Indulines are a series of dyestuffs of blue, bluish-red or black shades, formed by the interaction of para-amino azo compounds with primary monoamines in the presence of a small quantity of a mineral acid. They were first discovered in 1863 by J. Dale and H. Caro, and since then have been examined by many chemists. They're derivatives of the eurhodines (aminophenazines, aminonaphthophenazines), and by means of their diazo derivatives can be de-amidated, yielding in this way azonium salts; conseq… (More on Indulines)