Who Defines Cut - is it purely subjective?

[knowverylittle]

These are probably newbie questions that I should be able to answer by now:

Poor, Fair, Good, Premium, Ideal, Ideal H&A - are these industry standard terms or can they vary from retailer to retailer?

AGSL seem to grade cut but the GIA does not. Does this mean retailers create their own subjective boundaries when categorizing the cut?

Is cut always a function of Depth and Table percentages?

Does everyone consider the HCA (I know it uses crown and pavilion angles) superior to any other rule of thumb?

 

[valeria101]

H&A is a model of symmetry with light return as a byproduct. The other ratings are... well defined for other things. Among all these there are overlaps of different sorts and degrees. I don't think this helps! AT ALL!

In the end, each stone is out there on it's own, and measuring light return gives the measure of the cut if one decides that light return is the goal. Did you see how wiggly are those charts relating cut parameters and light return? Constructing indeces(and/or benchmarks) based on those non-linear functions is not really straightforward, so neither are those commercial standards. I'd look beyond them...if I were you

I suspect that HCA selected those parameters because they can be measured in practice. Starting with the athematical model of the cut, I guess other parameters could be selected as well, but would be les straight-forward. It is possible that these parameters (crown and pavilion angles or %) happen to be the most reliable given some senzitivity analysis (for example, do you remember the discussion about minor facets?). However, the deterministic model of light return analysis behing HCA looks quite sound and it surely does take into account the most cut parameters yet, as far as I know.

Diagnostic tools working with each stone should fare better than any standard. A model of the stone works better the more 'numbers' it takes into account (given that those % and angles come as averages and there is some variance there behind them). I don't remember to have seen compsrisons among these methods, but I suspect the diference would not be blatant. After all, the greatest difficulty is to get anything beyond the GIA report, unfortunately!

Hope this helps...

 

[knowverylittle]

Thanks, looking for how AGS define an Ideal Cut I found this:
http://www.niceice.com/cut.htm

Think I must have skim read it before - there are too many sites to read! So the AGL considers more than just table + depth. In that case should I give preference to a AGL report over a GIA, I though GIA was the best. Presumably a Sarin + some manual work would give the equivalent AGL cut?

 

[valeria101]

I added to that previous post (sorry for the confusion)... I'd skip all those standards, unless you are interested in theory, for a good brilliance diagnostic, really...

 

[DiamondExpert]

AGS, as you have seen, has clearly defined ranges for their terminology.

Beware, however, of terms thrown about like "premium, ideal, etc.", which serve only those spouting them.

True, GIA does not do cut grade, but a proportional Sarin/OGI analysis (usually the software is linked to the AGS-defined ranges) will get you that info in AGS terms.

The HCA has its own built in limitations and prejudices, which I think Garry Holloway mentions at the site.

The best brilliance diagnostic is to see the stone, in combination with others and in all lighting conditions.

 

[oldminer]

Cut is defined by every seller as they see fit. Well, not really, but sometimes it does look that way. Without solid standards there are many differing approaches to grading this elusive standard. Sellers welcome this and at the same time many wish there were a better set of standards to make judgments of quality.

One can look at light return measurments as a part of finding an Ideal stone, but high light return ALONE does not define a fine diamond. One can use AGS or AGA standards, parameters, and define craftmanship of cutting, but ALONE these parameters do not define all there is that goes into a truly IDEAL cut stone either.

What defines the very best, the ideal, is a combination of highest light return, fine cutting craftmanship, and correctness of the shape (for fancy shapes). There is no one system yet doing all this, so we must do our best to grade as we can with the tools that we do have.

In time, there will be a unified system encompassing all the data. We do know what is required, but we just are not there quite yet. Cut grading is a serious enterprise, not just smoke and mirrors. It is not yet a pure science and may not be for some time to come. There will be advances in the coming months and years without any doubt.

 

[knowverylittle]

Thanks for clarifying my thoughts, these were most useful:

>>...terms thrown about like "premium, ideal, etc.", which serve only those spouting them...
>>Cut is defined by every seller as they see fit. Well, not really, but sometimes it does look that way.
>>but ALONE these parameters do not define all there is that goes into a truly IDEAL cut stone either

Simply put I am trying to pick flaws in the idea of selecting the cheapest 'ideal' cut for a given Color/Clarity/Carat with a thin->med girdle.

Is is safe to say a '000' diamond will be pretty impressive in terms of light return etc and a much safer buy than a regular 'Ideal' cut based only on table and depth %.

 

[oldminer]

Not every AGS 0 is equal to every other one. The other two zeroes, AGS 000, do not make any major difference if the stone is an AGS 0 with too much depth. Those are not the very best cut diamonds regardless of the AGS stamp of approval. AGS 0 is a great concept, but errs on the liberal side, to a small extent.

If you are judging by parameters, and you find an AGA 1A that rates only "good" "good" for polish and symmetry, that diamond will be vastly superior to some AGS 000 stones.

If you find an AGS 0 stone that meets the AGA 1A parameters, then you will have a very brilliant diamond.

An AGS 0 that meets the AGA 1B requirements should be a very decent stone, too. However, if you have an AGS 0 that falls into the AGA 2 category, then you really have one of those sort of "off" ideal cuts I am talking about.

The polish and symmetry grade have importance, but when the diamond is cut right, they only play a minor role. It is a great marketing game, but polish and symmetry grades from Excellent to Good are not as important as the cut percentages and angles. If Symmetry or Polish is rated only "Fair" or "Poor", then one must be very cautious with the stone and find out why the grading of those factors is low. Better yet, just go on to another diamond.

 

[knowverylittle]

Thanks oldminer, I'll read your site + charts this lunchtime.

Wow, glancing at your site it seems you will soon have 30 years experience working in the business.

 

[oldminer]

I started in the family business in December 1967, the day after I became a member of the Army Reserves. I had a low draft number and was a "volunteer" for six years, but thankfully never had to go to Vietnam to save them from themselves. That is a long time ago. I hope we remember lessons learned then as we face this mess in Iraq.

So, I have been in the jewelry business 36 years at this point. I figure I am still good for a few more years. Enjoy the website and learn what you can BEFORE you make a decision on what is right for you to buy. There are so many good choices mixed with many not so good ones.

 

[knowverylittle]

>>So, I have been in the jewelry business 36 years at this point
My goodness, congrats on sticking with it!