Vincent van Gogh's paintings of sunflowers aren't as vivid as they used to be and the sun is to blame, say researchers who have solved a problem that has long stumped art conservationists. A team of chemists experimenting with ultraviolet light and tubes of paint belonging to 19th-century artists found that by mixing in white paint to make his yellows brighter, van Gogh doomed his sunflowers to turn brown over time, the Guardian reports.
"While he wanted to show a light, pale and delicate yellow, it instead becomes a darker, brownish yellow" after sunlight kicks off a chemical reaction, the lead researcher explains. To preserve van Gogh's masterpieces and other works from the same era, he says, conservationists will need to keep the paintings cool in summer—and away from sunlight. "This type of cutting-edge research is crucial to advance our understanding of how paintings age and should be conserved for future generations," an official at Amsterdam's van Gogh Museum tells LiveScience. (Read more Vincent Van Gogh stories.)