The iron sand is put in a clay tub (furnace) called a "tatara". The clay tub measures about 4 feet tall, 12 feet long, and 4 feet wide. The tub is then dried and heated. The clay tub is heated to a high temperature, about 1000 ºC (1.832 ºF). Then, it is mixed with charcoal to give tamahagane hardness. 