8 Natural Dyes

S. Karpagam Chinnammal

1.    Introduction

Colouring materials have been used by man for many thousands of years. Dyes are substances that add color to textiles and it may be natural or synthetic. The concept of ‘eco friendly textiles’ is gaining momentum in the present era of ecological concern. With increasing awareness of the environmental preservation, control of pollution and health hazards associated with synthesis, processing and use of some synthetic dyes based on carcinogenic or allergic amines there is a worldwide interest in dyeing textiles with colorants extracted from renewable natural resources. Natural dyes comprise those colorants that are obtained from animal, vegetable or mineral resources without or with mild chemical processing and generally considered as safe and eco friendly.

2.   Learning objectives

• To get familiar with the history of natural dyes
• To be acquainted with the sources of natural dyes
• To get an insight into the classification of natural dyes
• To learn the various methods of dye extraction

  3.  History

Dyeing is an art which is practiced from ancient period. Ability of natural colours to dye textiles is also known from ancient times. Description about natural dyes is found in atharvavedha. The wall paintings of Ajanta, Ellora and sithannavasal are evidences of use of natural dyes since pre historic times. India was forerunner in the art of natural dyeing. In the epics frequent reference are made about a yellow garment used by gods called ‘PITAMBAR’. Some of the records of the court historians are written and illustrated with natural dyes.

The palace deterioration and the ceiling of the temples of Hallebid and bellur in Karnataka widely testify to the mastery of the India craftsman in the use of natural dyes. The coloured exquisite silk and muslin fabrics of India have been found belonging to the period of 16th and 17th centuries. Thus use of natural dyes is an old age history since ancient periods. A fragment of coarse madder dyed cotton fabric in a plain weave, found during the excavation of the ancient Harappan sites, indicates that even the peoples of Mohanjodaro (3000BC) used natural dyes. Several historical examples found during excavation show, that natural dyes are used since ancient time. The paintings on the walls in padmanabhapuram palace is a evidence that vegetable colours were used in the 18th and 19th centuries.

The use of natural colourants and dyeing of textiles in different colours was well known in china, Egypt and india in 3000 BC. The dyeing of textiles had also practiced in Egypt where the known textiles, linen mummy wrapping dating from 2000 BC, have been found dyed with either indigo or woad. The safflower (a yellow dye), an old world herb, was used by the Egyptians to obtain yellow and its shades. In 715 BC, dyeing of woolen material with natural colourants was established as a craft in Rome.

Among the various natural colourants, cochineal is a traditional red dye of prehistoric mexico and still prevalent in southern mexico. It was found that dyeing had been practiced during the Indus valley civilization at Mohenjodaro and Harappa during 3500 BC. In Rajasthan, still traditional natural colour dyeing is being followed by using some vegetable and mineral colourants eg bandhini. Kalamkari is a well known painting which is done with vegetable colors and is practiced in many parts of india.

Before 1856 , natural materials derived from insects, plants, shellfish, and minerals were the only known source of dyestuffs. These sources included the root of the herb madder for red dye and the indigo plant for blue dye. In the early days of the roman empire, garments colored with tyrian purple , a dye derived from shellfish of the Mediterranean sea, were worn by the imperial family and the nobility. As late as the 4th century AD, cloth colored with tyrian purple was the symbol of royalty.

The art of dyeing was stimulated in the 13th century by the discovery of achil, a purple dye made from a species of lichen .Northern Italy, where, the discovery was made, became the centre of dyeing in Europe. In the 16th century, explorers brought back from the Americas such dyestuffs as cochineal and logwood. Other important sources of natural dyes included quercitron, weld, fustic, brazilwood. Safflower and indigoplants. Kermes is identified in the bible book of Exodus, where references are made to scarlet coloured linen.

Natural dyes have been used since ancient times for coloring and printing fabrics. Until the middle of last century, most of the dyes were derived from plants or animal sources by long and elaborate processes. Among these indigo, tyrian purple, alizarin, cochineal and logwood dyes deserve special mention. Until about 100 years ago, people in many parts of india were still using various forms of natural dyeing. In 1856 the first synthetic dye , mauve was derived from coal tar by henry perkin. Since then a great number of synthetic dyes have been developed and it started to over rule the conventional natural dyeing and the use of natural dyes has almost ceased.

