American Gem Society (AGS): An educational institution for gemological studies. The AGS Labs were created primarily to develop and promote universally-accepted standards for grading cut.
Blemish: 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.
Brilliance: 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. While other gemstones also display brilliance, none have the power to equal the extent of diamond’s light-reflecting power. 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.
Brilliant Cut: 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. It is called a brilliant cut because it is designed to maximize brilliance. Round diamonds, ovals, radiants, princesses, hearts, marquises, and pears all fall within this category of cut.
Carat: 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.
Carbon Spots: 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, rather than a white or transparent appearance, when viewed under a microscope. In most cases, these dark inclusions are not visible to the naked eye, and do not affect the brilliance of the diamond.
Cleavage: 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 in preparation for the cutting process (sawing is the other method).
Clouds: A grouping of a number of extremely tiny inclusions that are too small to be distinguishable from one another, even under magnification. The result is that, under a microscope, this grouping often looks like a soft transparent cloud inside the diamond. Of course, clouds cannot be seen with the naked eye. Usually, this sort of inclusion does not significantly impact a diamond’s clarity grade.
Color Grading: A system of grading diamond colors based on their colorlessness (for white diamonds) or their spectral hue, depth of color and purity of color (for fancy color diamonds). For white diamonds, GIA and AGS use a grading system which runs from D (totally colorless) to Z (light yellow).
Crown: 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 (on emerald cuts and other step cuts).
Crown angle: The angle at which a diamond’s bezel facets (or, on emerald cuts, the row of concentric 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 in broken up into its spectral hues, creating a beautiful play of color inside the diamond. The crown angle also helps to enhance the brilliance of a diamond.
Culet: 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. Once a diamond is set in jewelry, though, the setting itself generally provides the pavilion with sufficient protection from impact or wear. Large or extremely large culets were common in diamonds cut in the early part of this century, such as the Old European or Old Mine Cut. However, such large culets are rarely seen today. Most modern shapes have either no culet at all, or a small or very small culet.
Cut: This refers both to the proportions and finish of a polished diamond. As one of “the Four Cs” of diamond value, it is the only man-made contribution to a diamond’s beauty and value.
Depth: The height of a diamond from the culet to the table. The depth is measured in millimeters.
Depth Percentage: On a diamond grading report, you will see two different measurements of the diamond’s depth-the actual depth in millimeters (under “measurements” at the top of the report) and the depth percentage, which expresses how deep the diamond is in comparison to how wide it is. This depth percentage of a diamond is important to its brilliance and value, but it only tells part of the story. Where that depth lies is equally important to the diamond’s beauty; specifically, the pavilion should be just deep enough to allow light to bounce around inside the diamond and be reflecting out to the eye at the proper angle. Keep in mind, also, that a depth percentage that might be excessive for one diamond cut might be necessary for another type of cut. For example, a 75% or 78% depth in a princess cut diamond would be typical and quite attractive. However, a depth of even 65% would be unnecessary and even detrimental to a round diamond’s beauty.
Diamond: 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 soft black material used to make pencils).
Diamond Cutting: The method by which a rough diamond that has been mined from the earth is shaped into a finished, faceted stone. As a first step, cleaving or sawing is often used to separate the rough into smaller, more workable pieces that will each eventually become an individual polished gem. Next, bruting grinds away the edges, providing the outline shape (for example, heart, oval or round) for the gem. Faceting is done in two steps: during blocking, the table, culet, bezel and pavilion main facets are cut; afterward, the star, upper girdle and lower girdle facets are added. Once the fully faceted diamond has been inspected and improved, it is boiled in hydrochloric and sulfuric acids to remove dust and oil. The diamond is then considered a finished, polished gem.
Diamond Gauge: An instrument that is used to measure a diamond’s length, width and depth in millimeters.
Dispersion: Arranged around the table facet on the crown are several smaller facets (bezel and star facets) angled downward at varying degrees. These facets, and the angles at which they are cut, have been skillfully designed to break up white light as it hits the surface, separating it into its component spectral colors (for example, red, blue and green). This effect, which appears as a play of small flashes of color across the surface of the diamond as it is tilted, is what we refer to as the diamond’s dispersion (also called “fire”). This play of color should not be confused with a diamond’s natural body color (normally white, though sometimes yellow, brown, pink or blue in the case of fancy color diamonds) which is uniform throughout the entire diamond and is constant, regardless of whether it is being tilted or not.
Emerald Cut: A square or rectangular-shaped diamond with cut corners. On the crown, there are three concentric rows of facets arranged around the table and, on the pavilion, there are three concentric rows arranged around the culet. This type of cut is also known as a Step Cut because its broad, flat planes resemble stair steps.
Eye-Clean: An term used in the jewelry industry to describe a diamond with no blemishes or inclusions that are visible to the naked eye (i.e. a human eye which is not aided by magnifying devices such as a jeweler’s loupe or a microscope).
Facet: The smooth, flat faces on the surface of a diamond. They allow light to both enter a diamond and reflect off its surface at different angles, creating the wonderful play of color and light for which diamonds are famous.
