Thursday, June 11, 2009

Carving Cuff Bracelets from Bronze Clay

I've had a sketch of a bronze bracelet in my sketchbook for months now, and I decided it was time to try it.

For the first experiment I made the cuff too thick, 12 cards, thinking I would carve a lot away. That was more to remove than I realized, and the cuff had all sorts of issues. The major problem was one of cracking during the drying process. Although the clay had been nice and pliable when rolling and cutting, the stress of drying curved around the bracelet mandrel caused lots of surface cracking to appear. I tried filling the worst of these, but carving down into the clay made it obvious that they were much deeper than I could possibly repair. So I expected the bracelet to crack during firing, which it did.

Another issue was one of keeping the bracelet curled around the mandrel properly while drying. I goofed here and lined the bracelet up with the wrong mark, so that it was too big to begin with, and then it opened even further. No surprise, then, that the bracelet is more of a half moon, not even remotely wearable.

I also learned that it's much harder to carve away the negative space for this bas relief -- keeping crisp edges for the design was tricky. I now realize the need for some of the even smaller carving tools, which I plan to order. I had drawn a much more complex image to start with, but it simplified as I worked. ;-)

Even so, this was a great test piece and I learned a lot of valuable information. The firing seems to have been successful. I used a 250°/hour ramp and 3 hour hold at 1500°, with this the only piece in the sink. It was placed in the back of the box and developed some patina (better on the back side, wouldn't you know) with the pattern I've come to expect: red at the top fading to green/blue at the bottom. That makes sense from a physics point of view: the oxide film is thicker at the top, and is reflecting longer wavelengths. I experimented with polishing the highlights, and I will do some patina experiments as well (chemicals shipped yesterday), since that's an area that I as a chemist can really enjoy.

The second iteration is on my table now, carving almost completed: thinner, no cracking, better carving, nice tight fit. Wish me luck. I'm so thrilled with it, I've got butterflies in my stomach over trusting it to the kiln goddess. Sneak peek: