The blue print process involve the use of iron compound.

This is coupling reaction in which benzene diazonium chloride react with phenol or aromatic amine to give dyes.

A mordant is any substance which can be fixed to the fibre and which can be dyed later on mostly hydroxide or basic salts of chromium aluminium and iron are used as mordant. A dye which imparts different colours in the presence of different mordant is referred to as a mordant dye. For ex. alizarin is a mordant dye when mordanted with aluminium salt solution. It imparts rose red colour to fabric but the same fabric is dyed blue when it is mordanted with barium salt and it dyes violet is mordant with Ferric salt.

Direct dyes stick to the fibre through hydrogen bonding. They belong to the class of azo dyes. They are used to dye the fabric directly by placing it in not aqueous solution of dye e.g. martius yellow, Congored etc.

Basic dyes contain NH2 or –NR2 groups as colour bearing group or colour enhancing groups they are generally used for Wool, cotton, leather, paper, polyester, nylon etc. e.g. aniline yellow, crysodine G, butter yellow, malachite green etc.

Direct dyes stick to the fibre through hydrogen bonding. They belong to the class of azo dyes. They are used to dye the fabric directly by placing it in not aqueous solution of dye e.g. martius yellow, Congored etc.

Disperse dye are usually applied in the form of dispersion of finely divided dye in a soap solution in the presence of Phenol, Cresol, Benzoic acid etc. They are mainly used to dye decron, nylon, synthetic fibre. Example Celliton (blue).

Malachite green prepared by the condensation of Benzaldehyde and dimethyl aniline.

Fluorescin is obtained by the reaction of Phthalic anhydride and resorcinol.

It has red crystal soluble in alkalies and the solution imparts red colour to fabrics