Choosing Faceting Angles

faceting angles - brilliant round diamond
“Fancy Gray Violet, Round Diamond by Leibish & Co,” round brilliant cut, 0.11 cts, by Fancy Diamonds. Licensed under CC By 2.0.

Back in the old days, gem cutters chose faceting angles by trial and error. Enough faceters were cutting every imaginable gem material that the research was fairly well done. However, no scientific method existed for comparing the data nor any systematic method for sharing it. Hence, some opinions slipped into the published records.

With the advent of computerized ray tracing programs, such as GemRay, this situation changed. Gem cutters tested old theories and added new insights. Although many old principles have been clarified or improved, the move to shallower crown angles represents the only significant change. Some of …

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