Many theorists think that an oval pavilion should come to a point just like a round brilliant. Figure 2 shows the theoretical ideal, which is a round brilliant stretched in one direction but retaining the depths of the original round stone –as though the stone was rubber; Octonus uses this concept in their DiamCalc© software.

This requires cutting similar facets at different azimuths and slopes. Ideally the side mains 'e' are the same as the 'original' round. The data here are for a 4:3 ratio with 'best' slopes for diamond at the side mains. The need to cut at odd azimuths requires a machine with adjustable indexing or special index wheels.

By choosing the same slope for the side mains as for a round brilliant of the same material, there is no 'bow tie' reflection of the viewer's head across the width of the gem; however, the end mains are at a much shallower slope and give poor light return.

Cutters often increase the slope of all facets, increasing the depth of the stone, to reduce this problem but, in so doing, the increased slope of the side facets results in the 'bow tie'.


Fig.1 Same indexes & main slopes as round.

If you look closely at Fig.1 you can see that the scallops are shallower at the ends; if cut to normal thckness, the scallops at the sides may meet to form a knife-edge.



Fig.2 All proportions maintained.

In Fig.2 note the alignment of joins and meets with the red lines, which is indicative of a perfectly-stretched round (compare to Fig.1).

All scallops have the same depth in this design.