Stoneware is a vitreous or semi-vitreous ceramic made primarily from stoneware clay or non-refractory fire clay. Stoneware is fired at high temperatures. Vitrified or not, it is nonporous; it may or may not be glazed.

Definition and description

One widely recognised definition is from the Combined Nomenclature of the European Communities, a European industry standard. It states:

The key raw material in stoneware is either naturally occurring stoneware clay or non-refractory fire clay. The mineral kaolinite is present but disordered, and although mica and quartz are present their particle size is very small. Stoneware clay is often accompanied by impurities such as iron or carbon, giving it a "dirty" look, and its plasticity can vary widely. Non-refractory fire clay may be another key raw material. Fire clays are generally considered refractory, because they withstand very high temperatures before melting or crumbling. Refractory fire clays have a high concentration of kaolinite, with lesser amounts of mica and quartz. Non-refractory fire clays, however, have larger amounts of mica and feldspar.