Colors K thru Z: Reading a GIA Diamond Grading Report

Gary Roskin
Roskin Gem News Report

In looking through the Sotheby’s catalogue for November’s Magnificent Jewels auction in Geneva, we came across a pair of brown diamond earrings. They appear to be “matched,” with accent diamonds chosen to highlight the brown color.

GIA 2225887498 and GIA 6227887490
Sotheby’s Magnificent Jewels Auction – the diamond earrings, Lot 518.

Both earrings are set with a smaller and more saturated brown cushion at each post, with light to dark brown round brilliant cuts (RBCs) around the center pear shapes. Both Pears, approximately 14 carats each, have GIA reports, with one getting a color grade of “M, Faint Brown”, and the other, a color grade of “U-V Range.”

Two things caught our attention: 1. how closely they are matched, and yet so far away in the alphabet of color, and 2. one was graded brown, and the other was not.

That’s Odd

Shouldn’t both reports say “Brown” if the diamonds are matching? And how is it that they look so similar (albeit in a photo) and be so far apart on the grading scale – an M to a U-V?

Reading the GIA Color Grading Scale Past J

If the diamond has a yellow body color, and falls somewhere between K and Z on the grading scale, then the diamond is color graded in the traditional position, face down through the pavilion, looking at the diamond’s inherent body color. A letter grade, or letter grade range, is all that’s necessary – because the body color is yellow.

Grading Brown or Grey

The color grading scale, D through Z, is for diamonds of yellow, brown, and grey body color. When using just the alphabet to describe a color grade, assigning only a letter grade assumes that the diamond is tinted yellow. And in this case of the diamond earrings, the diamond graded as “U-V Range” is assumed to be tinted yellow.

If, on the other hand, the diamond has a brown or grey body color, and falls somewhere between K and Z, then not only is a letter grade assigned, but it also receives a descriptive grade, like “Faint Grey/Brown” (along with K, L, M), “Very Light Grey/Brown” (along with N, O, P, Q, R), or “Light Grey/Brown” (along with S, T, U, V, W, X, Y, Z). For our diamond earrings here, there is one graded “M, Faint Brown.”

Quick Recap

We have two pear shapes that appear to be matched, one graded “M, Faint Brown,” and the other graded “U-V Range.”

Why a grade range, instead of just one letter grade?

Typically, in the M through Z portion of the scale, a diamond’s color grade will be noted as a two grade range since master stones, in what is typically referred to as the “Cape range,” are not viewed as important to the quality or value of the diamond. [It could also be the case where a laboratory may not have masters for every letter grade past the letter M. So a range would account for the professional guesstimate of the grade. – gr]

What is “Cape”?

All too often, we casually refer to a yellowish colored diamond as a “Cape” stone. What does that mean? In Stephen Hofer’s Collecting and Classifying Fancy Coloured Diamonds, “Cape” is named for Cape Province, South Africa, where diamonds found there in the late 1800s were primarily a pale yellow color.

The “Cape range” from K to Z simply refers to pale yellow diamonds having more color than “near colorless” and less color than “Fancy Yellow.” Calling a diamond a “Cape stone” has became such an iconic color reference that the descriptive nomenclature remains to this day.

Interesting, Complicated, and Academic

So here’s what’s odd: If this “U-V range” pear shape looks like the “M, Faint Brown,” shouldn’t its report then read “U-V Range, Light Brown”?

We spoke to Tom Moses, GIA’s executive vice president and chief laboratory and research officer to discuss some possibilities.

Moses agrees that if the diamond were graded primarily yellow, (slightly brownish- or even brownish-yellow) there would simply be a letter grade or letter grade range. If the diamond were to be graded as a slightly yellowish- or yellowish-brown, being a mostly brown diamond, then not only would there be a letter grade range, but also the description of Faint Brown, Very Light Brown, or Light Brown.

Graded Face Down

Remember, diamonds in this color range are graded face down. And when GIA saw this diamond face down, they saw more yellow than brown. And so the color grade was applied correctly as U-V Range.

To back this up academically, we see that the diamond has strong blue fluorescence, which indicates that there are N3 centers, and with N3 centers, we have yellow diamonds.

Could That be the Reason Why?

Fluorescence may actually be the culprit as to why the U-V Range graded diamond faces up brownish, and why it is a closer match than the grade differences between the two diamonds would suggest.

Let’s assume, because we have absolutely no proof, that the fluorescence masks the yellow face up, leaving only the slightly brownish tint to appear as the dominant color.

Let’s also assume, because there’s still no proof of any of this, that because there is less brown than yellow, the lesser brown of the U-V Range graded diamond matches more closely to the M, Faint Brown grade of the other pear.

Why not? The jeweler certainly didn’t have to figure out “why.” The jeweler only had to find two 14 carat pear shapes that matched. And it looks like the jeweler did a fine job.

Do We Buy that?

Upon speaking with a jeweler the other day, he mentioned that his brown diamond had come back from the lab as “Faint Brown” with no letter grade. Now that’s odd, since Faint Brown would fall into the K through M range.

Again, talking to Tom Moses at GIA, as it turns out, there are those diamonds that have less transparency, and so to offer a letter grade is sometimes inappropriate since we are grading against transparent masters.

Will you ever encounter one? Maybe. Should you be concerned? Not if it looks pretty enough to set into a piece of jewelry.

Remember, we are not buying the diamond grading report. We are buying the diamond.

Roskin Gem News Report
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