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 terracotta, the term we now use for basic unglazed 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. Most pottery produced in recent centuries has been glazed. Tiles are almost always glazed, and modern architectural terracotta is very often glazed architectural terra-cotta. Glazed brick is also common. Domestic sanitary ware is invariably glazed, as are many ceramics used in industry, for example ceramic insulators for overhead power lines. The most important groups of traditional glazes, named after their main ceramic fluxing agent, are: \n* Lead-glazed earthenware, is shiny and transparent after firing, which only needs about 800 °C (1,470 °F). Used for about 2,000 years around the Mediterranean, in Europe and China. Includes sancai and Victorian majolica. \n* Tin-glazed pottery, which coats the ware with an opaque white glaze. Known in the Ancient Near East and then important in Islamic pottery, from which it passed to Europe. Includes faience, maiolica, majolica and Delftware. \n* Salt-glazed ware, mostly European stoneware. It uses ordinary salt. \n* Ash glaze, important in East Asia, simply made from wood or plant ash, which contains potash and lime. \n* Feldspathic glazes of Asian porcelain. Modern materials technology has invented new vitreous glazes that do not fall into these traditional categories.

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