A unit of metric measurement used for diamonds and colored gemstones. One carat (ct.) equals 100 points, 200 milligrams, or 1/5 of a gram. The chart below illustrates carat weights for diamonds.
|Carat||Diameter (mm)||Height (mm)|
An isolated opening that breaks the surface of a diamond or colored gemstone. For diamonds, see also Plotting Diagram.
CHEMICAL VAPOR DEPOSITION (CVD) DIAMOND
See Lab-Grown Diamond.
A shallow, jagged surface break on a diamond or colored gemstone. For diamonds, see also Plotting Diagram.
A scale that considers blemishes and inclusions, to rank diamonds from FL (flawless) to I (included). The scale is divided into 12 sub-grades, as detailed below:
FL Grade (Flawless)
(Flawless) describes diamonds in which a skilled observer does not see any inclusions or surface blemishes, after thorough examination at 10-power magnification under standardized lighting conditions.
IF Grade (Internally Flawless)
(Internally Flawless) describes diamonds that have no internal characteristics observable under the conditions described above, but that may have minor blemishes confined to the surface.
VVS Grades (Very Very Slightly Included)
(Very Very Slightly Included) describe diamonds with very, very small inclusions that are difficult for a skilled observer to see, under the conditions described above.
VS Grades (Very Slightly Included)
(Very Slightly Included) describe diamonds with very small inclusions ranging from difficult to somewhat easy to observe, under the conditions described above.
SI Grades (Slightly Included)
(Slightly Included) describe diamonds with small inclusions that are easy or very easy to see, under the conditions described above. Occasionally, inclusions in the SI category are visible to the unaided eye.
I Grades (Included)
(Included) describe diamonds with medium or large inclusions that are usually obvious to the unaided eye, under standardized lighting conditions.
A major fracture or weak point in a diamond that is breakable in certain definite planes or directions, usually due to weak molecular bonding. On an EGL USA report, it would be noted as an extended version of a feather symbol. See also Plotting Diagram.
In a diamond or colored gemstone, a cloud-like, semi-transparent area created by minute pinpoint inclusions. On EGL USA reports, it is plotted for diamonds (see also Plotting Diagram) and noted for colored gemstones.
COLOR CHANGE (CHANGE OF COLOR)
In some diamonds, known as chameleons, a phenomenon in which their color changes when exposed to certain intensities of heat or when kept in darkness for an extended period of time. In some colored gemstones, a phenomenon in which their hue appears to vary when exposed to different types of light.
See Color Grade.
An assessment of the homogeneity of color in a colored diamond, as seen through its crown. It is measured on a scale ranging from uneven to even (which is preferred).
A scale that identifies diamonds or colored diamonds according to color.
For colorless to light diamonds, color is graded on a scale from “D” (colorless) to “Z” (possessing a strong tonal modifier, such as brown, gray, green, pink, or yellow.) The chart below depicts the most typical modifier: yellow.
|N-R||Very Light Yellow|
Colored diamonds are distinguished by a combination of hue, tone, and saturation. Fancy colored diamonds are graded on a scale from fancy light to fancy vivid. Colored diamonds outside of the fancy range are rated as faint to light. While remarkable diamonds exist in many colors, natural fancy vivids are typically the most rare and valuable. The chart below depicts these variations for a yellow diamond.
For a colored diamond, the basis of its color. This can include foundations described as natural, enhanced, high pressure and high temperature (HPHT)-treated, etc.
A diamond distinguished by a combination of hue, tone, and saturation. See also Color Grade.
A diamond (also known as a blood diamond) mined to fund violent conflict and/or civil war against a legitimate government. Such mining is, typically, also linked to dire human rights abuses. Blood diamonds have originated in Africa: Angola, the Central African Republic, Côte d’Ivoire, the Democratic Republic of the Congo (DRC), Liberia, the Republic of Congo, and Sierra Leone. It should be noted, that the amount of conflict diamonds as a percentage of world diamond production has fallen dramatically, currently resting at about 4 percent. In countries where legislation is in place prohibiting the sale of conflict diamonds, the percentages are much lower. See also Kimberley Process.
The intensity of a diamond’s brightness, a ratio of the brightest pixels compared to all of the pixels in a face-up view of the stone. See also Light Performance.
The part of any faceted diamond or colored gemstone above the girdle. See also Proportions.
For a diamond or colored gemstone, a visible crystalline structure of variable transparency on the interior of the stone. This can occur naturally or as a result of a treatment, and typically serves as an identifying characteristic. On EGL USA reports, it is plotted for diamonds (see also Plotting Diagram) and noted as an identifying characteristic for colored gemstones.
The small facet polished across what would otherwise be the sharp point or tip of the pavilion of a faceted diamond or colored gemstone. This is described on a range from none (a sharp point) to extremely large (an extended, flatter surface). For diamonds, see also Proportions.
A diamond or colored gemstone shape in which the outline is square or rectangular, with rounded corners and/or bowed sides. See also Cut (Shape and Style).
CUT (SHAPE AND STYLE)
A description of the silhouette or form created by the contours and facets of a diamond or colored gemstone. Shapes vary from round to fancy cuts, such as cushion, emerald, heart, marquise, oval, pear, princess, and triangle. And style includes variations of brilliant, step, mixed, and, for colored gemstones, cabochon cuts. Beautiful stones can be found in virtually any shape or style.
A ranking based on the combined analysis of a diamond’s proportions, polish, and symmetry — factors that determine the way light interacts with the stone. On an EGL USA Cut Grade Diamond Report, most preferred stones are graded on a scale from very good to ideal to ideal plus.
DIAMOND’S NATURAL ATTRACTION (DNA)™
For diamonds, this process enhances the appearance of clarity. While the treatment is stable for normal wear, it is not considered permanent. In most cases, should damage to the treatment occur, the diamond can be repaired and its enhancement restored. EGL USA clearly identifies such stones with laser inscriptions, along with special Enhanced Diamond Reports. For diamonds, see also Plotting Diagram.
For colored gemstones — such as alexandrites, emeralds, rubies, and tourmalines — feather filling can also enhance the appearance of clarity. In addition, it can improve durability.
FL (FLAWLESS) GRADE
HEARTS & ARROWS CUT
HIGH PRESSURE AND HIGH TEMPERATURE (HPHT)
HIGH PRESSURE AND HIGH TEMPERATURE (HPHT) DIAMOND
I (INCLUDED) GRADE
IDEAL CUT DIAMOND
IF (INTERNALLY FLAWLESS) GRADE
INTERNAL LASER DRILL
INTERNAL LASER DRILLING
KIMBERLEY PROCESS (KP)
LASER DRILL HOLE
- Topaz and Beryl
SHAPE OF DIAMONDS
SI (SLIGHTLY INCLUDED) GRADE
On a diamond, chemical coatings can disguise less desirable interior hues. On a colored gemstone, coatings can improve color and overall appearance. And on a pearl, coatings can create the illusion of a smoother surface and/or enhanced luster. On an EGL USA report for any stone type, coatings are clearly noted. In addition, EGL USA does not provide color or clarity grades for coated diamonds.
See also Annealing, Feather Filling, High Pressure and High Temperature (HPHT), Irradiation, Internal Laser Drilling, Laser Drilling, and Surface Coating.
VS (VERY SLIGHTLY INCLUDED) GRADE
VVS (VERY VERY SLIGHTLY INCLUDED) GRADE