World Of Gems Conference 2017 Proceedings Book

WORLD OF GEMS CONFERENCE V - 29 - SEPTEMBER 2017 INTRODUCTION T he challenges of building a fancy cut grading system are most clear in the context of GIA’s current system for round brilliants. Our cut grading system for rounds involved several areas of research. It began with extensive computer modeling to understand the impact of proportions on brightness and fire in a 57- or 58-facet round brilliant dia- mond. As we conducted visual observations of real diamonds in standardized light settings and solicited feedback from the trade and public, preferences for certain other aspects, such as the amount of fire and specific contrast pattern, became clearer. We also discovered how symmetry and the effect of cutting techniques called painting and digging affected the face-up appearance. CHALLENGES A fancy shape is defined as an outline other than round. That shape can be curved like an oval, cushion, pear, marquise, and heart; or straight-sided like a princess, radiant, and emer- ald. We have looked at over 16,000 fancy-shape diamonds, building a database of observations and detailed parameters of each one. We conducted observations of fancy-shape diamonds and performed a number of surveys in Tucson, Hong Kong, Tel Aviv, Antwerp, Mumbai, and NewYork City, meeting with cut- ters, brokers, gemologists, appraisers, and a variety of those in the retail portion of the trade. Those observations helped us rank sets of diamonds of various shapes and also revealed information as to why certain patterns were preferred over others. The surveys used images of real diamonds and other repre- sentations of diamonds to determine: symmetry issues, pref- erences for length-to-width ratios, how weight ratio affects perception of the quality of cutting, and girdle thickness is- sues, including protection of points and corners.We also sur- veyed how bowties affected the perception of the quality of cutting in the face-up appearance of a diamond. A major challenge we faced from the start of this project was capturing adequate measurements from fancies. Technology has advanced enough over the last few years that our ability to capture the right kinds of accurate measure- ments from fancies is now quite good. Because a diamond is measured as a shadow profile, any concave area, such as the cleft of a heart, cannot be measured in this fashion. Crit- ical features for the heart outline were missing because of this measuring limitation: the curve and symmetry of the lobes; the depth and symmetry of the cleft; the angularity of the cleft; and the orientation of girdle facets relative to the table. These deficiencies are now captured by an additional face-up measurement. A design aspect, called Weight Ratio, is used to assess hid- den weight in the GIA round brilliant cut grading system. Ex- cess weight is typically added by making the girdle unnecessarily thick, crown or pavilion angles steeper, or adding extra rows of facets near the girdle (resulting in a deep pavilion or thick crown). A new challenge we face is that cer- tain fancy-shape designs require a girdle to be extremely thick in some areas, or pavilion angles to be steeper, which tend to add additional weight. How do we allow for these particu- lar design considerations that are necessary to yield greater beauty, while penalizing others that are simply “hiding weight” that doesn’t contribute in a positive way? Something as fundamental as the shape outline has proven challenging because taste or personal preference can play a role. For instance, as the shoulders become more pro- nounced on an oval, at some point it is no longer oval, but cushion. When we surveyed the trade, not everyone agreed on where the border between the two shapes should lie. Length-to-width ratios for various shapes are also strongly linked to taste because our surveys showed a broad distribu- tion of preferences. Also, different regional markets showed diverging preferences for particular length to width ranges. We didn’t have these issues with rounds. Another challenge we face is how to distinguish between personal taste and more universal negative appearance as- pects. Observers from different countries and different parts of the trade typically gave an oval diamond with a ‘crushed CHALLENGES OF BUILDING A FANCY SHAPE CUT GRADING SYSTEM Al Gilbertson, GIA GG, CG (AGS) FANCY SHAPE ABSTRACT