Bisque vs glaze firing: a plain explanation for studio members

The first firing turns dry, fragile greenware into bisque: still porous, but hard enough to handle and glaze without falling apart. Bisque is usually fired to a relatively low temperature, often around cone 04 or 06. Pieces can touch in a bisque load because there is no glaze to fuse them together.

After glazing, pieces are fired again at the temperature the clay and glaze are made for. In this firing the glaze melts into glass and the clay matures. Pieces can’t touch each other or the shelf with glazed surfaces, which is why glaze loads hold fewer pieces and why bottoms must be wiped clean.

Pyrometric cones measure the combined effect of temperature and time, which is what actually matures clay and glaze. Cone numbers with a leading zero (like 06 or 04) are lower temperatures; numbers without one (like 6 or 10) are higher. Cone 6 is the most common range in community studios; cone 10 is high fire, often in gas kilns.

Always match your clay body and glaze to the cone they are made for. A low-fire glaze in a cone 6 firing will run; a cone 10 clay in a cone 6 firing won’t mature.

• Greenware has to be fully dry before bisque, which can take days.
• Each firing has to wait for a full enough load of the same type.
• Each kiln has to cool before it can be unloaded.
• Glazing happens between the two firings, on the member’s schedule.