Grade This

We’ll start with an easy one: clarity-grading a 2.25-ct. diamond supplied by Los Angeles diamond wholesaler Gaby Landau of J. Landau Inc. Accompanying the diamond is a Gemological Institute of America Gem Trade Lab report, and on the stone paper is a “sticky” with Sarin measurements. Why the GIA report and a sticky? What are the similarities and what are the differences? And based on the following information, how would you grade the diamond?

Splitting the difference. Landau included the two separate information slips because she knows that GIA doesn’t provide as many cutting details as a Sarin report does. This is a standard service she furnishes to all her clients, providing crown angle and pavilion measurements for better evaluating the diamond’s cut.

Take a look at the measurements provided by GIA, then note the measurements provided by Landau and the Sarin report.

The Sarin measurements on both the Landau report as well as the GIA report are well within the standard measurement accuracy tolerance of .02 mm. It’s important to note, however, that the table, crown height, pavilion depth, girdle thickness, and total depth percentages are all based on the 100% figure, calculated from the average diameter measurement. This measurement can change by .02 mm and still be considered accurate. Therefore, it’s important not to simply reject a diamond based on a .5% or 1% difference from your personal preferences.

Back to grade school. Now for the test: Look at the photographs of the diamond. The most important clarity grade-making inclusions are, according to the GIA report, the clouds in the center of the table. Because “cloud” tops the list of inclusions plotted on the diagram, it’s the factor most important to the grade. There is another cloud grouping, out toward the girdle edge at approximately 7 o’clock. Carefully examine the stone at 10 o’clock at the girdle edge. There is a feather that may be difficult to see from the top, since most of the feather is on the pavilion side.

Here is the list:

  • cloud

  • feather

  • crystal

  • additional clouds not shown.

Based on your knowledge of diamond grades, would you rate these inclusions as SI1 or SI2 (somewhat easy to see at 10x)? (Note: Do not use SI3, since GIA does not use that grade, and we are comparing your grade to a GIA report.)

Remember, if you disagree with the lab, that’s perfectly legal. Diamond grading is subjective, so it’s your opinion of the grade. However, since your customer will more than likely believe the lab report instead of you, being more consistent with the lab can only make life much simpler. Try to grade the diamond as would the lab. (See p. 219 for answers.)

Answers to Grade This

And the answer is.clarity grade SI1.

Because there are two groupings of similarly graded clouds, along with the feather, assigning a clarity grade is easy. Each one of these inclusions by itself would most likely be graded SI1. Remember that there is a range in each grade, so if you were thinking that the three inclusions would add up to SI2, you were much closer than someone who graded the stone as VS2. The grade was probably on the low side of SI1.

The clouds in the table are too obvious to be VS2, but not extensive enough to be considered SI2. The feather on the edge is too long and deep to be considered anything but SI, and not long or deep enough to be an SI2.

Special thanks to Gaby and Joe Landau of J. Landau Inc., 550 S. Hill St., Suite #1607, Los Angeles, CA 90013.


Splitting the difference


Sarin GIA GTL Difference


Diameter

8.38-8.44 mm

8.37-8.44 mm

.01 mm on minimum measurement


Depth

5.25 mm/62.4%

5.24/62.3%

.01 mm/.1%


Crown Angle/height

34.9º/15.0%



Pavilion angle/depth

41.5º/44%



Table percentage

4.79 mm/57%

57%

same


Girdle thickness

thin-medium/1.4%

medium

no range on GIA report

AGS Cut Grade 1 (provided by Landau)