|Color is usually considered the most important element of colored stone grading. But many lighter-toned and less saturated gems exhibit 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.
Note that the primary color is capitalized. Modifying colors and some other descriptive terms are lower case.
TONE is the term used to describe a gem's lightness or darkness. GIA uses 2 through 8 only because tones that are any lighter or darker are almost impossible for the human eye to detect.
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.
|GEMOLOGICAL INSTITUTE OF AMERICA CLARITY TYPES|
|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.
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.