Step 4: Gem Grading
The Gemological Institute of America (GIA) reporting standards are the most commonly accepted in the industry. In 2005, the GIA introduced a new, modern diamond cut grading method.
What’s The Difference Between Traditional and Modern Diamond Cut Grading Methods?
If you haven’t already, read the lesson on traditional diamond cut grading methods. This will teach you to grade diamonds in the field, away from your lab and reference materials. In addition, the standards for grading diamond finish remain unchanged. (The lesson on traditional methods also discusses economic and practical issues regarding choosing a diamond cut).
Traditional cut grading methods are still exceptionally valuable. However, they aren’t accurate enough for the new standards. Modern diamond cut grading requires measurements to a closer tolerance than you can estimate by sight. Sight estimation is the hallmark of traditional grading.
Measurement Tolerances for Modern Diamond Cut Grading
|Crown angle average||0.5°|
|Pavilion angle average||0.2°|
|Average star length||5.0%|
|Average lower-half length||5.0%|
|Average crown height||0.5%|
|Average pavilion depth||0.5%|