Learn: Diamonds > Index

O4C’s – The four Cs of diamonds are Cut, Color, Clarity and Carat.
60 60 – Round diamonds proportioned with tables of approximately 60 percent combined with depth percentage of approximately 60 percent. The 60/60 combination generally favors white light return over fire.

A

ABRASION – An area of unpolished surface usually seen at a facet junction as a result of wear.
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 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.
APPRAISAL – 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 few years.
ARTISANAL MINING – Rudimentary digging at the surface of alluvial deposits using simple tools. Artisanal diggers are vulnerable to those who would prey on them. Resolve.com is an NGO’s helping artisanal miners.
ASET – Angular Spectrum Evaluation Tool. A simple hand-held reflector device can be used to assess light return, contrast and leakage in loose diamonds and diamonds set in jewelry. Developed as the basis of the AGS light performance cut grading system.
ASSCHER – Eight sided square step emerald cut with large corners.
AZIMUTH – A measurement of the direction that a facet is facing in compass terms.

B

BAGUETTE –  Long stick like (French bread) step cut tapered or rectangular.
BEARDED GIRDLE – A series of tiny feathers at the girdle that can result from the cutting process.
BEZEL – Crown facets.
BLOCKING – Faceting the 8 main facets on the crown and the pavilion.
BRANDED DIAMONDS – Proprietary branded cuts that feature unique facet arrangements and/or a unique set of characteristics and qualities.
BRILLIANCE – Brilliance describes the reflections of white light coming from the diamond.
BRILLIANT – Cutting style with radiating pavilion facets.
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.
BRILLIANTEERING – The process of splitting main facets on brilliant style cuts.
BRUISE – A tiny area of impact accompanied by very small, root-link feathers; typically occurs at a facet junction.

C

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.
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 be 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.
CERTIFICATE – Common term abbreviated to cert for a gemological laboratory report.
CHEVRONS – “V” shaped sets of facets on the pavilion of a princess cut
CHIP – A shallow opening caused by damage to the stone’s surface that typically occurs at the girdle, facet junction, or culet.
CLARITY – The inclusion rating of a diamond. Grading is done by AI and or trained graders and assessed at 10X magnification.
CLEAVAGE A break in a diamond that 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.
CLOUD – Areas of tightly grouped pinpoints that can be large or small and vary in density.
COATING – A thin layer of synthetic diamond or a dye to change a diamond a non-diamond material designed to cheat.
COLOUR – Colour of yellow and brown diamonds are graded D-Z in 17 steps. Was done by carefully comparing the diamond against known master sets of diamonds but these days is largely done with instruments.
CONFLICT DIAMONDS – Diamonds illicitly obtained with conflict. The Kimberley Process was instituted in 2002 to stem the flow of conflict diamonds.
CONTRAST – Varying brightness between adjoining facets and areas.
CROWN – The top portion of the diamond above the girdle.
CROWN ANGLE – The angle between the table and the girdle.
CROWN HEIGHT – The height from the girdle to the table divided by the average diameter or the width and shown as a percentage.
CRYSTAL – A mineral crystal contained in a diamond.
CUBIC ZIRCONIA (CZ) – Popular synthetic imitation diamond simulant.
CULET – The tip of the pavilion. It can be pointed or have flat facet from very small to large.
CUSHION – Square or rectangular shape with rounded corners.
CUT – Proportions, symmetry and polish quality of a polished diamond.
CVD – Chemical Vapor Deposition method to grow synthetic or LGD diamonds.

D

DEPTH – The measurement from the table to the culet represented in both millimeters and divided by the average diameter or the width and shown as a percentage.
DEPTH PERCENTAGE – The depth of the diamond divided by the average diameter or the width and shown as a percentage.
DIAMCALC – Ray tracing diamond analytics program designed by OctoNus 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 –DeBeers instrument to identify type II diamonds referred for spectral analysis as suspected synthetic or treated diamonds.
DIPLOMA OF DIAMOND TECHNOLOGY – Gemmological Association of Australia top diamond qualification.
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.

E

 

EGL – (European Gemological Laboratories) A collection of independent soft or loosely grading affiliated labs operating in several international markets.
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.
EYE-CLEAN – If the inclusions in the diamond cannot be seen with the naked eye, the diamond is considered eye clean. One definition: No visible inclusions when viewed in the face-up direction by a person with 20/20 vision from a distance of 12 inches or 30cm in normal lighting.

