Samurai Sword "Katana"
Brief Overview of Katana (Japanese Sword)
The Swords forged with Spirit of Japan
Katana (Samurai Sword) is a generic term for swords forged in the originally developed way in Japan. They are classified as Katana (Tachi, Uchigatana), Wakizashi and Tanto depending on size. Craftsmen who make Katana are called 'Toko (sword craftsman),' 'Tosho (sword master)' or 'Katana kaji (swordsmith).
The Very Soul of the Samurai
Its beautiful shape has symbolic meaning as well as its use as a weapon since ancient times, and many are highly appraised as art objects. Old and unbroken lines, including the Imperial family and shrines, value treasure swords (such as Amenomurakumono tsurugi) as a proof of power. They also functioned as a support pillar of spiritual culture, 'the very soul of the samurai against the backdrop of the military government. They feature a process of folding and forging' two types of metal, hard brittle steel and soft iron, so the Toshin (body of blade) and Nakago (core) are combined together. The Nakago has holes (Mekugi holes) to fix the body of blade to the Tsuka (handle) with pin fasteners.
Katana is not only a Weapon, but also an Art-craft
Different from swords of other countries, the biggest feature of Katana is that the body of blade itself has artistic value, aside from the fittings (Koshirae). Katana is found in a poem titled 'A Poem About the Katana' by Ou-yang Hsui in Baisong. This poem describes a merchant of Yueh (South China) who goes to Japan to buy Katana already being called treasure swords given their artistic qualities found in the fittings and appearance. Although the main point of A poem About the Katana' is to lament that books already lost in China still exist in Japan, and not about Katana, it shows that the beauty of Katana was already recognized by overseas curiosos from the late Heian period to the early Kamakura period as one of Japan's exports.
1. Documentary of Katana, the Samurai Sword (46:53)
2. Documentary of Japanese Swords (27:23)
Ability and Mentality of Katana
'Not to Break and Not Bend'
It is thought that the process of creation of Katana has been developed basically in order to achieve three conflicting natures, 'Not to break, not bend, and sharply cut' simultaneously. In the modern metallurgy, 'not break and not bend' is called 'compatibility of strength and tenacity' and improvement research of structural material has still being done night and day. Because saving trouble even a little makes this compatibility balance lost.
'Not to Break and Sharply Cut'
Also, 'sharply cut' and 'not break' are difficult to be compatible. This has been realized by having so-called functionally-gradated structure that the cutting edge is hard, and the hardness is gradually decreased to the core, which makes compressive residual stress generate at the cutting edge. The explanation above is a case showing that the ideal condition is realized in the whole blade, so in fact, invisible defects can make a sword easily broken. However, a Katana in the ideal condition is called 'the world's strongest cutting tool,' and with reason. The sharpness of Katana are stated everywhere. As a notable example, 'Kabuto-wari (helmet splitting)' with Katana by the Dotanuki group led by Kenkichi SAKAKIBARA is famous. With best pieces of katana, if you drop one sheet of paper on it, it will be cut by its weight.
Katana is specialized for 'Cut Off'
A Katana is not really light if you compare in the blade length, because its handle is longer than other swords. However, among the swords for double-handed use, it is one of the lightest ones. A Katana is originally suitable to 'cut off.' However, it is necessary to slide and pull when cutting so that the direction of force is added at a right angle against the object to cut, because the sword itself is light. With the same reason, when sharpening a sword to 'cut and kill,' it is sharpened in the direction to slide like a kitchen knife (similar in the way to handle double-edged sword). Tracing the history, from the Kofun period to the Nara period, when swords became separated between ceremonial use and actual use, 'Keito Tachi' and 'Kurozukuri-no Tachi' were only for 'cutting off.' In the Heian period, 'Kogarasu' adopted 'Kissaki moroha-zukuri (double edged tip style)' to be suitable also to 'stab,' but later, Tachi and Uchigatana didn't adopt Kissaki moroha-zukuri and had a curve to be suitable to 'cut' by wristing.
Values and Roles of Katana
It is quite an abnormal situation when people fight risking their lives, not just in battle, and they need to have a special determination. In such time, it is no wonder that 'the very soul of the samurai' of Katana, the mental and religious value as sacred treasures and the artistic value are needed as realistic force, in a way. There exist a lot of swords made during the war-torn period that are engraved with names of Shinto and Buddhist deities the owners believed in or with mantra, which interestingly reflects warriors' naked feelings. From the engineering aspect, in the periods when the theory of metallic crystal or phase transition was not resolved, sword craftsmen kept making an effort and achieved cutting tools that were excellent scientifically as well, which attracts much interest even now. This is because engineering control in the black box style is realized by accumulating and transmitting lots of meta-information including apparent change, texture, and smell that are not theorized or verbalized. In fact we don't interpret people's expression by fine and strict definition, but have an advanced ability to 'read the mind,' and especially since the Japanese are excellent in this ability, attempts to use Japanese manufacturing as an engineering system has begun in recent years.
