The hamon appears as a milky colored trail that follows the edge of the blade. It is the result of the heat treatment (tempering) to harden the cutting edge of the katana.
The HAMON draws a more or less regular line and each of these lines has a name and can sometimes be typical of a school or even a smith.
The most frequent HAMON is straight, but many forms exist.
This is an essential step that will make the difference between a good sword and a lesser quality sword.
This step consists in plunging a metal brought to a high temperature into a cold bath in order to preserve at room temperature a modification of the molecular structure obtained when hot and thus increase the hardness of the steel.
For this purpose, Japanese smiths developed the concept of partial hardening, a technique that Westerners, with a few exceptions, only mastered very late and never as well. The concept is simple: by covering a part of the blade with a mixture of fire clay, charcoal powder, silica and other elements kept secret by each blacksmith, the back and sides of the blade are isolated from the cold (i.e., the parts of the blade whose suppleness is to be maintained).
Thus, when the blade is soaked in water, only the edge is cooled quickly enough to form a hard steel, which will give the edge of the weapon an extreme hardness while maintaining a high resistance to shocks for the whole.
This selective hardening also forms the hamon line, the shapes of which are characteristic of schools and smiths: the less protected part cools quickly (making it harder) while the more protected part cools more slowly (allowing it to retain its flexibility). The point of contact between the two parts then undergoes a thermal shock, which will allow the austenite to take on its solid, shiny structure known as martensite.
The burning and history of Katana blades.
In the pattern of the blade, "yaki-kara" refers to the area closest to the mune (opposite side of the blade), which is the top of the pattern, "yaki-no-tani" refers to the area closest to the blade, which is the bottom of the pattern, and "koshi" refers to the slope from the head to the valley.
The burning blade of a Japanese sword starts from the bottom of the ha-machi, and the area 1 or 2 cm from the bottom of the ha-machi is called yakidashi, which shows the characteristics of the period and the school.
- From Heian period to early Kamakura period
unburned (e.g. pottery)
- Middle Kamakura period (1185-1333 CE)
Koshiba (blade at hip height)
- From the period of the new sword
Kyo-yakidashi, Osaka-yakidashi, Edo-yakidashi
Types of Hamon
There are many types of Hamon with various shapes but the main shapes are the straight Hamon lines or the wavy Hamon lines.
Here are some patterns that exist
This Hamon is in a straight line parallel to the edge of the sword. This type of Hamon is very old and is present on the most ancient Katanas, it has remained the most classical shape. There are variations of this Hamon because it has been much appreciated and used by many smiths like the hiro-suguha or chu-suguha or hoso-suguha.
Slightly wavy Hamon
The Gunome represents a series of semi-circles referring to the stones used in the traditional game of GO, seen from the side. The name of this hamon is therefore directly inspired by the game of GO. Then, with the Kamakura period various hamon based on Gunome were produced like gunome choji, gunome kataochi or gunome kaku.
This Hamon looks like a light wave of water. This hamon started to appear at the end of Kamakura period, the founder of this hamon is the famous Masamune. This hamon became one of the most popular and influenced many blacksmiths, especially in Okinawa.
Ko-Midare Hamon is a hamon with small irregular and very complicated patterns. This Hamon line was often represented on swords forged at the end of the Heian period, it is meant to stand out from the traditional Hamon with few shapes.
Real VS Fake Hamon
The hardening line, as its name indicates, is the result of the hardening process (differentiated heat treatment) which allows the steel to harden after heating and cooling in water or oil.
A blade can be hardened but without showing the hardening line, since it is the polishing of the blade that reveals the hardening line.
On very low end katanas (non-tempered blades), the blade is passed over a grinding wheel which will draw a false temper line.
On other non-tempered katanas the use of acid allows to draw a false hamon.
On medium range models (non-differentiated tempered blades), acid is also used to reveal a temper line.
On high-end models (clay-differentiated tempered blades) it is the manual polishing that will reveal the temper line.
You can learn more about the Katana and all the nomenclature on our Katana guide.