Fancy Shape: Any diamond shape other than round.
Feathers: These are small fractures in a diamond. They are usually caused by the tremendous stress that the diamond suffered while it was growing underground. In some cases the feather both begins and ends within the diamond’s surface and, in other cases, the feather begins inside the diamond and extends to the surface. When viewed under magnification, some feathers are transparent and others have a light white appearance to them. The term “feather” comes from the fact that, under magnification, these fractures often seem to have an indistinct, feathery shape to them. While the idea of buying a diamond with “fractures” may sound scary, the reality is that, with normal wear and care, most feathers pose no risk to the diamond’s stability. Consider this: even with the feathers, these diamonds survived their growth and their journey to the surface intact. Once on the surface, they also survived the mining process, as well as the brutal stresses of the diamond cutting process. Though diamonds are certainly not invulnerable to damage, basic consideration to their care and handling during everyday wear will most likely protect them over the course of several human lifetimes.
Finish: This term refers to the qualities imparted to a diamond by the skill of the diamond cutter. The term “finish” covers every aspect of a diamond’s appearance that is not a result of the diamond’s inherent nature when it comes out of the ground. The execution of the diamond’s design, the precision of its cutting details, and the quality of its polish are all a consideration when a gemologist is grading finish. If you examine a diamond’s grading report, you will see its finish graded according to two separate categories: polish and symmetry.
Fire: See “dispersion”.
Fluorescence: An effect that is seen in some gem-quality diamonds when they are exposed to long-wave ultraviolet light
(such as the lighting frequently seen in dance clubs). Under most lighting conditions, this fluorescence is not detectable to the eye.
However, if a diamond is naturally fluorescent, it will emit a soft colored glow when held under an ultraviolet lamp or “black light.”
Fluorescence is not dangerous to the diamond or to the wearer; it is a unique and fascinating quality that occurs naturally in a number of gems and minerals.
Gemological Institute of America (GIA): Founded in 1931 by Roger Shipley, this non- profit organization upholds the highest standards for grading diamonds and other precious gems. The GIA has one of the most-respected and well-regarded gemological laboratories in the world; GIA was responsible for developing and standardizing the diamond grading system that is used today by nearly all other gem labs.
Girdle: The outer edge, or outline, of the diamond’s shape. The girdle is not graded, but rather it is described by its appearance at its thinnest and thickest points. The descriptions of girdle thickness range as follows: extremely thin; thin; medium; slightly thick; thick; extremely thick. While it is less desirable for a round diamond to display an extremely thin or extremely thick girdle, such girdle widths are more common and acceptable in fancy shapes.
For example, shapes such as pears, marquises or hearts may be cut with extremely thick girdles at their points (and at the cleft, in the case of a heart) in order to protect these delicates corners from damage. Most diamonds have smooth girdles that are fashioned by a “bruter” (a diamond cutter who is responsible for shaping the diamond’s basic outline) early on in the cutting process. In some cases, cutters go a step further and do additional cutting on the girdle. In these cases, they may decide to create a “polished” girdle or a “faceted” girdle. In both cases, the difference between these and a regular, smooth girdle is generally not distinguishable to the eye. A polished or faceted girdle doesn’t improve a diamond’s grade. Most labs grade a girdle’s thickness, not its appearance.
Heart-shape Cut: A type of fancy diamond cut, which is cut to resemble the popular Valentine’s Day shape.
Inclusion: A clarity characteristic found within a diamond. Most inclusions were created when the gem first formed in the earth.
Laser-Drill Holes: One of the few man-made inclusions that can occur inside a diamond. Why on earth would anyone want to drill holes into a perfectly good diamond? It may seem counter-intuitive, but drilling this type of hole into a diamond can actually raise its clarity grade. In some diamonds, the clarity grade may be determined mainly by the presence of just one or two dark included crystals in a diamond that is otherwise relatively free of inclusions. In certain circumstances, the diamond cutter will decide to use a procedure to remove the dark inclusions and, hopefully, increase the clarity of the diamond. First, a hole is precisely made with state-of-the-art equipment; it extends no further than it needs to, and its width is so small (about the size of a pinpoint) that a loupe or microscope is usually required to detect it. Next, a strong acid solution is forced into the new hole.
Since diamonds are resistant to acids, the solution actually dissolves the included crystal while leaving the diamond completely unharmed. The end result is a more transparent diamond. The structural stability of the diamond is not compromised in any way by this hole, and the process is permanent.
Length-to-width ratio: A comparison of how much longer a diamond is than it is wide. It is used to analyze the outline of fancy shapes only; it is never applied to round diamonds. There’s really no such thing as an ‘ideal’ ratio; it’s simply a matter of personal aesthetic preferences. For example, while many people are told that a 2 to 1 ratio is best for a marquise, most people actually tend to prefer a ratio of around 1.80 to 1 when they actually look at marquises. And though the standard accepted range for the length-to- width ratio of a marquise generally falls between 1.70 to 1 and 2.05 to 1, there are customers who insist on having ‘fatter’ marquises of about 1.60 to 1 and other customers who want longer, thinner marquises of 2.25 to 1.
