Summer 2009

Unconventional Diamond Cuts

In March, the New York lab received a number of diamonds with unusual and unconventional facet distributions. They ranged in shape from round and cushion to pear and rectangular, but all had one feature in common: a fully faceted dome-shaped crown, with either no table at all or only a tiny “culet”-style facet in the center of the crown (figure 1). We were surprised to see these experimental cuts being applied to fairly large diamonds, most of them between 2 and 7 ct, as well as to diamonds of different colors.

Diamond cuts that lack a table facet invariably pose challenges for calculating overall dimensions and crown and pavilion angles, since typically the table serves as the basic reference plane against which these angles are measured. The cut description (shape and cutting style) also becomes more difficult, because none of the standard terms in the GIA lexicon fully explain these designs.

We were pleasantly surprised, however, to see that a number of the stones showed a balanced contrast pattern, which is very unusual for nontraditional diamond cuts (and even for the standard fancy cuts). When we compared one of the round shapes with a round brilliant cut (graded by GIA as “Excellent”) of the same diameter, the latter appeared darker overall, with a less subtle contrast pattern. We have not analyzed the light path by ray tracing, but we believe that the fragmented specular reflection or glare of the additional crown facets, in combination with an efficient light-path migration inside the diamond, results in this brighter and more sparkly look.

We contacted the client and learned that this new cut has been patented and will be marketed as “Antwerp Twins.” The name was chosen to reflect the cut’s city of origin and the fact that these diamonds have two “dome-faceted” sides (crown and pavilion), as shown in figure 2. 

While unconventional cuts can be challenging to measure, classify, and grade, we appreciate the opportunity to view the results of this type of innovation.

Ronnie Geurts