A glaze firing, also called a glost firing, is the kiln firing that melts glaze onto bisqueware. For stoneware and porcelain it is usually the hottest firing, to around cone 6 or cone 10, and it also matures the clay.
What Is Glaze Firing?
In a typical studio, pieces are fired twice. The bisque firing makes the clay hard and porous, then glaze is applied and the glaze firing melts it into glass. For stoneware and porcelain, the glaze firing goes much hotter than the bisque, so it also brings the clay to its full density and strength.
Glazed pieces must not touch each other or the kiln shelf where they are glazed, or they will fuse together. Potters leave the foot unglazed, use kiln wash on shelves, and may set runny glazes on waste slabs or cookies to catch drips.
The firing schedule shapes the result. A hold at the top can help glazes smooth over pinholes, and slow or controlled cooling changes the surface of matte and crystalline glazes. Witness cones in the load show what heatwork the glaze actually received, which helps when results differ from the label. Unloading only once the kiln has cooled to near room temperature protects both the glaze and the clay from cracking.
This pottery glossary entry from Le Studio Art Space is general educational content. Always follow the clay, glaze and kiln makers’ data for your own materials and equipment.