HISTORICAL BACKGROUND OF DYES

HISTORICAL BACKGROUND OF DYES

For many centuries, people did not know much about what took place when a fabric was dyed. Only when chemist and physicist had obtained enough knowledge that the process was understood. But even without scientific knowledge people got remarkable results with their dyes. The act of dyeing a fabric is believed to have been known in China as long ago as 3000BC. On the evidence of cultural and religious records, both madder, a dye prepared from the root of the madder-herb, and indigo, a blue dye obtained from indigofera plants which were used in India from around 2500BC.

At relatively the same time, dyeing of cloth in yellow, red, green was also practiced in Egypt. The sun flower and old world herb also called dyers thistle, was used by the Egyptians around 2000BC to obtain yellow and red shades by 1450BC. Ways of dyeing fine fabrics, mainly linen in a full range of blues had been gradually evolved.

The natural dyes used up to the middle of the 19^th century, the greater part of them, are of vegetable origin, involved many problems both in respect to sources ad the processes. The use of natural indigo involved protracted fermentation processes to liberate the dye in a soluble, colourless form. After a cloth had been steeped in a vat, oxidation in air gave blue dyeing on cotton and wool. Many of these natural dyes have no affinity for textile fibers until such fiber is treated with a mordant to receive the dye. Among the mordant dyes was alizarin derived from madder root widely cultivated at one time in Europe, Turkey and India. It yielded a fast red on aluminium mordant, a purplish black on iron mordant, intermediate shades were obtained by using a mixture of mordant.

The origin of synthetic dye can be traced back to 1856 when it was discovered by an English chemist by name WILLIAM HENRY PERKIN. He discovered that under certain circumstance aniline could be oxidized to form a mauve coloured material which dyed silk.

In 1857, Perkin established a factory to manufacture the patented dye (mauves) which at first called aniline purple or Tyrian purple and later mauve, a French word for mallow, a plant with purplish flower. He developed new methods of applying the dyestuff and visited dyers to show them how they should be used.

In 1868, a team of German chemists proved that alizarin, the colouring principle of madder root, is a derivative of the chemical compound anthraquinone. The synthetic of alizarin from anthraquinone was the first preparation of a natural vegetable dye by purely chemical means.

Research was directed towards determining the structures of important natural dyes and then to synthesizing them. The first success was the synthesis of artificial alizarin from coal-tar anthracene in 1868. In 1880 indigo was first synthesized, though an economic manufacturing process was not known until 20 years later. A decline in the cultivation of madder and indigo resulted as dyers came to accept the synthetic products.

Organic chemistry became successful in research centers of Europe of dyes, many of them owning nothing to nature were perfected by dye makers. These include azo dyestuff, certain organic compounds having the general formula RN=NR, which today constitute the largest group of synthetic dyes, azoic dyes, a group of organic dyes derived from azo benzene, mostly red and yellow, Congo red, the first direct cotton dye used without mordant. In 1992-1993 acetate dyes mainly azo or anthraquinone dyes were highly dispersed to make them capable of penetrating fibers and in 1956, fiber reactive dyes were combined chemically to form a link with the material. Today, dyestuff research extractions continue as indicated by the large annual volume of patent literature.