Katana

A sword has two conflicting jobs. It must hold an edge, which needs hard steel, and it must not snap, which needs soft steel. Japanese smiths solved this by using both. The steel itself, tamahagane, is smelted from iron sand in a clay furnace over several days. The smith folds and hammers it repeatedly to even out the carbon, then wraps a hard outer layer around a softer core. Before quenching, the blade is coated in clay, thin along the edge and thick along the spine, so the two parts cool at different speeds. The edge hardens, the spine stays flexible, and the blade curves on its own as it cools. The wavy line left where the clay ended is the hamon, and no two are the same.

A samurai wore two swords, the long katana and a short companion blade, and the pair was a mark of rank that no one else could legally carry. Swords were signed by their smiths, handed down through families, and sometimes given names. After 1876 the government banned wearing them, and after 1945 many were confiscated or destroyed. Sword-making survives today as a licensed craft rather than an industry: a smith may legally produce only a limited number of blades a year, and the best are treated as art objects, not weapons.