By Bryan Boyne (g.g.) , Thursday, July 21, 2016
The following information provides general definitions of common terms related to diamonds and diamond grading. The first section contains terms related to diamond anatomy along with intuitive visuals. The second section contains a list of clarity characteristics and the final section contains general diamond terms. You will find listings on cut-related terms, diamond shapes, gem labs, treatments and more -many of which have links to in-depth articles. We hope you find this glossary useful, but please feel free to contact us if you don’t find the answers you are looking for!
AZIMUTH – A measurement of the direction that facets are pointing.
BEZEL – The main crown facets.
CHEVRONS - “V” shaped sets of facets on the pavilion of a princess cut.
CROWN – The portion of the diamond above the girdle.
CROWN ANGLE – The angle created by the intersection of the girdle and bezel facet.
CROWN HEIGHT – The measurement extending from the girdle to the table.
CULET - The tip of the pavilion. It can be pointed or have an additional facet varying in size from very small to large.
DEPTH – The measurement extending from the table to the culet.
DEPTH PERCENTAGE – The depth of the diamond expressed in relation to the average diameter. (total depth/diameter)
GIRDLE – The small vertical plane around the perimeter of the diamond. It can vary in thickness and can be faceted, polished or unpolished.
KEEL – The equivalent of a culet on a non-brilliant style facet arrangement, it forms a line on the bottom of the pavilion, rather than a point.
LOWER GIRDLE- The pairs of facets below the girdle and between the pavilion mains.
MAINS – The main facets that normally extend from the girdle to the culet on the pavilion and from the girdle to the table on the crown. The crown mains are also called bezel facets.
PAVILION – The portion of the diamond below the girdle.
PAVILION ANGLE – The angle created by the intersection of the girdle and the main pavilion facet.
STAR – The small triangular facets between the table and the upper girdle facets.
TABLE – The largest facet on the top of the crown.
UPPER GIRDLE- The pairs of facets above the girdle and between the crown mains. (bezel facets)
Characteristics that form the basis of diamond laboratory clarity grades are divided into two types. Inclusions are features that are internal to the diamond or extend into the diamond from the surface. Inclusions are plotted in red on a lab report. Blemishes are features that are confined to the surface of the diamond such as abrasions, scratches, and bruises. Blemishes are plotted in green on a lab report.
ABRASION - An area of unpolished surface usually seen at a facet junction as a result of wear.
BEARDED GIRDLE - A series of tiny feathers at the girdle that can result from the cutting process.
BRUISE - A tiny area of impact accompanied by very small, root-link feathers; typically occurs at a facet junction.
CARBON - A layman’s term, it refers to a black inclusion, sometimes called a carbon spot. It is typically a dark crystal or group of crystals and may not actually composed of carbon.
CAVITY - An angular opening created when part of a feather breaks away or when a surface-reaching crystal drops out or is forced out during polishing.
CHIP - A shallow opening caused by damage to the stone’s surface that typically occurs at the girdle, facet junction, or culet.
CLOUD - Many tightly grouped pinpoints that might be too small to distinguish individually but together have a hazy appearance.
CRYSTAL - A mineral crystal contained in a diamond.
ETCHED CHANNEL - A rare characteristic resulting in a void caused by a dissolution event sometime during a diamond’s formation. A trigon is a form of etching.
EXTRA FACET - An additional facet usually put on to remove an inclusion close to the surface or to repair a minor issue.
FEATHER - A common clarity feature caused by a slight separation in the crystal lattice of the diamond. General trade term for a break in a gemstone, often white and feathery in appearance.
GRAIN CENTER - A small, concentrated area of crystal distortion; can be white or dark, and might have a thread-like or pinpoint-like appearance.
GRAINING - Optical discontinuities that are observable with a 10x loupe or a standard gemological microscope. They can be internal or appear on the facet surface, colored or reflective.
INDENTED NATURAL -A portion of the rough diamond’s original surface that dips below a polished diamond’s surface.
INSCRIPTION - Laser inscribed numbers and/or letters, usually corresponding to a lab report number.
INTERNAL GRAINING -Lines, angles, or curves that might appear whitish, colored, or reflective, or affect transparency at 10X; caused by irregularities in crystal growth.
KNOT - An included crystal that comes to surface and is polished as part of the facet. The outline of the crystal can usually be seen under magnification at the surface.
LASER DRILL (hole) - A tiny surface-reaching tunnel with a thread-like appearance, produced by a laser light beam.
