Some older members of the diamond industry share a strange fallacy that if a diamond has proportions of 60% depth and 60% table, then it will be beautiful. It’s a great idea, but it does not always work.
These two extreme examples have bad proportion combinations. Both are 60:60, both are ugly diamonds.
The pavilion angles on these two stones are 36 degrees and 45 degrees. This range actually exists. Of all of the diamonds within this range of pavilion angles, only those between 40.2 and 41.2 degrees are likely to be worthy of consideration.
Girdle thickness is another variable – a very thin girdled stone can end up with too steep / deep in crown and pavilion angles and the opposite can be true if the girdle is too thick.
GIA is the largest most prolific lab and there are 40 crown and pavilion angle combinations for 60% table sized diamonds that receive its top cut grade of Excellent (although Pricescope addicts would only recommend about 20 of these). AGS list 26 angle combinations that potentially should achieve AGS 0 or Ideal (compared with 32 for a 56% table size).
These virtual diamond images were simulated using DiamCalc for the diamonds with 60:60 table:depth ratio and thin girdle but different pavilion angles.