The main factors which led to the consumption of synthetic dyes were the availability of wide spectrum of colours and ease of application. Nobody was aware of the adverse effect of synthetic dyes on human health and ecology until 1990s.Now, we are aware about the threats raised by synthetic dyes and many countries have started banning carcinogenic dyes and implementing eco certification. Natural dyes offer an important alternative in these regards as these are safer in use with minimum health hazard, have easy disposability are biodegradable and have a higher compatibility with the environment. Recently, a revival of interest in the use of natural colorants in textile coloration has been growing.

4. Sources

Many plants and some animals have been identified as potentially rich in natural dye contents.

4.1. Natural dyes obtained from Plants

The majority of natural dyes are obtained from plants and they dominate the sources of natural dyes. Various parts of plants like the leaves, the skins of fruit, the bark, roots, wood, seed or flowers are used to make dyes. There is a whole variety of plants which can be used to make plant dyes. They are extracted mainly by aqueous extraction and wood parts yield maximum 10-20%yield and flower yields minimum 0.3-0.6 %.Lichens are very small plants which grow on rocks. There are many colours of lichens and they are very good for making dyes. Cudbear for example comes from the lichen, Lecanora tartarea and produces lilac color dye. Some of the sources of plant dyes are given in the table

4.2. Natural dyes obtained from Animals/Insects

Animal dyes are colourants obtained from animal sources like insect, shell fish, and shells.

Cochineal, is a dye produced from insects living on cactus plants. A red powder is obtained when the female insect is dried in the sun and ground Another red dye obtained from the dried bodies of the female insects Kermes vermilio or licis is Kermes . They yield only 0.1-2 % of dye.

A small insect, Lucciferalacca, a pest on plants secrets a sticky fluid which envelopes their bodies, the secretion form a hard encrustation over the twigs. Lac dye (a bright red colour) is obtained by boiling this tree incrustation. They contain only 1‐2 % dye it being an acid dye can be directly dyed on protein fiber such as wool and silk. It also produces very dark shades on nylon. The hues can be modified by post mordanting treatment with metal salts. The dye has very good light and washing fastness.Tyrian purple is produced from the secretions of the sea mollusk Murex. The dye produced is deep violet in colour , very fast and expensive.

4.3. Natural dyes obtained from Minerals

Natural colourants obtained from sand, clay, and ores are categorised as mineral dye. Some of the important mineral colourants are chrome-yellow, iron-buff, narkin-yellow, Prussian-blue and manganese brown. Ocher is a dye obtained from an impure earthy ore varying from light yellow to brown or red.

4.4. Natural dyes obtained from microbes

Some bacteria produce coloured substance usually pigments. Microbes as a dye source offer an advantage as these can be easily grown on cheap substrates under controlled conditions

5. Classification

Natural dyes can be classified based on its sources, chemical constitution, application methods and colour produced .

 5.1. Classification based on sources

Based on the source, natural dyes are classified into three categories ie plant/vegetable, animal and mineral dyes.

5.1.1. Vegetable dye

Colourants obtained from different parts of a plant are called vegetable dyes. The common dyestuffs obtained from different vegetable origin are given below

5.1.2. Animal dye

Colourants obtained from animal sources like insect and shell fish are grouped under animal dyes. Eg. Tyrian purple, lac, Cochineal and kermes

5.1.3. Mineral dye

Natural colourants obtained from sand, clay, and ores are categorised as mineral dye.

 5.3. Classification based on method of application

Based on the method of dyeing and the material to which it is applied, natural dyes can be categorised as

5.3.1. Direct dyes are those dyes that have amazing attraction for the cellulosic fibres. They are dyed under boiling temperature. Eg.Turmeric, harda, pomegranate rind

5.3.2. Acid dyes these dyes are applied from an acidic medium. The carboxylic or sulphonic group present in the dye form an electrovalent bond with amino groups present in wool and silk. Back tanning an after treatment with tannic acid improves the fastness of these type of dyes, e.g., saffron.

