Metal Clay Questions

Problems with clay not sintering

Question

I am having problems with white copper clay, after months of trying different things. I have been in contact with Bill Struve of Metal Clay Adventures. He has changed the firing schedule to 650 degrees for 30 min then high ramp to 1900 degrees for 2 hrs. This schedule has (so it seems) has stopped the cracking, but they aren’t shrinking completely and I tried bending one piece and it broke and was solid black in the center. Does that mean it didn’t sinter completely? Any advice? I hate to keep bothering Bill.

November, 2015 from Facebook.

Answer

I don’t use metal clay much anymore. But, when I was working with clay, I had a lot of problems with the base metal clays. I had the same problem with cracking and it being black in the center. It’s just not fired completely. I’d do a series of test pieces (of a similar mass to your finished piece) and keep track of what you are doing. Try firing longer and hotter. Run through various temperatures and times, firing one piece at 1925, the next at 1950 and see what happens to the clay. Record your results. That’s the best way to go as everyone’s kiln is different: Your 1900 degrees is not his 1900 degrees – yours might only be at 1825. To check: you can purchase a probe thermometer (the probe is sold separately) and verify the internal temperature of your kiln – while firing. I have one with a probe that I insert in the vent hole of my kiln. (Sounds like an alien abduction!)  Keep track of any differences and adjust your kiln accordingly. So, experiment – it’s so much easier and cheaper (in the long run) than constantly ruining your work. Good luck.