Tamahagane: The Steel of the Katana

tamahagane

“The sword is the soul of the samurai.” – Shogun Tokugawa Ieyasu

Shinobi are known for their use of a wide variety of weapons. Arguably one of the most recognizable is the traditional katana. The katana is the long bladed sword that was popularized by the samurai warrior in feudal Japan as early as the 15th century. The design of the sword made it uniquely versatile because the edge of the blade, called the “ha” in Japanese, sits up in the sheath, allowing the warrior to slice his opponent as the sword is drawn

In its battle prime the katana was considered a crucial element of any warrior’s arsenal, so much so that Shogun Tokugawa Ieyasu (1543-1616) once wrote, “The sword is the soul of the samurai.”

Like a true warrior, the katana is a rare incarnation of something with the apparent potential to be nothing more than ordinary. Born of simple sand dredged from the river, grains are melded together demanding excruciating time, patience, and determination. The form is folded and broken repeatedly, strengthening and sharpening with every revision before it can achieve insurmountable greatness. Neither the man who dedicates himself to become a warrior, nor the sand that rises up to become the katana, are ordinary.

For true sword wielders, passion for the katana is only matched by that of its maker. Sword making is more than just a manufacturing process, it is an art ingrained in the fabric of Japanese culture, and it begins with the crucial element of creating the perfect steel.

Smelting Steel (Tamahagane)

Creating the katana begins from the foundation of the weapon, which is a type of metal the Japanese call “tamahagane (玉鋼).” The word “tama” means round and precious, and the word “hagane” means steel.

This process requires two to five days and nights to complete. Smelters would use nearly 25 tons of iron-bearing river sand and charcoal into the furnace adding sand every 10 minutes. The source of the iron ore in most Japanese sword steel is a type of black sand called “satetsu,” which is formed by the erosion of natural iron ore deposits. There are two main types of iron sand: acome and masa. Both grades are typically used to make the katana, but may be formed individually to create two separate pieces of steel. The person in charge of mixing the ingredients for the tamahagane is called the “murage.”

Charcoal is added as the source of carbon, which causes the iron to become steel. Higher carbon (kawagane) is very hard and produces a razor-sharp edge. Low carbon (shingane) is softer and allows for shock absorption. These two separate tamahagane are crucial pieces of the weapon. The amount of carbon used usually varies between 0.6% and 1.5%.

The rectangular, clay furnace used in the process is called a “tatara” and is built specifically to produce one batch of tamahagane. Temperatures in tatara can reach up to 2,500 degrees Fahrenheit. When the process is finished, the tatara is broken and the tamahagane is removed. The quality of the steel is determined by its color. Bright silver pieces are ideal for blades.

tamahagane
Traditional Japanese tatara furnace

Driving out Impurities

After the tamahagane is created, pieces are chosen to be sent to the swordsmith where the impurities or “slag” must be removed. The steel it heated until softened, but never melted. It is then hammered out until it becomes elongated, at which point it is folded in half. The process is repeated approximately ten times for the shingane and significantly more for the kawagane. The layers of the folded kawagane create the grain (hada), which is visible after the blade is polished. The final step is to heat and hammer the steel into the shape of a long, thin metal wedge.

Combining the Tamahagane

The last process in turning steel into the blade of the katana is to bring the two types of tamahagane together. The kawagane, which is the harder steel, is used to make the jacket. To accomplish this, the kawagane is hammered out until it is slightly longer than the shigane, which is the core steel. It is then re-heated and wrapped around the shingane and hammered together until they bond together. It is crucial that there are no gaps between the two. Any bubble or debris left in this process would compromise the integrity of the weapon. The combined tamahagane are finally hammered into an elongated, slightly curved shape, which is the foundation of the beautiful and dangerous sword it will become.

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