Lithopone, C.I. Pigment White 5, is a mixture of inorganic compounds, widely used as a white pigment powder. It is composed of a mixture of barium sulfate and zinc sulfide. These insoluble compounds blend well with organic compounds and confer opacity. It was made popular by the cheap production costs, greater coverage. Related white pigments include titanium dioxide, zinc oxide ("zinc white"), zinc sulfide, and white lead. The material came in different "seals", which varied in the content of zinc sulfide. Gold seal and Bronze seals contain 40-50% zinc sulfide, offering more hiding power and strength. Although its popularity peaked around 1920, approximately 223,352 tons were produced in 1990. It is mainly used in paints, putty, and in plastics.
Barium sulfide is produced by carbothermic reduction of barium sulfate. Zinc sulfate is obtained from a variety of zinc products, often waste, by treatment with sulfuric acid.
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John L. Mitchell created this method of calcination for production of lithopone in 1918 in hopes of increasing the quality of lithopone while reducing and controlling the formation of zinc oxide waste. Calcining is a thermal treatment process applied a solid material in order to cause thermal decomposition at below the melting point of the product. It begins with a zinc sulfate solution made by the reaction of sulfuric acid and zinc oxide then compressed to obtain the solution. A precipitation of raw materials: barium sulfide and zinc sulfate is dried then thoroughly grounded. The powder is then placed in an airtight furnace and heated from 200 to 950°C. The key is the lack of oxygen preventing the formation of zinc oxide from the desired zinc sulfide therefore maintaining the density and purity of lithopone