X rays used to study pigment degradation in Van Gogh painting

BBC : Yellow pigment used by Vincent Van Gogh in his painting Flowers in a Blue Vase has reacted with a layer of varnish, causing the once brilliant hue to turn gray and crack. Although Van Gogh never varnished his paintings, art dealers and others often did so after he died. Researchers used x rays created by particle accelerators to examine the atoms and molecules of the original paint, the varnish, and the micrometer-thin interface layer between the two. Flowers in a Blue Vase differs from many of Van Gogh’s other works in that he used cadmium yellow pigment rather than his usual chrome yellow. The researchers were surprised to find that the discoloration was due to the cadmium forming oxalates in the varnishâmdash;this is the first time that effect has ever been seen. Because some of the paint has found its way into the varnish, conservators are reluctant to remove the varnish and must find other ways to conserve the painting.