When asked to give advice for beginners, it occurred to me that a lot of people are currently introduced to copper and bronze clay before having the chance to experience silver clay. When a student starts taking my classes as a beginner, I automatically start with silver. But is there a reason not to start with base metal clays, just because historically silver clay was there first?
On the right side of the screen, with the Articles and Tutorials, you will find a project that can be made with just copper clay, or with a combination of the three clays. It’s called “Cinnamon Stick Earrings”, and is open to many interpretations. I hope it helps you get started.
I’ve been asked about embedding copper wire in pieces before firing. From my experience with pure (bare) copper, it doesn’t fire well. After firing, if you try to bend the wire it will break.
Bronze wire works fine. If you don’t clean it or buff it after firing, its color will be very similar to copper.
My student Georgia Bassen, who lives like there is no tomorrow, read my last posting on Friday morning, and on Friday night she came to class with these gorgeous copper clay pieces that she pulled out of the carbon while it was still hot:
You can see more of Georgia’s work in the photo gallery. Some of her pieces are made with copper and bronze clay fired together as clay. She is the only one I know of so far who has managed to do this. Firing bronze and copper clay together is tricky, and I hope to post about it as soon as I know more.
A strange thing has started to happen lately. Pieces of copper and bronze have been coming out of the kiln with little holes in them, especially hollow forms. I asked myself what had changed recently in the way I was firing, and the only thing I could think of is that I have been firing without a lid for the first phase of the firing. I took a good look at the carbon. I hadn’t changed it since I started firing without a lid. A large part of the granules had turned into fine powder, and some of it was white and light brown. I realized that most of the carbon had turned into ash, and it was no longer producing enough carbon dioxide to drive the oxygen away from the firing box. Too much oxygen in the box during the second phase (sintering), and inside the hollow forms, resulted in holes, where the particles of the metal could not fuse together.
I changed the carbon and the problem was solved. I still fire the first phase without a lid, though. This is how the carbon looks after the first phase of firing:
After the carbon has cooled down a little I vaccuum this ash.
So I think we can’t use the same carbon indefinitely, especially if we fire without a lid. Vaccuming the ash helps, but changing the carbon once in while is necessary. Old carbon could have been one of the culprits with pieces that did not properly sinter.
Although patina tends to fade away over time, and I have not been able to find a reliable way to preserve it, I am still curious about what makes it happen. I have tried both kinds of carbon, new and old, and the results were the same. I did notice, though, that the more pieces I have in the box, the less patina I get. The amount of carbon, relative to the number of pieces in the box, seems to make a difference.
In the past few days I have been emptying the box into a sieve while the carbon was still very hot. The colors were amazing. Here are the colors on fired copper right off a very hot box:
If you try it, be careful. Wear a mask and goggles and hold the box with insulating gloves. Take the box out with a kiln fork and lay it on an incombustible surface like concrete or bricks.
Powder metal is widely used for industrial applications. There are two main advantages in making parts by sintering powder metal rather than casting molten metal into molds. First, the object can sinter at a temperature significantly lower than the melting tempeature of the metal. Second, the resulting object is porous, which allows it to hold lubricants or let them pass through. I once made a small silver clay bottle and put in it a few drops of scented oil. It’s been years now, and I can still smell it.
Here is a short video clip that I found on YouTube:
Lately I’ve been firing in the 2.5″ tall box rather than the 4.5″ tall. I elevate it on posts (broken tiles will do) so it’s as high as possible in the kiln chamber. The bottom of the box is right above the lowest heating element, so the heat can flow under the box and up.
I use this box in both the front loader and the top loader. The size of the box and the placement in the kiln allow me to fire in two layers in the front loader as well, with full sintering!
I also stopped using the lid, so any stainless steell tray that is no higher than 2.5″ will serve the purpose. My student Suzanne Roady was unable to sinter pieces that kids made in a school project. The pieces were 0.5″ thick. Elevating the box and removing the lid resulted in full sintering.
Firing without a lid, though, will require purchasing carbon more often. A lot of it burns leaving ashes behind.
