Dyes are used to give colour to many products including textiles, leather, hair and food. Natural dyes such as indigo and madder have been extracted from plants for centuries. Synthetic dyestuffs were first produced in the 1850s – beginning with mauveine and magenta. Aniline and aromatic hydrocarbons obtained from coal tar provided the raw materials. Dyes are classified according to the way they are applied. Acid dyes, in which the colour-producing component is part of a negatively-charged ion, are used for wool, silk, polyamide and acrylic fibres. Direct dyes, applied directly from a neutral aqueous bath, are used for cotton, rayon and other cellulose fibres. Both types are usually sulphonic acid salts. Vat dyes such as indigo (widely used for blue denim) are insoluble substances, usually containing ketone groups. Both vat dyes and sulphur dyes are applied to cellulosic fibres as an aqueous solution of a chemically-reduced form, and then oxidised to precipitate the insoluble dyestuff within the fibres.
Further information on dyes can be found at:
www.dylon.co.uk/flash.htm
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