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The uniqueness of the Japanese sword lies in the technical innovations devised by the Japanese in an effort to resolve the three conflicting practical requirements of a sword: unbreakability, rigidity, and cutting power. Unbreakability implies a soft but tough metal, such as iron, which will not snap with a sudden blow, while rigidity and cutting power are best achieved by the use of hard steel. The Japanese have combined these features in a number of ways which have given their swords a very distinctive character.
First of all, most Japanese blades are made up of two different metals: a soft and durable iron core is enveloped in a hard outer skin of steel which has been forged and reforged many times in order to produce a complex and close-knit crystalline structure.
Second, the cross-section, widening from the back to a ridge on both sides, then narrowing to a very acute angle at the edge, combines the virtues of thickness for strength and thinness for cutting power.
Third and most important of all, a highly tempered edge is formed by covering the rest of the blade with a special heat-resistant clay and heating and quenching only the part left exposed.
The result is a steel which is even harder then the rest of the outer skin and can take a razor-sharp edge.
A fourth feature, the distinctive curve away from the edge, owes its origin to another practical demand: the need to draw the sword and strike as quickly as possible and in a continuous motion.
Where the sword itself forms part of the approximate circumference of a circle with its center at the wearer's right shoulder and its radius the length of his arm, drawing from a narrow scabbard will naturally be easier and faster than with a straight weapon. But to the Japanese specialist the beauty of a sword lies in more than just its fulfillment of practical requirements or its almost mechanical perfection of finish and cleanness of profile.
The Japanese swordsmith has given his product a number of features which, although they may have a strictly practical origin, have been elaborated far beyond the simple requirement of hard-wearing efficiency in slaughter. One example of this is the forging of the outer skin, a process necessary to produce steel of adequate purity and hardness: this has been done in a multitude of different ways so as to obtain a wide variety of distinct grains in the surface of the blade. But it is the tempering process which has received the most careful attention. The heat-resistant clay is wholly or practically scraped away from the area of the edge in a seemingly inexhaustible range of outlines resulting in an enormous number of patterns of hard crystalline steel which guarantee that no two swords will ever be the same: and yet these outlines have no practical function beyond the simple requirement that the edge must be tempered in one way or another. |