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Present Status of Natural Dyes

Present Status of Natural Dyes

Indian Journal of Fibre & Research Vol. 26, March-June 2001 , pp. 191-201

Present status of natural

M L Gulrajani" Department of Textile Technology, Indian Institute of Technology, 11001 6,

The present status of natural dyes with reference to the stake holders of natural dyes, estimates of requiremcnts, availability of natural dyes. technology for production, and some important natural dyes and is critically discusscd. Application techniques and fastness properties of natural dyes arc also brieOy discussed. It is suggested that the natural dyes are not substitutes of synthetic dyes. Some of the limitations of natural dyes such as use of banned metal salts as mordants, poor fastness properties and use of agricultural land for growing can be overcome through research and development.

Keywords: Environment protection, Mordants, Natural dyes

1 Introduction • Water pollution by heavy metals and large Natural dyes find use in the colouration of , amounts of organic substances. food, drugs and cosmetics. Small quantities of dyes are also used in colouration of paper, leather, shoe The following properties are often considered to be polish, , cane, candles, etc. In the beginning, the advantages of natural dyes 2: there were dyes derived only from natural sources. Some processing was required but essentially the dye • They are obtained from renewable resources. itself was obtained from a , mineral or animal. • No health hazards, sometimes they act as health After the accidental synthesis of by William cure. Henry Perkin in 1856 and its subsequent • Practically no or mild chemical reactions are commercialization, heralding the advent of involved in there preparation dyes (now synthetic dyes), the use of natural dyes • No disposal problems. receded. • They are unsophisticated and harmonized with The limitations of the natural dyes that were nature. responsible for their decline are: • Lot of creativity is required to use these dyes judiciously. • Availability, 3 • Colour yield, According to Hi1l , the research effort devoted to • Complexity of process, and natural dyes is negligible. If there had been significant • Reproducibility of shade. research on the use of natural dyes, it is probable that they would have already been much more widely used Besides these, there are the following perceived than they currently are. As there is much catching up technical drawbacks of natural dyes I.2: to do after 150 years of neglect, there is plenty of scope for rapid developments. This applies to the • Limited number of suitable dyes. techniques of agricultural production, processing and • Allow only , natural , and to dyeing. be dyed. • Great difficulty in blending dyes. 2 Stake Holders of Natural Dyes • Non-standardized. The use of natural dyes has increased substantially • Inadequate degree of fixation. during the last couple of years. These dyes are being • Inadequate fastness properties. mainly used by:

• Phone: 6591404; Fax: 0091-11 -6514033; • Hobby groups, E-mail: ml [email protected] • Designers, 192 INDIAN J. FIBRE TEXT. RES ., MARCH-JUNE 200 1

