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Article > New Cut Grading Systems: the Technology Provider's Challenge | ||
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Diamond Grading Articles | |
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Part 4: The role of geometry measurements Diamond geometry, consisting of linear and angular measurements, are and will remain crucial to any cut grading system, especially to computer simulation and diamond grading methods, which do not have the benefit of looking directly at the diamond, but rather have to rely on the three-dimensional data provided by a geometry measurement device. For demonstrating the role of geometry measurements, I will use the DiaVision™ software product that works with the DiaMension™ hardware platform, both developed and manufactured by Sarin™ Technologies in Israel, a pioneer in diamond geometry measurements for over fifteen years. The most important feature of DiaVision™ is the accurate three-dimensional model it creates of the diamond. All examinations, calculations, grading and diamond measurement are done on this model. The model contains complete linear and angular information on each and every facet, including directional angles data which is crucial for symmetry observations and grading. I will elaborate on this feature later in this article. Finally, the entire diamond measurement, data collection, grading calculation, and data presentation process last a mere ten to twelve seconds with the latest generation of DiaVision™ software.  Figure 1 Figure 1 shows a summary of the diamond's linear and angular measurements from the diamond's side view. We can see the diamond's diameter, table size, total depth, crown height, girdle thickness, pavilion depth, culet size, average crown angle, and average pavilion angle in an easy-to-understand graphical layout. These average measurements are traditionally used for grading the diamond proportions.  
In Figure 2 we can see the new angular measurements on each and every facet of the diamond, from the diamond's top and bottom views. This information is a vital source for symmetry and ray tracing calculations. Gem lab research has shown that no light performance observation or grading can be complete without using the individual facet angle information. We are at a point where the traditional average measurements simply won't do. Figure 3 shows us the directional angle of every facet, from the diamond's top view. Similar data is available for the bottom part of the diamond. The numbers in this image represent the directional angle of the facet, starting at zero for the first bezel facet measured.  
Figure 4 shows a different transformation of this data, usually more useful for diamond manufacturers at the quality assurance stage. These numbers are the directional shift of every facet from the optimal direction they should be at, according to the diamond's symmetry axes. Thus, we can see positive as well as negative directional shifts, depending on whether the facet is shifted clockwise or counterclockwise. A directional shift value of zero means that the facet is perfectly positioned on the diamond. Another useful view is the top-down symmetry view, shown in Figure 5. This view shows the diamond surface as completely transparent, to allow an unobstructed view of the diamond's symmetry problems. In this example we can easily spot a slight crown-pavilion twist problem by examining the misalignment of the upper- and lower- girdle halves. Similar and more severe problems can be easily spotted with this view.  Figure 6 Finally, Figure 6 shows an interesting example of using the three-dimensional view in conjunction with the photorealistic view incorporated in DiaVision™. This photorealistic view is shown using a software component developed by OctoNus™, containing a unique view simulating the Holloway Ideal-Scope™. If we look at the image on the left, we see a white area on the upper-girdle halves, representing severe light leakage from this area of the diamond. To discover the cause of this problem or how to avoid it in the future, we must turn to the DiaVision™ three-dimensional model, where we now look at the girdle thickness in the vicinity of the light leakage problem. We can easily observe that the girdle thickness at the meeting point of the upper-girdle halves and the girdle, 6.4%, is much thicker than the girdle thickness at the meeting points of the crown bezels and the girdle around it, 4.0% and 5.3%. This is a result of a common practice among diamond manufacturers known as girdle painting. This practice evolved when manufacturers wanted to add weight to their diamonds at the most obvious place for doing this - the girdle, but in a way that will not harm the diamonds' proportion grade. Since many gem labs only measure or grade the girdle thickness at the meeting points between the crown bezels and the girdle, adding thickness and thus weight, to the meeting points of the upper-girdle halves and the girdle seemed like the natural thing to do. However, as cut grading systems change to include light performance considerations, this practice can no longer continue without consequences. Diamond manufacturers who want to avoid these light leakage problems and prepare themselves for the manufacturing standards of the near future, can start doing so by using products like DiaVision™ that empower them to detect and correct these problems by re-training their manufacturing employees to the new cut grading standards. | |||||
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