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Estimating Pavilion Angle
Many labs use pavilion depth percentage instead of pavilion angle. The correlation between them is important to understand.
The pavilion angles are very inconsistent. The culet is centered due to a balancing act with an inconsistent girdle. This would make for very poor symmetry.
An off-center culet due to inconsistent pavilion angles or inconsistent pavilion depth. Inconsistent depth could be seen from the side profile of the tilted girdle plane.
Off center culet.
The ideal pavilion angle of 40.75 ° corresponds to a pavilion depth percentage of approximately 43%. Again this is important to bear in mind for understanding ideal depths and for communicating these facts to other dealers or to retail clientele. In the figure below, note the relationship of flatter and steeper angles to the corresponding depth percentages.
In addition to correct pavilion angles, consistent pavilion angles are also important to achieve proper symmetry in the finished diamond. You will often see diamonds with off-center culets. This is caused by the cutter's choice in leaving the pavilion angles inconsistent. For example, one side is 39.5 ° and its opposite is 42.5 ° allowing the culet to favor the higher angled side.
An off-center culet may also be caused by inconsistent depths of the pavilion main facets. This is obvious when viewing the girdle plane, which should run parallel to the table.
