Firing stoneware and porcelain is dramatic, exciting, and endlessly fascinating. The suspense is heightened by the uncertainties which attend the process, and by the possibility of happy as well as unfortunate accidents. And all potters come to a philosophical acceptance of the fact that firing may result in failure, discouragement, and disappointment. In some ways, firing high-temperature wares is simpler than firing earthenware. The glazes tend to have a longer range, which lessens the danger of overfiring or underfiring, and the action of the heat and flame on the pots frequently bestows a bonus of color nuance or variation having a natural sort of beauty which could never be achieved by plan. On the other hand, the high temperature also increases the likelihood of kiln mishaps, such as pots sticking to shelves, kiln crumbs falling onto and marring the glazes, shelves and supports giving way, or of pots slumping and warping out of shape. As in all other kinds of pottery making, stoneware and porcelain require careful and expert firing. The cycle of firing is the heart of the whole process of pottery making. Stoneware, and more particularly porcelain, requires special firing procedures because of the degree of softening which occurs in the clay during the high maturing heat of firing.
No matter how inspired or insightful a pot is in concept and design, or how beautifully made it is, a pot may be lost from improper setting in the kiln. There is no escape from thorough craftsmanship here. The first essential in firing is a certain cleanliness and order about the process. Kilns have a tendency to become surrounded by broken and discarded refractories, bits of discarded clay, used cone plaques, broken or abandoned pots, and other debris. Worse still is disorder inside the kiln--broken bits of shelves or supports, crumbs of clay or chips of broken pots, and loose crumbs on the walls and crown. All this confusion should be kept under reasonable control. It is especially important to clean out the kiln after firing, and to sweep loose bits off the inside of the kiln to prevent their falling or blowing onto the glazes during firing.
The best kiln shelves are those made from silicon carbide. These are expensive, but outlast the clay refractory shelves by many times. They are very resistant to the fatigue which results from repeated heating and cooling and will bear great loads, even at high temperatures. New shelves should be lightly washed with a mixture of kaolin and flint in about equal amount. It is not good to allow too great a thickness of kiln wash to build up on the shelves because this causes an uneven and rough surface. After each firing, the shelves should be inspected, and if any bits of glaze have fallen onto the shelves they should be chipped off, and some kiln wash brushed on the area. Shelves should be carefully stored in wooden racks. More kiln shelves are usually lost from being kicked over onto the floor