Titanium dioxide

Titanium dioxide is a white powder made of titanium and oxygen. It's the most widely used white pigment, found in paint, paper, plastics, sunscreen and toothpaste. Its secret is a very high refractive index: it bends light more strongly than diamond, so each tiny grain scatters light in every direction.

Titanium is mined in minerals like ilmenite and rutile, where it's already bonded to oxygen but mixed with iron and other impurities. Factories purify it by one of two routes. In the chloride process, the ore is heated with chlorine and coke to make liquid titanium tetrachloride, which is distilled clean and then burned with oxygen to give fresh, pure TiO₂. In the older sulfate process, the ore is dissolved in sulfuric acid, the iron is removed, and titanium dioxide is precipitated and roasted. The grain size is carefully controlled, because grains about a quarter of a micrometer across scatter visible light best.

In a TV, it makes the reflector sheet brilliant white, helping send stray light back toward the screen. Heated with barium carbonate, it becomes barium titanate, the material inside ceramic capacitors.