Help me narrow my search - Cut Specs: Table, Crown, Depth, etc.

[Scott Kane]

This is my working "short list" for narrowing my search. What do you think, specifically the "Cut" proportions and specs? I purchased an expert Idealscope, so I can play around with that too. I''m trying to simplify the search for vendors. Is there a formula or something to figure ideal proportions? I know about the HCA, but say I want the ideal proportions for a round brilliant with a TIC or FIC. How do I figure table, crown angles, depth, etc?

Round Brilliant:
1. Certified - AGS or GIA Preferred
2. AGS 000 / HA / AGA Ideal Cut:

* Table....................53-58% (54-57% even better)
* Crown angle..........34.0-34.8
* Crown height.........14-16.3%
* Pavillion depth.......42.8-43.2%
* Girdle...................Thin to Medium
* Total depth............58-62.3% (60-62% even better)
* Polish...................Excellent to Very Good

3. Holloway Cut Advsier - 2 or lower TIC (Tolkowsky) or FIC (fiery)
4. Eye Clean (from 6 inches) - SI1 or better (maybe SI2 if it passes eye clean)
5. Face-up White - I or better (maybe J)
6. 1.2ct+ (6.80mm+)
7. Budget - $4000

 

[stone-cold11]

TIC crown angles range from 32.5 - 35.5 I think, FIC is 36 and above.

So if you are just using the crown angles you listed, you will only get TIC.

 

[Lorelei]

Here is the cheat sheet some of us use as a guide to find a well cut near Tolkowsky type round

depth - 60 - 62% - although my personal preference is to allow up to 62.4%
table - 54- 57%
crown angle - 34- 35 degrees
pavilion angle - 40.6- 41 degrees
girdle - avoid extremes, look for thin to slightly thick, thin to medium etc
polish and symmetry - very good and above

note - with crown and pavilion angles at the shallower ends ( CA 34- PA 40.6) and steeper ( CA 35- PA 41) check to make sure these angles complement in that particular diamond - eyeballs, Idealscope, trusted vendor input - check as appropriate!

As the above implies, configurations depend on each other. A little give here can still work with a little take there.

From expert John Pollard.

With that said, here's a "Cliff's Notes" for staying near Tolkowsky/ideal angles with GIA reports (their numbers are rounded): A crown angle of 34.0, 34.5 or 35.0 is usually safe with a 40.8 pavilion angle. If pavilion angle = 40.6 lean toward a 34.5-35.0 crown. If pavilion angle = 41 lean toward a 34.0-34.5 crown.

GIA "EX" in cut is great at its heart, but it ranges a bit wider than some people prefer, particularly in deep combinations (pavilion > 41 with crown > 35).


Fiery Ideal Cut;

depth as above although some FIC have greater depths and sometimes can look a little small for the weight as a tradeoff.
table - smaller is preferable - 53- 57% thereabouts
crown angle greater than 35.5 deg
pavilion angle - no more than 40.6 degrees

BIC Brilliant Ideal Cut Crown angle is less than 32.5°
TIC Tolkowsky Ideal Cut Crown angles between 32.5° and 35.5°
FIC Firey Ideal Cut Crown angle as above