GIA: "OBSERVATIONS OF OVAL-, PEAR-, AND MARQUISE-SHAPED DIAMONDS: IMPLICATIONS FOR FANCY CUT GRADING".

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Date of Publishing: 2024.
No. of Pages: 25.

A cut grading system useful at all levels of the diamond trade must encompass the visual appeal of polished diamonds. This paper presents results from observations of oval-, pear-, and marquise-shaped diamonds for face up appearance and outline appeal. In a controlled environment, an international cross section of diamond buyers, sellers, cutters, and appraisers observed sets of research diamonds in each shape; internal observation 
teams also examined diamonds submitted to GIA for grading services. Observers consistently disliked diamonds with prominent windowing but showed a broader range of opinions regarding the “bow tie” and “crushed ice” patterns typically found in these rounded fancy shapes. The distribution of opinions indicates significant differences in both regional preferences and personal taste for certain outlines and appearance patterns. Virtual facet 
maps, calculated from the three-dimensional wireframe file of a polished diamond, provide a quantitative visualization of these patterns. The geometric complexity of fancy shapes with multiple faceting arrangements requires the use of those same 3D files for assessing or predicting light behavior in a polished diamond.