• Traditional dyers and printers, pleasing colour combinations. She has also been • Non-government organizations (NGO's), conducting workshops in natural dyeing and tryin g to • Museums, rebuild the skills long lost (www.icr.com.au). While • Academic institutes and research Himani Kapila is actively trying to promote the use of associations/laboratories, and dye in Bihar, designing with has been the • Industry. main activity of Padmini Balaram. There are many more such creative designers in India and abroad. The use of natural dyes, particularly by women as a National Institute of Design is creating a data on hobby, has continued in spite of the advent of natural dyes and products. synthetic dyes. Of late, this activity has increased Kim Ji-hee of Catholic Universi ty in Taegu, apart considerably, particularly in US where many guilds from conducting research on traditional dyes, is also have been formed to discuss about these dyes and an accomplished textile artist. She uses traditional organize workshops and training programmes on a Korean dyes and textile production methods to regul ar basis. A quarterly journal 'Turkey Red Journal' produce contemporary artworks. In many of her covers information about the workshops and the works, she imitates the pojagi or traditional Korean activities of various hobby groups. The easy wrapping cloth by pi ecing together natural dyed fabric accessibility of internet has also given fillip to this using a traditional Korean stitching method. She then activity, where the various individuals exchange notes forms a collage by assembling these fabrics with almost on daily basis. One such popular site is handmade Korean mulberry paper, gold foil , stitchery '[email protected]' where one can get very and traditional folding techniques. useful tips from the most profound user Carolyn Lee The industry in many countries has and, of course, many other persons. Some schools evolved around local talent in th e art and of have also introduced Natural Dyes as a co-curricular dyeing with natural dyes and weaves them to activity. Many companies have come out with hobby produce speciality fabrics. Printing of natural dyes by kits for beginners. In India, Alps Industries have come direct, resist or dyed style is the speciality of printers out with a large range of 'do-it-yourself kits (Table I). of Rajasthan while with natural dyes is Designers have very effecti vely utilized natural practised in Shi Kalahasti , dyes as a design tool. The non-reproducibility and (www.icr.com.au). non-uniformity of shades make each creation a unique Fine Turkish recognized for their va lue and pi ece. Various kinds of design production methods, beauty are made with natural dyes obtai ned from such as tie-and-dye or stitching (), resist plants, and trees (www.about-turkey.com). printing, stencilling, , Indian Ajrakh, Kalamkari, Perhaps, one of th e most successful natural dyes Ikal, etc. are being practised by the designers to create project is the DOBAG (Dogal Boya Arastirma ve unique products. Weavers Studio, Calcutta Gelistirme Projesi) of (Turkey). The (www.weaversstudio.com) is one unique set-up where DOBAG project got underway in the autumn of 1981 Darshan Shah has very effectively combined many in the di strict of Ayvacik. There are now two techniques to create visually attractive products. DOBAG co-operatives - one in the Ayvacik region Jagada Rajapa is a weaver-designer who has been with 220 families as members and other in the working with weavers in remote villages and helping Yuntdag region with 130 members. Serife Atlihan them to look at their traditional designs and select from Marmara University, Istanbul, lives mai nl y in Table I- US companies selling natural dyes through internct the DOBAG village and helps the weavers and does Jane's Works, hllp:llgrecnc.xtn .nelf- fibre/dyes. html quality control on each (www.dobag.com.au). Thc Mannings Catalog, hllp:llthe-mannings.colll In India, we have ARANY A, a natural dyes project Carol Leigh's Hillcreek Fiber Studio, hllp:llwww.hillcreek.com supported by Tata Tea and located in Pristine hills of Louet Sales, hllp:llwww.cybertap.colll Mawia Handprints, hllp:llwww.lllai wa.com Munnar in Kerala. It gives employment to th e La Lana , hllp:llwww.taaosfiber.com physicall y handicapped and fam ily members of the Misty Mountain Farm, hllp:llwww.mistymountainfarm.com employees of Tata Tea. The Spinnery, hllp:llwww.thespinnery.com Another interesting project is the Akha Jim (Asian Alps Industries, hllp://www.alpind.colll Tribal ). Under thi s project, Akha tribes of Alexandria Textiles, hllp:llwww.alextex.com Northern Thailand produce bedspreads, wall hangings Eanh Guild, hllp:llwww.eanhguild.colll and tri bal jackets from hand-spun and hand-wovcn GULRAJANI: PRESENT STATUS OF NATURAL DYES 193 cotton dyed with natural dyes. The production is plants and cotton without the use of synthetic supervi sed by American Jim Godman chemicals, and (g) evaluation of the potential of (www.bangkokneLcom/Goodman.html). Thailand is microbial as textile dyes. The project is also the home of Mat Mi , made form natural dye­ being co-ordinated by a textile histOlian, Ann dyed . Shankar. The main beneficiaries of this project shall The Mexican Indians, also known as Zapotec be members of rural co-operatives and rural folk due Indians, living in the Central Valley of the state of to the equitable distribution of income by increased Oaxaca have evolved their wool- art, rural employment and increased crop variety. adapting and absorbing the ideas from other cultures A similar project funded by CEC on ' Cultivation through hi story. The Zapotecs use sheep's wool and and Extraction of Natural Dyes for Industrial Use in natural dyes derived from the plants and insects of Natural Textiles Production', completed in 1997 by this rich region. Designs are varied. Some are the collaborators from Jena, (TLL), Wieren traditional Zapotec designs while others are adopted (L1VOS), University of Bristol, and IACR Long from the Mayan and Aztec art (www.Southwest Ashton Research Station (GB), has led to the furn ishings.com). Natural dyes are also exclu sively conclusion that natural dyes can provide a viable used for dyeing Porcupine quills by native Americans. altern ative to syntheti c dyes in an industrial context Ann Svenson has described the art of production of (www.nf-200.org). This project studied the agronomy, 4 Kuba textiles . The Kuba people of Zaire, formerly the biochemistry and dye production capacity of several Belgian Congo, li ve in the fertile land s of equatorial species of dye plants. The project scientists were Africa between Kansai and Sankuru Rivers. Kuba David Cooke (dave.cooke@bbsrc. ac.uk), David Hill cloth is woven from the fibres of the Raphia Vinifera and KelTY Stokers ([email protected]). Palm. Production of these textiles is a multiple - stage As a consequence of this initial work, a three-year process that involves the participation of children, major project has been initiated through a LINK men and women of the same clan. The process programme between the academic partners includes gathering and preparing the raffia fibres for (U niversity of Bristol and Silsoe Research Institute) weaving and , weaving the basic cloth and industry by the MAFF who have contributed unit, dyeing the embroidery fibres, and embellishing almost £ 300,000, which has been matched by £ the woven cloth with embroidery, applique and 400,000 from the private sector, viz. Willet patchwork. International Ltd, Gortham and Bateson (Agriculture) The township of Momostenango in Guatemala is Ltd, Express Separations Ltd and Agrifusion Ltd. The known for its natural dye rugs. The rugs are produced objectives of the work are to grow woad on an fro m both cotton and wool. Solola is the only town in agricultural scale, using modern forming techniques, Guatemala where women wear natural dyed qui lip coupled to a breeding programme aimed at producing (woman's shirt). Of course, Mayan women wear traje, a greater yielding, stable variety of the crop. The a natural Mayan clothing. woad will be harvested using the specially designed Non-government organizations (NGOs) are also harvesters and the indigo precursor will be extracted extensively engaged in promoting natural dyes in using a process which will take 12 min to produce the rural areas. Presently, Punjab Durrie Weavers (an dye against the old 12-week long process. At the NGO) is implementing a major project on the instigation of the industry involved and based on the ' Development and Use of Natural Dyes in Textiles' in demands of the consumers for more environment­ India. This two-ycar $453,000 UNDP-funded project friendly materials, the end product will be used in the has very ambitious objectives of (a) establishment of manufacture of water-based, ink-jet inks for a database of dye-yielding pl ants and traditional computers (www.lars.bbrsc.ac.uk/plantsciJindink2.htm). dyeing methods. (b) establishment of a bank of dye­ A project for the cultivation and extraction of indigo yielding plant materials from Western India, (c) from woad is in operation in southwest of France. compilation of a short-list of plants with appropriate This project, started in 1995, is being funded by dye properties and suitable growth characteristics, (d) Office National Interprofessionnel des Plantes establishment of the veracity of traditional dyeing aParfum, Aromatique et Medicinales Midi-Pyrenees methods with regard to the dye-fastness with Regional Council. The project is being implemented traditional dyeing methods, (e) economical production by Laboratoire de Chimie Agro-Industrielle/Centre of high-quality indigo, (f) economic cultivation of dye d'Application et de Yraitement des Agroressources. \94 INDIAN J. FIBRE TEXT. RES ., MARCH-JUNE 2001

