A glaze is a glassy coating applied to ceramics and fused to the surface by firing in a kiln. Glazes make porous earthenware watertight, provide a smooth and hygienic surface, and add colour, sheen and decoration. They are made from silica combined with fluxes and other materials, and are applied by dipping, pouring, brushing or spraying, or in the case of salt glaze, by introducing salt into the hot kiln.
Different types of glaze characterise particular traditions: clear lead glazes on English earthenware and slipware, opaque white tin glazes on delftware and maiolica, salt glazes with an orange-peel texture on stoneware, celadon and monochrome glazes on Chinese ceramics, and the dramatic flambé, crystalline and lustre glazes of art pottery. Colour comes from metallic oxides, and decoration may be painted under or over the glaze. Over time, glazes can develop fine networks of cracks called crazing, which may be a sign of age, though it can also be deliberate. Glaze texture, colour and wear are useful clues when identifying and dating ceramics.
