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Glossary of Terms
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
24.5 degrees The diamond proportions are designed to capture light and contain it, by not allowing the reflective angle to be less than 24.5 degrees. If within 24.5 degrees the light escapes. Also referred to as the internal critical angle.
34.5 degrees This angle was formulated as an ideal crown angle to allow the internal light a final escape route so the dispersion and scintillation can be viewed
4 Cs Color, clarity, carat weight and cut.
40.75 degrees This critical pavilion angle was formulated to reflect light by staying outside of the 24.5 degree internal critical angle. See 24.5 degrees.
A.D. Leveridge Gauge A recommended millimeter measuring gauge for measuring diamond diameters and depths. It comes with valuable weight estimation tables and formulas.
aberration See spherical aberration.
abraded facet edges See abraded facets.
abraded facets Can be caused by poor polishing by the cutter, storing diamonds improperly with other diamonds or general wear and tear in a mounting. Takes on a whitish to grayish appearance especially on facet edges. Under magnification it may look like tiny nicks.
achromatic lens One of three lenses in a triplet loupe for the purpose of correcting the chromatic aberration. See chromatic aberration.
acid boil One part nitric, two parts sulfuric is heated to boiling for the purpose of cleaning diamonds. Extreme caution is advised.
acute angle Less than 90 degrees. The more acute an angle on a diamond the higher the risk for chips and nicks.
adamant The word diamond was derived from the Greek word adamant.
adamantine luster Adamantine comes from the Greek word adamant meaning diamond. Adamantine luster means diamond-like luster. It is a property of certain gemstones, especially diamond, of very high reflectivity.
adamaund 15th century English word for diamond.
adimantum This early word for diamond likely preceded adamant.
aerial photography One of many methods for diamond prospecting, a precursor to mining.
alluvial deposits Diamond deposits affected by the forces of rivers, streams, ocean, glaciers and the wind. Many times the shape of the diamond crystal will identify it as coming from an alluvial deposit by its smoothed features. Also referred to as secondary deposits.
americium-241 A radioactive element detected in some color-treated green diamonds.
amorphous carbon A soot produced by partly-burned hydrocarbons, kerosene or natural gas.
angle of incidence Equals the angle of reflection using the reflective surface as the base of the angle. It is the incoming source of light versus the reflection being the exiting light.
angle of reflection Equals the angle of incidence using the reflective surface as the base of the angle. It is the exiting light versus the incoming being the source.
angle To achieve maximum brilliance and dispersion proper angles are prescribed. The crown angles and the pavilion angles use the plane of the girdle as an angle reference.
annealed copper stalk The copper stalk is heated and cooled to the specification of the cutter using it on the diamond cutting dop. This copper stalk method is still used by some claiming that the bending of the stalk can achieve greater accuracy in the outcome of the diamond's symmetry.
annealing See annealed copper stalk.
apatite A calcium phosphate mineral representing 5 on the Mohs Hardness Scale.
apex The point or edge of joining lines or planes cresting an angle. The girdle is the apex of the crown and pavilion. The culet is the apex of the pavilion.
aplanatic lens A lens designed to eliminate spherical aberration.
Australia A diamond producing country where lamproite is the diamond bearing igneous rock instead of kimberlite. Famous for its production of browns and pink colored diamonds.
axes Plural of axis. These are three imaginary perpendicular lines by which the cubic system is defined in diamond.
B.S.D. Abbreviation for brilliance, scintillation and dispersion.
Bahia In 1755, the location of a discovery of diamonds in the state of Brazil.
balance scale A mechanical type scale that relies on a system of counter-weights to offset the diamond in question.
Barnato Diamond Mining Company In 1873 Barnett Isaacs and his brother Harry Isaacs founded this company in Kimberly. Eventually Barnett (Isaacs) Barnato merged his company with Kimberly Central Company.
Barnato, Barney Barnett Isaacs was one of the brothers who started the Barnato Diamond Mining Company, which, after a struggle, fell under the control of Cecil Rhodes and DeBeers.
bearding Man-made inclusions caused by too much force in the bruting (girdling) process. On the surface of the girdle under magnification, it looks like tiny chips. Below the surface the chips often extend small feather-like inclusions resembling a man's beard.
