AGS0 cut - why such a low HCA score?!

[joeq]

I have been looking at a lot of stones lately, trying to focus on stones in AGS0 range because cut is very important. One of the stones I saw really caught my eye:

Weight: 1.750 Ct,
Diameter(mm) 7.73 (7.70-7.76)
Total Depth % 62.5 4.83mm
Crown Angle '' 35.3 (35.1 - 35.4)
Crown Height % 15.8 (15.0 - 16.6)
Pavil Angle '' 41.3 (41.1 - 41.6)
Pavil Depth % 43.2 (42.7 - 43.9)
Culet % 0.3
Table Size % 56.0 (55.8 - 56.1)
Girdle 1.5% (1.2 - 1.9) Medium

All of the measurements are right in the middle of the AGS0 ranges. It seemed to have a lot more brillance than the other stones I saw, when looking from various angles and light sources.

However, it scores an abysmal 4.5 on the HCA! What gives? The stone is a little deep so there may be some leakage when looking directly top-down. But at other angles it seems to be fine. A little leakage hurts that much?

Do you think my eyes were fooling me? All of the other stones were also AGS0, and to my eyes, this one looked like the best. If I put this one next to a stone that gets a 1.6 on HCA, what differences (if any) would I notice?

 

[Rhino]

There are a few various possibilities why it may have appeared nicer than the other seemingly better scoring HCA score diamond.




One is that the AGS stone may have had superior craftsmanship (even possibly H&A) than the other better scoring stone. Just becuase a diamond gets a better HCA score does not automatically mean the diamond has a better "make" than the stone with the worse score. A diamond can have a great HCA score and inferior craftsmanship. The HCA assumes superior craftsmanship when reality dictates otherwise. If you drop me an email I can demonstrate this to you with links to stones on our site that we've previously tested. We just tested a 35.4 crown angle with a 41.1 (not as bad as the one you just saw) that does have high symmetry though and appears better in some light conditions than others. It depends on the light conditions you were observing the stones in and what phenomena was being observed. Sometimes people are observing a phenomena they think is *good* when in reality it may be very *bad*. =D YIKES!




However if you thought that the 35.3/41.3 combo was the best you've seen ... then you haven't seen the best yet my friend.

Peace,


Rhino

 

[joeq]

I realized that a stone that leaks through its pavilion will look brighter if there is light under the pavilion. I looked at the stones by lifting them, rotating them around, etc. so I think some of the brilliance was simply the light coming in from the pavilion. My guess is, once it is mounted, the pavilion will be mostly covered and the stone will lose much of its brilliance.

So ironically, the stone that leaks the most light looks the most brilliant?!

 

[oldminer]

The diamond is a little too deep, the crown a little too steep, the pavilion angle a bit too shallow. What does this add up to? A diamond that fits the parameters, but does not do as well as many others do.

It probably is a very good looking stone, but in comparison to many other Ideal Cuts, it will not be the best of the bunch...

Any grading system, such as AGS or my own AGA system, that works by parameters needs to be decently liberal enough not to make it impossible to commercially find a stone that grades well. This is business sense and reality added to idealism about cut grading. If you try the AGA system you may find the diamond grades well, but not in the top grade. My way of thinking about the very top grade is that is ought to be very narrow. Why else seek out perfection if it cannot be recognized?

You and other consumers can do your own AGA cut grading on the www.gemappraisers site....