The process of Mokume Gane from non-ferrous and precious metals.
The basis for Mokume Gane emerges from welding thin layers (1.6 mm) of different metals and alloys of contrasting colours without solder and flux. The metals must have similar characteristics in their metallurgy and process.
Billets with 10 - 20 layers are ideal. The plates should be arranged in such a way that there is a clear contrast in colour between them. Each single plate must be absolutely flat with a sandblasted surface and free of any oxidation. The sheets are arranged to a block in the sequence to your taste. The welding is done by heat and pressure. This causes moving and mixing the molecules of the metals at the grain boundaries of the planar surfaces, and a new molecular crystal structure - a kind of block mass - is arising. A characteristic factor for the welding process is that the fusion happens at a temperature only little below the fusion point of the metals/alloys.
The finished metals are delivered as plates. Besides standard metals like silver-copper and copper-brass numerous combinations are possible.
The Japanese know of special alloys which don't only vary in colour but also allow different nuances in colours during the final oxidation.
These are typical japanese metals:
Shakudo (Copper with 4% Gold)
Shibuichi (Copper with 15 - 25 % Silver)
Kuromi-Do (Copper with 1% Metallic-Arsenic)
During further processing the typical patterns are positioned by various methods. One can use cutters, gravers, drills, punchers, chisels as well as engraving techniques, etching, press cut and chasings.
A billet of 15 layers and a thickness of 4 mm is being engraved. The cut should break through several layers later enabling a multi-lined pattern.
Now the billet is forged and rolled. The thickness of the metal decreases, and the cut is beginning to get filled with the metal from below.
By re-forging the billet is getting thinner and thinner. The cut is filling up more and more, and the pattern is beginning to be visible.
The cut is now filled up. The layers which were visible in the slot, have moved to the surface and are showing up as a pattern.
In the beginning the billet was 4 mm thick. With 15 layers that comes to 0.26 mm per layer (approx. 4 sheets of writing paper). In the end the thickness of the plate is 0.5 mm. With 15 layers that amounts to 0.033 mm per layer (approx. the thickness of foil). The surface of such thin layers should not be grind as it could be damaged badly, and the metal below might then become visible. This means that the surface of the finished piece of art must be forged extremely smoothly so it doesn't leave any hammer marks.