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Diamond Glossary

American Gem Society (AGS): Established in 1934 by Robert M.Shipley and a small group of independent jewelers. Its aim is to establish a high standard of business ethics, professionalism and consumer protection in the jewelry industry. AGS labs provide internationally recognized grading reports.

Blemish: Under Clarity grading blemish refers to unique diamond birthmarks that are found externally of a cut diamond. Blemish also includes marks that have been made during cutting and polishing or even nicks, abrasions or scratches which occur while wearing.

,: Refers to the reflected light that comes out of the diamond after internal reflection. Diamonds have one of the highest reflective indexes, therefore no other gemstones can compare to the brilliance of a diamond.

Brilliant Cut: Diamonds (or any gemstones) with this particular type of cut have numerous facets, the traditional brilliant cut creates 57 facets on a diamond. If an additional cut, called the culet, is included a brilliant cut has 58 facets. This cut is specifically designed to bring out exceptional brilliance in a diamond by maximizing light output through the crown or more particularly the table of the diamond.

Carat: The metric unit used to measure the weight of all gemstones including diamonds. A Carat weighs 200 milligrams. This specific weight unit of a carat has its origins from the weight of a Carob tree seed. Carob tree seeds are small and show a very high weight consistency (200milligrams) therefore it became the standard choice for weighing precious gemstones in ancient times when there were no standardized weighing units.

Carbon Spots: These are inclusions in a diamond that gives a dark appearance. Carbon spots are not really because of carbon but due to the presence other small crystals or minerals. Carbon spots can be removed by laser drilling. This process may not reduce the value of the diamond as a diamond with eye visible carbon spot has about the same value as a clear but laser drilled diamond.

Cleavage: Due to their perfect octahedral structure, diamonds have cleavage lines along 4 planes (Isometric-hexoctahedral carbon atom arrangement). Diamonds will break cleanly along either of these planes when struck by a blow. These cleavage planes are taken advantage of by diamond cutters to create facets in the diamond.

Clouds: Microscopic inclusions that are found grouped together which are too fine to be distinguished individually. They appear like soft clouds inside the diamond. These clouds are visible only under magnification and they do not cause any discernable impact on the Clarity grading.

Color Grading: A grading system developed to grade the color of diamonds. For non fancy diamond colors, the grading ranges from Colorless to Light yellow. Color grade rating was developed by GIA and is internationally recognized. They run from D (completely colorless) to Z (light yellow). Fancy colored diamonds come under a separate grading system.

Crown: Defined as the top portion of a cut diamond, it lies above the girdle and consists of the table and surrounding facets below it. The crown generally is the most visible portion of the diamond.

Crown angle: This is the angle made by the crown facets surface and the girdle plane. The crown angle is responsible for dispersing light entering the diamond and its angle of exit after being split into its spectral components. Therefore the crown angle plays a vital role in creating the ‘fire’ of a diamond.

Culet: A culet is a small cut made at the bottom of the pavilion. Without this culet, the pavilion would end in a sharp pointed tip which could get chipped therefore culet cut is made to prevent this chipping. Generally culet in the present day are made very small unlike earlier times where the culet were made very prominent (Old European or Old mine cut).

Cut: This refers not to the shape of the diamond (e.g. heart, round etc.) but to the design used for shaping the diamond (e.g. Brilliant cut). It is one of the most important grades in the 4Cs of a diamond grading. The cut affects three attributes of a diamond which are the fire, scintillation and brilliance of the diamond. The cut is the only value adding step that can be given to a natural diamond.

Depth: This refers to the height of the diamond measuring in millimeters from the top (table) straight down to the bottom (culet or tip of the pavilion).

Depth Percentage: The depth of the diamond divided by the width of the diamond expressed in terms of a percentage is called the depth percentage. This percentage is critical to the brilliance of a diamond as it controls the quality of internal reflection within the diamond. Each type of Cut for example a round brilliant cut or a princess cut diamond has an ideal percentage. Deviating from this ideal depth percentage can lead to reduction in the internal reflection causing the diamond to lose its brilliant allure.

