HCA vs. AGA vs. AGS

[harvey]

I am looking at a 1.22 carat g color SI2 eyeclean EGL-USA certed diamond. Here is the AGA cut grading report and how the diamond''s cut grades out according to AGS standards: The diamond looks amazing, one of the best I have seen while shopping for an engagement ring for the last 2 months at reputable stores/dealers.

AGA
Cut: Round
Weight: 1.22 carats
Table % 58 Grade: 1A
Crown Angle 35 Grade: 1B
Crown Height % 14.7 Grade: 1A
Pavilion Depth % 44 Grade: 2A
Girdle Thickness Medium to Medium Grade: 1A
Total Depth % 62 Grade: 1A
Polish / Symmetry Excellent Grade: 1A * Not a primary determining factor.

Final Grade: 1B

In addition when I apply the AGS criteria the diamond scores the following AGS grades(0-10): crown angle-0, table-1, pav depth-1, girdle-0, cutlet-0, polish/symmetry-0.

The diamond grades well with both of the above grading schemes. I know its "all about the crown and pavillion angles" the latter of which I do not have a direct reading on, but do these cut grades mean nothing with a poor HCA score of 4.6!! or do the good cut grades with the amazing look of the diamond mean that the HCA is not always the "best" way to analyze a diamonds performance? Any thoughts. This must mean that either the AGA/AGS stds really are not worth applying to diamonds or that the HCA is not alwys the best indicator of a diamonds performance.

 

[pqcollectibles]

The HCA is a much more accurate weeding tool when angles are used. If you had the pavillion angle, you might get a much different result. In this case, you've got 3 out of 4 things telling you the diamond is worth considering. It scores well by AGA and AGS cut proportions standards. And, your eyes are telling you the diamond is a good performer. If it caught your eye and spoke to you, it may be the one.

 

[Garry H (Cut Nut)]

The critical issue is the 44%.
Is it 43.x
or 43.y?
or 44.z?

either way the stone will not get a great HCA result.

 

[valeria101]

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On 6/2/2004 11:31:12 PM harvey wrote:



This must mean that either the AGA/AGS stds really are not worth applying to diamonds or that the HCA is not alwys the best indicator of a diamonds performance.

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Well... why do you expect these grading systems to agree? I think they were all made on different principles. Besides, the AGA allows averaging grades for different characteristics, but AGS does not - one "fault" and you have an AGS1 instead of AGS0 !

The HCA judges light return and little else matters (ok, there is the score for "spread" there).

Diamonds are cut to achieve both an attractive shape and light return - these two are not one and the same. Light return can definitely be achieved within a tighter set of parameters than "nice shape" - and then lots of cutting receipes that would deliver great light are never even attempted because the shape is not acceptable.

With all these parameters in mind, it makes some sense to develop a set of parametes and cut grades to identify stones that have both great shape and light return - but those are few and far between. What to do with the others that just do not make it? So standards are more or less strict - all worth using and understanding....

Hope this 0.2 worth of mine makes sense