EXAMPLE B: Optical symmetry (not graded by labs) Also called Patterning or Hearts & Arrows Patterning What is evaluated here?
• Good physical symmetry resulting from a detailed indexing of the facets (crown and pavilion facets appear in their correct place on the ‘clock’). • How precisely patterned and flat facets are relative to their opposites (that there is no shift in the azimuth). When a cutter takes the facet (polishes it) from E to W, rather than from N to S, it can cause an azimuth shift, resulting in facet yaw. This will show in optical symmetry. • Variation between crown and pavilion angles: It is acceptable to have some variation (subject to limitations) as long as there is no E-W yaw and opposite facets average correctly. Some might consider this an angles/proportions issue, but it is directly related to physical symmetry, as the question here is opposite facet relations, averaging and resultant light interaction. For that matter, it has been observed that a slight variation in opposite angles can improve overall scintillation and contrast as long as there is no presence of E-W yaw.