F

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 COLOUR – Refers to diamonds with desirable body coloUr with grading systems outside the yellow brown D-Z range.
FANCY SHAPE – Any non-round diamond is referred to as a fancy shape.
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.
FGAA – Fellow of the Gemmological Association of Australia qualified gemmologist
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.
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 colours and different strengths. About 25-30% of diamonds fluoresce, commonly blue. Can sometimes cause haziness and can remove some yellow tints.
FRACTURE – 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 artificial substance.

G

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.
GIA-GTL – Gemological Institute of America Gem Trade Lab. The well-respected independent laboratory which grades diamonds and includes a diamond grading report with each diamond.
GIRDLE – The edge usually as many small facets or in older diamonds as a frosted rough bruted surface. Thickness at the thickest part is divided by the average diameter or the width and shown as a percentage.
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.
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.
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.

H

HARDNESS – Resistance to scratching, measured on the mohs scale 1-10, with diamond being the hardest natural substance at 10.
HCA – HollowayCutAdviser.com, online tool that provides some indications of potential performance IGIbased on crown, pavilion and table sizes to screen and reject diamonds likely to have poor performance.
HEARTS AND ARROWS – Patterns that show high symmetry across a wide range of proportions as seen with a special viewer.
HELIUM – Sophisticated scanners for accurate measuring and modeling of polished and rough diamonds from OctoNus Software.
HRD – (Hoge Raad voor Diamant) Once 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.

I

IDEAL – Specific term for the top cut grade at AGSL, and general term for diamonds with the best cut quality.
IDEAL SCOPE – A simple bright pink reflector device used to assess a round diamonds cut quality by visual assessment of pink light returned, light leakage and symmetry patterns available from Ieasl-Scope.com for loose diamonds and 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.
INCLUSION – Features that are internal to the diamond or extend into the diamond from the surface, plotted in red on a lab report.
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.
IRRADIATION – Treatment technique to alter color in a diamond by bombarding it with radiation.

K

KEEL – The long thin meeting of pavilion facets on a rectangular step cut diamond.
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.
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.

L

LAB REPORT – An identification and quality analysis report from a gemological lab, often referred to as a certificate.
LASER DRILL hole – A tiny tunnel with a thread-like appearance, produced by a laser light beam or intersecting beams to change the nature of inclusions.
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 top of a diamond that leaves via the pavilion. Or light entering the pavilion and returned to the eye. A window in a diamond.
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. Pear 1.50 – 1.75 : 1 Marquise 1.75 – 2.25 : 1 Heart 0.98 – 1.02 : 1 Oval 1.33 – 1.66 : 1 Emerald 1.50 – 1.75 : 1 Radiant/Princess 0.95 – 1.05 : 1
LGD – synthetic or Lab Grown Diamonds made with HPHT or CVD.
LIGHT PERFORMANCE – The general term for a collection of diamond attributes including brilliance, brightness, fire, leakage, scintillation 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.
LOWER GIRDLE – Facet pairs that split pavilion main facets below the girdle.
LOWER-GIRDLE FACET The facets on the pavilion of a round brilliant just below the girdle.

M

MAINS – The main 3 or 4 sided facets that from the girdle to the culet. Usually 4 sided kite shaped on the crown from girdle to the table.
MARQUISE – Elongated boat or eye shaped diamond cut.
MELEE – Small diamonds used as accent diamonds, up to 0.20ct and usually bought and slaod with a small range of color and clarity grades.
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.
MOISSANITE – Synthetic moissanite is a modern diamond simulant with good hardness, dispersion and thermal conductivity that tricks CZ heat probes. Identified with a loupe as it is doubly refractive.

N

NAIL HEAD – A term referring to a diamond that is proportioned extremely deep and appears dark in the table.
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.

O

OBSCURATION (HEAD SHADOW) – light from above that is blocked by the head.
OCTONUS – A company founded at Moscow State Uni that research and develop sophisticated rough diamond planning and polished grading instruments.
OGI – OGI Systems is a manufacturer of inexpensive 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 – An oval brilliant style cut.

