Japanese sword

A Japanese sword is one of several types of traditionally made swords from Japan. Bronze swords were made as early as the Yayoi period, though most people generally refer to the curved blades made from the Heian period to the present day when speaking of "Japanese swords". There are many types of Japanese swords that differ by size, shape, field of application, and method of manufacture. Some of the more commonly known types of Japanese swords are the katana, tachi, ōdachi, wakizashi, and tantō.

Etymology

The word katana was used in ancient Japan and is still used today, whereas the old usage of the word nihontō is found in the poem the Song of Nihontō, by the Song dynasty poet Ouyang Xiu. The word nihontō became more common in Japan in the late Tokugawa shogunate. Due to importation of Western swords, the word nihontō was adopted to distinguish it from the Western sword.
Meibutsu is a special designation given to sword masterpieces which are listed in a compilation from the 18th century called the "Kyoho Meibutsucho". The swords listed are Koto blades from several different provinces; 100 of the 166 swords listed are known to exist today, with Sōshū blades being very well represented. The "Kyoho Meibutsucho" also listed the nicknames, prices, history and length of the Meibutsu, with swords by Yoshimitsu, Masamune, Yoshihiro, and Sadamune being very highly priced.

Anatomy

Blade

Each blade has a unique profile, mostly dependent on the swordsmith and the construction method. The most prominent part is the middle ridge, or shinogi. In the earlier picture, the examples were flat to the shinogi, then tapering to the blade edge. However, swords could narrow down to the shinogi, then narrow further to the blade edge, or even expand outward towards the shinogi then shrink to the blade edge. A flat or narrowing shinogi is called shinogi-hikushi, whereas a flat blade is called a shinogi-takushi.
The shinogi can be placed near the back of the blade for a longer, sharper, more fragile tip or a more moderate shinogi near the center of the blade.
The sword also has an exact tip shape, which is considered an extremely important characteristic: the tip can be long, medium, short, or even hooked backwards. In addition, whether the front edge of the tip is more curved or straight is also important.
The kissaki is not usually a "chisel-like" point, and the Western knife interpretation of a "tantō point" is rarely found on true Japanese swords; a straight, linearly sloped point has the advantage of being easy to grind, but less stabbing/piercing capabilities compared to traditional Japanese kissaki Fukura types. Kissaki usually have a curved profile, and smooth three-dimensional curvature across their surface towards the edge—though they are bounded by a straight line called the yokote and have crisp definition at all their edges. While the straight tip on the "American tanto" is identical to traditional Japanese fukura, two characteristics set it apart from Japanese sword makes: The absolute lack of curve only possible with modern tools, and the use of the word "tanto" in the nomenclature of the western tribute is merely a nod to the Japanese word for knife or short sword, rather than a tip style.
Although it is not commonly known, the "chisel point" kissaki originated in Japan. Examples of such are shown in the book The Japanese Sword by Kanzan Sato. Because American bladesmiths use this design extensively it is a common misconception that the design originated in America.
A hole is punched through the tang nakago, called a mekugi-ana. It is used to anchor the blade using a mekugi, a small bamboo pin that is inserted into another cavity in the handle tsuka and through the mekugi-ana, thus restricting the blade from slipping out. To remove the handle one removes the mekugi. The swordsmith's signature mei is carved on the tang.

Mountings

In Japanese, the scabbard is referred to as a saya, and the handguard piece, often intricately designed as an individual work of art—especially in later years of the Edo period—was called the tsuba. Other aspects of the mountings, such as the menuki, habaki, fuchi and kashira, kozuka, kogai, saya lacquer, and tsuka-ito, received similar levels of artistry.

Signature and date

The mei is the signature inscribed on to the tang of the Japanese sword. Fake signatures are common not only due to centuries of forgeries but potentially misleading ones that acknowledge prominent smiths and guilds, and those commissioned to a separate signer.
Sword scholars collect and study oshigata, or paper tang-rubbings, taken from a blade: to identify the mei, the hilt is removed and the sword is held point side up. The mei is chiseled onto the tang on the side which traditionally faces away from the wearer's body while being worn; since the katana and wakizashi are always worn with the cutting edge up, the edge should be held to the viewer's left. The inscription will be viewed as kanji on the surface of the tang: the first two kanji represent the province; the next pair is the smith; and the last, when present, is sometimes a variation of 'made by', or, 'respectfully'. The date will be inscribed near the mei, either with the reign name; the Zodiacal Method; or those calculated from the reign of the legendary Emperor Jimmu, dependent upon the period.

