The artist used a light-sensitive yellow paint that slowly turns brown under light.

Source: LEX VAN LIESHOUT/AFP/Getty Images/Artnet

Van Gogh’s series of paintings depicting sunflowers are gradually fading: yellow paints are progressively withering to an olive-brown colour because the artist used light-sensitive pigments. The news came from Belgian and Dutch researchers who have been studying the phenomenon for two years.

A team of researchers at the University of Antwerp and the Delft University of Technology have studied an 1889 painting from the collection of Amsterdam’s Van Gogh Museum. They found that a chrome yellow paint made some works susceptible to discolouration.

“Van Gogh used two types of chrome yellow, which is a synthetic pigment that was widely available at the time,” expert Frederik Vanmeert at the University of Antwerp told Artnet. “One of these types of chrome yellow is quite stable because it has an orange hue, but the other type, which has a pale yellow color, is quite sensitive to degradation, so it will alter its color over time.”

The researchers used microscopic x-ray imaging and chemical mapping techniques to examine the paint without taking swabs or pigment samples, the Guardian reports.

According to Vanmeert, the research can be applied to works by other 19th century artists as many of them used the same paints: “The exact number is not known, but [the problematic pigment] is a type of yellow Van Gogh frequently employed, so it will be present in a large number of his paintings, and is also presumed to be present in the paintings of a large number of his contemporaries.”

The Van Gogh Museum closely follows the research and works to protect artworks from further discolouration. Five years ago, the museum lowered the light levels in its galleries. Now, curators and conservators review the lightening system again.

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