Katana

A Japanese sword, or katana, with a straight blade

History

All through Japanese history, the Japanese sword or katana has acquired a reputation not only as a war weapon, but also as a political tool.

The first katana were not curved but straight, and were forged from around 300 BC. Later centuries, along with the different eras of Japanese history, saw the introduction of curved blades, with different variations. This distinctive feature allows the sword to be drawn much more easily. Furthermore, it allows the sword to better follow the line of the opponent's body, causing wider cuts.

The katana usually goes with a wakizashi (a shorter blade) to form a set called daisho. The katana was the sword favoured by the samurai, as it also represented their social status. Indeed, they were the only ones allowed to carry such weapons. According to the Bushido, the moral code of the samurai, the katana constituted their very soul. That is why, even during their sleep, a samurai did not leave his weapon. Likewise, nobody could easily make a samurai part with his weapon. The katana could be obtained at the age of 13 during the gempuku, a ceremony which gave the sword wielder his real name, his adult name. Samurai disappeared in 1866, after an edict that forbade anybody to carry a katana.

Forging

Katana forging is a complex art that continuously evolved through history. The remarkable forging processes invented by the Japanese is the reason behind the fame surrounding the weapon and the legends about its cutting edge.

Maru blades

Katana are forged from steel (iron containing some carbon). Whereas the katana used to be forged from tamahagane (Japanese steel melted in low furnaces), today blades are called 1045, 1060, or 1095, as they contain respectively 0.45%, 0.60% and 0.95% carbon. And there exist other variations: 1055, 1070...

Carbon allows for a harder blade. Thus, the higher the carbon content is, the more easily the cutting edge is sharpened, and the more efficient the blows become. Nevertheless, this hardness implies a lower flexibility, and the sword will not absorb shocks that well and might break. That is why the carbon content rarely exceeds 0.95%. A blade made from 1095 steel has a really good cutting edge and a suitable flexibility.

Composite blades

Composite blades are among the most unequalled examples of the prowess of Japanese smithing. It resolves the hardness versus flexibility problem. Unlike Maru swords, which are composed of only one steel block, a composite sword features a hard steel on the outside of the blade and a heart and back of softer steel to absorb vibrations. There exist numerous different compositions, as illustrated in the diagram below.

The lamination of a composite katana blade

The heat treatment, or hamon

The most remarkable historic detail of the Japanese sword was the hamon. The goal behind the heat treatment is to create martensite, highly saturated in carbon, on the cutting edge. Martensite is extremely hard and allows the blade to be polished until a razor sharp cutting edge is obtained, although this hardness makes it very brittle. The term used is selective quenching, for the Japanese have invented a process that allows the smith to transform the carbon in martensite only on the cutting edge of the weapon, while keeping the remaining of the blade as it is, in order to keep a good flexibility.

The heat treatment, or selective quenching consists of coating the blade with a mix made mainly from refractory clay, but also wood charcoal and polishing stone (these last two components are included to avoid the mix blowing up when exposed to the heat). The mix is applied on the whole blade except for the cutting edge. Thus the heat treatment is only applied to the cutting edge, as the other parts of the blade are isolated from the heat by the clay. Once the clay has dried, the whole is heated to 800° Celsius (1472° Fahrenheit) before being tempered in water or oil.

The temper line, or hamon, that result from the process is the token of an undeniable quality: the exceptional hardness of the cutting edge, combined with an everlasting flexibility.

The hamon in a closeup of a katana

On the authenticity of the katana

A sword forged in Japan will always be called a "Nihonto" as a distinguishing feature. In order to protect the sword, the Japanese government made good use of post-war demilitarization constraints. Only a few smiths are allowed to create sharp-edged blades, and in limited numbers.

One must also remember that a Nihonto is considered a work of art by the Japanese legislation, and that acquiring such a sword implies a great number of obligations. One must possess experience of swords and be able to maintain them, as they are historical items, and obviously not items to be playfully used in one's garden. The average cost of a nihonto is between $6,000 and $15,000, although some items have been auctioned at more than $100,000 dollars.

Fortunately, it is possible to acquire hand-made high quality swords, created outside Japan, at a much more affordable price.

A katana made by a famous brand is not necessarily a token of quality (some of these swords are forged industrially). Also be careful with certificates, which are more a marketing stunt than anything else. The only certificates that actually mean anything are authenticity certificates delivered by NBTHK with antique nihonto swords. Do your research before buying a blade, as a good smith will always respect some essential processes. The tempering especially, will truly be realized with clay - avoid fake decorative hamons at all cost!

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• This article and photos were provided by the folks at Katana Craft, makers of fine custom katana.