Making Iron

The ironmaking process in eighteenth- and nineteenth-century America used cold-blast furnaces that mimicked designs first used four hundred years earlier. A thick stone furnace shaped like a flat-topped pyramid served as the place where minerals became metal. Fillers dumped alternating layers of charcoal fuel, iron ore, and limestone flux into the top of the furnace. As the charcoal burned, air forced into the furnace from the outside raised the temperature to 2,000-3,000 F., creating several byproducts. Carbon gases escaped up the furnace stack, molten iron sank to the bottom, and impurities called slag floated on the liquified metal. Workers drew off the useless slag, and guttermen channeled the iron into connected castings called pigs.

Pennsylvania · United States