Editing Japanese sword (section)

==Manufacturing==
{{further|Japanese swordsmithing|Japanese sword polishing}}

[[File:Blacksmith Munechika, helped by a fox spirit, forging the blade Ko-Gitsune Maru, by Ogata Gekkō.jpg|thumb|240px|Blacksmith Munechika (end of the 10th century), helped by a fox spirit, forging the blade ''kogitsune-maru'' ("Little fox"). The spirit is represented by a woman surrounded by foxes. Engraving by [[Ogata Gekkō]] (1859–1920), 1873.]]
Japanese swords are generally made by a division of labor between six and eight craftsmen. ''Tosho'' (''Toko'', ''Katanakaji'') is in charge of forging blades, ''togishi'' is in charge of polishing blades, ''kinkosi'' (''chokinshi'') is in charge of making metal fittings for sword fittings, ''shiroganeshi'' is in charge of making ''habaki'' (blade collar), ''sayashi'' is in charge of making scabbards, ''nurishi'' is in charge of applying lacquer to scabbards, ''tsukamakishi'' is in charge of making hilt, and ''tsubashi'' is in charge of making ''tsuba'' (hand guard). ''Tosho'' use apprentice swordsmiths as assistants. Prior to the Muromachi period, ''tosho'' and ''kacchushi'' (armorer) used surplus metal to make ''tsuba'', but from the Muromachi period onwards, specialized craftsmen began to make ''tsuba''. Nowadays, ''kinkoshi'' sometimes serves as ''shiroganeshi'' and ''tsubashi''.<ref>[https://web.archive.org/web/20210518010440/https://www.touken-world.jp/tips/14761/ 刀装具の名工] Nagoya Japanese Sword Museum Nagoya Touken World</ref><ref>[https://www.youtube.com/watch?v=z9l9dgEEaPw Bizen Osafune Japanese Sword.] Setouchi City, Okayama Prefecture.</ref>

Typical features of Japanese swords represented by ''katana'' and ''tachi'' are a three-dimensional cross-sectional shape of an elongated pentagonal or hexagonal blade called ''shinogi-zukuri'', a style in which the blade and the [[Tang (tools)|tang]] (''nakago'') are integrated and fixed to the hilt (''tsuka'') with a pin called ''mekugi'', and a gentle curve.
When a ''shinogi-zukuri'' sword is viewed from the side, there is a ridge line of the thickest part of the blade called ''shinogi'' between the cutting edge side and the back side. This ''shinogi'' contributes to lightening and toughening of the blade and high cutting ability.<ref name="rekishi200936">''歴史人'' September 2020. p36, p47, p50. {{ASIN|B08DGRWN98}}</ref>

Japanese swords were often forged with different profiles, different blade thicknesses, and varying amounts of [[grind]]. ''Wakizashi'' and ''tantō'', for instance, were not simply scaled-down versions of ''katana''; they were often forged in a shape called ''hira-zukuri'', in which the cross-sectional shape of the blade becomes an isosceles triangle.<ref name="rekishi200936"/>

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).

The forging of a Japanese blade typically took weeks or even months and was considered a sacred art.<ref name="soul">{{cite book | last = Irvine | first = Gregory | title = The Japanese Sword: The Soul of the Samurai | publisher = London: V&A Publications | year = 2000 }}</ref> 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 (called a ''togi'') as well as the various artisans that made the ''koshirae'' (the various fittings used to decorate the finished blade and ''[[Saya (scabbard)|saya]]'' (sheath) including the ''tsuka'' (hilt), ''fuchi'' (collar), ''kashira'' (pommel), and ''tsuba'' (hand guard)). It is said that the sharpening and polishing process takes just as long as the forging of the blade itself.

[[File:Scene-de-forge-edo-p1000665.jpg|thumb|240px|left|Engraving from the Edo period depicting forge scenes.]]

The legitimate Japanese sword is made from Japanese steel "[[Tamahagane]]".<ref name = "鉄の本">鉄と生活研究会編 『鉄の本 (Book of iron) 』  {{ISBN|978-4-526-06012-0}}</ref> The most common lamination method the Japanese sword blade is formed from is a combination of two different [[steel]]s: a harder outer jacket of steel wrapped around a softer inner core of steel.<ref>{{cite book|last1=Tanaka|first1=Fumon|title=Samurai Fighting Arts: The Spirit and the Practice|date=2003|publisher=Kodansha International|page=35}}</ref> This creates a blade which has a hard, razor sharp cutting edge with the ability to absorb shock in a way which reduces the possibility of the blade breaking when used in combat. The ''hadagane'', for the outer skin of the blade, is produced by heating a block of raw steel, which is then hammered out into a bar, and the flexible back portion. This is then cooled and broken up into smaller blocks which are checked for further impurities and then reassembled and reforged. During this process the billet of steel is heated and hammered, split and folded back upon itself many times and re-welded to create a complex structure of many thousands of layers. Each different steel is folded differently, to provide the necessary strength and flexibility to the different steels.<ref>[https://www.pbs.org/wgbh/nova/samurai/ NOVA | Secrets of the Samurai Sword | PBS<!-- Bot generated title -->]</ref><ref>"A History of Metallography", by Cyril Smith</ref><ref>{{Cite web |url=http://www.samuraisword.com/REFERENCE/making/japanse_swordmaking_process.htm |title=Japanse Swordmaking Process ~ www.samuraisword.com<!-- Bot generated title --> |access-date=2009-06-23 |archive-date=2009-09-23 |archive-url=https://web.archive.org/web/20090923131554/http://www.samuraisword.com/REFERENCE/making/japanse_swordmaking_process.htm |url-status=dead }}</ref> The precise way in which the steel is folded, hammered and re-welded determines the distinctive grain pattern of the blade, the ''jihada'', (also called ''jigane'' when referring to the actual surface of the steel blade) a feature which is indicative of the period, place of manufacture and actual maker of the blade. The practice of folding also ensures a somewhat more homogeneous product, with the carbon in the steel being evenly distributed and the steel having no voids that could lead to fractures and failure of the blade in combat.

