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Adding Gemstones
Some natural stones may be undamaged by PMC firing, particularly at the low temperatures of PMC3, but there is always a risk that they will discolour or crack. Gems composed of laboratory-grown corundum, spinel or CZ, however, are created at very high temperatures and will always survive any of the firing scenarios shown on the two preceding pages.
Please Note: Organic materials such as pearl, opal, bone, shell, wood and most glass objects (see page 14) are not suitable for firing and should not be set into PMC. Important: Never fire a doublet.
To Set a Small Faceted Stone
- Prepare a seat or rim that will provide enough metal to surround the gem. This can be added to a form or built into the original shape.
- Make a conical hole with a pencil point or similar tool.
- Use a straw or similar tool to remove clay from beneath the stone.
- Set the gem in position and press it down until the table is below the surface of the work. Remember that the clay around and under the stone will be contracting and will squeeze the stone upward. To compensate, press the stone deeply into the clay.
- Fire as usual; air cool.
To Set a Flat-Back Stone
- Create a smooth flat area for the stone.
- Roll out a rod then flatten it to make a thick strap. Wrap this loosely around the stone then use PMC paste to join it securely to the base. If necessary, this can be scraped smooth when dry.
- For large stones, make a small cut in the back to allow the PMC to shrink without tearing.
To Set a Heat-Sensitive Stone
- Photocopy the stone enlarged by 12% or 28% (depending on which PMC you are using). Make a bezel around this shape and attach as above.
- Wrap enough tape or polymer clay around the stone to compensate for PMC shrinkage, then press PMC over it to make a bezel. Remove the stone and attach the bezel to your piece as described above.