Katana construction

[Dept of PMM Hall of Steel]

Katana construction was the labour-intensive bladesmithing process developed in Japan for forging katana and other Japanese blades.
Katana and wakizashi were often forged with different profiles, different blade thicknesses, and varying amounts of grind. Wakizashi were not simply scaled-down katana; they were often forged in hira-zukuri or other such forms which were very rare on katana.
The daishō was not always forged together. If a samurai was able to afford a daishō, it was often composed of whichever two swords could be conveniently acquired, sometimes by different smiths and in different styles. Even when a daishō contained a pair of blades by the same smith, they were not always forged as a pair or mounted as one. Daishō made as a pair, mounted as a pair, and owned/worn as a pair, are therefore uncommon and considered highly valuable, especially if they still retain their original mountings (as opposed to later mountings, even if the later mounts are made as a pair).
Authentic Japanese swords are fairly uncommon today, although genuine antiques can be acquired at significant expense. Modern katana and wakizashi are only made by the few licenced practitioners that still practice making these crafted weapons today, and even the "type 98 katanas" of World War II are rare.
In Japanese, the scabbard for a katana is referred to as a saya, and the handguard piece, often intricately designed as an individual work of art — especially in later years of the Edo period — was called the tsuba. Other aspects of the mountings (koshirae), such as the menuki (decorative grip swells), habaki (blade collar and scabbard wedge), fuchi and kashira (handle collar and cap), kozuka (small utility knife handle), kogai (decorative skewer-like implement), saya lacquer, and tsuka-ito (professional handle wrap, also named emaki), received similar levels of artistry.
Composition
The composition of steel used for katana varied from smith to smith and lode to lode of iron ore. One formula from World War II shin guntō production was as follows:
elemental composition:
Iron
95.22% to 98.12%
Carbon
0.10% to 3.00%
Copper
1.54%
Manganese
0.11%
Tungsten
0.05%
Molybdenum
0.04%
Titanium
0.02%
Silicon
Varying amount
Miscellaneous compounds Trace amount
Modern traditional and reproduction katana
Traditional katana are still made in Japan and occasionally elsewhere; they are termed "shinsakuto", and can be very expensive. These are not considered reproductions as they are made by traditional techniques and from traditional materials. Swordsmiths in Japan are licensed; acquiring this license requires a long apprenticeship. Outside of Japan there are a couple of smiths working by traditional or mostly-traditional techniques, and occasional short courses taught in Japanese swordsmithing.[1] The only Japanese-licensed smith outside of Japan, Keith Austin (art-name Nobuhira or Nobuyoshi) died in 1997.[2]
A very large number of low-quality reproduction katana are available; their prices usually range between $20 to about $200. These cheap blades are machine made and machine sharpened. Usually they are minimally hardened or heat-treated and the hamon pattern (if any) on the blade is applied by scuffing, etching or otherwise marking the surface; there is no difference in hardness or temper of the edge.[3] The metal used to make low-quality blades is mostly cheap stainless steel, and typically is much harder and more brittle than true katana. Finally, cheap reproduction katana usually have fancy designs on them since they are just for show. Better-quality reproduction katana typically range from $200-300 to about $1000 (though some can go easily above two thousand for quality production blades, folded and often traditionally constructed and with a proper polish [4]), and high-quality or custom-made reproductions can go up to $15000-$50000 [5]. These blades are made to be used for cutting, and are usually heat-treated. High-quality reproductions made from carbon steel will often have a differential hardness or temper similar to traditionally-made katana, and will show a hamon; they won't show a hada (grain), since they're not often made from folded steel. A wide range of steels are used in reproductions, ranging from carbon steels such as 1070 and 5160, stainless steels such as 440C, and specialty steels such as L6 and D2. Most cheap reproductions are made from inexpensive stainless steels such as 440A (often just termed "440").[6] With a normal Rockwell hardness of 56, stainless steel is much harder than the back of a differentially hardened katana, (HR50), and is therefore much more prone to breaking when used to make long blades. Stainless steel is also much softer at the edge, (a traditional katana is usually more than HR60). Cheap swords designed as wall-hanging decorations often also have a rat-tail tang, which is a thin, usually threaded bolt of metal welded onto the blade at the hilt area. These are a major weak point and often break at the weld. [7]
Construction
The legitimate Japanese sword is made from Japanese steel "Tamahagane".[8] The forging of a Japanese blade typically took hours or days, and was considered a sacred art.[9] 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 specialists as well.
