Changes in Japanese Tatara Iron Making Technology

  • Tatara Iron Making

Tatara iron making is a traditional method passed down for a thousand years.

Long ago, people gathered iron sand from mountains, rivers, and oceans and fired it with charcoal to make iron. They made various improvements to their techniques over time, culminating in this unique iron making method. Characteristic to Japanese tatara iron making is the tatara furnace.

The Box Furnace

Old-fashioned iron manufacture was carried out in Chugoku, Tohoku, Kanto, Hokuriku, Kyushu, and other regions of Japan. In the Chugoku region, where Shimane is located, iron ore was used originally, but when the base ingredient changed to iron sand, producers switched to a box furnace. Kanto, Tohoku, and other regions used iron sand and box furnaces as well, but many shaft furnaces have also been found there. Iron production began long ago and survived through the Japanese middle-ages (approx. 12C to 17C) and up to the modern era in parts of the Chugoku and Tohoku regions. Other regions saw these methods disappear before the Kamakura Period (1185-1333).

Development of the Furnace and Underground Structure

  • Early tatara furnaces of the late 6th century were made in various shapes, and small in diameter.

    The long, box-shaped furnace first appeared during the Nara Period (710-794). Bellows could now be placed along the long sides of the furnace to send air inside evenly, creating the basic layout for later developments.

    Furnaces of the middle-ages were larger, more highly developed forms of the previous age, reaching a size of up to 3 meters long, 90 cm wide, and 110 cm tall (10×3×3.5 ft.).

  • Recreation of a late 6th century solitary furnace (Wakō Museum)
    Recreation of a late 6th century solitary furnace (Wakō Museum)

The increase in furnace size was directly correlated to the increase in the size of the underground structure. This underground structure stabilized the furnace temperature and prevented moisture from rising into the furnace and causing an explosion. In modern times, charcoal was added directly underneath the furnace in the “hondoko,” and on either side of that were tunnels called “kobune.” The underground structure including the hondoko and kobune is called “tokotsuri.”

The increase in underground structure size and more efficient bellow structure allowed for a larger tatara furnace.

  • Modern furnace (Sugaya Tatara Sannai)
    Modern furnace (Sugaya Tatara Sannai)
  • Underground structure full-scale model (Okuizumo Tatara and Sword Museum)
    Underground structure full-scale model (Okuizumo Tatara and Sword Museum)

The Introduction of the Tempin Bellow

For tatara, the introduction of the “tempin” or “scale” bellow was revolutionary. It was also a leading factor of the flourishing of tatara in the modern Chūgoku region.

Increased demand for iron required larger furnaces which in turn required even bigger blasts of air to increase furnace temperature. This was originally accomplished through the use of foot bellows, and the tempin bellow was an improvement on the original design. As opposed to one large, single bellow, the tempin bellow has one bellow for each foot, and when one was pressed down the other would rise, similar to a seesaw. This greatly increased production efficiency.

Bellow workers were called “banko.” During production, air had to be pumped into the furnace for 70 hours at a time without stopping. 3 workers would comprise a team, and each person would work for 1 hour before taking a 2 hour break. This division of labor was called “kawari-banko,” a Japanese term meaning, “to take turns.”

The End and Revival of Tatara Iron Making

Tatara Iron Making saw a swift decline upon the introduction of western mass-production methods. With the closing of the last tatara ironworks at the end of the Taisho Period (1912-1926), the history of tatara iron making came to a close.

While tatara production did see a short revival in order to keep up with demand for military swords during the Pacific War, it was once again suspended for many years. In 1977, in conjunction with a shortage of the steel used to make katana, The Society for Preservation of Japanese Art Swords and the Agency for Cultural Affairs established the Nittoho Tatara as the only tatara allowed to produce tamahagane, steel used to make katana.

Japanese tatara iron making made a comeback.

  • The Kamaishi Mining Tanaka Ironworks thrived using western technology such as blast furnaces and coke
    The Kamaishi Mining Tanaka Ironworks thrived using western technology such as blast furnaces and coke
  • Yahata Ironworks introduced German technology
    Yahata Ironworks introduced German technology
  • Adding charcoal at the Nittoho Tatara
    Adding charcoal at the Nittoho Tatara
  • Removing finished iron
    Removing finished iron