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Old 05-22-2018, 10:51 AM
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Pete VanderLaan Pete VanderLaan is offline
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It is not the same as with other opals. Your phosphate is a phase separation glass: One phosphate glass embedded in a silica glass. On reheat the phases separate leaving a bazillion fine bubbles to reflect light.

A fluorine opal is very different, using fluorine to combine with either alumina or calcium to make crystals that are in the glass. If you didn't have the alumina or the calcium, it wouldn't make the crystals. Those crystals grow, collapse and grow again as the glass winds down its intensity.

If your samples are either breaking up on the saw, or just by themselves, You are likely at least two full points out on the mismatch, perhaps more.
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