Fancy cut – any shape other than a round brilliant; Asscher, Emerald, Heart, Oval, Pear, Marquise, Princess, Radiant
When grading fancy cut diamonds often times the overall look of the stone is more important than all the proportion details you would look for in a round brilliant. Color and symmetry are still very important, but your eye and personal taste will ultimately determine if the diamond is beautiful. For fancy cuts, there is no worldwide consensus about beauty.
There are three main cutting styles (the arrangement of the diamond’s facets) for
Fancy cuts; brilliant cut, step cut, and mixed cut. The most popular cutting style is the brilliant cut.
Brilliant cut – a cutting style where triangular and kite shaped facets start at the diamond’s center and go outwards towards the girdle (example – Oval shape diamond)
Step cut – a cutting style with long, narrow, four sided facets cut in rows parallel to the girdle on both the crown and pavilion (example – Emerald shape diamond)
Mixed cut – a cutting style that combines the step cut and brilliant cut (example – Princess shape diamond)
Table, Crown, and Girdle
For fancy cuts, graders measure the table width and stone width then calculate table percentage. Brilliant fancy cuts are measured from the belly (slight curving center of the long side of a Pear, Heart, Oval, and Marquise) bezel facets. Step cuts are measured in the middle of the stone because the facets are not always parallel and this measurement provides consistent results.
The following formula is used to calculate table percentage: Table width divided by stone width x 100 = table percentage rounded to the nearest one percent. Large tables are common for fancy shape diamonds.
Crown angles are estimated for fancy cuts diamonds. To obtain the estimate, graders look along the length of the stone’s profile. For brilliants, graders examine the bezel facets at the belly and for step cuts, graders examine the profile of the middle row of facets.
Unlike round brilliant cut diamonds where a numerical value is applied to the crown angle, a fancy cut diamond’s crown angle is listed as acceptable, slightly shallow, very shallow, slightly steep, and very steep.
Girdle thickness for fancy cut diamonds is evaluated in the same manner as it is for round brilliants however, allowances must be made. For example, when evaluating girdle thickness for a heart shape diamond the cleft and point will have a thicker girdle than the rest of the stone because of the shape.
To evaluate pavilion depth, graders consider three main factors; face-up appearance, total depth percentage, and the relationship between crown height to pavilion depth. To determine a final assessment of the diamond, graders consider all of these things individually then together.
First, graders look at the stone face up to determine the stone’s brilliance. The appearance will determine if the pavilion is steep or shallow. If the stone looks glassy or if the girdle’s reflection can be seen at the sides of the table the pavilion is most likely shallow and if the stone looks dark the pavilion is most likely steep.
After evaluating face up appearance, graders consider the total depth percentage. This is the diamond’s depth from the table to the culet and is expressed as a percentage of the width.
The following formula is used to determine total depth percentage: Stone depth divided by stone width x 100 = total depth percentage
The normal range for total depth percentage is 55% to 65%. If the total depth percentage falls outside the range graders will begin to evaluate other proportions. If the stone is deep, graders will look for a high crown, thick girdle, or deep pavilion. If the stone is shallow, graders will look for a thin crown, thin girdle, or shallow pavilion. Note – even if the diamond has a total depth percentage within the normal range it is still important to examine each component of the diamond.
To evaluate pavilion depth, graders look at the profile of the diamond and compare the crown height to the pavilion depth. A well-proportioned diamond’s pavilion should be approximately 2.5 to 4.5 times the depth of the crown.
Bow-Tie and Pavilion Bulge
The final step in evaluating the pavilion is the bow–tie effect and pavilion bulge. The bow-tie effect is a dark area across the center of an elongated brilliant cut. When viewing the diamond face up the bow-tie will be visible in all stones however, this should be faint and not dark. Pavilion bulge is the outward curve of the pavilion facets on a step cut diamond. Cutters will sometimes cut the top row of pavilion facets wide and at a steep angle. This creates a bulge and increases weight, which in turn causes light leakage and can make the stone difficult to set.
Culet size is graded in the same manner for fancy cuts as it is for round brilliants. In fancy cuts the culet is sometimes elongated so the grader will only consider the culet’s width as a factor in its size.
Shape Appeal (“Eye-pleasing”)
Shape appeal is not the same as symmetry. Shape appeal is what shape is pleasing to your individual eye.
When determining symmetry all of the diamonds parts are compared to its whole. Symmetry = balance. To have good symmetry a diamond’s parallel parts should be the same size and shape from the face up and profile view. (Example – both lobes on a heart shape diamond should be the same size and shape)
Length to Width Ratio
Length to width ratio is a characteristic of fancy cuts and is an aspect of shape appeal. Length to width ratio is the relationship between the length and width of the diamond. Certain ratios are more “eye pleasing” than others. To calculate the ratio you will need the length and width of the stone. Once those numbers are determined, you divide length by the width and round to the nearest hundredth. That becomes the first number in the ratio with the width always being one.
The formula for length to width ratio is as follows: Stone length divided by the stone width
Example: Using an Oval with a length of 9.00mm and a width of 6.00mm
9.00mm divided by 6.00mm = 1.50
The length to width ratio is 1.50:1