Figure 3 shows what happens if the scallops are cut at various indexes shown in Fig.2, keeping the same minimum thickness of 1.0% between the pavilion and crown scallops. Note the original example of 0.86% and 0.83%, with equal thickness at both ends, shown in black, when the indexes are equally-spaced and halfway between the mains and stars.



Some cutters do this twisting of break facets intentionally for reasons they deem important. More recently, GIA and AGS have written on this subject as to how it affects the appearance and weight of a diamond.

If the index is closer to the main than to the star index, as shown above the black example, the thickness decreases at the tips of the mains and increases at the join of the break facets.

If it is closer to the star index (at the join of the breaks) than to the main index, as shown below the black example, the reverse is true.

This discussion has been limited to index wheels with a full set of evenly-spaced notches, which is typical of general-purpose faceting machines. It was intended to show that the intentional twisting seen in some diamonds is less than can be provided by such wheels.

For diamond-cutting, click wheels are made with only those teeth necessary and can be made with any spacing the cutter requests from a click-wheel manufacturer.

Figure 4 is of special interest to reduce depth of scallops. On an 8-pointed round brilliant cut with Tolkowsky’s main slopes and standard indexes, as in Fig.1, the combined depth of pavilion and crown scallops is 1.69%. By adding another set of break facets between these, the combined depth of pavilion and crown scallops is reduced to 0.75%. The slopes of the girdle facets are different from Fig.1.



Figure 4b shows an interesting variation; the pavilion and crown are rotated so that the middle break facet of one aligns with the main facet of the other. In this way the thickness variation of the girdle is almost eliminated.



Bruce L. Harding 2004 Nov 16