If you've noticed your favorite Van Goghs getting darker, it's not because you've caught the troubled Dutch painter's depression. Some of the master Post-Impressionist's late images, which he painted in the South of France, have succumbed to a chemical reaction called reduction, dulling some bright pigments and alarming preservationists worldwide.
To create his trademark pale golds, Van Gogh mixed the bright yellow lead chromate pigment with the white lead sulphate, creating a combination that was subtler than the pure yellow but susceptible to a reaction that creates viridian, a darker shade of spring green. Reuters reports that scientists from four countries have been assembled to develop techniques for preserving the pigments, lest some of the Dutch painter's most joyful images darken into more depressed tones. See more in the video below: