Conclusion

In conclusion, we would like to note that the division of diamond symmetry distortions into «major» and «minor» ones arose on the market during last decades and that it is supported because training centers spread it when teaching gemologists. However, such a symmetry classification has some drawbacks: it analyzes neither the reasons leading to such-and-such symmetry distortions nor the influence of these distortions on the appearance and optical properties of a diamond. In this paper, we were trying to follow the definitions historically appeared on the market, and the concepts of «minor» and «major» symmetry we adopted do not always correspond with the degree of the influence of the symmetry distortions on the optical properties of the stone under study. This problem is worth being discussed separately, and so far we would only like to note that these distortions must be clearly distinguished, because, for example, actual variations of pavilion facet angles, caused by non-roundness of the girdle, have much stronger influence on the optical properties of the diamond than their quasi-variations caused by a tilt of the table. Meanwhile, the current reports of Sarin and OGI devices do not specify the reason of the angle variations, and leading gemological laboratories do not even mention these variations in their reports. The question still not answered is what major and minor symmetry distortions are with respect to two types of consumer’s perception of diamonds. The first type concerns the visual perception of the optical properties of diamonds, such as Scintillation, Brilliance, and Fire. Those symmetry distortions leading to degradation of the optical properties of a diamond can likely be considered as «substantial» or, even better, as «distortions affecting its optical properties». The second type concerns the visual perception of the quality of diamond cutting performed by the manufacturer. We attribute this type to the following symmetry distortions: table inclination, table displacement, culet displacement, edge pointing error, and upper facets displacement with respect to the lower facets. The quality of a diamond with respect to the symmetry of this type is especially clear to an expert equipped with a loupe. A high expert’s grade of the skill of the manufacturer who has succeeded in the symmetric, almost ideal geometry of the stone can, of course, affect the price of the cut diamond. Such symmetry distortions, or rather their absence, can be considered as an «illustration of manufacturer’s skills» or «assembling quality».

The authors wish to thank Mr. Pol Van der Steen (DiamCad, Belgium) for the example of a diamond with a «triangular» girdle.

References:

1. Diamonds. Technical specifications. Classification. TU 117-4.2099-2002, pp. 10-13.

2. HRD – Institute of Gemmology, Diamond Grading Course Book, 1997. pp. 125 – 132.

3. GIA Diamond Grading. 1993. Assignment 9, pp. 2-15.

4. http://www.gemology.ru/cut/english/grading1/3.htm

5. http://www.ideal-scope.com/