Diamond Cut Grading #illumedati

Hey everyone! It’s Whatever Wednesdays again, and I’m here to continue my series on Diamonds. Today we’re going to talk about Diamond Grading.

I’d recommend reading the previous posts first, if you haven’t already:

What You Need to Know About Diamonds

Diamond Cut Types

Diamonds Old Mine Cut

Stock Photo from: Pixabay

What is Diamond Cut Grading?

Well, in my prior post, I talked about the 4 C’s. Cut, Carat, Clarity, and Color.

I dedicated a paragraph to the latter 3 C’s, which are Carat, Clarity, and Color. However, because I think the single most important part of a Diamond is its cut, I’ve dedicated this whole post to it.

Diamond Cuts are graded slightly differently by different gem labs. In my prior posts, I explained why I believe that Geological Institute of America (GIA) certified and American Gem Society (AGS) certified diamonds are the ones I favor because of their stringent and reproducible grading.

Ok, so what are the grades?

Well, first let’s go over their general grading:

GIA’s sample grading report: Click here

AGS’s sample grading report: Click here

GIA’s scale for Cut is:

Excellent, Very Good, Good, Fair, Poor

AGS’s scale for Cut is:

Ideal, Excellent, Very Good, Good, Fair, Poor

Wait… the scales are different?


You’ll notice that only AGS certifies diamonds up to an “Ideal” diamond. I’ll go into more detail about what “Ideal” means. For now, just know that if you want that kind of quality, you’ll want an AGS cert. However, if you are ok with a “Near Ideal” diamond, then you can go with either a GIA or AGS cert. There are plenty of great diamonds that are certified as “Ideal”.

Ok… so what is “Ideal”?

Well, first of all, the “Ideal” designation from AGS is only available for Round Brilliant Cut and Princess Cut diamonds. The reason for this is because AGS has established standards for “Ideal” for these cuts. For other cuts, the variation is too large to really give an “Ideal” designation.

Round Brilliant Cut

I’ve mentioned it before, but back in 1919, Marcel Tolkowsky wrote a thesis on the proportions for an Ideal Cut diamond, which was proven correct. For those who are mathematically inclined, Jasper Paulsen hosts his thesis on his website: Here

However, it’s not 1919 anymore, and while Tolkowsky came up with the ideal proportions, it was later discovered that this “Ideal” has some slight variations based on differences in the crown and pavilion angles. Unless you’re a math genius, you won’t be able to discern how good a diamond’s cut is just from its various dimensions.

Luckily, there is something called the Holloway Cut Adviser (HCA). It was created by Garry Holloway. Using that link you can input the dimensions of diamond and get an idea of how good it is. If cut is important to you (and I hope it is), then you should make sure any diamond you buy is “within TIC Range” (TIC = Tolkowsky Ideal Cut range)

However, please note that the Holloway Cut Adviser should only be used as a tool to reject stones. To truly accept a stone you will need to see its Idealscope or ASET. (I’ll talk about this later)

Princess Cut

I talked about the Princess Cut before in my prior post Diamond Cut Types.

Remember that I said if a Round Brilliant is considered “100%” brillance, then a Princess Cut is “75%” brilliance. However, an Ideal standard does exist for the Princess Cut in order to maximize its brilliance. If you want to look at their cut charting guidelines for Princess Cut, you can find them here.

What is an Idealscope or ASET?

These are tools for looking at a loose diamond and evaluating for light leakage.


Image from whiteflash.com

This is where the terminology of “hearts and arrows” comes from in regards to the Round Brilliant Cut. As the story goes, sometime in the 1980s, someone from Japan noticed that the highest quality diamonds exhibited this pattern when viewed through an Idealscope. You can imagine “hearts and arrows” creates the imagery of “cupid” and “love”, which are great for diamonds and engagement rings. For this reason, you will hear “hearts and arrows” a lot when shopping for diamonds as jewelers tend to throw it around all the time. However, a true hearts and arrows diamond should be as crisp, clear, and symmetrical as above.

So, what does that mean?

Just because you can see hearts and arrows doesn’t mean the diamond is great. Even a slight mismatch or overlap results in significant light leakage. If you want to, you can go ahead and plug in a “Very Good cut graded” diamond’s dimensions and an “AGS Ideal 0 cut graded” diamond into the Holloway Cut Adviser.


This is very similar to an Idealscope but provides slightly better information and is better evaluating fancy cut diamonds.

You’ll notice that the AGS certification shows the ASET. However, there are no Idealscope or ASET images in GIA certifications.

Do you have an Idealscope?


I also have a loupe… because… I’m a nerd.

When I was researching diamonds, I found them fascinating. I wanted the diamond I picked out to be as perfect as possible and to be able to show her the arrows. You can’t show the “hearts” in a diamond which has already been set because those images are from looking at the table (face) side down.

The reason I wanted the loupe was because I wanted to be able to show her that her diamond had a laser inscription on it.

Ok… anything else I should know?

Well, if you really want to get crazy, you read this 151 page pdf from AGS about how they grade diamonds.

However, please remember that the difference in size between a 0.9 carat diamond and a 1 carat diamond is miniscule (~0.2 mm). Additionally, the difference between a 1.75 and 2 carat diamond is also small (~0.4 mm). See below:

If you have to compromise, I would compromise on any other C before I compromised on its cut.

Can you show us your wife’s diamond and/or her engagement ring?

I considered putting the “glam” pictures that I received after buying the engagement ring, but I feel kind of weird about posting them.


Cut matters.

Hearts and arrows is just a marketing term, don’t believe the hype.

If you want an “Ideal” diamond, make sure it has AGS cert.

However, there are still really great diamonds that are “near Ideal”… so

Make use of the Holloway Cut Adviser and ask for the Idealscope (or ASET) images.

Get a loupe if you want to be able to see the laser inscription.

If you have to compromise, I would compromise on any other C before I compromised on its cut.

I’ll talk about “Best Bang for Buck Diamond Engagement Ring” next week.



Agree? Disagree? Questions, Comments and Suggestions are welcome.

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