What turns a princess cut diamond into an ideal princess cut diamond?

This is the third in a series of articles that we have posted to Diamondtalk discussing the characteristics and light performance of the four-pointed Princess Cut Diamonds.

The first two threads can be found here:

http://www.diamondtalk.com/forums/s...ead.php?t=55424

http://www.diamondtalk.com/forums/s...ead.php?t=55680

In contrast to the research, knowledge, and information accrued on the round brilliant diamond shape, begun with the seminal work of Towlkowsky back in the early 1900's and further developed and expanded upon over the past several years,little is currently known about what factors are important in maximizing light performance in the 4-pointed Princess Cut.

Internet (www.bluenile.com et.al) and various brick and mortar jewelers are marketing their "Signature" Princess Cut Diamonds by stressing the importance of Crown Height percentage, Table and Depth percentage, and the level of Polish and Symmetry.

Their advocacy stresses that Crown height percentages should be in the range of 8-13%, Table and Depth percentages in the ranges of 65-74%, and Polish/Symmetry to be in the range of Very Good/Excellent.

Much of this approach to defining the "Ideal" Princess Cut is based on the extrapolations of "numbers" that have been shown by Towlkowsky to be suitable for the round "Ideal" Cut, the introduction of the "American Ideal" 60/60 Table-Depth percentage round in the late 50's-early 60's, and the more recent GemAppraisers (www.gemappraisers.com) chart for Princess Cuts that defines Cut quality along a "numbers" continuum that ranges from 1A (Excellent) to 4B (Poor).

On the other hand, our examination of a large number of Princess Cuts as well as our own Cut research over the past three years in the development of our SuperbCert Signature Princess Cut Diamonds has shown that these aforementioned "numbers" are useful only to a limited degree and are not sufficiently accurate and consistent to predict a high level of superior light performance in 4-point Princess Cuts.

Light entry and exit in this fancy shape diamond differs significantly from that of the round brilliant.

A diamond's light performance is the key element and in our opinion should be a determining factor in the consumer's purchasing decision.

To this end, in our cutting research we haved used the Brilliancescope Light Performance Analyzer, a spectrophotometer that is manufactured by Gemex Systems (www.gemex.com). Briefly, the diamond is illuminated in a carefully controlled light environment and the machine precisely measures the light reflected back through the diamond's crown at six different angles from the light source.Results are transmitted to Gemex via the Internet where it is processed into a Light Analysis report. Thousands of diamonds were evaluated to determine the range of Light Performance achievable and serves as the basis for Gemex's Comparative Light Performance Evaluation Scales.

The scales are simple linear graphs that shows how the diamond performs in relation to the entire performance range. In addition to these linear graphs, five light views and one symmetry view are provided which display the distribution, intensity, and interaction of the light components being measured and the symmetry/contrast in the diamond.

For more detailed information and FAQ's go to the Gemex website, www.gemex.com

The analysis and direction provided by the Brilliancescope has clearly demonstrated to us that there are several facets which work in tandem and are critical in optimizing light output and minimizing light leakage in the 4-point Princess Cut Diamond.

On the Crown side they are:

1. The two Crown facets labelled Crown-1 and Table Break. The Table Break facet splits the crown facet in two as it junctions with the Table. 2. The Star facet(s) are triangular and re-form the Table Break or Crown-2 facet into a triangle. 3. The Point facet junctions with the Table facet and connects the two adjacent Star facets.

On the Pavillion side they are the:

1. The Triangle facet, 2. The Pavillion facet, 3. The Pavillion Break Facets.

We have found that the interaction between the facet angle, facet size, and facet(s) placement are critical in determining light performance intensity, distribution, and combination (brilliance, dispersion, and scintillation).Very slight changes in either facet angle, size, or placement will have a significant positive or negative effect on the diamonds light performance and light leakage.

For example, on the Crown side, the size and angle of the Table break facet, star facets, and point facets are critical. On the Pavillion side, the Triangle facet is key element in affecting dispersion, scintillation, and contrast.

In addition, the spacing between the lower girdle facets (that flank the main pavilion facet) are critical.

Summary:

Internet and Brick & Mortar jewelers are designating and selling 4-pointed Princess Cuts as "Ideal" Cuts based on "numbers" that have been for the most part extrapolated from better cut round brilliants which have significantly different light optic characteristics and on charts that arbitrarily define what "good" numbers are.

Our research indicates that "numbers" for Princess Cut diamonds do not provide a consistent, accurate, or reliable prognostication of superior light performance on which to base a buying decision. We have found that several facets on the Crown and Pavillion sides of the diamond act in tandem for their Cut angle, size, and alignment in order to maximize light performance and minimize light leakage.

Measurement of light performance as provided by the Brilliancescope (www.gemex.com) shows that good "numbers" do not necessarily translate into superior light performance for the 4-point Princess Cut and that consumers would greatly benefit by seriously considering light performance analyses as a basis for their purchasing decisions.

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http://www.diamondtalk.com/forums/showthread.php?t=59892