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Question on polishing opal doublet/triplet's surface


#1

Hello Orchidians, Quick Question: how can scratches on the surface
of an opal doublet/triplet be removed? I haven’t had the problem,
but wondered if there is any remedy should a nick or scratch be made
on the clear cover over the opal. I’m not a lapidary and don’t know
the first thing about polishing stones. Thanks to Hanuman for all
the time and effort put into Orchid. Looking forward to some ideas
here. Judy in Kansas

Judy M. Willingham, R.S.
Biological and Agricultural Engineering
237 Seaton Hall
Kansas State University
Manhattan KS 66506
(785) 532-2936


#2

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


#3

Hi Judy, What I do in a case like that is to unset the stone (if
necessary) then “file” out the scratches by hand using 1,500 or 2,000
grit wet-or-dry silicon carbide paper glued onto something like a
popsicle stick. Do this wet, and make rocking motions and alter the
direction of the strokes so you don’t file a flat spot on the stone.
Usually the scratches on a worn stone are shallow enough that this is
all it takes to get them out.

Then re-polish using any standard lapidary polish such as cerium
oxide on a leather disc. You’re not going to build up much heat by
hand sanding as described; doing this wet simply helps flush away
debris and keeps the sanding paper from clogging up. But you should
certainly be careful of heat buildup in polishing, as this may detach
the glue. So be sure to polish wet.

My favorite stone polish is actually grease-based 50,000 diamond on
a hard felt wheel but that does build up significant heat, so I
wouldn’t use this on a doublet.

Hope that helps,
Hans Durstling
Moncton, Canada