Forging Technique of Katana
The forging technique of Katana, a highly advanced technique at the time, strove to achieve three highly sought after qualities, 'Not to break, not to bend, and a razor sharp cutting edge.
Tatara-buki method; the type of steel used to make a Katana is called Japanese steel or Tamahagane. Tamahagane is made using the 'Tatara-buki method,' an original Japanese steel making process. Not depending upon iron ore imported from other countries, using black iron sand found on beaches in Japan, achieves fast reduction at low temperature, and creates high-quality steel with few impurities, compared to the modern steelmaking processes.
Heated Tamahagane is hammered with a Tsuchi (hammer) to make a thin flat plate. When qenched in water and rapidly cooled, the excess carbon flakes off. This is called 'Mizuheshi' (removal of carbon using water). These are raw metal making processes called Heshi (removal process).
This case-hardened piece is called Heshi gane (removed metal), which is broken into small metal pieces using a Tsuchi (hammer). These metal pieces are stacked on the tip of a forging tool called 'Teko', and wrapped in Japanese traditional paper. Straw ash is applied, and then coated with clay slurry, then it goes into the furnace (Hodo) to heat until the clay surface melts. The straw ash and clay prevents scaling loss of the steel during heating and oxidizing. It is then hammered with a Kozuchi (light hammer) to form 6x9cm block. If there are not enough iron pieces, more are stacked, heated, hammered with a Kozuchi, and formed into an ingot weighing 1.8kg to 2.0kg. This is the process known as 'Tsumi wakashi' (stacked and heated). Other than Tamahagane, pig iron (Sentetsu) which contains a lot of carbon, and pure iron called Hocho tetsu also undergo Tsumi wakashi and Shita-gitae processing mentioned below.
The red-hot block is struck and elongated using a Tsuchi (hammer), and folded back into the middle of its length, which is called a 'folding method of forging' and it is done repeatedly. In fact, the word 'Muko-zuchi,' describes the method by which Tosho (Yokoza, master) and his disciple (Sente, helper) alternately strike the body of the blade with a Tsuchi, and this has become the root of the word 'Aizuchi wo utsu (chiming in).' In this step, folding is done about five or six times.
After finishing Shita-gitae with three types of steel, Tamahagane (literally "jeweled steel"), Sentetsu (pig iron), and Hocho tetsu (literally "kitchen knife steel," pure iron), they are hammered using a Kozuchi (light hammer) again to make metal pieces, selected to produce the proper steel composition, they are stacked and formed like the first Tsumi wakashi. In this step, four kinds of steel having different carbon content, Shingane (center metal), Munegane (back metal), Hanokane (blade metal) and Gawagane (side metal), are made.
Shingane are folded back 7 times, Munegane 9 times, Hanokane 15 times and Gawagane 12 times. By repeatedly forging after folding back the steel struck and elongated, impurities such as sulfur, excess carbon and non-metal impurities are removed, and a strong and homogeneous steel is created.
After getting four kinds of steel, Shingane (center metal), Munegane (back metal), Hanokane (blade metal) and Gawagane (side metal) by Shita-gitae (forging), the second Tsumi wakashi (stacked and heated metal) and Age-gitae (finishing forging), three layers of Munegane, Shingane and Hanokane are forged and welded, and struck and elongated to get four times the material, 20mm thick, 40mm wide, and 90mm long, and then cut into four. This is called the 'Core metal (芯金).' Gawagane is also heated, and struck and elongated to become twice as long as the Core metal, and is then cut in the center to make two Gawagane of the same length as the Core metal. Gawagane, Core metal and the other Gawagane are stacked in this order, heated, forged, and welded, then struck and elongated into a 15mm thick, 30mm wide, 500 to 600mm long plate. Teko' is cut off, then 'Nakago' which becomes the grip of a sword is heated, forged and welded.
Sunobe,' is done by striking and elongating to form the shape of the Katana, and Kissaki (piercing tip) is made by cutting off the end. Since this rough shape determines the final finished shape of a Katana, it is carefully formed by striking with a Kozuchi.
Mune (back) of the blade is struck to start the base of a triangular shape, and the blade side (Hirachi) is struck and elongated to reduce thickness. Then the Mune of the Nakago is struck to round the back edge, and lastly 'Shinogichi (ridge line)' is struck and formed. The whole body of the blade is heated at a lower temperature until it becomes reddish brown.
