Structue erected for the purpose of firing ceramics. Originally the possibility of firing clay to a harder state could have been discovered by the accidental burning of a straw basket sealed with mud.
Already during the Neolithic times the practice of firing pots directly in a fire, such as with pit firing, had already been surpassed by some cultures.
The first improvement was to separate the fire box from the ware chamber containing the clay vessels to be fired. The heat entered the ware chamber from vents in the floor and flowed up through a central flue at the top of the kiln. This design gave a more even heat rise and kept the fuel material away from the surface of the pots, both of which served to protect the pots from damage. The Neolithic Longshan culture was the first to develope this further simply by increasing the number and decreasing the size of the floor vents.
During the Shang Dynasty (16th-11th century BC) famous for its bronze technology the first steps was taken toward what would later become the down draft kiln, by besides the main smoke opening at the top of the domed ware chamber also to build small chimneys in the walls of the ware chamber. The firing began with a low fire and everything open. When the wares was totally dried and all heat was now blasting straight up through the center of the kiln a lid was placed over the central chimney which force the heat to circulate back down among the wares, up, and out through the wall chimneys. This gave an even heat and so high firing temperatures that the first porcelain could to be made, some of which was also glazed. The fast heat rise and the closing of the dampers together produced an oxygen starved atmosphere in the kiln, to such a degree, in fact, that the nature of the firing was one of carbon-soaking. In this type of atmosphere the clay bodies are turned gray to black from the excessive amounts of carbon that is not completely combusted.
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