Monday, March 26, 2012

The Sterling Silver Clay Learning Curve

Although I've completed quite a few projects now in sterling clay, with minimal issues, this week introduced me to a range of more severe difficulties.

Silver Lining Brooch
©2012 Vickie Hallmark
sterling silver
This cloud brooch was the largest project and looks great from the front. On the reverse there are areas that bubbled. When this happened earlier this week to a set of smaller pieces, I thought perhaps it was a kiln temperature overage. For this firing, the temperature was reduced from 1500 to 1480°F, but the bubbles still appear on the back only. In this case, the brooch was supported laying flat on fiber blanket with a screen over the top to prevent trapping carbon in the carving.

©2012 Vickie Hallmark
sterling silver clay
bubbles from trapped moisture?

Bubbles are most pronounced in the cloud appliqué and surrounding area, which makes me think that they might more likely be due to trapped moisture. The appliqué was made as a separate 1 card (texture up to 2 cards) thick piece that was added after drying. Perhaps moisture was trapped under the dry surface. I'm not certain how long the piece dried before firing, although I sort of thought it was overnight.

Beyond the bubbling, I managed to break my first piece of fired clay.  It seems I got a bit cavalier about this piece. I had the brooch all cleaned up and ready to patina when I decided to give one final tweak to the pin clasp, right in its weakest area. I snapped one of the toes of the clasp right off. In retrospect, it's obvious that I actually should have reinforced that piece to begin with, so this was my opportunity to do so in a second step.

©2012 Vickie Hallmark
 sterling silver clay repair
After adding more clay, I skipped the open firing and went directly to the carbon firing. The repair looks flat and dark after firing, much like after the open shelf firing, so at first glance it looks unsintered. However, a quick bit of clean up reveals nice shiny silver below a shallow dark layers.

©2012 Vickie Hallmark
sterling silver clay repair

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