Bellataire A joint company, General Electric and LKI (Lazare Kaplan, Inc.), also known as Pegasus and GEPOL (General Electric, Pegasus Overseas Ltd.) doing the color treatment process in the lightening of diamonds and color enhancing. Also see HPHT.
bellies Refers to the midsections of the elongated fancy shapes. It also refers to the bulging center pavilion facets of emerald cuts.
bench mining A mining method where they cut a slot going to the underground collection area in an open pit mine and blast the rock in the steps forcing the diamond-bearing gravel downward.
bezel A setter's term referring to a layer of metal covering the perimeter of the stone being set. This type of setting makes it difficult to measure diamond diameters accurately. Also see bezel main.
bezel main The eight primary facets on the crown of the brilliant cut diamonds. When finished they are kite shaped.
binocular microscope Versus the monocular, offers three dimensional and stereoscopic viewing to allow both of your eyes to detect the depth or a more precise location, of an inclusion.
blemish An external imperfection, in contrast to an inclusion, which is internal.
block-cave method A mining method which entails digging a cave underneath the kimberlite rock until it falls in. The crumbled gravel is more easily processed after it is funneled out into the collection areas.
blocker A diamond cutter who specializes in the first eighteen facets of the diamond. Usually this applies to production shops that have several different specialists that only complete certain stages of the polishing process.
blocking An extremely critical step in the cutting of the diamond to its first eighteen facets. This includes eight bezel (top) mains, eight pavilion (bottom) mains and the table and culet.
boart An alternate spelling for bort, a lower grade of rough diamond unsuitable for polishing.
boron An element that is sometimes found in diamonds causing blue in type 2B natural blue diamonds.
bort A lower grade of rough diamond unsuitable for polishing.
bottom halves Lower girdle facets.
Brazil This country was established as a diamond source after the first discovery in 1725.
break facets See upper girdle facets and lower girdle facets.
brilliance The richness or intensity of reflections of white light in the face-up position.
brillianteerer The diamond cutter who specializes in the last forty facets of the brilliant cut. See brillianteering.
brillianteering The last stage in cutting a brilliant which on a round is the remaining forty facets. These facets are the sixteen upper girdle facets, the sixteen lower girdle facets and eight stars. The girdle facets are sometimes called upper and lower halves.
bruise Caused by a sharp blow to the diamond's surface. Like bearding it has the appearance of tiny feathers extending into the stone.
bruted girdle Almost all elliptical shaped diamonds are bruted to achieve their shape. It is the forcing or bruting of diamond off of a stone being fashioned into its desired shape. When referring to the finished girdle it is gray versus faceted or burnished.
bruter The craftsman that specializes in the bruting, (girdling), or rounding of the elliptical shaped diamonds. See bruted girdle.
bruting See bruted girdle.
burnished girdle A polishing effect without faceting that is accomplished by letting up on the pressure of the bort (industrial diamond) on the diamond being girdled.
C.I.B.J.O. International Confederation of Jewellery, Silverware, Diamonds, Pearls and Stones.
calcite Number three on the Mohs Hardness Scale consisting of calcium carbonate.
carat A specific weight measurement for gems and diamonds in the metric system. There are •ve carats to a metric gram. Not to be confused with karat.
carbon Diamond's primary composition. A diamond made of pure carbon would be colorless.
carbon spots They do rarely occur in diamond and are usually mistaken for dark included crystals.
cavity An indentation in the stone's surface caused by the opening of an inclusion during or after the diamond has been polished.
