- May 10, 2012
AME can you elaborate? Thanks
1.86 ct, GIA triple ex
angles: 35, 41.2
medium - slightly thick faceted
HI DS! *waves*
Thank you for starting your own thread. Sorry for being tardy to the party! I would be happy to elaborate in here. The reason I said "no" on that stone is that the interplay on those specific angles is not ideal, nor is the table percentage. Specifically: the crown and the pavilion angles are too flat in ratio to each other, so light is not going to properly reflect back up out of the stone like it should, and you will likely get a "ring" of darkness in the stone where the light just goes right through it. If either angle was a bit steeper, it would reflect more light back through the top of the stone, and you would get significantly better results. A 58% table is outside the lines on a true ideal, but when used with the proper crown and pavilion angles and a depth around upper 61s-62%, can work out ok.
Something to note about stones with "larger" tables is that they reflect more white light than colored light, meaning you'll get more white flashes than rainbow sparkles. "Smaller" tables tend to produce more colored light than white light, meaning you get more rainbow sparkle than white return. To many untrained eyes, it's not noticeable, but to someone like me, that's more obvious.
I personally have a hard time "believing" the GIA cut grading system of "excellent" because it's a HUGE net of what falls under excellent (note: GIA does NOT use the term IDEAL, that is AGS), where AGS has significantly tighter ranges than that. You can sometimes see that a GIA Very Good graded stone is actually more beautiful and has better numbers than what they might call Excellent, which I just find so bizarre, and AGS might grade the VG and Ideal/0, and the Excellent a 1.
In general, to really nail it on the perfect proportions, a general cheat sheet to stick to:
Total depth between 59 – 61.8%
Table diameter between 53 – 57%
Crown angle between 34.3 – 34.9 degrees
Pavilion angle between 40.6 – 40.9 degrees
Girdle thickness between thin to medium, faceted (bruted isn't bad, but faceted would be better)
Culet size: none
When you're dealing with a table of 53-54, you want the depth to be in the 59-60 range, not the 61-62 range. I harp on the 55 because it's RIGHT in the middle of the range, and when the angles jive nothing beats the light return.
The angles mentioned in degrees are a range, obviously you're going to have interplay, so there's not a specific ratio there, ideally a 34.5 crown and a 40.7-40.8 pavilion, but that's not always going to happen. You have to see what the numbers on each stone are.
We'll gladly chime in if you have more stones you want input on.