The steel for the swords is produced by smelting iron sand in a large clay furnace called a tatara. The steel bloom, or kera, produced contains steel that varies greatly in carbon content, ranging from wrought iron to pig iron. Three types of steel are chosen for the blade; a very low carbon steel called hocho-tetsu is used for the core of the blade, called the shingane. The high carbon steel, called tamahagane, and the pig iron, called nabe-gane, are combined to form the outer skin of the blade, called kawagane.[10][11][12] Only about 1/3 of the kera produces steel that is suitable for katana production.[13]
The most famous part of the manufacturing process was the folding of the steel. Japanese swords and other edged weapons are manufactured by the Chinese method of repeatedly heating, folding and hammering the metal. The low carbon hocho-tetsu is folded several times by itself, to purify it. The high carbon tamahagane and the higher carbon nabe-gane are then forged in alternating layers. The nabe-gane is heated, quenched in water, and then broken into small pieces to help free it from slag. The tamahagane is then forged into a single plate, and the pieces of nabe-gane are piled on top, and the whole thing is forge welded into a single block, which is called the age-kitae process. The block is then elongated, cut, folded, and forge welded again. This process, called the shita-kitae, is then repeated from 8 to as many as 16 times. After 20 foldings, (220, or about a million individual layers), there is too much diffusion in the carbon content, and the act of folding no longer gives any benefit to the steel. This process forms the kawagane, (or, skin-steel). Careful positioning of the grain in the steel is used between layers, differing, depending on what part of the blade the steel will be used. The steel is coated in a mixture of clay, water and straw-ash to protect it from oxidation and carburization. The clay, in turn, acts as a flux, pulling impurities out from between the layers.[14][15][16] This practice became popular due to the use of highly impure metals, stemming from the low temperature yielded in the smelting at that time and place. The folding did several things:
• It provided alternating layers of differing hardenability. During quenching, the high carbon layers achieve greater hardness than the medium carbon layers. The hardness of the high carbon steels combine with the ductility of the low carbon steels to form the property of toughness.[17][18]
• It eliminated any bubbles in the metal.
• It homogenized the metal, spreading the elements (such as carbon) evenly throughout - increasing the effective strength by decreasing the number of potential weak points.
• It burned off many impurities, helping to overcome the poor quality of the raw Japanese steel.
• It created up to 65000 layers, by continuously decarburizing the surface and bringing it into the blade's interior, which gives the swords their grain (for comparison see pattern welding).
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, wood-like grain itame, wood-burl grain mokume, and concentric wavy grain (an uncommon feature seen almost exclusively in the Gassan school) ayasugi-hada. The difference between the first three grains is that of cutting a tree along the grain, at an angle, and perpendicular to its direction of growth (mokume-gane) respectively, the angle causing the "stretched" pattern. The blades that were considered the most robust, reliable, and of highest quality were those made in the Mino tradition, especially those of Magoroku Kanemoto. Bizen tradition, which specialized in mokume, and some schools of Yamato tradition were also considered strong warrior's weapons.[citation needed]
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. 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. 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 bends easily and does not hold an edge. To control the cooling, the sword is heated and painted with layers of sticky clay. A thin layer on the edge of the sword ensures quick cooling for a hard edge, with a thicker layer of mud on the rest of the blade causing slower cooling and softer, more bendable steel to allow the blade to bend instead of breaking. When the application is finished, the sword is quenched and hardens correctly. 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.
Eventually the Japanese began to experiment with using different types of steel in different parts of the sword.

The vast majority of good katana and wakizashi are of wariba-gitae type. 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. More complex models allow for parrying without fear of damaging the side of the blade. 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. The last generally accepted model, the shiho-zume-gitae, is quite rare, but added a rear support.
