Figure 3 shows a cut which is optically better because the slopes of similar facets are the same all the way around the gem; this results in a ridge at the bottom of the pavilion - instead of a point, just as in Fig.2.

In a long oval the end facets 'a' of the pavilion may disappear. In this one, which has a 4:3 ratio, these facets are insignificant (as shown at the top) and can be removed by changing the slope or azimuth of halves 'ab' and 'bc' (as shown in red at the bottom).

In Fig.3 the scallops are uneven but less than in Fig.2.


Fig.3 Same main slopes as round but special azimuths.

Fig.3a shows a modification in which four extra facets 'd' are cut at the pavilion tip to form a pointed culet; these will be at a lower slope than the mains; all other facets and data are the same as in Fig.3.


Fig.3a Same as Fig.3 with extra facets at culet.

Figures 3 and 3a are the best designs illustrated here, but both require the special azimuths listed in Fig.1. As stated before, these require equip-ment capable of adjustable azimuths or specially-made index wheels with notches at these azimuths. I made one of these for my own use (Raytech-Shaw faceter), but a factory such as Adri will make them for your diamond-cutting handpieces.

Octonus says that cutters have been unable to make ovals such as they illustrate (Fig.2). The reason is probably that they do not use these special azimuths or vary the slopes properly.

Figure 4 shows the azimuths for a round brilliant that has been stretched by various common ratios (per commercial head findings).

I made only one index wheel, per the 5:4 ratio (the median), and made a fine-looking 4:3 oval with it, so you don't need them all.


Fig.4 Azimuths for common oval ratios.


B. L. Harding    2006 Feb 04