In the 1100’s Europeans had mastered a technique for producing cast iron, some 1,500 after the Chinese. This was by means of a blast furnace, so called because of the blasts of air required to achieve a high enough temperature to melt iron. Water and sometimes wind power were used to operate the bellows and for crushing up the iron ore to increase its surface area. Blast furnaces gradually grew in capacity to meet the demand for the new cast iron, which had wider applications than wrought iron, but two distinct problems arose as a result.
Charcoal began to run short as Europe’s trees were increasingly felled, and slag impurities prevented as much as 50 percent of the iron from being run off for casting. The introduction of coke and lime into the process, solved both of these problems, but not for several centuries to come.