Central Selling Organization (CSO) An organization in which all of the major diamond producers sells their diamonds on a cooperative basis.
chain balance A mechanical type of carat weight scale that incorporates a •ne chain on the counter-balance side of the scale.
chip Damage to the diamond on its surface. Usually uneven in its appearance or smooth when fractured parallel to an octahedral face. Larger than a nick.
chromatic aberration The third of three lenses is added to a triplet loupe to correct the chromatic aberration or the dispersion that doesn't allow light to all focus at the same point.
clarity enhanced See fracture filled.
clarity grade The position of a diamond's clarity grade falls on a GIA scale that ranges from flawless down to I3. The lack of or amount of inclusions and blemishes, along with size and location, designates the clarity grade.
cleavage A piece of cleavage is an octahedral face that has been cleaved off a whole crystal either by man or nature. See cleavage feather, cleavage grain.
cleavage feather Internal imperfection (inclusion) that sometimes resembles a bird's feather and runs parallel to the cleavage plane (octahedral face) of the diamond.
cleavage grain Each cleavage plane is made of three single grains. Cleavage plane should be used in place of grain for the purposes of describing the splitting or internal cleavage feathers.
cleavage plane These are the planes that parallel the eight octahedral faces. A cleaver after detecting the plane can split a diamond in these directions. See cleavage feather.
cleave To split a diamond parallel to one of its triangular octahedral faces.
cleaving The splitting of a diamond parallel to its cleavage plane. See cleavage plane.
cloud An inclusion that is generally made up of a multitude of tiny feathers or crystals. Sometimes very slight and sometimes making the diamond hazy.
coffee brown Dark brown in color grade.
cognac A more desirable color than the dark brown it shows an orange-brown mixture similar to the color of cognac.
color A large part of the value of a diamond is determined by its color. Each diamond falls into a color grade set by the GIA standard color grading scale which starts at "D" and ends at "Z" before entering the fancy color ranges. D-F is considered colorless, G-J is considered near colorless and K and below is light yellow and darker.
color grading tray Used to help determine the color grade of a diamond. The tray, sometimes called a trough, has a wedge shaped groove long enough to put several diamonds in it, including master-stones. The non-fluorescent off white surface color is included with the GIA Diamond Lite or many dealers offer paper versions. Also see master comparison stones.
color zoning Color patches that has been noted in synthetic blue diamond but does occur in natural diamonds. A term commonly used in colored stones.
color-altering-elements Elements such as nitrogen and boron reflect certain color back to our eyes. A colorless diamond is free of color-altering-elements.
colored stones Refers to gemstones that are non-diamond. Also referred to as soft stones.
conchoidal A type of fracture that is non-diamond such as glass. Resembles a shell-like smooth surface.
core samples One of the diamond prospecting methods, a precursor to mining.
corundum Ruby and sapphire which is number nine on the Mohs hardness scale.
counter-weight Used in the mechanical style carat balance scales.
critical angles The internal critical angle is the escape route of light. In order to capture light, the reflected light angle must be greater than 24.5 degrees. The pavilion's critical angle is 40.75 degrees to maximize return of internal reflected light.
crown angles See crown bezel facets.
crown bezel facets The eight main kite shaped facets on the crown (top) of the diamond. The ideal angle of the bezel facets at this writing is 34.5 degrees.
crown Consists of all the facets above the girdle (top), where the incident light enters the diamond through the table and exits as brilliance, dispersion and scintillation, out of the main bezel facets, upper girdle facets and the stars.
crown main facet See crown bezel facets.
crystal inclusion See included crystal.
crystal system Diamond is in the isometric or cubic crystal system.
CSO See Central Selling Organization.
cubic Diamond's crystal system is referred to as cubic or isometric. Cubic is often a shortened phrase for cubic zirconia a leading diamond imitation.
cubic zirconia A popular diamond imitation that is very soft and very inexpensive.
culet A protective facet at the convergence of all the pavilion (bottom) facets. When the cutter chooses not to polish a culet on the diamond, it may still be referred to as a pointed culet. A large culet is a negative characteristic since it allow unnecessary escape of light.
cut To cut a diamond can include polishing, girdling, cleaving or lasering to achieve the fashioned shape desired. The cut will also be used instead of the terms "proportions" or "make" of the diamond in question. Should not be used to replace shape of a diamond.
