14 DAY TRIAL // It is said that the long samurai sword, the famous katana, could cut even a hair in the air. This property is not only due to the ability of the Japanese swordsmiths, but also to the composition of the Japanese traditional steel.
The best quality steel achieved by using Japanese traditional techniques is called tamahagane ("jewel steel"). Jewel, indeed, as a good quality tamahagane is 50 times more expensive than the ordinary steel. This steel is also used for making Japanese swords, knives and other kinds of tools.
The Japanese use special iron sand for getting tamahagane, called satetsu. As satetsu reserves are scarce, it was smelted only by swordsmiths. This ore is characterized by a low amount of impurities and of a better quality than most iron ore.
Iron sands come in two quality categories: "masa", with an extremely slight impurities percentage, including acid granite and black mica (this is destined exclusively for forging the best katana) and "acome", with very low impurities level, but of lower quality due to its content of salty basaltic stone and other volcanic rocks. As acome sand is easier to process, it is mainly used for crafting high quality cutlery, tools and expensive guns.
The main deposits of these ores are found in northern Japan, in areas like Kame-ishi, Yasuki, Kame-ishi and others.
The smelting process for getting tamahagane differs from modern methods for mass steel production.
The tamahagane is smelt in tatara, a clay tube 1.2 m (4 ft) tall, 12 ft (4 m) long and 1.2 m (4 ft) wide. Tatara is fired with soft pine charcoal until dry at approximately 1000? C (1.832? F) to get dry and well heated. The satetsu is put in this furnace. The smelting can take from 36 to 72 hours, with 4 to 5 people working constantly at the furnace. Each 10 minutes new layers of charcoal and satetsu are added. The mix of satetsu and pine charcoal confers tamahagane its qualities.
When the process is ready, the tatara is broken to take out the steel ingot (named kera). For getting 2.45 tonnes of tamahagane one needs about 10 tonnes of satetsu and 12 of charcoal. The best quality steel is considered that of the edge of the kera, where more oxidation occured.
A good quality tamahagane has about 1% of carbon; over 1.5 % is considered of poor quality. The color can also indicate the quality: bright silver means the metal will go for the blade of a katana.