Evidence of primitive iron manufacture has been found in the regions of Chūgoku , Tōhoku, Kantō, Hokuriku, Kyūshū, and in other parts of Japan. In the Chūgoku region, where Shimane is located, iron ore was used originally, but when the base ingredient changed to iron sand, iron producers adopted box furnaces. Kantō, Tōhoku, and other regions used iron sand and box furnaces as well, but many shaft furnaces have also been found in those regions. Iron production began long ago and survived through the Japanese Medieval period (approx. 1185–1568 CE) and up to the modern era in parts of the Chūgoku and Tōhoku regions. Other regions saw these methods disappear before the Kamakura period (1185–1333).

• Tatara furnaces in the late sixth century were made in various shapes and small in diameter.

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

  Furnaces made during Japan’s Medieval period were larger, more highly developed forms of the furnaces from the previous age, reaching a size of up to 3 meters long, 0.9 meters wide, and 1.1 meters tall (10 × 3 × 3.5 feet).

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

For tatara, the introduction of the tenpin, or “seesaw,” bellows was revolutionary. It was a leading factor in the flourishing of tatara in the modern Chūgoku region.

Increased demand for iron incentivized the creation of larger furnaces which needed greater amounts of air flow to ensure high furnace temperatures. This was accomplished through the use of foot bellows, and the tenpin bellow was an improvement on the original design. As opposed to one large, single bellows, the tenpin bellows has one bellows for each foot, and when one was pressed down, the other would rise, similar to a seesaw. This greatly increased production efficiency.

Bellows workers were called banko. During production, air had to be pumped into the furnace for 70 hours at a time without stopping. The bellows were worked in teams of three. Each person would work for an hour before taking a two-hour break. This pision of labor was called kawari-banko, meaning “alternating banko.”