How Diamonds Are Graded

You walk into a jewelry store prepared to buy a diamond ring (or lotta bling). They all sparkle; they are all beautiful. What criteria can you use to choose one?

One important characteristic you can count on for this assessment is the grade of the diamond. Here is how the grade is determined.

The Four C’s

Gemologists have perfected a system and a scale for grading diamonds from the least to the most, as you would expect. They look at the four C’s: Color, Clarity, Carat-Weight and Cut, as well as some other characteristics. We will define each of these.

• Color – The whiter the better. Yellow diamonds are graded lower than white ones.
• Clarity – The fewer flaws the better. Visible or invisible flaws lower the value of a diamond.
• Carat-Weight – In general, the bigger the carat, the better the grade.
• Cut – An expert diamond cutter can raise the value of a stone by the cuts he chooses to make.

The Grading of Color

The people who grade diamonds generally work in a grading laboratory. The most respected laboratory in the U.S. is the GIA (Gemological Institute of America). Each laboratory has a slightly different grading system, so we will stick with GIA. Just know there are other reputable labs, but not all labs are highly thought of.

White diamonds have different colors ranging from colorless to quite yellow (we’ll save other colors for another article).

The gemologists have “master” diamonds which they use to compare a stone and decide on its color grade. The grades range from D to Z – D being completely colorless and Z being distinctly yellow. The diamond is carefully inspected to determine this grade. Grades D – F are considered Colorless; G – J diamonds are Near Colorless; K – M are Faint Yellow; N – R are Very Light Yellow; and S - Z are Light Yellow. The less color, the more costly the diamond.

The Grading of Clarity

Clarity indicates whether you can see through the diamond clearly. The more clarity, the more it costs. A diamond with no flaws, or inclusions, will get an FL (meaning flawless). A gemologist examines the faceted diamond from all angles, in good light, under a microscope or loupe to determine its clarity. The diamond cutter has already cut the diamond so as to minimize the inclusions if possible. If they can be seen with the naked eye, the stone will rank lower on the clarity scale. Here are the six primary GIA designations:

• FL – flawless
• IF – internally flawless
• VVS – very very slightly included
• VS –very slightly included
• SI – slightly included
• I – included

Within these six, there are further gradations, so you might see SI1 or SI2 on a diamond’s certificate, for example, if one accompanies the diamond.

We might add, all these grades are somewhat subjective, depending on the jeweler’s judgment.

Grading The Cut

A diamond cutter takes great care to cut the rough stone into smaller pieces and then into facets in order to maximize the gem’s value and hide flaws as best as possible. This process is undertaken with the aid of computer imaging technology nowadays (which reminds us that a great many beautifully cut diamonds were produced before the invention of the computer).

A gemologist judges the cut of the diamond based on standardized proportions known to produce the brilliance diamonds are known for. They evaluate the diameter of the round parts and the depth of the faceted stone for certain known ratios which produce the best results. The cut is graded from high brilliance to low according to the following scale:

• Excellent
• Very Good
• Good
• Fair
• Poor

You will obviously pay more for the upper end of the scale.

Carats Are Measures of Weight

Stones are weighed in grams, using a very accurate scale for that purpose. One carat weighs exactly .2 grams (200 milligrams). So if you weigh a diamond, and it is .1 grams, you know you have a half-carat diamond.

The heavier the diamond, the higher the price, everything else being equal. A larger carat diamond will be worth far more than a smaller carat one, however, because the larger carat stone is exponentially more rare.

We hope you have gained an appreciation of the job of the gemologist. When shopping for a diamond, you will be better equipped to choose wisely.