Last year, conservators at the Van Gogh Museum in Amsterdam noticed that areas of bright yellow paint in many of the artist’s works, such as Sunflowers, were turning shades of green and brown. To find out why, they teamed up with scientists at the University of Antwerp in Belgium.
Online news reports claimed that the scientists found prolonged exposure to LED lights to be the cause of the darkening. That conclusion, however, is inaccurate. “This was not a study into the effects of LED lighting,” says Ella Hendriks, a senior conservator at the Van Gogh Museum. “It was a study on the aging process of the yellow pigment.”
Lead by Koen Janssens, the Antwerp researchers tested samples of the browning paint and identified it as chrome yellow. Janssens and his team then found that exposure to light caused samples of chrome yellow to darken. Lighter shades of the pigment, he explained, darkened quickly because they contain a high amount of sulfur, which makes them more susceptible to chemical reactions. Dark shades of chrome yellow contain little sulfur, and were less effected by light.
The darkening of the paint is permanent, says Janssens, and “to reverse this chemical reaction would likely cause more damage to the paintings.” But the study did not isolate which band of light caused the browning or attribute it solely to LED bulbs.
This information is still of use to museums. As institutions phase out halogen and incandescent lighting in favor of energy-efficient alternatives like LED bulbs, they need to understand the possible effects these lights will have on artworks. “Like other museums, we are considering the switch to LED lighting,” says Hendriks. “We will certainly take this information on board with us when making a final decision.”