A lake pigment is a pigment made by precipitating a dye with an inertbinder, 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.
Etymology
The term "lake" is derived from the term lac, the secretions of the Indian wood insect Laccifer lacca. It has the same root as the wordlacquer, and comes originally from the Hindi word lakh, through the Arabic word lakk and the Persian word lak.
Chemistry
Many lake pigments are azo dyes. They characteristically have sulfonate and sometimes carboxylate substituents, which confer negative charge to the chromophore. The metallic salts or binders used are typically colourless or almost so. The organic component of the dye determines the color of the resulting precipitate. In ancient timeschalk, white clay, and crushed bones were used as sources of the calcium salts. Today metallic salts are typically chromium or cobalt, and the resulting lake pigment is diluted with an inert materials such as alumina.
History and art
Lake pigments have a long history in decoration and the arts. Some have been produced for thousands of years and traded over long distances. The red lakes were particularly important in the history of art; because they were translucent, they were often used in layers of glazes over a more opaque red to create a deep, rich red color. They are common in paintings by Venetian artists of the 16th century, including Titian, to depict fine draperies and fabrics.
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.
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.
