AGA/HCA question

[mrmarius]

Hello,

I was using the HCA to try and determine what stones of different AGA classes would come out to. Basically I was plugging in different sets of values from the AGA chart on this site so when I am out I might be able to estimate HCA.

When I entered the following set of Class 1A values:

58.7% Depth, 53% Table, 34.3 Crown Angle, 42.8% Pavilion

I got "the total depth suggests the girdle is dangerously thin, or the data you entered is incorrect." I also got the same error when I used 16.3 crown % with the other numbers.

Is this correct? Did I do something wrong? So even though these numbers suggest a class 1A stone, the HCA seems to be saying this stone would be a class 3 or even 4. Perhaps this suggests that the AGA charts should be further refined (or complicated) by a cut class also being dependent on values in their relation to each other.

Marius

 

[Garry H (Cut Nut)]

You are entering theoretic proportions that do not exist as 3D objects.
those warnings come up to tell you that the data you have is wrong. Maybe you have not added some % on for girdle thickness.

You will not gain much from this experiment anyway.

 

[oldminer]

When I made these charts there was no HCA. I referred to the parameters I found in actual finely cut diamonds to give the range of what appeared to create the very "best" subjective ranges. Some of the possible permutations cannot exist and maybe that is what you are finding. You are near the shallow limit in total depth so the only variable is girdle thickness which may calculate to below zero and then simply not be a possible combination.

Besides, the HCA is a way to make a judgement on a stone you cannot see. The AGA charts are a way to help make judgements on actual stones that you have in hand to view.

Many times the HCA and AGA charts agree. However, the theoretical stone must be possible. The HCA can predict when you have chosen an impossible combination of parameters. No problem.

The best way to find a diamond is to look for actual stones. Trying to disprove or discredit the AGA charts is okay with me, but besides being thoroughly reviewed and used by the trade for more than 15 years now, you will find that actual diamonds recognized by the vast majority of the diamond business that rate a fine cut with high brilliancy are within the paramters set forth. The HCA will frequently do the same and also give you guidance on many diamonds outside the region of the present recgnized "ideal" parameters, but also ones which have excellent light return and great looks.

While somewhat compatible, the HCA and the AGA charts are not joined in some mystical way. They are distinctly different approaches from different ideas of what constitutes fine diamonds. The AGA is conservative based on a tradional approach. The HCA is a combination of traditional and new thinking. Both seem to be good helpers in finding pretty diamonds.

 

[Garry H (Cut Nut)]

Well said Dave

 

[mrmarius]

>Some of the possible permutations cannot exist and maybe that is what you are finding. You are near the shallow limit in total depth so the only variable is girdle thickness which may calculate to below zero and then simply not be a possible combination.

>The HCA can predict when you have chosen an impossible combination of parameters.

Ok, that makes sense to me. I didn't understand when Gerry had said that I was entering theoretic proportions. Now I understand that the combinations of proportions I entered would not exist on a real diamond.

>Trying to disprove or discredit the AGA charts is okay with me...


I wasn't trying to do that... I just found something that confused me and asked about it, that's all. Thanks for explaining it to me.