Chemistry of Dyeing (रञ्जनम्)

Dyes, mordants and pigments accompanied the development of Indian culture from ancient days. The major chemical arts and crafts in early period were pottery, jewelry making, dying of cloths, tanning of leather, cosmetics, glass making, etc. Several evidences are available in favor of these in literature and many have been obtained from archaeological excavations.

Introduction

Ever since the dawn of civilization man's inclination to make different objects more pleasing by painting them with beautiful colors and by dyeing objects like fabric and pottery led to the discovery of delightful coloring materials. Painting and dyeing have got their utilitarian value also. They protect the surface from getting damaged in changing atmospheric conditions, hide the defects on the surface of different objects like structural walls, cloth and hair. etc., and prevent metals from getting corroded.

The principal dyeing materials were turmeric madder, sunflower orpiment, cochineal, lac and kermes. Some other substance having tinting properties were Kampillaka, Pattanga and Jatuka. The term dye, is derived from old English word daeg or daeh meaning "colour". The earliest dyes were probably discovered by accident and may have been noticed from the stains from available berries, fruits and nuts and blossoms, leaves, stems and roots of shrubs. The exact period of the commencement of the art of dyeing in the world is not ascertained.

Pottery - Preparation and Painting

Pottery and pottery-painting were practiced in India ever since the dawn of civilization. In archaeological parlance, pottery is regarded as index to culture; an alphabet to history. Generally it is studied typologically, a correlation with others, rather than extensive technological analysis. However technological details such as - composition of clay, tempering agents, nature and components of the slips or glaze, nature of firing, porosity test and different chemical analyses - stand witness to not only the technological advancement of that culture but throws light on social, cultural, religious, economic, political aspects of that culture. Pottery both of fine and coarse types found in excavation sites of the Indian sub-continent are of many varieties, such as Red Ware, Buff Ware, Gray Ware, Black and Red Ware etc., broadly classified based on their colors.

People in very ancient settlements were well-acquainted with the art of making potteries of burnt clay and painting various designs on them. A large variety of ochres, haematites, pigments and organic colors were used by potters for painting the pots. This art of using pigments for beautification of pottery led to the development of paint technology in India.

Archaeological evidences of pre-historic settlements unearthed in various parts of India have revealed a large number of earthen ware items implying that the inhabitants of these early settlements were well-acquainted with the techniques related to pottery making, dye preparation and painting. It is interesting to note that regarding the pre-historic cultures, archaeologists have given a broad classification as Buff-ware culture and Red-ware culture based on the colours of the potteries distinctively found in those settlements. Potters' wheel was the characteristic implement of the Indus valley civilization.

The characteristic ‘red and black’ pottery of Harappan civilization and a few polychrome potteries that have also been unearthed in these sites are painted in green and red on a buff slip. Chemical analysis revealed that red or Solomon colours in these objects are due to the presence of iron components in the clay. The slip of bright red colour is due to ferric oxide. The black and chocolate designs that are found painted on the body of the pottery owe their colour to oxides of manganese. The colouring agents used by the Indus valley people are used even today by potters. Many of the ancient techniques of selecting and applying colouring materials have come down to the present time also.

Slip treatment was given to the pots before they were fired. Slipping serves two purposes it helps in closing the pores and provides smooth surfaces helpful in painting a design on them. Slipping was done by dipping the pot after burnishing in a solution or by painting with a solution formed by the finest portion of the clay used for making the pot or of any suitable materials such as ochres, pigments.

It is important to note that knowledge of colors and causal components were well known to the people. It is significant that the colors of these slips neither vanish nor fade in firing.

• Light pink shades - traces of iron in clay
• Dark pink - addition of red ochre in clay or as a slip directly
• Dark red - red oxide added to slip
• Yellow - addition of yellow ochre

Black and chocolate shades - manganiferous hematite was used (in combination if manganese is more produces pure back color, if iron preponderates it gives a chocolate color)

The technique of painting pots before firing and also painting designs on them after firing was in vogue. Mostly organic colours were used to paint the surfaces. For white pigment, lime, limestone, chalk and rice powder were used. To prepare black pigment, burnt coconut shell powder, soot, powdered charcoal, black iron oxide etc. were found to be used in some other settlements.

During Vedic times and later on, ritual pots were painted with floral and geometrical designs in red, yellow blue and green colours. The solvent used for these pigments was plain water.

• Vermilion (mercuric sulphide) or dhau (ruddle) was used from red pigment
• Turmeric and yellow ochre was used for yellow colour
• Blue from indigo
• Green from leaves of particular trees and iron sulphate
• Grey was prepared from a kind of haematite
• Orange pigments were obtained by mixing red and yellow colours
• Copper sulphate was mixed with red pigment to obtain purple pigment

It is evident that methods like filtration, decantation, making pastes by rubbing on granite with little water, boiling with ingredients like calcium, catechu, soda etc, plant identification and collection of barks and leaves, and fermentation using rice starch were the adopted chemical processing techniques in preparation of pigments.

Dyes for Textiles

The art of dyeing fabrics for ornamentation and decoration in India has an ancient origin. It can be gathered from the Vedic texts that clothes were mainly made of wool; and the garments were often dyed red, purple and brown. Apparently the people were acquainted with the art of dyeing with certain natural vegetable coloring matters. Panini (c. 500 B.C.) also makes mentions of indigo, lac and red ochre for dyeing cloth (IV.I, 42).

