Scientists using a high-energy X-ray instrument say they have solved the long-running debate over what kind of paint Picasso used in his masterpieces.

It was common house paint, said Volker Rose, a physicist at the Argonne National Laboratory who led the study, published in Applied Physics A: Materials Science & Processing.

“We were looking into pigments taken from Picasso’s white paint, which from a material perspective is zinc oxide, and we were able to study the impurities that are there,” Dr. Rose said.

The scientists also bought samples of decades-old house paint on eBay. After comparing those samples with Picasso’s paint, they determined that the two shared the same chemical makeup.