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Polishing peridot


#1

Hi,

I am a beginning jewelry maker and accidentally took a white (120
grit) 3M bristle brush to a (set) rose cut peridot. OOPS. Is there a
way I can getback the shine? I tried using 50,000 diamond paste and a
felt buff but it didn’t work.

Sincerely, Nanette


#2

I’ve been faceting since 1996 and have done a few repair jobs when
jewelers slipped when setting and when they then tried to fix it,
too. Although peridot can be difficult to polish, that is not the
problem here. The difficulty is that facets can only be polished well
on a flat lap when the facet’s surface is absolutely flat to the lap.
Using a buff might take out a scratch. but it would simultaneously
destroy the flatness of the facet.

If the facet is small, as on your rose cut, you will also destroy
the sharp edges of the facet.

There are a few faceters who might undertake to polish a large table
while the stone is still set. If there are no prongs in the way, a
really good faceter could feel when the table was flat to the lap,
and use a pre-polish lap to remove the scratch and then, using the
same feel, could repolish on a diamond or oxide lap. If you’re very
good at this, the table is repolished and the edges remain sharp or
even become sharper. However, facet meets can change if much material
has to be taken off. If the table is a rectangular step cut, this
isn’t a problem, but on a round brilliant, the star facets are not
going to meet exactly if much material has to be taken off. So a
really good repair means recutting these, too, and that means
removing the stone from the mount and redopping it to get control of
where those facets are placed. Another problem is that the repolish
is likely to be better than the original polish, so for the very
discriminating you either have to polish at less than your best to
match what is there or repolish the whole crown.

Short answer for your rose cut peridot is, send it to one of the
faceters who specialize in this kind of thing and reconcile yourself
to taking it out and then resetting it. One of the best at these
repairs is Anthony Lloyd Rhees at
http://www.ganoksin.com/gnkurl/ep80vl

Tony can re-dop the stone and find the exact settings for each
facet using a mirror and a special grease. Each facet has to be found
separately so it is exacting work, but it is not all that expensive
for what it is. In some cases it might be easier to find a
replacement stone, but IDK about rose cuts in the size you might
need.

Hope this info is helpful.


#3

Thank you Roy. Fortunately, it was not a very expensive stone and a
goodlesson was learned! If I scratch a cabochon in the future, what
product would you recommend I use to shine it back up? I do not have
any lapidary equipment, just a Foredom flex shaft.

Cheers, Nanette


#4
Thank you Roy. Fortunately, it was not a very expensive stone and
a goodlesson was learned! If I scratch a cabochon in the future,
what product would you recommend I use to shine it back up? I do
not have any lapidary equipment, just a Foredom flex shaft. 

One neat little tool I’ve found useful on occasion is a unique type
of mounted rubber wheel. What’s different is that the abrasive in
them is diamond.

Available in a several shapes, and grits of coarse medium and fine
(or something like that), they work wonders at high speeds, on tough
to polish materials, including softer stones. I like being able, for
example, to take a ring with an opal that I may have just for sizing,
and be able to return it with the dull matte surfaced worn opal
shined up again and looking nicer. It doesn’t remove all scratches
like a new properly repolished opal would, but it’s glossy and shiny
enough to be a nice improvement in a few seconds, which I then don’t
need to charge extra for. You can tell these visaully, since that
costly abrasive isn’t through the whole diameter of the wheel.
Instead, what’s mounted on the arbor is a yellow plastic hub, with
the diamond abrasive portion being on the outside of that center
yellow core. These little guys cost between about 8 and 15 dollars
each or so, depending on grit and shape, but last a long time. These
are not as good, of course, as properly recutting or repolishing a
worn or scratched stone on proper lapidary wheels. but for a quick
improvement to minor wear or the like, they’re often useful. If you
really want a proper, like new polish though, you’re usually best off
unmounting the stone and recutting or repolishing it properly, or
sending it to someone with the equiment and know-how to do it for
you. Still, for the situation you describe, these diamond abrasive
wheels might have been good enough to salvage your peridot. I’d
suggest the medium grade (grey abrasive color) to start, then finish
with the pink finest grade. Several suppliers carry these (Rio, Otto
Frei, Stuller, Gesswein, etc), sometimes under different labels (all
the same wheels. various names…)

Peter


#5

Nanette,

Glad your scratch wasn’t a deal breaker. the big three of polishing
are cerium oxide (glass, quartz, opal, other soft stones), alumina,
and 50k diamond. Actually, 14K diamond on cabs works pretty well. A
felt wheel on the foredom and one or the other of these polishes
should work. A little water or oil for lube. The list of what works
with what would be long, but ought to be pretty easy to find
somewhere on the 'Net. Either the felt buff or a little leather buff
ought to be all you need. If a scratch is deep and won’t come off
with a repolish, you might have to prepolish with 600 or 1500 or 3K
diamond grit. Cabochons are not that hard to polish and you could
easily try one thing after the other until something worked. The
polishes that don’t work will not damage the stone.

Hope this is somewhat helpful as a general guide.


#6

Thank You Peter,

I just bought some to have on hand for the next time I have an
’oops’ moment.