CNN recently profiled a Japanese swordsmith and the ancient, exacting process he follows to craft a katana.
The blades are forged from tamahagane, a steel whose layers contain differing amounts of carbon. Shimojima painstakingly heats, softens and then folds the steel in order to remove impurities and even out the carbon content.
“A single layer becomes two layers, then two become four, four become eight and so on,” he explains. “By folding 15 times, over 32,000 layers are produced. However, it does not mean that the more layers, the better. There’s of course a limit, and if you exceed the limit you lose … the strength required to serve as a sword.“
Next, the sword is shaped — although it begins completely straight. As the steel is hardened through a process of repeated heating and cooling (known as yaki-ire), the differing densities in the blade’s structure create its signature curve.
“In the space of 10 minutes, we heat up the blade to about 800 degrees centigrade and rapidly cool it down in water,” Shimojima says. “It seems like a simple process. However… it’s a matter of making a split-second judgment.”
I’ve long been fascinated by Japanese swords. They’re really quite beautiful in their aesthetics, simplicity, and utility.