Glaze
Ceramic glaze raw materials generally include silica, which will be the main glass former. Various metal oxides, such as sodium, potassium and calcium, act as a flux to lower the melting temperature. Alumina, often derived from clay, stiffens the molten glaze to prevent it from running off the piece. Colour comes from iron oxide, copper carbonate or cobalt carbonate. Tin oxide or zirconium oxide, are used to make the glaze opaque.