Hello all, I have been an enthusiastic lurker for far to long, time
to join the fun!
I have a many-pointed star shaped facetted citrine with significant
chips on the cullet and one of the points. The facetting is
concave, and I have been advised that not all cutters will repair
concave facetting… Can anyone offer me guidance, or perhaps a
referral? Thanks!
Ann
Ann B. Cahoon
Flying Marquis Studio
@Flying_Marquis_Studi
Ann,
Concave cutting is done with a special attachment to cut the curved
facets. Most faceters do not cut concave stones. We can recut the
stone for you if you are interested, but I would need to see the
stone to give an estimate. If you are interested contact me directly
and we can discuss details.
Mark
www.upstategems.com
custom cut designer cabs/concave facetted gems
I know of one fellow who an absolute ‘maven’ stone cutter! His name
is Martin Rugroden, in Maple Grove, MN send him my best regards 763 -
416 - 4385 a.k.a. Precision Facetting, he is better than “great”
…Gerry, de Setter!
Hi Ann,
This sounds like one of the snowflake cuts from Wobito Gems. You
might send them an inquiry to see if it’s their cut – I don’t know
of anyone else doing anything remotely similar. They’d be the best
people to do a repair or replacement. Their URL is www.wobito.com
I’ve always considered this cut a bit on the fragile side and quite a
challenge for creative designers.
If this approach doesn’t yield results let me know and I may be able
to recommend other options.
Hope this helps.
Rick Martin
MARTIN DESIGNS
Thanks to all who have responded for the feedback- it’s been very
helpful! Rick- my stone is not actually one of the Wobito cuts, but
it was very interesting to see their work and the gallery of
finished pieces (cleared some cobwebs in terms of ideas for setting
the little monster).
This leads me to a second, related question for those of you in the
know about these things- WHY concave facets? They are certainly
lovely, but what specifically and technically do they achieve over
standard facets? Thanks in advance for the education!
Ann
Ann, Concave facets change the optics of the gemstone. When light
hits a flat facet it is reflected back in a single ray. But, when
light hits a concave facet, it does not all hit at the same time,
therefore the light is reflected back in an arch. This causes some
really unusual and often beautiful effects.
I have a concave trillion citrine that was highly color zoned in the
rough. I usually do not facet this material because the color
zoning almost always shows in the finished gem. But when cut with
concave facets it mixes the different color zones and gives the stone
a beautiful look. There is a photo of the stone at this link:
http://www.upstategems.com/new.html
Also, with material that are highly dichroic (the stone will look
two different colors depending on which direction you look at it),
you do not have to worry quite as much about trying to eliminate one
of the colors (as long as both colors are attractive. I have a 15
carat pink tourmaline that has two distinctly different pink colors
for its dichroism. The finished stone looks like there are hundreds
of different color bands. Poor picture but you can see it here:
http://www.upstategems.com/concave.html
I hope that this is helpful.
Mark
Hello Ann, It has been long known that a curved facet would magnify
the optics inside gemstones releasing a bounty of color and
brilliance. This type of cutting began long ago with carvers and
also faceters mounting spheres on the arbor spindle to make the
table into a lens or place dimples in the stone. In the late 1980’s
my father the late Doug Hoffman invented, developed and patented the
OMF concave faceting apparatus. OMF stand for “Optical Magnified
Facet” and is a separate base that rotates and reciprocates a
cylinder cutting lap (mandrel) that allows the faceter to place
precision repeatable concave facets about the indexing of the
gemstone. Here is a link to a somewhat recent article by Colored
Stone Magazine that tells more about it.
http://www.tucsonshowguide.com/stories/cuts.cfm Here is a link
showing OMF cut stones by artist Richard Homer set in jewelry and
comparisons of native cut stones that Richard recut.
I have many more links if you are interested.
Thanks 
Zane Hoffman