Katana

: This article is about the Japanese sword. For the motorcycle, see Suzuki Katana..

Manufacturing

Japanese swords and other edged weapons are manufactured by an elaborate method of repeatedly heating, folding and hammering the metal. This practice was originated from use of highly impure metals, stemming from the low temperature yielded in the smelting at that time and place. In order to counter this, and to homogenize the carbon content of the blades (giving some blades characteristic folding patterns), the folding was developed (for comparison see pattern welding), and found to be quite effective, though labour intensive.

Related Topics:
Weapon - Metal - Smelting - Carbon - Pattern welding

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The distinctive curvature of the katana is partly due to a process of differential quenching. The back of the sword is coated with clay, insulating it and so causing it to cool slower than the edge when the blade is quenched. This produces a blade with a hard edge and soft back, allowing it to be resilient and yet retain a good cutting edge.

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This process also makes the edge of the blade contract less than the back when cooling down, something that aids the smith in establishing the curvature of the blade.

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While some people believe that katana and wakizashi were constructed alike, this was not always the case. They were often forged with different profiles, different blade thicknesses, and varying amounts of niku. Wakizashi were also not simply a 'scaled down' katana, they were often forged in hira-zukuri or other such forms, which were very rare on katana.

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Manufacturing processes are described in greater detail in following subsections.

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Composition

Traditional Japanese steel is considered to be one of the best for creating swords. The total composition varied from smith to smith and lode to lode of ore.

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One more modern formula (from World War II):

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The high percentage of carbon gave the blade strength while the silicon increased the flexibility of the blade as well as its ability to withstand stress. The katana was designed only to cut flesh, so the composition was not always adequate to effectively break armor.

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Construction

The forging of a Japanese blade typically took hours or days, and was considered a sacred art. As with many complex endeavors, rather than a single craftsman, several artists were involved. There was a smith to forge the rough shape, often a second smith (apprentice) to fold the metal, a specialist polisher, and even a specialist for the edge itself. Often, there were sheath, hilt, and tsuba (handguard) specialists as well.

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The most famous part of the manufacturing process was the folding of the steel. Steel was repeatedly 'folded', bent over itself and hammered flat. This did several things:

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• It eliminated any bubbles in the metal.
• It evened out the metal, spreading the elements (such as carbon) evenly throughout.
• It created layers, by continuously decarburizing the surface and bringing the surface into the blade's interior, which gives the swords their unique grain. The layered structure (see Bulat steel) provides enhanced mechanical properties of the steel.
• Lastly, it strengthened the metal (perhaps by more evenly distributing the imperfections).

Contrary to popular belief, continued folding will not create a "super-strong" blade; once impurities are burnt off and the carbon content homogenized, further folding offers little benefit and will gradually burn out the carbon, leading eventually to a softer steel less able to hold an edge. The number of folds varied from sword to sword, but those with more than about a dozen folds are uncommon, and authentic swords with more than two dozen folds are unknown. It should be noted that a blade folded 12 times will have more than 4,000 'layers' underneath the initial blade to begin with, and that 20 folds would produce a blade with over a million layers. Beyond this number, the molecular structure of the blade is such that further folding would most likely serve no further purpose.

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Generally, swords were created with the grain of the blade (called 'hada') running down the blade like the grain on a plank of wood. Straight grains were called 'masame-hada', whereas wavy grains were called 'ayasugi-hada'. Certain schools of construction had the grain running directly into the blade, resulting in a ringed pattern. If it resembled stretched knotted wood, it was called 'itame-hada'; if it was round in shape, it was called 'mokume-hada'. The difference is one of cutting a tree perpendicular to its direction of growth (mokume) or at an angle (itame), the angle causing the "stretched" pattern. The blades that were considered the most robust, reliable, and of highest quality were those made in the Bizen tradition, which specialized in mokume.

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One of the core philosophies of the Japanese sword is that it has a single edge. This means that the rear of the sword can be used to reinforce the edge, and the Japanese took full advantage of this fact. When finished, the steel is not quenched or tempered in the conventional European fashion. Steel’s exact flex and strength vary dramatically with heat variation, and depending on how hot it gets and how fast it cools, the steel has vastly different properties. If steel cools quickly, from a hot temperature, it becomes martensite, which is very hard but brittle. Slower, from a lower temperature, and it becomes pearlite, which has significantly more flex but doesn’t hold an edge. To control the cooling, the sword is heated and painted with layers of sticky mud. A thin layer on the edge of the sword ensures quick cooling, but not so fast as to crack the sword steel (this makes the actual edge of the sword extremely hard martensite). A thicker layer of mud on the rest of the blade causes slower cooling, and softer steel, giving the blade the flex it needs (this makes the rear and inside of the sword into pearlite). When the application is finished, the sword is quenched and hardens correctly.

Related Topics:
Martensite - Pearlite

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Eventually the Japanese began to experiment with using different types of steel in different parts of the sword. Examples are shown below:

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The vast majority of 'good' katana and wakazashi are of 'wariba-gitae' type, but the more complex models allow for parrying without fear of damaging the side of the blade. The last generally accepted model, the 'shiho-zume-gitae', is quite rare, but added a rear support.

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The 'makuri-gitae' is made using two steels, one folded more times than the other, or of a lesser carbon content. When both sections have been folded adequately, they are bent into a 'U' shape and the softer piece is inserted into the harder piece, at which point they are hammered out into a long blade shape. By the end of the process, the two pieces of steel are fused together, but retain their differences in hardness. To make han-sanmai-awase-gitae or shiho-zume-gitae, pieces of hard steel are then added to the outside of the blade in a similar fashion.

