Understanding the basics of diamond grading will enhance your buying experience and insure that you select a diamond that best fits your needs. And you don’t have to get lost in a forest of gemological details. Our guide will help you put things in perspective and focus on what is most important to you.
The “four C’s” refer to Color, Clarity, Cut and Carat. It is the combination of these four factors that determines a diamond’s performance and beauty.
1. The Carat
This is the easiest factor to understand, although there is a little wrinkle here too! Carat is a measure of weight: 5 carats = 1 gram, 1carat = 0.20 gram.
Carat weight is stated decimal terms, such that one carat is written 1.00ct. One and a half carat = 1.50ct, three quarters of a carat = 0.75ct and so on.
Diamonds under one carat are commonly talked about in terms of points which are simply percentage points of a carat (1.00ct= 100 points). So a quarter of a carat (0.25ct) is said to be 25 points, half carat is 50 points, 0.98ct is 98 points and so on. Because a carat is a unit of weight, diamonds of exactly the same carat weight can appear to be different sizes, depending on the proportions of the cut. A thicker or deeper cut will look smaller than a stone with a larger surface area or “spread”.
Rarity and value increase with diamond size- an important concept to appreciate. A 1.00ct diamond of a certain quality is far rarer than the same quality in a 0.50ct diamond. Therefore, the cost of the 1.00 is more than simply twice the cost of the 50 pointer. As a result, the per carat price of like quality diamonds increases with size.
Note: Carat is sometimes confused with Karat. Whereas carat is a measure of gemstone weight, Karat is a measure of gold purity. 24 Karat is pure gold, 14K is 14/24 pure (58.5%), 18K is 18/24 pure (75%).
2. The Clarity
Nearly every diamond contains some external blemishes or internal inclusions that can be detected with magnification. To the extent that diamonds are free of these characteristics they are more rare and valuable. Diamonds with higher clarity or purity are more expensive than diamonds with lower clarity and more imperfections. In addition to being rarer, stones with higher clarity are capable of reflecting and refracting light better.
Diamonds are graded for clarity based upon the number, size and location of these tiny inclusions. They also serve to create a very unique identifying signature for a specific diamond, much like a fingerprint.
The clarity grading system most widely used around the world is the GIA scale. Professional grading is done in controlled conditions under 10X magnification.
3. The Color
Almost all diamonds possess some degree of body color, usually yellow or brown. A small percentage of diamonds are colorless, and an even smaller number possess body color so strong that they are classified as “fancy colors”.
Color is graded on the scale developed by the GIA and is almost universally used today to classify diamonds in the world market. The normal range of this alphabetic scale starts at D (colorless) and runs through Z (light yellow or brown). Colorless stones are rarer and more valuable than stones with body color in the normal range. However, diamonds graded as fancy are analyzed differently and can be extremely valuable.
It is helpful to think of the scale in terms of grade ranges: D,E,F are considered colorless, G,H,I,J are near-colorless and lower grades are slightly tinted to lightly tinted.
Differences between color grades are extremely subtle. Professional diamond grading is done in controlled lighting conditions with the stones in table-down position, with the grader looking through the girdle of the stone in order to see the slight differences in body color. Diamonds in the near-colorless to colorless range will appear white or colorless to the eye when viewed through the table.
In addition to the increased rarity and value of colorless stones, body color also impacts the quality of light emanating from a diamond. Body color acts as a sort of filter that diminishes to an extent the pure nature of light returning to the eye. Colorless diamonds that are well-cut exhibit the best spectral display or fire.
4. The Cut
Cut is the only diamond value factor that is the result of human input. This important factor may be the most difficult to understand because it is the most technical, but gaining a basic understanding does not have to be daunting. Cut refers to the proportioning, alignment and finish of a diamond’s polished faces or facets. Proper cutting enables a diamond to perform at its best and release its full potential for fire and brilliance. A well cut diamond will be more beautiful and more valuable than a poorly cut stone.
In addition, a cutter will usually have to sacrifice more of the rough stone to produce a well cut finished stone, thereby ending up with a smaller diamond than had he taken liberties with the cut. Well cut stones therefore yield less weight from the rough and are therefore more expensive to produce.
Fire, Brilliance and Scintillation
These are the three aspects of diamond performance and they are distinct elements.
Fire refers to a diamond’s ability to act as a prism and to break white light into its spectral colors. Diamonds with good fire will exhibit little sparks of red, green, yellow and blue as light refracts through and out of the stone to the eye.
Brilliance is the total amount of light returned to the eye and results in the overall brightness of the stone.
Scintillation is the sparkle of the diamond and is determined by the cutting style and execution of the cut.
The quality of a diamond’s cut is a complicated interaction of proportions and finishing factors. Many combinations can result in beautiful finished stones. Because the above mentioned performance elements are distinct, it is possible for the cutter to make tradeoffs in the process. For instance, making the table facet a little larger may make the stone slightly more brilliant and slightly less fiery. So while there are cut guidelines, in the end beauty is in the eye of the beholder.
The cut grade as determined by the GIA is Excellent, Very Good, Good, Fair and Poor.
Note: The word cut is also used in reference to a diamond’s shape – round cut, marquise cut, princess cut, etc. It is less confusing to restrict the term cut to a discussion of the proportions, alignment and finish of a polished diamond.
Polish refers to the degree of smoothness of each facet of a diamond as measured by a gemologist. When a diamond is cut and polished, microscopic surface defects may be created by the polishing wheel as it drags tiny dislodged crystals across the diamond’s surface. The polish grade as determined by the GIA is Excellent, Very Good, Good, Fair and Poor.
Symmetry refers to how precisely the various facets of a diamond align and intersect. This can include extra or misshapen facets, off center culets and tables, and wavy girdles. The symmetry grade as determined by the GIA is Excellent, Very Good, Good, Fair and Poor.
Fluorescence refers to a diamond’s tendency to emit a soft colored glow when subjected to ultraviolet light (UV). Fluorescence can occur in different intensities. Gemological laboratories rate the fluorescence of each diamond on a scale: None, Faint, Medium and Very Strong.
Because the fluorescent glow is usually blue (the complementary color to yellow), fluorescence can make lower color diamonds appear up to one grade whiter.
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