The alloys produced by early iron workers. were made by heating a mass of iron ore and charcoal in a forge or furnace having a forced draft. Under this treatment, the ore was reduced to the sponge of metallic iron filled with a slag composed of metallic impurities and charcoal ash. This sponge of iron was removed from the furnace while still incandescent and beaten with heavy sledges to drive out the slag and to weld and consolidate the iron. Occasionally this technique of ironmaking produced, by accident, a true steel.