Van Gogh doomed his sunflowers by adding white pigments to yellow paint

When Vincent van Gogh moved to the south of France in the late 1880s, he began to paint sunflowers in vibrant chrome yellow. But even before his untimely death, some of his paintings had lost their sheen and started to turn brown.

The researchers found that sunlight kicks off a chemical reaction that ultimately turns yellow paint brown. The sunlight oxidises the oil in the paint, releasing electrons. These are then taken up by the yellow pigment – lead chromate – turning it green. The mix of green paint with oxidised oil produces a chocolate brown colour.

The team led by Koen Janssens at the University of Antwerp took samples of yellow chrome paint from left-over tubes belonging to 19th century artists. To simulate the effects of sunlight, they exposed them to UV light. After three weeks, paint from one of the artists, the Flemish Fauvist, Rik Wouters, had transformed from bright yellow to deep brown.

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