Diamond: It is a mineral composed of almost pure carbon occurring in an isometric crystal lattice arrangement. It is the hardest naturally occurring substance known due to its unique carbon arrangement forming the crystal. An allotrope of diamond is the graphite which has completely different properties although it is made of the same carbon element.

Diamond cutting: It consists of five basic steps for fashioning a diamond which are marking, cleaving, sawing, girdling and faceting. Diamond cutting also involves the finishing touch of boiling it in HCL (hydrochloric acid) and sulfuric acids to clean the cut diamond. Diamond cutting is a value adding step and is responsible for the brilliance for which diamonds are known for.

Diamond gauge: It is an instrument which is use to measure the physical parameters of the diamond such as its width, length and depth. All measurements are taken in millimeters.

Dispersion: Breaking up of white light into its constituent spectrum of colors in this case by the diamond is known as dispersion. The dispersion is responsible for the fiery rainbow color of the diamond popularly termed ‘fire’. The dispersion capability of a diamond is determined by the angles at which the facets of the diamond are cut. The natural color of the diamond is not a result or cause of this dispersion and should not be confused.

Eye-clean: A common term used to describe Clarity grades where inclusions or blemishes are not visible to unaided eyes, therefore the term eye-clean. Generally diamonds that are eye-clear falls in the rating between SI – I.

Facet: The flat polished surface of a cut diamond. Facets are responsible for the brilliance that is associated with diamonds. The traditional Round brilliant cut diamond has 58 facets including the culet. Different cuts or shapes of diamonds have different facets.

Fancy shape: Apart from the Round brilliant cut other types of cuts for example Princess cut diamond, heart shape cut diamonds etc. are classified under fancy shaped diamonds.

Feathers (Glets): These are imperfections present in the diamonds and are classified under Clarity grading. Feathers are a result of the great stress that a diamond undergoes in its formation stage. Feathers are breaks or tiny fractures present within the diamond. Generally feathers do not compromise the structural integrity of the diamond and do survive normal wear unless they are very large. When view under magnification these appears feathery white and therefore derive their name ‘feather’. Treated diamonds have their feathers filled with filler that makes the feather invisible to untrained eyes.

Finish: Refers to the quality of workmanship imparted to a diamond by a cutter. It encompasses all aspects of the diamonds exterior appearances generally in terms of the precision of symmetry, design and polish of the cut diamond. A finish of a diamond does not refer to the inherent properties of the diamond. A finish grading is given on the polish and symmetry in any diamond grading report.

Fire: Look up ‘dispersion’.

Fluorescence: Generally diamonds react to ultra violet light to produce a soft glow of light (generally blue or green) called fluorescence. Light fluorescence can be desirable as it does, in some cases, hides the yellow color of the diamond, but high fluorescence does make the diamond look oily or cloudy sometimes and can be undesirable. All diamonds show varying degrees of fluorescence.

Gemological Institute of America (GIA): Established by Roger Shipley in 1931. GIA is one of the most renowned and recognized organization in the diamond industry. The GIA developed a uniform diamond grading system based on the 4Cs that has become industry standard for diamond grading.

Girdle: The widest part of the diamond which forms a narrow band is called the girdle. It separates the crown from the pavilion. Generally the girdle is where microscopic unique diamond identification numbers are etched. Girdles are classified only based on their thickness such as thick, slightly thick, medium, thin and extremely thin.

Inclusion: Under Clarity grading, inclusions refer to unique diamond birthmark that are found internally of a diamond. Inclusions are completely naturally made. Inclusions can be removed by laser drilling however doing this reduces the value of the diamond.

Laser drill holes: This is a type of diamond treatment done to increase the Clarity grading of a diamond. Laser drilling allow for making microscopic holes into the diamond to remove inclusions. Once this procedure is done a diamond is considered a treated diamond and could lose its resell value.

