Sunflowers, 1888

The case of Van Gogh’s browning sunflowers has been solved and a reduction reaction is being branded as the culprit! Through sharp detective work by a team at Antwerp University in Belgium it was deduced that a reduction of Chromium (IV) to Chromium (III) is responsible for color changes in several of the artist’s most famous works. 

Chrome yellow paint, a toxic substance thought by many to be the cause of the madness that ultimately drove Vincent Van Gogh to cut off his own ear, was the yellow paint of choice for many artists in the late 19th century. Though it has been known for some time that this color pigment darkens upon UV and sunlight exposure, scientists were puzzled at the fact that not all paintings containing the chrome yellow pigment were affected. Few additional clues were known as to the underlying cause of this phenomenon until the Antwerp team published the results of their study in the 15th of February 2011 issue of Analytical Chemistry.

By means of state-of-the-art x-ray analysis the Antwerp team identified the reduction reaction in a sample of chrome yellow that had been artificially aged using UV light. The microscopic x-ray beam not only revealed a nanometer thin coating of Chromium (III) on the pigment, but also suggested that the compound was especially conspicuous in samples that contained Barium and Sulfur. This newfound evidence indicated that white paint was responsible for accelerating the browning process when mixed with the chrome yellow pigment that Van Gogh was so fond of.

It is the hope of the Antwerp team that cracking this historic whodunit case will assist in the effort to return the degraded paintings back to their original state. Sherlock Holmes would surely be pea-green with envy over the bottomless bag of technological tricks available to modern day scientists.