5.3.3. Basic or cationic dyes are applied from neutral or slightly acidic pH. These dyes on ionization give coloured cations and form an electrovalent bond with the –COOH group of wool and silk. The light fastnes of these dyes are poor light

5.3.4. Vat dyes are water insoluble dyes. They are reduced with Na- hydrosulphite and transformed to water soluble form, solubilised with alkali and applied to the fibres. The original colour is formed only on oxidation followed by treatment with a hot soap solution, e.g., indigo.

5.3.5. Disperse dye are applied under neutral or slightly acidic pH on synthetic fibres. They can also be applied to silk and wool. Its solubility is very low. These dyes can be post-mordanted with chromium, copper and tin salts, e.g., lawsone and many other flavone and anthroquinone dyes. The above five groups of dyes are Substantive dyes ie they have attraction to the substrate and needs no mordant.

5.3.6. Mordant dyes or adjective dyes have no affinity for the fibre. Ex. madder, fustic, persian, berries, kermes, cochineal etc. They are applied in the presence of metal salts. These metal salts form a complex with the dye and work as fixing agents and are called mordants.

5.4. Classification based on colour

The main colour of natural dyes depends on the chromophoric group of the colourants .They form different colours with different mordants. Some plants may have more than one colour depending upon which part of the plant one uses. The hue shade of the colour a plant produces will vary according to time of the year it is picked, how it was grown, soil content etc. Classification based on the important colours are

  Red colour dyes: Most red dyes are hidden in roots or barks of plants or camouflaged in the bodies of dull grey insects. They are based on anthraquinone and its derivatives and are stable to light and washing. The prominent vegetable sources that give red colour are madder (RubiatinctorumL.), manjistha (RubiacordifoliaL.), brazil wood/ sappanwood(CaesalpinasappanL.). cochineal(Coccuscacti L.) , lac (Coccuslaccae) and kermiz are animal sources that give red colour. Lac is the oldest and Cochineal is the brightest of all natural red dyes

Yellow colour: Yellow is the liveliest and perhaps the most abundant of all hues in nature. The plants that yield yellow colours are plenty. Parijatka, marigold, teak and pomegranate give yellow colour. About 90% of the yellow dyes are flavonoids. Normally, the shades produced are pale and fade quickly. Turmeric, produce dull deep shade but is susceptible to light. Wash fastness rating of natural yellow dyes varies from fair to excellent. Some of the important yellow dyes are obtained from berberry (Berberisaristata), tessuflowers (Buteafrondosa, monosperma)and kamala (Mallotusphilippensis).Other sources of yellow dye are black oak (Quercusvelutina), turmeric (Curcuma longa),weld (Reseda luteola)and himalalayanrhubarb(Rheum emodi).

Blue colour: The only viable choice among the blue natural dyes is Indigo. Natural indigo is obtained by fermenting the leaves of various species of Indigofera. Oxidation is a vital step to get the colour. Another example of blue colour is woad. These dyes have excellent fastness to light and washing

Black colour: Black shades are obtained from tannin rich plant and are substantive towardscellulosic and protein fibre and imparts good overall fastness properties. Examples – logwood, harda, custardapple etc.

Brown color: can be obtained from cutch, sumach, eucalyptus

Green colour: is hard to get directly from natural source it is obtained by mixing indigo and yellow however canna and lily give nice florescent green

Orange /peach color: Can be obtained from dahlia and annatto using different mordants

6.   Methods of dye extraction

Natural dyes can be taken from various sources. The collected source material is shadow dried in air or sun dried within a temperature range of 37-40°C to reduce the moisture content. After drying, it is ground to break down the material into very small units or preferably powder form. Usually, natural colourants are soluble in water, but in the raw form the colour component present in these sources needs to be extracted so that it can be applied on textiles. Extraction refers to separating the desired colour component by physical or chemical means with the aid of a solvent. Based on the solubility of natural colorants, different extracting methods are being adopted and finally it is filtered, evaporated and dried.

