Your simple guide for the four Cs of diamonds — cut, color, clarity, and carat weight. After reading through this guide, you'll be ready to understand the diamond report issued by the EGS lab or any other gem lab.
Cut
The cut of a diamond — its roundness, its depth and width, the uniformity of the facets — all determine a diamond's brilliance. Many gemologists consider cut the most important diamond characteristic because even if a diamond has perfect color and clarity, a diamond with a poor cut will have dulled brilliance.
The width and depth have the greatest effect on how light travels within the diamond, and how it exits in the form of brilliance.
Too Shallow: Light is lost out the bottom causing the diamond to lose brilliance.
Too Deep: Light escapes out the sides causing the diamond to appear dark and dull.
The diamond's proportions, specifically the depth compared to the diameter, and the diameter of the table compared to the diameter of the diamond, determine how well light will reflect and refract within the diamond.
| Diameter | The width of the diamond as measured through the girdle |
| Table | The largest facet of a gemstone |
| Crown | The top portion of a diamond extending from the girdle to the table |
| Girdle | The narrow band around the widest part of a diamond |
| Pavilion | The bottom portion of a diamond, extending from the girdle to the culet |
| Culet | The facet at the tip of a gemstone. The preferred culet is not visible with the unaided eye (graded "small" or "none") |
| Depth | The height of a gemstone measured from the culet to the table |
Polish & Symmetry
Polish and symmetry are two important aspects of the cutting process. The polish grade describes the smoothness of the diamond's facets, and the symmetry grade refers to alignment of the facets. With poor polish, the surface of a facet can be dulled, and may create blurred or dulled sparkle. With poor symmetry, light can be misdirected as it enters and exits the diamond. The polish and symmetry grades are clearly listed in each diamond detail page and within the EGS diamond grading report. For the most beautiful diamond, look for a symmetry grade of ideal (ID), excellent (EX), very good (VG), good (G) or fair (F).
Diamond measurements are calculated and applied to a cut grading scale that makes it easy to understand how well each reflect light
Color
A diamond, acting as a prism, divides light into a spectrum of colors and reflect this light as colorful flashes called fire. Just as when looking through colored glass, color in a diamond will act as a filter, and will diminish the spectrum of color emitted. The less color in a diamond, the more colorful the fire, and the better the color grade.
To determine the correct color, all submitted diamonds are compared to an internationally accepted master set of stones, the color of which ranges from D, or colorless (the most sought after) to Z, the yellowest.
Other colors occur in diamonds such as brown, orange, pink, blue, etc. The most intense of these shades are determined as "Fancy" colors and referenced on the EGS Diamond Report.
| D | Absolutely colorless | The highest color grade, which is extremely rare |
| E | Colorless | Only minute traces of color can be detected by an expert gemologist. A rare diamond. |
| F | Colorless | Slight color detected by an expert gemologist, but still considered a "colorless" grade. A high-quality diamond |
| G-H | Near-colorless | Color noticeable when compared to diamonds of better grades, but these grades offer excellent value |
| I-J | Near-colorless | Color slightly detectable. An excellent value |
| K-M | Faint yellow or brown | |
| N-R | Very light yellow | |
| S-Z | Light Yellow |
Fluorescence
The visible effects of fluorescence grades of faint, inert, negligible, and medium, can only be detected by a trained gemologist. A fluorescence grade of strong or very strong can make a diamond with a near-colorless grade look even whiter yet in some instances give the diamond a slight hazy or oily appearance. Some people seek diamonds that produce this unique effect, while others definitely avoid it. The visible effects of fluorescence grades of faint, and medium, can only be detected by a trained gemologist. A fluorescence grade of strong or very strong can make a diamond with a near-colorless grade look even whiter yet in some instances give the diamond a slight hazy or oily appearance. Diamonds with a strong or very strong fluorescence are priced slightly lower than other diamonds.
Clarity
Diamonds that are absolutely clear are the most sought-after and therefore the most expensive. But many diamonds have inclusions — scratches, trace minerals or other tiny characteristics that can detract from the pure beauty of the diamond. The EGS uses the industry standards of a detailed system of rules and standards to summarize the number, location, size, and type of inclusions present in a diamond.
In order to grade the clarity of a diamond, it is necessary to observe the number and nature of any internal characteristics in the stone as well as their size and position. This analysis is carried out using the scope and a loupe 10x under the experienced eye of laboratory gemologists.
| FL, IF Diamonds | Flawless | No internal or external flaws. Internally Flawless: No internal flaws |
| VVS1, VVS2 Diamonds | Very, Very Slightly Included: | Very difficult to see inclusions under 10x magnification |
| VS1, VS2 Diamonds | Very Slightly Included | Inclusions are not typically visible to the unaided eye |
| SI1, SI2 Diamonds | Slightly Included | Inclusions are visible under 10x magnification, and may be visible with the unaided eye |
| I1, I2, I3 Diamonds | Included |
Carat
The weight of a diamond is measured in carats (ct.). It does not measure size; nor should it be confused with "karat," a measure of gold purity. A carat is 0.2 grams and there are 100 points (or 200 milligrams) per carat. With an accuracy of 1/100,000 ct, the EGS scales provide a highly precise diamond weight and this weight is specified on the Diamond Report to two decimal points.