Working with Clay 4: Bisque Firing

 Before firing, water evaporates from the clay, shrinking it. But there is still water present on a chemical level, combined with the alumina and silica. This water doesn’t evaporate until it is fired 1022F/550C. At this point, the vessel will shrink further. So, clay vessels shrink in two stages. Because the vessel shrinks, there must be a passage for air to escape, because hot air expands as the clay shrinks. If you make an enclosed shape, or if there are air bubbles in the clay, firing will cause an explosion, hurting not just your piece, but all the other pieces in the kiln.

Dunting is when two pieces of different thicknesses are fused together, and pull apart in the firing process, leading to large cracks and an unstable weak structure.