NATURAL - A piece of the rough diamond crystal that is left on the stone, usually to save weight and usually at the girdle.
NEEDLE - A thin, elongated crystal that looks like a tiny rod at 10X.
NICK - Like a chip but smaller with no apparent depth.
PINPOINT - A very tiny crystal that looks like a dot at 10x.
PIT – A tiny opening that resembles a white dot with no apparent depth.
POLISH LINES – Fine parallel grooves and ridges left on a gem’s facet as a result of the polishing process.
POLISH MARK – Whitish film on the surface of a facet, caused by excessive heat during polishing. (also called a burn mark or burned facet)
SCRATCH - A linear abrasion on the surface of a diamond with no apparent depth.
SURFACE GRAINING – Grain lines seen on a facet’s surface, brought out by polishing due to differences in hardness between the layers of the grain.
TWINNING WISP - Series of pinpoints, clouds, or crystals that forms in a diamond’s growth place; associated with crystal distortion and twinning planes.
General Diamond Terms
4 Cs – The four Cs of diamonds are Cut, Color, Clarity and Carat. Cost is another C that is pretty important!
60/60 DIAMONDS – Round diamonds proportioned with tables of approximately 60 degrees combined with depth percentage of approximately 60 percent. The 60/60 combination generally favors white light return over fire.
ASSCHER – Square step cut with clipped corners.
AGS 0 – The top grade in the AGS system, it usually refers to cut quality, but color and clarity are also graded on the same 0-10 scale. See also Triple Zero.
AGS GRADING SCALE – Evaluation is done on a 0-10 scale with 0 being ideal, or “zero deductions”. In addition to cut quality, color and clarity are also graded on the numerical scale but the GIA equivalents are also stated on the report. See also Triple Zero.
AGSL - (American Gem Society Laboratories) A US based laboratory considered the foremost authority on diamond light performance cut grading and serving clients worldwide.
ARTISANAL MINING – Rudimentary digging at the surface of alluvial deposits by individual diggers using simple tools. Artisanal diggers are vulnerable to those who would prey on them. The Diamond Development Initiative is specifically designed to help artisanal miners.
ASET – Angular Spectrum Evaluation Tool, the graphical foundation of the AGS light performance cut grading system. A simple hand-held reflector device can be used to assess light return, contrast and leakage in loose diamonds and diamonds set in jewelry.
BAGUETTE – Very elongated (like the namesake French bread), step cut, normally used as accent stones. They can be tapered or straight.
BLOCKING – A preliminary step in diamond cutting where the basic proportions and symmetry of the diamond are established and the first 8 facets on both crown and the pavilion are placed.
BRANDED DIAMONDS – Proprietary cuts that feature unique facet arrangements and/or a unique set of characteristics and qualities. Hearts on Fire, A CUT ABOVE®, Leo, and Lucida are examples of branded diamonds.
BRILLIANCE – The effect created by light return as a result of a combination of brightness and positive contrast.
BRILLIANT – Cutting style that features vertical triangular or kite-shaped facets that radiate from the center. The round brilliant and princess cut are examples of this facet style which results in a much different ‘flavor’ than step cuts featuring prominent horizontal facets.
BRILLIANTEERING – The process of cutting the final forty facets on the diamond including the upper and lower girdle and star facets.
CARAT – A unit of weight: 1.00 carat = .20 grams. Carat weight is widely equated to diamond size, however diamonds can have exactly the same weight and significantly different dimensionality, depending on cut proportions.
CERTIFICATE – Common term for a gemological laboratory report.
CERTIFIED GEMOLOGIST (AGS) - The credential awarded to a student who has completed the GIA graduate gemology program and the AGS diamond program and is employed by an AGS member store.
CLARITY – The degree to which a diamond has internal inclusions and external blemishes. Laboratory clarity grading is done by trained graders and assessed at 10X magnification.
COATING – A thin layer of synthetic diamond over a non-diamond material designed to defeat certain types of diamond testers and/or to give a material better resistance to scratching.
COLOR – Refers to body color. Diamonds in the normal range are graded D-Z depending on how much body color they exhibit, usually yellow or brown. Laboratory color grading is done by carefully comparing the diamond against known master sets of diamonds.
CONFLICT DIAMONDS – Diamonds illicitly obtained and involved in fueling conflict between militant groups and legally established governments. The Kimberley Process was instituted in 2002 to stem the flow of conflict diamonds.
CONTRAST – The differential brightness between adjoining facets which contributes to the perception of brilliance, fire and scintillation.
