A group of researchers from Moscow State University in collaboration with "LAL" company performed independent studies of diamond cut with the use of their own computer model. [The detailed description of model]. While maintaining the shape and pattern of the facets of a round diamond, they varied its cut parameters in order to find out those values providing the maximum light return and fire (colored rays of light arising due to the dispersion of the gem). Taking into account the conservatism of the diamond market, only the following cut parameters were considered in the studies reported: the table size (Dp) - 60% and 53% (the results obtained for diamonds having other values of Dp will be published later); the girdle thickness (in narrow part) (h) - 1%; the lower girdle facet size (q) - 82%. The light-diamond interaction was modeled for various types of light sources.

"Macroanalysis". The pavilion angle ranged from 35° to 52°, the crown angle - from 15° to 45°. Among all the possible combinations of the parameters, there were a few parameter sets that maximized the light return and fire of the diamond. Some of the sets are currently used by manufacturers or coincide with those previously obtained by Tolkowsky and researchers from GIA. This argues for the validity of the proposed model. Other parameter sets that yield high coefficients of light return or fire are beyond conventional ranges (cut classes). The calculated fields with close light return coefficients have a complex shape with a pronounced diagonal orientation in the crown angle - pavilion angle coordinate system (see Fig.1).

	Figure 1 The light return coefficient nLR_30 for a diamond with the table size Dp=53%. The illumination: diffused (a source of diffused daylight of the "Office" type).

The relationship between the fire strength and the crown and pavilion angles is even more complex. It strongly depends on the illumination conditions. [Details].