Light performance and cut grade

[FB.]

If we took a selection of diamonds of varying cut grades - such as Ideal(AGS-0), GIA-Ex, GIA-VG, GIA-Gd - roughly how much difference in light performance would be expected?
Or...how about HCA scores; 1-2 compared to 3-4 or 5-6?
I appreciate that there is some stone-by-stone considerations to be made, but how does the typical specimen within each group perform?

Just how much better would you say an ideal cut perform, compared to an Excellent or Very Good cut?
My experiences of comparing diamonds suggest that ideal cuts are better, but not so much better that all other cut grades must be avoided.

I'll start the ball rolling with my own perception of real-world light handling in a variety of conditions (marks out of 10 for how they look).

Ideal: 9
GIA-Ex: 8
GIA-VG: 7
GIA-Gd: 6

Basically, I'm saying that I can see a difference, but not such a difference as many people make it sound.

I feel that I am conditioned to believe - from what other people say - that the cut grades give the following:

Ideal: 9
GIA-Ex: 7
GIA-VG: 5
GIA-Gd: 3

Basically, the message from many people seems to be: forget anything less than ideal and try for super-ideal.

My own experiences suggest that even the lowly-regarded "Very good" cut grades can look very nearly as good as ideal, to the average person, in many conditions.

I'd be interested to hear others views.

FB

 

[Rockdiamond]

Great post fb!
I wholeheartedly agree!
In fact, I strongly believe that there would be people who would actually prefer some VG cut grades ( or AGS 1 or 2) more than other EX cut grade- or AGS0 stones. Not only "average" people- but also knowledgable folks who know what they are looking at.

For this reason, I feel that the classifications can be misleading.
If we add in the term "performance" even more so.
Since not everyone wants to see the same thing in a diamond, the term performance seems to miss the point.

An analogy: The Mercedes AMG is faster than a Porsche 911- this can be documented. Yet some will still prefer the way the Porsche delivers the power- even if it''s less powerful.
These folks may feel the Porsche performs better - even though statistically, the AMG is faster.

Just because a diamond returns more light does not necessarily mean it''s prettier to all observers.

 

[dinamit]

Interesting post FB, I''ve often wondered about this myself. All I can say is that I have a GIA ''VG'' that scores 1 on the HCA. I''ll be very intrested to read OP thoughts.

 

[Todd Gray]

Date: 9/15/2009 3:27:04 PM
Author:FB.
My experiences of comparing diamonds suggest that ideal cuts are better, but not so much better that all other cut grades must be avoided.

As you might expect, the answer to the question is not as easy as one might assume... It all depends on the individual characteristics of each diamond being considered. I would say that not all ideal cut diamonds are created equal, the fact is that the "ideal cut" classification is a range and there are combination''s of measurements which are more desirable than others within the range of possibility.

The same concept holds true for non-ideal cut diamonds, I''ve seen plenty of non ideal cut diamonds which are gorgeous and certainly provide a level of visual performance which rivals that offered by the ideal cut diamonds we represent - I believe we even make a statement to this regard on our web site... However in my experience the number of non ideal cut diamonds cut properly to achieve a higher level of visual performance are few and far between...

Real world example... A few years ago a friend of mine in the diamond business stopped by to prove to me once and for all that a non-ideal cut diamond could look as nice as one of our ideal cut diamonds... He produced a diamond which looked more like the tip of a sharpened #2 pencil than a diamond and it was absolutely gorgeous! I said so and he replied "ah ha, see!" but then I said "so you have like, about a thousand diamonds in that duffel bag of yours?" which he confirmed and I said "so show me another one as beautiful as this..." and he couldn''t. End of story. End of theory.

Who has the time or the inclination to ship 1000 diamonds about in the hopes of finding "the one" which offers the visual performance to rival that offered by many of the ideal cut options? As a dealer I have a choice, ship in 1000 diamonds and possibly find one that "is all that" or sift through 100 lab reports and find 40 center range ideal cut diamonds which are "more than likely" to hit the spot from the start. I''ll take the ideal cut odds any day of the week.