CUBIC ZIRCONIA (CZ) - The most popular lab grown imitation diamond (simulant) on the market today.
CUSHION – Square to rectangular shape with rounded corners. Also known as antique cushion.
CUT – Aspects of the proportioning and polishing of the finished diamond. Light performance and beauty are impacted more by cut quality than any other aspect. Sometimes ‘cut’ is also used in reference to the shape, e.g. emerald cut.
DIAMCALC – Robust diamond analytics program designed by Octonus Software in Russia to study diamond light performance.
DIAMOND DETECTOR – An instrument designed to indicate whether a stone is a diamond or some other substance.
DIAMONDSURE – Detection device developed by DeBeers to identify natural diamonds and refer suspected synthetic or treated diamonds for further testing.
DISPERSION – The prismatic separation of white light into its individual color components as a result of refraction. The resulting colored sparkles produced by the crown are referred to as Fire.
DOSSIER – A slightly scaled down GIA document for diamonds under one carat. The report does not include a stone plot but the diamond is laser inscribed for identification purposes.
EGL – (European Gemological Laboratories) A collection of independent or loosely affiliated labs operating in several international markets.
EYE-CLEAN – If the inclusions in the diamond cannot be resolved with the naked eye, the diamond is considered eye clean. Whiteflash defines it as: no visible inclusions when viewed in the face-up direction by a person with 20/20 vision from a distance of 10 inches in normal overhead lighting.
FACET – A flat polished surface on a finished gem.
FACETWARE – Cut grade software from GIA that will give a prediction of overall cut grade based upon basic inputs from a GIA report or other source.
FACEUP APPEARANCE – The impressions the diamond makes when viewed through the table with the naked eye.
FANCY COLOR – Refers to diamonds with body color beyond the normal range (beyond Z). Fancy color diamonds have their own grading system.
FANCY SHAPE – Any non-round diamond is referred to as a fancy shape.
FIRE (DISPERSION) – colored sparkles created by refraction and the dispersion of white light into its individual components.
FISH EYE – The unappealing effect created when the girdle is seen reflected in the table at a small angle of tilt. This is the result of a shallow depth and large table.
FLUORESCENCE - When exposed to ultraviolet (UV) light, many diamonds temporarily luminesce, emitting visible light of different colors and different strengths. About 25-30% of diamonds fluoresce, usually blue. While primarily an identification characteristic, fluorescence can have impacts on diamond appearance and value that are important to understand.
FILLING – Introducing a substance into breaks in a diamond in order to improve its appearance. Fillings are not permanent and can be altered or removed by heat and ultrasonic cleaning.
FINISH – Symmetry and Polish are together considered as finish characteristics and are indicative of the care and craftsmanship of the cutter.
GGG – (Gadolinium Gallium Garnet) Followed YAG as an early lab grown simulant and preceded CZ.
GIA – (Gemological Institute of America) The most widely known and respected gemological laboratory, GIA created the grading scales for diamond color and clarity used by the international diamond trade.
GIA EXCELLENT - The top grade in the GIA cut grade system. Some equate diamonds graded GIA Excellent with ideal cuts but there are important caveats.
GRADUATE GEMOLOGIST (GIA) - The credential issued to a student who has successfully completed the entire set of courses offered by the Gemological Institute of America and passed the final exam. The credential is commonly abbreviated GG.
HARDNESS – Resistance to scratching, measured on the mohs scale 1-10, with diamond being the hardest natural substance at 10.
HCA – Holloway Cut Advisor, a simple online tool that provides some indications of potential performance based upon a few basic measurements. It is intended to be a basic screening tool to reject diamonds likely to have performance deficits.
HEARTS AND ARROWS – Patterning achieved in a round diamond through a high degree of facet precision. The level of optical precision can be assessed with a special viewer that reveals 8 hearts from pavilion view and eight arrows from table view. Often abbreviated H&A.
HELIUM – Sophisticated scanners for accurate measuring and modeling of polished and rough diamonds from Octonus Software. See also Sarine devices.
HRD – (Hoge Raad voor Diamant) Well respected gemological laboratories, established in Antwerp, Belgium with offices in several major international markets.
HTHP – High Temperature High Pressure, treatment that can improve the color of diamonds.
IDEAL – Specific term for the top cut grade at AGSL, and general term for diamonds with the best cut quality.
IDEAL SCOPE – A simple reflector device used to assess light return and light leakage. Ideal-Scope can be used to view loose diamonds as well as diamonds set into jewelry.
