Gemology Tools uses the Cut Grading system developed by David S. Atlas (and modified by Joseph W. Tenhagen) for the National Association of Jewelry Appraisers.

To use the Round Brilliant cut grading module click the icon with the diamond profile and A+. Tip: Holding the mouse over a Speed Button for a second will bring up a hint in a second (in this case "Round Diamond Cut Grading.")

For the other shapes open the Cut Grading menu and select the desired shape.

Data Entry:

Average Diameter: Enter the average diameter OR enter both the large diameter and the small diameter separated by a comma. New Feature: When grading a round diamond you will always measure for the Large Diameter and the Small Diameter. Rather than having to get out your calculator to figure the Average Diameter we now allow you to enter both numbers separated by a comma. GT will then figure the Average Diameter for you when you press Enter to move to the next field.

Depth in MM's: Enter the depth in millimeters.

Table %: In the Table field you have the option of entering the data in millimeters or percentage of average diameter. Double click in the Table field to toggle between the two options. Example: you have an average diameter 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.

Pavilion Depth %: Enter the pavilion figure as a percentage of the average girdle measurement.

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). See Notes on Girdle Thickness at the bottom of this page.

 
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. See Notes on Girdle Thickness at the bottom of this page.

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.

Polish and Symmetry: Select the polish and symmetry grade from the drop-down list.

Saving a Cut Grade Report: You can save a Cut Grade Report with a customer’s name and address included in it for the print out. After you have entered all the data, click on the Save button, Give the file a unique name.
 
Opening a Cut Grade Report: You can open a previously saved report by clicking the Open button. Highlight the report name and press OK.


Here is something new:



New Feature: When grading a round diamond you will always measure for the Large Diameter and the Small Diameter. Rather than having to get out your calculator to figure the Average Diameter we now allow you to enter both numbers separated by a comma. GT will then figure the Average Diameter for you when you press Enter to move to the next field.





A cut grade example: Enter these numbers into the Round Diamond Cut Grader: Average Diameter: 6.55mm, Depth: 4.01mm,Table Size: 62%, Crown Angle: 34 degrees, Pavilion Depth %: 44, Girdle Thickness: = Slightly Thick and Polish and Symmetry: Good. Press F2.

As you can see in the example below the final cut grade is 2A.

 

What are those numbers on the right side of the screen? Percentages are in the left column and millimeters are in the right column. The program has calculated that a Table of 62% and a crown angle of 34 will give you a Crown Height of 12.82%. This translates into a Crown Height of 0.84 mm (using the sample data). The Girdle Thickness at the Slightly Thick selection is 3.95% unless you selected a User Defined Girdle Thickness. 3.95% of 6.55 mm is equal to 0.26 mm. The Pavilion Depth Percentage is what you entered (44% and 2.88 mm). These values are added and displayed as Estimated Depth (60.77% and 3.98 mm using the sample data). Your Depth Percentage is then subtracted from the Estimated Depth Percentage for difference of 0.46%. The difference in millimeters (0.03 mm) is also displayed. Within a certain margin of error there can only be one set of correct numbers for any given diamond. Because diamonds aren’t cut perfectly, and because we can’t measure them perfectly it will be rare when you’re numbers match up perfectly with the "correct numbers." But you should be within a reasonable tolerance. The program will show a caution if your difference is greater than 5%. Press Enter to go back to the data entry screen if you want to play with the numbers. Try changing the crown angle or the pavilion depth percentage and see what that does to the final comparison. If you had to estimate the total depth because of the mounting, it is very easy to be off by .2 mm. If you are positive about all of your entries except the depth, then the program can help tell you what the depth is.

VIEW:  On the Output Screen you have the option to Print, or View your grading report.  If you select View, you will see the view screen. Here you will be able to Print a straight text copy, Save the report to a file, or Copy the report to the Windows clipboard. If you copy the report to the clipboard and insert it into a word processor, it will appear with the columns in a centered format (they will not line up properly). This is because the report originated in a fixed-pitch font (Courier New). If you select all of the text in the report and change the font to Courier the columns will line up.

PRINTING:  If you want to print a report click the Print button. If you want to add a header to print on every report select File and then Print Header. If you don't want a header but your pages are printing too high (overwriting your existing letterhead) then increase the number in the Blank Lines box of the Print Header menu and click the Clear button.

Notes on Girdle Thickness:   When grading the thickness of the girdle use the standard visual
  method. However, when you are arriving at the girdle thickness

  percentage for approximate contribution to the total depth percentage,
  you measure at the widest part of the scallop (below the crown bezel
  facet. Thus, the percentage is much larger. Typical girdle percentages:

                       Extremely Thin:  1.00%
                       Very Thin:         1.50%
                       Thin:                  2.65%
                       Medium:            3.20%
                       Slightly Thick:    3.95%

                       Thick:                 5.10%
                       Very Thick:        6.50%
                       Extremely Thick: 8.00%

  The reason the wide part of the scallop is used for the percentage is
  because of the orientation of the diamond when proportion grading.
  Look at the profile of the diamond with the outline of the table and
  the bezel facet. The crown height ends at the point of the kite shaped
  bezel facet and the pavilion begins at the top point of the pavilion

  main facet. In between these points is the widest part of the girdle
  thickness. A medium girdle can easily be 3% on a 1 carat diamond.

  Notes:
  If you have a girdle thickness of 3.50% (if you know this, you
  are one of the very few who measure girdles) and you think it is still
  a medium girdle, select User Defined, enter 3.5, press <Enter>, and
  then select Medium. This will give you a medium girdle with a 3.5%
  reading in the Output Screen.

  Most diamond girdles are not a single thickness all the way around the

  stone. To give a split grade on girdle thickness, select "Range" from the
  menu.  Then you can enter two thicknesses. The program will require
  that you enter the overall average girdle thickness as a percentage.
  Example:   Your stone has a Medium to Thick girdle with an average
  percentage of about 4.2%.  Select Medium from the list box on the left,
  then Thick from the list box on the right. You have to enter a number in
  the average thickness box. The number you enter has no effect on the

  grade of the diamond.  The grade is determined by the definitions (i.e.
  Medium). The reason to enter the girdle thickness percentage is so    you can double check your figures. Even though it has no effect on the
  grade you must still enter the percentage. If you don't want to deal with
  it just enter the number 4.

See Also: Print Header

See Also: Fancy Diamond Cut Grading

See Also: Crown Angle Calculator