Although barium sulfate is almost completely inert, zinc sulfide degrades upon exposure to UV light, leading to darkening of the pigment. The severity of this UV reaction is dependent on a combination of two factors; how much zinc sulfide makes up the pigments formulation, and its total accumulated UV exposure. Depending on these factors the pigment itself can vary in shade over time, ranging from pure white all the way to grey or even black. To suppress this effect, a dopant may be used, such as a small amount of cobalt salts, which would be added to the formulation. This process creates cobalt-doped zinc sulfide. The cobalt salts help to stabilize zinc sulfide so it will not have as severe a reaction to UV exposure.
Fluorine Chemical, Lithopone 30% CAS No. 1345-05-7, white powder, relative density: 4.136 ~ 4.39 g / mL, insoluble in water. It is a mixture of zinc sulfide and barium sulfate. Inorganic white pigment, widely used in plastics such as polyolefin, vinyl resin, ABS resin, polystyrene, polycarbonate, nylon and polyoxymethylene, and white pigments of paints and inks. It is less effective in polyurethane and amino resins and less suitable in fluoroplastics. It is also used for coloring of rubber products, paper, varnish, tarpaulin, leather, watercolor paint, paper, enamel, and the like. Used as a binder in the production of electric beads.