Photograph by Carl Tremblay

My snodgrass displays a blob of material, slightly smaller than a tennis ball, with a fissure that reveals a vivid golden-yellow interior. It is a lump of dried urine from a cow fed mango leaves ages ago in India for the purpose of coloring its urine, which when dried became the pigment called Indian yellow, frequently seen in Indian miniature paintings. The method of producing the pigment was introduced into India, probably from Persia, in the fifteenth century; the British banned it in 1908 because a diet of mango leaves eventually killed the cow.

This sample of a traditional pigment is part of the artists' materials collection at the Straus Center for Conservation, atop the Fogg and Busch-Reisinger Museums. It is of both scholarly and practical value. The scholarly interest derives simply from knowing how artists of earlier eras obtained their results, says Snodgrass, associate conservation scientist at the center. The chunk's practical value is that, through spectroscopic analysis of its color, conservators know how to replicate Indian yellow with modern pigments when it appears in old art works they are restoring, or spot fakes made with pigments of implausible chemical provenance.

Edward Waldo Forbes, director of the Fogg from 1909 to 1944, amassed 2,000 samples of pigments made by traditional methods in all parts of the world. Most of the pigments are powders stored in vials, as shown in the photograph. Rutherford Gettens, a chemist affiliated with the Fogg, made a complementary collection in the 1930s. He had colors painted out on 2,700 test blocks, each color applied in oil, size, and other binders (see photograph). Then he popped the blocks into the oven, or put them on the roof, or exposed them to sundry gases to see how the colors held up. The passage of 60 years has provided further useful evidence of the colors' permanence, or lack thereof. These collections are prized by conservators worldwide. The very modern Straus Conservation Center is the place to go if one wants to scrutinize the color of the past.

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