Pottery
Clay, shaped and fired into something permanent.
Pottery is ware made from clay and hardened by heat. It is one of the most durable archaeological materials — broken pottery survives where wood, cloth and metal do not — which is why potsherds do so much of the work in dating a site.
Clay bodies
| Body | Firing temperature | Result |
|---|---|---|
| Earthenware | 1,000–1,150 °C | Porous; needs glaze to hold liquid |
| Stoneware | 1,200–1,300 °C | Vitrified, non-porous, durable |
| Porcelain | 1,200–1,400 °C | White, translucent when thin, very hard |
Forming
Pinching, coiling and slab building need no equipment and are the oldest methods; coiling in particular can produce very large vessels. Throwing on a wheel is faster and produces radial symmetry, but only works for round forms. Handles, spouts and feet are usually added afterwards and joined with slip.
Firing
Work is dried to leather-hard, then bone-dry, then bisque fired to drive off chemically bound water and make the piece strong enough to handle and glaze. A second glaze firing melts the glaze into a glass layer fused to the body. Firing a piece that is not fully dry will crack or explode it, because trapped water turns to steam.
Glaze
Glaze is a thin glass coating: a silica former, a flux to lower its melting point, and a stabiliser. Colour comes from metal oxides — cobalt for blue, copper for green or red, iron for browns and celadons. The same oxide can give completely different colours depending on whether the kiln atmosphere is oxidising or reducing.