Got rocks...

Most of the coloured gemstones, especially those below 7 on the Mohs Scale, cannot withstand the temperature needed to fire PMC Silver or PMC Gold. The inclusions in most natural stones have a different rate of expansion than the surrounding material. When you heat these stones, the different rates of expansion can result in cracks or splitting of the stone.

Traditional gemstones, however, are not the only material which you can include with PMC+. After completing our initial testing of gemstones for use of PMC+, we turned our attention to other stones: river rocks, driveway stones etc. Many of these are ignacious rocks such as granite. Surprisingly. when fired they not only withstand the heat, thay also can turn colours.

So start collecting interesting rocks and place them in your kiln.
Fire at 1650F for 10 minutes, using a slow ramp up to the maximum temperature and a slow cool down period.

NOTE:
Natural stones frequently change colour as a result of firing.