Continuing Sterling Clay Experiments - The Bubble Saga

Over the weekend, I ran two more loads of sterling clay, with mixed results. I had the working theory after my failures last week that moisture was the root of my bubble problem. The latest experiments say that cannot be the issue, leaving me without a working theory for what is causing the problem.

Flock earrings

©2012 Vickie Hallmark

sterling silver

Flock earrings, reverse

©2012 Vickie Hallmark

sterling silver

After drying these Flock earring components to death, they fired in my test run perfectly. I went back to the full 1500°F with no signs of overheating. No signs of bubbles, front or back.

Treetop pendant 2

©2012 Vickie Hallmark

sterling silver, before patina

Then I committed the more intricate work waiting on the bench -- two pendants and a sculptural pair of earrings.  The front is pristine.

Treetop pendant 2, reverse

©2012 Vickie Hallmark

sterling silver, before patina

The back of this pendant has major pox. No fiber blanket was used, but I did prevent trapping carbon in the openings during shrinkage by encasing the pieces in stainless steel screen.

After drying for several days, trapped moisture seems unlikely to be the problem. The isolation of the bubbles to the reverse of the piece still stumps me. One hint I see is that textured backs are giving more trouble, although I did get bubbles on one corner of a smooth back earring. The texture was made with tear-aways, lubricated with olive oil. Of course, I used olive oil on the front textures, too, with no problem, so olive oil shouldn't be the culprit.

I'm still thinking. Any ideas?