Researchers at the Gemological Institute published findings from the second of their multi-part scientific study on diamond cut. This study concerns the effect of proportions on "fire" in round brilliants, and was published in the Fall 2001 issue of the Institute’s peer-reviewed journal, Gems and Gemology.
The main conclusion: There is no single "best" set of proportions for a round brilliant that maximizes fire. In other words, there is no one "Ideal" cut.
The researchers also found that the lengths of star- and lower- girdle facets play an important role in improving both fire and brilliance, something ignored in most previous studies on cut.
GIA president William E. Boyajian has said the Institute plans to add more information regarding cut to its diamond grading reports in 2002.
In many ways, GIA is just confirming what the market already knows. And yet the market still pays more for "Ideal" cuts (AGS triple zeros). Again, this is not necessarily because Ideals are measurably more brilliant or fiery, but because many carriage-trade jewelers will only buy Ideal cuts. These jewelers like to have an edge; by selling something different they get a bigger margin. It’s the same logic that’s behind the push for "branding" and for stones with extra-facet. As GIA president William E. Boyajian has said in the past: "The term ‘Ideal’ is confusing … We cannot recommend its use in modern times."