Scientific Gem Testing Laboratories (SGTL) started business in 1980 as an independent organization in Australia. They developed the AUSCERT Diamond Certificate as their grading report. SGTL acts as an independent third party to help diamond shoppers verify the quality of the diamond they are purchasing.
SGTL notes that the cut or “make” of the diamond displays the art of the diamond cutter’s skill and workmanship. It allows the hidden brilliance, sparkle and fire of the diamond to escape. A poorly cut diamond will look lifeless, dead and worst of all, glass-like. Secondly, the Make is an exact science, conforming to strict angles and proportion calculations.
The cut of the diamond is the only property that is very dependent on human intervention. Thus, it is also prone to human error and the desire to retain as much stone weight as possible from the diamond’s original rough state. This boosts profit margins.
The following table shows the cut grade parameters for round diamonds used by SGTL and the AUSCERT Diamond Certificate.
SGTL Cut Grade Parameters
| Lab | Scientific Gem Testing Laboratories(SGTL) | ||||
| Cut > | Ideal | Excellent | Very Good | Good | |
| Table width % | 53 - 57.5 | 52.4 - 60.5 | 52.4 - 62.4 | 50.5 - 64.8 | |
| Crown Height % | Not Addressed | Not Addressed | Not Addressed | Not Addressed | |
| Crown Angle % | 33.8 - 35.3 | 32.7 - 35.8 | 32.2 - 36.4 | 31.2 - 37.8 | |
| Pavilion Depth % | 40.2 - 43.5 | 42.3 - 43.8 | 41.7 - 44.7 | 41.1 - 45.5 | |
| Pavilion Angle | 40.2 - 41.0 | 40.2 - 41.2 | 39.8 - 41.8 | 39.4 - 42.3 | |
| Girdle Thickness | Thin to Sl. Thick |
Thin to Sl. Thick |
Thin to Thick |
Thin to Very Thick |
|
| Total Depth% | Not Addressed | Not Addressed | Not Addressed | Not Addressed | |
| Culet size % | Pointed to Medium | Pointed to Sl. Large | Pointed to Sl. Large | Pointed to Very Large | |
Compared to the cut grate parameters of other grading laboratories, the SGTL appears to be relatively strict and provide valuable tool for Australian diamond buyers.