Furnace built like a tower for reducing ore into metal. Can be used as part of non ferrus metal reduction, but is normally associated with iron production. Ore (iron ore for iron production), coke (originally charcoal) and a flux (typically limestone) and tipped into the top. Molten pig iron and slag are removed periodically from the base of the furnace. After 350 years, blast furnaces remain the only way to economically produce large quantities of Iron.