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Metallurgical effects on my swords

Pavel Bolf

HADA, steel folding structure and HAMON, hardening line.

HADA, the pattern of the folded steel, is one of the typical features of the Japanese sword. It is formed during the processing of the forged steel, its repeated folding and forge welding. The process of translating the steel is repeated 8-15 times , depending on the quality of the input steel and the desired result.

The reloading of steel melted in the TATARA primitive furnace is a necessary process to obtain relatively homogeneous and pure steel. Steel produced by the traditional process contains impurities, has an unevenly distributed carbon content and is porous. The reloading process mixes areas with different carbon content and thus homogenises the material. At the same time, the material is purified of unwanted impurities such as charcoal pieces, slag and the like.

The formation of the HADA structure is thus essentially a secondary phenomenon. However, the quality of the steel processing is also reflected on an aesthetic level precisely in the form of the folding structure. The pattern is influenced by the way the initial packet is folded, the number of folds, the way the packet is folded, the way it is forged, the composition of the packet during the final folding of the blade structure in which different steels are combined, and even the actual drawing of the packet into the bar and the subsequent forging of the blade. The swordsmith can influence the contrast, depth, fineness and pattern of the steel being folded. Some swordmaking schools have created a typical HADA pattern for them. For example, one of the oldest sword schools, GASSAN, creates an AYASUGI pattern in the structure of the steel in the form of regular waves or circles. Some schools combine patterns by stacking packets with differently processed steel. For example, the YAMATO school's swords have a MOKUME pattern on the sides and a MASAME pattern with a horizontal structure on the blade.

The basic HADA patterns are:

  • MASAME, a pattern with a horizontal layer structure
  • MOKUME, resembling a wood pattern.
  • ITAME, with a fibrous to dotted structure.
  • AYASUGI, a wave pattern.
  • NASHI JI, a fine HADA pattern reminiscent of the texture of a sliced pear.
  • MU JI. This structure is not readable to the eye. The steel has a completely homogeneous appearance.

Individual patterns can be combined or mixed. The density and contrast of the patterns may vary depending on the processing method. The polishing of the blade also has a great influence, where the polisher can suppress or accentuate the texture. A structure with large distinctive patterns and contrast is called Ó-HADA.

The structure of the overlay and the composition of the final packet also influence the final step in blade manufacture, hardening - YAKI IRE.

Different schools have hardened their typical hardening patterns. There are two methods of hardening blades. The first, used for example by the ICHIMONJI school, does not use clay paste in the hardening process. This defines the boundary of the HAMON temper line and is also used to create the pattern of this line. In the case of the ICHIMONJI school, the blade without the covering paste is heated in such a way that the high temperature required for the formation of the HAMON line is reached only on the edge. The amount of heating thus also defines the amount of hardening that occurs. In this way, the typical CHÓJI hardening is produced.

In the case of the use of paste, the pattern of the desired hardening line is drawn. The paste made of clay, which prevents the water from coming into contact with the covered surfaces of the blade, thus defines the border and the pre-drawn hardening pattern.

There are a number of HAMON patterns. Straight SUGUHA, wavy MIDARE, GUNOME curves, CHÓJI clove flower and a number of other patterns and combinations. In the SHONTO period after 1600, sword makers began to focus on creating intricate and flamboyant HAMON patterns. They tried to imitate flowers floating on the surface of water and similar motifs. A typical example of a swordmaker who achieved extreme skill in this area is Yoshimichi with his typical SUDARE BA pattern. The creation of perfect hardening patterns led to the use of more advanced techniques. The use of hardening paste has become an art, as has the creation of hardening patterns. In swords before this era, the HAMON was mainly a functional part of the sword. The hardening on swords of the KOTO period before 1600 is more natural in nature. This is most evident on swords of the 12th-13th Century. More natural and less violent hardening techniques gave rise to other natural metallurgical effects. One of these is UTSURI. This manifests itself as another line above HAMON. In some cases as a shadow of varying intensity, sometimes it contains or is bordered by light reflecting particles - NOT UTSURI. UTSURI is a secondary effect that is a manifestation of the way the blade is heated when it is clouded. Apart from the processing and quality of the steel, its form is influenced by the heating time and the difference in temperature of the individual bands during heating.

An interesting effect is KOSHIBA. It appears as a cluster of reflective particles at the beginning of the UTSURI line. This effect occurs almost exclusively on quality blades made in 12. And 13th Table. It demonstrates the sensitivity of steel and its ability to form different metallurgical structures depending on the length of heating and minimal temperature variations during hardening.

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