Diamond Symmetry

Most labs grade Symmetry as Excellent, Very Good, Good, Fair or Poor on a GIA report. The basis of lab grading includes microscopic examination to ensure that facets meet perfectly; this can result in very different results to the optical symmetry that we have discussed in this tutorial. During the GIA’s 70,000 observation study, diamonds with ‘Good’ symmetry, but proportions that would have qualified them for the top category, were generally not preferred by both trade & consumers survey participants. That is why GIA have decided to allow diamonds to be in a cut grade above its Symmetry or Polish. However AGS insist that diamonds that receive its top cut grade, AGS 0, have Ideal Symmetry (‘Ideal’ which is meant to be a level above GIA Excellent).When polishing a rough diamond the aim is to cut the heaviest, most valuable diamond possible. This often means polishing a diamond with imperfect symmetry to avoid inclusions or just to achieve a “magic weight” (like 1.00ct). The polished diamond may be slightly off round, have variations in girdle thickness, tilting of the table, and off centering the table or the culet etc. Contrary to popular belief, symmetry defects in a diamond are often the result of a highly skilled cutter, rather than an indication of poor skills. The diamond images we have used in this tutorial are mostly symmetrical. But in the real world very few diamonds are perfectly symmetrical, but symmetry is less important to the overall beauty of a diamond than the critical facet proportions. You may never notice any difference between diamonds with Ideal, Excellent Very Good or even some Good symmetry diamonds.

Price difference for Round diamonds 1-1.49ct, F-H, VS1-SI2, GIA and AGS 58%-63% Depth, 53%-58% Table Data for April, 2004
Polish & Symmetry	% Price difference
Ex/Ex or Id/Id	0%
Ex/VG or Id/VG	-6.5%
VG/VG	-8.3%
VG/G	-9.8%
G/G	-11.6%

The Ideal-Scope reference chart is an effective way to judge symmetry because the patterns we observe with it display “optical” symmetry. Another category of high symmetry diamonds is Hearts and Arrows.