When it comes to buying diamonds, GIA and AGS are the only labs that I would personally rely on and recommend to readers. Unlike other questionable labs like EGL/IGI or private labs/appraisers, GIA and AGS represent some of the strictest and most consistent grading standards in the industry.
This means that you know what you are paying for as the 4Cs of the diamond had been accurately assessed.
Despite their authority in the world of diamond grading, GIA and AGS do have their subtle differences from each other. In a round brilliant cut, both labs use different nomenclature and methodologies in determining the cut grade of the stone.
At the top grading tiers of each lab, diamonds are rated as triple Excellent by GIA and triple ideal (000) by AGS.
|GIA Triple Ex||AGS 000|
|Excellent Cut||Ideal Cut|
|Excellent Polish||Ideal Polish|
|Excellent Symmetry||Ideal Symmetry|
Some of the most common questions that I get from readers are usually in the line of: “Should I choose an AGS 000 stone over a GIA 3 Ex diamond?”, “Since AGS is grading diamonds for light performance, does it mean every diamond scoring triple zeros will look great?”, “Is a diamond with GIA Excellent ratings similar to another with AGS 0s?” and other related queries.
Well, the answers is no.
Due to the type of methodology the labs employ and the different criteria for determining cut grade, diamonds assigned with the same cut grade do not necessarily have the same level of light performance.
Here’s a fact. Not all GIA triple-excellent diamonds are created equal. Some are less brilliant than others while some are noticeably brighter. The same applies to diamonds graded by AGS although the degree of variation is somewhat lesser than GIA’s.
The table below shows the relationship between pavilion/crown angles and how the different labs utilize proportions to grade a diamond’s cut.
In the blue zones, those are “sweet spots” for AGS ideal 1s and 0s. In the red zones, it shows the proportions that are sweet spots for GIA Excellent cuts. As you can see, there are some overlapping areas whereby GIA and AGS have common ground.
If the same diamond graded by GIA as a 3EX is sent to AGS for assessment, it might not necessarily be graded as an AGS triple-0 stone. Vice versa, a 000 AGS diamond might not necessarily attain a triple excellent GIA grade.
To put a long story short without going into the nitty gritty details, GIA determines the diamond’s cut grade using a combination of factors such as face-up appearance, proportions and craftsmanship elements (symmetry/polish).
On the other hand, AGS utilizes a system where individual facets of the diamond are measured in 3D instead of GIA’s 2D approach. They then subject these measurements to a ray tracing test to measure how light actually travels within the diamond. Using their proprietary ray-trace software, the light performance of the diamond is subsequently determined.
Personally, I do prefer the AGSL diamond grading report when it comes to assessing cut quality. This is because of the additional light performance data (ASET) that they provide in their top tier grading report.
Now, don’t get me wrong, I have nothing but respect for GIA. In fact, I completed my diploma and gemological studies at GIA where I also learned how they managed to implement consistent grading standards across their labs globally.
As a consumer who is shopping for an engagement ring, it is important that you rely on tangible data like videos/idealscope/ASET to make an informed decision.
The reality is, most vendors do not want to provide these data for you because it increases their costs of operations and reveals the shortcomings of their diamonds.
The AGS Lab makes diamond selection alot more transparent and simple because you don’t have to rely on the vendor to provide you with light performance images. And as a result of this, you seldom see mediocre diamonds being sent to AGS for grading.
Instead, jewelers would rather send their mediocre goods to GIA for a blanket GIA 3Ex rating because it’s much easier to achieve and puts their diamonds in a better light.
When diamonds are grading for cut quality, there is a range of proportions, appearances and performance that exist in each tier of rating. Below are 5 diamonds that were all graded by AGS to be 000 (triple ideal) and I’ve compiled the photographs of their face up views below.
Do they look totally alike to each other? Well, they don’t and you can let your eyes be the judge…
a) 1.20 Carat I Color VS1 Clarity
b) 1.33 Carat H Color SI1 Clarity
c) 0.92 Carat J Color VVS1 Clarity
d) 1.33 Carat J Color SI1 Clarity
e) 1.74 Carat G Color VVS2 Clarity
Likewise, diamonds graded by GIA with the same cut grade would also display different personalities and outlooks. Check out another 5 diamonds which I’ve compiled below with their face-up photos.
i) 1.20 Carat J Color VS2 Clarity
ii) 1.16 Carat H Color SI1 Clarity
iii) 1.01 Carat F Color VVS2 Clarity
iv) 1.00 Carat D Color VVS2 Clarity
v) 2.60 Carat J Color SI2 Clarity
The idealscope is a handy tool for evaluating a diamond’s light performance. In essence, we want to see more red which indicates light return and less white which indicate light leakage. The black colored regions represent light obstruction and create contrast within the stone.
The images below correspond to the respective diamonds that were shown earlier.
Next, here are the respective images for the GIA graded stones…
With the use of optical performance evaluation tools, we can clearly see the discrepancies between the diamonds. It’s straightforward and helps you evaluate a diamond’s performance in an objective manner.
Now, do you understand why shopping based on a certificate alone isn’t enough? A GIA grading report by itself doesn’t tell you exactly how the diamond looks like nor does it tell you exactly how well it performs.
When it comes to critically assessing light performance in a diamond, both GIA & AGS lab reports do not offer sufficient details for consumers to make an informed purchase.
One misconception that many consumers have is that they can’t go wrong with an AGS triple-zero diamond since it is graded with light performance in mind. Well, the truth is far from that.
Both of these AGS diamonds are triple 0s and one of them (No. 2) is actually showing a slight fish eye effect due to its shallow depth!
1) 1.01 carat D color VVS1 AGS ideal cut
2) 1.00 carat F color SI2 AGS ideal cut
3) 0.80 carat I color VVS2 GIA excellent cut
4) 0.70 carat I color SI1 GIA excellent cut
If you intend to buy a diamond “blind”, please think again. My point here is that you need to exercise due diligence and caution when making huge purchases.
If you are interested in a step by step guide where I will reveal the insights and concepts to choosing a beautiful diamond, make sure you read this comprehensive guide.