcondition, can be mixed and dyed together. However,a post-rnordanting treatment may not work outsuccessfully unless mastered carefully .

By scientifically understanding and analyzing thechemical structure of the natural dyes a suitablemethod could be worked out for the application ofthese dyes on different substrates. A challenge anenlightened dyer has to face if he or she is planning toventure in this field.10 Fastness of Natural Dyed Materials

Natural dyes are considered fugitive even thoughone finds many fabrics dyed with natural dyes inmuseums, wherein the cloth has retained its originalcolours throughout the centuries of exposure.

Poor light fastness of some of the natural dyes canbe attributed to the inherent propensity of the dyechromophore to photochemical oxidation. Thechromophore in some cases can be protected fromphotochemical oxidation by forming a complex withtransition metal, whereby a six membered ring isformed. The photons sorbed by the chromophoricgroups dissipate their energy by resonating within thering and hence the dye is protected.

It is apparent from above that a post-treatment witha metal salt can result in an improvement in the lightfastness of some natural dyes. However, a posttreatment with metal salt also resul ts in change of thehue. Therefore, the post-treatment should be chosencarefully. This type of post-treatment with copper orchromium or combination of their salts is given tosome synthetic dyes to improve their wash and lightfastness .The poor wash fastness of many natural dyes ismainly attributable to following factors: Weak dye-fibre bond between the natural dye and

the fibre . Change in hue due to the breaking of the dye

metal complex during washing. Ionization of the natural dyes during alkaline

washing. Since most of the natural dyes havehydroxyl groups which get ionized under alkaline


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conditions, many fabrics dyed with natural dyesunder acidic conditions change colour on washingwith alkaline detergents or soap.

The wash fastness of some of the natural dyescould be improved by a post-treatment with alum or adye-fixing agent, which results in the formation a dyefibre complex or a crosslink between the dye and fibrerespectively.

Tannins, being large molecular compounds, do notdiffuse into the fibre easily. Hence, dyeings based ontannins show poor rub fastness on cotton. One can dovery little about it except limiting the quantity of thetannin used.

To have a palette of colour with good fastnessproperties, one has to experiment and fill theknowledge gap.11 Imperatives to the Use of Natural Dyes One of the major imperatives to the use of naturaldyes is the knowledge gap. Very few serious

attempts have been made to generate newinformation on the use of natural dyes. Most ofthe research in this area is carried away by theempirical information reported in literature thatdoes not have any scientific reasoning or basis.

Non-availability of the natural dyes in thestandardized form, which may be powder, pasteof solution. Using the raw material for dyeing hasmany limitations. Besides its being of unknowncomposition, it generates considerable amount ofbiomass that is cumbersome to handle n thedyehouse.

Severe shortage of trained dyers. Most of thetextile chemists in the country are trained to usesynthetic dyes. Even the teachers have very poorappreciation for this centuries-old technology ofdyeing. f this technology is to be used forgenerating revenue, employment and for creating

a strong base for renewable resources for the dyeindustry, a comprehensive training programmehas to be launched, may be by making it a part ofthe syllabus.

Dearth of books on the technology of dyeing withnatural dyes providing the scientific basis to thesubject. Adverse publicity being given to natural dyes,spearheaded by the synthetic dye manufacturingcompanies. Some of the points beingoveremphasized are discussed above. It must bekept in mind that natural dyes are not substitutesof synthetic dyes. They have their own marketand any expansion in this market is not going tobe at the cost of synthetic dyes. Some of thelimitations of natural dyes, such as use of bannedmetal salts, poor fastness properties and use ofagricultural land for growing natural dye-plants,being highlighted can be easily overcome byR&D.

ReferencesI Sewekow Ulrich, Milliand 4(1988) E-145.2 Glower Brian, 1 Soc Dyers Colour 114(1998) 4.3 Hill D J, Rev Prog Color 27(1997) 18 .4 Svenson Ann E WAAC Newsletter 8(1) (1986) 2.5 Anon, Eur Chern 26 March 1998, 10 .6 Raise, http://www.raise.org/natural/pubs/dyes/dyes.s tm7 U.S. Domestic Imports, http://www.ita.doc.gov/industry/

otealtrade-DetaiI8 India Hortibusiness On-Line, http://www.agroindia.org/

HOL9 Frey F, Melliand Int (2) (1997) 88.lO Dye Plants and Dyeing by John and Margaret Cannon (The

Herbert Press, UK), 1994, 76.Dye Plants and Dyeing by John and Margaret Cannon (TheHerbert Press, UK), 1994, 38.

12 Gulrajani M L, Deepti Gupta, Varsha Agarwal ManojJain, Indian Text 1 102(5) (1992) 78.13 Natural Dyes and Their Application to Textiles edited by M

L Gulrajani and Deepti Gupta, liT Delhi), 1992.

Present Status of Natural Dyes

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