AGS PGS Report
AGS PGS Report: What does this Mean?
You may have seen this report on a diamond webpage and wondered how does this translate to what the diamond looks like. This report is called the AGS PGS Report. AGS (American Gemological Society)is a diamond grading lab. PGS stands for Performance Grading Software. The company is similar to GIA in that they grade diamonds and point out certain characteristics that are unique to the diamond. They measure carat weight and grade color, clarity, cut, and finish (polish/symmetry). The AGS report uses the follow for cut grade, 0=Ideal (or the best cut grade), 1= Excellent (2nd best cut grade), and so on down to 10 (being the worst). AGS measures a diamonds brightness, dispersion and leakage as seen in this report to determine the light performance grade. There is leniency up to 0.49 in order for it to still make the overall AGS IDEAL CUT GRADE. For example, if Leakage had a 0.20, and contrast has 0.25, the diamond would still make the overall IDEAL Cut grade seen on the "Light Performance Deduction" portion of the report. And as long as the finish and proportions are Ideal it would make the AGS IDEAL Cut Grade at the very bottom of the report.
Below is an example of diamond that did not make IDEAL on the AGS PGS Report. Notice that it's not just the light leakage that suffers here. In this case there are brightness, contrast, and weight ratio issues as well. We'll explain about why in another tutorial.
Where do these reports come from?
This report was generated at Good Old Gold using our Sarin machine. There is a lengthy tutorial on the Sarin HERE this is some general information. The Sarin measures all of the facets of a diamond and generates multiple reports including the AGS PGS report. This report generates an exact model of the scanned diamond with it's measurements (ie. table %, depth, length, etc). AGS worked with Sarin to include a report for their cut grade on round 57 facet diamonds and on princess cut diamonds. This AGS PGS report and the GIA Facetware Report both come from the same scan. If you look at both, there are obvious differences in the report appearances and their approach on cut. More on that in another tutorial.
Is this an offical AGS Report?
Yes, and No. "YES", the report was created by AGS and "NO" the diamond (unless it has an AGS Certificate) hasn't been physically inspected by them. Good Old Gold generates the AGS PGS report which give us a window of what AGS would likely say about the diamond. The report is designed to determine the cut of the diamond but there can be other factors that may make AGS override what this report states.
What is the red diamond image seen below?
This is the AGS version of an ASET which is computer generated using the proportions of the scanned diamond. This image is a representation of what you would see if you viewed the diamond in person through the ASET viewer. As explained in the red reflector tutorial, a diamond either reflects light or leaks light. The different colors represent at what angle light enters the diamond. The red, blue, and green colors represent light that is reflected outward and white represents light leaking through. See example below. If you are able to visit our store, you can request to see any of our diamonds under the viewer.
This is an ASET® viewer.
The two diamonds in the below example (one graded by AGS and one graded by GIA) are shown with the two versions of the ASET image. The first image is a manual photo under the ASET viewer and the second is Sarin generated.
Next to each of the images are the diamonds official reports (AGS 1st one) & the (GIA 2nd one) The 2 diamonds in the above examples have a picture of the computer generated ASET through our SARIN Machine.
Does a GIA Excellent Cut diamond automatically make AGS Ideal?
No, and vice versa. AGS Ideals are not always GIA Excellent Cut and GIA Excellent Cut diamonds aren't always AGS Ideal. There are differences in the way each company grades cut. More is discussed about these differences in theUnderstanding the GIA and AGS Cut Grading Systems tutorial. See examples below. One of the criteria for a diamond to be classified as our Ascendancy Hearts & Arrows and Platinum Select Hearts & Arrows is that they receive both GIA Excellent Cut grade and AGS Ideal Cut grade.
The measurements are slightly different on the Sarin compared to the official AGS or GIA report. Is this a mistake?
No. Unless the numbers are off by more than a half of a percent, its perfectly normal. Variations in the calibration of different Sarin machines or foreign substances on the surface of a diamond may result inconsistency.
Why don't I see this same report on Fancy Shapes?
Currently AGS does not offer a AGS PGS report for fancy shape diamond. A SARIN report on fancy shapes will only show the diamonds measurements and not give a cut estimate. It's still early in our industry on the study of cut on fancy shapes. AGS started doing this in certain shapes and (as of 2017) GIA doesn't grade cut for fancy shapes at all.
What are some reasons why a GIA Excellent Cut might not make AGS Ideal and vice versa?
There are various reasons for this. One thing is for certain, both grading lab companies approached there cut grading differently so you will naturally have situations where one won't agree with the other. Here are some examples.
EXAMPLE 1: GIA EXCELLENT with AGS 1 LIGHT PERFORMANCE
AGS generally sees leakage as a major factor over numbers. Here is an example of an GIA Excellent Cut that didn't make AGS Ideal. It had enough leakage to knock it down to "1" (AGS Excellent, 2nd best cut grade). The reasons for this can be explained further in another tutorial. Notice that the brightness has a deduction of 0.73 and contrast of 0.37? (Totalling a 1.10). As I mentioned earlier, any total deduction of 0.50 or greater will knock down the light performance to "1" or more.
EXAMPLE 2: GIA VERY GOOD CUT with AGS IDEAL LIGHT PERFORMANCE
An interesting example of a diamond with virtually no leakage and made AGS IDEAL LIGHT. The GIA Very Good Cut had nothing to do with this. It actually has to do with the girdle being at the very thin mark which is too much for GIA's tolerance. There are other examples of a perfect diamond in regards to light return and it's a GIA VG because of a similar girdle to this. The symmetry and girdle issue is separate from light performance.
You could learn further about the ASET® here Red Reflectors Tutorial and further your knowledge in understanding how to interpret them.
-Tutorial by Charles Ciarfello, for questions email firstname.lastname@example.org