Natural dyes – the eco friendly alternative !
Nature celebrates with colours and these celebrations are a visual treat. The living world bursts in to a colourful expression, especially around the onset of spring (वसंत ऋतू ) Even non living forms seem to join the celebrations with their myriad hues. And these colours have always fascinated mankind right through the ages. No wonder then that Man has tried to bring colours in to his life.
TheUntamedEarth brings you this article which talks about man’s tryst with colours and its beginning with natural dyes. It also explores the relevance of natural dyes today.
TheUntamedEarth thanks Dr Sujata Saxena of ICAR – CIRCOT for this wonderfully informative article.
Natural dyes – the eco friendly alternative !
Dyes are colored substances which enhance the aesthetic value of a substance by imparting them a reasonably permanent colour. In olden days they used be derived from natural sources like plants, animals or minerals with plant parts such as leaves, stem, bark, roots and flowers being the main source. Human association with colours dates back to prehistoric times. The myriad colours of nature have inspired man through the ages to recreate those in the garments and other items of usage, by harnessing locally available materials. Remnants of coloured cotton or flax textiles have been found at the archeological excavations sites of almost all ancient civilizations such as India, Egypt, Greek, Aztec and others in spite of the degradable nature of the natural fibre textiles. Fragments of the red coloured cotton cloth dating back to around 3000 B.C. were found in the excavations at Mohenjo – Daro, a site of Indus valley civilization. As the civilizations developed, the art of colouration of textiles from the dye bearing materials also progressed. In India, the craft of dyeing and printing of textiles developed to a great extent and contributed significantly to the its wealth. Indian Calicos or printed cottons were extremely popular in Europe in 17th and 18th centuries; they had such a disastrous effect on domestic textile production in England that their import was banned by English parliament in 1721 A.D. Many villages in India were specially set or wholly utilized only for catering to the huge export demand.
India is believed to be the oldest centre for cultivation and use of indigo dye from where it was introduced to Roman and Greeks. Other than indigo, plants such as madder, aal, pomegranate, safflower, turmeric etc. were cultivated for dyes. Besides, there were many other trees as well as creepers, shrubs and small herbs yielding dyes and auxiliaries which were collected from the forests for use in dyeing.
Synthetic dyes however are of petroleum origin and therefore difficult to biodegrade. Only a part of these gets fixed onto the fabrics during dyeing. The rest remains in the dyebath and along with other dyeing auxiliaries and chemicals gets discharged as effluent making it highly coloured and polluting. Effluent treatment process followed by most of the industries is not able to degrade the dyes and these are merely separated as solid colored sludge requiring further disposal. Natural dyes on the other hand are of biological origin and hence are easily biodegradable and do not give rise to such problems.
The environmental awareness about the pollution caused by the use of synthetic dyes has resulted in a global revival of interest in natural dyes since the last decades of 20th century. The ban on certain azo dyes synthesized from suspected carcinogens by Germany and other EU countries in 1995, has further boosted this interest. A niche market for textiles dyed with natural dyes is thus created due to the demand from environment conscious consumers and it has led to a rediscovery of natural dyes. As the bulk of traditional knowledge which was passed down from father to son and from the master craftsman to the apprentice was lost due to the years of neglect, attempts were made all over the world to reconstruct the dye extraction and application processes by interacting with a few surviving practitioners of this art in remote villages and scanning whatever old records of this practice were available. It led to the publication of a number of books and articles about the various natural dye sources and their application processes. Many natural dyes if applied properly, can match the colourfastness properties of good synthetic dyes.
Textiles dyed with natural dyes have their own beauty as the colours are soft and earthy, though the colour range is rather limited.
Sources of natural dyes …
Natural dyes unlike synthetic dyes are not available in ready to use form. These are obtained from natural materials and based on their source of origin are broadly classified as plant, animal, mineral and microbial dyes, though plants are the major source of natural dyes.
