Ceramic glaze is an impervious layer or coating of a vitreous substance which has been fused to a ceramic body through firing. Glaze can serve to color, decorate or waterproof an item. Glazing renders earthenware vessels suitable for holding liquids, sealing the inherent porosity of unglazed biscuit earthenware. It also gives a tougher surface. Glaze is also used on stoneware and porcelain. In addition to their functionality, glazes can form a variety of surface finishes, including degrees of glossy or matte finish and color. Glazes may also enhance the underlying design or texture either unmodified or inscribed, carved or painted.
The most important groups of traditional glazes, each named after its main ceramic fluxing agent, are:
- Ash glaze, important in East Asia, simply made from wood or plant ash, which contains potash and lime.
- Feldspathic glazes of porcelain.
- Lead glazes, plain or coloured, are shiny and transparent after firing, which need only about 800 °C (1,470 °F). They have been used for about 2,000 years in China e.g. sancai, around the Mediterranean, and in Europe e.g. Victorian majolica.
- Salt-glaze, mostly European stoneware. It uses ordinary salt.
- Tin-glaze, which coats the ware with lead glaze made opaque white by the addition of tin. Known in the Ancient Near East and then important in Islamic pottery, from which it passed to Europe. Includes Hispano-Moresque ware, Italian Renaissance maiolica (also called majolica), faience, and Delftware.