A pigment obtained, usually by roasting cobalt glance with
   sand or quartz, as a dark earthy powder. It consists of crude cobalt
   oxide, or of an impure cobalt arseniate. It is used in porcelain
   painting, and in enameling pottery, to produce a blue color, and is
   often confounded with smalt, from which, however, it is distinct, as it
   contains no potash. The name is often loosely applied to mixtures of
   zaffer proper with silica, or oxides of iron, manganese, etc.