REDS
Alizarin, the colouring principle of madder, which can also be obtained from coal-tar, is employed in many colour combinations and gives a fine durable red. Hydrochloric acid changes it to violet. Carthamine and cochineal also produce good reds; the latter is turned orange by the action of hydrochloric acid.
Hydrochloric acid turns ammoniacal cochineal pink, but merely discolours the red made from archil. Direct extracts of red wood are unaffected by it.
The colouring matter of logwood, extracted by treating the powder obtained from an aqueous decoction of the wood with spirit, is sold as hematoxylin. Metallic salts convert it to a violet black, salts of tin change it to pink, alkalis to blue, and acids to yellow. Durable pinks are obtained directly from carthamine, the colouring matter of Carthamus Tinctorius.