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Precision Cut Gems


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

 





(click on the pics to see at higher resolution)


 
 
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.
 
Bad Meetpoint 1
Bad Meetpoint 2
Good Meetpoint 1
Good Meetpoint 2
 






 
Brilliance
 








 
 
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.
 
Bad Polishing 1
Bad Polishing 2
Good Polishing 1
Good Polishing 2
 







Angles & Light Return
 








 
 
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).



 
Windows in Gemstones
Windows in Gemstones
Gemstones with no Window
Gemstones with no Window







 








Page last updated:  Friday, July 09, 2010 11:23:06 PDT