At the base of a bole 20 feet (6.1 m) long were laid great trees called blocks.
On these were laid blackwork, partly smelted ore about half a yard thick.
This smelted lead, which ran down channels provided for the purpose and was cast into sows of about 11 hundredweight.
Some of this was smelted in a foot-pump blown furnace, but some was left to be used when the bole was next fired.
That was in turn replaced by smelting in cupolas, a variety of reverberatory furnace in the 18th century.