On several paintings by artists of the end of the 19th century and the beginning of the 20th Century a darkening of the original yellow areas, painted with the chrome yellow pigment (for the scientifically minded PbCrO₄, PbCrO₄·xPbSO₄, or PbCrO₄·xPbO) is observed. The most famous of these are the various Sunflowers paintings Vincent van Gogh made during his career.

Van Gogh’s sunflowers, made in the late 1880s, are known for their vibrant yellow colour, a vibrancy obtained with the use of this new paint, and now an iconic look.

Curators around the world have watched in dismay as that vivid yellow has faded to a muddy brown over the course of the last century. Now, the Journal of Analytical Chemistry reports that chemists have found out why: in the presence of sunlight, the chromium in the yellow paint reacts with the white pigment Van Gogh used to lighten it. There is a way to halt the process, which is to treat them like like medieval tapestries, and hang them in the cold and the dark!

The Boston Globe wryly observes,

It’s definitely sad that the paintings are fading. It’s strangely appropriate, too, though. Van Gogh’s sunflower paintings are about the life cycle: they show, gathered in the same vase, bright yellow sunflowers in the prime of life, and drooping, withered ones in its twilight. The sun is now fading the painted sunflowers, just as it faded the real ones. Van Gogh’s sunflowers are growing older in a way that intensifies and even embodies what they’re all about. In a way, the paintings are becoming more themselves.