Faceting limits

By Bruce L. Harding
Holden, Massachusetts, USA
Copyright GIA

Table of content

Introduction	Bezel-to-Table Rays	Faceter`s Options
Objectives	Bezel-to-Bezel Rays	Maximum Table Width
Dead Center	The Basic Faceting Chart	Minimum Table Width
The Viewer`s Head	Internal Reflections From the Bezel	Optimum Table Width
Table-to-Table Rays	Range of Reflections Through Table	Charts for Specific Materials
Table-to-Bezel Rays	«Live» Center	Comments

Conclusions	Reference	Appendix

Introduction

    The pavilion and bezel slopes commonly recommended for faceting are the result of trial-and-error and human judgment. This explains why references differ in their recommendations.
     Trial-and-error is an effective way to solve complex problems until a better way comes along, but it usually finds only the best solution in the range of experimentation. Other good solutions may exist – beyond the bad ones – but are found only by accident. This has been as true in faceting as in many other scientific fields.
     Inspired by an exceptionally brilliant but strangely-cut emerald, the writer went in search of these other solutions and found that there are indeed two ore three areas of good design for each gem material.
     This article presents the first and most important result of that search – charts for each of the common faceting materials which show areas of good and bad pavilion and bezel slope combinations; it also defines maximum and minimum table sizes briefly (more later). The faceter can choose from the various «good» areas according to what he thinks is best or to suit the limited proportions of his rough material.
     The text describes the formation of these charts so that you can understand them better. Technical details are omitted; it is assumed that you are either familiar with gemology optics or don`t care. The mathematics involved are quite simple but are deferred to an appendix for those who care to understand them or who may need to create additional charts.