Jan
07 PMC Gems

The use of gemstones in Precious Metal Clay (PMC) is a great way to add some instant colour and sparkle. The best type of clay to use when setting any gemstone is PMC3 as it shrinks only about 10 per cent giving the clay plenty of space to shrink around the stone.

Lab grown gems

Until now most of the stones fired with PMC, have been lab grown gems such as cubic zirconias, synthetic spinels and Corrundums. They are a great way to practise gem stone setting as they are inexpensive and come in a wide range of colours and shapes.

Lab grown gems can also be torch or kiln fired. Although all lab grown gems from The PMC Studio are guaranteed to withstand torch or kiln firing up to 800C, it is best to fire test gems bought elsewhere. In this case you should test your stones by heating them without PMC. The general theory being that if a stone withstands being heated once, it is likely to withstand it a second time. The same applies to natural stones.

Natural gemstones

Only natural stones that can withstand a constant heat of 600C for 45 minutes can safely be fired with PMC3. If a stone does not tolerate the heat it will change colour, crack or explode in the kiln.

As PMC is such a new medium, not much scientific testing has been done using natural stones. The same gemstones from different mines and different suppliers will have different results. Results to date also indicate that success is not always based on the hardness or colour of the stone.

Currently the most commonly used natural stones are: peridot, diamonds, moonstone, pyrope garnet, sunstone and blue sapphires. These have managed to be fired without too much colour change.

Fairly new is the use of Sunstone. This unusual stone from Oregon in the US has performed very well in the pieces I have made so far. I have used them with PMC3 paste, syringe and lump clay and fired and polished them several times without any detriment to the stone. Although these stones are a little bit more expensive than the lab grown gems, I like them simply because they are so unusual and add some warmth to the colour of the silver. They are also available in a range of cuts from simple cabouchons to the higher quality, facetted stones, so you can choose to match the type and design of your piece.

Finally, the best thing to do when considering natural stones is to simply give them a try - provided you don’t mind losing a few! It’s great fun ….