Also known as the 'direct reduction' method of
smelting iron , this process was known from as early as 900 B.C. The ore is heated in a low, cylindrical shaft furnace, constructed of stone, fueled with charcoal, and fanned with a bellows to a temperature from 1100-1220 degrees C and reduced directly to a spongy lump, producing iron ore and large quantites of
slag . Though not discovered until the 15th century, this iron could be converted to
steel by leaving it within the furnace for a longer time, so that the iron spent more time in contact with carbon monoxide gas.
