Katana
The katana is generally defined as the standard sized, moderately curved (as opposed to the older "tachi" style featuring more curvature) Japanese sword with a blade length greater than 60 cm (23 1⁄2 inches).
With a few exceptions, katana and tachi can be distinguished from each other, if signed, by the location of the signature (mei) on the tang (nakago). In general, the mei should be carved into the side of the nakago which would face outward when the sword was worn. Since a tachi was worn with the cutting edge down, and the katana was worn with the cutting edge up, the mei would be in opposite locations on the nakago.
The katana is characterized by its distinctive appearance: a curved, slender, single-edged blade with a circular guard and long grip to accommodate two hands. It has historically been associated with the samurai of feudal Japan.
Some historians have said that katana were among the finest cutting weapons in world military history.
Etymology and loanwords
"Katana" is the term now used to describe nihontō that are 2 shaku (606 mm / 23.9 in) and longer, also known as "dai" or "daito" among Western sword enthusiasts although daito is a generic name for any long sword.
As Japanese does not have separate plural and singular forms, both "katanas" and "katana" are considered acceptable forms in English.
Pronounced [katana], the kun'yomi (Japanese reading) of the kanji 刀, originally meaning dao or knife/saber in Chinese, the word has been adopted as a loanword by the Portuguese language. In Portuguese the designation (spelled catana) means "large knife" or machete.
Forging and construction
Cross sections of Japanese sword blade lamination methods
Katanas are traditionally made from a specialized Japanese steel called tamahagane, which is created from a traditional smelting process that results in several, layered steels with different carbon concentrations. This process helps remove impurities and even out the carbon content of the steel. The smith begins by folding and welding pieces of high and low carbon steel several times to work out most of the impurities. The resulting block of steel is then drawn out to form a billet.
At this stage, it is only slightly curved or may have no curve at all. The gentle curvature of a katana is attained by a process ofdifferential hardening or differential quenching: the smith coats the blade with several layers of a wet clay slurry, which is a special concoction unique to each sword maker, but generally composed of clay, water and any or none of ash, grinding stone powder, or rust. The edge of the blade is coated with a thinner layer than the sides and spine of the sword, heated, and then quenched in water (some sword makers use oil to quench the blade). The slurry causes only the blade's edge to be hardened and also causes the blade to curve due to the difference in densities of the micro-structures in the steel. When steel with a carbon content of 0.7 percent is heated beyond 750 °C, it enters the austenite phase. When austenite is cooled very suddenly by quenching in water, the structure changes into martensite, which is a very hard form of steel. When austenite is allowed to cool slowly, its structure changes into a mixture of ferrite and pearlite which is softer than martensite. This process also creates the distinct line down the sides of the blade called the hamon, which is made distinct by polishing. Each hamon and each smith's style of hamon is distinct.
After the blade is forged, it is then sent to be polished. The polishing takes between one and three weeks. The polisher uses finer and finer grains of polishing stones in a process called glazing, until the blade has a mirror finish. However, the blunt edge of the katana is often given a matte finish to emphasize the hamon.
Usage in martial arts
Katana were used by samurai in practising several martial arts and modern martial artists still use a variety of katana. Martial arts in which training with katana is used include Iaijutsu, battōjutsu, iaidō, kenjutsu, Shinkendo, kendo, Aikido, Ninjutsu.
Storage and maintenance
If mishandled in its storage or maintenance, the katana may become irreparably damaged. The blade should be stored horizontally in its sheath, curve down and edge facing upward to maintain the edge. It is extremely important that the blade remain well-oiled, powdered and polished, as the natural moisture residue from the hands of the user will rapidly cause the blade to rust if not cleaned off. The traditional oil used is choji oil (99% mineral oil and 1% clove oil for fragrance). Similarly, when stored for longer periods, it is important that the katana be inspected frequently and aired out if necessary in order to prevent rust or mold from forming (mold may feed off the salts in the oil used to polish the katana).