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About Our Grading
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Color is usually considered the most important element of colored stone grading. But many lighter-hued gems exhibit features like exceptional brilliance, dispersion, dichroism, etc. that make them stand out. We try to take all those factors into consideration. Adjustments are made to the color grade for clarity and cut quality.
IMPORTANT NOTE: Gem grading is a subjective process. Individual perceptions and tastes can result in different grades for the same gem.
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| COLOR GRADING |
Color is the main indicator of value in colored gemstones. The Gemological Institute of America describes color in three variations — Hue, Tone and Saturation.
HUE is the basic impression of color immediately noted by the eye. Gems usually have a dominant hue and a modifying hue.
TONE is the lightness or darkness of a color sensation. The GIA divides tone into 11 steps from colorless or white through increasingly darker grays to black. The GIA uses 7 of these steps in grading tone in transparent colored stones.
2: very light
3: light
4: medium light
5: medium
6: medium dark
7: dark
8: very dark
The generally accepted optimum range with most gemstones is 4—7 where the stone is neither too light nor too dark. Personal tastes may differ of course.
SATURATION is the strength, purity or intensity of the hue. It is described on a 7 level scale (0 through 6)
0: n/a
1: brownish/grayish
2: slightly brownish/grayish
3: very slightly brownish/grayish
4: moderately strong
5: strong
6: vivid
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| CLARITY GRADING |
It is important for colored stone buyers to understand that not all transparent gems form the same way in nature. There are major variations in gemstone clarity by gem type. We grade according to the Gemological Institute of America Type Classification system below. It does not apply to translucent, opaque or cabochon cut gems like fire agate and opal. The value of some gems like demantoid garnet and rutilated quartz is actually increased by the presence of certain inclusions.
TYPE 1: Gems of this type grow in exceptionally clean natural crystals and usually have no eye-visible inclusions. See examples in the table below.
TYPE 2: Minor inclusions are to be expected in stones of this type group and some may be eye visible.
TYPE 3: These gem crystals usually grow in nature with many inclusions. Many are commonly eye-visible in cut stones.
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| GEMOLOGICAL INSTITUTE OF AMERICA CLARITY TYPES |
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Type I
Usually eye clean
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Type II
Usually included
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Type III
Almost always included
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Aquamarine
Chrysoberyl, yellow and green
Heliodor
Morganite
Quartz, smoky
Spodumene, all
Tanzanite
Tourmaline, green
Zircon, blue
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Andalusite
Alexandrite
Corundum, all
Garnet, all
Iolite
Peridot
Quartz, amethyst, citrine, ametrine
Spinel, all
Tourmaline, all but green, red and watermelon
Zircon, all but blue
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Emerald, Red Beryl,
Tourmaline: red and watermelon
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| Our clarity grades follow the general guidelines of the Gemological Institute of America. We classify our transparent stones as: |
1. Eye-clean (EC)
2. Slightly Included (SI)
3. Moderately included (MI)
4. Heavily Included (HI)
5. Severely Included (Inc)
All final colored stone clarity grading is done without magnification, as recommended by the GIA. But all stones are inspected under 10-power magnification and those general findings are usually noted in our descriptions.
There may be some exceptions to the clarity designations above in our initial stone offerings as we are changing from another system. If there are questions please contact us.
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| CUT GRADING |
Cut quality can have a major effect on a stone’s value (see About Gem Cutting).
This is another area where personal tastes can differ a lot. Color is unquestionably the most important element in colored gems but many give almost equal importance to brilliance.
Brilliance is a stone’s ability to return light and its body color back to the eye. Proper proportions are the key to unlocking a gem’s brilliance and improper proportions may result in windowing or extinction.
Windowing is a see-through effect in gems cut too shallow (see About Gem Cutting). Stones with a 50% or more window are color-graded to the lighter center hue of the gem.
Extinction refers to dark areas when the stone is examined face-up. It results from cutting the pavilion too deep or leaving too much pavilion ‘bulge,’ as often happens in stones cut to retain weight.
Nearly all gems exhibit some combination of brilliance (or lack of it), windowing and extinction. An overall cut grade is determined by balancing them and factors below against one another.
Other important considerations in cut-grading faceted gems are overall light-return, symmetry and proportions, whether facet meet-points are accurate (no over or under-cutting); whether crown facets are aligned with pavilion facets; girdle thickness, pavilion bulge, crown height vs. pavilion depth, table size and the finish or quality of polish. |
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