P

PAVÉ – The French word for cobble stones and pavement.  Small diamonds set very close to one another to create a solid field diamonds. Micro pavé is tiny diamonds set under a microscope.
PAVILION – The facets below the girdle.
PAVILION ANGLE – The angle of the main pavilion facet.
PAVILION MAIN FACET The eight facets found on the pavilion of a round brilliant diamond. Their points touch the girdle.
PEAR – Tear drop brilliant style diamond shape.
PHOSPHORESCENCE – A small percentage of fluorescent diamonds emit light for seconds or even minutes after the UV light is turned off.
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.
PLOT – A clarity diagram on Full Grading Reports and not on Dossiers. Used to identify the diamond and assist in finding the inclusions in a retail store.
POINTS – 1/100th of a carat. For example, a 1/4 carat diamond weighs 25 points.
POLISH – The adamantine polish or finish on a diamond’s facets.
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)
PRICING – Diamonds are priced based on carat weight (not size). The Rapaport Diamond Report lists values used in the trade.
PRINCESS – Square or slightly rectangular shape brilliant style facets.
PROPORTIONS – The angles of the crown, pavilion, and percentages of other parameters including the table and girdle relative to the average diameter or width of a diamond.

R

RADIANT – Square or rectangular brilliant style cut with angled corners forming an octagonal outline.
RAPAPORT – An economist who established a price guide published weekly.  The Rapaport Diamond Report lists values used in the trade.  Buyers and sellers use discounts against the prices in negotiations to simplify the complexity of remembering thousands of values.
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 – Mirror backed fakes or paste.
ROSE CUT – Flat bottomed (no pavilion) sliver of diamond with crowon facets and no table. Common in ancient jewelry and Indian formal jewels. Often foil backed.
ROUND BRILLIANT – The classic 57 facet (58 with a table).

S

SARINE – A non-contact measuring device that measures dimensions and angles of every facet of the diamond and generates a 3d STL file. Also used for planning and cutting rough diamonds.
SCINTILLATION – The flashes and contrast seen as a diamond is moved.
SCRATCH – A linear abrasion on the surface of a diamond with no apparent depth.
SHALLOW CUT – Rarely seen these days other than in triangular shapes cut from macles. Can show a Fish Eye.
SIGHT HOLDER – One of several companies who are invited to purchase rough diamonds directly from diamond miners.
SIMULANT – A fake material passed as a real  gemstone, but with different properties.
SINGLE CUT – A small round diamond with less than 57 facets. Usually only 17 and commonly used in high end Swiss watches.
SPREAD – See Weight Ratio. How big a diamond appears for its carat weight.
STAR – Triangular facets between the table and the upper girdle facets.
STEEP/DEEP – Diamonds deep pavilion angle and steep crowns that have small Spreads and often a lot of light Leakage.
STEP CUT – Rectangular and trapezoidal facets and few or no triangular facets such as Emerald cuts and baguettes.
STONTIUM TITANATE – A diamond simulant with a lot of dispersion (fire) but very soft.
SUPER IDEAL – Marketing term for Hearts and Arrows diamonds.
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.
SYMMETRY – The accuracy of facet angles and azimuths as well as precise junctions of facet meet points.
SYNTHETIC DIAMOND – Man made grown diamond with the physical and optical properties as natural diamond.

T

TABLE – The large top facet.
TABLE CUT – Ancient diamond created by rubbing two octahedral diamond crystals together to create cut tables on both.
TABLE PERCENTAGE – The width of the table is divided by the average diameter.
TOLKOWSKY – Mathematician from a diamond cutting family who calculated the ideal proportions of round diamonds in 1919.
TRANSITIONAL CUT – A rounded diamond cut evolved from old mine and old European cuts that was developed after rounding and sawing tools were invented.
TRAPEZOID – A four sided step cut used as shoulder diamonds.
TRIANGLE – Three sided step cut.
TRILLIANT – Triangle with brilliant style facets.
TRIPLE ZERO – Refers to the top cut grade and also zero cut, D and Flawless graded by the AGS Lab.
TWINNING WISP – Series of pinpoints, clouds, or crystals that forms in a diamond’s growth place; associated with crystal distortion and twinning planes.

U

UPPER GIRDLE – The pairs of triangular facets above the girdle and between the crown mains.
VIRTUAL FACET – When you look through one facet and you see two facets directing your line of sight in a different direction. This can happen over and over again making each successive facet appear smaller and smaller. Crushed ice or pinfire diamonds can have one hundred or more virtual facets. Baguettes can have less than twenty.

V

VPA – AGS software program from that displays cut information in a color coded way from an STL file from a 3D scan.

W

WEIGHT RATIO – Calculated diamond Weight to Spread. A 1.00 carat larger spread of 1.00. A 1.20ct diamond with a diameter of 6.44mm has a spread of 0.83.

X

XRT – X-ray equipment used to find large diamonds in side rocks.
XXX – GIA’s top cut quality

Y

YAG – (Yttrium Aluminum Garnet) A lab grown synthetic material that was used as an early diamond simulant.