Glaze is a layer or coating used on pottery or ceramics. It may be called vitreous enamel or porcelain enamel. Powdered glass is fused onto ceramics by firing to between 750 and 850 °C (1,380 and 1,560 °F). The powder melts, flows, and then hardens to a smooth, lasting vitreous coating on metal, or on glass or ceramics. This is done in a kiln. 