AGS – American Gem Society A professional jeweller’s society which was founded in 1934. AGS has a laboratory that grades diamonds and offers diamond grading reports. AGS has a specific cut grading system for round diamonds.
AGS Cut Grading Scale 0 Ideal 1 Excellent 2 Very Good 3-4 Good 5-7 Fair 8-10 Poor
APPRAISAL A written estimate of the approximate retail replacement value of the item described. They can be used for insurance purposes and should be updated every few years.
BEZEL FACET On a round brilliant diamond, these are eight large kite-shaped facets on the crown. Also called top main facet.
BRILLIANCE Brilliance describes the reflections of white light coming from the diamond.
BRILLIANT CUT DIAMOND Round diamond with 57 facets (58 if there is a culet). Round brilliant cut diamonds are more brilliant than any of the fancy-shaped stones.
CARAT The standard unit of measurement of the weight of a diamond. One carat equals 1/5 of a gram or 1/142 of an ounce. 1 carat=100 points.
CAVITY A type of inclusion consisting of a large or deep opening in the diamond.
CLARITY The degree to which a diamond is free from blemishes/inclusions. Clarity is graded on a scale from Flawless (FL) to Imperfect (I).
CLARITY ENHANCEMENT Any process used to improve the apparent clarity of a diamond. This may include filling fractures and cavities with glass/resin.
CLEAVAGE A break in a diamond which is parallel to one of its crystallographic planes. A cleavage may be caused by inherent internal strain or by a sharp blow. The break may extend to the surface of a diamond.
CLOUD A group of tiny, white inclusions which give a “cloudy” appearance.
CROWN The part of the diamond that is above the girdle. It consists of the table and the crown facets below it.
CROWN ANGLE The angle measured between the girdle plane and the bezel facets. Along with the table size, the crown angle helps determine the amount of dispersion displayed by the diamond.
CROWN HEIGHT The part of the diamond that is above the girdle.
CROWN HEIGHT PERCENTAGE The crown height expressed as a percentage of the average girdle diameter.
CRYSTAL A type of inclusion. A crystal is a mineral deposit trapped inside the diamond.
CULET The smallest (58th) facet at the bottom of a full-cut diamond. Some diamonds do not have a culet (none or pointed is how the culet of that diamond will be described).
CUT The cut (make) of a diamond refers to the proportions given to the polished diamond by the diamond cutter. The cut is the most important of the 4Cs (cut, color, clarity, carat) in determining the diamond’s overall beauty.
DEPTH The distance between the table and the culet as measured in millimeters.
DEPTH PERCENTAGE The depth of the diamond divided by the average width.
DISPERSION The fiery, rainbow colors emanating from a diamond as white light is broken-up into colors.
EGL European Gemological Laboratory – EGL has franchises in a number of cities around the world which grade diamonds and offer a diamond grading certificate.
EYE-CLEAN In clarity-grading, eye-clean diamonds should have no inclusions that are visible through the table to the unaided eye.
FACET The polished planes on the surface of a diamond.
FEATHER A fracture in a diamond that looks like a white feather.
FIRE The rainbow colors seen in a diamond as a result of dispersion.
FLUORESCENCE The property in many diamonds that makes them glow in an environment rich in ultraviolet light. Diamonds can fluoresce in a number of colors, but generally all but blue are to be avoided. Faint to medium fluorescence is rarely detected under ordinary lighting conditions. Strong or very strong fluorescence may make a diamond appear “milky” or “oily”, especially in sunlight. Blue fluorescence may enhance the color of diamonds rated “H” in color or below (I,J, etc.) by hiding their yellow tint. Diamonds rated D-F with medium+ fluorescence may sell at a discount.
FRACTURE A chip or break on a diamond that is not in the direction of a cleavage plane. Irregular in shape, they usually appear step-like or as a splinter.
FRACTURE FILLING A diamond enhancement process whereby a cavity in a diamond is filled with an artificial substance.
