Tamahagane is the best quality steel obtained using Japanese traditional techniques. The word tama translates as round, precious,the word hagane means steel.
A good quality tamahagane can cost 50 times more than the ordinary steel. This steel is used to make Japanese swords, knives, and other kinds of tools.
The tamahagane is obtained out of special iron sands also called satetsu. The sands distinguish by their low amount of impurities. It is considered to be of better quality than iron ore.
There are known two different types of iron sand: 1) “masa”, is the best one with a very low content of impurities. Its composition includes acid granite and black mica. The best Japanese swords are forged of iron obtained of this sand; 2) “acome” also contains a small amount of impurities but is still considered a lower quality sand because of its salty basaltic stone and other igneous rocks composition. Because acome sand is easier to smelt it is mainly utilized to make high quality cutlery, tools and expensive guns.
These sands are mined basically in the northern part of Japan. Areas such as Kame-ishi, Yasuki, Kame-ishi, etc are rich in iron sands.
The tamahagane is smelt in a clay tube called tatara. It is heated to a high temperature about 1000 ºC (1.832 ºF) to get dry and well heated. Only after this the iron sand is put in this furnace. The smelting process lasts from 36 to 72 hours, during which every 10 minutes new portions of iron sand are added. This mainly depends on the number of people working on it. They are called murage.
The final result is obtained when iron sands are mixed with charcoal to give tamahagane hardness.
A good tamahagane should contain around 1% of carbon and not go over 1.5 %.
Here is the chemical components contained in both sands (percents):
When the tamahagane is ready the tatara is demolished to release the steel. The best steel is thought to be the one on the edges of ingot. The reason is that, this is the area where the oxidation process occurred on a higher level. Specialists can determine the quality of tamahagane by its color. A bright silver indicates a very good block of metal, which mainly goes for blades forging.
Besides tamahagane, there are metals of great quality such as orosigane, hotyotetsu and zuku.