Diamonds Education: SGTL Cut Grades
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.
Learn more about SGTL and the AUSCERT Diamond Certificate
