- AGS – American Gem Society
- A professional jeweler’s society founded in 1934. AGS has a laboratory which
grades diamonds and offers a diamond grading report. AGS has a cut grading
system for round diamonds.
- AGS Cut Grading Scale
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
- BEZEL FACET
On a round brilliant diamond, these are eight large kite-shaped facets on the
crown. Also called top main facet.
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.
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.
A type of inclusion consisting of a large or deep opening in the diamond.
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.
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.
A group of tiny, white inclusions which give a “cloudy” appearance.
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.
A type of inclusion. A crystal is a mineral deposit trapped inside the diamond.
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
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.
The distance between the table and the culet as measured in millimeters.
- DEPTH PERCENTAGE
The depth of the diamond divided by the average width.
The fiery, rainbow colors emanating from a diamond as white light is broken-up
European Gemological Laboratory – EGL has franchises in a number of cities
around the world which grade diamonds and offer a diamond grading certificate.
In clarity-grading, eye-clean diamonds should have no inclusions that are
visible through the table to the unaided eye.
The polished planes on the surface of a diamond.
A fracture in a diamond that looks like a white feather.
The rainbow colors seen in a diamond as a result of dispersion.
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.
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
Gemological Institute of America Gem Trade Lab. The well-respected independent
laboratory which grades diamonds and includes a diamond grading report with
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
- 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.
International Gemological Institute. A laboratory which offers a grading
report. IGI also produces written appraisals.
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
- 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.
||1.50 – 1.75 : 1
||1.75 – 2.25 : 1
||0.98 – 1.02 : 1
||1.33 – 1.66 : 1
||1.50 – 1.75 : 1
||0.95 – 1.05 : 1
A small magnifying lens used to examine diamonds. 10x magnification is the
- 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.
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
- OLD EUROPEAN CUT DIAMOND
The earliest known form of brilliant cut diamond with a very small table, heavy
crown and large depth.
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.
Very small inclusions in a diamond.
1/100th of a carat. For example, a 1/4 carat diamond weighs 25 points.
The way the cutter finishes the facets on a diamond. Labs grade finish from
poor to excellent.
Sparkle. The tiny flashes of light noticeable in a diamond when the observer
moves his/her head.
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.
Labs grade symmetry from poor to excellent, based on the diamond’s proportions
and the relation of one facet to another (meet-point faceting).
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
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