Smelting and melting of copper and its alloys such as leaded bronze were smelted in crucibles similar to those of the Roman period which have thinner walls and flat bases to sit within the furnaces. The technology for this type of smelting started to change at the end of the Medieval period with the introduction of new tempering material for the ceramic crucibles. Some of these copper alloy crucibles were used in the making of bells. Bell foundry crucibles had to be larger at about 60 cm (Tylecote 1976: p73). These later medieval crucibles were a more mass-produced product.