Before revision: Japanese katana 350px ForgingTamahaganeJapanese smiths discovered, similarly to many others, that iron sand (with little to no sulfur and phosphorus) heated together with coal (carbon) made the steel they called tamahagane.
After revision:  ForgingTamahaganeJapanese smiths discovered, similarly to many others, that iron sand (with little to no sulfur and phosphorus) heated together with coal (carbon) made the steel they called tamahagane.