Tuesday, August 26, 2008

Bronze Clay Experiments

I finally got to try the new bronze clay. A friend and I managed to consume between us a 100g pack in an afternoon. It is definitely different than silver clay in some handling respects.

The clay itself dries out much faster and much slower than the silver clays. How can it be both??

Well, while working it dries to the point of developing cracks really fast. I'm glad it's not expensive, because it seemed there were flakes of it coming off on everything. It took a bit of practice to get a handle on how much water to spritz on and knead in and to work quickly enough to prevent cracking.

And then it dries completely really slowly. I had read that there seemed to be more cracking with hot-plate or dehydrator drying, so I just left it overnight. While I had no evidence of spontaneous cracking in the finished pieces I made, I did have blistering, which most likely is because of remaining water deep inside the clay.

My major complaint is how much of a pain it is to fire this stuff. It has to be buried in activated carbon to prevent oxidation of the copper and tin, so a stainless steel covered box is required. Then a slow temperature ramp and long hold at 1550 is required. The only kiln I have that can do that is the big 18" square Paragon Pearl. Now I think that kiln is running a bit hot. I have a lot of extra texture on many of the fired pieces that comes from the carbon bits pressing into the bronze. That obscured some of the fine textures I'd made, but didn't obliterate the more pronounced textures.

I did enjoy the fact that the low cost of the clay meant I felt I could just play around. So I "practiced" some techniques I'd like to do in silver. I made a couple of hollow lentils and found that to be really easy. I made a small box with a fitted lid, which taught me the virtue of planning ahead to prevent adjusting on the fly. So I had a nice inexpensive way to work out the procedures. Unfortunately, the box deformed under the weight of carbon (even loaded vertically). It's as if the box shrank, but the carbon prevented it from all moving together. The surface was ruined by blistering from residual water and too high a temperature, and all my fine texture was lost. The construction was sound, however, so I learned from the process even though the product is unusable. Probably I should have fired all the pieces separately and then assembled in a second firing. Go for the finished product on the first try; that's me!

My favorite piece is the bird lentil, made from my very first photopolymer plate. That was such a simple process! I sketched the bird with leaves, scanned it into the computer, increased the contrast and printed it onto transparency. Then the doubled transparency was laid over the photopolymer with a sheet of glass on top and exposed in the Texas summer sun for 1.5 minutes. A few minutes of washing with a soft brush and more sunlight to cure completely and it was ready to use! I bought an inexpensive kit at the PMC Conference from Sherry Fotopoulos that came with all the materials and a DVD of the procedure. Lots of other suppliers carry kits as well, such as Whole Lotta Whimsy and Cool Tools. The lentil is the same on the reverse side, except for the single blister, of course.

Other observations:
1) Once I broke the tail on the snake, repairing as I would with silver clay did not hold through the kiln.
2) Items that were cut exactly the same size came out different finished sizes. There were a total of four bead caps and one is much smaller than the others.
3) The lentils partially "flattened" under pressure from the carbon, even though they were loaded vertically.
4) No pretty patinas on this first carbon pass. Some of the pieces have an ugly greenish cast on parts, which you can see in the photos. There is a tiny hint of reddish color on a couple of pieces.
5) Very fine textures just didn't work.
6) I tried carving with the microcarver tools from Dockyard for the first time, and the bronze clay cut really beautifully. I can see how that could lead somewhere fun.
7) I did put the extra clay in the refrigerator as suggested, and when I pulled it out it was truly easier to work with.
8) Liver of sulfur worked slowly. I tried using the small torch to intensify colors, but didn't get anything really. I will try more surface finishing, including tumbling, soon.


  1. Thanks so much for taking your time and tell about your bronze clay experiment - it´s truly generous.
    I had my first experience with pmc last month in France with Kate McKinnon and I was very impressed about how creative you can get with pmc and thought also about using and trying bronze clay. Your work is gorgeous and the first attempts to bronze are great.

  2. Oh, I've wanted to take a class with Kate McKinnon for ages!!! I've promised myself that I will go to France for one in the future if she does it again. The saddest thing is that she's coming to Texas, an hour away, and I can't do the class because it overlaps my niece's wedding. ;-(

    I did buy one of her bracelets at Bead & Button, and I wear it regularly.