Refractory materials are used in furnaces, kilns, incinerators, and reactors. Medieval Sarum also seems to have had industrial facilities such as kilns and furnaces. The first were simple shaft kilns, similar in construction to blast furnaces. Technologies included stone and copper drills, updraft kilns, large pit kilns and copper melting crucibles. Charcoal from the Forest of Dean enabled Romans to operate pottery kilns and ironworks. Similar devices called rotary kilns are used in cement manufacturing. Overworked and underpaid, many potters refused or fled from being conscripted into the imperial kilns. Most softwood lumber kilns operate below temperature. However, making and selling imperial style ceramics in private kilns was strictly forbidden. Bricks were the usual material for building the kilns. The clay is formed into round pellets and fired in rotary kilns at . The clay was shaped and fired in a series of brick and tile kilns. Dehumidification kilns are very similar to conventional kilns in basic construction. They were similar to the nearby Panamint Charcoal Kilns near Death Valley. These were updraft kilns, often built below ground.