[[File:Katana brique.svg|thumb|Cross sections of Japanese sword blades showing lamination types.]]

The shingane (for the inner core of the blade) is of a relatively softer steel with a lower carbon content than the hadagane. For this, the block is again hammered, folded and welded in a similar fashion to the hadagane, but with fewer folds. At this point, the hadagane block is once again heated, hammered out and folded into a 'U' shape, into which the shingane is inserted to a point just short of the tip. The new composite steel billet is then heated and hammered out ensuring that no air or dirt is trapped between the two layers of steel. The bar increases in length during this process until it approximates the final size and shape of the finished sword blade. A triangular section is cut off from the tip of the bar and shaped to create what will be the kissaki. At this point in the process, the blank for the blade is of rectangular section. This rough shape is referred to as a {{transliteration|ja|sunobe}}.

The {{transliteration|ja|sunobe}} is again heated, section by section and hammered to create a shape which has many of the recognisable characteristics of the finished blade. These are a thick back ({{transliteration|ja|mune}}), a thinner edge ({{transliteration|ja|ha}}), a curved tip ({{transliteration|ja|kissaki}}), notches on the edge ({{transliteration|ja|hamachi}}) and back ({{transliteration|ja|munemachi}}) which separate the blade from the tang ({{transliteration|ja|nakago}}). Details such as the ridge line ({{transliteration|ja|shinogi}}) another distinctive characteristic of the Japanese sword, are added at this stage of the process. The smith's skill at this point comes into play as the hammering process causes the blade to naturally curve in an erratic way, the thicker back tending to curve towards the thinner edge, and he must skillfully control the shape to give it the required upward curvature. The {{transliteration|ja|sunobe}} is finished by a process of filing and scraping which leaves all the physical characteristics and shapes of the blade recognisable. The surface of the blade is left in a relatively rough state, ready for the hardening processes. The {{transliteration|ja|sunobe}} is then covered all over with a clay mixture which is applied more thickly along the back and sides of the blade than along the edge. The blade is left to dry while the smith prepares the forge for the final heat treatment of the blade, the yaki-ire, the hardening of the cutting edge.

This process takes place in a darkened smithy, traditionally at night, so that the smith can judge by eye the colour and therefore the temperature of the sword as it is repeatedly passed through the glowing charcoal. When the time is deemed right (traditionally the blade should be the colour of the moon in February and August which are the two months that appear most commonly on dated inscriptions on the tang), the blade is plunged edge down and point forward into a tank of water. The precise time taken to heat the sword, the temperature of the blade and of the water into which it is plunged are all individual to each smith and they have generally been closely guarded secrets. Legend tells of a particular smith who cut off his apprentice's hand for testing the temperature of the water he used for the hardening process. In the different schools of swordmakers there are many subtle variations in the materials used in the various processes and techniques outlined above, specifically in the form of clay applied to the blade prior to the yaki-ire, but all follow the same general procedures.

[[File:刀 次郎太郎直勝 Katana forged by Jirotaro Naokatsu 2.jpg|thumb|Example of a ''hamon''. It is not the entire white ''hadori'' area, but a fuzzy line within the ''hadori''. It is difficult to photograph, and to appreciate ''hamon'', the viewer must hold the sword in his hand and change the angle of the light on the blade as he views it.<ref name="jre220122"/><ref name="300421nagoya"/>]]
The application of the clay in different thicknesses to the blade allows the steel to cool more quickly along the thinner coated edge when plunged into the tank of water and thereby develop into the harder form of steel called [[martensite]], which can be ground to razor-like sharpness. The thickly coated back cools more slowly retaining the [[pearlite]] steel characteristics of relative softness and flexibility. The precise way in which the clay is applied, and partially scraped off at the edge, is a determining factor in the formation of the shape and features of the crystalline structure known as the [[Hamon (swordsmithing)|hamon]]. This distinctive tempering line found near the edge is one of the main characteristics to be assessed when examining a blade.

[[File:Japanese sword sharpener at work 1909.jpg|thumb|Sword [[Knife sharpening|sharpener]] practicing his trade, around 1909]]
The martensitic steel which forms from the edge of the blade to the hamon is in effect the transition line between these two different forms of steel, and is where most of the shapes, colours and beauty in the steel of the Japanese sword are to be found. The variations in the form and structure of the hamon are all indicative of the period, smith, school or place of manufacture of the sword. As well as the aesthetic qualities of the hamon, there are, perhaps not unsurprisingly, real practical functions. The hardened edge is where most of any potential damage to the blade will occur in battle. This hardened edge is capable of being reground and sharpened many times, although the process will alter the shape of the blade. Altering the shape will allow more resistance when fighting in hand-to-hand combat.

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, grooves and markings (hi or bo-hi) may be 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 the hilt later. The tang is never supposed to be cleaned; doing this can reduce the value of the sword by half or more. The purpose is to show how well the steel ages.

Some other marks on the blade are aesthetic: dedications written in Kanji characters as well as engravings called ''horimono'' depicting gods, dragons, or other acceptable beings. Some are more practical. The presence of a groove (the most basic type is called a ''hi'') reduces the weight of the sword yet keeps its structural integrity and strength.