alizarin

alizarin, a red dye originally obtained from the root of the common madder plant, Rubia tinctorum, in which it occurs combined with the sugars xylose and glucose. The cultivation of madder and the use of its ground root for dyeing by the complicated Turkey red process were known in ancient India, Persia, and Egypt; the use spread to Asia Minor about the 10th century and was introduced into Europe in the 13th.

Laboratory methods of preparing alizarin from anthraquinone were discovered in 1868, and, upon commercial introduction of the synthetic dye in 1871, the natural product disappeared from the market for textile dyes, though natural rose madder is still occasionally used, as a lake, for artists’ colours. The application of alizarin to cotton, wool, or silk requires prior impregnation of the fibre with a metal oxide, or mordant. The shade produced depends on the metal present: aluminum yields a red; iron, a violet; and chromium, a brownish red.