  6.1. Aqueous extraction

Aqueous extraction is using water for the extraction. Natural dyes are available in crude, crushed, water extracted powder and paste form. In case of crude form, the vegetable matters are dried, crushed and soaked in water and subjected to heating/boiling for about 1 to 2 hrs depending upon the material in presence of some electrolytes. Delicate parts such as leaf, flowers etc require 60 -80° C for 20-30 minutes extraction time, while bark and heart wood require 95-98°C for 60-120 minutes. It is allowed to stand for sometime. The colorant present in plant are transferred to the aqueous solution. Extracted content is cooled and filtered to separate aqueous solution of coloring components present in vegetables matter and roughages. The filtrate is then subjected to dryness under vaccum sublimation or water bath at 60° C

But, in case of water extracted powder form and paste form, this extraction procedure is not required. In those cases, a fixed quantity of dye is dissolved in fixed volume of water and this aqueous solution is directly used for dyeing.

The drawbacks of the process are, the fabric is boiled till the desired colour is obtained so massive amount of heat is consumed, due to prolonged heating the dye molecules of heat sensitive dyes are damaged, fair amount of dye is wasted due to incomplete exhaustion.

6.2. Acid or alkali assisted extraction

For better results, sometimes colour is extracted from various sources under acidic/alkaline condition. (Acidic pH is obtained by adding hydrochloric acid and alkaline pH by adding Sodium carbonate in aqueous media). Madder is slightly acidic and hence alkaline extraction gave better results. Flavonoids and anthraquinones are soluble in alkaline solutions. Acidic condition was more suitable for Red sandal wood and jackfruit wood.

6.3. Solvent Extraction

Sometime colorants present in natural sources are insoluble in water and some dyes are degraded by high temperature boiling, in such cases the crushed or cut vegetable matters are subjected to extraction in soxhelet apparatus using organic solvents like methanol, ethanol, hexane, alcohol or acetone at their respective boiling temperature for 20-24 hr. After the extraction process, the solvent is Evaporated and the colourants obtained as dry powder. Methanol is the commonly used solvent.

6.4. Supercritical fluid extraction (SCFE)

Supercritical fluid extraction is an advancement marking a significant step over the use of conventional solvent extraction technology. It uses super critical Carbon dioxide, as extraction media. Advantages are it is a highly purified and eco friendly technique. The energy costs is lower in SCFE than the conventional techniques

6.5. Ultrasonic and microwave assisted extraction process

In this process the extraction efficiency is increased by the use of ultrasound or microwaves thus reducing the quantity of required solvent, time and temperature of extraction. In sonicator dyeing the natural dye containing plant material is treated with water or solvent in the presence of ultrasound, cavitaions or small bubbles are formed in the liquid. These increase in size but upon reaching a certain size they cannot retain shape and it bursts creating high temperature and pressure and this improves the extraction efficiency in a short time. Also the process can be performed at lower temperature and therefore extraction of heat sensitive dye molecule is better. In microwave extraction, the source is treated with minimum amount of solvent in the presence of microwave energy, which increases the rate of the process and extraction can be completed in shorter time with better yield.

Both these processes are considered green process due to reduction of extraction temperature, solvent and time which results in lower consumption of energy.

6.6. Enzyme assisted extraction process

In this process individual or combination of enzymes (e.g.amylase, pectinase , cellulase) is sprayed on source material and left for better soaking. These enzymes helps to release the surrounding materials like pectin , starch etc thereby aiding in extraction of dye under milder conditions. The material is taken with water and shaken in orbital shaker for about an hour at optimum temperature. The extracted solution can be used for dyeing directly or it can be filtered, dried and purified for further use.

7. Conclusion

This module has highlighted the history, source, classification and extraction of natural dyes. Most of the natural dyes are ecofriendly and they inflict no harm to the consumer or the environment and it is a susutainable process. In the era of eco friendly textiles, Natural dyed products are the products for the future.

REFRENCE

1. Application and charcterisation of natural dyes, Sankar Roy maulik, Asian dyer , june-july 2015 P. 30, 33
2. Colouration of textiles by natural dyes, L Ammayappan, Seiko and S.Chakraborthy, Asian dyer, October-November 2013, p.30-32
3. A. Arora,Text book of Dyes, Sonali publication, New Delhi 2009 P.9,65,70