Outside of the 4 Cs, there are several other diamond features that are often included in grading reports: polish, symmetry, girdle thickness, and fluorescence, among others.
However, they do not influence diamond prices to the same extent the 4 Cs do.
Below we examine the most important quality characteristics in diamond grading and take a closer look at the definitions of these features:
Diamond clarity, as its name suggests, refers to how clear a stone looks. All diamonds have some natural imperfections such as black spots, lines, surface blemishes, etc.
The smaller, fewer, and less visible such flaws are in a stone, the higher its clarity grade.
Diamonds of poor clarity have imperfections that are easily visible with the naked eye, while high-clarity stones look fairly clean, even when seen under magnification.
Color is one of the most important quality characteristics of a diamond. Diamond color is graded according to whether there are any tints in the stone that make it look less colorless as well as how easy it is to see them.
Diamonds with a top color grade have no additional hues and appear perfectly white. The lower the color grade of a stone, the easier it is to spot yellowish tints in it.
Diamond cut is another extremely important quality characteristic.
Generally, cut refers to the number, position, and shape of a stone’s facets, and cut quality is related to how proportional the key parts of a diamond are to each other.
This proportionality is usually measured by calculating ratios based on the stone’s width, length, depth, or diameter.
Certain cut proportions result in better light reflection by the diamond, maximizing its brilliance. In general, the closer a diamond’s measurements are to these proportions, the more highly the quality of its cut is graded.
The most robust cut standards that exist are those for round-cut diamonds, whereas grading scales for other cuts are not as well established.
Carat weight is a measure of how much a diamond weighs in terms of carats, and 1 carat is equal to 200 milligrams.
Although carat is not a characteristic that influences the appearance of a diamond in the same way color, clarity, and cut do, it is an important factor in diamond pricing.
In general, bigger diamonds are more expensive not just in terms of total price, but also in terms of price per carat. This makes sense – after all, bigger diamonds are much rarer to find, and that’s why they sell at a premium.
Although polish is not part of the 4 Cs and can be considered a secondary quality characteristic, it still contributes to the appearance of a diamond.
Stones with top-graded polish have a smooth surface that lets light enter the diamond easily and produce brilliance.
Diamonds with poor polish have a rough surface that obstructs light entry and thus makes the stone look less brilliant.
This quality characteristic refers to how symmetrical a diamond’s facets are as well as how well aligned the different parts of the stone are with each other.
No diamond is cut perfectly symmetrical, but asymmetry becomes a problem when there is obvious misalignment of facets or irregularity of their shape.
Fluorescence is the ability of the diamond to emit a glow (usually blue) when exposed to UV light.
Diamond reports usually include information on whether a stone exhibits fluorescence as well as how strong it is.
The girdle of a diamond is actually its edge, or the widest part of the stone (in round cuts). The way the girdle is usually graded is by simply stating how thick or thin it is.
In general, girdles that are too thin are undesirable as they can get chipped easily. Extremely thick girdles are also problematic because they can make the stone look disproportional.
The culet is the facet at the bottom of a diamond and is especially common in round cuts. A diamond can have a culet, or it can have none, in which case the stone’s bottom will simply be pointed.
Diamonds with no culets can be at an increased risk of chipping at the bottom, unless it is well protected by the setting.
While some jewelers argue that having a culet is more desirable, if the culet is relatively big, it could be too visible through the stone’s top.