J. J. Rein’s description of a traditional Japanese method of malleablising annealing

More surprising than the inlaid work on the forged iron armour and the weapons, is its direct employment on cast-iron Tetsu-bin,a  vases and other articles. As is well known, the cast iron cannot, on account of its hardness and brittleness, be worked with the hammer, chisel and burin. The way in which these properties are lessened by the reduction of the carboniferous contents has been observed by Lehmann and Wagener in Kiôto.b  It is a peculiar decarburising process, by which the kettle or pot receives a structure like to that of soft iron or steel, and can then be treated in the same way as in the Zoganc-work on forged iron.

The process of decarburisation of the surface is called Yakerud (to burn), and is performed with a primitive apparatus. Old damaged rice kettles out of which the bottom has been knocked serve as ovens. These are plastered over on the inside with a fire clay (Oka-saki-tsuchie and sand mixed in equal parts), so that a cylindrical space of the size of the hole in the bottom, remains open. The Kamaf or kettle thus prepared, is turned over upon a thick plate or slab, three or four centimeters thick, made out of the same fire-proof material, which serves as a grate, and is perforated like a sieve for this purpose. In order to give this plate greater firmness, it is bound around with an iron band. The holes have a width of about 1.5 centimeters. In order to give the air free play, several stones are laid under the edge of the slab. Then the Tetsu-bin to be burned, whose outside has been carefully cleaned beforehand from dust and sand, is placed in the Kama, directly on the grate.

The difference in size between the Kama and the Tetsu-bin must be such that a space of at least five centimeters remains open around the latter. This open space is then filled with the best charcoal in pieces the size of a nut, till the Kama is filled to the rim, when the coal is kindled.

In order to increase the draught, two or three Kamas filled in the same way are set one over the other, forming a kind of chimney. When the coals have ceased glowing, others are put in, and when the second instalment is burned out, the Tetsu-bin are taken out and turned upside down (with the opening underneath), set again in the Kama and burned twice in this position. Under favourable circumstances, the surface is now sufficiently soft and tough, as is ascertained with a file. It is often the case that the furnace must be heated ten times. After the cooling the decorations are then carved as in forged iron, without danger of breaking the edges, or recoil of the burin.

(J. J. Rein, Japan nach Reisen und Studien, vol. 2, 1886, pp. 518–520; The industries of Japan, 1899, pp. 434–435).

a鐵瓶, ‘iron kettle’.
bKyōto 京都.
f釜, ‘kettle’, or 窯, ‘oven’.

This page is a supplementary text for Cast iron in China and Europe.