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 or more. 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.
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. The presence of a so-called "blood groove" or fuller does not in actuality allow blood to flow more freely from cuts made with the sword. It leads to no demonstrable difference in ease withdrawing a blade nor reduce the sucking sound that many people believe was the reason for including such a feature in commando knives in World War II. The grooves are analogous in structure to an I beam, lessening the weight of the sword yet keeping structural integrity and strength. 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).
Furthermore the grooves (always done on both sides of the blade) make a whistling sound when the sword is swung (the tachikaze). If the swordsman hears one whistle when swinging a grooved katana then that means that just one groove is making the whistle. Two whistles means that both the edge of the blade and a groove are making a whistle, and three whistles together (the blade edge and both grooves) would tell the swordsman that his blade is perfectly angled with the direction of the cut.
Polishing
When the rough blade is completed, the swordsmith turns the blade over to a polisher called a togishi, whose job it is to refine the shape of a blade and improve its aesthetic value. The entire process takes considerable time, in some cases easily up to several weeks. Early polishers used three types of stone, whereas a modern polisher generally uses seven. The modern high level of polish was not normally done before around 1600, since greater emphasis was placed on function over form. The polishing process almost always takes longer than even crafting, and a good polish can greatly improve the beauty of a blade, while a bad one can ruin the best of blades. More importantly, inexperienced polishers can permanently ruin a blade by badly disrupting its geometry or wearing down too much steel, both of which effectively destroy the sword's monetary, historic, artistic, and functional value.
On high quality blades, only the back of the blade and the adjacent sides, (called the shinogi-ji), are polished to a mirror-like surface. To bring out the grain and hamon, the center portion of the blade, (called the hira), and the edge, (the ha), are usually given a matte finish. Microscopic scratches in the surface vary, depending on hardness. Smaller but more numerous scratches in the harder areas reflect light differently than the deeper, longer scratches in the softer areas. The harder metal appears more matte than the softer, and the manner in which it scatters light is less affected by the direction of the lighting.[19]
Stages
The process is divided into two stages: Shitaji togi (Foundation polishing) and Shiage togi (Finish polishing).
Shitaji togi
Shitaji togi sets the geometry of the blade and encompasses all main stages; utilizing large waterstones of increasingly finer grit. The sword is first inspected for straightness: If it isn't straight for whatever reasons, the duty of correcting it falls to the polisher. Straightening usually involves using wooden jigs to correct any bends in the blade. From this point on, a polisher works to form and grind surfaces and geometry as needed; note that these stages are also where damage is repaired through careful reshaping. The relatively-small point area of the blade, the kissaki, is distinct enough that it must be worked on by dividing the polishing among smaller subregions. Any present hi (fullers) are also polished but not with the large main stones, instead a variety of methods are used including smaller-sized stones, a migaki-bo (hardened-steel burnishing needle) or even fine-grit sandpaper.
Artificial waterstones are nowadays used for the foundation polishing stage, but almost never used for finishing, as they will produce inferior results compared to natural stones.
Shiage togi
Shiage togi is the stage that places the mirrorlike finish on a blade; the most notable differences between this and the previous stage are that the stones are of considerably smaller size, and that the blade remains stationary, instead having the abrasives and tools moved over it. In this stage, a blade is painstakingly worked on section by section, using wafer-thin slices cut from the main stones. After this is done, the blade's look will still be slightly unbalanced, and is corrected with a special nugui mixture that adjusts it. This stage is also where the yokote line is brought out; it may be either artificial or following the existing line (more often than not however, they are usually lost during a prior polishing stage). The final major step involves fully-burnishing the rear and sides.
The finishing process brings out and enhances all details of a blade so that they are readily-visible for observation and analysis, which entails results that must be free of any visual imperfections.
Hamon finishes
There are two main styles of hamon finishes, "hadori" and "sashikomi nugui".
