[Jewelry making - Article 00009] - Re: [Orchid] Opal fakes?

[Peter W . Rowe]

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>    What is the Gilson synthetic opal made from? I thought it was made
>    from Pyrex.

    you may be thinking of something like "Slocum" imitation opal, which
    has no water content in it's makeup and therefor more closely
    resembles a glass. Whether pyrex or not, I can't say. But Gilson is a
    true synthetic.That means it's structure and chemical composition is
    similar to that of natural opal. That means it's a structure made of
    multiple spheres of amorphous silica, with water bound to the small
    gaps between adjacent spheres. Play of color is due to interference
    effects, like what happens with a diffraction grating, caused by the
    multiple layers of evenly sized spheres. Just like natural opal.
    Large scale structural differences, such as the "honeycomb" effect,
    are due more to the growth process and environment differing in
    nature, and no doubt speed, from the natural growth process. But
    silica gel spheres are not pyrex glass, even though there is
    certainly a chemical similarity, as there is with crystaline quartz
    too.

Peter

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