Gres (palabra proveniente del francés grès, arenisca) es el término genérico que designa una pasta cerámica, formada por arcillas, materiales desgrasantes, como el sílice y fundentes, como el feldespato. Sus principales características son su dureza y su baja absorción de agua una vez cocido a su temperatura de sinterización vítrea. El rango de cocción oscila desde los 1200°C a los 1300°C, dependiendo de su composición química. Con el gres se pueden fabricar una cierta variedad de productos como sanitarios, tuberías de saneamiento, vajillas, alfarería entre otros, pero sin duda el mayor campo de aplicación es la producción de pavimentos y revestimientos de baldosas.

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Stoneware is a rather broad term for pottery or other ceramics fired at a relatively high temperature. A modern technical definition is a vitreous or semi-vitreous ceramic made primarily from stoneware clay or non-refractory fire clay. Whether vitrified or not, it is nonporous (does not soak up liquids); it may or may not be glazed. Historically, across the world, it has usually been developed after earthenware and before porcelain, and has often been used for high-quality as well as utilitarian wares. Stoneware is not recognised as a category in traditional East Asian terminology, and much Asian stoneware, such as Chinese Ding ware for example, is counted as porcelain by local definitions. Terms such as "porcellaneous" or "near-porcelain" may be used in such cases. One widely recognised definition of stoneware is from the Combined Nomenclature of the European Communities, a European industry standard. It states: "Stoneware, which, though dense, impermeable and hard enough to resist scratching by a steel point, differs from porcelain because it is more opaque, and normally only partially vitrified. It may be vitreous or semi-vitreous. It is usually coloured grey or brownish because of impurities in the clay used for its manufacture, and is normally glazed." Five basic categories of stoneware have been suggested: \n* Traditional stoneware - a dense and inexpensive body. It is opaque, can be of any colour and breaks with a conchoidal or stony fracture. Traditionally made of fine-grained secondary, plastic clays which can used to shape very large pieces. \n* Fine stoneware - made from more carefully selected, prepared, and blended raw materials. It is used to produce tableware and art ware. \n* Chemical stoneware - used in the chemical industry, and when resistance to chemical attack is needed. Purer raw materials are used than for other stoneware bodies. Ali Baba is a popular name for a large chemical stoneware jars of up to 5,000 litres capacity used to store acids. \n* Thermal shock resistant stoneware – has additions of certain materials to enhance the thermal shock resistance of the fired body. \n* Electrical stoneware - historically used for electrical insulators, although it has been replaced by electrical porcelain.

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