[Jewelry making - Article 00302] - Re: [Orchid] Repairing a ring of stones

[Bruce Holmgrain]

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>         According to my GIA gem ref. guide Star sapphire shouldn't be
>     heated above 1600C and rapidly cooled as it may change the color
>     permanently. 

    Mike, you might also point out that 1600C is over 2900F. That is a
    bright white heat. 

    Also, you might note that a corundum that cracks under heat was
    likely a completely untreated stone. The GIA asserts that over 90%
    of the corundum that is on the market has at least been heat
    treated. Untreated stones are a little/lot more valuable that the
    treated ones. 

    Lastly, my own experience with synthetic stars is that they will
    accept more abuse that any other. That includes heat and physical
    shock. Quenching is still a no-no as they don't conduct heat well
    enough to contract at a uniform enough rate.

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