About Tatara
Iron Produced from the Tatara
There is the kera-oshi method and there is the zuku-oshi method, and the products
made from them are kera (a mass of steel) and zuku (pig iron), respectively.
After the kera has been broken up at a metal working area on site, the pieces
are sorted through at the haganezukuri-ba (“steel-making
site”). The best portions will become tama-hagane. The remainder, on the basis
of such factors as size,
surface fractures, and amount of iron slag in the compound, is sorted out into
silvereye, manufacturing powder, bu-kera (kera with a carbon content between
that of tama-hagane and iron), and kera-hoso (small clumps of bu-kera). The tama-hagane,
silvereye, and manufacturing powder is packaged and shipped as is for sale. The
remainder will be sent together with the pig iron to a metal-working shop where
it will be finished into sage-hagane or knife steel and then shipped.
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Spindles used for
breaking up kera at the metal working site (Wako Museum). The spindles are dropped from a high place and break up the kera. |
The work performed at the metal-working shop differs from the forging that is done today. It includes an operation for fusing and removing the iron slag contained in the kera through forging it in a half-melted state. As such, it is a kind of smelting process and can also be described as a steel-working operation, in which the pig iron and kera scrap are decarbonized and turned into soft steel. Accordingly, the manufacturing method for the steel that reaches the metal-working shop from zuku-oshi can be said to be the Japanese version of an indirect iron-manufacturing method.
The kera-oshi method, by contrast, is a process for creating steel directly, since steel is produced directly from the iron sand. It is a traditional technology unique to Japan and is lauded as a national cultural heritage.
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| Varieties of tool used at metal working factories (Wako Museum). |
