A katana is a sword with a curved single-edged blade. It was favored by the samurai of feudal Japan and it is usually worn with its edge facing upward.
The process of making a katana starts with high-quality steel known as tamahagane. The swordsmith heats iron sand and charcoal in a clay furnace to generate crude steel. This raw steel is then hammered, folded, and welded repeatedly to remove impurities and create a layered structure in the blade.
A hard outer layer of kawagane is wrapped around a softer, more ductile core of shingane. This combination provides a sword with both exceptional sharpness and durability.
When the tempered steel is cooled, it takes on the distinct wavy line or “hamon” seen in a katana. This wavy pattern is an indication of the differential heat treatment called yaki-ire, during which the sword’s tang and back edge are quickly cooled while the body and spine are cooled more slowly. This difference in cooling speed and degree causes the hamon.
The smith then shapes the blade using files and planes, followed by rough polishing with a stone. After that, oil and fat are removed by use of straw ash and the sword is shaved to remove unevenness. Next, the Hirachi and Shinogichi are stricken and elongated to shape the sword. A katana is ready to wear when it has an elegant finish, including brass menuki and ray skin handle. The final touches include a black lacquered wood scabbard. click on this page