Torch-firing quick-fire copper is much like torch-firing low-shrinkage silver clay: the piece will not be as strong as it can be when kiln-fired, but for pieces that don’t undergo wear and tear, or components that are not a structural part of a piece, this may not be all that important.
It takes a little longer, about 6 minutes. I suggest turning on the radio and listening to two songs in a row (or just Hey, Jude) while you are torching. Here is a video clip demonstrating firing a copper piece, 6 cards thick, and an overlay of copper clay fired over steel clay:
Jenny James sent me an email, saying that she wasn’t able to sinter quick-fire copper with a torch, even after 20 minutes. She ended up firing it on the screen on her stove top for 30-40 minutes and succeeded.
If you try that, you can do it outside, using a burner that is used for camping. Place a screen or copper sheet over the burner and place the pieces in a circle, where the flame is.
I answered Jenny that what I think happened, is that her torch did not supply enough flame. Either the flame wasn’t big or hot enough, or the piece was too big for torch-firing. The flame has two roles in base-metal clay firing:
1. To supply heat;
2. To consume the oxygen around the piece in order to prevent oxidation. In fact, that’s what the carbon does by burning. Here is a photo of the carbon burning right after the kiln finished its cycle.
Obviously there was much more flame on the stove to protect the piece from oxygen.
So Jenny went on to her second experiment. Here is what she wrote:
“More heat and less oxygen when torch firing, I tried something new. I laid the piece ON TOP of a little dish of carbon. I then fired for 8 minutes with my small butane torch. It heated up WAY faster to a much brighter glow, and the piece was entirely engulfed in flame. It sintered BEAUTIFULLY in 8 minutes and was super strong! I will keep testing it for shorter periods of time tonight and see just how quick it can really be fired.” Later she wrote: “In 4 minutes the piece sintered perfectly and was super hard – unable to break it with pliers. All of the tests were done with 8 mm thick and 2 cm x 2 cm. By firing it on top of carbon it fires as easily as torch firing silver.”
I’d like to thank Jenny for her input. I would also like to thank Ron Taylor, who sent me a photo of a piece that he created at my workshop in San Diego. Ron came to class with a rendering of a piece that he wanted to make with a combination of copper and silver, and the piece came out exactly as he planned it, including its size!