Metal Musings Blog

I spent today rolling out my three shibuichi ingots into useable sheet.

Here’s a picture of my Durston rolling mill.

Above, I’m pickling the cast ingots in Sparex pickle. “Pickling” dissolves the dark oxides formed when the molten metal hits oxygen in the atmosphere. I use a small crockpot to keep the liquid hot, so it works faster. Three to four minutes per pickling cycle ought to do it.

Here’s the small 20% shibuichi ingot after pickling, and a quick brushing of the surface. Sorry for the lousy focus…my bad.

Here is the ingot after the first round of rolling, and after I annealed it. Annealing is heating the shibuichi to glowing red – this softens the hardened metal. Shibuichi “work hardens” quite easily when being rolled (gets hard and brittle), and if I don’t anneal it pretty often, it will crack and ruin all my hard work. I’ll pickle the ingot again, followed by brushing to remove the dark oxides.

Here’s the ingot emerging from the rolling mill. Notice how nice and smooth the rough cast surface is now.

And above, the ingot has had several rounds of rolling, annealing,and pickling. Notice the crack developing at the top. Hopefully this crack won’t get too much worse as I continue rolling, lengthening and thinning the shibuichi. I’ll just have to take the crack into consideration when designing. I can probably get two to three small pendants from this piece.

And here is the finished 20% shibuichi sheet. Note the arrow to remind myself of the crack…

Above, here is a magically computer-edited series of one of the other ingots. The red rectangle is a tracing of the original ingot, and each of the others is after a round of rolling, annealing,and pickling. Notice how each time lengthens the shibuichi sheet (thinning the sheet as it goes). Since the rolling mill tends to bend the sheet as it exits, I also forge the sheet flat on my anvil after most of the rounds of rolling. That explains the textured surface you can see on the three sheets on the right.

I noticed something interesting happening with the shibuichi I haven’t noticed before. The sheet on the right is how shibuichi appears after freshly brushing the surface. The sheet on the left is noticeably silver colored after pickling – I think this is “depletion gilding”. Depletion gilding is a jewelry technique where you can build up a pure silver surface in a silver alloy containing copper, by repeatedly burning the copper at the surface into an oxide layer, then pickling, which dissolves away the copper oxides, but leaves the silver. Just a cool thing I’ve never seen before, probably because I didn’t know enough to notice it!

And, here are all three shibuichi sheets, completed and ready to use.

Since I’ve spent the last week working on my web site format change, my wife is making me get serious about starting a new knife, so I have to make some shibuichi ingots for the knife handle scales. Shibuichi is an ancient Japanese precious bronze art alloy, typically made of 75% copper and 25% silver. It comes out as kind of a hard pinky bronze, which will patinate to a dark grayish color. Although it is a somewhat expensive alloy, it engraves and carves really nicely. I probably used an ounce of silver in the ingots I made today (about $35 worth).

Here I’m weighing out the copper scraps for a single ingot on my little electronic scale. Once I have the amount of copper I want, I’ll figure out how much silver I need to add (in the white lid at the bottom of the photo).

Above is the equipment I’m using to create the shibuichi alloy, melt it and cast it into a small, thin ingot. From the left is my oxy/acetylene torch, here just burning acetylene (no oxygen) – very smoky, and used like this to put a layer of soot on my ingot mold, the little black assembly at the top of the image. The soot will keep the shibuichi from soldering itself to the mold. Also in the picture is a small melting crucible, a container of borax flux for cleaning the scuzz off the melted metal, and the flint striker to light the torch.

Here you can see the crucible and assembled ingot mold. In this melt I’m going to use up a little extra bit of shibuichi and some scrap. Since shibuichi is so expensive, I collect all my scrap for re-use. This ingot I’ll probably use for a couple of small pendants. I cast my own shibuichi because it’s the only way I can get the thicknesses I need for knife scales, and commercially available thin sheet shibuichi costs about $30 per square inch. This much commercial shibuichi in 16 guage thickness would probably cost about $100.

Above, I’ve cast the ingot and opened the ingot mold. The shibuichi is the copper colored rectangle in the sooty mold at the top.

And here are the three ingots I cast today, two 25% silver shibuichi ingots, and one about 20% from the scraps I had on hand, since some of the scraps were 15% shibuichi and I estimated…

I’ll eventually put the ingots I cast today through a rolling mill to lengthen them and make them the proper thickness for my knife scales.