History

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.^[3]

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).^[3]

The katana was paired most often with the wakizashi or shōtō, a similarly made but shorter sword, both worn by the members of the warrior class. It could also be worn with the tantō, an even smaller similarly shaped dagger. The katana and wakizashi when paired with each other were called the daishō and they represented the social power and personal honor of the samurai.^{[citation needed]}

The katana originated from the Tang blade, which as its name suggests, originated from Tang Dynasty. During the Tang Dynasty, it was popular for Japanese scholars to go to China to study. It is no surprise the katana originated from one of the most popular weapons during that time period. The Tang blade looks exactly like a katana, except the edges are not curved. Such new form of curvature is actually most likely attributed to blades from the Arabian Empire at that time, though the shape may have evolved independantly due to the natural hardening of the metal used. The Tang Dynasty was the world center during its time, and it would not be uncommon for traders from all over the world, including those from that area to sell their wares. Curvature in blades had existed in Asia a long time ago, but this new kind was of interest at that time. It can be said that the katana is a combination of the Tang blade with Arabian style curvature.^{[citations needed]} Katanaes where tested on cindemed prisoners. It was constered an honor to die from that level of a weapon. They would start with an arm or a lang. Then they would slice one man in half. Then they would stand to men side by side and then slice both of them in half. They would continue with this prosess until the sword stoped in one of the men. Then that sword would be labeled as a one body sword, two body sword, three body sword....

Forging and construction

Main article: Katana construction

The authentic Japanese sword is made from a specialized Japanese steel called "Tamahagane"^[4] which consist of combinations of hard, high carbon steel and tough, low carbon steel^[5]. There are advantages and setbacks to both types of steel. Having a lot of carbon within the steel allows the blade to hold a sharp edge but can be too brittle and may break in combat. Having a small amount of carbon will allow the steel to be more malleable, making it able to absorb impacts without breaking but becoming blunt in the process. The makers of a katana would use the best attributes of both kinds of steel by placing the high carbon steel in the front of the blade for a sharp edge while placing the low carbon steel in the back where it can absorb most of the impact.

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.^[6]

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. This process also creates the distinct swerving line down the center of the blade called the hamon which can only be seen after it is polished, a katana forger's signature.

The hardening of steel involves altering the molecular structure of that material through quenching it from a heat above 800 °C (1,472 °F) (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 polishing 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. The blade curvature also adds to the cutting power. A katana must folded over a 1000 times before it is for complete.

Usage

The katana's unique design and in particular its sharpness necessitate quite a few specialized precautions to handle it. Failure to observe these precautions can easily lead to damage to the weapon or severe injury.

Combat

See also: Battōjutsu, Iaidō, Iaijutsu, Kenjutsu, and Shinkendo

Storage and maintenance

If mishandled in its storage or maintenance, the katana may become irreparably damaged. It is extremely important that the blade remain well-oiled and polished, as the natural moisture residue from the hands of the user will rapidly cause the blade to rust if not cleaned off. 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).^[7]