After it cools down, the black taint is removed by grinding with a rough polishing stone, and the Hirachi (blade) and Shinogichi (ridge line) are hammered using a Kozuchi (light hammer), and cold forging process is applied. The straight lines of Mune and blade are adjusted, and unevenness is shaved with a special plane for shaving metal called Sen (銑, with the radical of 金 and 舌, by right). In this step, 'Hawatari (length of the blade) and the 'Machi (notch)' is determined.
Namatogi' is done to grind out the shaving marks left by using the plane and this is done using a polishing stone. Then, after oil and fat are removed using straw ash with water, and the sword is dried.
As preparation for 'Yaki-ire (quenching)' to rapidly cool the heated blade with water or other liquid, 'Tsuchioki (soil coating)' where three types of Yakiba-tsuchi soil (soil used for quenching) are applied to the Hirachi (blade), Hamon (blade pattern) and Shinogichi (ridge line) are done. Yakiba-tsuchi soil (soil used for quenching) is applied thinly and evenly over the Hirachi (blade side), then Hamon (blade pattern) is designed with a writing brush using Yakiba-tsuchi soil for quenching for Hamon. Lastly, a thicker coating of Yakiba-tsuchi soil (for quenching) is applied for the Shinogichi (ridge line) from the Hamon (blade pattern) to Mune (back). By using thicker concentration of Yakiba-tsuchi soil, for quenching, on the Shinogichi (ridge line), when cooling rapidly by Yaki-ire, the blade side is quickly cooled and quenched completely, and the Mune side is cooled relatively slowly and not fully quenched. Quenching makes a sword harder, the metal expands, and creates the distinct curve of a Katana. The Mune expands less, and takes on the property of tenacity rather than hardness, and this supports the blade side steel which is hard, but otherwise easily broken.
Generally during Yaki-ire, Tosho dims the light of the workshop, and judges the temperature of steel by its glow. The blade coated with Tsuchioki is inserted deeply into the Hodo, and the whole blade from end to end is heated uniformly to about 800 degrees. The temperature is most important, and the optimal heat condition is checked with the greatest care, the body of blade is then plunged swiftly to a water tank and rapidly cooled. As mentioned above, the blade warps in the water, and it is pulled out after it is fully cooled, and is then ground with a rough polishing stone, and the Yakiba (焼刃, cutting edge) is checked. After that, the blade is reheated in a charcoal fire for 'Yaki-modoshi (tempering).' This work is called 'Aitori (neutralizing).' Since it also warps to the side a little, it is struck while on a wooden base with a Kozuchi (light hammer) to adjust straighten the blade. The Nakago (core) is also tempered and formed. After Yaki-ire (quenching), the surface of the blade is very hard and this is called Martensite. Depending on how the Martensite looks, the Hamon (blade pattern) that looks like round particles on the surface of the metal to the naked eye, is called Nie (literally "boiling"), and separates from the Nioi (literally "scent") that looks like fine lines because the individual particles cannot be distinguished. Other than water, some of other cutting tools are quenched in oil, and as were Japanese military swords during the war, but today, it seems to be reare that a Katana is quenched in oil. Although quenching in oil reduces failure, it is not suitable for modern swords that are meant to become a work of art because it cannot achieve a fine Hamon (blade pattern).
The sword craftsman modifies the curvature of the Katana after Yaki-ire (quenching) is finished, and does a rough grinding. In this step, final adjustment is done by checking for small scratches, blade thickness and Jiba (blade surface).
Nakago (core) is finished with a Sen (a grinding tool) or a file, and for a Mekugi (fastening pin) hole used for securing the Tsuka (handle grip), usually one hole is drilled and two for a sword used for Iaido (Japanese martial art). Then, Yasurime (to prevent hands from slipping on the grip), which is unique to sword craftsmanship, is added.
Lastly, the craftsman carves his own name, address or year the sword was made on into the Nakago (core) as Mei (an inscription) with a Tagane (borer). Generally, the name and address of the sword craftsman are inscribed on the front side (outside when wearing Tachi or Katana), and the year or name of the owner in the back side, but there are exceptions such as back-inscription or no inscription at all. This is the end of the work for the sword craftsman, then a Togi-shi (polisher) polishes the sword finally, but before the Muromachi period, the sword craftsman himself also polished the sword. There is a big differences in polishing Katana compared to other cutting tools; ensuring ornamental elements of a Katana, as a craftwork, is focused on as well as assuming sharpness as a cutting tool, and the whole body, not just the blade part, is polished.