In order to value your stone, a gemologist must first ascertain it’s exact grades. This is a complex process with multiple factors taken into consideration. A gemologist will start with the 4 C’s (carat weight, color, cut and clarity grade) but diamond grading does not end there. To shed some light on what the process involves, we have put together an outline of the steps typically followed.
Step 1. Identifying the Shape and Cut
Shape– a gemologist will be able to establish the shape your diamond without close inspection. The most common diamond shapes include, but are not limited to: round, princess, cushion, oval, radiant, emerald and pear. Round diamonds are the most popular and therefore typically the most valuable of diamonds shapes.
Cut grade– this refers to the proportions of the stone and how it interacts with light. A diamond’s cut directly affects the way it sparkles and shines. Cut grades range from Excellent to Poor.
Step 2: Calculating Carat Weight
Diamond weight is measured in carats (ct.), a highly precise unit of measurement equal to 1/5 of a gram.
The higher the carat weight, the larger the stone and more valuable it is. There is a chance, however, that the carat weight could change after valuation. A chip or poor cut grade, for example, would mean that the stone needs to be recut. This would result in the stone losing carat weight and value.
Step 3: Color Grade
In order to establish your stone’s color grade, a gemologist will compare it to a master set of diamonds. This contains a stone that represents each of the different color grades. They move your diamond up and down the line of already graded stones, and see where it best fits in the set. The color grades range from D-Z, with D being colorless and the most valuable, and Z being light yellow and the least valuable.
However, if the color is stronger than a Z, the diamond falls into the natural fancy colored diamond category. Here, unlike with white diamonds, the presence of color adds value.
Step 4: Clarity Grade
The clarity of your diamond refers to the flaws, or lack thereof, in a stone. Flaws are categorized as either inclusions (internal flaws) and blemishes (external flaws). These include:
- Scratches and chips: on the outside of the stone, mostly from wear
- Crystal: mineral crystal enclosed within the stone
- Cloud: group of small pinpoint sized diamond crystals
- Feather: break in a diamond
- Cavity: opening on the diamond’s surface
- Needle: needle shaped inclusion
Clarity grades range from FL to I3. A flawless diamond (FL), means that it has no inclusions, and carries the maximum value. On the other end of the scale, an I3, with the I stands for ‘included,’ will be worth significantly less.
The location of the inclusion matters when grading the diamond. If it is in the center of the stone, the diamond will receive a lower grade due to its high visibility. If it is on the side of the diamond and less visible, it’s clarity grading will not be as badly effected.
Step 5: Checking for Treatments
There are a variety of ways to treat and enhance a stone’s color and clarity. While this improves the look of a stone, it has a negative effect on value. For this reason, it is important for gemologists to establish if a diamond has been enhanced.
Color treatments include irradiation (turns a stone greenish blue), annealing (generates red, pink, purple, orange, yellow, brown, and black), and high pressure high temperature treatment (gives diamond colors a more vivid look).
Clarity treatments include fracture filling (hides cracks in the diamond), and laser drilling (involves drilling a small hole into your diamond and bleaches away the internal inclusions).
Step 6: Assessing the Condition of the Diamond
The condition of your diamond has a lot to do with how well you took care of the stone, or the jewelry that it is set into. Getting your diamond cleaned before sending it in to be valued, if it is very dirty, might be a good decision. While diamonds are one of the strongest materials on the planet, they can chip, scratch and break.
Step 7: Fluorescence
Fluorescence is a visible light that some diamonds emit when they are exposed to ultraviolet light. While most fluorescence will show up as blue, it can also in rare occasions emit a yellow, white, or orange hue. Diamonds that fluoresce lose value, as fluorescence has a tendency to make the diamond appear cloudy.