Not All GIA “Excellent” Cuts Are Created Equal!

We’ve talked about Cut being the most important of the 4 Cs when picking your Center Diamond. Cut relates how well a diamond reflects available light. We recommend only the top grades in Cut- AGS’s “Ideal” and GIA’s “Excellent”- for your Center Diamond, because the more a diamond sparkles the brighter and bigger it looks.

GIA Cut Scale with Example Images
Courtesy of the Gemological Institute of America

We also told you that GIA’s “Excellent” Cut Grade was too broad of a range, because some “Excellent” Cuts reflect light much better than the rest, due to having perfect Proportions. Let’s take a look at the difference between a standard GIA “Excellent” and a GIA “Excellent” with perfect Proportions, so you can pick the best possible Cut for your Center Diamond.


Let’s start as we always do, blind comparison to get some first impressions. No zoom, no filters, shot on a DSLR camera with no fancy equipment.
Especially for Cut, it’s best to compare in person. Very difficult to compare sparkle through a screen.

GIA Excellent with perfect proportions versus standard GIA Excellent
Both diamonds around 1 carat. Which one’s the standard GIA “Excellent” and which is the perfectly-proportioned GIA “Excellent”?

On the left, the perfect-proportioned GIA “Excellent”. On the right, the standard GIA “Excellent”.

Now let’s take a look under an ASET Scope, to see how much light each stone is reflecting and from where.

Perfectly-Proportioned GIA Excellent
Top-Sparkle GIA “Excellent”
  • GIA Report # 1418655599
  • “Excellent” Cut, Polish, Finish
  • 56% Table ✅
  • 62.8% Depth ✅
  • 35.5 Degree Crown Angle (A little more fire aka rainbow-colored light than brilliance aka white light)
  • 40.6 Degree Pavilion Angle ✅
  • LGF Length: 80% ✅
  • 50% Star Facet Length ✅
Standard GIA Excellent
Standard GIA “Excellent”
  • GIA Report # 2418092114
  • “Excellent” Cut, Polish, Finish
  • 61% Table (a little high)
  • 61.8% Depth ✅
  • 35 Degree Crown Angle ✅
  • 41.4 Degree Pavilion Angle (a little high)
  • LGF Length: 80% ✅
  • 50% Star Facet Length ✅

Even though they’re both GIA, under an ASET scope these two do not belong in the same organization. That’d be like comparing Ocean’s 8 to Ocean’s 11.

The standard “Excellent” is leaking light and lacking in contrast (see how the arrows don’t extend cleanly to the edges of the stone?). Meanwhile the perfectly proportioned “Excellent” should be hanging in the Louvre. Beautifully symmetry, excellent contrast, strong light return.

How do these compare in person, to the naked eye?

In my opinion, it’s something that you catch once you know what you’re looking for. The standard “Excellent” Cut is still a great diamond. If you move it under a light source, it sparkles nicely. But the “Excellent” with perfect Proportions gets all the little things right- thin arrows, great contrast, perfect octagonal table. Those details are the difference between a great diamond and an incredible one.

Javi Perez, President

Javi Perez,
President

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