fired

In ceramics, fired means the clay or ceramic body has been heated to a high enough temperature that chemical and physical changes become irreversible. The firing process drives out water, causes clay minerals to recrystallize, and can form glass phases that bond particles together. Once fired, the material no longer softens when wet and gains its final strength and durability.

Firing temperatures vary widely by material and product type. Earthenware fires at roughly 1000 to 1150 degrees Celsius, stoneware between 1200 and 1300 degrees Celsius, and porcelain typically between 1200 and 1450 degrees Celsius. Higher temperatures produce denser, less porous ware with greater strength and chemical resistance. The specific temperature and duration determine the final properties of the piece.

Kilns used for firing include updraft kilns, downdraft kilns, tunnel kilns for continuous production, and electric kilns for smaller studios. In industrial production, pieces move through a tunnel kiln over many hours, gradually heating, soaking at peak temperature, and cooling. The firing atmosphere, whether oxidizing or reducing, also affects color and surface quality, especially in stoneware and porcelain.

Common firing problems

Pieces can crack or warp if cooled too rapidly or if moisture is trapped inside. Bloating or blistering occurs when gases escape from the clay body during firing. Underfired ware remains porous and fragile; overfired ware can deform or slump. These defects make the piece unsuitable for its intended use, whether tableware, tile, or structural product.

Fired is distinguished from raw or green ware, which is unfired clay, and from bisque, which has undergone a first firing at lower temperature before glazing and a second firing. In industrial settings, fired ware forms the foundation of quality control: strength testing, absorption measurement, and color assessment all apply only to fired samples, not to unfired clay.