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Sunday, July 11, 2010

Successful Firing of Sensitive Gemstones uisng Activated Carbon

Aqua Czs fired in Silver Metal Clay (using activated carbon to preserve colour)

Last week, I test fired the new gemstones that had arrived at BeadFx (posted o7/04/10). The one stone I was most excited about was an Aqua Cubic Zirconia which sadly failed my original kiln and torch firing tests. The stones turned brownish:
Left stone (brownish) is the result of (open) kiln firing aqua czs. Right stones are unfired aqua czs.

I was disappointed by I had one last test to try, which I did this week. Firing the piece in a kiln embedded in activated carbon, and guess what? I had success!!!!

Several weeks ago I posted about firing gemstone in metal clay (posted 06/20/10), in this post I referred to a great resource from Mardel Reins at Cools Tools - Gemstone Firing Guide. In this reference she mentioned that she came to the idea that perhaps it was the heat and oxygen that caused some gemstones to fail her test firings in metal clay. The advent of the new metal clays the require firing in an oxygen free environment (which is achieved by placing them in a pan covered in activated carbon) gave her the idea to test this theory with some of the failed gemstones. (you can read the full story on the link).

Thanks to this information I decided to try this on the new aqua czs. And this is what I did:
  • I made a metal clay piece and embedded the aqua cz's in the metal clay.
  • Dried it completely.
  • Once completely dry. I used my butane torch to burn off the binder. I placed my piece on my kiln brick and ignited the piece (once the piece ignited, I turned off the torch, this is important as you don't want to overheat the piece and damage the stone).
  • I repeated igniting the piece and then letting the flame go out until the piece did not flame any more. This was to burn off the binders.
  • After all the binder was burned off I carefully placed the piece in a steel pan with activated carbon covering it completely.
  • I fired it in my kiln at 1575F for 1.5 hours (the reason I didn't go higher was a time factor, in theory a higher temperature and longer will work as well).
  • Cooled the piece naturally (remember you don't want to thermally shock your gemstones by quenching them).
  • Polished.
Success the aqua colour was maintained!!!

1 comment:

Nat said...


And the pendant is so pretty! Love it!

Thank you for sharing your experiments with us all. It's very helpful and saves us time and money.