GIA-GTL Gemological Institute of America Gem Trade Lab. The well-respected independent laboratory which grades diamonds and includes a diamond grading report with each diamond.
GIRDLE The outer edge of a diamond which forms a band around the stone. The girdle can be faceted, polished or unpolished
GIRDLE THICKNESS The measurement describing the percentage of the diamond’s average girdle diameter.
GRADING REPORT Sometimes called a “certificate”, although labs do not “certify” diamonds. The grading report, issued by an independent laboratory, should accurately describe the proportions, weight, color, clarity, symmetry, polish and possible fluorescence seen in the diamond being evaluated. Some labs such as GIA and AGS are felt by many experts to be more consistent and stringent in their grading than some other labs.
IGI International Gemological Institute. A laboratory which offers a grading report. IGI also produces written appraisals.
INCLUSION A naturally-occurring imperfection in a diamond. Some examples are: feathers, crystals, needles, clouds and pinpoints
LASER DRILLING A diamond enhancement technique whereby a laser is used to drill to an inclusion which is then bleached to enhance the diamond’s appearance.
LASER DRILL HOLE A tiny tube created in a diamond by laser drilling, which is often done to treat diamonds.
LENGTH-TO-WIDTH RATIO A comparison of the length and width of the girdle outline on fancy-shaped diamonds. The ratio is found by dividing the length of the diamond by the width. The width is always stated as 1. Some L to W ratios are considered to be more appealing than others, but this is a matter of personal preference. Pear 1.50 – 1.75 : 1 Marquise 1.75 – 2.25 : 1 Heart 0.98 – 1.02 : 1 Oval 1.33 – 1.66 : 1 Emerald 1.50 – 1.75 : 1 Radiant/Princess 0.95 – 1.05 : 1
LOUPE A small magnifying lens used to examine diamonds. 10x magnification is the standard.
LOWER-GIRDLE FACET The facets on the pavilion of a round brilliant just below the girdle.
MINE CUT DIAMOND An early form of the brilliant diamond with a squarish-shaped girdle, high crown, small table, deep pavilion, and very large culet.
MOHS SCALE The 10-point scale of mineral hardness. Diamond scores 10 on Mohs Scale. The diamond is the hardest of all known natural substances.
NATURAL These blemishes can be found on some polished diamonds when some of the rough is left on the diamond. This is often done so the cutter can maximize weight in a diamond.
OLD EUROPEAN CUT DIAMOND The earliest known form of brilliant cut diamond with a very small table, heavy crown and large depth.
PAVILION The portion of the diamond below the girdle.
PAVILION ANGLE The angle measured between the girdle and the pavilion main facet.
PAVILION MAIN FACET The eight facets found on the pavilion of a round brilliant diamond. Their points touch the girdle.
PINPOINTS Very small inclusions in a diamond.
POINTS 1/100th of a carat. For example, a 1/4 carat diamond weighs 25 points.
POLISH The way the cutter finishes the facets on a diamond. Labs grade finish from poor to excellent.
SCINTILLATION Sparkle. The tiny flashes of light noticeable in a diamond when the observer moves his/her head.
SHAPE There are eight common diamond shapes. They are round, marquise, pear, oval, heart, princess/radiant, emerald, and trillion. The round is the most popular (the rest are called “fancy-shaped”). There are also other shapes created and sold by manufacturers.
STAR FACET One of the eight triangular facets found on the upper crown section (next to the table) of a brilliant-cut diamond.
SYMMETRY Labs grade symmetry from poor to excellent, based on the diamond’s proportions and the relation of one facet to another (meet-point faceting).
TABLE The largest facet which sits on top of a diamond. This is where most of the light enters and exits a diamond.
TABLE PERCENTAGE The width of the table divided by the average diameter.
UPPER-GIRDLE FACET One of the 15 facets found on the lower crown portion of the diamond (abutting the girdle).