The Katana sword has long been a symbol of the warrior class in Japan. The slender, razor sharp blade is an innovation that came somewhat late in the samurai’s history; other sword types like the curved tachi and the straight chokuto existed for millennia before it.
A katana’s beauty is found not just in its blade but also in its hilt and scabbard, or saya. Forging these pieces requires considerable skill and experience as the materials used must be strong, light, and watertight. They are also a canvas upon which swordsmiths can express their artistic and technical ability.
In order to forge a katana, smiths start with a block of metal known as tamahagane. This is made using the traditional Japanese method of steel making called the Tatara-buki method, which uses black iron sand extracted from the ocean floor to create high quality steel without impurities.
After the tamahagane is formed, it is reheated in charcoal fires and tempered, which makes it extremely hard. After that it is cooled rapidly in a process known as yaki-ire. This gives the blade its distinctive wavy line called hamon, and also makes it very tough.
The hamon is caused by differences in the way each of the alternating layers of high and low carbon steel expand during quenching. A skilled smith will be able to achieve even and consistent hamon throughout the blade, demonstrating his or her mastery of the forging technique. The polisher then refines the hamon with a series of stones of increasing granularity to give it its beautiful luster. find out more information