The Musée Ariana’s collections illustrate the main ceramic techniques. Ceramics is a general term for any object made of clay and fired at over 500°C.
Earthenware is the simplest technique and consists in hardening a clay object by firing it at a low temperature. Earthenware remains porous after firing, but can be covered with an alkaline or lead coating, a glaze, which makes it impermeable and glossy. Earthenware can be readily decorated with coloured liquid clays, known as slips, applied to the fired ware (or “bisque”) before glazing.
Faience is earthenware covered with a glaze rendered opaque by the addition of tin oxide. Majolica, a term of Italian origin, refers to 16th century Italian faience. Faience decoration is said to be “grand feu” or “high-fired”, if painted onto the raw glaze and fired together with the latter at around 1000°C; “petit feu” or “low-fired”, if applied to the already once-fired tin glaze and then fixed in a muffle kiln at a low temperature of between 600 and 800°C. This technique provides a far wider range of colours than the “grand feu” process. Creamware is made from very fine, light coloured clay, strengthened with ground, calcined flints and lime and coated with a lead glaze.
Hard-paste (or “true”) porcelain is white composite ceramic ware formed from a mixture of 50% kaolin (china clay), 25% quartz and 25% feldspar. After being fired at a high temperature (around 1400°C), porcelain vitrifies, becomes translucent and produces a bell-like sound when struck. To make it glossy, porcelain is generally covered with a glaze, a transparent or coloured vitreous coating. The attribute "hard-paste" refers to the fact that the glaze is resistant to scratching by steel. Underglaze decoration is applied directly to the bisque, while overglaze enamel colours, as well as gold, are added to an already fired glaze.
Soft-paste porcelain, which contains no kaolin, is formed of a mixture of white clay and ground frit (vitreous substance). Fired at around 1000°C, the surface of soft-paste porcelain is not resistant to steel.
Stoneware is clay that is very hard and varied in colour, and which can be vitrified by firing at 1200-1280°C.