The Cupola is at the heart of the modern iron caster’s foundry and can be used for industrial large-scale operations as well as small person applications. Cupolas are the most efficient and fastest furnaces for melting iron. The Cupola has been used for many years; in his book Pyrotechnia (1540), Vannoccio Biringuccio writes about some of the earliest crucible furnaces and cupolas for metalworking. Stewart Marshall, author of Building small Cupola Furnaces, credits John Wilkinson for the widespread use of the cupola to melt and recast pig iron that was much different than the melting of iron ore. His success was so well known that he was wrongly credited with inventing the cupola furnace.
The cupola is typically a cylindrical shape made out of rolled sheet metal and lined with a ceramic refractory. The Cupola has a few main components: the cylindrical body, tuyeres, a sloping bottom lined with sand, a tapping spout, slag hole, and drop door on the bottom used to clean out and empty the body once the pour is finished. The iron is placed directly onto the fuel in the furnace without any crucibles or other containers. As the metal melts it drips down to the bottom of the furnace where it sits until a full ladle is ready to be tapped out. The nice thing about the cupola, according to Stewart Marshall’s book Building Small Cupola Furnaces, is that they are continuous melters; they continuously melt iron as long as chargers are being put in, unlike the typical crucible furnace that melts one charge at a time.