Saturday, October 15, 2011
Firing copper clay
In a previous post I mentioned how copper and bronze clay have to be fired in an oxygen free environment. This also applies to steel clay, rose bronze clay and the new PMC Pro (a stronger form of silver clay that has some copper in it for strength.)
There are various containers for firing these clays. I use a stainless steel container that gets a black coating on it during firing that is messy and dirty. (My vacuum cleaner is seeing the light of day more often now.) Even though there are containers that don't get a black coating I figure that I already had a container and might as well use it. It's been working great so why mess with a good thing.
My friend Carol Scheftic takes a photo of her pieces before they go into the kiln so that if something goes wrong she knows where it was located in the container and thus may be able to figure out why the piece did not sinter. I've started to do this too. (It also helps my brain remember how many pieces are in there. ) It's not obvious when the firing is done because a one inch layer of carbon is covering the top.
Here's a photo of a load before firing. Because the pieces need to be toward the back of the container the number of pieces that can be fired are minimal. (Unlike silver which is fired on an open shelf. Several shelves can be stacked with ceramic spacers between them which allows for even more pieces and the silver can be placed anywhere on the shelf.) Because the firing time is shorter and there are more pieces in a firing, silver is much cheaper to fire. But, much more expensive to buy. I'm still trying to figure out if the cost of working with the base metal clays are really any cheaper in the long run.