Lake pigment

A lake pigment is a pigment manufactured by precipitating a dye with an inert binder, usually a metallic salt. The word lake is a homonym of lake as body of water and does not refer to it.

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 unstable when exposed to light.

Chemistry

The metallic salt or binder used must be inert and insoluble in the vehicle, and it must be white or very neutral. It must have low tinting strength so that the dye itself determines which wavelengths are absorbed and reflected by the resulting precipitate. In ancient times chalk, white clay, and crushed bones were used, being sources of calcium carbonate and calcium phosphate. 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.

History and types

Lake pigments have a long history in decoration and the arts. Some have been produced for thousands of years and traded over long distances.

• Indigo lake was originally produced from the leaves of woad, and was known in ancient Egypt. In the late Middle Ages, a fashion for woad as a textile dye led to overplanting and soil exhaustion in many parts of Europe. After trade routes opened to the east, indigo was imported from India as a substitute for woad, and the cultivation of woad became uneconomical in Europe. Today, the dark blue dye known as indigo once produced from woad and Indigofera tinctoria is largely of synthetic origin. The dye and pigment are both fugitive.^[1]

• Rose madder lake, originally from the root of the madder plant, is also known as alizarin crimson in its synthetic form. Since rose madder is fugitive when exposed to light, its use has been largely superseded, even in synthetic form, by quinacridone pigments.

• Carmine lake was originally produced from the cochineal insect, native to Central and South America. It is also called crimson lake. When the Spanish conquered the Aztec Empire (1518-1521), they encountered Aztec warriors garbed in an unknown crimson color. Cochineal became their second most valuable export from the New World, after silver, and the Spanish zealously guarded the secret of its production for centuries.^[2] Carminic acid, the organic compound which gives carmine its color, was synthesized in 1991.

Indigo and rose madder are now produced more cheaply from synthetic sources, although some use of natural products persists, especially among artisans. The food and cosmetics industries have shown renewed interest in cochineal as a source of natural red dye.

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