| A review of the “foundation” of GIA’s new cut grade system |
| by Garry Holloway |
Published
30/11/2004
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Diamond Grading
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GIA Category 2
| RD16 HCA 0.7 | RD07 HCA 4.8 | RD03 HCA 2.4 | 
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| Ideal-Scope Lighting | Ideal-Scope Lighting | Ideal-Scope Lighting | | | | 
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| Jewellery Shop Lighting | Jewellery Shop Lighting | Jewellery Shop Lighting | | | | 
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| Disco Lighting | Disco Lighting | Disco Lighting | | | | 
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| GIA photo 0.82ct | GIA photo 0.76ct | GIA photo 0.55 | | | | DiamCalc Scores | Improved | DiamCalc Scores | DiamCalc Scores | Light Return Mono | | 0.98 | 1.00 | Light Return Mono | | 0.82 | | Light Return Mono | | 0.97 | | Light Return Stereo | | 0.94 | 0.98 | Light Return Stereo | | 0.89 | | Light Return Stereo | | 0.97 | | Contrast | | 0.91 | 1.03 | Contrast | | 1.25 | | Contrast | | 0.90 | | Specifications | Specifications | Specifications | Table Size | 53% 54 | 53% | Table Size | | 53% | Table Size | | 63% | Crown Angle | 33.5° 33.8 | 33.5° | Crown Angle | | 36.5° 36.4 | Crown Angle | | 32.0° | Pavilion Angle | 40.6° 40.4 | 40.6° | Pavilion Angle | | 41.4° 41.5 | Pavilion Angle | | 41.0° 40.9 | Star Length | 50% 51.9 | 50% | Star Length | | 55% 59.4 | Star Length | | 60% | Lower Girdle | 75% 76 | 85% | Lower Girdle | | 90% 89 | Lower Girdle | | 80% | Girdle Thickness | Thin-Med 3.3 | 3.3 | Girdle Thickness | | Thin-Med 3.1 | Girdle Thickness | | Med-Stk 3.7 | Culet Size | VSM | | Culet Size | | None | Culet Size | | None | Total Depth | 61.2% | | Total Depth | | 64.1% | Total Depth | | 58.6% | Polish | G | | Polish | | VG | Polish | | G | Symmetry | VG | | Symmetry | | VG | Symmetry | | G | COMMENTS: A pattern has developed; the second stone in grades 1 to 4 appear to be the worst | This stone was downgraded because of ‘Good’ polish. GIA claimed combined proportions make the pavilion mains look very dark; with a small table the lengthening the LG’s (to 85%) makes a diamond with these proportions perform very well. | An interesting stone. Very high contrast and scintillation contribute to many small firey flashes; some are only visible because light return is poor. A contentious choice; if it were the same diameter as most of the smaller samples, would it have been selected? (See discussion) | The large table lets this stone down. Diamonds with large tables benefit from shorter LG’s, which add a little more contrast. ‘Good’ polish & symmetry also lower this stones grade. The table and upper girdle facets were said to be dark; this is not evident in the photo in G&G Fire, page 194 |
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