Chrome yellow is a bright, warm yellow pigment that has been used in art, fashion, and industry. It is the premier orange pigment for many applications.
Production of chrome yellow and related pigments
The raw pigment precipitates as a fine solid upon mixing
lead(II) salts and a source of
chromate. Approximately 90,000 tons of chrome yellow are produced annually as of 2001.
[
]
Chrome yellow pigments are usually encapsulated by coating with transparent oxides that protect the pigment from environmental factors that would diminish their colorant properties.
Related lead sulfochromate pigments are produced by the replacement of some chromate by sulfate, resulting in a mixed lead-chromate-sulfate compositions Pb(CrO4)1-x(SO4)x. This replacement is possible because sulfate and chromate are isostructural. Since sulfate is colorless, sulfochromates with high values of x are less intensely colored than lead chromate.
Permanence
Chrome yellow is moderately resistant to fading from exposure to light when it is chemically pure. Observations have found that over time though, it begins to darken and suffer discoloration by turning brown. This degradation is seen in some of Van Gogh's pieces.
The pigment tends to react with hydrogen sulfide and darken on exposure to air over time, forming lead sulfide,
Notable occurrences
Vincent van Gogh used chrome yellow in many of his paintings, including his famous Sunflowers series. Studies focusing on the techniques used in Van Gogh's Sunflowers series have revealed how Van Gogh skillfully mixed various shades of chrome yellow to achieve different effects.
History
The pigment is derived from lead chromate, a chemical compound that was first synthesized in the early 1800s. The discovery of lead chromate, the primary component of chrome yellow, is credited to the French chemist Louis Nicolas Vauquelin. Vauquelin was studying the mineral crocoite, a natural form of lead chromate, when he identified the presence of a new element, chromium. The discovery led to the synthesis of a variety of new pigments, including chrome yellow.[
]
Safety
Because it contains not only lead but hexavalent chromium, chrome yellow has long been the focus on safety concerns. Its use is highly regulated. Its former use as a food colorant has long been discontinued. The continued wide use of this pigment is attributed to its very low solubility, which suppresses leaching of chromate and lead into biological fluids. The LD50 for rats is 5 g/kg.[
]
See also
-
List of colors
-
List of inorganic pigments
Further reading
-
Kühn, H. and Curran, M., Chrome Yellow and Other Chromate Pigments, in Artists’ Pigments. A Handbook of Their History and Characteristics, Vol. 1, L. Feller, Ed., Cambridge University Press, London 1986
External links