cutter Generally referred to someone that does one of several stages of polishing on the wheel (scaife). Can also loosely refer to a specialist who only does girdling, cleaving, sawing or lasering.
cutting position The cutter must choose the position to orient the diamond in its tang and dop to attack one of twelve single grains at a perpendicular direction. Even after the position is discovered the cutter must make sure the octahedral face that includes the single grain that he is cutting off of is pointed into the wheel. Without this direction of attack or cutting position the scaife will be scored and the diamond will not cut.
cutting wheel A cast iron wheel, used to polish diamond, that is belt or direct driven by an electric motor. Also referred to as a scaife.
cyclotron The first of the irradiation methods to emerge in the early 1940s to change or enhance the color of a diamond.
cz See cubic zirconia.
dark crystal Many times confused with carbon spot which is a rare occurrence in diamond. See crystal.
dark-field illumination The trademarked GemoLite microscope by GIA, uses bright circular light with the dark-field in the background to view diamonds and gemstones under magnification. This allows the inclusions to stand out so they may be viewed without the surface reflections.
de Beer brothers These brothers were the original owners of the farm where the South African diamond rush started in 1868. They sold the farm in 1871 for 6300 pounds.
de Beer farm See de Beer brothers.
De Beers Consolidated Mines Ltd. Officially incorporated on March 13, 1888 by the four life governors and shareholders, Rhodes, Barnato, Beit and F.S. Philipson-Stow. Their original holdings and control of the South African rough diamonds allowed them to monopolize and therefore control the price of rough by restricting supply. Today De Beers still controls a vast majority of the supply of rough diamonds all over the world.
De Beers Mining Company In 1880 Cecil Rhodes founded what was then called the De Beers Mining Company after years of aggressive claim buying. This eventually was incorporated into De Beers Consolidated Mines Ltd.
depth The depth of a diamond is usually expressed as a percentage. Ameasurement between the table and the culet is taken and divided by the narrowest diameter.
diamant One of the root words of the present day diamond spelling. Diamant is likely French in origin.
diameter Expressed in millimeters, by measuring the narrowest and the widest points from one edge of the girdle to the edge 180 degrees with a Leveridge gauge or other millimeter gauge. Most diamonds will be at least slightly out of round so these two numbers are significant for determining roundness and depth percentage.
diamond The word originated from old French, diamant. The hardest known substance on earth, in the cubic (isometric) crystal system.
diamond balance A carat scale that relies on counterweights to offset the diamond or gem's weight.
diamond cleavage See cleavage.
Diamond Corporation An organization started by Oppenheimer in 1929 to channel diamond sales through a single outlet to control stability of the market.
Diamond Producers' Association It included the large South African producers, the South African Government and the original Diamond Corporation. The members of this association have contracts with the Diamond Trading Co. and Industrial Distributors, Ltd. for the purchase and marketing of the diamonds they acquire.
diamond scribe A tool mounted with an industrial quality diamond to engrave or sometimes to test authenticity of diamond by the amount of damage it leaves on its surface.
Diamond Trading Company, Ltd. A marketing organization for the liquidation of diamonds from the Diamond Purchasing and Trading Co., Ltd.
Diamondlite A GIA/GTL trademarked color grading instrument which includes background lighting.
diamantaire An expert in diamonds and the diamond trade.
dispersion Diamond and other gemstones have the ability to refract (bend) light displaying the spectral colors of white light.
dop A cutter's holding device used while polishing diamond. The dop would be held by the tang. In some automated diamond cutting systems the dop and tang are incorporated into one design.
double refraction Some gemstones due to crystalline structure refract (bend) the entering light in two different directions. Synthetic moissanite, the popular diamond imitation, is doubly refractive. Diamond is singly refractive.
doubleering Coming from Dutch origin, it is generally an inclusion that has broken the surface and takes on a rainbow effect. Not to be confused with the flash affect of fracture filling.
doubly refractive See double refraction.
DPA See Diamond Producers'Association.
DTC See Diamond Trading Company, Ltd.
