Dyes

Dyes are materials of tremendous interest which absorbs strongly in the visible region. Some examples of natural dyes are Indigo and Tyrian purple. Nowadays many varieties of synthetic dyes are available in the market. Some examples of dyeing methods are vat dyeing, mordant dyeing, direct dyeing, disperse dyeing, ingrain dyeing etc. Vat dyes are insoluble in water. In vat dyeing, leuco base materials are exposed to air, which, on oxidation yields dye. This method is mainly used for indigo dyeing. Mordant dyes are comprised of an acidic group. In direct dyeing, dye solution is directly applied to the material to be dyed. This method is also known as substantive dyeing. Disperse dyeing is preferred for less polar and moderately polar fibers. In ingrain dyeing method, dye is formed on the fabric by chemical reaction between the reactants. If the fabric is soaked in the diazonium salt solution and later in an alkaline solution of phenol or amine, it will result in azo dye. Some other important dyes are anthraquinoid dye, phthalein dye, triphenylmethane dye and heterocyclic dye.