Pigment made by precipitating a dye with an inert binder, or mordant
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.[1] 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.[2]
Etymology
The term lake is derived from the term
lac, the secretions of the Indian wood insect Kerria lacca (formerly Laccifer lacca or Coccus lacca).[3][4] 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.[5]
Chemistry
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 salts or binders used are typically colourless or almost so.[1] The organic component of the dye determines the color of the resulting
precipitate. In ancient times
chalk, 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 material 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 (sometimes the mineral-based pigment vermilion, or sometimes a red lake mixed with lead white or vermilion) 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.[2]
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.
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, also called crimson lake, was originally produced from the
cochineal insect, native to
Central and
South America. 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.[6]Carminic acid, the
organic compound which gives carmine its color, was
synthesized in 1991.[7] Researchers are now examining the potential to genetically engineer microbes to produce carminic acid.[8]
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.[8]
References
^
abK. Hunger. W. Herbst "Pigments, Organic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2012.
doi:
10.1002/14356007.a20_371
^
abDavid Bomford and Ashok Roy, A Closer Look - Colour, National Gallery Company, p. 41.
^Allevi, P.; et al. (1991). "The 1st Total Synthesis of Carminic Acid". Journal of the Chemical Society, Chemical Communications. 18 (18): 1319–1320.
doi:
10.1039/c39910001319.