DWT See pennyweight.
dyamaund An old English word which was the precursor to the modern spelling of diamond.
electronic scale A modern day weighing device for diamonds and gemstones relying on electronic circuitry versus a mechanical balance.
elliptical cuts All of the diamond shapes made up of arcs or curves as in the round brilliant, oval, marquis and heart shape versus the straight edge shapes as in the emerald cut etc.
etch features Highly unusual but can easily be mistaken for laser drill holes. They can vary in length and usually form straight lines or step-like patterns. They are hollow and when they break the surface of a diamond the hexagonal or rectangular cross section is apparent. Etch features are easiest to pick out by their angular patterns versus the straight or slightly bent direction of the laser drill hole.
Eureka The first major diamond discovered in South Africa in 1867.
extra facet An additional facet left by the cutter due to error or weight retention. Considered a blemish.
eye-clean clarity When viewing a diamond with your naked eye the inclusions and blemishes cannot be detected even though they may be quite obvious under 10x magnification.
faceted girdle A series of facets that are polished on the girdle of the elliptical shapes. This may be done to improve the shape of an elliptical fancy shape; eliminating the gray girdle for the purpose of improving a colorless grade or a fancy color grade; to thicken an extremely thin to very thin girdle.
fancy color A color grade falling outside or beyond the D-Z range. Some of these colors can be extremely valuable especially when they are considered intense or vivid.
fancy shape All the shapes outside of the round brilliant, single cuts and old cuts. This would include the marquis, pear shape, oval, heart shape, emerald cut, radiant cut, princess cut or any of the contemporary and custom cuts.
feather A very common diamond inclusion that occurs internally as a fracture or cleavage. It often resembles a bird's feather.
feldspar Number six on the Mohs hardness scale. A group of crystalline structures that are all aluminum silicates with at least one other mineral included such as potassium, sodium, calcium or barium.
fish-eye When light travels through the girdle and reflects from a flat-angled pavilion, the image of the girdle is transmitted just inside the table. The girdle image or reflection would serve as the outer perimeter of the fish's eye and the center of the diamond would serve as the lifeless appearance of a fish's eye due to its severe lack of brilliance.
FL Abbreviation for flawless. It designates a clarity grade for the absence of blemishes and inclusions under 10x magnification.
flash effect Fracture filling is usually accompanied by the flash effect which would include shades of blue, violet, green and others. More than one of these colors may occur in a single diamond but they will clearly be separated.
Flawless See FL.
fluorescence May also be referred to as luminescence. It is the energy or light produced due to a reaction of atoms when exposed to contacting incident light. The most common color of diamond fluorescence is blue but other colors do occur such as light red, yellow, green, orange or subtle combinations of them.
fluorite Number four on the Mohs hardness scale. It consists of calcium fluoride with perfect octahedral cleavage.
focal plane Due to the curvature of the lens in a magnifier, the focal plane is inconsistent. The focus will only occur in the center of the magnified area. This spherical aberration is corrected by adding a second lens of a different curvature to correct the curvature of the first for a consistent focal plane.
four grain convergences Diamond has six four grain convergences in its granular structure. These convergences are the hardest part of a diamond due to the four single grain influences versus the softer single grain influence.
four point orientations A cutter places the table on an area where the four single grains converge. A very common orientation and it includes almost all sawed stones.
fracture Diamond's fracture is classified as uneven. The external fracture will have an appearance of unevenness or jaggedness. This fracture travels in a different direction than the cleavage. Internally it would be referred to as a feather fracture.
fracture feathers They do not follow the cleavage fracture which would be parallel to the octahedral face.
fracture filled Asilica type substance (similar to glass) is heated to a liquid state and forced under pressure into an open inclusion. When using the term "open" this can be a hairline opening to the surface. It has been established that with age or depending on the amount of light exposed to the stone, the filling will darken or discolor. The obvious flash effect is unmistakable. Shades of blue, violet, green and others give away the fracture filling. Many times the flash effect is very subtle and can be easily over- looked.
frayed facet edges Possibly wear and tear from everyday abuse in a ring but more likely the cutter has done a poor job polishing the facets. Could be caused by cutting off grain or by a wheel that has not been properly cared for.
garnet Considered a semi-precious gemstone that also occasionally occurs in diamond as an inclusion.
geiger counter A device measuring the level of radiation as in the irradiated green diamonds that have been exposed to americium-241.