 

[stone-cold11]

That would seem weird given that there is a possibility that a GIA Ex can get an AGS0 grade. So you are saying that even in this situation a GIA Ex grade stone will look worse than if it is send to AGS and get an AGS0 cut grade?

 

[Todd Gray]

Date: 9/15/2009 5:51:11 PM
Author: Stone-cold11
That would seem weird given that there is a possibility that a GIA Ex can get an AGS0 grade. So you are saying that even in this situation a GIA Ex grade stone will look worse than if it is send to AGS and get an AGS0 cut grade?

It depends on the diamond... Let's say that you have two ideal cut diamonds:

AGS Ideal 0 weighing 1.01 carats, VS-2 clarity, F color / negligible fluorescence, total depth of 62.3% with a 56% table diameter and a crown angle of 35.1 degrees offset by a pavilion angle of 41.2 degrees with a medium to slightly thick, faceted girdle and a pointed culet.

GIA 3X weighing 1.01 carats, VS-2 clarity, F color / negligible fluorescence, total depth of 61.0% with a 55% table diameter and a 34.5 degree crown angle offset by a 40.8 degree pavilion angle with a thin to medium, faceted girdle and no culet.

Both are technically "ideal cut" diamonds, but I wouldn't even consider the first option because IMO the total depth is too deep; the crown angle is too steep; the pavilion angle is too steep; and I (personally) don't like a steep / steep = deep stone... I'd hop all over the second option assuming that the inclusions were appealing because it's a center range ideal cut diamond that meets my expectations, e.g. my concept of an ideal cut diamond.

Is that what you're asking Stone Cold?

 

[stone-cold11]

Yap.

 

[FB.]

Stone-cold

A few GIA-Ex's are also AGS-0's, but there seems to be a tendency for the vast majority of GIA-Ex stones to be cut with larger angles than is ideal, due to GIA's more lenient grading system that allows cutters to pad the stone with extra weight, yet still get a top grade "on paper". The best GIA-Ex's can match the AGS-0's, but the majority don't.

My generalisation was to take a typical example from each cut group - an average, if you like.

 

[stone-cold11]

What about the AGS0 that falls in GIA's VG grade? There are overlap and each lab has a different standard and range.

 

[Rockdiamond]

Interesting discussion!

Todd makes some great points- however, what if a person prefers the look of a slightly larger table?
Many people do.
In such cases, the "performance" of an Ideal cut may not be the most pleasing to the eye.

It also leads to the question of why should people go straight for the more costly alternative, if they might actually find the non ideal, and lower priced stone, more attractive?
I have found that it would never be a 1000-1 comparison.
You''d not need to look at 1000 non ideals to find a beauty.
I''ve seen many gorgeous GIA VG cut grade stones- in fact I can''t remember seeing one I''d call "off make" or badly cut.

For buyers who''ve seen and compared, and still go for Ideal, the reasoning is great.
My point is that advising folks that ideal is "better" when they''ve never even seen the comparison could end up having people spend more on a diamond they might actually love less.

 

[denverappraiser]

Date: 9/15/2009 6:08:56 PM
Author: Todd Gray

It depends on the diamond... Let's say that you have two ideal cut diamonds:


AGS Ideal 0 weighing 1.01 carats, VS-2 clarity, F color / negligible fluorescence, total depth of 62.3% with a 56% table diameter and a crown angle of 35.1 degrees offset by a pavilion angle of 41.2 degrees with a medium to slightly thick, faceted girdle and a pointed culet.

This isn’t an AGS-0. It’s at best an AGS-3 (and it quite possibly would be a GIA excellent)

Date: 9/15/2009 6:08:56 PM
Author: Todd Gray

GIA 3X weighing 1.01 carats, VS-2 clarity, F color / negligible fluorescence, total depth of 61.0% with a 55% table diameter and a 34.5 degree crown angle offset by a 40.8 degree pavilion angle with a thin to medium, faceted girdle and no culet.

Assuming no other issues that would cause it a downgrade, this one would be an AGS-0.

