The Tatara Iron Manufacturing Method
Tatara iron manufacturing is a method that involves the use
of iron sand as the source material. The iron sand is reduced through the heat
of combustion of charcoal in order to obtain iron. Iron is usually refined
from ore, but iron ore is scarce in Japan. Iron sand, however, is found in
abundance, and the tatara method was developed to make use of this resource.
There are two ways producing iron with the tatara. The first is called the kera-oshi, or “steel pressing” method (the direct iron manufacturing method), in which steel is produced directly from the iron sand. The other way is called zuku-oshi, or “pig iron-pressing,” because its objective is to produce pig iron.
With the kera method, you start with a mass of the root material for steel, then forge the steel through pounding and stretching the material. This method is generally known. Moreover, because steel can be put to flame and strengthened, the method has been used for producing Japanese-style swords, cutlery, tools, and the similar implements.
Because it has high carbon content and melts easily, pig iron can also be used for cast metal. However, most of it is carried to a metal-working shop where the carbon content will be lowered to produce a type of steel called sage-gane(low-carbon steel) or, after lowering the carbon content further and softening the material, it will be turned into steel that will be used for knives.
The iron sand used is also of two vastly different types. They are the masa iron sand used chiefly with the kera-oshi method, and the akome iron sand used for the zuku-oshi pressing method. Masa iron sand comes from a kind of granite made of acidic rock and has low titanium content. Akome iron sand comes from a kind of diorite made of basic rock and has high titanium content, with the presence of TiO2 at 5% or greater.
|Kera on display at the Wako Museum|