Other major European projects are: (a) Oro Blu Museum of Los Angeles, etc. as well as for private Project (), and (b) Flax company project. collectors and dealers. In India, Kharbade of National A process for better way of extracting and Research Laboratory for Conservation of Cultural producing powdered form of natural indigo has also Property, Lucknow, is actively engaged in the been developed by Guinean scientists working at the analysis and characterization of natural dyes in Quebec Centre for Textile Technology. As per this historic textiles. process, the are fermented anaerobically for few hours, after which the liquor is filtered, decanted 3 Estimates of Dye Requirements and dried in the sun to produce the powdered form of The consumption of synthetic dyes has been the dye (www.idrc.calaventure/eteintur.html). estimated to be close to one million tonnes per year. As per the report of the German Ministry of Food and There are many more examples of gainful Agriculture and Forestry, about 90,000 tonnes of collaboration between research in stitutes and user natural dyes can be produced every yearS industries. For example, the DOBAG project The production of natural dyes requires agricultural mentioned above is administered by the Dean of the land. It is estimated that about 250-500 million acres faculty of Fine Arts of Marmara University, Istanbul. of land will be required to produce about 100 million Similarly in India, there is the Alps Industries­ tonnes of plant material needed to produce one TIFAC-IIT (Delhi) project, being guided by the million tonnes of natural dyes. This land requirement author and discussed elsewhere in thi s paper. corresponds to 10-20% of the area cultivated for grain The agronomical research at the Department of throughout the world. Agronomy of Pisa University is aimed at th e A market and technical survey on natural dyes has following issues of the production industrial chain been conducted recentll. USA is one of the major (from raw material production to quality control) of importers of natural dyes. The total imports of these luteola, Anthemis lin cloria, Anlhemis dyes which is about 3500 tonnes per year works out to linctoria, Genisla tinctoria, lincloria, /salis be 0.4% of the synthetic dyes 7. In terms of value, the linCloria and Polygonum linClorium.: (a) germplasm US import market reached $41 million in 1998 which collection of several dye species and evaluation of was an increase of 70% from 1994 and an increase of their agronomic potential, (b) agronomic aspects of 22% from 1997. Imports of natural dyes by EU cultivation of madder, woad and weld, (c) seed countries were 5538 tonnes for the year 1998. This production of madder, weld and woad, (d) chemical accounts for 0.55 % of the synthetic dyes 8. The EU evaluation of pigments by HPLC, and (e) dyein g imports market for natural dyes reached properties of natural dyes, colour measurement, and approximately 63 million ECUs (US$70 million) in light and wash fastness. 1998, which was an increase of 46% from 1994 and Research work on the extraction, puri fication and 10% from 1997. The primary importers in for characterization of the natural dyes by sophisticated natural dyes and colourants are Germany (32%), techniques such as TLC, HPLC, UV-VIS and IR France (17%), Italy (14%) and the UK (10%). Besides spectroscopy, mass spectroscopy and NMR is being this, in many countries the dyes are produced for carried out in many academic in stitutes all over the local consumption which may al so be about 1000 world. There are others working on the theory of tonnes. dyeing by natural dyes and developing newer and Tt is apparent from above that the present easier methods of application as well as developing requirement of natural dyes is about 10,000 tonnes pretreatments to improve dye uptake and after­ which is equivalent to 1 % of the world synthetic dyes treatments to improve the fastness properties. consumption. Research on the analysis and radiocarbon dating of the historical textiles is of interest to museums. 4 A vailability of Natural Dyes Laboratory for Hi storical Colorants, housed in the From the information available on the internet, it is In stitute of Geophysics and Planetary Physics at observed that there are over a dozen companies UCLA, set up in 1974 is engaged in the analysis of offering natural dyes, mostly in small packing. List of historic and ethnographic colorants. It has analyzed some of these companies is given in Table l. Mostly samples for the Museum of International Folk Art, the women dominate this activity. Some of the prominent Kunsthistoricshe Museum in Vienna, the School of among them are Michelle Wiplin ger, Carol Todd, American Research in Santa Fe, the Natural History Carol Leigh and Trudy Van Stralen. GULRAJANI: PRESENT STATUS OF NATURAL DYES 195

