Vincent van Gogh is famous for his use of bright chrome yellow colors, a class of compounds consisting of lead, chromium and oxygen. But that unique mixture has changed over time, according to results of a detailed spectroscopic investigation of van Gogh’s Sunflowers painting at the Van Gogh Museum in Amsterdam.

“There are different shades of the pigment, and not all of them are photochemically stable over time. Lighter chrome yellow has sulphur mixed into it, and is susceptible to chemical degradation when exposed to light, which leads to a darkening of the pigment,” said Letizia Monico from the Institute of Molecular Science and Technology.

The scientists also identified parts of the painting that should be monitored particularly closely for possible changes.

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Image Above: Sunflowers, 1889, Vincent van Gogh (1853-1890). Credit: Van Gogh Museum, Amsterdam (Vincent van Gogh Foundation)