Samurai Sword

A katana is a type of Japanese sword (,nihontō), and is often called a "samurai sword." The term katana may be applied to the standard size moderately curved Japanese sword with a blade length of greater than 60 cm (23.6 inches)

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 sharpness and cutting ability, to the point that its purported cutting capabilities have reached mythical status.

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

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)

The authentic Japanese sword is made from a specialized Japanese steel called "Tamahagane". 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.

A coating of clay mixed with ashes and a small portion of rust is applied to every surface but the edge of the blade during hardening. This provides heat insulation so that only the blade's edge will be hardened with quenching.

The hardening of steel involves altering the molecular structure of that material through quenching it from a heat above 1472 Fahrenheit (800 Celsius) (bright red glow), ideally no higher than yellow hot. If cooled slowly, the material will break back down into iron and carbon and the molecular structure will return to its previous state. However, if cooled quickly, the steel's molecular structure is permanently altered. The reason for the formation of the curve in a properly hardened Japanese blade is that iron carbide, formed during heating and retained through quenching, has a lesser density than its root materials have separately.

After the blade is forged it is then sent to be polished. The polish takes between one and three weeks. The polisher uses finer and finer grains of polishing stones until the blade is like glass. This makes the blade extremely sharp and reduces drag making it easier to cut with.

Japanese sword usually refers to the katana (or nihontō), a traditional Japanese sword.

The term may also refer to:
Chisakatana, a shortened katana
Chokutō, a type of straight and (usually) single-edged Japanese sword that dates back to pre-Heian times
Daikatana, a pseudo-Japanese term meaning "large sword"
Dōtanuki, a very thick, long handled sword resembling a katana
Hachiwara, a type of blunt, knife-shaped weapon resembling a jitte
Kodachi, a Japanese sword that is too short to be considered a long sword but too long to be a dagger
Nagamaki, a Japanese weapon popular between the 12th and 14th centuries
Ninjatō, the most common name for the reputed sword a ninja would have carried
Nodachi, a large two-handed Japanese sword
O-katana, a katana slightly longer than a regular katana
Ōdachi, a type of long Japanese sword
Shin gunto, a style of japanese katana designated as part of the uniform for officers of the Imperial Japanese Army from 1934 until the end of World War II
Shinken, a sharp Japanese style sword uses for high level iaido or tameshigiri (cutting) practice
Tachi, a Japanese sword, often said to be more curved and slightly longer than the katana
Tantō, a common Japanese single or, occasionally, double edged knife or dagger with a blade length between 15 and 30 cm
Tsurugi, a Japanese word used to refer to any type of broadsword, or various Chinese heroes' weapons or Chinese swords
Uchigatana, a Japanese blade and predecessor of the katana
Wakizashi, a traditional Japanese sword with a shōtō blade between 30 and 60 cm
Zanbatō, an especially large type of Japanese sword, the historical use of which is completely fictional