[Jewelry making - Article 00173] - Re: [Orchid] Question on polishing opal doublet/triplet's surface

[Don Rogers]

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    Judy, assembled opal, either doublets or triples present some unique
    problems for re-polishing, but with care, it can be successfully
    accomplished.  The venerable part is the adhesive seam between the
    opal and the backing, and in the case of triplets, also between the
    opal and quartz cap.  If either of these seams have started to
    deteriorate, evident by discoloring or fogging along the edge, there
    is little you can do to salvage the stone.  If the seam is intact,
    your task is to not cause any damage to the seam while doing the
    re-sanding and polishing.  Heat used to wax dop the stone can cause
    problems, but the wax doping is the preferred method.  Using and
    epoxy to dop the stone present the problem of not being able to
    dissolve the epoxy without damaging the seam.  Besides the heat and
    solvent issues with the seam, the polish media itself can cause
    problems, especially Cerium Oxide.  It can pack into unseen cracks
    in the seam and will discolor the stone. The only way to remove it
    is to grind it out. 

    As the surface of a doublet is different from a triplet, the polish
    techniques will be a slightly different.  The doublet, having an
    opal surface should be sanded out to 1200 or finer.  For triplets
    with a quartz cap, a well worn 600 sanding is OK.  For a re-polish,
    I usually do this by hand, using a well worn sanding belt with a
    stiff backing.  Cup a piece of this belt in the palm of on hand and
    then using  the dop, stroke the opal back and forth. Make sure you
    have a wet sanding surface during this step.  Once you have all of
    the scratches removed, and an even 1200 finish on the stone, you can
    then polish it on a leather pad with Linde-A or a similar alumna
    polish which will be less likely to pack into cracks.  This can be
    done on either a machine, or by hand, but the hand process will be
    much slower.  I prefer to use a leather pad, Elk hide is preferred,
    on a 6" wheel spinning no faster than 1725rpm.  With the pad
    thoroughly wet, then apply a little Linde a and then  while
    spinning, mist the pad with some water and then work the stone,
    applying moderate pressure, in spurts of one or two seconds.  You
    should be able to polish out a well sanded stone in about 30 seconds
    using this method.  The short spurts of polishing are so there is
    not heat buildup on the stone. 

    The key to a successful re-polish of any stone is to completely sand
    out the scratches without changing the shape or size of the stone. 

Don Rogers
Campbell Gemstones

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