Barium sulfate can be used as a pigment , too . Taking advantage of its opacity to X-rays , the sulfate is used as a radiocontrast agent for X-ray imaging of the digestive system ( `` barium meals '' and `` barium enemas '' ) . Lithopone , a pigment that contains barium sulfate and zinc sulfide , is a permanent white that has good covering power , and does not darken when exposed to sulfides .