Throughout history, the Japanese sword has had no equal. Its quality, beauty, and strength far surpass even the legendary Damascus and Toledo blades, and its cutting edge is said to be sharper than any other blade in the world. To this day, metallurgists have never been able to exactly duplicate the steel found in these marvelous works of art. The sword is known as the "soul of the Samurai", and in Japanese mythology it was one of the three sacred gifts given to the emperor by the Sun Goddess as a token of legitimate authority. What were the properties of the sword that gave it such metallurgical and spiritual significance? In this series of articles, we'll take a look at the methods used to manufacture sword and naginata blades, as well as their accessories (kodogu). We'll also learn about their proper care and handling. In this first section, the kitae, or forging process is discussed.
For battlefield applications, the steel used in naginata and sword blades was required to have two distinct properties. First, it had to be flexible enough to withstand direct impacts and thrusting types of cuts without breaking. Conversely, it had to be hard enough to retain its notoriously sharp cutting edge. How could one piece of steel be both flexible AND hard? Only the Japanese were able to develop forging and heat treating methods which resulted in steel that had BOTH properties.
Careful metallurgical examination of a Japanese sword reveals that it is composed of not one, but TWO distinctly different types of steel. It contains a soft "core", called shingane, which is made of low carbon steel. Wrapped around this is a harder "jacket" made of higher carbon steel, or kawagane. It is important to note that the finished blade is NOT a laminate, but instead consists of two separate pieces of steel which, through the forging process, have been welded together.
The forge consists of a "furnace", built into the earthen floor of the smithy, that's heated by special charcoal capable of burning at high temperatures. An air bellows, which is an integral part of the forge, provides a continuous flow of oxygen to the charcoal. This is an important design feature unique to Japanese bellows. It allows the volume and speed of the air flow, and as a result the temperature of the coals, to be precisely controlled. Directly adjacent to the forge is an anvil and a hydraulically powered air hammer. In earlier days, one or two apprentices did the hammering.
Before beginning his work, the swordsmith purifies himself and prays before the Shinto shrine located in the smithy. He prays for divine guidance, and that his efforts will please the deity. The finished blade is said to contain the soul of the swordsmith, as well as the soul of all future owners of the blade who will become its caretakers. It is for this reason that the blades are thought to have spiritual significance.