The katana is a type of Japanese sword (shinken), often called a “samurai sword.”
The term katana may be applied to any curved Japanese sword with a blade length of greater than 60 cm. The term is sometimes incorrectly used as a generic name for any kind of Japanese sword.
The katana is characterised 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.
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 in length. During the early 16th century, average length was much closer to 60 cm, but late in the 16th century, it was again approximately 73 cm.
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”. 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.
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).
The katana’s unique design and in particular its sharpness necessitate quite a few specialised precautions to handle it. Failure to observe these precautions can easily lead to damage to the weapon or severe injury.