People in the early civilizations used clay to make their vessels and sculptures which they fired accidently; probably after discovering some burnt clay in a campfire. This very basic firing process evolved gradually into a more professional one.
For firing, unfired clay pottery or bisque fired pottery is covered with suitable burning materials and placed in a pit made in the ground. A bed of dry leaves, wood and coal that will burn slowly is laid at the bottom of the pit and the pottery is placed over this bed. The entire work is covered with more leaves and wood creating a pile. This pile is lit around the edges, once it is properly stacked and is left to smolder for several hours.
Today’s ceramic industry is very much advanced and use specially designed furnaces that use petrol or electricity as a power source.
Remember, the ceramic product shrinks to a size 33% smaller than the original mould.