Diamond Grading Pitfalls

The Grading Certificate: Grading Laboratories

There are several well-recognized grading laboratories where properly trained and qualified graders evaluate diamonds. Grading has to be done under standard conditions, taking into consideration the type, colour and quality of the light source, the colours of the environment and so forth. However, slight differences, may occur in the grading between different laboratories. These differences usually do not have a serious effect on the price of the diamond, except in the case of expensive investment stones. Slight grading variations may occur due to the fact that there is an element of personal judgment involved in the grading process.

The GIA (Gemological Institute of America) grading laboratory is regarded as the international reference grading organization.

Although some retail merchants are quite capable of doing a correct grading, some unfortunately are not, and their grading conditions are often not standardized. It is therefore advisable to only buy diamonds with grading certificates from registered, independent grading institutions.

Properly detailed certificates (often in the form of a folder or envelope) should reflect the following information about the diamond:

Weight (carat weight): 1 carat is sometimes divided into 100 “points” (0,50ct therefore equals 50 points).
Colour: D, E, H etc, down to Z. This should be clearly stated on the report. (refer to the previous article on “The 4 C’s of Grading).
Clarity: FL (Flawless) down to I3 (Obvious eye visible inclusions or fractures).
Cut(Style): Round Brilliant, Princess, Oval etc.
Cut/Polish Quality: Excellent, Very Good, Good etc.
The different measurements of the diamond, are usually included.
A certificate/ diamond number for future reference.

There are laboratories that laser engrave this reference number onto the girdle of larger stones for identification. It is only visible under proper magnification.

Very small diamonds are usually not laboratory graded/certified because the value does not justify the additional cost of grading.

Important to note: A grading certificate reflects the detail and quality of the diamond. It is not a valuation certificate. A valuation in done based on the grading, but taking other variables like local demand and exchange rates into account.

The following are grading certificates from some of the recognized grading institutions:



This one is not, and not worth the paper.


What is wrong with the grading? Well, virtually everything apart from the description of RBC (round brilliant cut) and the carat weight (if correctly done).

It is neither a proper grading certificate, nor is it of any use as a valuation document.

(This turned out to be a 0.71ct round brilliant cut, J colour, SI1 clarity stone with a good polish. Even in today’s terms the value should be around R 29 000.)

The golden rule applies: “when in doubt, don’t buy, get advice”.

(SSW Sept ’17)