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Anatomy of the katana

Each blade has a unique profile, depending on the smith, the construction method, and a bit of luck. The most prominent is the middle ridge, or 'shinogi'. In the earlier picture, the examples were flat to the shinogi, then tapering to the blade. However, swords could narrow down to the shinogi, then narrow further to the blade, or even expand outward towards the shinogi then shrink to the blade (producing a trapezoidal shape). A flat or narrowing shinogi is called 'shinogi-hikushi', whereas a 'fat' blade is called a 'shinogi-takushi'.

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The shinogi can be placed near the back of the blade for a longer, sharper, more fragile tip or a more moderate shinogi near the center of the blade.

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The sword also has an exact tip shape, which is considered an extremely important characteristic: the tip can be long (o-kissaki), short (ko-kissaki), medium (chu-kissaki), or even hooked backwards (ikuri-o-kissaki). In addition, whether the front edge of the tip is curved (fukura-tsuku) or straight (fukura-kareru) is also important.

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A hole is drilled into the tang, called a mekugi-ana. This hole is to anchor the hilt, and some of the older blades have more than one due to the length of the blade.

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Decoration

Almost all blades are decorated, although not all blades are decorated on the visible part of the blade. Once the blade is cool, and the mud is scraped off, the blade has designs and grooves cut into it. One of the most important markings on the sword is performed here: the file markings. These are cut into the tang, or the hilt-section of the blade, where they will be covered by a hilt later. The tang is never supposed to be cleaned: doing this can cut the value of the sword in half. The purpose is to show how well the blade steel ages. A number of different types of file markings are used, including horizontal, slanted, and checked, known as ichi-monji, kosuji-chigai, suji-chigai, o-suji-chigai, katte-agari, shinogi-kiri-suji-chigai, taka-no-ha, and gyaku-taka-no-ha. A grid of marks, from raking the file diagonally both ways across the tang, is called higaki, whereas specialized 'full dress' file marks are called kesho-yasuri. Lastly, if the blade is very old, it may have been shaved instead of filed. This is called sensuki. While ornamental, these file marks also serve the purpose of providing an uneven surface which bites well into the 'tsuka', or the hilt which fits over it and is made from wood. It is this pressure fit for the most part that holds the tsuka in place during the strike, while the mekugi pin serves as a secondary method and a safety.

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Some other marks on the blade are aesthetic: signatures and dedications written in kanji and engravings depicting gods, dragons, or other 'acceptable' beings, called horimono. Some are more practical, grooves for lightening and extra flex (as well as an intimidating sound, called tachikaze, when swung with force). Grooves come in wide (bo-hi), twin narrow (futasuji-hi), twin wide and narrow (bo-hi ni tsure-hi), short (koshi-hi), twin short (gomabushi), twin long with joined tips (shobu-hi), twin long with irregular breaks (kuichigai-hi), and halberd-style (naginata-hi). Contrary to popular belief, these grooves have nothing to do with improving the flow of enemy blood.

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Polishing

When the rough blade was completed, the swordsmith would turn the blade over to a polisher called a togishi, whose job it was to polish the steel of the blade to a glittering shine and sharpen the edge for battle. This takes hours for every inch of blade, and is painstaking work with different kinds of very fine stone. Early polishers used three types of stone, whereas a modern polisher generally uses seven. It almost always takes longer than actually crafting the blade does, and a good polishing makes a blade look better, while a bad polishing makes the best of blades look like gunto.

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One of the ways which blades can be judged is by what this polishing reveals: the crystal-like qualities of the blade become quite visible, and the hamon (known in English as the temper line, where the sharp edge fades into the normal steel of the blade) shows the unique nature of the sword. Each blade is distinct in its hamon and the grain (hada) of its steel. The hamon, which is determined primarily by how the mud is applied, is often used as a kind of signature of the smith, above and beyond his own signature, and each tradition of swordsmiths often has a particular style of hamon it prefers over all others. Hamon vary from straight to wavy to shaped like crabs or zigzags, and in their wandering they reveal important facts about the blade itself. A good polishing reveals what speed the edge was cooled at, from what temperature, and what the carbon content of the steel is. This is because it displays either nioi, which is a mix of extremely fine martensite with troostite (another type of tempered steel), or the more crystalline and obvious nie, which contains a lot of less fine martensite.

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Furnishings

From here, the blade is passed on to a hilt-maker. Hilts vary in their exact nature depending on the era, but generally consist of the same general idea, with the variation being in the components used and in the wrapping style. The obvious part of the hilt consists of a metal or wooden grip called a tsuka, which can also be used to refer to the entire hilt. The cross guard, or tsuba, on Japanese swords (except for certain twentieth century sabers which emulate Western navies') is small and round, made of metal, and often very ornate. (see related article on Koshirae)

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There is a pommel at the base known as a kashira, and there is often a decoration under the criss-crossed wrappings called a menuki. A bamboo peg called a mekugi is slipped through the tsuka and through the tang of the blade, using the hole called a mekugiana drilled in it. This anchors the blade securely into the hilt. To anchor the blade securely into the sheath it will soon have, the blade acquires a collar, or habaki, which extends an inch or so past the cross guard and keeps the blade from rattling.

Related Topics:
Kashira - Menuki - Mekugi - Mekugiana - Habaki

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The sheaths themselves are not an easy task. There are two types of sheaths, both of which require the same exacting work. One is the saya, which is generally made of wood and considered the 'resting' sheath, used in place of a more fragile and expensive sheath. The other sheath is the more decorative or battle-worthy sheath which is usually called either a jindachi-zukuri or a buke-zukuri, depending on whether it was supposed to be suspended from the belt by straps or thrust through a sash, respectively. Other types of mounting include the kyu-gunto, shin-gunto, and kai-gunto types for the twentieth-century military, but these swords were generally mass-produced and highly inferior, and few true Japanese swords are mounted in these styles.

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