Katana are traditionally made from a specialized Japanese steel called tamahagane,created from a traditional smelting process that results in layered steels with different carbon concentrations. This process helps remove impurities and even out the carbon content of the steel.
The Katana’s gentle curvature is made by a process of differential hardening or differential quenching: the smith coats the blade with several layers of a wet clay slurry, which is a special concoction unique to each sword maker, but generally composed of clay, water and any or none of ash, grinding stone powder, or rust. This process is called tsuchioki. The edge of the blade is coated with a thinner layer than the sides and spine of the sword. It is then heated, and then quenched in water (few sword makers use oil to quench the blade). The slurry causes only the blade’s edge to be hardened and also causes the blade to curve due to the difference in densities of the micro-structures in the steel. When steel with a carbon content of 0.7% is heated beyond 750 °C, it enters the austenite phase. When austenite is cooled very suddenly by quenching in water, the structure changes into martensite, which is a very hard form of steel. When austenite is allowed to cool slowly, its structure changes into a mixture of ferrite and pearlite which is softer than martensite. This process also creates the distinct line down the sides of the blade called the Hamon, which is made distinct by polishing. Each Hamon and each smith’s style of Hamon is distinct.
Example of a hamon
After the blade is forged, it is then sent to be polished. Traditional hand polishing takes between one and three weeks. The polisher uses a series of successively finer grains of polishing stones in a process called glazing, until the blade has a mirror finish. However, the blunt edge of the katana is often given a matte finish to emphasize the hamon.
Only a small amount of people use the traditional method of sword making doing everything by hand with no power tools at all, these sword maker undergo years of apprenticeship and are tightly licensed. Replica Katanas have flooded the market and you can buy a decoration katana that will break on the first swing if ever used for about £20/$30. A properly made Katana should cost anywhere from £150/$200 upto thousands of pounds or dollars if made by a true master in the old fashion. You can buy Katana’s on our site that are made semi traditionally, using all the correct methods but implementing the use of power tools to speed up the process. This does not affect the finish or usability of our swords but does make them much more affordable.