Japanese Sword's Hamon

Published: 17/08/2021 Comments: 0

In Japanese swordsmithing, the Japanese sword's Hamon (刃文, literally "blade pattern") is recognized as the sharpened section of the blade, is a tempering line and visual point of demarcation on a Japanese sword which separates the harder edge and the softer spine(mune). You may find various lines, shapes, patterns, or geometric figures that extend along the length of the blade, called tempered lines or "Hamon". From Katana and Wakizashi to Tanto and Tachi, countless Japanese swords have Hamon, which is a visible effect created on the blade by the differentially hardened process.

The Hamon is the outline of the hardened zone (yakiba) which contains the cutting edge (ha). The Swordsman first heats the entire blade and then coats the spine of the blade with a thick special mixture of clay. Next, the Swordsman will quench the entire blade with water or oil. Since the spine is covered with a thick layer of clay, it cools more slowly than the edges, resulting in a firm edge and flexible spine. 

Since the clay is thinning out greatly before the edge. This enables a swordsmith to control the speed at which different areas of the blade change temperature during the heating and cooling process of tempering. The result is a harder cutting edge and a softer spine. 

The Hamon outlines the transition between the region of harder martensitic steel at the blade's edge and the softer pearlitic steel at the center and back of the sword(for example spine 40 HRC vs edge 60 HRC).

This tempering when done properly is not just visible on the surface but goes all the way through inside of the blade.

The aesthetic qualities of the Hamon are quite valuable—not only as proof of the differential-hardening treatment but also in its artistic value—and the patterns can be quite complex.

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