Length

What generally differentiates the different swords is their length. Japanese swords are measured in units of shaku. Since 1891, the modern Japanese shaku is approximately equal to a foot, calibrated with the meter to equal exactly 10 meters per 33 shaku.
However, the historical shaku was slightly longer. Thus, there may sometimes be confusion about the blade lengths, depending on which shaku value is being assumed when converting to metric or U.S. customary measurements.
The three main divisions of Japanese blade length are:

Less than 1 shaku for tantō.
Between 1 and 2 shaku for shōtō.
Greater than 2 shaku for daitō.

A blade shorter than one shaku is considered a tantō. A blade longer than one shaku but less than two is considered a shōtō. The wakizashi and kodachi are in this category. The length is measured in a straight line across the back of the blade from tip to munemachi. Most blades that fall into the "shōtō" size range are wakizashi. However, some daitō were designed with blades slightly shorter than 2 shaku. These were called kodachi and are somewhere in between a true daitō and a wakizashi. A shōtō and a daitō together are called a daishō. The daishō was the symbolic armament of the Edo period samurai.
A blade longer than two shaku is considered a daitō, or long sword. To qualify as a daitō the sword must have a blade longer than 2 shaku in a straight line. While there is a well defined lower limit to the length of a daitō, the upper limit is not well enforced; a number of modern historians, swordsmiths, etc. say that swords that are over 3 shaku in blade length are "longer than normal daitō" and are usually referred to as ōdachi. The word "daitō" is often used when explaining the related terms shōtō and daishō. Miyamoto Musashi refers to the long sword in The Book of Five Rings. He is referring to the katana in this, and refers to the nodachi and the odachi as "extra-long swords".
Before about 1500 most swords were usually worn suspended from cords on a belt, edge-down. This style is called jindachi-zukuri, and daitō worn in this fashion are called tachi. From 1600 to 1867, more swords were worn through an obi, paired with a smaller blade; both worn edge-up. This style is called buke-zukuri, and all daitō worn in this fashion are katana, averaging 70–74 cm in blade length. However, Japanese swords of longer lengths also existed, including lengths up to 78 cm.
It was not simply that the swords were worn by cords on a belt, as a 'style' of sorts. Such a statement trivializes an important function of such a manner of bearing the sword. It was a very direct example of 'form following function.' At this point in Japanese history, much of the warfare was fought on horseback. Being so, if the sword or blade were in a more vertical position, it would be cumbersome, and awkward to draw. Suspending the sword by 'cords' allowed the sheath to be more horizontal, and far less likely to bind while drawing it in that position.
Abnormally long blades, usually carried across the back, are called ōdachi or nodachi. The word ōdachi is also sometimes used as a synonym for Japanese swords. Odachi means "great sword", and Nodachi translates to "field sword". These greatswords were used during war, as the longer sword gave a foot soldier a reach advantage. These swords are now illegal in Japan. Citizens are not allowed to possess an odachi unless it is for ceremonial purposes.
Here is a list of lengths for different types of blades:

Nodachi, Ōdachi, Jin tachi: 90.9 cm and over
Tachi, Katana: over 60.6 cm
Wakizashi: between 30.3 and 60.6 cm
Tantō, Aikuchi: under 30.3 cm

Blades whose length is next to a different classification type are described with a prefix 'O-' or 'Ko-', e.g. a Wakizashi with a length of 59 cm is called an O-wakizashi whereas a Katana of 61 cm is called a Ko-Katana.
Since 1867, restrictions and/or the deconstruction of the samurai class meant that most blades have been worn jindachi-zukuri style, like Western navy officers. Since 1953, there has been a resurgence in the buke-zukuri style, permitted only for demonstration purposes.