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A katana (??) is a type of Japanese sword (niponto nipon=Japan to=sword), and is often called a “samurai sword.” The term katana may be applied to the standard size moderately curved [as opposed to the older ‘tachi” style featuring more curvature] curved Japanese sword with a blade length of greater than 60 cm (23.6 inches).[1] The term is sometimes incorrectly used as a generic name for any kind of Japanese sword.

The katana is characterized by its distinctive appearance: a curved, slender, single edged blade, circular or squared guard, and long grip to accommodate two hands. It has historically been associated with the samurai of feudal Japan, and has become renowned for its extraordinary sharpness and cutting ability, to the point that its purported cutting capabilities have reached mythical status.

Originally used as a general term for single-edged sword, as opposed to tsurugi, which are double-edged swords, the term is now used specifically to describe nihonto that are around 70–90 cm (27.6 to 35.4 in) long with a curved blade.[citation needed] This distinguishes them from chokuto, which feature straight blades.

Pronounced kah-ta-nah, the kun’yomi (Japanese reading) of the kanji ?, the word has been adopted as a loanword by the English language. As Japanese does not have separate plural and singular forms, both “katanas” and “katana” are considered acceptable forms in English.[citation needed]

Daikatana (usually given as the kanji ??) is a pseudo-Japanese term meaning “large sword”. (In Japanese, ?? is actually read daito, and is a less-used synonym for uchigatana. [2]) The reading mistake comes from the different ways Japanese Kanji can be read, depending on their combination or not in a word. It has been used in some (English-language) fictional works to represent a kind of large katana (perhaps better known as an otachi); the video game Daikatana, for example.

The katana originated in the Muromachi period (1392–1573) as a result of changing battle conditions requiring faster response times. The katana facilitated this by being worn with the blade facing up, which allowed the samurai to draw and cut their enemy in a single motion. Previously, the curved sword of the samurai was worn with the blade facing down. The ability to draw and cut in one motion also became increasingly useful in the daily life of the samurai.[2]

The length of the katana’s blade varied considerably during the course of its history. In the late 14th and early 15th centuries, katana blades tended to be between 70 and 73 cm (27.6 and 28.7 inches) in length. During the early 16th century, average length was much closer to 60 cm (23.6 inches), but late in the 16th century, it was again approximately 73 cm (28.7 in).[2]

The katana was paired most often with the wakizashi or shoto, a similarly made but shorter sword, both worn by the members of the warrior class. It could also be worn with the tanto, an even smaller similarly shaped dagger. The katana and wakizashi when paired with each other were called the daisho and they represented the social power and personal honour of the samurai.

The legitimate Japanese sword is made from a specialised Japanese steel called “Tamahagane”[3]. The katana gets its gentle curve from quenching during forging, as it is straight prior to quenching. A process of differential tempering causes martensite to form predominantly in the edge of the blade rather than the back; as the spine has lower retained lattice strain, it cools and contracts, and the blade takes on a gently curved shape.[4]

What is used to harden a Japanese blade is a coating of clay mixed with ashes, as well as a small portion of rust, coating all but the edge. This gives heat insulation so that only the edge will be hard with quenching.

Hardening steel, through quenching from a heat above 1472 Fahrenheit (800 Celsius) (bright red glow), ideally no higher than yellow hot, at least within the common alloys of steel. If cooled slowly, it will break back down to iron and carbon. Though, if cooled quickly, it will stay as it is. The reason for the acquisition of the curve in a properly hardened Japanese blade is that iron carbide has a lesser density than what its root materials have separately.