Firing is the process of bringing clay and glazes up to a high temperature. The final aim is to heat the object to the point that the clay and glazes are “mature” that is, that they have reached their optimal level of melting.This process is usually accomplished in two steps: bisque firing and glaze firing.
When a kiln reaches about 660 F, the chemically bonded water will begin to be driven off. By the time the clay reaches 930 F, the clay becomes completely dehydrated. At this point, the clay is changed forever; it is now a ceramic material.
Ceramic glaze is an impervious layer or coating applied to bisqueware to color, decorate, or waterproof an item. In order for earthenware, it needs a glaze.
The artisan apply a layer of glaze to the bisqueware, leave it to dry, then load it in the kiln for its final step, glaze firing.
The glazed item is carefully loaded into the kiln for the glaze firing. The kiln is heated slowly to the proper temperature to bring the clay and glazes to maturity and then slowly cooled again. Only after the kiln has cooled, can the kiln be opened and unloaded. This second kiln firing caused a remarkable change in the clay and glaze. Pieces are transformed from a soft, fragile substance to one that is rock-hard and impervious to water and time.