Advice For Grading Dark Colored Gemstones
Faceted dark colored gemstones can have intense colors but little brilliance. A simple formula can help a gemologist estimate a fair value for these gems.
Answer: Grading faceted dark colored gemstones can present some challenges. However, a simple calculation can help you estimate a fair value for these beautiful stones.
How to Grade Dark Colored Gemstones
First, grade each stone based on the visible color as if the whole gem showed that color.
Next, estimate the percentage of the gem that is showing black.
Deduct that percentage from the value of the gem.
This drastically lowers the per-carat value of the gems. However, it's the only way to give a fair value to these stones. This is what I do when I grade dark colored gemstones like the ones you describe for my clients. I've had no negative feedback over this practice.
Hope this helps,
Steve Beitman, GG, Central Coast Gem Lab
International Gem Society
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