There are three broad groups of pottery - Earthenware, Stoneware and Porcelain. 

• Earthenware is pottery (i.e. made from clay) which has not been fired to the point of vitrification and so is slightly porous after the first firing. 

• It is made waterproof by the application of slip (a liquid clay mixture applied before firing) before the second firing or the application of a tin or clear glaze. For both practical and decorative reasons, earthenware is usually glazed. 

Earthenware is fired at a lower temperature than Stonware and Porcelain, it readily absorbs water if not glazed, and does not allow light to pass through it. Coarse earthenware is made from clay and grog (ground up fired pots).

It is the colour of the clay as it is dug from the ground - buff, brown and red.

A modern earthenware recipe would be: 25% ball clay, 25% china clay, 35% flint, 15% china stone. The first or biscuit firing temperature is 1100 - 1150°C and the second, glost (glaze) firing 1050 - 1100°C.

Nearly all ancient, medieval, Middle Eastern, and European painted ceramics are earthenware, as is a great deal of contemporary household dinnerware.

To overcome its porosity (which makes it impracticable for storing liquids in its unglazed state, for example), the fired object is covered with finely ground glass powder suspended in water and is then fired a second time. During the firing, the fine particles covering the surface fuse into an amorphous, glasslike layer, sealing the pores of the clay body.