Kiln
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A kiln is an oven that is used for hardening, burning, or drying anything. Kilns have been used for converting wood into charcoal or to dry green lumber so that the lumber can be used immediately. Modern lumber kilns are also partially depressurized to speed the drying process and reduce fuel usage. Kilns are also used for cremation (at high temperature) and drying of tobacco leaves (at low temperature).
Kilns are also used to chemically refine clay objects by heating them until a chrystaline matrix of silica and alumina forms, to make them hard and durable. This process is simply referred to as "firing." Clays contain aluminium and magnesium silicates which will degrade under high temperatures leaving oxides of aluminium, magnesium and silica, which can form glass at high temperatures.
A kiln is required to come to a high temperature, and so the design of the ovens normally focuses on insulation, and the ability to add fuel over a course of time. Care must be taken not to heat the kiln too rapidly or to too high a temperature.
Kiln technology is very old. The development of the kiln from a simple earthen trench filled with pots and fuel (pit firing) happened in several simple stages. Heat was conserved more efficiently around pots by building a firing chamber, baffles and a stoking hole. A chimney stack improves the draw of the kiln, and uses fuel more completely. Early examples of kilns found in the United Kingdom include those made for the making of roof-tiles during the Roman occupation. These kilns were built up the side of a slope, such that a fire could be lit at the bottom, and the heat would rise up into the kiln.