Shingane: Low-Carbon Iron Folded on Itself for a Sword's Soft Core

Shingane is the soft core of a Japanese sword: very low-carbon iron, folded several times on itself to purify it, so it stays nearly pure iron and barely hardens. Coat it in clay, water and straw ash at each heat, fold and weld it, then draw it into a bar to fit inside the harder edge steel. The picture: our diagram, a bar folded into layers.