HCA rated higher than EGL - huh

[brody05]

Please help explain how EGL-USA can rate polish and symmetry good but when the dimensions are entered in the HCA it comes up Very good for both light return and scintillation and excellent for fire and spread and overall 1.7 total performance. The diamond in question is;

.67 round brilliant
H SI2
5.82 x 5.74 x3.40
depth 58.8%
table 58%
crown 12.1
pavilion 43.9
polish good
symmetry good
m-stk girdle
no fluoro

also whats your opinion on this;
.71 round brilliant
I SI2
5.7 x 5.67 x3.51
depth 61.7%
table 59%
crown 15% 0r 36.1 angle
pavilion 43% or 40.7 angle
polish very good
symmetry very good
? girdle
no fluoro

Both diamonds are similar prices and I am unsure of which one to buy or rather which one is better. I feel very comfortable with the dealer on the 2nd of the two which means a lot in my book.
Any advice would be gratefully accepted.
Thanks

 

[phoenixgirl]

To answer your first question, light return (fire, brilliance, scintillation, etc.) is affected by but not determined by polish and symmetry. What I mean is, you could have a crap stone with excellent polish and symmetry but the wrong crown and pavilion angles. However, most well performing stones do have excellent symmetry, but I even saw an idealscope image of a stone with "fair" symmetry that showed very good light return. You have to keep in mind that if the symmetry is too far off, it might affect your stone's light return despite what the HCA says (the HCA is assuming the stone is symmetrical).

Have you seen the stones? I would want to make sure that the inclusions are not visible.

Stone #1 looks bigger than stone #2 (5.78mm vs. 5.685mm) and performs a lot better on the HCA (although if we knew the angles for stone #1, its score would be more accurate). So I guess if the choice is between these two, I would go with #1. I got 1.6 for stone #1 and 3.2 and 4.4 for stone #2 depending on which measurements I used.

 

[Garry H (Cut Nut)]

Sorry, did you ever think that a commercially attractive (to cutters) cut grading system with tolerances wide enough to drive a turck through that is based on a 90 year old students thesis should be of value?

This is a very nice example of a BIC - this stone will be of greater value to people in the trade who call themselves "diamondmen of the new age" in the next year.

It is in fact....................................................................................drum roll..........................................................................................................................................a...............................................................BIC

enjoy it

 

[brody05]

Thankyou both so much, your help has been great, I especially like the picture, cheers.