Hamon (swordsmithing)
Encyclopedia
In swordsmithing
, (from Japanese
, literally "blade pattern") is a visual effect created on the blade by the hardening
process. Blades made in this manner are known as differentially hardened, with a harder ha than mune (for example: mune 40 HRC
vs ha 58 HRC) as a result of clay applied on the blade during the cooling process. Less or no clay allows the ha to cool faster, making it stronger but more brittle; more clay allows the mune to cool more slowly and retain its resilience.
The hamon is the transition between the region of harder martensitic
steel
of the blade
edge and the softer pearlitic
steel of the back of the sword. This difference in hardness is the objective of the process; the appearance is purely a side effect. However, the aesthetic qualities of the hamon are quite valuable—not only as proof of the differential hardening treatment but also in its own right—and the patterns can be quite complex.
Many modern reproductions do not have natural hamon because they are thoroughly hardened monosteel; their hamon is faked via various processes such as acid etch
, or more crude ones such as wire brush
ing. Some modern reproductions with natural hamon are also subjected to acid etching to enhance that hamon's prominence.
"Amakuni and his son, Amakura, gathered up the broken blades and examined them. They were determined to create a blade that would not break in combat and locked
themselves away in seclusion for 30 days. When they reappeared, they carried with them the curved blade. The following spring there was another war. Again the
soldiers returned, only this time all the swords were intact and the emperor smiled on Amakuni."
Although impossible to ascertain who actually invented the technique, surviving blades by Yasutsuna from around 749-811 AD suggest that at the very least Yasutsuna helped establish the tradition of differentially hardening the blades.
Bladesmith
Bladesmithing is the art of making knives, swords, daggers and other blades using a forge, hammer, anvil, and other smithing tools. Bladesmiths employ a variety of metalworking techniques similar to those used by blacksmiths, as well as woodworking for knife and sword handles, and often...
, (from Japanese
Japanese language
is a language spoken by over 130 million people in Japan and in Japanese emigrant communities. It is a member of the Japonic language family, which has a number of proposed relationships with other languages, none of which has gained wide acceptance among historical linguists .Japanese is an...
, literally "blade pattern") is a visual effect created on the blade by the hardening
Hardening (metallurgy)
Hardening is a metallurgical and metalworking process used to increase the hardness of a metal. The hardness of a metal is directly proportional to the uniaxial yield stress at the location of the imposed strain...
process. Blades made in this manner are known as differentially hardened, with a harder ha than mune (for example: mune 40 HRC
Rockwell scale
The Rockwell scale is a hardness scale based on the indentation hardness of a material. The Rockwell test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload. There are different scales, denoted by a single...
vs ha 58 HRC) as a result of clay applied on the blade during the cooling process. Less or no clay allows the ha to cool faster, making it stronger but more brittle; more clay allows the mune to cool more slowly and retain its resilience.
The hamon is the transition between the region of harder martensitic
Martensite
Martensite, named after the German metallurgist Adolf Martens , most commonly refers to a very hard form of steel crystalline structure, but it can also refer to any crystal structure that is formed by displacive transformation. It includes a class of hard minerals occurring as lath- or...
steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
of the blade
Blade
A blade is that portion of a tool, weapon, or machine with a cutting edge and/or a pointed tip that is designed to cut and/or puncture, stab, slash, chop, slice, thrust, or scrape animate or inanimate surfaces or materials...
edge and the softer pearlitic
Pearlite
Pearlite is often said to be a two-phased, lamellar structure composed of alternating layers of alpha-ferrite and cementite that occurs in some steels and cast irons...
steel of the back of the sword. This difference in hardness is the objective of the process; the appearance is purely a side effect. However, the aesthetic qualities of the hamon are quite valuable—not only as proof of the differential hardening treatment but also in its own right—and the patterns can be quite complex.
Many modern reproductions do not have natural hamon because they are thoroughly hardened monosteel; their hamon is faked via various processes such as acid etch
Etching
Etching is the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio in the metal...
, or more crude ones such as wire brush
Wire brush
A wire brush is a tool, consisting of a handle, usually wood or plastic, occasionally bone, and a brush. The brush is usually made from a large number of steel wire bristles. The steel used is generally a high carbon variety and very hard. Other wire brushes feature bristles made from brass or...
ing. Some modern reproductions with natural hamon are also subjected to acid etching to enhance that hamon's prominence.
Origins
According to legend, Amakuni Yasutsuna developed the process of differentially hardening the blades around the 8th century AD. The emperor was returning from battle with his soldiers when Yasutsuna noticed that half of the swords were broken:"Amakuni and his son, Amakura, gathered up the broken blades and examined them. They were determined to create a blade that would not break in combat and locked
themselves away in seclusion for 30 days. When they reappeared, they carried with them the curved blade. The following spring there was another war. Again the
soldiers returned, only this time all the swords were intact and the emperor smiled on Amakuni."
Although impossible to ascertain who actually invented the technique, surviving blades by Yasutsuna from around 749-811 AD suggest that at the very least Yasutsuna helped establish the tradition of differentially hardening the blades.