The Use Of Iron – Tetsu 鉄
From the earliest times, iron or tetsu has played an important part in the construction of Japanese armour. The raw material was an ore of iron called magnetite extracted from rivers. Iron was smelted in open topped furnaces fuelled with charcoal. After several days and nights of firing, a spongy mass of impure metal formed in the base of the furnace that was dragged out and broken into pieces whilst hot. This material called tamahagane was the raw material for swordsmiths, armourers and common blacksmiths. In its raw form, tamahagane was a heterogeneous mixture of iron steels and slag that needed considerable forging before it could be used. The process used was to hammer out a block to twice the length, fold it in half and weld it solid. By repeating this process the block was homogenised and the slag hammered out. The processed metal would be supplied to the armourer in the form of sheets that would be hammered to the thickness required.
Early lamellar armours incorporated iron scales over the more vulnerable areas but always alternating them with scales of rawhide, the iron resisting penetration whilst the hide absorbed the energy of a blow by being compressed. As metalworking skills increased, larger pieces of iron could be produced that enabled armours of plate to be produced. The Japanese abhorred raw metal and iron, if not lacquered were given a controlled coating of rust, a process called russeting that can vary in colour from a rich chestnut brown to almost black.
The Restoration Path 修復の仕事
I often am asked to either repair or completely replace missing or damaged sections of armour. When doing this I am mindful of how this will effect the originality of the piece.
My first point of call is to see if I can source a period replacement if this is not the case I will attempt to use original iron from period scrap armour. Where this is impossible due to the size I will substitute the original tetsu with a modern mild still plate. I all cases I will form the metal to resemble the original. I also use a traditional method of priming the surface of the metal by burning on urushi. Once lacquered it is nearly impossible to detect the replacement.