Diamond Grading

Why Purchase a Graded Diamond?
Diamond Graders
Equipment
Grading Procedure
Wet Grading

Why do I want a Graded Diamond?

Diamond grading is performed at one of the many different laboratories around the world, as well as by smaller independent and less recognized companies. The purpose is to have a professional expert examine a diamond and place it into a category which the layman can use as a guide to compare diamonds of similar qualities. In fact no two diamonds are exactly the same, but it gives a sense of reassurance of what is being purchased. Your diamond should come with a laboratory certificate indicating the cut, colour, clarity grade and the weight of your diamond. Additionally you will normally receive information relating to the proportions, blemishes, symmetry of the cut, fluorescence and other notes appertaining to your diamond.

Diamond Graders

To become a diamond grader generally takes around a year, and usually requires written as well as practical exams. However if you work for a laboratory, this period is shortened to around 6 months of intense supervised practical grading and will not require any form of examination at the end of that period. If you can't grade well, you will be out of a job!. Until recently a graders initials used to appear on the bottom of diamond reports but this is no longer practiced except from the smaller laboratories. If this is your occupation you are expected to grade around 20 diamonds a day, which does not sound like many, but if the diamonds are high grades, this represents a large work load and requires years of experience.

Equipment

The first and most important piece of equipment is the loupe (eye glass), 10 times magnification and corrected for both colour and spherical aberration. This is a defect of optical systems that arises when light striking a mirror or lens near its edge is focused at different points on the axis to the light striking near the centre, and occurs when the lens has spherical surfaces. A good lens usually costs in excess of £100. We use lenses by H G Schneider and find them to be very agreeable. Zeiss make a cheaper 10x aplanatic lens available from Rubins or the Gemmological Association in London which we use for general purpose work.
A quality microscope is also required, a little more expensive, costing £3000 upward, specifically with dark field illumination. We use the Leica stereo microscope with a cool light fibre optic feed for finding very small inclusions at higher clarity grades. We also have a video microscope to scan diamonds for our records. Good tweezers, a small jar of alcohol or distilled water, measuring equipment, paper and pencil are requisite.

Grading Procedure

To start every diamond is accurately weighed on an electronic scale to the nearest 1000 th of a carat (0.001). If a stone weighs 0.009 it is rounded up and 0.008 is rounded down. This is standard practice in accordance with diamond club rules, but in all other industries 5 is rounded up and 4 is rounded down.

Example:
Weight 2.329 carats will be reported as 2.33 carats.
Weight 2.328 carats will be reported as 2.32 carats

According to Trading Standards, jewellers are technically allowed to round up at the 2.325 carats to 2.33 carats but this is frowned upon in the trade.

The diamond is then measured in millimetres to the nearest one hundredth of a millimetre in all directions with a micrometer and the extremes noted. Accuracy to +- 0.02 is normally expected. All laboratories now use laser based measuring systems to determine diamond proportions such as OGI or Sarin systems and we favour the former for versatility.

The diamond is now bathed in alcohol and wiped with a special lint free cloth ready for colour and clarity grading.

The diamond is then preliminarily graded for colour and clarity, and then second graded in most labs. If the two graders agree the report is printed. If there is a disagreement, a third grading is required, and the majority opinion used for the report. It is usual for several graders to examine a fine diamond and only one with the lower grades.

Wet Grading

We use a technique called wet grading. To do this we mix up a detergent and distilled water solution, about 1:1000 of detergent. A small make up brush is dipped into the fleaker and then pressed against the side to remove excess water, then swiped across the diamond. This removes all the dust and grease residue from the surface. If done correctly, the water dries almost immediately, leaving a perfect window into the diamond.