Alps Industries is one major natural dye producing have a limited number of dyes with good fastness company. The company has a production capacity of properties rather than having too many colours around 300 tonnes per year. Other Indian companies (sources) with limited fastness properties. are: Satal Katha, Sam & Ram, Amma Herbal, D. While selecting the proper palette of colours, one Manohar Lal, etc. would like to have atleast one , one red and a Water extracts of natural dyes such as weld, yellow to start with. Due to the limited number of chlorophyll, logwood and are also being natural dyes available, the correct choice of the dyes produced by De la Robbia (Milan) since 1992. The is very important. Information on some important dyes are sold in bulk as powders ready for use 4. natural dyes is given bellow. Livos Pflanzenchemic Forschungs-und Entevicklung GmbH has developed natural dyes in 6.1 Blue Dyes Germany. They are also marketing kits for use in a The Colour Index lists only three natural blue dyes; domestic washing machine to dye cloth 4. Apart from namely Natural Indigo, sulphonated Natural Indigo these companies there are a large number of other and the flowers of the Japanese 'Tsuykusa' used manufacturers. Many of them produce only single mainly for making awobana paper. dyes, namely indigo, lac, cochineal, catch, etc. The only viable choice among the blue natural dyes is indigo. Natural indigo is obtained by fermenting the 5 Technology for Production of Natural Dyes and leaves of various species of , running off Colourants the liquor and oxidizing it to precipitate the dye. Technology for production could vary from simple Woad (lsatis tinetoria L.) is another important source aqueous to complicated solvent system to of indigo. The plant is grown mostly in Northern sophisticated supercritical fluid extraction techniques Europe and the British Isles. depending on the product and the purity being Until 1887, indigo was derived exclusively from achieved. Purification may entail filtration or reverse plants. In that year more than 7,00,000 hectares of osmosis or preparatory HPLC and drying of the land in Bengal was cultivated with the indigo plant product may be by spray or under vacuum or by a (lndigofera tinetoria). The annual production of pure freeze drying technique. Analysis and characterization dye was around 8,000 tonnes worth 100 million is another area of fundamental research, not only to Marks (Rs. 240 crores, taking current value of DM = identify new molecules of interest but also to Rs. 24.00). Bengal produced 80% of the world authenticate valuable museum pieces. One can production. Other growing regions were Java and harness the catalytic ability of enzymes to hydrolyze 9. the dye- bonds as is the case in the With the synthesis of indigo in 1880 and its production of indigo, use microbes to generate successful commercial exploitation in 1897 by BASF, anthraquinone-based colourants the way Lusijfer the production of natural indigo decreased. The king Laeea produces the lac dye or use biotechno­ of natural dyes went into oblivion. There are some logical methods to increase the yield of colorants in signs of its revival. plants. The current demand of indigo in the country is 6 Some Important Natural Dyes estimated to be around 800 tonnes per year, priced at around $ 20 million. This is equivalent to about 1110 Colouring matter could be obtained from all almost the production of natural indigo in the country in all vegetable matter. However, only a few of these 1897. sources yield colourants which can be extracted and work out to be commercially viable. Similar is the The main ingredients of natural indigo are indigotin case of colourants obtained from animal origin. (I) and indirubin (II). Basically, three primary colours are required to get any given hue (or colour). This type of approach has been worked out for synthetic dyes. However, in the case of natural dyes, the dyeing procedures are different for different dyes and they cannot be blended to get the required colour easily. Never-the­ {Ju less, while looking for different colours, it is better to 196 INDIAN J. FIBRE TEXT. RES ., MARCH-JUNE 2001

