Japanese Swords | MITSUBISHI MATERIALS CORPORATION

Japanese Swords

 

Japanese swords and their rich individual histories have fascinated people for centuries. Swords were first used as weapons in the Tumulus Period (3rd century).
Swords seen in the Asuka (592-710) and Nara (710-794) Periods were called chokuto, or straight sword, a name that reflects their use for thrusting rather than slashing.
The evolution of what was to become the classic Japanese katana the world has come to know began in the Heian Period (794-1192), which saw a surge in the demand for swords due to the many internal conflicts that took place during that period, the most famous of which is perhaps the clash between the Genji and Heike Clans known as the Genpei Kasen. Before this time, imported swords were valued over domestic blades for their quality.
With each successive conflict, however, these early Japanese swordsmiths (tosho) improved their craft, eventually arriving at the characteristic curved blade, or wanto that distinguishes the Japanese katana from other swords seen around the world.
The introduction of cavalry to Japanese warfare spurred improvements in the length and arc of the blade to allow mounted warriors to more effectively wield their swords in battle, which is called tachi.
With the emergence of samurai as the ruling class of the military government established in the Kamakura Period (1192-1333), skillful craftsmen cultivated under the Shogunate began to produced new types of bladed weapons such as the tanto (short sword), naginata and yari (pole weapons). Development continued as Japan faced the two Mongol Invasions (1274 and 1281) in the late Kamakura Period.
It was at this time that the prevailing method of battle shifted from individual combat to coordinated unit tactics, and bladed weapons were produced to meet the needs brought about by this change.
Some of them are now national treasures. The Muromachi Period (1336-1573) saw the introduction of short swords, or kozori, swords for indoor fighting, or wakizashi, and the two-sword samurai style that we are familiar with today.
They were also important products in overseas trade. By the Sengoku Period (1467-1590), which saw the rise of two famous samurai, Oda Nobunaga and Toyotomi Hideyoshi, the quality of swords had improved to such a degree that they had become prized possessions and symbols of authority, taken as spoils of war and presented as honors.
The introduction of firearms brought rapid change. Armor design shifted to emphasize ease of movement and improved protection.
Along with this came the appearance of the uchigatana, a sword whose weight and length made it ideal for combat. The uchigatana is what we generally think of nowadays as the Japanese sword. In the Edo Period (1603-1868), laws were established to restrict sword ownership by class, limiting, for example, tradesmen and craftsmen to short swords.
As peace spread during the Edo Period, sword use declined. At the end of the period (1853), however, sword use rose as forces within the nation again plunged into conflict.
Although personal possession of swords was prohibited in 1876, they continue to fascinate us because we feel the proud history of the samurai that made them famous as they built the Japan we live in now.


Forging a Japanese Sword
Forging a Japanese sword requires strength and specialized skill, and swordsmiths are masters at creating designs, selecting material, and finishing. The following are the major steps involved in making Japanese swords.

Tip of the Japanese Swords

1. The key is that the tip does not to break or bend.

The strength of Japanese swords is ensured by the selection of the best material for each part. The process of realizing the ideal combination of core softness and outer-layer hardness is called tsukuri-komi. Using softer metal (shingane) in the core helps to absorb and reduce impact, and wrapping it with a harder metal (kawagane) prevents the blade from bending.

Metallurgy

Tanto
Tamahagane, as a raw material, is a highly impure metal. Formed in a bloomery process, the bloom of sponge iron begins as an inhomogeneous mixture of wrought iron, steels, and pig iron. The pig iron contains more than 2% carbon. The high-carbon steel has about 1 to 1.5% carbon while the low-carbon iron contains about 0.2%. Steel that has a carbon content between the high and low carbon steel is called bu-kera, which is often resmelted with the pig iron to make saga-hagane, containing roughly 0.7% carbon. Most of the intermediate-carbon steel, wrought iron and resmelted steel will be sold for making other items, like tools and knives, and only the best pieces of high-carbon steel, low-carbon iron, and pig iron are used for swordsmithing.



