Recently, some of yellows in Van Gogh’s paintings have turned to brown. Chemists using X-Ray machines discovered that a chemical is the root cause of the discoloration. They discovered the problem was two fold. First, Van Gogh added white to his yellow paint to create the bright lemon colored yellow that characterised many of his paintings. Second, the type of paint he used is contributing to the browning of the yellow. Back then, many artists used these lead-chromate paints. The Chemists actually obtained some of this old paint from a museum and they found that when they added white to the yellow and subjected it to ultra violet rays, the yellow paint quickly turned brown.