What is ceramics?

Derived from the Greek keramos meaning “clay”, the generic term “ceramics” refers to all clay-based objects that have undergone an irreversible physical-chemical transformation during firing. Dating back to the Neolithic Period, ceramics constitutes the earliest “fire art” invented by man, predating both glass- and metalworking. Ceramics is not only an important cultural marker in most societies, it also represents the most abundant manmade material.

Whether utilitarian or artistic in nature, ceramic objects reflect changing lifestyles and testify to a society’s technical advances (notably its mastery of the four natural elements: earth, water, air and fire). Ceramic creations reveal a people’s customs, its eating habits and cultural practices during a given period.

From everyday objects to research subjects to exceptional works of art, ceramics remain an inexhaustible source of inspiration.

Pottery

Terracotta objects made from common clay, varying in colour from grey to red depending on the clay’s composition. Red clays are ferruginous, while white clays contain varying amounts of chalk, silica and/or kaolin. Pottery can be made by shaping, turning or moulding, or by the layering of clay coils. Firing is carried out between 800° and 900° C. Pottery is glazed when the porous paste has been rendered impermeable with the application of a glaze or enamel.

Faience

Ceramics made from a tender, clayey, porous paste covered by an opaque, impermeable glaze. Several types of faience exist: lead-based faience, stanniferous faience (containing tin oxide) and faience fine made from top quality clay chosen for its whiteness. Faience can be adorned with both “high-fire” and “low-fire” glazes and designs. For the former, the faience is subjected to a single firing, with the design – painted onto unfired enamel – supporting the high-temperature firing required for the paste and enamel (around 900° C). For the latter, the design is applied to a pre-fired object following the enamel’s application; the colours mixed with fondants can support only a low-temperature firing (650° to 700° C).

Porcelain

Porcelain is a type of ceramic whose paste has been thoroughly vitrified (rendering it impermeable) and that stands out for its whiteness (similar to faience fine, which can be difficult to distinguish from porcelain). Porcelain is generally characterized by its exceptional translucency. This type of ceramic was invented in China in the 7th or 8th century. Following its first importation to Europe during the Middle Ages, Europeans began producing imitations, manufacturing various types of white translucent ceramic.
Hard-paste porcelain (impervious to steel) and soft-paste porcelain (lacking kaolin and can be marked by steel) constitute the two main families of European porcelain, which are generally covered with a transparent glaze or enamel allowing for the whiteness of the paste to show through.

Today, the Manufacture workshops produce four separate porcelain pastes: hard paste (dating from the 18th century and containing 75% kaolin), soft paste (this variant of the 18th-century paste, containing very little kaolin and 50% bone ash, is the only phosphatic soft-paste in France), new paste (invented around 1882, containing 45% kaolin), and white paste or Antoine d’Albis paste, similar to hard paste (named after the Manufacture department head who perfected it around 1965).

Stoneware

Made with paste containing a high percentage of silica and supporting high-temperature firings (1200° to 1400° C), stoneware is partially vitrified during firing.

While pottery and faience are made using porous pastes that must be rendered impermeable with the application of a glaze or enamel, stoneware is similar to porcelain in that its paste is thoroughly vitrified and therefore impermeable even unglazed.

Therefore, ever since stoneware’s invention around the 4th century in China, its subsequent introduction to the Middle East and its development in Europe starting in the Middle Ages, potters have only applied glazes to stoneware for aesthetic purposes, while exploring and combining various materials and forms.

A ceramic is an inorganic non-metallic solid made up of either metal or non-metal compounds that have been shaped and then hardened by heating to high temperatures. In general, they are hard, corrosion-resistant and brittle.

'Ceramic' comes from the Greek word meaning ‘pottery’. The clay-based domestic wares, art objects and building products are familiar to us all, but pottery is just one part of the ceramic world.

Nowadays the term ‘ceramic’ has a more expansive meaning and includes materials like glass, advanced ceramics and some cement systems as well.

Traditional ceramics – pottery

Pottery is one of the oldest human technologies. Fragments of clay pottery found recently in Hunan Province in China have been carbon dated to 17,500–18,300 years old.

The major types of pottery are described as earthenware, stoneware and porcelain.

Earthenware is used extensively for pottery tableware and decorative objects. It is one of the oldest materials used in pottery.

The clay is fired at relatively low temperatures (1,000–1,150°C), producing a slightly porous, coarse product. To overcome its porosity, the fired object is covered with finely ground glass powder suspended in water (glaze) and is then fired a second time. Faience, Delft and majolica are examples of earthenware.

Stoneware clay is fired at a high temperature (about 1,200°C) until made glass-like (vitrified). Because stoneware is non-porous, glaze is applied only for decoration. It is a sturdy, chip-resistant and durable material suitable for use in the kitchen for cooking, baking, storing liquids and as serving dishes.

Porcelain is a very hard, translucent white ceramic. The earliest forms of porcelain originated in China around 1600BC, and by 600AD, Chinese porcelain was a prized commodity with Arabian traders. Because porcelain was associated with China and often used to make plates, cups, vases and other works of fine art, it often goes by the name of ‘fine china'.

To make porcelain, small amounts of glass, granite and feldspar minerals are ground up with fine white kaolin clay. Water is then added to the resulting fine white powder so that it can be kneaded and worked into shape. This is fired in a kiln to between 1,200–1,450°C. Decorative glazes are then applied followed by further firing.

Bone china – which is easier to make, harder to chip and stronger than porcelain – is made by adding ash from cattle bones to clay, feldspar minerals and fine silica sand.

Advanced ceramics – new materials

Advanced ceramics are not generally clay-based. Instead, they are either based on oxides or non-oxides or combinations of the two:

• Typical oxides used are alumina (Al2O3) and zirconia (ZrO2).
• Non-oxides are often carbides, borides, nitrides and silicides, for example, boron carbide (B4C), silicon carbide (SiC) and molybdenum disilicide (MoSi2).

Production processes firstly involve thoroughly blending the very fine constituent material powders. After shaping them into a green body, this is high-temperature fired (1,600–1,800°C). This step is often carried out in an oxygen-free atmosphere.

The high temperature allows the tiny grains of the individual ceramic components to fuse together, forming a hard, tough, durable and corrosion-resistant product. This process is called sintering.

Applications of advanced ceramics

Advanced ceramic materials are now well established in many areas of everyday use, from fridge magnets to an increasing range or industries, including metals production and processing, aerospace, electronics, automotive and personnel protection.