Hadori
The hadori style is named after the hadori stone used, a waterstone selected for its slightly-greater coarseness which helps lighten the hamon and make it stand out against surrounding areas. The hadori style cannot exactly replicate the hamon as the finishing is actually a trace of the original; thus its quality depends mainly on the nature of the hamon itself, available equipment and the skill of the polisher. This process is relatively new, having been developed in the past century.
Sashikomi nugui
The shashikomi nugui style is named after the nugui mixture used to produce the final effect. First, the entire hamon is run over by a hazuya stone, a process which also is done to the jihada as well. Next a jizuya stone is used to bring out the hada or grain of the blade. Sashikomi nugui is usually composed of magnetite or tsushima and other compounds depending upon the desired color for the jihada. The nugui mixture is applied to the whole blade and if properly done, the hamon will be whiten slightly but surrounding areas will considerably darken. In this case, the hamon's appearance is exactly preserved. This process is normally only done on blades with well-defined hamons and grain patterns.
Evaluation
Polishing is a crucial step in preparing a blade for analysis, since it brings out and enhances all external details as mentioned earlier. This is important because details such as the shape, geometry, particular proportions, appearance of the hamon and grain pattern and so on, are distinctive enough that they can be used to accurately determine the heritage and origin of a blade. As such, they can be considered a more trustworthy signature of a smith than the actual signature itself.
A good polishing reveals what speed the edge was cooled at, from what temperature, and what the carbon content of the steel is. It does this by displaying either predominantly nioi, which is a mix of extremely fine martensite with troostite (another type of tempered steel), or the larger martensite crystals called nie, which look like individual dot-like mirrors.
Mountings
For more details on this topic, see Japanese sword mountings.
From here, the blade is passed on to a hilt-maker, or sayashi. 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 hand 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 koshirae.)
There is a pommel at the base known as a kashira, and there is often a decoration under the braided 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 hand guard and keeps the blade from rattling.
The sheaths themselves are not an easy task. There are two types of sheaths, both of which require exacting work to create. One is the shirasaya, which is generally made of wood and considered the "resting" sheath, used as a storage sheath. The other sheath is the more decorative or battle-worthy sheath which is usually called either a jindachi-zukuri, if suspended from the obi (belt) by straps (tachi-style), or a buke-zukuri sheath if thrust through the obi (katana-style). Other types of mounting include the kyū-guntō, shin-guntō, and kai-guntō types for the twentieth-century military.
References
1. ^ Basic Japanese Forging, Sword Forum online magazine, January 1999
2. ^ Keith Nobuhira Austin July 5, 1934-April 20,1997
3. ^ Americanized Japanese Swords, Sword Forum online magazine, January, 1999 — Comparison of Westernized Interpretations against Traditional Japanese Blades
4. ^ [1]
5. ^ The Samurai Sword, Discovery Channel documentary
6. ^ Is Stainless Steel Suitable for Swords?, Sword Forum online magazine, March 1999
7. ^ http://www.sword-buyers-guide.com/authentic-japanese-swords.html
8. ^ 鉄と生活研究会編　『鉄の本(Book of iron)』 　ISBN 9784526060120
9. ^ Irvine, Gregory. The Japanese Sword: The Soul of the Samurai. London: V&A Publications, 2000.
10. ^ http://www.hitachi-metals.co.jp/e/tatara/nnp0109.htm
11. ^ http://www.samuraisword.com/glossary/index.htm
12. ^ "A History of Metallography", by Cyril Smith
13. ^ http://www.hitachi-metals.co.jp/e/tatara/nnp01.htm
14. ^ http://www.samuraisword.com/REFERENCE/making/japanse_swordmaking_pr...
15. ^ "A History of Metallography", by Cyril Smith
16. ^ http://www.hitachi-metals.co.jp/e/tatara/nnp0109.htm
17. ^ http://www.pbs.org/wgbh/nova/samurai/
18. ^ http://www.hitachi-metals.co.jp/e/tatara/nnp01.htm
19. ^ A History of Metallography by Cyril Smith - The MIT Press 1960 Page 53-54

This entry is from Wikipedia, the leading user-contributed encyclopedia.