salle techniques céramiques

Glossary of ceramic techniques

Clay: Permeable earth with plastic qualities suitable for the production of ceramics.

Ceramics: A generic term encompassing any object made of clay and fired at a temperature above 500°C.

Faience: Earthenware covered with a glaze that is rendered opaque through the addition of tin oxide. This technique was developed in the Middle East in the late 8th century. Its white surface enables it to mimic Chinese porcelain. The decorative component of faience is referred to as grand feu or 'high-fired' if it is applied directly onto the raw glaze and fired together with the latter in an oxidising atmosphere (one rich in oxygen) at a temperature of around 1000°C. In contrast, the decoration is described as petit feu or 'low-fired' if it is applied to the fired enamel and then fixed in a muffle kiln at a temperature of between 600°C and 800°C. The range of colours available with the petit feu technique is broader than that available with grand feu. Lustreware, invented in Mesopotamia in the 9th century, is achieved by painting motifs onto the fired glaze using a mixture of metal oxides (copper and silver) and vinegar. After being fired at 650°C in a reducing atmosphere (one low in oxygen), the lustre needs to be polished using a hard stone to reveal its metallic reflections.

Creamware: Made from very fine, light-coloured clay with the addition of calcined flint and lime, and covered with a lead glaze, creamware is fired at a temperature of 1000°C to 1200°C. It was developed in England in the 18th century. Cheaper than porcelain, it has a cream-coloured surface to which a painted or printed decoration can be applied.

Stoneware: Hard clay of variable colouring, which is vitrified by firing at a temperature of between 1200°C and 1280°C. Stoneware has existed in China since the 7th century, while the first examples in Europe were made in Germany in the 14th century.

Stonepaste: A sandy-textured ceramic, rich in silica (from sand, flint or powdered quartz) and fired at a temperature of around 1000°C. It is composed of 60 to 90% silica, combined with a small amount of clay. Stonepaste was developed in the Middle East towards the end of the 11th century to imitate Chinese white porcelain. This technique was not imported into Europe.

Porcelain: A composite white ceramic created from a mixture of 50% kaolin, 25% quartz and 25% feldspar. After being fired at a high temperature (approximately 1400°C), porcelain vitrifies, becomes translucent, and produces a bell-like sound when struck. To make it glossy, porcelain is generally coated with a vitreous coating known as a glaze, which may be transparent or coloured. Porcelain is described as 'hard-paste' when its glaze is scratch-resistant to steel. Underglaze decoration is applied directly to the bisque; overglaze enamelling and gold are applied to the fired glaze and are fixed through successive firing at a lower temperature.

Soft-paste porcelain: Containing no kaolin, this is produced from a mixture of white clay and frit (a vitreous material). Fired at around 1000°C, soft-paste porcelain’s glaze is not scratch-resistant to steel. Bone china, produced mainly in England, is an English porcelain in which the feldspar is replaced by bone ash.

Earthenware: The simplest ceramic technique, which consists in hardening a clay object by firing it at a low temperature (between 500°C and 1000°C). Earthenware remains porous after firing, but can be covered in an alkaline or lead coating (glaze), which makes it impermeable and glossy. Earthenware can readily be decorated with coloured liquid clays known as slips, which are applied to the bisque before glazing.