Learn thelanguage of light.

An educational institution for gemological studies. The AGS Labs were created primarily to develop and promote universally-accepted standards for grading cut.

A clarity characteristic that occurs on the surface of a diamond. Though some blemishes are inherent to the original rough diamond, most are the result of the environment the diamond has encountered since it was unearthed.

The brightness that seems to come from the very heart of a diamond. It is the effect that makes diamonds unique among all other gemstones. Brilliance is created primarily when light enters through the table, reaches the pavilion facets, and is then reflected back out through the table, where the light is most visible to your eye.

One of three styles of faceting arrangements. In this type of arrangement, all facets appear to radiate out from the center of the diamond toward its outer edges. Round diamonds, ovals, radiants, princesses, hearts, marquises, and pears all fall within this category of cut.

The unit of weight by which a diamond is measured. One carat equals 200 milligrams, or 0.2 grams. The word comes from the carob bean, whose consistent weight was used in times past to measure gemstones.

An inaccurate term used by some people in the jewelry industry to describe the appearance of certain inclusions in a diamond. The term refers to included crystals that have a dark appearance under a microscope. In most cases, these dark inclusions are not visible to the naked eye.

The propensity of crystalline minerals, such as diamond, to split in one or more directions either along or parallel to certain planes when struck by a blow. Cleavage is one of the two methods used by diamond cutters to split rough diamond crystals (sawing is the other).

A grouping of a number of extremely tiny inclusions that are too small to be distinguishable from one another, even under magnification. Under a microscope, this grouping often looks like a soft transparent cloud inside the diamond.

A system of grading diamond colours based on their colourlessness (for white diamonds) or their spectral hue, depth and purity of colour (for fancy colour diamonds). For white diamonds, GIA and AGS use a grading system which runs from D (totally colourless) to Z (light yellow).

The upper portion of a cut gemstone, which lies above the girdle. The crown consists of a table facet surrounded by either star and bezel facets (on round diamonds and most fancy cuts) or concentric rows of facets reaching from the table to the girdle.

The angle at which a diamond's bezel facets intersect the girdle plane. This gentle slope of the facets that surround the table is what helps to create the dispersion, or fire, in a diamond. White light entering at the different angles is broken up into its spectral hues.

A tiny flat facet that diamond cutters sometimes add at the bottom of a diamond's pavilion. Its purpose is to protect the tip of the pavilion from being chipped or damaged. Most modern shapes have either no culet at all, or a small or very small culet.

This refers both to the proportions and finish of a polished diamond. As one of the Four C's of diamond value, it is the only man-made contribution to a diamond's beauty and value.

The height of a diamond from the culet to the table. The depth is measured in millimetres.

On a diamond grading report, two different measurements of depth appear — actual depth in millimetres, and depth percentage, which expresses how deep the diamond is in comparison to how wide it is. This depth percentage is important to brilliance and value, but where that depth lies is equally important.

A crystal made up of 99.95% pure carbon atoms arranged in an isometric, or cubic, crystal arrangement. It is this unique arrangement of the carbon atoms that makes diamond look and behave differently from other pure carbon minerals such as graphite.

The method by which a rough diamond mined from the earth is shaped into a finished, faceted stone. Cleaving or sawing separates rough into workable pieces; bruting grinds the outline; faceting adds the table, culet, bezel and pavilion facets — followed by star, upper girdle and lower girdle facets.

An instrument that is used to measure a diamond's length, width and depth in millimetres.

Arranged around the table facet are several smaller facets angled downward at varying degrees. These facets break up white light as it hits the surface, separating it into its component spectral colours. This effect — a play of small flashes of colour across the surface — is also called fire.

A square or rectangular-shaped diamond with cut corners. On the crown, there are three concentric rows of facets arranged around the table; on the pavilion, three concentric rows around the culet. Also known as a Step Cut because its broad, flat planes resemble stair steps.

A term used in the jewellery industry to describe a diamond with no blemishes or inclusions that are visible to the naked eye — that is, a human eye unaided by magnifying devices such as a jeweller's loupe or a microscope.

The smooth, flat faces on the surface of a diamond. They allow light to enter a diamond and reflect off its surface at different angles, creating the play of colour and light for which diamonds are famous. A round brilliant has 58 facets (or 57 if there is no culet).

Any diamond shape other than round.

