Imagine Van Gogh’s paintings of yellow sunflowers. Now imagine the flowers brown. Eh, not so good. Sadly, we may someday see what that would look like. Because the bright yellow paints on the canvas are slowly turning muddy. Now, an international team of scientists has ___1___ the chemical reaction that ___2___—the first step toward stopping it. Their findings appear in the journal Analytical Chemistry.
Van Gogh’s use of strong bright colors to convey mood and emotion ___3___ in art history. And his Sunflower series wouldn’t be the same without the vibrant “chrome yellow” pigment that was new at the time. But ___4___.

To find out why, researchers used sophisticated x-ray analyses to determine the exact chemical composition of the paint as it browns. First, they exposed three tubes of chrome yellow to UV radiation until one turned a chocolate color. Analyzing that sample, they identified specific changes in the paint’s chromium compounds. They then found the same chemical signature in the darkened areas of two van Gogh paintings. Until a chemical ___5___ is found, the researchers have some ironic advice: keep sunlight away from van Gogh’s sunflowers.
【視聽版科學(xué)小組榮譽(yù)出品】