Use this tool to figure the new proportions of a diamond that has to be recut. Select Retain Diameter (lumpy, deep stones), Retain Depth (shallow crowns and/or shallow pavilions), or Retain Neither.

Important Note: You must press Enter after entering the Girdle Thickness field (in the Original column) in order for the diagrams to work properly.

Important Note: You must get the white, dashed outline (Recut outline) to fit entirely inside of, or on top of, the solid blue outline (Original outline). This includes the girdle. If your "Ideal" table percentage of 57% causes your Recut table to be above the Original table you'll have to increase your table percentage or make other changes(see example, below).

Caution: There are many variables that go into the process of re-cutting a diamond.  A diamond cutter may not be able to cut to the exact angles you request or the original estimations may be off a little.  A girdle is almost never exactly even all the way around.  For these and many other reasons you should give a range of estimated weight loss to your customer.  Use the figures produced by this program as an estimate for projected weight loss.

Girdle Thickness: 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.  You should enter the narrowest girdle percentage of widest part of the scallops. For example, if you measured all eight of the widest part of the scallops and they ranged from 4.3% down to 2.9% you should enter 2.9% into the girdle thickness box.

You should never enter a girdle thickness for the Recut diamond that is thicker than the original diamond. If you are trying to retain the original diameter you will have to stay with the original girdle thickness (or try Retain Neither).

Below is a list of approximate girdle thickness percentages as measured at the WIDEST part of the girdle scallop:

Extremely Thin:1.00 %
Very Thin1.50 %
Thin2.65 %
Medium3.20 %
Slightly Thick3.95 %

Thick5.10 %
Very Thick6.50 %
Extremely Thick8.00 %

Enter data in the following format for a demonstration:

Retain Diameter:

Small Diameter:7.15
Weight:1.40
Table Percentage66
Crown Angle39
Pavilion Depth46
Girdle Thickness3


Below is a screen shot of the data entered for the above sample.

 

Press Enter after entering the data for each field.  You must press Enter after entering the Girdle Thickness field in order for the diagrams to work properly.  After entering Girdle Thickness you will see two diamond outlines in the black box on the right.  The blue outline is the Original Diamond outline and the white, dashed outline is the Recut Diamond outline.  As you can see when you enter the above numbers, the Recut Diamond (white) outline does not fit inside the Original Diamond (blue).  This means that we can't have the diamond recut to the suggested figures. We need to change something, so try entering 60 in the Recut Diamond table input box.

 

As you can see, this makes the crown height of the two stones match exactly at .98 mm.  That may be cutting it a little close if the table has to be re-polished but it should work out fine. We now have the Recut outline fitting inside the Original outline (a requirement to get an accurate weight loss figure). Our final weight loss estimate is 7 points (.07 carat).

Change any (or all) of the fields on the Recut side to see what this does to the Recut Outline. Changing any of the fields will naturally change the Estimated Weight Loss.

At the bottom of the screen, in the Result box, you have a direct comparison of the two diamonds in millimeters. Using the above data, you will get a Crown Height of 0.98 mm, a Pavilion Depth of 3.29 mm, and a Girdle Thickness of 0.21 mm, for a Total Depth of 4.49 mm.  The Recut data (based on Table: 60%, Crown Angle: 34.5°, Pavilion Depth: 43%, and Girdle: 3%) shows a Crown Height of 0.98 mm, a Pavilion Depth of 3.07 mm, and a Girdle Thickness of 0.21 mm, for a Total Depth of 4.27 mm. 

Rarely, you will have a diamond that needs recutting with an extremely thick girdle. This is when moving the Recut image is desirable.  Use the Movement Spinners (Up or Down, the Right and Left spinners are disabled) below the black image box.  Clicking the Up spinner once will move the Recut image up slightly. Click until the image is in the most desirable position but keeping the Recut image entirely in (or on) the Original image.

Retain Depth:

The Retain Depth method works the same as the Retain Diameter method except you enter the depth of the stone instead of the diameter.  The program figures the diameter based on the angles and percentages you enter.  The diameter of both stone images is located at the bottom of the Result box (right above Net Weight Loss). The Movement Spinners are disabled in this method.

Retain Neither Depth Nor Diameter:

The Retain Neither method works the same as the Retain Diameter method except you enter the diameter of the Recut stone after entering all the data for the Original stone. The stone images will not appear until you have entered the Recut stone's diameter.  If you need to change data on the Original Stone, make your change and press [Enter] until you pass the Recut stone's diameter. If you had a major chip on the girdle you may have to shift the Recut image to one side (as well as up or down). Use the Movement Spinners below the black image box.

Try entering the data below:

Small Diameter:7.00
Weight:1.34
Table Percentage66
Crown Angle38
Pavilion Depth45
Girdle Thickness5

Since this diamond has a 3% chip on the side, at the girdle, enter 6.78 for the Recut diameter.  This should be enough to allow for the chip.  Press Enter to show the images.  Use the Right Movement Spinner to move the Recut image (white) so the right sides of both girdle images are on top of each other.  You can move the Recut image up and down a little.  Our example shows an estimated weight loss of approximately 0.18 carats. If your customer didn't want to lose this much weight you could lessen the loss by increasing the crown and pavilion angles (but sacrificing "Ideal" proportions).

Note:  If the Total Depth doesn't approximately equal the actual total depth of the original diamond then some of the angles are probably off. A diamond with a 7.00 mm average diameter, a 64% table, a 35 degree crown angle, a 44% pavilion depth, and a 2.5% girdle thickness will always have a total depth very close to 4.14 mm.  Obviously, diamonds are not cut with exact precision and our methods of measuring diamonds are far from perfect. You will often have slight differences in girdle thickness or have some crown angle facets at a slightly different angle than others on the same stone.  All of this affects accuracy so don't expect to be perfect.  We try to keep within a tolerance of 1 to 2 percent.

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.