If you seek “IDEAL” in a fancy shape, you will NEVER select an 80% deep diamond over one with a 65% depth, provided they have equal light return and brilliancy. The one with 65% depth will be SUPERIOR then, simply because it looks larger. The 80% depth stone may be a great performer, but it falls down on an apparent size issue. This means the 80% depth stone could never be IDEAL when something BETTER equals its light performance and also has a stronger attribute, namely apparent size.
You can readily select the finest POTENTIAL fancy shapes by numbers and parameters. This system will not predict which ones will give the very finest light return, but you can eliminate all the stones that will be too thin, too thick, not durable or ugly in length-to-width ratio. This is not an imaginary benefit that was dreamed up somewhere, but comes from years of grading diamonds and being interested in what other experts want and expect from the finest fancy shapes. An ugly fancy will NEVER be an IDEAL. A very deep fancy will never be a true IDEAL. A fragile stone will never be IDEAL. Too deep a stone, no matter how brilliant, is not IDEAL. Too thin a stone, no matter how large or accidentally brilliant, will never be IDEAL.
IDEAL is the ULTIMATE, not simply due to a performance based on brilliancy. Brilliancy alone may be the way the general industry would like to grade fancy shapes and/or rounds, so that any diamond, no matter how poorly cut, is “IDEAL” as long as it is brilliant. This is simplistic and a foolish methodology. Such an approach is biased to favor cutters and dealers at the expense of integrity and serves to further erode the faith consumers ought to have in diamond vendors.
IDEAL is an absolute concept of TOP QUALITY light return and cutting, and it should encompass all the aspects of each stone being graded. Anything less is not really an unqualified Ideal cut.
The AGA Cut Class grades provide the shape information that one adds to brilliancy information. This brilliancy information can be from Ideal-Scopes used with round diamonds and with the AGS-ASET-Scope for fancy shapes. These little tools plus the AGA Cut Class Grader combine to give dealers and consumers a system to pre-screen and even grade if a diamond as to whether it is truly IDEAL.