World Of Gems Conference 2017 Proceedings Book

WORLD OF GEMS CONFERENCE V - 30 - SEPTEMBER 2017 FANCY CUT DIAMOND GRADES ice’ appearance the following grades: excellent 25%; very good 25%, good 26%, fair 16%, and poor 8%. This even spread of opinions across the grades shows that the crushed ice pattern is strongly tied to personal preference. So, what grade should this crushed ice appearance receive? Pattern preferences have been much more difficult to identify with most fancy shapes. Fortunately we have been able to pinpoint a number of pattern elements that most people dis- like to some degree. This means these negative aspects are not so much taste related, but are common among the trade and public worldwide. WHAT MIGHT BE CONSIDERED FOR A FANCY-SHAPE CUT GRADE While we want the system to be as inclusive as it can be, we felt these common shapes – pear, oval, marquise, heart, cushion, and square and rectangular princess, radiant, and emerald – were a good starting point. They must also meet some basic requirements to be considered for a fancy-shape cut grade. The diamond must be measurable (must have a table) on a standard measuring device (Sarin, Helium, OGI, etc.), and have an outline that is “standard” for that shape. Standard outline means no modifications, such as a pear with flat sides, or a rectangle with rounded corners. And with the ex- ception of heart, the outline cannot have concave areas. Pavilions on the curved shapes must have mains (kite- or di- amond-shaped facets between the girdle and the culet). Pavilions on the straight-sided shapes must have mains, chevrons, or steps. We are excluding mixed (half brilliant/half step) and portrait cutting styles at present. THE BIGGEST CHALLENGE The last stage of development of the round brilliant cut grading system combined the various aspects of appear- ance, design, and craftsmanship into a predictive grading system based primarily on proportion combinations. When we parameterized the round brilliant, we had one facet arrangement to consider, which could be described with 6 parameters. That simple approach applied to a typical range and reasonable spacing of those six parameters required us to create a look-up table containing 38.5 million unique proportion sets. Applying the same concept to just one of several possible oval brilliant facet arrangements requires over 300 million proportion sets to cover the 12 parameters identified. However, there are several common crown facet variations, and pair those variations with 4, 6 or 8 pavilion main arrangements and the number of combinations would be multiplied even more. Such a system would become exponentially more complex and unmanageable when you consider that oval shapes come in a spread of length-to-width ratios, typically from 1.2 to 1.6. For each 0.1 increment, we need another layer of pa- rameters, which increases the numbers we just spoke of by a multiplier of five for each facet arrangement. Pears are even more complex as they may have 4, 5, 6, 7, 8, or 9 mains, and 6, 7, or 8 bezel facets. When we add up all the possibilities for the eight shapes we are considering, we are looking at over 14 billion proportion sets. If printed, that would look like several phone books of look-up tables. You can see how fol- lowing the method of parameterization that we used in the round system isn’t going to be viable for fancy shapes. Thus the greatest challenge in creating a fancy shape cut grading system is the development of tools for predicting fancy cut grades. These tools will not be based on combina- tions of averaged proportions, so they will work differently than the Facetware™ cut grade estimator. SUMMARY Fancy shapes are inherently more complex than rounds. We are tackling eight shapes rather than one as before. Each of