Plant origin dyes …
In natural dyes, out of the three primary colours- blue, yellow and red, blue is almost always obtained from indigo while there are various sources for red and yellow dyes. Some of the important dye sources derived from plant parts like leaves, wood, bark, stem, roots and flowers etc. are listed below.
Blue dye (indigo) – Leaves of the plants from the Indigofera genus like I. tinctoria, I. errecta, I. sumatrana are the best source of this dye. This very important dye popularly known as the ‘king of natural dyes’ has been in use from the ancient times to the present day, for producing blue color. Today it is the most popular dye for denim fabrics though most of it is synthetic. Both are chemically similar – the chemical being known as indigotin - but the colour of natural indigo appears richer due to the presence of the small amounts of a red dye indirubin. Apart from Indigofera species, there are several plants which can be used to produce indigo dye. Woad was the natural indigo producing plant in Europe. Dyers knotweed (Polygonum tinctorium), Pala Indigo (Wrightia tinctoria) and Khum (Strobillanthes flaccidifolius) are some other plants traditionally used to produce indigo.
Red dyes - Main plant sources are madder – European madder (Rubia tinctorum- roots) and Indian madder – manjishtha or manjith (Rubia cordifolia – roots and stem), aal (Morinda citrifolia – roots and bark), safflower (Carthamus tinctorius – florets), Sappan wood or patang (Caesalpina sappan) / Brazilwood (Caesalpinia echinata), ratanjot (Onosma echioides – roots and bark).
Yellow dyes - Turmeric (Curcuma longa- rhizome), saffron (Crocus sativus – dried stigma of flowers), annatto (Bixa orellana – seeds), Barberry (Berberis aristata - roots, barks and stems), Flame of the Forest, tesu or Palas (Butea monosperma – flowers), pomegranate (Punica granatum - rinds), Myrobolon (Terminalia chebula – fruits and leaf galls), marigold (Tagetus sp.), onion (Allium cepa – outer skins), dolu or Indian rhubarb (Rheum emodi - roots and rhizome), Kamala (Mallotus phillipensis – fruits) etc.
Brown dyes - Catechu or cutch obtained from the heartwood of Acacia catechu dyes cotton, wool and silk to brown color.
Animal origin dyes …
Tyrian purple from the Murex mollusc found in Mediterranean sea was a prized natural dye in ancient days due to its brilliant purple shade and very good fastness properties. It was highly expensive, as thousands of molluscs were needed to get a gram of the dye and hence was reserved for the use of the royalty. Most of the other animal dyes are derived from insects and yield red colour, for example lac, which is the hardened secretion (stick lac) of the insect Kerria lacca, cochineal obtained from the bodies of female insect Dactylopius coccus, Kermes from the insect Kermes licis also produces crimson red colour.
Mineral origin dyes …
Some mineral pigments found in nature such as cinnabar, red ochre, yellow ochre, raw sienna, malachite, ultramarine blue, azurite, gypsum, talc, charcoal black etc. have been used for coloration purposes. Apart from the red ochre which was used by the monks for coloration of their robes, these were mainly used in paintings and murals along with gum as binder and did not find application in textiles.
Bacterial and fungal origin dyes …
Some bacteria also produce coloured substances as secondary metabolites. Bacillus Brevibacterium, Flavobacterium, Achromobacter, Pseudomonas, Rhodococcus spp. are some of the pigment producing bacteria. Serratia marcescens produces deep red pigment. Some bacteria have also been reported to produce indigo upon exposure to petroleum products. Pigments from fungus Monascus purpureus are used for coloration of some traditional oriental food items and also for fabric coloration. Orchil dye from lichens was used for violet and purple shades as a cheap alternative to expensive Tyrian purple. Some mushrooms are also known to yield dyes. These were extensively used in Europe for dyeing. Cortinarius species have intensely colored fruiting bodies and are reported to be the best mushroom dyes. Cortinarius sanguineus (blood – red webcap) contains about 6% red pigments. Apart from the above mentioned sources, various researchers have been exploring local flora for its potential to dye textiles. Leaves, flowers, wood, bark etc. of several plant materials have been utilized for dyeing of various textile substrates with varying results in terms of deepness of color produced on textile substrates and its colorfastness properties. Every year new additions are being made to the list of plant species which can be used as dye source.
