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Studies of Hamon Patterns

Suishinshi Masahide who is known as the “founder of Shin-shintō” made many swords in his life.He trained more than 100 students and had a great influence as an educator. As a researcher, he studied about sword-making methods and wrote a number of books. This is a portrait of Masahide at the age of 62 and other portraits of him are also known.
It is unclear who this author Takahiko was, but it is considered that he was related to Dewa-Shōnai(Yamagata prefecture) and called himself Sōma Takahiko. It is said that in April, in Bunka 1(1804) when Masahide visited Shōnai, he gave Takahiko a book on forging methods. It is written in the portrait that Masahide and Takahiko had known each other for over 20 years. From this fact, it is possible that Takahiko was also one of Masahide’s students.

It was first published by the student, Takehiro Yasuhide with the title “Tōken Buyō-ron”. Later, some contents were revised and was republished with the title “Tōken Jitsuyō-ron”. He wrote his opinions in Q and A form between him and the students.
Consideration of the curator: As it is shown in this exhibition, in the 1000 years after Japanese swords were born, many different kinds of hamon have been created. In the modern study, it is said that the hamon style alternated between gentle hamon and gorgeous hamon by reflecting the times. It is interesting how Masahide is expressing the reasons of this change of hamon style as “because of peace or war” or “depending on the time”.

This literature consists of 3 volumes. Volume 1 is about the figure of the swords such as the curvature or niku-oki　(thickness). In Volume 2 and 3, he is giving his opinions on the sword-making methods in history in Q and A form.
Consideration of the curator: During the long war-less time continued in the Edo period, many gorgeous and commercial swords were made instead of practical swords. But since time was moving toward the Bakumatsu　(end of Edo period) when the conflict age begun, this book is showing how he suffered in his sword-making considering the actual demand and the meaning of swords as practical weapons.

Science of Hamon Patterns

Cross-sectional structure of Japanese swords

Japanese swords are known for being “hard to break,” “hard to bend,” and “razor sharp.” To fulfill these expected functions, the materials used in the sword have to be hard to make it hard to bend and razor sharp, while at the same time being soft enough for the sword to be hard to break. To solve this conflict, the low carbon content steel is used for the inner layer and high carbon content steel for is used for the outer layer of Japanese swords.

Quenching

After the Japanese sword has been formed, the blade is coated in clay before quenching.
The quenching process is as follows: first, the sword is heated to a high temperature (approximately 800 ℃, depending on the swordsmith). Then, the sword is rapidly cooled in water. This process hardens the edge of the sword. If, however, the heat is not high enough or the cooling down speed is not rapid enough, the sword will not be appropriately quenched.

Quenching and temper line patterns

Referring to the clay coating mentioned earlier, the clay is applied thinly to the edge of the sword, the area which should be heated or cooled and quenched easily. However, the clay coating is applied thickly to the rest of the sword. This is the area which should be harder to heat or cool down and is therefore difficult to quench.
The speed of heating or cooling differ, depending on the thickness of the clay and the sword itself. The edge of the sword is cooled down rapidly and becomes hard steel (microstructure). The patterns that appear between the area that is quenched and the one not quenched is called the tempered line.
Why are tempered lines reflective?
The quenching process makes the tempered line patterns appear. The surface of this area is rough and has angularities. When a light is shined on the sword, this area shows a diffused reflection, which is considered one of the reasons why the temper line pattern of a sword appears bright.
It is important to note that the conditions of the materials differ and temperatures of different areas of the sword vary when the smith is forging the sword. Moreover, what happens during the quenching process is not constant. The surface of the sword is also not always even and flat. People’s eyes are capable of catching very subtle differences—as described above—on a micro- and macroscopic scale and these variations are then perceived as changes in the patterns.

Recording Hamon Patterns

Kanchiinbon meizukushi

This is a document which was handed down from the sub-temple of Tōji, Kanchi-in. It is one of the first primitive books of swords which was originally written in the Kamakura period and transcribed in Ōei 30(1432). The top half of the page is showing a simple drawing of a tang. The inscription and the file marks are also transcribed but the document looks like a casual record.

Kanamono mokujutsusho

It is one of the oldest book of oshigata(hand tracing) containing both tangs and hamon. There are some inaccurate points such as the tang shapes and the tachi inscription being as the katana inscription but it is introducing the points to notice on the swords well and trying to record the styles of each swordsmith.

Kajihei Hosoda Heijirō Fujiwara Naomitsu Oshigata

It is an oshigata book made by Hosoda Heijirō Naomitsu(commonly known as Kajihei) who was a swordsmith in the Bakumatsu time（the end of Edo period）. It contains the tangs of swordsmiths who were active in the shintō period and shin-shintō period and some drawings of hamon. In those days, the tracing was taken by inking the tangs directly, putting the paper on top and rubbing the paper to transfer the shape to it.

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