Gold Reds

Many organic substances added to gold solutions throw down either the

metallic gold or the red oxide, which then unites with the organic

compound more or less decomposed and forms a red precipitate. Sugar,

gum, the decoctions of cochineal, gamboge, fustic, turmeric, sumach,

catechu, and Brazil wood, all afford red pulverulent colours. Boiled

with sugar, gold solution gives first a light and then a dark red.

Whatever their merits, the excessive costliness of these preparations

renders them inadmissible as pigments. At one time, indeed, a gold

compound known as purple of Cassius was so employed, but this soon

became obsolete on the introduction of madder purple.

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