The same dyeing process is carried out with natural Manjeet or Indian madder is another anthraquinone indigo as that used for the synthetic indigo. However, based red dye. The main colouring component of natural indigo has higher affinity and the dyed fabrics Manjeet is manjistin (VI). Other minor components have better fastness. found in Manjeet are purpurin (VII), pseudopupurin (VIII) and pupuroxanthin (IV). 6.2 Red Dyes Manjeet was an important dye for the Asian cotton The Colour Index lists 32 red natural dyes. The industry as the use of native plant was obviously prominent among them are madder (Rubia tinctorum much more economical than imported products. It is L.), Manjeet ( L.), Brazil still used in Nepal in areas where interest in use of wood/Sappan wood (Caesalpina sappan L.), AI or native dyes is being promoted. The whole plant, not Morinda (Morinda citrifolia L.), Cochineal (Coccus just the , is dried and used to dye various fibres cacti L.) and Lac dye (Coccus laccae). All these dyes red and pinks. are based on anthraquinone molecule except Brazil (e.1. Natural Red 24) is the main colouring and Sappan wood based dyes. These dyes are prone to component of Ceasalpinia echinata Lam (Brazil oxidation and hence are not suitable. wood) and Ceasalpinia Sappan L. (Sappan wood). The most important colourants in madder are the Brazilin (IX) gets oxidised to form the red Brasilein anthraquinones, (III), purpuroxanthin (IV), (X). rubiadin (V), manjistin (VI), purpurin (VII) and o OH pseudopurpurin (VIII). Madder has atleast six identifiable components, all ~ ~OH having different absorption maxima (i.e. different o colour). Hence, the colour obtained from a given (Ill) madder dye is the composite colour of all these

