The kanna-nagashi method is used to collect iron sand in early modern-style tatara iron manufacturing. This is a brief but somewhat detailed explanation.

Mainly the yama variety of iron sand is used with this approach. First, the collector chooses a location where soft granite is exposed. This granite should have a high iron content, and be weathered enough so that it can be broken off. The location should also have a good water supply for washing. An iron sand collection facility called a kanna-ba (lit., “kanna place”) is built at this spot. Next, a reservoir is built on top of the mountain. The water from it is made to run along the mountain ridge. The earth is broken up on the mountain with a pickaxe, and carried down the reservoir stream anywhere from 0.5 to 4.0 km to the ore-sorting facility. This is described as suiro hashiri, or “running the waterway.” The ore-sorting (or washing) facility is comprised of three or four washing ponds. In the Izumo region, the washing ponds that the sand passes through are called, in order, oike, nakaike, otoike, and hi. The ore is gradually sorted until iron sand constitutes up to 80% of the material collected. The lighter earth drifts downstream, while the heavy iron sand sinks to the bottom. Extremely pure iron sand can be sorted out through repeating the process.

Scene of iron sand collection in progress

Given that the reservoir water was also an important source of irrigation for farmers, iron sand collection is limited to the usual agricultural slack months in winter between the autumnal and vernal equinoxes. Also, because the work was done in the slack months, it was a good source of cash for the farmers, and the mine operators came to rely greatly on this seasonal labor. In this connection, it was said to be a most satisfactory result if 100 tons of iron sand were collected at a single kanna-ba during this period.

However, the kanna-nagashi approach also had its downside. An immense amount of soil would get deposited downstream from breaking up large volumes of earth. The riverbed would rise to the point that would stand higher than the land around it. This would cause floods, and irrigation of lands would become impossible due to contaminants in the river. Conflicts between miners and farmers arose as a result, and domains frequently issued orders banning kanna-nagashi.

On the other hand, farmlands expanded as a result of dredging undertaken by the domains, and the raising of livestock likewise prospered. Also, mountains did not suffer any devastation, as the lumbering of forests was done systematically every 30 years. The San'in region miners engaged in a diverse range of pursuits that included agriculture, mining, and animal husbandry, and so created a stable economic base for themselves.

The iron sand used in tatara was not exclusively of the yama variety. Depending on the location, kawa and hama iron sand were also used. The method for obtaining it was a simple one, wherein the sand would be run through a straw mat or bamboo sieve and the iron sand that accumulated below it collected. However, another method involved setting up a bamboo drainboard in an iron sand-collection boat, piling sand up on top of it, ladling water over it, and collecting the iron sand that accumulates in the bottom of the boat. Farmers undertook this work on a kind of subcontracting basis. The sand they collected would be bought by the tatara smith.

Varieties of tool used to collect kawa iron sand (Wako Museum)

Before the introduction of the kanna-nagashi method, iron sand seems to have been collected by digging shallow ditches. The Gei-han tsushi (A survey history of the Aki domain) explains the origins of the method as follows: “[Iron sand] is produced mainly on high plateaus and not through creating deep holes as with gold and silver mining. Hence, digging deep holes is unnecessary. The word kanna was given [to this technique] because iron (kana) collected from the earth is taken to the water side and washed, while a ditch or hole (ana) is left behind in the ground after having taken the iron.”

As demand for iron increased with the passage of time, collectors put more effective methods of collecting iron sand into operation, and the kanna-nagashi method was developed. So when exactly did kanna-nagashi get its start?

According to Professor Masatoshi Kawase of Hiroshima University, “It is likely that kanna-nagashi began around the Warring States period. It may have its origins in the nekota-nagashi method for collecting gold, which quite closely resembles the kanna-nagashi technique. This is because use of the nekota-nagashi method is thought to have become widespread at gold and silver mines during the Bunroku (1592-96) and Keicho (1596-1615) eras, when mining flourished at these locations.” In fact, it is certain that the kanna-nagashi method was being used prior to 1610, Shice Horio Yoshiharu—an important military figure who came to the Izumo region during the Keicho era—that year banned kanna-nagashi activities on the upper reaches of the Hi'i River.

Kanna-nagashi reached its peak in the mid-18th century, and tatara iron manufacturing in the Chugoku region likewise experienced vigorous development during that time.

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