Earthenware is the oldest and most widespread form of ceramic or pottery, and is the most fragile as it is fired at a relatively low temperature (a minimum of about 700 degrees centigrade). It is porous and it chips easily, as can be seen on the rims of antique earthenware plates. Because of this many very early earthenware objects now found in museums have had to be reconstructed from broken pieces, with missing parts matched as well as possible, or deliberately contrasting, with new material. Earthenware, somewhat improved, is still used today where its properties better fit a need than other forms of pottery.

Storage Pot, Harappan, Indus Valley, 3,300 to 1,750 BC.
Courtesy Government Museum, Chennai

As the firing temperature is increased, and the quality of the clay and its preparation improves, for example by removing larger unwanted particles (inclusions) and kneading to remove small air pockets, the robustness improves. The formation of a ceramic is a very complicated chemical process, with the ingredients changing composition at various temperatures and durations of firing. Stoneware, for example, is heated at a sufficiently high temperature for its constituents to vitrify, or form a glassy (but opaque) substance that is very hard and no longer porous.

More details on the process and chemistry involved in making pottery are covered in later sections.