How is a genuine hamon temper line created on a Japanese katana?
Updated Feb 2026
A genuine hamon is produced through differential clay tempering, a traditional Japanese technique. The smith applies a layer of clay mixture to the blade before heating — thin on the cutting edge and thicker along the spine. When the blade is rapidly quenched in water or oil, the thinly coated edge cools fast and transforms into hard martensite steel, while the thickly insulated spine cools slowly and remains as softer, tougher pearlite. The visible boundary between these two structural zones is the hamon. The pattern of the hamon — whether straight (suguha), wavy (notare), or clove-shaped (choji) — depends on how the smith applied the clay. A genuine hamon has organic depth and irregularity, unlike etched or printed lines which appear flat.