Abrasion: Minute chipping of facet junctions which results from one diamond rubbing against another or from blows during normal wear.
American Gem Society: Founded in 1934 and commonly referred to as AGS, this laboratory believes that cut grading is the most important factor in determining a diamond's beauty. AGS utilizes a 0-10 grading system for Cut, Color, and Clarity which was originally developed by AGS and GIA founder Robert M. Shipley. Along with the GIA, the AGS Laboratories are recognized as one of the most consistently accurate diamond grading laboratories.
Blemish: Clarity characteristic confined to the surface of the diamond.
Brilliant Cut: A gem cut in the brilliant form which has fifty-eight facets: the table, thirty-two facets on the crown, twenty-four facets on the pavilion, plus the culet.
Carat Weight: The metric carat, which equals 0.200 grams is the standard unit of weight for diamonds and other gemstones. There are 100 points to a carat: 100 points = 1.0 carat.
Carbon Spot: This is a common term loosely used to refer to any black-appearing inclusion in a diamond when the stone is viewed face-up with an eye loupe. Actually, true black inclusions are rare, although occasionally particles of graphite or other very dark minerals may be seen.
Cavity, chip, or nick: Terms used to describe an opening or hole on a polished surface.
Clarity: The relative position of a diamond on a Flawless-to-Imperfect scale. Clarity characteristics are classified as inclusions (internal) or blemishes (external). The size, number, position, color, and nature of a diamond's clarity characteristics determine the clarity grade.
Cloud: Describes any hazy or "milky" area seen in a diamond.
Color: Grading color involves how much the color (or tint) of a stone varies from "colorless". Most diamonds have a trace of yellow, brown, or gray body color. The highest color rating for a diamond is "D" or colorless, with proceeding ratings or "grades" through the alphabet to "Z" where the diamond may be light yellow, light brown, or light gray.
Crown: The top portion of a diamond above the girdle. For the standard Brilliant Cut, the crown is composed of the table facet, eight bezel facets, eight star facets, and sixteen upper girdle facets.
Crown Angle: The line determining the crown angle is a straight line formed by the plane of the bezel facet.
Culet: The culet is the bottom point of a diamond, located at the base of the pavilion. It is generally described in terms as none or pointed, Very Small, Small medium, slightly large, large, very large, and extremely large. A larger culet is not desirable because it becomes visible through the table of the diamond.
Cut: "Cut" refers to the proportions and finish of a fashioned diamond. Proportion grading involves the analysis of the angles of the crown and pavilion facets, the size of the table and culet, and the overall symmetry of the stone. Finish grading is largely an evaluation of the skill and care used in fashioning a diamond.
Dark Included Crystal: An included crystal which is colored or appears black.
Deep Cut: A diamond which is cut too deep and allows light to be leak or escape through the opposite sides of the pavilion.
Depth Percent: The ratio of the depth of the diamond to its diameter.
Dispersion: See Fire.
EGL: European Gemological Laboratory USA: Commonly referred to as EGL, this company provides independent grading reports of loose diamonds utilizing the diamond grading system developed by GIA. Note: The EGL also uses an SI3 clarity category not recognized by the GIA or the AGS laboratories.
Extra Facet: Any polished surface in addition to the number of facets required for a particular cutting style and placed without regard for the stone's symmetry. Extra facets are often found around the girdle.
Face-up Position: Term used to describe the viewing of a diamond from the top view-point; the same position it will be viewed once set in an item of jewelry.
Fancy Colored Diamond: A diamond with an attractive natural body color other than light yellow, light brown, or light gray.
Feather: A term used to describe any break in a diamond (either cleavage or fracture).
Fish-Eye: The term used for a diamond with a very shallow pavilion whose girdle reflection is visible in the table when viewed face-up.
Fire: Once known as dispersion, it is the breaking up or separation of white light into spectral (rainbow) colors. See Dispersion.
Flawless: Clarity grade where diamond is free from all blemishes or inclusions when examined with a 10x loupe.
Fluorescence: Some diamonds when subjected to ultra-violet light from the sun or from a black light will emit a blue fluroescence. Generally, fluorescence is not an issue unless the intensity is described as strong, very strong, or distinct. In these instances, the diamond may appear cloudy or milky when viewed in natural daylight. Surprisingly, fluorescence is desirable in lower color grades such as J or K because the fluorescence improves the "face-up" appearance of the diamond.
