At the beginning of August – we added some Lab Created Gems for use in Metal Clay. A couple of the gals here who work with metal clay extensively wanted to double check that the stones would handle the heat without significant colour change.
To test them, they were placed into a kiln and fired, without being embedded in metal clay.
For the first firing, the gems were placed into a cold kiln. Ramp rate (speed of temperature increase) was set to full (as fast as the kiln will go), the temperature was set to 1650 degrees Fahrenheit (the hottest you would want to fire silver clay) and the hold was for 2 hours. The kiln was allowed to cool to room temperature before the gems were removed.
Of the six different gems that were fired, only two had changed, although one had changed quite dramatically.
- The White (Clear), the sapphire, the ruby and the pink had no change at all.
- The Violet had lost some its original colour and most of it’s sparkle.
- The most dramatic change was the Emerald. It turned a dark golden brown topaz. 🙁
A second firing at a lower temperature was tried next with the violet and emerald. Again we started with a cold kiln, set the ramp to full, the temperature to 1500 degrees Fahrenheit and the hold to 2 hours. Again we let the kiln cool to room temperature before removing the gems from the kiln.
This time, the violet stone had changed very, very slightly with the colour being not quite as deep as before firing but it still retained some of its vivid sparkle.
The emerald turned colour again becoming more of an olivine brown.
So while all of the stones survive intact, the violet stone will want careful firing at the lowest temperature your clay calls for, or to be set afterwards in a prong or bezel setting. We anticipate that it will lose some of it’s colour.
The emerald, we can’t recommend firing in place if you want to retain any of it’s green colour. This one will need to be set after the piece is fired.