Dye Extraction …
Unlike synthetic dyes which are available in a purified ready to use form, natural dye bearing materials contain only a small percentage of coloring matter along with a large quantity of other plant or animal constituents and therefore extraction of colouring matter is an essential step. Most of the practitioners prepare their own dyes. It is economical and also ensures authenticity. Dye extract is prepared by soaking the dye containing material (after powdering for hard materials like bark, roots, wood etc. in water in earthen or metal (stainless steel or copper) vessels and then boiling and simmering the solution. Residual matter is then removed by filtering through a cloth and the extract is used for dyeing. Sometimes, depending upon the dye material, addition of acidic or alkaline substances such as vinegar or lime may facilitate better dye extraction. It may also change the hue of dye by changing the dye components that get extracted. Indigo is extracted by an entirely different process known as fermentation. Freshly harvested indigo leaves and twigs are soaked in warm water whereby the indigo present in the leaves as glucoside gets released by the action of an enzyme, also found in leaves. The fermentation is complete in about 10-12 hours and the greenish yellow liquor containing the indigo is then transferred to beating vats. Here it gets oxidised by the atmospheric air to the blue colored indigotin which settles down at the bottom. It is collected, washed and after removing excess water is pressed into cakes and marketed.
Application of Natural Dyes …
Natural dyes are generally used to dye textiles made of natural fibres like wool, cotton and silk where they strengthen their inherent eco-friendly nature though dyeing of synthetic fibre textiles such as polyester, nylon etc. has also been reported. Natural dyes can be used to dye textiles at all stages such as fibre, yarn or fabric. Wool is generally dyed in yarn form and traditional dyers almost always prefer yarn dyeing for all materials as it offers versatility in designing during weaving. As in synthetic dyeing, the textile material to be dyed is first made free from accompanying impurities like wax, pectin, oil, grease etc. and made white and absorbent. Traditionally, multiple treatments with sheep or cow dung along with alternate wetting and sun bleaching of the fabric were used to achieve this and the process used to take many days. Presently, the fabric is generally scoured with soap or alkali and bleached with hydrogen peroxide to quicken the process. For synthetic dyes, the amount of dye used is normally given as % shade which is the amount of dye used to dye 100 gram fabric. The same convention may be used for natural dyes. As the actual dye content of the natural dye bearing materials is very low, it is common to use 15-25 % shade whereas only about 1-3 % shade is required for synthetic dyes as these are purified chemical products.
Only a few natural dyes like turmeric can directly dye textile materials and are called direct dyes. Majority of natural dyes need mordants for fixing on to the textiles particularly for cellulosic textiles like cotton which unlike wool and silk, do not have amino or carboxyl group for attaching with the dye molecule. Mordants are the substances which have affinity for textile fibres as well as dyes and thus act as a link between them. Such dyes are known as mordant dyes.
Advantages of Natural Dyes …
Natural dyes are eco – friendly as these are obtained from renewable resources as compared to synthetic dyes which are derived from non – renewable petroleum resources. They are biodegradable, hence the effluent produced in natural dyeing can be easily treated thereby reducing the pollution from dyeing units. The residual vegetable matter left after extraction of dyes can be easily composted and used as fertilizer. They produce soft colours which are soothing to the eye which are in harmony with nature.