Fracture Filled Diamond: A diamond which has been "filled", through a fracture or break in the diamond, with a colorless substance to improve its clarity rating.
Gemological Institute of America: Known to most jewelers as GIA, it is the educational, research, and testing center for the jewelry industry. World renowned and founded in 1931, GIA is a non-profit organization which provides professional training and other services for jewelers and gem enthusiasts.
Girdle: The girdle is the outer edge or diameter of a diamond. the girdle is rated in terms of thickness which ranges from Extremely Thin to Extremely Thick. The girdle of most diamonds are generally polished or faceted. In a few cases the girdle remains unpolished.
Hearts & Arrows Cut: One of many "branded ideal cuts". Fashioned to exacting standards, this cut produces a hearts and arrows pattern when viewed under 10x magnification from the table or pavilion.
HPHT Diamond: Short for High Pressure High Treatment. A type of "process" or enhancement treatment for diamonds which improves a diamonds color.
I1, I2, and I3: Clarity grades which describe diamonds with inclusions which are obvious when viewed under 10x and are visible to the unaided eye in the face-up position.
Ideal Cut: Also referred to as the American Ideal Cut, this diamond's symmetry is similar to those theorized by Marcel Tolkowsky, however the table can very from 53%-57%. The ideal cut diamond will have similar crown and pavilion angles and an overall depth of approximately 60%.
Included Crystal: A crystal of diamond or other mineral which is contained within a diamond.
Inclusion: Clarity characteristic penetrating into or contained within a diamond.
Internally Flawless: Clarity grade in which a diamond is free from all inclusions but may possess minor surface blemishes. Normally these stones may be made flawless by minor repolishing.
Irradiated diamond: A diamond that has been bombarded with sub-atomic particles to improve or change its color. The color is considered permanent, although in some cases it may be removed by repolishing or by high temperatures.
Laser Drill Hole: A man-made hole in the diamond resulting from laser drilling, usually tubular in appearance. Laser drilling is normally done to lighten dark inclusions.
Natural: A portion of the original crystal "skin". Naturals may be located anywhere on a stone, but usually are on or near the girdle.
Pavilion: Portion of the diamond below the diamond's girdle. For standard Brilliant Cut, it is composed of sixteen lower girdle facets, eight pavilion main facets, and the culet.
Pinpoint: A very small included crystal which ordinarily appears as a tiny white dot under 10x magnification.
Plot: Diagram which shows the schematic positioning and description of its external and internal clarity characteristics. All inclusions are plotted in red and all blemishes except extra facets are plotted in green. Extra facets and prongs on mountings are plotted in black.
Polish: Refers to the finish or final polish grading. It is largely an evaluation of the skill and care used in fashioning a diamond.
Scintillation: Term used to describe the sparkle in a diamond. Best viewed during the movement of a diamond.
Shallow Cut: A diamond which is cut too shallow and allows light to leak or escape before it can be refracted and reflected back through the table. See Spread Cut.
SI1 and SI2: Clarity grades which contain noticeable inclusions which are easily visible under 10x magnification.
SI3: Clarity grade utilized primarily by the EGL, USA. This grade describes diamonds which have inclusions which are somewhat easy to see with the naked eye in the face-up position. Neither the GIA or the AGS recognize this grade, although it is commonly used throughout the jewelry industry.
Spread or Swindled Cut: An attempt to obtain a greater spread of a diamond by reducing the proportions of the finished stone above the girdle. Generally a "spread or swindled cut" diamond has a table of 63-70%.
Symmetry: Refers to the alignment and positioning of the facets on a diamond.
Table: The largest diamond facet located on top of the stone.
Table Percentage: The ratio of the table diameter of the diamond to its overall diameter.
Tolkowsky Cut: Diamond whose symmetry is equivalent to those theorized by Marcel Tolkowsky: 53% table, 43.1% pavilion depth, with crown angles of 34-1/2 degrees, and pavilion angles of 40-3/4 degrees. Taking into consideration the width of the girdle, there would be an overall depth of approximately 60%.
Twinning Line: Indications of irregular crystal growth.
VS1 and VS2: Clarity grades which contain minor inclusions of a size, number and location between those difficult to locate and those somewhat easy to locate under 10x magnification.
VVS1 and VVS2: Clarity grades which contain minute inclusions so small or insignificant that they are difficult to locate under 10x magnification.
Well Cut Diamond: Properly proportioned diamond which allows for maximum light refraction and reflection.