'e' CH1CHI NH11 eO OH lodh (SympLocos racemosa) or of myrobolans 'B' CH1CH101i (TerminaLia chebula), both quite rich in , is '4' (H1 (H1 NH(QCH) added to the dye bath by traditional dyers. Colours OH ° eH) obtained range from orangish-yellow, to brown ~COOH depending on the used. Colours have good HO~OH o fastness to washing and fair fastness to light. Kamala (Mallotus phillipinensis) is a small (XII) evergreen tree belonging to the Euphorbiaceae family, Lac dye being an can be directly dyed on flowering in the forests of tropical Asia from India to protein fibres such as wool and silk. It also produces Malaysia and Phillipines, China and Australia. The very dark shades on . The hues can be modified tree bears in the form of pods. The dye is an by post-mordanting treatment with metal salts. The orange-red powder, which occurs as a glandular dye has very good light and washing fastness. pubescence on these pods and is gathered by shaking Cochineal is another important natural red dye the ripe capsules harvested in February - March. produced mostly as a food colour in and Peru The colouring matter of Kamala comprises several (www.cochineal.c1/ingles.html).AnInternational chalcones, such as rottlerin (XVI) and isorottlerin. Congress on Cochineal and Natural Colours was held The traditional method for dyeing with Kamala in Oaxaca, Mexico, last year to discuss the comprises single bath for mordanting and dyeing. The agronomical aspects, industrialization and uses, etc. colour obtained is fast to soap, alkalis and acids but shows poor fastness to light. In combination with salts (Source: IALC Online Newsletter). l2 of tin, iron and copper, it gives a range of colours • 6.3 Yellow Dyes Another yellow natural dye of great importance is Yellow is the most common colour in the natural weld. It is grown throughout Europe, West Asia, dyes. However, most of the yellow colourants are North Africa and ; however, it is not fugitive. The Colour Index lists 28 yellow dyes. Some grown in India. The main colouring component of of the important yellow dyes are obtained from weld is luteolin (XVII). The yellow and olives Barberry (Berberis aristata), Tesu flowers (Butea produced by weld are light fast. In England, it was frondosa. monosperma) and Kamala (Mallotus used with woad or indigo to produce the colour philippensis). known as Lincoln or Kendal green. Weld has been Other sources of yellow dyes are Black gradually superseded by black oak which, weight for (), (Curcuma Longa), Weld weight, produces a greater strength of colour. () and Himalayan rhubarb (Rheum An important anthraquinone-based yellow dye is emodi). extracted from Himalayan rhubarb (Rheum emodi). It 198 INDIAN J. FIBRE TEXT. RES ., MARCH-JUNE 2001 is a stout herb, grown mainly in the from which are responsible for converting puterescible Kashmir to Sikkim. About 11,000 kg of rhizomes are animal skins into the stable product leather by collected annually from Kullu and Kangra valley of process. Himachal Pradesh. Rhizomes and roots are dug up in In the dyeing of textiles, tannins form the basis of September from 3-10 year old plants, washed, cut into 'so called' natural mordant. As stated above, tannins small pieces, dried and stored in airtight containers. are phenolic compounds, and those tannins, which Roots contain a number of anthraquinone derivatives have o-dihydroxy (catechol) groups, can form metal the most prominent among them is chrysophanic acid chelates, giving different colour with different metals. (XVIII), the main source of the natural dye. An after-treatment with metal salts not only alters the light sorption characteristics of tannins but also makes them insoluble in water. Hence, they are fixed on the textile substrate, giving good washing fastness. Besides these reactions, it is postulated that tannins form following three types of bonds with proteins (XIII) (XIV) (e.g. wool and silk) and cellulose (e.g. cotton and viscose ): OH HO~O~ ~ "=/ OH Hydrogen bonds between the phenolic hydroxyl groups of tannins and both the free amino and OH amido groups of protein, or the hydroxyl and j 0 M HO'CX' OH , I """ carboxyl groups of other polymers. I I OH CH '>-.. c.... Ionic bonds between the suitably charged IIo anionic groups on and cationic groups on (XV) (XVI) protein. Covalent bonds formed by the interaction of any ~OHOH quinone or semiquinone groups that may be HO,;/'" 0 - present in the tannins and any other suitable "'" I I reactive groups in the protein or other polymer. , ~CHJ~ WOH 0 o The stability of the tannin-fibre bond depends on (XVID (XVIJI) the pH, ionic strength and metal chelators. Wool and silk can be easily dyed in a range of The vegetable tannins may be divided structurally colours with this dye. The colours obtained are yellow into two distinct classes depending on the type of without any mordant, brown (Cu), olive green (Fe), phenolic nuclei involved and the way they are joined red-violet (Cr) and bright yellow (Sn). Colours are together. very fast to light and washing. 7.1 Hydrolyzable Tannins 7 Tannins Tannins of this class are characterized by having as Tannins are the most important ingredients in the a core a polyhydric alcohol, such as glucose, the dyeing with natural dyes producing yellow, brown, hydroxyl groups of which are esterified either grey and black colours. They also modify the affinity partially or wholly by gallic acid or its congeners. of fibres towards different dyes. A back tanning Tannins having this structure can be readily process improves the wash fastness of some dyes. hydrolyzed by acids, bases or enzymes to yield the However, the treatment with tannins makes dyeings carbohydrate and a number of isolable crystalline dull. phenolic acids. Thus, they are called hydrolyzable Tannins are naturally occurring compounds of high tannins. molecular weight (about 500 - 3000) containing The other acid isolated from hydrolyzable tannins phenolic hydroxyl groups (1-2 per 100 Mw) to enable is ellagic acid. Therefore, sometimes the hydrolyzable them to form effective crosslinks between proteins tannins of vegetable origin are divided into two and other macromolecules. The term tannins was groups, namely gallotannins and ellagitannins. Some introduced by Seguin in 1796 to describe the of the important raw materials for these tannins are: substances present in number of vegetable extracts Myrobolan fruit (Terminalia chebula), Oak and GULRAJANI: PRESENT STATUS OF NATURAL DYES 199 wood (Quercus alibi and other species), leaves hydoxy or carboxy groups sorbs these ions, either by (Rheas typhoon), nuts (Quercus iniactoria) and forming a metal-complex or metal salt. These metal rind (Punica granatum). ions then provide sites for the mordant dyes. Hence, introducing metal ions in the fibre, either directly or 7.2 Condensed Tannins as tannin-metal complexes, can increase the affinity Tannins of this class contain only phenolic nuclei. On of cotton towards mordant dyes. treatment with hydrolytic reagents, the tannins of this It is apparent from above that the tannins by class tend to polymerize, particularly in acid solution to themselves do not act as mordants but tannin-metal yield insoluble amorphous often red coloured products salt combination can only act as a mordant for the known as phlobaphenes. Most tannins of this type are natural mordant dyes. formed by the condensation of two or more molecules of Alternatively, if one applies water-soluble salt such flavan-3-0Is, such as catechin. as alum to the cotton substrate and then insolublizes Catechin was first isolated 140 years ago by Runge this, say by treatment with alkali such as calcium from the tannins of Acacia . Acacia catechu is carbonate or sodium carbonate, then an insoluble salt a deciduous tree of up to 25 m in height and is native of aluminium is deposited in the material. The to India, Burma and Sri Lanka. The colouring insoluble salt of aluminium provides the metal­ component obtained from this tree is popularly known chelating sites for the natural mordant dye. This kind as 'Cutch', which produces copper red colours on of mordant treatment can form the basis to get bright cotton, wool and silk of very good wash and light shades of natural metal-complexing dyes. Allegro is fastness. perhaps the only natural dye manufacturing company 8 Mordants that is marketing pre-dried aluminium hydroxide gels Mordants are considered as an integral part of the for use as mordant. natural dyes or, to be more precise, the natural dyeing Since some of the natural dyes can form metal­ process by the most dyers of natural dyes. This is an complexes and thereby give different colours, there is anomaly, which continues to be perpetuated by a tendency to use all types of metal salt for this different authors and practitioners of natural dyeing. purpose. The restrictions to the use of metal salts have A close look at the chemical structures of natural been put by the famous 'German Ban'. Accordingly, dyes will show that these dyes, like synthetic dyes, the indicative maximum permissible quantities of also consist of vat dyes, acid dyes, basic dyes, different metals in the ultimate product are as follows: disperse dyes, direct dyes and mordant dyes (i .e. dyes As (1.0 ppm), Pb (1 .0 ppm), Cd (2.0 ppm), Cr (2.0 capable of forming a complex with metals). Many ppm), Co (4.0 ppm), Cu (50 ppm), Ni (4.0 ppm), and dyes can fall under more than one class of dyes. For Zn (20 ppm). instance, in the case of mordant dyes, there are dyes The upper limits of the presence of metals vary which have affinity for the fibre; however, their from product to product and are different for different uptake as well as hue can be modified by pre­ Eco-Marks. However, there is no upper limit on treatment or post-treatment with so called mordants. aluminium, iron and tin. The upper limit on copper is Hence, they can be placed in more than one also fairly high. Hence, the salts of these metals could class/category of dyes. be safely used for complexing and mordanting. Tannins such as harda, tannic acid, etc. are However, their quantities should be optimized so as to considered natural mordants. By first dyeing, let us minimize the pollution load. say cotton, with these compounds, one introduces Similarly, anionic and cationic sites can be created additional hydroxyl and carboxyl groups in the fibre. on the cotton fibre by pre-treatment with suitable These groups by themselves can only increase the dye chemicals/ polymeric compounds to modify its uptake of basic dyes such as Barberine. A pre­ affinity for various natural dyes. Such pre-treatments treatment with tannic acid-tartar emetic combination can also qualify to be covered under the broad was used for dyeing of, 'Mauviene', the first synthetic category of mordants. basic dye, on cotton as well as for dyeing of other synthetic basic dyes. 9 Application of Natural Dyes A subsequent treatment of the tannin- treated cotton A classification of natural dyes on the basis of their with metal salts such as alum introduces aluminium application procedure has been given by Gulrajani13. ions in the fibre. The tannin-treated cotton at the As a guideline, the classification of some of the 200 INDIAN J. FIBRE TEXT. RES., MARCH-JUNE 2001 common natural dyes is given in Table 2. It is Furthermore, these dyes can be directly dyed on wool apparent from the table that some of the dyes can be and silk since these dyes also have some limited placed in more than one dye class. affinity for these fibres. However, these dyes can be The procedures of application of these dyes are fixed onto the fibres by post-mordanting treatment similar to those followed in the case of synthetic dyes. with metal salts. For example, the natural indigo is dyed by the same For getting the compound shade wherein more than procedure as the synthetic indigo. Both are vat dyes. one dye is required to be used, the same principle as Madder, being a mordant dye for cotton, requires adopted for synthetic dyes works. That is the creation of dye-sites in the fibre before the dyeing is natural dyes, which can be dyed under identical carried out. Conventionally, this was being done by condition, can be mixed and dyed together. However, first applying a water-soluble aluminium salt such as a post-rnordanting treatment may not work out alum and then converting it into an insoluble salt by successfully unless mastered carefully. treating it with calcium hydroxide. The aluminium­ By scientifically understanding and analyzing the calcium salts precipitated into the fibre acted as sites chemical structure of the natural dyes, a suitable for the madder dye. This formed the basis of the method could be worked out for the application of famous Turkey Red colour. these dyes on different substrates. A challenge an The process at some stage got modified wherein the enlightened dyer has to face if he or she is planning to material was first treated with tannin-containing plant venture in this field. material which provided sites for aluminium to form complex as described above. Thus, the tannin-alum 10 Fastness of Natural Dyed Materials treated cotton became the base material for the dyeing Natural dyes are considered fugitive even though of madder and other such dyes. one finds many fabrics dyed with natural dyes in Since wool, silk and nylon have cationic groups in museums, wherein the cloth has retained its original the form of protonated amino groups, these fibres can colours throughout the centuries of exposure. be dyed with natural acid dyes such as lac under Poor light fastness of some of the natural dyes can acidic pH in the same manner as synthetic acid dyes. be attributed to the inherent propensity of the dye Lac can be post-mordanted to give dye-metal chromophore to photochemical oxidation. The complexes. Hence, it is not only an acid dye but also a chromophore in some cases can be protected from mordant dye (like chrome-mordant dyes among the photochemical oxidation by forming a complex with synthetic dyes). transition metal, whereby a six membered ring is The chemical structures of many natural dyes are formed. The photons sorbed by the chromophoric similar to those of synthetic disperse dyes in the sense groups dissipate their energy by resonating within the that they do not have solubilizing groups and are only ring and hence the dye is protected. sparingly soluble in water. Hence, they can be dyed It is apparent from above that a post-treatment with on hydrophobic fibres such as and nylon. a metal salt can result in an improvement in the light fastness of some natural dyes. However, a post­ Table 2-Classification of natural dyes on the basis of application treatment with metal salt also results in change of the properties hue. Therefore, the post-treatment should be chosen Botanical Common name Dye class carefully. This type of post-treatment with copper or name/source chromium or combination of their salts is given to Indigofera tinctoria Indigo Vat some synthetic dyes to improve their wash and light Rubia tinctorum Madder MordantlDisperse fastness. Rubia cardifolia Manjeet AcidlMordantl Disperse The poor wash fastness of many natural dyes is Ceasalpinia sappan Sappanwood MordantlDisperse mainly attributable to following factors: Luccifer lacca Lac dye Acid/Mordant Berberis aritata Berberine Basic • Weak dye-fibre bond between the natural dye and Butea frondosa. Tesu MordantlDisperse the fibre. monosperma • Change in hue due to the breaking of the dye­ Mallotus philippensis Kamala MordantlDisperse Rheum emodi Dolu MordantlDisperse metal complex during washing. Quercus infectoria Gall nuts Acid/Mordant • Ionization of the natural dyes during alkaline Acacia catechu Cutch Acid/Mordantl washing. Since most of the natural dyes have Disperse hydroxyl groups which get ionized under alkaline GULRAJANI: PRESENT STATUS OF NATURAL DYES 201

