We have a pretty good idea of how these famous furnaces worked. The ovens were made of thick sheet metal, about 2 m in diameter, and consisted of three interlocking parts: a bottomless part in the shape of a large crown that flared out towards the top, a middle part in the shape of a crown that tapered towards the top, and a large lid with a central pipe serving as a chimney. This large, bottomless kettle was slightly raised to accommodate four short air intake pipes and four longer, curved pipes running up the side of the kiln to evacuate the fumes.