Brief History :: so far as is known the earliest pottery wares were hand-built and fired in bonfires. Firing times were short but the peak-temperatures achieved in the fire could be high, perhaps in the region of 900 degrees Celsius, and were reached very quickly. Clays tempered with sand, grit, crushed shell or crushed pottery were often used to make bonfire-fired ceramics, because they provided an open body texture that allowed water and other volatile components of the clay to escape freely. The coarser particles in the clay also acted to restrain shrinkage within the bodies of the wares during cooling, which was carried out slowly to reduce the risk of thermal stress and cracking. In the main, early bonfire-fired wares were made with rounded bottoms, to avoid sharp angles that might be susceptible to cracking. The earliest purpose-built kilns were pit-kilns or trench-kilns which were holes dug in the ground and that offered better control over firing >> more...