The Katana is a double-edged sword with a long blade that curves outward at the hilt. It is the main weapon of the Samurai, Japan’s feudal military warriors. The first katanas were inspired by Chinese swords, but after the Japanese severed cultural ties with China in the 10th century, they began to create their own version of the curved sword.
Sword craftsmen start making the katana by shaping hard, high-carbon steel known as Tamahagane to an appropriate length. They then fire it, or smelt it, at high heat, but never let it reach a molten state. This allows the metal to be shaped and forged while it is still hard. The smith then hammers tough, low-carbon steel into the channel formed by the tamahagane. This combination of high-hardness and high-toughness allows the katana to be as durable as it is deadly.
The smith then heats both sides of the tamahagane to a red-hot state, and quenches it on one side (the Shinogichi) and not on the other (the Mune side). This differential tempering, or yaki-ire, gives the sword its distinct curve, as well as its characteristic wavy line known as Hamon. This fusion of rigid and flexible steel allows the blade to be razor sharp and able to absorb shock, something that would be impossible if it were made from a single type of metal.
After modifying the curvature of the katana and doing a rough grinding, the smith checks for small scratches on the Jiba (blade surface) and Nakago (tang). He then drills holes called Mekugi, usually one for a sword used for Iaido, and two for a sword to be used for Kendo. find out more information