I've been up to mischief again. It's not exactly silver, but it is smithing...
For those who don't know, mokume gane is generally translated from the Japanese as "wood grain metal", and refers to the lamination and patterning of different metals; one of the more common patterns involves carving through the layers so that the resulting pattern looks somewhat like wood grain. As with pattern welded steel, there's a lot of variations you can introduce into the resulting pattern. Mokume was originally developed in Japan during the Edo period to furnish swords as an echo of the patterns formed by the folding, welding & reforging of the blade steels; as the need for swords declined, so mokume became used for other ornamentation - I was going to say "more ornamental", but if you've seen the swords, they're as much works of art as they are weapons. Fast forward to the late 1800s and the Japan society wrote about a technique they'd observed for silver-soldering a laminate of dissimilar metals - not quite what happens in the traditional process, but it has been extensively used since then (a particular example would be Alistair McCallum's fantastic work).
I use a development on the traditional method, where sheets of *very* clean metal are heated up to a fusing temperature whilst clamped together; I used to use the old method, where the sheets are wired together and placed in the forge, but these days I use 2 slabs of 1/2" tool steel bolted together to hold the sheets in close proximity; as they heat, the sheets will expand, increasing the clamping effort. A new thing for me - this assembly goes into a stainless foil bag along with a spoonful of granulated carbon (to absorb the oxygen) and is heated for a wee while in the kiln.
So, last night I had 14 sheets of 2mm thick 50x50mm squares of copper and brass, cut with a jigsaw as I decided I was bored with cutting that thickness with a jeweller's saw. Each of these was thoroughly cleaned by hand by scrubbing them with a block of pumice and some hot soapy water to remove any oxides; they were then rinsed in distilled water (the dehumidifier paying for itself again), dried carefully and degreased with isopropyl alcohol. At this point, they're so clean that a drop of water will sheet across them rather than sitting as a droplet.
The steel plates and bolt threads were painted with Tippex to prevent adhesion; once this dried, the copper & brass were stacked alternating and clamped between the plates. The bolts have to be done up quite tight; there are some suggestions to use a torque wrench. I painted the stack edges with borax to help scavenge any oxygen; the carbon in the bag helps with the rest of it. The whole lot then went into the stainless bag (be warned - this stuff is *very* sharp, I used to regularly cut myself on the edges) and the edges are double folded & hammered down to set them. Then, into the kiln at 700C (brass & copper) for 8 1/2 hours.
This morning I vented the kiln to drop the internal temperature; once it was down to about 150 I fished the bag out (welding gloves are very useful at times). Snipped the top off and removed the plate, slung the unused carbon and unbolted the plates. Owing to the use of both borax & carbon, the resulting billet is very clean, almost no oxide formation at all. I've forged it down to 24mm so far and the whole thing seems quite solid, no iffy looking areas that look about to delaminate.
The next stage is to grind the edges flush, then I'll flood them with a low temp solder, probably Easyflo (to further discourage delamination) and carry on forging down to sheet. Once it hits 3mm the individual sheets will be about .2mm thick and I can start patterning it.
I'll even take some photos along the way... If you're really lucky, they might even be relevant.
One of the problems I've had with mokume in the past is down to the technical nature of the material; I enjoy making it (time consuming though it is) but once I've got it, what do I do with the stuff? Having been on a silversmithing course recently with Brian Clarke, I've nailed the bits of the basic techniques that were giving me gyp and can progress...
Bookmarks