IGI- (International Gemological Institute) Based in Antwerp Belgium, IGI operates labs around the world, catering in particular to the large retail chains.
IRRADIATION – Treatment technique to alter color in a diamond by bombarding it with radiation.
KEYS TO SYMBOLS - Identifies the characteristics detailed on the stone plot, in order of their impact on the clarity grade.
KIMBERLY PROCESS – (KP) A chain of custody system involving the participation of governments and industry under the auspices of the United Nations designed to verify that rough diamonds entering the market are obtained from legitimate sources not involved in fueling conflict.
LAB REPORT – An identification and quality analysis report from a gemological lab, often referred to as a certificate
LASER DRILLING – Refers to laser techniques designed to improve apparent clarity by making a tiny hole in a diamond to vaporize an inclusion or to provide access for an acid which can dissolve it.
LEAKAGE- Light that enters the crown of the diamond that is not being returned to the eye. Alternatively stated, it is light that is entering the pavilion and returned to the eye. That area of the diamond is acting as a window instead of a mirror.
LIGHT MAP – A computer generated graphical display conveying information about a diamond’s light performance. Most commonly seen is the ASET map.
LIGHT PERFORMANCE- The general term for a collection of diamond attributes including brightness, fire, leakage and contrast.
LIGHT RETURN - Light entering the crown that is redirected to the eye resulting in brightness. The opposite of leakage.
LOUPE – A small magnifier used by jewelers. Standard power is 10x, but loupes are available in 15x, 20x or even higher power.
MARQUISE – Elongated brilliant style faceting with points on either end. Also sometimes referred to as navette.
MELEE – Small diamonds used as accent diamonds, up to 0.20ct but most frequently under 0.10ct
MINING – Involves three basic types of activity; in-situ heavily mechanized excavation of diamond bearing volcanic pipes, processing of marine deposits on the sea floor, and rudimentary artisanal digging around alluvial deposits.
MOISSANITE – Synthetic moissanite is a modern diamond simulant with good hardness and dispersion. It can fool the simple thermal conductivity probes used to easily detect cz and most other simulants. However, it is doubly refractive, allowing it to be identified with the trained eye.
NAIL HEAD – A term referring to a diamond that is proportioned extremely deep and appears dark in the table.
OBSCURATION (HEAD SHADOW) – When observing a diamond at close range, the light from above that is blocked by the head. A small amount of obscuration can contribute positive contrast and enhance brilliance and scintillation.
OGI – OGI Systems is a manufacturer of sophisticated diamond scanning technologies. See also Sarine and Helium.
OLD EUROPEAN – Early style round brilliant cut characterized by a small table and medium to large culet.
OLD MINE CUT –Early diamond cut characterized by a squarish outline, small table and large culet.
OPTICAL SYMMETRY – The degree of precision in the alignment of corresponding facets in 3 dimensional space. Because it is sometimes confused with the “meet point” symmetry graded on a diamond report, a better term is optical precision.
OVAL – A brilliant style cut which is elongated with rounded ends.
PAVÉ – A jewelry technique involving small diamonds set very close to one another forming a solid field of diamonds, like a road paved with stones. Micro pavé is typically done by a jeweler working under a microscope.
PEAR – Sometimes called a tear drop, it features a point on one end and rounded shape on the other with a brilliant cutting style.
PHOSPHORESCENCE – A rare property in diamonds wherein a diamond exposed to strong ultraviolet wavelengths will continue to emit light for a period of time after the light source is removed. The Hope Diamond exhibits red phosphorescence.
PLOT – A diagram that appears on most laboratory reports detailing the location and type of clarity characteristics upon which the clarity grade is based. Not all characteristics are necessarily plotted, just those required to identify the diamond and support the clarity grade.
POLISH – The degree to the cutter has achieved a mirror finish on all of the diamond’s facets.
PRICING – Diamonds are priced generally along the lines of rarity based upon size, color, clarity, and cut quality. The diamond market is highly globalized and there are pricing guidelines that are published regularly that serve as a basis for pricing in the trade.
PRINCESS – Square to slightly rectangular shape with brilliant style pavilion.
PROPORTIONS – The relationship between the crown, pavilion, table and girdle.
RADIANT – Square or rectangular cut with clipped corners forming an octagonal outline.
RAPAPORT – The wholesale pricing guide published weekly that is used within the trade to establish buying and selling prices of polished diamonds.
RAY TRACING- Computerized, mathematical analysis of the light ray paths entering and exiting a diamond depending on the proportioning and precision of the cut.
