For centuries, sword makers throughout the World have struggled to construct a sword that could be sharp enough to cut efficiently, rigid enough to carry out a challenging cut and be strong enough not break when used for cutting.  Japanese sword makers overcame these problems by using a blend of materials and a developing a unique method of construction that had never been used before.

Classical Japanese swords are constructed with a soft iron core surrounded by a hard steel outer layer.  The hard outer skin is folded and forged many times, this process reduces impurities and homogenizes the metal.  It is this hard outer skin that eventually forms the razor sharp cutting edge and the folding process also yields the jihada – the grain like pattern.  The pattern can be controlled by the direction that the steel is folded at each stage. This is then wrapped around the soft inner core, it is this iron core that gives the sword its strength.

One of the most crucial elements in the production process is the Yaki-ire stage.  This is the process where the hardening of the edge takes place, which in turn is responsible for the acute sharpness for which the Japanese sword is so famous.  This is achieved by covering the blade in a mixture called yakibatsuchi – a mixture of mainly ash and clay.  The wider back section of the blade would have a thick coating, while the edge would have just a thin coating.  When the blade is heated the thin layer of clay will allow the cutting edge to reach much higher temperatures than the thickly coated back edge. 

This process is carried out in a very formal and traditional way, however, the science behind the process is very exact.  The cutting edge must reach a critical temperature of 750°C, this is the temperature at which carbon and iron will combine and the structure of the metal changes to form austenite.  The sudden cooling of the metal caused by the quenching changes the austenite into martensite.  The back edge of the blade, where the thicker clay coating is applied, is protected from the dramatic heat changes and the resulting molecular changes.  

The Japanese sword is not the result of just one craftsman.  After the above process is complete the blade would be passed to a polisher.  Polishing a blade is a skill of its own that takes years of hard work and practice to master.  After the polisher had finished the blade would be passed to a third craftsman who would be responsible for the fittings of the completed sword.  These fittings would include the tsuka (hilt) and saya (scabbard).

There were also unique properties in the design of the blade.  The curved shape meant that only a small portion of the blade would be in contact with the target in the crucial initial moment of a cut.  The unique shape also lends itself to a quick draw and attacking in one continuous movement.

In addition to near practical perfection, the Japanese sword makers have turned the construction of the sword into an art form.  One of the most spectacular elements of this art form is the astonishing and beautiful patterns that are achieved along the length of blade – the jihada and hamon.  The jihada is the result of the incredible skill and patience used in the continual folding and forging of the hard outer layer.  The hamon is again the product of the skill and patience of the sword maker but this is achieved in the final stages of the creation of the blade and is a result of the coating of clay and the tempering process.  The patterns can vary considerably and are worthy of study in their own right and therefore, beyond the scope of this article.  

Japanese sword blades are classified by length:

Over 2 shaku (approx. 24 inches)  = Taichi or daito

Between 1 and 2 shaku (approx. 12inches to 24 inches) = Shoto or wakasashi

Under I shaku (12 inches) = Tanto

Note: A Japanese sword blade is measured in a straight line from the kissaki  (tip) to the mune-machi.

With the exception of the taichi some of the older swords would have attachments fitted to them.  These attachments included knives, a tool that could be used as chop sticks, a hair arranger and others.

Swords in modern Iai practice.

Modern iaido practice will begin with the student using a bokken (a wooden practice sword).  As the student advances the training will progress to an iaito (a training sword).  These swords are available as blunt or semi sharp. This enables the student to experience the feel of a genuine ‘Samurai sword’ while training, without the dangers of using a razor sharp blade.

After many years practice the student can advance to a shinken (very sharp sword).  These are available at different levels, ranging from a forged blade to a forged and folded blade. 

Respect for your sword is one of the basic principles of Japanese swordsmanship along with respect for your teacher, fellow student and dojo.  For an excellent article on dojo etiquette visit Hagakure central here.