What is the required total depth for GIA Excellent diamonds?

“Can you tell me the required total depth for a GIA Excellent diamond? A friend of mine is considering a 1.01 carat, I-color, VS-2 clarity, round brilliant cut diamond that has only been graded by a local jeweler. According to Sarin, the diamond measures 6.33 – 6.36 x 4.04 millimeters, and has a total depth of 63.7% with a table diameter of 55% and a crown angle of 35.5 degrees with a 16% crown height, and a 41.0 degree pavilion angle and pavilion depth of 43.5%. When I told him that the total depth is WAY too steep, he told me that the jeweler told him that the proportions of the diamond qualified for the GIA Excellent cut grade. I bought my wife’s engagement ring from Brian Gavin a few years ago, needless to say that it is gorgeous! Hardly a day goes by without my wife commenting on how sparkly her diamond is… and I’d love for my friend to buy something equally as impressive, but he lives across the country and has never seen it. How can I explain to him that the diamond he’s looking at is not it?”

Affect of Total Depth on GIA Excellent cut grade:

The total depth of a diamond is not really a factor in the GIA Excellent cut grade, nor is it factored into the cut grade assigned by the AGS Laboratory. Both gemological laboratories focus primarily on the relationship between the crown and pavilion angles, as well as the table diameter of the diamond.

While the proportions of a diamond certainly factor into light performance, it is important to note that it is not the only contributing factor. The degree of optical precision that a diamond displays is equally as important, since it also effects sparkle factor and determines the extent to which a diamond leaks light.

If we enter the measurements of the diamond into GIA Facetware® it does indeed indicate that the proportions of the diamond qualify for the GIA Excellent cut grade. But does that mean that this is a diamond your friend should purchase? Not from my perspective, because I think he could do better.

Effect of Total Depth on Visible Diameter:

I want to direct your attention to the outside diameter of the 1.01 carat diamond your friend is considering. According to the Sarin results, the diamond measures 6.33 – 6.36 x 4.04 millimeters. This is actually pretty small for a one carat round diamond. Notice that the outside diameter for this 1.003 carat, I-color, VS-2 clarity, Brian Gavin Signature round diamond is 6.40 X 6.45 X 3.93 which is almost one full millimeter larger at the widest point. There is a lot of carat weight buried in the total depth of the diamond your friend is considering, whereas that same carat weight is visible as outside diameter in the Brian Gavin Signature diamond which has been cut to better proportions.

In this instance, your friend is paying a premium to buy a one carat diamond, but getting one that faces up smaller than a 1.00 carat Brian Gavin Signature round diamond.

Experience tells me that this Brian Gavin Signature round diamond is going to exhibit a higher volume of light return because the 40.7 degree pavilion angle is more desirable, but also because it exhibits exceptional light performance in the ASET image. Ask your friend to obtain an ASET image for the diamond he is considering and send it to me, we’ll do a side-by-side comparison. But for now, you can explain to him that all the red which is visible in this ASET image, indicates that the diamond is gathering and reflecting light from the brightest light source available in the room, and reflecting it all back out the top! The blue indicates strong contrast, which increases sparkle factor.

Needless to say, there is much more to buying a diamond than whether the total depth meets the requirements for the GIA Excellent cut grade. Factors such as table diameter, crown angle, pavilion angle, girdle thickness, and culet size, also play a part. But so does the optical precision displayed by the diamond, which is exceptional in the case of every Brian Gavin Signature round diamond. Which is why hardly a day goes by where your wife doesn’t comment on the incredible sparkle exhibited by her BGD Signature diamond.