RHINESTONE (foil back) - Early imitation diamond created by backing cut glass with a reflective paint. Also sometimes referred to by the old fashion term “paste”, it has long been popular in costume jewelry.
ROSE CUT – Early diamond cut that featured a flat base (no pavilion) and triangular facets on the crown with no table facet. The appeal of the stone was in the reflections off of its facet surfaces rather than more complex light performance of later cuts.
ROUND BRILLIANT – The classic round shape with pavilion characterized by long triangular facets.
SARINE – A highly accurate non-contact measuring device that produces that provides dimensions and angles of every facet of the diamond and generates a 3d file that can be used in a variety of ways to analyze the diamond. Sometimes written Sarin- the former name of the company who manufactures this device (technically called DiaScan) and other diamond assessment technologies.
SCINTILLATION – The dynamic property commonly known as sparkle that derives from the on/off blinking of facets as the diamond, the light source or the eye of the observer moves.
SHALLOW CUT – A diamond that is proportioned so that the depth is small relative to its outer dimensions. This can cause deficits in light performance such as Fish Eye effect and other problems.
SIGHT HOLDER – One of a select number of major diamond manufacturers who are chosen to be able to purchase rough diamonds directly from the mines.
SIMULANT – A material that has a similar appearance to a gemstone, but does not have the same mineral make-up or the physical and optical properties of the stone it imitates.
SINGLE CUT – A round shape with a reduced number of facets – 9 on the crown including table, and 8 on the pavilion, with or without a facet on the culet. Common style for accent stones in older jewelry.
SPREAD – See Weight Ratio.
STEEP/DEEP – Diamonds that are proportioned with a combination of a high pavilion angle and steep crown, and which usually have light performance deficits and/or other problems.
STEP CUT- A facet arrangement featuring horizontal facets that create a series of steps, as opposed to the vertical facets seen in brilliant style arrangements. Emerald cut, Asscher, and baguettes are examples of step cuts.
STONTIUM TITANATE - An early diamond simulant that featured very high dispersion (fire) but was too soft (5.5 on the mohs scale) to be durable.
SUPER IDEAL – General term for diamonds that have the highest grade for cut quality from the lab, and also achieve levels of precision beyond those necessary to achieve the top lab grade, such as those with Hearts and Arrows patterning.
SYMMETRY – The degree of uniformity and precision with which contiguous facets are aligned. Also referred to as meet point symmetry.
SYNTHETIC DIAMOND – Laboratory grown product that has the same physical and optical properties of natural diamond.
TABLE CUT - Very early diamond cut that involved grinding off one point of an octahedral diamond crystal creating a large flat facet on top (table) with the other natural crystal faces intact.
TOLKOWSKY – Early diamond pioneer who described mathematically the ideal proportions of round diamonds in 1919. Much of his work has been validated by modern grading systems.
TRAPEZOID – A four sided step cut with two sides of uneven length. Usually used as side stones for a straight-sided center.
TRANSITIONAL CUT - A cutting style between the old mine and old European cuts that was a precursor of the modern round brilliant featuring a larger table and lower crown.
TRIANGLE – Three sided step cut.
TRILLIANT – triangular shape with brilliant style facet arrangement.
TRIPLE ZERO - Refers to the AGS Ideal cut grade. Initially it was a reference to a D Flawless Ideal cut graded on the AGS 0-10 scale. It later morphed into shorthand for an Ideal Cut with proportions 0, polish 0 and symmetry 0. Today, there is a fourth requirement for Ideal – light performance – but the certificate is still commonly referred to as Triple Zero.
VIRTUAL FACET – A diamond produces more individual sparkles than there are actual facets as a single facet can reflect light from multiple sources. These individual light events are known as virtual facets. The size, number and distribution of virtual facets is the key to light performance.
VPA – Visual Proportion Analyzer, a free software program from AGS that displays fine aspects of cut precision in a color coded graphical way. It requires as input a file from a 3D scan such as a sarine file (.srn).
WEIGHT RATIO - A calculation of diamond's overall weight in relation to its diameter. Also known as ‘spread’ it indicates the outside dimension or ‘footprint ‘ of a diamond relative to its weight. A round diamond of 1.00 carat with a diameter of 6.6mm would have its weight spread over a larger area than a 1.00 carat with a dimension of 6.4mm. Diamonds with too little spread are said to be “hiding” weight. Diamonds with too much spread can suffer from light performance deficits or other problems.
YAG – (Yttrium Aluminum Garnet) A lab grown synthetic material that was used as an early diamond simulant.