Now, a chemical analysis of the painting shows that moisture is the main reason for the deterioration, while light plays only a minor role, Letizia Monico, a chemist at the Italian National Research Council in Perugia, and her colleagues report online May 15 in Science Advances.

Researchers analyzed microscopic flakes of paint from “The Scream” along with paint samples with similar chemical composition that were artificially aged in the lab.

X-ray probes of the paint samples revealed cadmium sulfate, a breakdown product of cadmium sulfide, in paint flecks from the painting. Cadmium sulfate also showed up in artificially aged paints that were exposed to at least 95 percent humidity in both light and darkness, but similar samples exposed to light in 45 percent humidity didn’t show signs of decay. This suggests that moisture is the main culprit in aging “The Scream,” and that although the painting may be fine under normal lighting, it should be kept at 45 percent humidity or below.

This new understanding of the artwork may inform the preservation of other paintings by Munch’s contemporaries, such as Matisse and van Gogh, which also contain decaying cadmium sulfide pigments. But Monico cautions that every painting is a unique, complex chemical landscape, so conservation strategies must be devised on a case-by-case basis.

— Science News magazine