Amido Black 10B is a synthetic acid dye containing both NN and CC chromophore groups (pyrazolone dye). It is a dark red to black powder; soluble in water; used as a stain for protein-containings. Chemical designation is 4-Amino-5-hydroxy-3- [(4-nitrophenyl)azo]- 6-(phenylazo)- 2,7-Naphthalene disulfonic acid, disodium salt. Acid dyes are water-soluble dyes employed mostly in the form of sodium salts of the sulfonic or carboxylic acids. They are anionic which attach strongly to cationic groups in the fibre directly. They can be applicable to all kind of natural fibres like wool, cotton and silk as well as to synthetics like polyesters, acrylic and rayon. But they are not substantive to cellulosic fibres. They are also used in paints, inks, plastics and leather.