As a bloomery's size is increased, the iron ore is exposed to burning charcoal for a longer time. When combined with the strong air blast required to penetrate the large ore and charcoal stack, this may cause part of the iron to melt and become saturated with carbon in the process, producing unforgeable pig iron which requires oxidation to be reduced into cast iron, steel, and iron. This pig iron was considered a waste product detracting from the largest bloomeries' yield, and it is not until the 14th century that early blast furnaces, identical in construction but dedicated to the production of molten iron, were built.