Japanese sword blades were often forged with different profiles, different blade thicknesses, and varying amounts of grind. Wakizashi and tantō were not simply scaled-down katana but were often forged without a ridge (hira-zukuri) or other such forms which were very rare on katana.
To produce a difference in hardness, the steel is cooled at different rates by controlling the thickness of the insulating layer. By carefully controlling the heating and cooling speeds of different parts of the blade, Japanese swordsmiths were able to produce a blade that had a softer body and a hard edge.[30]This process also has two side effects that have come to characterize Japanese swords: 1.) It causes the blade to curve and 2.) It produces a visible boundary between the hard and soft steel. When quenched, the uninsulated edge contracts, causing the sword to first bend towards the edge. However, the edge cannot contract fully before the martensite forms, because the rest of the sword remains hot and in a thermally expanded state. Because of the insulation, the sword spine remains hot and pliable for several seconds but then contracts much more than the edge, causing the sword to bend away from the edge, which aids the smith in establishing the curvature of the blade. Also, the differentiated hardness and the methods of polishing the steel can result in the hamon 刃紋 (frequently translated as "tempering line" but better translated as "hardening pattern"). The hamon is the visible outline of the yakiba (hardened portion) and is used as a factor to judge both the quality and beauty of the finished blade. The various hamon patterns result from the manner in which the clay is applied. They can also act as an indicator of the style of sword-making and sometimes as a signature for the individual smith. The differences in the hardenability of steels may be enhanced near the hamon, revealing layers or even different parts of the blade, such as the intersection between an edge made from edge-steel and sides made from skin-steel.[31][32]
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In later times, this effect was often imitated by partially mixing various metals like copper together with the steel, forming mokume (wood-eye) patterns, although this was unsuitable for the blade. After the 14th century, the Japanese technology had reached a pinnacle, and little more could be done to improve the mechanical properties even by modern standards, thus more attention began to be paid to the patterns in the blade as an aesthetic quality. From then on advancements progressed along an artistic path and swords became regarded for their beauty as much as their suitability as a weapon. Intentionally decorative forging techniques were often employed, such as hammering dents in certain locations or drawing out the steel with fullers, which served to create a mokume pattern when the sword was filed and polished into shape, or by intentionally forging in layers of high slag content. By the 17th century, decorative hardening methods were often being used to increase the beauty of the blade, by shaping the clay. Hamons with trees, flowers, pill boxes, or other shapes became common during this era. By the 19th century, the decorative hamons were often being combined with decorative folding techniques to create entire landscapes, often portraying specific islands or scenery, crashing waves in the ocean, and misty mountain peaks.[43]
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 (nakago), or the hilt section of the blade, during shaping, where they will be covered by a tsuka or 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. Different types of file markings are used, including horizontal, slanted, and checked, known as ichi-monji, ko-sujikai, sujikai, ō-sujikai, katte-agari, shinogi-kiri-sujikai, 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 hilt which fits over it. It is this pressure fit for the most part that holds the hilt in place, while the mekugi pin serves as a secondary method and a safety.
When the rough blade is completed, the swordsmith turns the blade over to a polisher (togishi) whose job 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.[citation needed]
Bronze items are typically cast, not forged. Secondary operations involve removing material from the roughcasting, polishing, and the application of decorative elements. Some Chinese swords used high-tin bronze for the edges, since it is harder, and keeps a sharp edge longer, but is more brittle than the softer, lower-tin alloy used for the blade's core. Bronze alloys with lower tin content are tougher, or more resistant to fracturing.
After forging a magnificent samurai sword, a Japanese swordsmith of the Tokugawa period seeks a worthy owner for it. Swordsmith Sensei Masa and his apprentice Michio spend days hammering, shaping, polishing and sharpening the blade. Sensei knows it will be difficult to find the right owner since many samurai are "thugs and bullies who do not follow the Bushido." When a strong, confident warrior tries to buy the sword, Sensei dismisses him as too cruel and arrogant. When wealthy Lord Toda argues he deserves the sword because he is noble, Sensei refuses him as too privileged. When a ronin dedicated to Kenjutsu argues the sword should be his, Sensei finds him too selfish. Many candidates are eliminated before Sensei finds the perfect samurai for his perfect sword. Dramatic oil illustrations emphasize samurai mannerisms, facial expressions and moves while the text captures the rhythms of the Japanese language. An attractive and informative introduction to sword-making in ancient Japan with insight into the samurai code of honor. 2ff7e9595c
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