a characteristic green light when heated at high temperature, barium salts are often used in green pyrotechnic formulas, although nitrate and chlorate salts are more common. Barium sulfate is commonly used as a component of "strobe" pyrotechnic compositions. Copper industry As barium sulfate has a high melting point and is insoluble in water, it is used as a release material in casting of copper anode plates. The anode plates are cast in copper molds, so to avoid the direct contact of the liquid copper with the solid copper mold, a suspension of fine barium sulfate powder in water is used as a coating on the mold surface. Thus, when the molten copper solidifies in form of an anode plate it can be easily released from its mold. Radiometric measurements Barium sulfate is sometimes used (or else PTFE) to coat the interior of integrating spheres due to the high reflectance of the material and near Lambertian characteristics. Production Almost all of the barium consumed commercially is obtained from barite, which is often highly impure. Barite is processed by thermo-chemical sulfate reduction (TSR), also known as carbothermal reduction (heating with coke) to give barium sulfide: BaSO4 + 4 C → BaS + 4 CO In contrast to barium sulfate, barium sulfide is soluble in water and readily converted to the oxide, carbonate, and halides. To produce highly pure barium sulfate, the sulfide or chloride is treated with sulfuric acid or sulfate salts: BaS + H2SO4 → BaSO4 + H2S Barium sulfate produced in this way is often called , which is French for "permanent white". Blanc fixe is the form of barium encountered in consumer products, such as paints. In the laboratory barium sulfate is generated by combining solutions of barium ions and sulfate salts. Because barium sulfate is the least toxic salt of barium due to its insolubility, wastes containing barium salts are sometimes treated with sodium sulfate to immobilize (detoxify) the barium. Barium sulfate is one of the most insoluble salts of sulfate. Its low solubility is exploited in qualitative inorganic analysis as a test for Ba2+ ions, as well as for sulfate. Untreated raw materials such as natural baryte formed under hydrothermal conditions may contain many impurities, a.o., quartz, or even amorphous silica. History Barium sulfate is reduced to barium sulfide by carbon. The accidental discovery of this conversion many centuries ago led to the discovery of the first