Marquise Cut: A type of fancy shape diamond which is elongated with points at each end.
Naturals: Small parts of the original rough diamond’s surface which are left on the polished diamond, frequently on or near the girdle. While these are blemishes, they might also be regarded as a sign of skilled cutting; the presence of a natural reflects the cutter’s ability to design a beautiful polished gem, while still retaining as much of the original crystal’s weight as possible. In many cases, naturals do not affect the clarity grade. In most cases, they are undetectable to the naked eye.
Another type of natural is the Indented Natural; in this case, the portion of the original rough diamond’s surface which is left on the polished diamond dips slightly inward, creating an indentation. Usually, the cutter makes an effort to cut the polished diamond so that the indented natural will be confined to either the girdle or the pavilion (making it undetectable to the naked eye in the face-up position).
Oval Cut: A type of fancy shape diamond which is essentially an elongated version of a round cut.
Pavé: A style of jewelry setting in which numerous small diamonds are mounted close together to create a glistening diamond crust that covers the whole piece of jewelry and obscures the metal under it.
Pavilion: The lower portion of the diamond, below the girdle.
Pear Cut: A type of fancy shape diamond that resembles a teardrop.
Point: A unit of measurement used to describe the weight of diamonds. One point is equivalent to one-hundredth of a carat.
Polish: Refers to any blemishes on the surface of the diamond which are not significant enough to affect the clarity grade of the diamond. Examples of blemishes that might be considered as ‘polish’ characteristics are faint polishing lines and small surface nicks or scratches. Polish is regarded as an indicator of the quality of as diamond’s cut; it is graded as either Ideal, Excellent, Very Good, Good, Fair or Poor.
Princess Cut: A type of brilliant cut fancy shape that can be either square or rectangular.
Radiant Cut: A type of brilliant cut fancy shape that resembles a square or rectangle with the corners cut off.
Ratio: A comparison of how much longer a diamond is than it is wide. It is used to analyze the outline of fancy shapes only; it is never applied to round diamonds. There’s really no such thing as an ‘ideal’ ratio; it’s simply a matter of personal aesthetic preferences. For example, while many people are told that a 2 to 1 ratio is best for a marquise, most people actually tend to prefer a ratio of around 1.80 to 1 when they actually look at marquises. And though the standard accepted range for the length-to-width ratio of a marquise generally falls between 1.70 to 1 and 2.05 to 1, there are customers who insist on having ‘fatter’ marquises of about 1.60 to 1 and other customers who want longer, thinner marquises of 2.25 to 1.
Semi-mount: A jewelry setting that has the side stones already mounted, but which contains an empty set of prongs which are intended to mount a diamond center stone that the customer selects separately.
Single-cut: 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 jewelry and other jewelry that utilizes numerous small diamonds set closely together.
Step Cut: One of three styles of faceting arrangements. In this type of arrangement (named because its broad, flat planes resemble stair steps), there are three concentric rows of facets arranged around the table and, on the pavilion, there are three concentric rows arranged around the culet. Other styles of faceting arrangements include the brilliant cut (in which all facets radiate out from the center of the diamond toward its outer edges) and the mixed cut (in which either the crown or pavilion of a diamond is cut as a brilliant cut, and the other part of the diamond is cut as a step cut).
Symmetry: Refers to variations in a diamond’s symmetry. The small variations can include misalignment of facets or facets that fail to point correctly to the girdle (this misalignment is completely undetectable to the naked eye). Symmetry is regarded as an indicator of the quality of as diamond’s cut; it is graded as either Ideal, Excellent, Very Good, Good, Fair or Poor.
Table: The flat facet on the top of the diamond. It is the largest facet on a cut diamond.
Table percentage: The value which represents how the diameter of the table facet compares to the diameter of the entire diamond. So, a diamond with a 60% table has a table which is 60% as wide as the diamond’s outline. For a round diamond, gemologists calculate table percentage by dividing the diameter of the table, which is measured in millimeters (this millimeter measurement does not appear on diamond grading reports) by the average girdle diameter (an average of the first two millimeter measurements on the top left-hand side of a diamond grading report). For a fancy shape diamond, table percentage is calculated by dividing the width of the table, at the widest part of the diamond, by the millimeter width of the entire stone (this total width measurement is the second of the three millimeter values in the top left-hand corner of the diamond grading report. Contrary to popular misconception, having a small table percentage (53% to 57%) does not make a round diamond any more brilliant than a diamond with a larger table.
Trilliant Cut: A type of brilliant fancy shape that is triangular.
4Cs of Diamond Grading | Diamond Cut | Diamond Clarity | Diamond Color | Carat Weight | Diamond Certificates | Diamond Size Chart | Diamond Fluorescence | Diamond Ring Settings | Diamond Glossary
General Shapes Information | Asscher Cut Diamonds | Cushion Cut Diamonds | Emerald Cut Diamonds | Heart Shaped Diamonds | Marquise Cut Diamonds | Oval Diamonds | Pear Shaped Diamonds | Princess Cut Diamonds | Radiant Cut Diamonds | Round Brilliant Diamonds