conditions, many fabrics dyed with natural dyes a strong base for renewable resources for the dye under acidic conditions change colour on washing industry, a comprehensive training programme with alkaline detergents or soap. has to be launched, may be by making it a part of The wash fastness of some of the natural dyes the syllabus. could be improved by a post-treatment with alum or a • Dearth of books on the technology of dyeing with dye-fixing agent, which results in the formation a dye­ natural dyes providing the scientific basis to the fibre complex or a crosslink between the dye and fibre subject. respectively. • Adverse publicity being given to natural dyes, Tannins, being large molecular compounds, do not spearheaded by the synthetic dye manufacturing diffuse into the fibre easily. Hence, dyeings based on companies. Some of the points being tannins show poor rub fastness on cotton. One can do overemphasized are discussed above. It must be very little about it except limiting the quantity of the kept in mind that natural dyes are not substitutes tannin used. of synthetic dyes. They have their own market To have a palette of colour with good fastness and any expansion in this market is not going to properties, one has to experiment and fill the be at the cost of synthetic dyes. Some of the knowledge gap. limitations of natural dyes, such as use of banned metal salts, poor fastness properties and use of 11 Imperatives to the Use of Natural Dyes agricultural land for growing natural dye-plants, • One of the major imperatives to the use of natural being highlighted can be easily overcome by dyes is the knowledge gap. Very few serious R&D. attempts have been made to generate new information on the use of natural dyes. Most of References the research in this area is carried away by the I Sewekow Ulrich, Milliand, 4(1988) E-145. empirical information reported in literature that 2 Glower Brian, 1 Soc Dyers Colour, 114(1998) 4. does not have any scientific reasoning or basis. 3 Hill D J, Rev Prog Color, 27(1997) 18. • Non-availability of the natural dyes in the 4 Svenson Ann E, WAAC Newsletter, 8(1) (1986) 2. standardized form, which may be powder, paste 5 Anon, Eur Chern, 26 March 1998, 10. 6 Raise, http://www.raise.org/natural/pubs/dyes/dyes.stm of solution. Using the raw material for dyeing has 7 U.S. Domestic Imports, http://www.ita.doc.gov/industry/ many limitations. Besides its being of unknown otealtrade-Detai I composition, it generates considerable amount of 8 India Hortibusiness On-Line, http://www.agroindia.org/ !HOL biomass that is cumbersome to handle In the 9 Frey F, Melliand Int, (2) (1997) 88. dyehouse. lO Dye Plants and Dyeing, by John and Margaret Cannon (The • Severe shortage of trained dyers. Most of the Herbert Press, UK), 1994, 76. textile chemists in the country are trained to use II Dye Plants and Dyeing, by John and Margaret Cannon (The synthetic dyes. Even the teachers have very poor Herbert Press, UK), 1994, 38. appreciation for this centuries-old technology of 12 Gulrajani M L, Deepti Gupta, Varsha Agarwal & Manoj Jain, Indian Text 1, 102(5) (1992) 78. dyeing. If this technology is to be used for 13 Natural Dyes and Their Application to Textiles, edited by M generating revenue, employment and for creating L Gulrajani and Deepti Gupta, (liT Delhi), 1992.

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