Kevin and his associates at Rio Grande conducted numerous tests on a wide range of gems to determine their tolerance to PMC firing temperatures. He emphasized that each gem is a unique object with individual properties, so in the end every time you set a stone it is an experiment. It helps, however, to have some guidelines, and these are available on the attached sheet.
At the conference Kevin showed over a hundred photos of gems, a few of which are included here. The test consisted of firing gems taken directly from Rio Grande's stock in a conventional PMC kiln at a time and temperature recommended for PMC3. Each stone was photographed before and after the firing, but bear in mind that lighting and other photographic influences can be deceiving when viewing the results.
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