To make iron from iron ore, you need to eliminate the oxygen to create pure iron. The most primitive facility used to refine iron from iron ore is called a bloomery . Charcoal is essentially pure carbon. Carbon and carbon monoxide combine with the oxygen in the iron ore and carry it away, leaving iron metal. By heating and hammering the bloom, the glassy silicates mix into the iron metal to create wrought iron .
Wrought iron is tough and easy to work, making it perfect for creating tools in a blacksmith shop.
Huge quantities of air blast in at the bottom of the furnace. The calcium in the limestone combines with the silicates to form slag . At the bottom of the blast furnace, liquid iron collects along with a layer of slag on top. Periodically you let the liquid iron flow out and cool. Typically the liquid iron flows into a channel and indentations in a bed of sand.