Litharge consists of the monoxide of lead, PbO, and is formed by heating lead in air. It has a yellow colour, and if melted and slowly cooled forms a fine crystalline mass. By more careful cooling crystals of the form of rhombic octahedra may be obtained. It also occurs native in some Mexican localities. It is largely employed in the manufacture of flint glass, as a glaze for earthenware, in the production of red-lead, white-lead, and of most of the lead compounds or preparations.