Definition: 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.