Small fractures in a diamond, usually caused by the tremendous stress the diamond suffered while it was growing underground. Under magnification, feathers often have an indistinct, feathery shape. With normal wear and care, most feathers pose no risk to the diamond's stability.

The qualities imparted to a diamond by the skill of the diamond cutter. Finish covers every aspect of a diamond's appearance not a result of its inherent nature out of the ground — graded according to two categories: polish and symmetry.

See dispersion. The play of small flashes of spectral colour across the surface of a diamond as it is tilted.

An effect seen in some gem-quality diamonds when exposed to long-wave ultraviolet light. If a diamond is naturally fluorescent, it will emit a soft coloured glow under an ultraviolet lamp. Fluorescence is not dangerous to the diamond or the wearer.

Founded in 1931, this non-profit organisation upholds the highest standards for grading diamonds and other precious gems. The GIA was responsible for developing and standardising the diamond grading system used today by nearly all other gem labs.

The outer edge, or outline, of the diamond's shape. The girdle is described by its appearance at its thinnest and thickest points, ranging from extremely thin to extremely thick. Pears, marquises and hearts may be cut with extremely thick girdles at their points to protect delicate corners.

A type of fancy diamond cut, shaped to resemble the popular Valentine's Day heart — combining a rounded top with a pointed base.

A clarity characteristic found within a diamond. Most inclusions were created when the gem first formed in the earth — small mineral crystals or structural anomalies that survived from the diamond's birth.

One of the few man-made inclusions inside a diamond. A precise hole is made with state-of-the-art equipment; a strong acid solution is then forced into it, dissolving dark crystal inclusions and leaving the diamond clearer. The structural stability is not compromised.

A comparison of how much longer a diamond is than it is wide. Used to analyse the outline of fancy shapes only — never applied to round diamonds. Standard marquise ratios fall between 1.70 to 1 and 2.05 to 1.

A type of fancy shape diamond which is elongated with points at each end — also called a navette, after the French word for boat.

Small parts of the original rough diamond's surface left on the polished diamond, frequently on or near the girdle. While these are blemishes, they may also be regarded as a sign of skilled cutting — reflecting the cutter's ability to retain as much of the original crystal's weight as possible.

A type of fancy shape diamond which is essentially an elongated version of a round cut — combining the brilliance of round with a flattering elongated outline.

A style of jewellery setting in which numerous small diamonds are mounted close together to create a glistening diamond crust that covers the whole piece of jewellery and obscures the metal under it.

The lower portion of the diamond, below the girdle — the cone-shaped section that ends at the culet (or point).

A type of fancy shape diamond that resembles a teardrop — round on one end, tapering to a point at the other.

A unit of measurement used to describe the weight of diamonds. One point is equivalent to one-hundredth of a carat.

Refers to any blemishes on the surface of the diamond not significant enough to affect the clarity grade. Examples include faint polishing lines, surface nicks, or scratches. Graded as Ideal, Excellent, Very Good, Good, Fair or Poor.

A type of brilliant cut fancy shape that can be either square or rectangular — combining the fire of a round brilliant with a contemporary geometric outline.

A type of brilliant cut fancy shape that resembles a square or rectangle with the corners cut off — bridging the worlds of brilliant and step cuts.

A comparison of how much longer a diamond is than it is wide. Used to analyse the outline of fancy shapes only — never applied to round diamonds. Personal aesthetic preference rather than absolute standard.

A jewellery setting that has the side stones already mounted, but contains an empty set of prongs intended to mount a diamond centre stone that the customer selects separately.

A very small round diamond with only 16 or 17 facets, instead of the normal 57 or 58 facets of a full cut round brilliant. Single cuts are occasionally used for pavé jewellery and other settings utilising numerous small diamonds set closely together.

One of three styles of faceting arrangements — named because its broad, flat planes resemble stair steps. Three concentric rows of facets are arranged around the table, and three around the culet on the pavilion.

Refers to variations in a diamond's symmetry — small variations such as misalignment of facets or facets that fail to point correctly to the girdle (completely undetectable to the naked eye). Graded as Ideal, Excellent, Very Good, Good, Fair or Poor.

The flat facet on the top of the diamond. It is the largest facet on a cut diamond — the principal window through which light enters and exits the stone.

The value which represents how the diameter of the table facet compares to the diameter of the entire diamond. A diamond with a 60% table has a table 60% as wide as the diamond's outline. Contrary to popular misconception, a small table percentage does not make a round diamond more brilliant than a diamond with a larger table.