Tatara-buki method; the type of steel used to make a Katana is called Japanese steel or Tamahagane. Tamahagane is made using the 'Tatara-buki method,' an original Japanese steel making process. Not depending upon iron ore imported from other countries, using black iron sand found on beaches in Japan, achieves fast reduction at low temperature, and creates high-quality steel with few impurities, compared to the modern steelmaking processes.

Tatara-buki is a traditional Japanese technique that is essential to the making of Japanese swords. However, in 1925, the fires of Japan’s tatara (furnaces) were all extinguished. In order to preserve Japanese swords as important works of art and cultural assets, Nittoho Furnace was restored and began operating again in 1977. Technicians and a supervisor known as a murage, who is well-versed in the furnace’s construction and operating method, still work at Nittoho Furnace, and produce Japanese swords using the traditional technique.