Zinc oxide pigment can cause discoloration of paper in its vicinity when the pigment is illuminated. In a photochemical reaction, water vapor and oxygen in the atmosphere combine in the presence of zinc oxide to form hydrogen peroxide. The peroxide may attack the paper support, eventually causing discoloration. Two examples of this type of discoloration were studied by x-ray diffraction and x-ray fluorescence analysis. It was shown that the areas of most discoloration on backing boards correspond to areas of high zinc oxide concentration on the associated prints.