We believe it favors diamond cutters who chase yield, they use a proportion based system which is technically in breach of my HCA patent, but with considerably deeper proportion ranges. When looking at AGS diamonds, we recommend only considering Ideal cut diamonds for the best quality.
However, the AGS Performance grading for the cut of a diamond now assesses the performance, proportions, and finish.
On top of this, GIA has a greater tolerance for larger tables.Also, the popularity of GIA diamonds mean that they are more liquid and this reflects positively on the resale value of the diamond and the ease of reselling that diamond. GIA also allows steeper crown angles when the table percentage is on the upper-limit of the ideal range. The AGS leadership recognized a need for cut quality analysis that the GIA was not addressing, and ultimately a decision was made to establish their own laboratory. Skilled professionals cut the stone to mathematically exact proportions so as much light as possible reflects from each of its mirror-like facets out the top of the diamond.
There have been people in the trade who have done consumer tests on whether consumers prefer a slightly steep deep diamond versus one that has a painted girdle. GIA’s approach uses proportion metrics developed by researching over 70,000 diamonds to evaluate 7 cut parameters: brightness, fire, scintillation, polish, symmetry, durability and weight ratio. A properly-cut diamond will refract the light that enters it and returns it through the top to produce the highly-desired sparkle.
Specifically, note how bright and sparkly the light return is when placed under a normal lamp.If the facets (the glossy flat surfaces of a diamond) are proportional, for instance, they refract and reflect light back to the eye in tremendous fashion. According to GIA, this approach focuses on the aspects of cut that make the round brilliant diamond look the way it does and the degree differences in proportions create observable distinctions.For a 61% table, which is the upper-limit of the top grade for AGS, GIA goes from 32.5/41 to 35.5/40.8 and AGS goes from 32.2/41.2 to 33.0/41.0. There are some practical benefits to purchasing a GIA graded diamond. AGS Ideal cut diamonds (AGS 0 cut grade) have an even more stringent set of parameters than GIA Excellent cut diamonds. This fact actually demonstrates why it is all the more important that you as a diamond prosumer understand the value of your diamond.In general, GIA seems to have a greater tolerance for steeper crown angles and bigger tables but tends to punish painted upper girdles more. If you stick to the recommendations in the "picking a diamond" tutorial, then you should be well within the GIA Excellent and AGS0 grades.In fact, AGS Laboratories was the first lab in the world to start issuing cut grades in their diamond grading certificates in 1996. Diamond cut grading is standardized by both GIA (Gemological Institute of America) and AGS.
In most cases, a lower depth % of two equal carat diamonds will appear larger due to the increased width. The current AGS cut grading system was updated in 2005.AGS takes the opposite view seeing certain kinds of painted upper girdles as a positive for light return. For over 100 years, the diamond industry has known about a set of proportions that created the best looking round brilliant diamond.
As we have always insisted, the determining factor for any stone will be the eyes of a diamond professional and ultimately you.