[Jewelry making - Article 00229] - Re: [Orchid] Restoring finish to opal

[The Doctor]

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>     Opal's soft so it could be done easily and quickly. 

    Opal can be as hard as 6 1/2 on the Moh's scale, nearly as hard as
    quartz, at 7 on the same scale. So, while not as hard as most gem
    materials, it isn't exactly soft, either. The real problem with opal
    is toughness, another element of gemstone durability. It is prone to
    breaking and chipping, especially on the edges. It can also craze or
    crack for several reasons, not the least of which is heating while
    polishing. People have thought of opal as a soft stone for too long,
    a lack of toughness is why setting opal in rings and bracelets is
    unadvisable. But at least it isn't as soft as soapstone or
    serpentine. 

    As for polishing out the scratches, most of what's been posted
    already is good advice. If it's a solid opal, you can easily polish
    it in place, either with silicon carbide sticks, or by charging
    small cup brushes with diamond compound and working down to finer
    grits. If (or when) the scratches are small enough for final
    polishing, there are many options. Some recommend cerium or tin
    oxides on felt, some recommend the same on leather. Either can be
    done with your rotary tool Foredom). Others have their own "secret
    recipe." One of the best opal polishers in SoFl (incidentally, his
    name is Dr. Huffman) tells me he uses his own blend of Linde A and
    tin oxide on leather. My best polish on opal has always been Holy
    Cow on felt. 

    If you're not comfortable with the process, contact a lapidary. A
    read-through of a mineralogical or gemological book or text can help
    you understand the differences between hardness and toughness, as
    well as those qualities as applied to gem materials such as opal,
    jade serpentine and talc, and the best ways to polish them safely
    and well. 

James in SoFl

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