The proper proportions of diamond can maximize its optic appearance: scintillation, brilliance and fire. Deviations of cut proportions can create some undesirable effects of diamond appearance, and sometimes require compensation by deviation of other corresponding proportions and angles.

In this poster we discuss a possibility of improving diamond optical appearance by some symmetry deviations. The problem is that today any symmetry deviation visible by loupe penalizes diamond cut quality by definition.

A general observation reveals that an overall diamond picture (pattern, appearance) is created by facet arrangement. Proportions and symmetry here are two sides of one coin. The following example illustrates relationship between deviations of proportions and deviations of symmetry.

At this example a stone at the Fig 1 is of course the best out of four because is has good proportions and ideal symmetry. Stones at the Fig. 2 and Fig. 3 have distorted symmetry and incorrect proportions respectively. Stone at the Fig 4 is a combination of improper proportions and symmetry.

There are two questions here:
1) Which stone is the best out of 2, 3, and 4?
2) Which stone is the worst out of 2, 3, and 4?

Fig. 1 Tolkowsky proportions (pavilion angle is 40.75 degree). Ideal symmetry.

Fig. 2 Average proportions are the same as Tolkowsky. Pavilion angles vary from 39.93 to 41.60 degrees because of 1.5% culet displacement.

Fig. 3 Pavilion is deeper than Tolkowsky proportions (41.50 degree).
Ideal symmetry.

Fig. 4 Average pavilion angle is 41.10 degrees and vary from 40.69 to 41.52 degrees because of 0.75% culet displacement.

Various symmetry distortions are connected with the number and shape of diamond virtual facets that are critical for scintillation. If a bigger stone has exactly the same shape and symmetry it will have the same number of virtual facets but with bigger size. Probably it is better to implement some special symmetry distortions in order to achieve more virtual facets and more scintillating diamond.

It is important to separate asymmetry of diamond shape (visual) and asymmetry of facet positions.

What is better: to distort symmetry in order to avoid some negative optical effects due to improper proportions or leave a stone with improper proportions and perfect symmetry?

Sergey Sivovolenko, OctoNus, Moscow, Russia
Yuri Shelementiev, Gemological Center MSU, Moscow, Russia