The various metals are also filled with slag, phosphorus and other impurities. Separation of the various metals from the bloom was traditionally performed by breaking it apart with small hammers dropped from a certain height, and then examining the fractures, in a process similar to the modern Charpy impact test. The nature of the fractures are different for different types of steel. The high-carbon steel, in particular, contains pearlite, which produces a characteristic pearlescent-sheen on the crystals.[22]



During the folding process, most of the impurities are removed from the steel, continuously refining the steel while forging. By the end of forging, the steel produced was among the purest steel-alloys of the ancient world. Due to the continuous heating the steel tends to decarburize, so a good quantity of carbon is either extracted from the steel as carbon dioxide or redistributed more evenly through diffusion, leaving a nearly eutectoid composition (containing 0.77 to 0.8% carbon).[23][24] The edge-steel itself will generally end up with a composition that ranges from eutectoid to slightly hypoeutectoid (containing a carbon content under the eutectoid composition), giving enough hardenability without sacrificing ductility[25] The skin-steel generally has slightly less carbon, often in the range of 0.5%. The core-steel, however, remains nearly pure iron, responding very little to heat treatment.[25] Cyril Stanley Smith, a professor of metallurgical history from MIT, performed an analysis of four different swords, each from a different century, determining the composition of the surface of the blades:[26]
Blade composition
Era Carbon (edge)   Carbon (body)    Manganese     Silicon  Phosphorus      Copper
1940s 1.02%            1.02%                   0.37%                     0.18%    0.015%          0.21%
1800s 0.62%               1.0%               0.01%                        0.07%     0.046%         0.01%
1700s 0.69%            0.43%           0.005%                         0.02%       0.075%         0.01%
1500s 0.5%            0.5%               0.005%                         0.04%        0.034%         0.01%

              In 1993, Jerzy Piaskowski performed an analysis of a katana of the kobuse type by cutting the sword in half and taking a cross section. The analysis revealed a carbon content ranging from 0.6 to 0.8% carbon at the surface, but only 0.2% at the core.
The steel in even the ancient swords may have sometimes come from whatever steel was available at the time. Due to its rarity in the ancient world, steel was usually recycled, so broken tools, nails and cookware often provided a ready supply of steel. Even steel looted from enemies in combat was often valued for its use in swordsmithing.
The different layers in this blade are evident due to the difference in their carbon content, which is exaggerated at the hamon giving it a wispy appearance.
According to Smith, the different layers of steel are made visible during the polishing due to one or both of two reasons: 1.) Either the layers have a variation in carbon content, or 2.) they have variation in the content of slag inclusions. When the variation is due to slag inclusions by themselves, there will not be a noticeable effect near the hamon, where the yakiba meets the hira. Likewise, there will be no appreciable difference in the local hardness of the individual layers. A difference in slag inclusions generally appear as layers that are somewhat pitted while the adjacent layers are not. In one of the first metallurgical studies, Professor Kuni-ichi Tawara suggests that layers of high slag may have been added for practical as well as decorative reasons. Although slag has a weakening effect on the metal, layers of high slag may have been added to diffuse vibration and dampen recoil, allowing easier use without a significant loss in toughness

2. Other crafts related to sword making

The creation of a Japanese sword requires more than the swordsmith who makes the blade. A number of other craftsmen take part in the process, craftsmen such as polishers (togi-shi) who add sharpness and beauty to the blade, scabbard makers (saya-shi) who ensure the perfect fit for each sword, lacquer painters (nu-shi) who coat the scabbard, silversmiths (shirogane-shi) who make the metal fittings placed between the blade and hilt, hilt wrappers (tsukamaki-shi) who craft sharkskin and other materials, and handguard makers (tsuba-shi).

3. How to distinguish tachi swords from uchigatana

When we look at a sword, we notice that some blades are exhibited with the sharp edge upward and others are exhibited with the sharp edge downward. This is the difference between tachi and uchigatana. While a Tachi is carried with the blade edge facing downward for easy drawing when riding on horseback, uchigatana is carried with the edge upward for easy drawing while on foot.

4. Iwaku – One of the attractions of Japanese Swords

It is also interesting to learn the legends related to each sword. For example, a famous Japanese sword called douji-kiriyasu-tsuna is said to have cut the head off an ogre. Heshikiri-hasebe is said to have been owned by famous warlord Oda Nobunaga. Nikkari aoe is said to have been so sharp it even killed a ghost.

5. How to become a swordsmith

Becoming a Japanese swordsmith takes five to ten years studying under a master and passing an examination given by the Japanese Agency for Cultural Affairs. There are currently approximately 350 licensed swordsmiths in Jwapan. Each licensed swordsmith is limited to producing 24 swords per year to maintain the high standard of quality.

6. Purchasing a Japanese sword?

Japanese swords are sold at sword and antique stores. A Japanese sword certified as a work of art can be purchased by anyone. These are for display only, however, because carrying one in a public place or removing it from its scabbard are strictly prohibited.