Types of Bellows
Bellows are an essential component of the traditional ironmaking process. To maintain an internal temperature hot enough to melt iron, the furnace requires a steady supply of oxygen, which is provided by the bellows. Three broad categories of bellows can be seen throughout the world: bellows made from wooden planks, bellows made from animal skin, and bellows made from piston-like tubes. Though the materials and shapes of the bellows differ, their function is generally the same: air is forced out of a confined space through a nozzle or pipe.
The earliest bellows used in open-air tatara from the late sixth century were made from animal skin. Deerskin bellows are mentioned in an eighth-century historical text called the Nihon shoki (The Chronicles of Japan). However, plank bellows are believed to have been adopted more widely from the eighth century onward.
There were two common types of plank bellows used in tatara ironmaking: hand-operated box bellows and foot-operated bellows that resembled a seesaw. In the late 1600s, ironworkers enlarged and improved the latter type to create tenbin (scales) bellows, so named for their resemblance to a huge set of scales. Tenbin bellows were more powerful and required fewer workers to operate. As this technology spread, box bellows were relegated to the smaller furnaces in ōkajiba forges and blacksmiths’ workshops.