This procedure involves drilling a hold to reach an inclusion, once the hole is made an acid solution in poured into the drill hole to dissolve the inclusion. Diamonds do not react to acids so exposing it to acid is quite safe. Laser drill holes do affect the strength or structural integrity of the diamond.

Length to width ratio: This refers to the comparative ratio between the length and width of a diamond. This ratio is used only in fancy shaped diamonds as a way to compare between various shapes since there are not fixed standards as there is in round brilliant cut diamonds. Unlike depth percentage,  there is no ideal length to weight ratio and preferences are purely based on personal choices.

Naturals: Original parts of a diamond which are left as they are by a cutter on a finished diamond. Generally naturals are placed near the girdle. Naturals considered as blemishes under clarity grading however they tend to be regarded as signs of skilled workmanship. This is because the cutter has managed to optimize the conversion of a raw diamond into finished diamond by maintaining as much carat as possible. Generally naturals are ignored in clarity grading and they are discernable only under magnification.

Some naturals occur as Indented Naturals. Here the indenting on the surface of a rough diamond may cause the natural to remain on the surface even after polishing. These types of indented naturals are generally place by a cutter on a girdle or toward the pavilion so that it is not prominent or detectable once the diamond is set.

Pavé: A setting style where numerous small stones are set very close to each other forming a pavement like surface covering. Generally pave styling covers the metal setting completely and they tend to glisten brilliantly.

Pavilion: This is the region below the girdle and opposite the crown. A pavilion generally tapers to a pointed tip in round brilliant cut. Like the crown, pavilion angle plays and important role in the internal reflection of the diamond. The tips of the pavilion are sometimes cut to protect it from chipping. This cut is called a culet.

Point: A carat is divided into a hundred points. Therefore a point is 1/100 of a carat. The division of a carat into points is to derive much more accurate weigh measurements as even small changes in weight do carry significant cost differences.

Polish: This refers to the smoothness of the facet surfaces. On a fine polished diamond there should be no cutting wheel or burn marks. The quality of polish indicates the skill of a cutter. Polish grading ranges from Poor to Ideal. Polish grading is always mentioned in a grading report.

Ratio: See ‘length to width ratio’

Semi-mount: Generally common in rings, a semi-mount is where a jewelry has been mounted with some gemstone but there is a space left empty (generally center space) to mount a diamond selected by a customer. Multiple stones are a norm in semi-mount.

Single-cut: Traditional round diamond cuts have 57 to 58 facets, but in a single-cut the diamond it has only about 16 to 17 facets. These single cut diamonds are used as pave and therefore lesser facets allow for better pave setting.

Step Cut: It is a method for faceting diamonds. In step cut the diamond is cut to produce flat consecutive planes or rows resembling steps on a stairway. Generally step cut results in long and narrow facets which run parallel to the girdle. A common type of step cut is where three consecutive or concentric facets run around the table and three around the cutlet. Other styles of step cut faceting include the most popular brilliant cut where all the facets radiate out from center towards the edges. Apart from diamonds other gems such as emerald, topaz, amethyst use step cut.

Symmetry: This is another grade apart from the 4Cs used to grade a diamond. It is based on the uniformity of similar facets and angles between various facets. Symmetry is very important to the overall appearances of the diamond and even small misalignment of facets or in the angles can make a large impact. Symmetry grading is rated as Poor or Fair, Good, Very Good, Excellent and Ideal.

Table: The table refers to the largest facet of the diamond. Generally this facet gives the diamond its apparent size. A table is generally the most visible area of the diamond and all the facets of the diamond is arranged to optimize light coming out from the table.

Table percentage: This is value obtained in terms of percentage by dividing the width of the table by the total diameter of the diamond. These measurements are always taken in terms of millimeters, for example a table percentage of 60% implies that the diamond table width is 60% of the width of the diamond. Reduction in table percentage or a smaller table percentage (53 to 57%) does not make a round diamond more brilliant than one with a greater table percentage.


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