Lake pigment

A lake pigment is a pigment manufactured by precipitating a dye with an inert binder, or "mordant", usually a metallic salt. Unlike vermilion, ultramarine, and other pigments made from ground minerals, lake pigments are organic. Manufacturers and suppliers to artists and industry frequently omit the lake designation in the name. Many lake pigments are fugitive because the dyes involved are not lightfast. Red lakes were particularly important in Renaissance and Baroque paintings; they were often used as translucent glazes to portray the colors of rich fabrics and draperies.

This sense of lake is unconnected with lake meaning body of water; it derives from the word lac (referring to a resinous secretion). It has the same root as the word lacquer, and comes originally from the Hindi word lakh, through the Arabic word lakk and the Persian word lak.

Many lake pigments are azo dyes. They characteristically have sulfonate and sometimes carboxylate substituents, which confer negative charge to the chromophore (colored species).

The metallic salt or binder used must be inert and insoluble in the vehicle, and it must be colourless or very neutral. The organic component of the dye determines which wavelengths are absorbed and reflected by the resulting precipitate. In ancient times chalk, white clay, and crushed bones were used as sources of the calcium salts. The salts that are commonly used today include barium sulfate, calcium sulfate, aluminium hydroxide, and aluminium oxide (alumina), all of which can be produced cheaply from inexpensive mineral ores.

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