Azoic dyes are pigments that are synthesized inside the fiber by coupling of two components neither of which is a dye itself. The two components are an aromatic diazonium salt and an aromatic compound, often a naphthol. Because of the use of naphthol as a compound as a component in the reaction , this class is sometimes called the “naphthol dyes”. Although the colored material produced in azoic are classified as dyes because the naphthol component has affinity for cellulose and is applied like a dye before the diazo component is added. The greatest advantage of azoic dyes is that they provided an economical way to obtain certain shades, especially red. The greatest limitation of azoic dyes is that they sometimes possess poor fastness to crocking.

Reactive dyes are relatively new, having been developed in the 1950s. They are sometimes called “fiber reavtive dyes”. As the name implies the reactive dyes chemically react with the fiber forming covalent bones. Since the covalent bonds between the dye and the fiber are strong , reactive dyes have excellent washfastness . Outstanding wash fastness is the greastest, but by no means the only , advantage of reactive dyes. Limitations of reactive dyes include higher cost than some other class.

vat dyes are like sulphur dyes in that they are pigments which must be reduced and oxidized during application. However , the similarity between sulphur and vat dyes ends there. Vat dyes have outstanding washfastness and lightfastness as a class. An exception to this rule is the vat dye indigo which has very poor washfastness. The biggest disadvantage of vat dyes is their relatively high cost.

disperse dyes are used mostly for polyester , nylon, and cellulose acetate although they will dye some other fibers. The name disperse dye comes from the fact that these dyes are almost insoluble in water and have to be dispersed in water to make the dyebath. Disperse dyes were developed when cellulose acetate was first marketed. Disperse dyes are the only acceptable dye class for acetate and unmodified polyester fibers.

       Jet Dyeing

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