In addition to these environmental benefits, natural dyes also offer functional benefits to the wearer and users of such textiles. Many of the natural dyes absorb in the ultraviolet region and therefore fabrics dyed with such dyes should offer good protection from ultraviolet light. Tannin treatment during mordanting itself is able to improve the UV protection of textiles. Many natural dye materials possess antimicrobial properties and therefore dyed fabrics have been reported to be odour free by the users. These fabrics were also found to be mosquito repellent and /or moth repellent. Many natural dyes such as myrobolon fruits, turmeric, manjishth root, Arjuna (Terminalia arjuna) bark, safflower florets etc. possess curative properties and have been used in traditional medicinal systems and these benefits may reach the wearer by absorption of medicinal compounds through skin. Textiles produced in Kerala, India by dyeing with herbs as per the traditional Ayurvedic system of medicine are known as ‘Ayurvastra’ and have become popular as health and well – being textiles and are being exported to various countries. Various companies are now marketing naturally dyed textiles as health and well – being textiles.
Limitations of Natural Dyes …
In spite of their several advantages, natural dyes at present are not part of the mainstream textile processing. Less than 1 % of textile production is being dyed with natural dyes and they are mainly used in cottage sector or small scale processing units. Their limited shade range and inability to dye synthetic fibres like cellulose acetate, polyester etc. and also availability and supply issues are a big hindrance for wider adoption. At the present level of world textile production, natural dyes can only replace a fraction of total textile dye consumption as food crops are the first priority for land use. There is a danger of deforestation if already depleting forest cover is over exploited for use in dyeing. It is due to these issues that though natural dyes would be the first option for dyeing organically grown textile fibres, Global standard for Organic Textiles (GOTS) has also permitted the use of safe synthetic dyes. Exploitation of the by products and waste material from food processing industry and establishment of collection and supply mechanism for some agro by products and forest products would be of help in improving the natural dyes availability. Use of non eco friendly mordants by some processors due to their ignorance, makes the natural dyeing application process non eco- friendly and false claims of natural dye usage for synthetically dyed textiles, are the issues affecting both consumers and natural dyeing practitioners and need to be tackled with training and government initiatives.
Policy incentives to promote better utilization of agro and agro processing residues, cultivation of dye plants in wastelands and setting up of natural dyeing units would help in popularizing use of natural dyes. Establishment of proper characterization and certification protocols for natural dyes textiles dyed with them would improve the consumer confidence in such textiles and benefit both producers and consumers. In future, if the availability of natural dyes can be increased to very high levels by biotechnological interventions such as tissue culture or genetic engineering resulting in mass production of these dyes by microbes at low costs; their usage can become sustainable for main stream textile processing. At present, use of natural dyes is sustainable only for small scale applications and they can complement synthetic dyes as an eco friendly option to the environment conscious consumer.
Dr. Sujata Saxena
Dr. Sujata Saxena has a Ph.D. in Chemistry and is currently working as Principal Scientist and Head of Chemical and Biochemical Processing Division at Central Institute for Research on Cotton Technology (CIRCOT), Mumbai. Her current research interests are pre-processing, dyeing and finishing of cotton and its blends using natural and eco-friendly agents and processes. She has special interest in developing methods for application of natural dyes to cotton and in improving their colourfastness properties.
She has been a consultant to National Handloom Development Corporation (NHDC), Lucknow for developing methods for dyeing of cotton textiles with lac, berberin and manjitha natural dyes. She was also associated with multi- institutional projects funded by UNDP (United Nations Development Programme) and ICEF (India- Canada Environment Facility) on development and promotion of natural dyes for cotton.
She has published more than 45 scientific papers, articles and book chapters, has applied for 4 patents and has presented more than a dozen papers at national and international Conferences.
She has been associated with National as well as International professional societies and is currently Joint Secretary of the Indian Fibre Society, Mumbai and Treasurer of Indian Society for Cotton Improvement, Mumbai. She has recently been awarded the Fellowship of Textile Association of India, Mumbai. She has been associated with various BIS sub-committees on textiles and is a reviewer for National and International journals.