Katana, the sharp sword of Feudal Japan’s samurai, is up there with chainsaws and spiked baseball bats as one of the most iconic weapons in pop culture. But it was only in the 1600s that the sword became widely used, as a result of the forging techniques developed by master swordsmiths such as Masamune. The challenge was to make steel that remained razor-sharp and could absorb the furious blows of a duel. The process to do so was a laborious one, lasting up to several months.
After forming the blade, sword craftsmen use a process called yaki-ire to heat and harden it. A clay slurry is applied to the body and spine of the blade, with a thicker application on the spine than the edge. Then it is heated and quenched in water to create a hard, sharp edge and a softer body. This differential cooling is what gives a katana its distinctive curve.
The sword is now ready for tempering, a process that adds strength and flexibility. The swordsmith applies a mixture of clay, sand and coal dust to the body and spine, while on the blade’s face, he uses more clay mixed with sand. When the metal is heated, these three materials separate, hardening the body of the sword while reducing its brittleness.
The katana is then polished to give it its beautiful shine and smooth feel. It is then inserted into its sheath, known as a saya, for protection and to keep it in good condition. It’s important to store a katana horizontally, as opposed to hanging it up, to prevent bending and warping of the blade. It should also be stored in a dry, cool place to prevent moisture from building up and leading to rust. The keywords I will use are