Proportion Factors In AGS Grading Reports – What It Means

Recently, one of our readers noticed something weird in an AGS lab report for a princess cut diamond and asked me the following question: “I was browsing through James Allen for a 1 carat sized princess cut and shortlisted a couple of diamonds in their True Hearts line.

When I brought up the certificate to look at details, I noticed a description called Proportions Factors under the Cut Grade section. It was listed as AGS Very Good 2.

I’m not sure whether this is something new because I don’t see anything similar in other AGS platinum light performance reports. I hope you can shed light on this.”

First of all, let me show you the copy of the grading report in question. You can clearly see that the stone receives a rating of “AGS Very Good 2” for Proportions Factors. You can view the full details of the diamond with this link.

proportions factors ags very good 2

Shown below is an example of a grading report for a typical AGS000 ideal princess cut. You can view the corresponding listing for this diamond here. Interestingly, both these diamonds were graded at the same time period in Jan 2015.

square modified brilliant 1 carat ideal cut

So, What Does the Proportion Factors Really Mean To The Layman?

The short answer is, the crown angle of the particular diamond is too high (48.5°). Even though the diamond exhibits ideal light return, polish and symmetry, AGS penalized this diamond because of its excessive crown angles. As a result, this diamond faces up smaller for its weight and is rightfully graded to be an AGS 2.

For people who are interested in more details, the long answer can get pretty technical. In essence, AGS classifies the diamond’s pavilion angles, crown angles, table size percentage, culet size, star facet length, lower girdle facet length, girdle thickness, weight ratio, durability and tilt collectively as Proportions Factors.

If you are wondering why AGS listed the Proportions Factor in the grading report for one diamond and not the other, my belief is that it is done purely for indication purposes. It is in my understanding that all diamonds that are subjected to an AGS grading process will undergo a proportions check. 

If there are no issues with the proportions factors (i.e. the diamond receives an ideal 0 rating), AGS will not list it in their grading report by default.

Why Was The Grade Assigned As “AGS Very Good 2” And Not 3 or 4?

Like GIA, AGS also utilizes some form of guidelines/charts when determining the cut grade of a diamond. In this particular diamond example, it is a 4 chevron princess cut and all the corresponding cutting chart guidelines can be found here.

Now, without a Sarin scan to tell me the actual angles/proportions of individual facets, I can only make an educated estimate as to how AGS derives a grade of “Very Good 2” for the diamond. This can be performed by using the following table provided by AGS.

cut guidelines chart for table 70%

* Assumption: the diamond has an upper pavilion ratio of 70% and lower pavilion ratio of 10%.

With that, I hope this clears up any questions you might have about AGS’s proportion factors. Basically, you don’t have to worry yourself with the technicalities of how the labs grade diamonds if you don’t want to.

For a consumer, you can simply stick with AGS triple ideal diamonds and generally be assured of a great looking stone.

If you are looking for ideal cut diamonds, White Flash and Brian Gavin are two of the best vendors offering quality products at reasonable prices. They have a stringent curation process in place which ensures you never have issues with proportion factors or other cut related issues.

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2 Comments

  1. Avatar
    Matt-
    August 13, 2018 at 10:01 am

    I am in the process of buying an engagement ring and my girlfriend has expressed that she would like a 5-stone ring, so 2 diamonds on each side of the main diamond. I have several questions regarding the quality of the side diamonds. To start, this is the center diamond I am looking at getting.

    https://www.jamesallen.com/loose-diamonds/round-cut/1.55-carat-f-color-vs2-clarity-excellent-cut-sku-5331144

    Before we get into the side diamond questions, can you give me your opinion on this diamond? It falls within your recommendations for cut and color, and it doesn’t have any glaringly obvious inclusions, but it also only gets 1 for proportion factors in the AGS report. I haven’t yet, but I plan on requesting an idealscope image of this diamond from James Allen.

    Ok, now onto the side diamonds. I obviously want quality side diamonds, but I’ve read you don’t want them to be better than the main diamond. My total budget is $20k, so with the above center diamond and assuming around $1k for a setting, I could spend up to $4k on side diamonds. Now here are my questions.

    Cut – Is it important that the side diamonds still fall within the cut guidelines you have on your website, or can those be relaxed a little? If they were still graded as ideal cut, but maybe slightly off your recommendations is that ok? Would a vendor like James Allen even let me dictate the side diamond cut, or are they just going to give me 4 diamonds to go with the setting? I haven’t really seen any standard 5-stone settings, so I plan on having it custom made through James Allen.

    Carat – This one is the biggest unknown. I read that for 3-stone rings they recommend that the side stones are 1/3 – 1/2 the size of the main diamond, but for a 5-stone ring I don’t know if 4 stones half the size of a 1.5 carat center diamond would even fit comfortably on a ring. My girlfriend has mention that she things anything below 0.3 carats would be too small to have noticeable sparkle, but then I worry that 4 side diamonds that are too big would overpower the center diamond, because she has also mentioned that she wants the center diamond to be prominent. Can you make any recommendations as to the size/proportions of the side diamonds?

    Color – Since the center diamond is F, I’m assuming I wouldn’t want anything better than F, but how much lower could I go before the side diamonds are noticeably more yellow than the center? I think G would be ok, but what about H or lower?

    Clarity – I think the goal with clarity is the same with the main diamond, that you don’t want any really obvious inclusions right on the top of the diamond. So, should I stick with VS2 or better to keep the eye-clean look, or since the side diamonds are smaller, would SI1 or SI2 be ok?

    Thanks for all the help.

  2. Avatar
    Paul Gian-
    August 15, 2018 at 10:03 pm

    The stone you shortlisted is a well cut diamond. The proportions factor is a very minor thing as it should relate to one of these issues: Weight Ratio, Durability, Girdle, Tilt, and Culet. I don’t have the diamond on hand and can’t tell you which of it is causing it to be rated as 1. Ask the JA gemologist about this.

    In any case, it isn’t a problem and I have no issues buying this diamond for myself.

    Read: https://beyond4cs.com/jewelry-guide/what-are-accent-diamonds/

    JA will not allow you to dictate the side diamonds unless it is a custom setting. I would say that James Allen uses very good accent diamonds. If you expect the top of the line accent stones, then you need to go to White Flash or Brian Gavin. And yes, cut quality on the sidestones are important. It does affect sparkle.

    https://beyond4cs.com/engagement-ring/three-stone-diamond-ring-setting-and-meaning/

    For carat size of accent stones, it is up to individual preferences. You may want to look at some of the previously purchased rings and find a 1.5 ct ring and LOOK at the sidestones of that ring in relation to the center stone. This should give you an idea of proportioning.

    The color/clarity issues are addressed in the link above. It is perfectly ok to go a few grades away from the center stone and NOT see any differences.

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