Professional Gemologist Certification Course
Modern Diamond Cut Grading Methods
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
Taking some of these measurements will require reticles in conjunction with a microscope or loupe.
| Table size | 1.0% |
| 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% |
| Total depth | 0.1% |
| Girdle size | verbal |
| Culet size | verbal |
If necessary, review calculating percentages and averages.
Evaluating the Cut
Like the traditional systems, modern diamond cut (or make) evaluations have two parts: proportion and finish.
The following information…
Donald Clark, CSM IMG
The late Donald Clark, CSM founded the International Gem Society in 1998. Donald started in the gem and jewelry industry in 1976. He received his formal gemology training from the Gemological Institute of America (GIA) and the American Society of Gemcutters (ASG). The letters “CSM” after his name stood for Certified Supreme Master Gemcutter, a designation of Wykoff’s ASG which has often been referred to as the doctorate of gem cutting. The American Society of Gemcutters only had 54 people reach this level. Along with dozens of articles for leading trade magazines, Donald authored the book “Modern Faceting, the Easy Way.”
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