Technological Progress

In this section the era from the start of the Edo period (1603) to the end of the bakufu and domainal system of government (1868) will be regarded as “early modern.”

As political and social condition in Japan gradually settled down with the start of the Edo period, demand for iron of the sort required in the daily lives of commoners rose alongside the formation of castle towns and large cities. Ironworks furnaces grew larger, and their underground structures became more complete. Improvements were also made in the areas of shipping and distribution, and iron-producing regions came to be concentrated more and more in the Chugoku region. At the same time, tatara furnaces were increasingly operated inside large takadono-style structures, which made it possible to produce iron throughout the year regardless of the weather. This was the case throughout the latter half of the 17th century. The kanna-nagashi method of extracting iron from iron sand by running water through it was developed by at least the first half of the 17th century, but its origin may stretch back to as early as the end of the Warring States period. This method made it possible to extract iron much more efficiently, but because the amount was still insufficient, the tatara was operated for only a limited number of months throughout the year.

Kanna-nagashi is so called because mountain sand containing iron sand is run through (nagashi) the current of a stream. The lighter particles of sand quickly flow downstream, while the iron sinks to the bottom (kanna is explained below). The percentage of iron that accumulates gradually increases as the process is repeated. This is called the specific gravity method of iron sorting. The method used before this was to simply dig a hole and collect iron sand.

Workers collecting iron sand

Perfecting Early Modern Iron Manufacturing

The most important technological revolution in the early modern period was the invention in 1692 in Izumo of the tenbin, or balanced bellows. Prior to this, workers used mouth or foot bellows. Furnace temperatures increased with the use of the tenbin bellows and it became possible to mass produce pig iron. Accompanying this development, large blacksmithing sites were also reequipped, and the zuku-oshi method became established.

Tenbin bellows

Around the middle of the 18th century, the advent of implements to break up large lumps of kera allowed steel to be produced efficiently. It became easy to extract carbon from the kera that was produced, because the temperatures were also higher due to the use of the tenbin bellows, thus establishing the modern, or kera-oshi method for directly manufacturing superlative steel. As such, perfection of the early modern tatara iron manufacturing method occurred at the end of the 18th century.

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