Bisque firing should be at 1000 – 1060 degrees C followed by a glaze firing at a higher temperature which matures both clay and glaze simultaneously.
Alternatively, bisque fire above the lower temperature of the clay firing range, then glaze fire to the firing range of the selected glaze. This method causes some difficulty with application when dipping the relatively vitreous bisque ware, but assists if using a brush on glaze, where a harder bisque is required.
All clays and glazes are listed with their firing ranges. When choosing your glaze, it is important to select one with a firing range above the lower temperature given for the chosen clay or the clay will be under-fired and could craze.
Bisque firing grogged clay and thinly cast ware can be faster than thrown and smooth clay, but should always be slower than 100 degrees C per hour up to 600 degrees C, and then 100-200 degrees per hour up to your top temperature and finishing with a soak of 30 minutes to ensure your kiln has achieved an even temperature. Glaze firing should be at 100-130 degrees C per hour with a 30 minute soak.
Bloating can result from firing clay above its vitrification point or from insufficient biscuit firing or too fast a ramp rate in the later stage of glaze firing. Bloating can also be caused by excess heat work produced by long, slow firing, such as when kiln elements are struggling to achieve the set point.
When stored in a cool, frost-free environment, clay will remain in perfect condition for use.