Neil Beaty
GG(GIA) ICGA(AGS) NAJA
Professional Appraisals in Denver

 

[elle_chris]

FB- You have a point. Ideal cuts vs very good may not even be noticaeble to most people. I guess the best place to compare would be outside of a jewelry store in various lighting to see the differences.

Todd- I don't believe that only 1 out of a thousand non-ideal cut stones iare gorgeous. I have a few, and i know i didn't go through thousands to find them.

(maybe a dozen but not a thousand)

The more I learn about diamonds the more open minded I'm becoming. I think taste does play a huge role in what someone picks. For instance, i like a bright diamond and have found that my GIA stone with a 34 crown and 41 pavilion is just a little brighter than my AGS0's with higher crown and lower pavilion angles. I have read here that this combo can cause all kinds of problems such as color entrapment and yet, my G looks pretty white. Go figure

 

[FB.]

Stone cold

AGS-0 has quite a narrow range of measurements that are acceptable. GIA-Ex has probably twice the range of measurements that are acceptable.
Therefore, GIA-Ex has a looser set of tolerances that allow some less-good combinations and that pulls down the average quality of all GIA-Ex.

Put it this way; would you expect a randomly chosen GIA-Ex to be as good as a randomly chosen AGS-0?
Most people wouldn't - and it's reflected in the ~10% higher price of AGS-cert stones. I would be fairly happy to buy an AGS-0 without question. I would not buy a GIA-Ex without more investigation into the details of the cut.

 

[elle_chris]

Date: 9/15/2009 6:36:09 PM
Author: FB.
Stone cold

AGS-0 has quite a narrow range of measurements that are acceptable. GIA-Ex has probably twice the range of measurements that are acceptable.
Therefore, GIA-Ex has a looser set of tolerances that allow some less-good combinations and that pulls down the average quality of all GIA-Ex.

Put it this way; would you expect a randomly chosen GIA-Ex to be as good as a randomly chosen AGS-0?
Most people wouldn''t - and it''s reflected in the ~10% higher price of AGS-cert stones. I would be fairly happy to buy an AGS-0 without question. I would not buy a GIA-Ex without more investigation into the details of the cut.

I wouldn''t randomly choose either. I''ve seen some number combos with AGS that I''m not comfortable with.

Btw- "Most people" would choose a GIA stone over AGS because most never heard of AGS. Also, where are you seeing the 10% markup over GIA graded stones? I''ve never seen that much. I''ve also noticed that most vendors who use AGS over GIA are the ones promoting H&A stones which come with a slight premium to begin with.

 

[John P]

These charts may be of interest
http://www.octonus.ru/oct/mss/gia-agspgs.phtml

Note that the PGS data above is overly-forgiving, as it was based on "perfect wire-frame" simulations. Grading would be lower if actual diamonds were used, depending on 3D cut consistency & other particulars.

Here is a less-forgiving comparison (GIA EX to AGS0 only) from 2006, based on the overly-strict AGS cut guides.
https://www.pricescope.com/idealbb/files/exideal1.pdf

If you were to merge the AGS PGS and AGS Cut-Guide data from the different charts it might become a better representation of "average" light performance numbers according to basic proportions sets. But general guides are not useful for specific stones.

Sound complicated? It is. In fact many sellers and manufacturers - of diamonds which could be successful at AGS - have eschewed their 3D light performance metric. Why? Because they prefer tidy two-dimensional charts that spell out & guarantee "what the diamond will get" from the lab before they send it there.

I think any expert will admit that a 2D lookup chart cannot possibly account for all facet variations which influence optics - yet the trade as a whole prefers the simpler system. This is why AGS introduced the more recent "Gold" report, which mimics GIA with tidy 2D lookup charts (Gold is stricter on the steep/deep side & more permissive on the shallow side than GIA).

Aside from dedicated productions, which have proven successful across all metrics, relatively few manufacturers or sellers employ - or choose to learn about - the more advanced metrics in our trade. If we were a more regulated industry I suspect coursework in proportions studies/ray-tracing, angular spectrum and computer-assisted-design (DiamCalc) would be required for formal credentials alongside color, clarity and finish training.