The Fancy Diamond Cut grading system used in Gemology Tools was developed by the National Association of Jewelry Appraisers.

The Fancy Shape Diamond Cut Grading module works the same way as the Round Diamond Cut Grading module. Open the Fancy Cut Grader by selecting the shape from the Cut Grading menu at the top of the program (i.e. Marquise Brilliant, Pear Shape Brilliant etc).

Enter the Length, Width and Depth data in millimeters.

Table: In the Table field you have the option of entering the data in millimeters or percentage of width. Double click in the Table field to toggle between the two options. Example: you have a stone width of 6.4 mm's and a table width of 3.74 mm's (which equals a table of 60%). If entering MM's you would enter 3.74 and the program will automatically convert it to the percentage for you. If entering % you would enter 60.

Crown Angle: Enter the crown angle in degrees. Press F7 when in the crown angle field if you want to run the Crown Angle Calculator. By using the Crown Angle Calculator you can measure the Crown Height in millimeters. The Crown Angle Calculator will do the rest for you.

Girdle Thickness:  There are several ways to enter the girdle thickness information.  If your diamond has a thickness which is relatively the same all the way around the stone you can select the appropriate term (i.e. Medium).

Range: Most diamonds have a range of girdle thickness terms (i.e. Slightly Thin to Thick).  If this is the case select Range from the Girdle Thickness list box. You will be asked to enter narrowest and widest thickness of the girdle.  You also must enter the Overall percentage (this isn’t important unless you want the comparison, but you must enter a number. If don’t want to compare then enter the number 4).  Click OK.

User Defined: If you want to change the default girdle thickness percentage for your term (Medium defaults to 3.2%) you should select User Defined.  When you select User Defined you are asked first for the percentage and then the term.  The girdle percentage is really only important if you want to use the overall depth percentage figured by the program to compare with your depth percentage.  This is great way to verify that the numbers you enter make sense.

Why do we give a default figure of 3.2% for the medium girdle thickness when everyone knows that 1.7% is the ideal thickness for a medium girdle?  The reason is because the part of the girdle used in proportion grading is the WIDEST part of the scallop, whereas when we were taught to estimate girdle thickness by sight we were told to view the narrowest part of the scallop. When you use the Proportion Scope to grade proportions, you put the diamond into the unit with a main bezel facet facing directly toward you.  This gives you a clear view of the crown angle on either side of the diamond's outline. This outline is also of the widest part of the scallop, which is the part of the girdle that contributes to the total depth of the diamond.

Example: Enter this data from the above sample: Length: 10.05, Width: 5.09, Depth: 3.01, Table Size: 64, Crown Angle: 36, Girdle: Thick, Polish and Symmetry: Good. Press F2.



As you can see, the sample diamond returns a NAJA cut grade of 2A.

See Also: Round Diamond Cut Grading

See Also: Crown Angle Calculator