tamahagane

Tamahagane is a traditional Japanese steel used to forge samurai swords, particularly katana. The name means jewel steel, and it is produced by smelting iron sand (satetsu) in a clay furnace called a tatara.

The tatara is charged with iron sand and charcoal and heated for several days to produce a bloom from which steel ingots with varying carbon content are extracted. The resulting pieces are sorted, and the best portions, known as kera, are selected for forging into tamahagane. The composition of tamahagane varies across the bloom, allowing smiths to choose a mix suitable for blade forging.

In swordmaking, tamahagane is repeatedly heated, folded, and forge-welded to create a blade with a hard, high-carbon edge and a tougher, lower-carbon body. The process also yields a distinctive grain pattern in the steel and, with differential heat treatment, a visible temper line along the edge.

Historically, tamahagane has been associated with traditional Japanese swords such as the katana, wakizashi, and tanto, with the craft reaching its peak during the Edo period. In modern practice, some smiths continue to produce blades using tatara-produced tamahagane, but many blades are made with modern steels or blends. Tamahagane remains valued for its historical significance and the nuanced balance it can provide between hardness and toughness.