This won't work very well or really at all in the ART process as
you have found. Fooling with time at temperature won't improve
things at all as you are finding out. A good result is more
accidental than intentional.
Well, while I will endorse the idea that these processes have not
been fully worked out for the art products, I cannot agree with the
above in regard to copper clay in particular.
First, the composition of commercial copper clay is different from
the industrial process, being based on methyl cellulose, not soap.
Your description of the process looks sound to me, just the same.
I have done many firings of bronze clay and several of copper. I
agree that bronze is more accidental than intentional, though some
people seem to have success with it. I’ve put it aside until it is
better worked out.
Copper, however, has worked for me every time, if it is fired in a
2-stage process such as you describe. It is heated to about 500F for
15 minutes on an open shelf, cooled, buried in carbon and fired to as
high as 1650, held for 3 1/2 hours. I’m not sure how the length of
time was established, but it does take time for the box and carbon to
I do not use this product extensively-- my interest in it is largely
because my students are interested, though I have visions of more
sculptural, larger work. I wanted to do those in bronze, but as I
say, I have set that aside for now.
Still, it IS possible to get some wonderful results with these
materials. Once again, I refer interested people to Hadar Jacobson’s
site, and her blog in particular.