Tamahagane (玉鋼 / "jewel steel") is a type of steel made in the Japanese tradition. The word tama means "round and precious", like a gem. The word hagane means "steel". Tamahagane is produced from iron sand, and mainly used to make Samurai swords, such as the katana, and some tools.
There are 2 main types of iron sands: akome satetsu (赤目砂鉄) and masa satetsu (真砂砂鉄). Akome is of lower quality and masa is of better quality. The person who decides the amount of the mixing parts is called the murage. Depending on the desired result, the murage mixes one or more types of sands.
The iron sand is put in a tatara, a clay tub furnace. The clay tub measures about 4 feet (1.2 m) tall, 12 feet (3.7 m) long and 4 feet (1.2 m) wide. The tub is then dried and heated. The clay tub is heated to a high temperature, about 1,000 °C (1800 °F). Then, it is mixed with charcoal to give tamahagane hardness.
The process of making tamahagane continues for 36 to 72 hours (a day and a half to 3 days), depending on how many people work and how much metal is to be obtained. The iron sand is added every 10 minutes and the mixture is frequently turned over.
When the tamahagane is finished, the clay tub is broken and the steel is removed. The best steel is on the edges of metal block, because this is where the oxidation process is stronger. The quality of tamahagane is determined by its color: bright silver pieces are very good for making blades.
Both types of tamahagane are now exactly where they need to be: the hard steel forms the sword's outer shell and deadly blade, while the tough steel serves as the katana's core. This perfect balance of properties is what made the katana the samurai's most durable and prized weapon. The highest quality tamahagane can cost up to 50 times more than ordinary steel made using modern methods.
The smelting process itself is an exercise of endurance, patients and intuition that create ever moving variables that all contribute to a unique steel that is then further refined in the forging and folding process. With the potential for failure or unintended results being very high, there are huge amounts of pressure for every smelt to be a success.
Tamahagane swords are manufactured in Japan. The word tamahagane means precious steel. Authentic hand forged tamahagane katana can be very expensive. Tamahagane steel is made by building and firing a Tatara, the traditional Japanese sword-steel smelter. There are not many Tatara operating today in Japan and even less that produce sword quality steel; the Tatara being the actual location where Tamahagane is made. The heavy costs involved with creating Tamahagane and its restricted availability make the base costs of producing Japanese swords much more expensive than simply using a flat bar of modern steel.
Some modern swordsmiths have made high quality reproduction swords using the traditional method, including one Japanese swordsmith who began manufacturing swords in Thailand using traditional methods, and various manufacturers. These however will always be different from Japanese swords made in Japan, as it is illegal to export the tamahagane jewel steel as such without it having been made into value-added products first.