How are different dyes made?

        Dyes are colour substances which impart their colour to the fabrics on which they are applied and for which they have a chemical affinity.

          Until the middle of the last century, the only dyes available were natural products obtained mostly from plants and flowers. Their range was limited. These natural dyes included: woad, a blue dye obtained from the plant woad; indigo, another blue dye from a plant. Some other dyes such as madder (red) safflower and turmeric (yellow) were extracted from certain kinds of sea-snails.

          The most important breakthrough in this field was made in 1856 with the discovery of the first synthetic dye by William Henry Perkin. This was mauveine, a bluish-purple dye discovered accidentally by William Perkin during experiments aimed at synthesizing the drug quinine. After this discovery, efforts were made to develop dyes from coal tar. As a result of these efforts, several thousand dyes were synthesized subsequently.

          These synthetic dyes were satisfactory when used with animal fibres such as wool, but they were easily washed off from vegetable fibres like cotton. This difficulty was overcome by treating the fibres with metal salts or with solutions of these salts in tannic acid before dyeing.

          After these dyes a large number of azo dyes were developed. Azo dyes are two component dyes used for cellulose fibres. The material is first treated with one component, and then put in the solution of the other component. The two components react to produce a dye within the fibres themselves. These dyes are highly resistant to washing.

          Another group of very stable dyes used for cellulose fibres is known as Vat dyes. These dyes, which include synthetic indigo used for dyeing blue denim, are mixed with chemicals to make them soluble for the dyeing process. After the material has been dyed, it is treated with other chemicals to make it more stable.

          Today we have a large number of synthetic dyes obtained from coal tar or petroleum products which are not only used to colour textiles, but also plastics, paper, leather, fur, oil, rubber, soap, food, cosmetics, ink and metal surfaces.