The steel bloom, or kera, that is produced in the tatara contains steel that varies greatly in carbon content, ranging from wrought iron to pig iron. Three types of steel are chosen for the blade; a very low carbon steel called hocho-tetsu is used for the core of the blade (shingane). The high carbon steel (tamahagane), and the remelted pig iron (cast iron or nabe-gane),[10] are combined to form the outer skin of the blade (kawagane).[6][11][12] Only about 1/3 of the kera produces steel that is suitable for sword production.[13]