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Precision
Cut Gems
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What is the difference between a gem and a precision faceted gem? And
why is it worth to take care about?
This site will show you what is a high valuable gem with investment
potential.
Everyone knows about the first 3 facts of the 4C´s
Carat, Clarity, Color
& ?
But it´s much harder to take account of the last C = Cut.
There are many ways to make mistakes in faceting a gem but only a very
few
ways to facet a high quality gemstone.
On this site I will show you
the most important facts (not all, I would have to write book about
it...).
Precision Faceting
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(click
on the pics to see at higher resolution)
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Meetpoint Accuracy
Have you been on a fair watching the
stuff of a dealer and been wondering about prices? There are e.g.
Spessartine Garnets, 2cts. good color, eyeclean for $ 10.- per piece
while the next dealer offers the same for 10 times more. Try to cast an
eye at both gems. To facet a high-quality gem takes the experienced
faceter
at least 3 to 4 hours and no one could offer highend-gems at
bargain prices. Most of the cheap gems are faceted in a
cheap way. You will hardly find any meetpoint faceted gemstones at low
prices. The 1st pic shows a Goshenite
4.45cts. with a four-fold pavilion. Every facet in a fold has a
different size and there are no meetpoints but "meetlines"...
On the left there is Fire Opal 4.85cts. with great color and less silk.
I´m sure this gem would have deserved a better work, easy to see
that the faceter has been very fast, although it is faceted for weight,
see the numerous marks.
To facet a gem with highest meetpoint accuracy is a hard and time
consuming job even for designs like in this green Tourmaline from
Namibia with 3.17cts. This design with all its parallel structures
shows every little mistake obviously. The faceter did a good job, the
lines are even and the light-return is high.
High-end "Rose de france"-Amethyst with 9.79cts. in a contrasty
trillion design. The faceter put some high-lights for liveliness in it
and also "dark" reflexes to increase saturation.
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Brilliance
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Polishing
This is a very poor Citrine, 4.82cts.: big
window, many lost meetpoints and a polish that still shows many
scratches. A typical stone that was cut very fast, the faceter
didn´t took any care about quality.
Normally then a gem is polished that way the facets are not even also
the rims are not "sharp" but rounded: This is the ultimate killer for
any brilliance!
Spessartine Garnet 6.62cts. from Africa has better meetpoints and the
facets are more flat. But there are still some facets that are not
completely polished and there are some dots on the table, see marks.
Altogether this one is by far better but quality could have easily been
upgraded to a top gem.
Fire Opal from Brazil, 7.65cts. with little silk and great color. The
surface is mirror-polished for highest lustre and brilliance. There are
some different polishing methods and a discussion about the ultimate
method
sounds always a bit like a religious war... Every gems prefers its own
method and sometimes the same gem from different localities polish
different. I did many tests with combinations of laps,
polishing-powders and speeds and did not found the best
and only for all materials. The Opals take a fast and superglossy
surface with Cerium-Oxide on a plexiglass
with some corrugated structures on it and even the rims are still very
sharp.
Fire Opal from the Juniper Ridge Mine in SE-Oregon, USA with heavy
35.07cts. This pic illustrates that also bigger facets are really
possible to polish very well with the right process.
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Angles & Light
Return
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Windows
A very often default in faceting are
"windows"
In the center of these gems are big dark areas, the corners are like
corona with much better reflexions. The angles of the starfacets in the
center are just too flat, so these are not able to return the light
back through the table to your eye.The pics at the right shows 3
bulleye-gems
(Goshenite 4.45cts., Blue Topaz 33.40cts. & Aquamarine 7.91cts.,
all from Brazil).
Both the Goshenite (left) and the Aquamarine (right) shows very flat
pavilions, the
light from the table "falls" through it like it does in piece of broken
glass.
The Blue Topaz (middle) shows also the reason for the "Ceylon Cut": it
increases
the weight of a gem because of its bulge. But the gem pays this
additional weight a heavy lost of sparkle and liveliness.
Full
reflexions
To
avoid windows it´s absolutely necessary to facet using the right
angles. Every gem/mineral has its specific refraction-index, e.g. beryl
~1.58. This results in the pavilion main-angle of 42°.
The pic left shows a Smoky Quartz (left, 65.00cts. from Brazil) and a
Girasol (right, 33.98cts. from Madagascar).
Due to exact angles they got an intense reflex-pic with many contrasty
sparkles.
The best values in light-reflexion is to obtain when the pavilion has
only one or two folds of facets using the angle the light-refraction
determines, (the Smoky Quartz at the left is two-fold, the Girasol at
the right is one-fold).
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Page
last
updated: Mittwoch, 23 Mai, 2018 20:55 MEZ
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