Forging
Part of being a Japanese swordsmith is to look at Tamahagane and be able to approximate predominant mineral types, as well as whether their piece comes from the inner or outer core of the Tamahagane’s molten mass created at the Tatara.
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I personally think the relationship and respect between work, material and worker is at least part of the reason the craft has had such a deep and rich history; preserved and practiced.
There are no tools for measurement of temperatures or analysis of Tamahagane mineral composition; it’s all determined by sense, honed through experience.
First step in the forging process is to heat up the Tamahagane and flatten it. Pieces will fall out during this process, remember to keep them in the mix and not loose them. Flatten all the Tamahagane to about 1/8” and cool it down in water. Once cold, strike it cold and it’ll break into pieces. The softer pieces will separate from harder ones, keep them separated accordingly. The main difference between the two being carbon content. The more carbon there is, the more brittle the metal. <carbon/metal chart>
The reason for separation between hard and soft Tamahagane is part of the centuries old science behind Japanese swords. Soft metal absorbs impact and lends flexibility, while hard metal holds the edge better. Separating the two now allows the smiths to work them back together into the sword’s required combination.
The Tamahagane is reassembled into a billet. The wafers are stacked and fitted like a puzzle, then rapped in wet rice paper and coated with clay. Besides being a jacket to the initial billet, the rice paper and clay serve to add their contribution of silicon to the mix as the billet is heated. Straw is used throughout the forging process for similar reasons.
The clay coating on the initial billet insulates the outer edge, allowing all the wafers to heat up evenly and be forged into a solid piece.
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