Having trouble understanding the AGA Princess Cut Chart

[niceguymr]

In reference to this chart... http://diamonds.pricescope.com/fnc1.asp

The chart seems to be straightforward, but I don''t understand how the numbers can overlap so much.

For example, If you can have a Princess Cut with the following characterstics...
Table 68%
Crown 15%
Girdle 4.5% Slightly Thick
Depth 75%
... and it would qualify as Class 1A Ideal Cut AND Class 4A Below Average.

I feel like maybe I''m not reading the chart correctly because this just doesn''t seem right. Can anyone help clarify this for me?

 

[belle]

first of all, the advice given in your other thread https://www.pricescope.com/community/threads/ags-square-princess-cut-guidlelines-chart-or-table.43998/ was very good. make sure you understand what you are looking at when trying to find a princess cut.
as far as the aga (not ags) charts are concerned, the overall score is an ''average'' of all of the components together. if you have one value that is a 1a and another that is a 4a, your overall grade would be 2b.

 

[valeria101]

They don''t overlap - the next grade (to the right) takes the numbers from the interval under it minus those of the interval of the next higher grade (to the left).

E.g. table grade 1A : 62-68%
table grade 2A: 60-72%

------------------ meaning... 2A gets (60-62 and 68-72)

''Guess the current writing makes it easier to read the grades mechanically, if the characteristics of a certain diamond match interval from different grades (i.e. 1A table, thicker 1B girdle, deep 2B pavilion or what not).

As far as I know...

Anyway, these grades do not claim to predict brilliance. And AGA has a different approach to do that (see at www.gemappraisers.com ). Unless you pic a seller that does their own cut grading based on measuring brilliance somehow (there is a fair number of competing systems - see Ideal Scope, ASET, Brilliance Scope, etc.), AGS is the only lab that issues a cut grade for princess cuts based both on proportions and brilliance.

My 2c

 

[oldminer]

AGA also issues a report on Cut Grade AND Brilliance. We don''t claim to be the size of the AGS Lab, but we were definitely first, first by many years, regardless of all the advertising to the contrary with lab generated diamond cut grading, especially fancy shape diamonds. No other lab grades so many varieties of the fancy shapes, as AGA does, even today. The AGS Lab, great and professional as it has become, has nothing on AGA in terms of experience and actual grading of fancy shaped diamonds for cut quality. Advertising something does not change the facts. I love AGSL anyway!!!! AGSL has definitely opened up the discussion of cut quality that I never could have affored to do alone. For that reason alone, and for the encouraging attitude of Peter Yantzer, AGSL chief, I have no real beef with their little exaggeration.

I believe you will see the direct measurement of Light Behavior, using the advanced technology we employ, will grow vastly in the months to come. I''ll be on the way to the Mumbai IIJS Show in a few days to demonstrate and sell it to many Sightholders who wish to improve their cutting output. We can do the same here in the USA for vendors who want to grade light performance. Many consumers have already gotten AGA light grades on their purchases when we issue lab reports.

Anyone having difficulty with the AGA Cut Class charts would have their problems fixed by using the DIY, do it yourself, cut grade calculator that is a part of the website where the charts are located. It takes the doubt away from the results. Also, rules of useage are posted there. The grade is NOT an average, but limited by the worst characteristics and the rules. It is a little more complex than an average, yet far from rocket science.

We''d be pleased to assist anyone who might need further coaching.