Chrome yellow (lead chromate) was discovered in 1809 and immediately became the brightest, most opaque yellow available. It dominated painting throughout the 19th century — until artists noticed it was turning green.

Chrome yellow was the most exciting yellow of the 19th century — intense, opaque, and cheap. Its eventual greening is now an art conservation tragedy visible in dozens of major works.

Van Gogh used chrome yellow extensively in his sunflower paintings. Conservators have discovered through X-ray fluorescence that many of his yellow passages are slowly turning grey-green as the lead chromate converts. This process cannot be reversed, meaning Van Gogh's sunflowers will never look as he painted them.