Vedic texts provide evidence to the fact that the art of dyeing and printing textiles was quite advanced in that time. It is said that the robe of a king who is initiated to perform Rajasuya Yajna was fully worked or painted with designs of various form of the yajna. Terms like रजयित्री (rajayitri) in Yajurveda indicate that dyeing of cloth was a profession in which people were engaged. .....वासःपल्पूलीं प्रकामाय रजयित्रीम् ॥ (Yaju. Shuk. 30.12)

Sathapatha Brahmana mentions the use of bridal dresses which were decorated with designs, and people used cotton, wool and silk and dyeing of wool from which cloth was made. The dyes mentioned were natural coloring agents like saffron, henna, extracts of plants and leaves, flowers and fruits etc. Buddhist literature testifies that colors were obtained for dyeing purposes from roots, stems, barks, leaves, fruits and flowers of trees and were used to decorate dresses of grhasthas. Indigo (nila), lac (laksha), turmeric (haridra), maddar (manjistha) and resin (rajana) were frequently used dyes. Kautilya's Arthashastra apart from mentioning various types of fabric makes a special mention of vanacitra, a type of dress material in which different floral designs are made while weaving itself. This implies that yarns were dyed in various colors and woven in different patterns.

Kautilya also mentions that the dyers were known as 'Rajaka' and they were paid double in amount as compared to washerman. Epics and Puranas are replete with the popularity of dyed clothes among all classes of people. Srikrishna is described as wearing yellow colored clothes while his brother Balarama was fond of blue robes. In the list of occupations rangopajivin is mentioned from which it is inferred that the art of dyeing was well developed. Clothes dyed in reddish colour (Kasai) were worn in hot weather. The "Parivrajaks" used to wear clothes dyed in red ochre (geruya).

Mordants

The discovery of a fragment of maddar-dyed fabric at Mohenjadaro, sticking to a silver-vase leads to an understanding that Indus Valley people were acquainted with the technique of dyeing cotton with red coloring matter of maddar (a plant) root and that the mordant process of dyeing cloth was known in India at least 5000 years ago. Archeological evidence of many dyeing vats are also found proving that dyeing of fabric was practiced on a large scale as a profession.

Coloring of any object can done by means of dye materials and pigments. Though dyes and pigments are coloring agents, dyes are defined as chemical compounds which have the property when in solution to color vegetable or animal fibres permanently with or without the use of auxiliary agents. Pigments are insoluble in the coating substrate materials whereas dyes readily dissolve in and add color to them. Pigment is an insoluble substance used to give color tint to paints and other surface coatings according to Newman (1963).

Reason for dye activity among dyes is found in their basic (alkaline) or acidic substituents. Protein materials like silk or wool have basic and acidic properties making them easier to dye. But dyeing cotton is difficult without the use of mordants, the substances capable of penetrating and adhering to fibres. The dye added after using mordants forms an insoluble product in cotton fibres.

Alum and other mordants

Varahamihira's Brhat Samhita details the preparation of fast dyes for textile fabrics by the use of Alum and other chemicals (like sulphate of iron and also cowdung). Alum is called as Tuvari described as fragrant earth found in Saurastra was used as a mordant before using maddar as the dye. Alum is hence called Saurashtri and when applied to white cloth serves as a mordant for dyes. Commonly used mordants were as follows

1. basic mordants namely iron sulphate and aluminium sulphates for acid dyes
2. acid mordant - tannic acid for basic dyes.

Beside alum, iron sulphate other fixing agents or mordants used were rind of lemon, flower of cotton, lime, lemon, green dried mangoes, myrobalans etc. Mordanting effect varied with each of these substances and influenced the final color; with some dyes alum produced yellow color and in others it yielded orange blue.

Reduction and Diazotization

Since all dyes are not water soluble, they have to be rendered so by chemical reduction process or they have to be synthesized on the fibres (usually cotton) by diazotization method. Indigo dye which was extensively used is an insoluble dye and people knew the technique of making it water soluble by reduction after which it would easily attach to the cotton fibres.

Dyes in Cosmetics

Dyes were used in cosmetics extensively. Examples include

• A paste of sandalwood colored with lac and other dyes smeared over the body and applied in different patterns
• Collyrium (anjana) made of dark powdered antimony was used to decorate eyes
• Vermilion (sindhura), lac (laksha), and gorochana (a yellow pigment) were used for marking tilaka on the forehead.
• Lac was used to dye lips, tips of fingers, toes, palms and soles of feet.
• Henna or madayantika (mendikaa, mehndi, gorante etc in different Indian languages) is a popular shrub in India whose leaves are made as a paste and mixed with lime to produce the brownish red color used to color palms and nails, and even feet.
• Rasaratnakara mentions the preparation of kunkuma used as tilaka from the boiled essense of palasapushpa.
• Colors were used for preparing rangoli also.

Hair dyes were used extensively to blacken the greyhair. Varahamihira gives a method of preparing hair dyes from grains of harika (paspalum scrobiculatum) and loha churna.