Aluminum oxide

A white, hard, insoluble powder that naturally occurs in some feldspars, alumina trihydrate, corundum, gibbsite, bauxite, ruby, and sapphire. It is used for abrasives, refractories, electrical insulation, high temperature crucibles, dental restoration, filler for paints, glass, and ceramics. When added to glaze mixtures, aluminum oxide increases viscosity during firing, prevents devitrification during cooling and adds durability to the final surface.