Gem Trade Laboratories (GTL) These labs are operated by GIA for the purposes of grading and identification of pearls, diamonds and gemstones and supplying detailed written reports.
Gemological Institute of America A nonprofit organization for the purposes of education in diamond and gem identification. They operate Gem Trade Laboratories and Gem Instruments Corporation. Included in their many publications is the highly respected Gems and Gemology quarterly periodical.
GEPOL General Electric Pegasus Overseas Ltd. the innovators of the original HPHT treated diamonds.
Gem-scope Also referred to as GemoLite, a trademarked microscope by GIA for the purpose of viewing diamonds and gemstones under magnification. It features light and dark field illumination, stereoscopic zoom magnification, a swivel base, an adjustable baffle, a diffuser and a diaphragm.
GIA color grading system See color.
GIA origin of color See origin of color.
GIA report Technically this is a GTL (Gem Trade Laboratory) report but the GIA report term is more commonly used. This report is for the purpose of gem and diamond authentication and identification. Regarding diamonds, the reports included are diamond grading services, diamond laser inscriptions, re-examinations, report updates, report verifications, master color comparison grading and colored diamond services.
GIA See Gemological Institute of America.
girdle facets See lower girdle facets, upper girdle facets and faceted girdle.
girdle reflection See fish-eye.
girdle thickness adjustment (GTA) In weight estimation a percentage must be added or subtracted in the formula to adjust for the effect that the girdle thickness will have on the weight.
girdle thickness Judged between the upper and lower girdle facets since this is where the girdle is at its thinnest. The vast majority of stones will have a range of girdle thickness due to the slight (or obvious) inconsistencies in symmetry by the cutter. Girdle thickness is described as follows: extremely thin, very thin, thin, medium, slightly thick, thick, very thick, extremely thick or a combination thereof.
girdle This area is the entire perimeter of the diamond where the crown and pavilion meet. This would include straight edge shapes such as the emerald cut and elliptical shapes such as the round brilliant or the marquis. The girdle can be faceted, gray, or polished (burnished) and can be described as extremely thin to extremely thick with many degrees in between. It is for protective purposes by avoiding a sharp edge (extremely thin), which is apt to chip under normal wear and tear.
girdler See bruter.
girdling machine Today's girdling machine is driven by an electric motor. It is similar to a lathe for the purposes of rounding the elliptically shaped diamonds. The two major types used today are the single and double spindle machines.
girdling See bruted girdle.
glassies Rough diamond that has transparent skin. Most rough has a thicker skin which makes clarity grading more difficult. The glassie almost looks as if it were already faceted.
grain There are twelve separate grains in diamond even when not visible. These grains must always be considered by the cutter when choosing a cutting position in relationship to the wheel (scaife). Each of the eight octahedral faces are made up of three grains, which that must be taken into account by the cleaver when cleaving (splitting), the diamond.
grainer An old style term used to describe carat weight in 1/4 carat increments. A two grainer is a 1/2 carat, a 3 grainer is a 3/4 carat, etc.
graining lines Often called twinning lines, wisps and knot lines. This irregularity in the granular structure of the diamond causes the parallel lines that can be colorless or tinted in off-white or other subtle tints, that can affect the clarity of the diamond dramatically.
gram A weight increment never used to weigh diamond but for the purpose of weighing precious metals. There are five carats in a metric gram.
granular structure There are twelve grains in a diamond crystal making up eight octahedral faces in the isometric or cubic system.
graphite Composed of pure carbon like diamond, but of a different molecular arrangement, giving it very different properties.
gray girdle The edge of some elliptically-shaped diamonds where the cutter has chosen not to facet or burnish the girdle.
graying A frayed facet edge that takes on an off-white or graying tone. Usually caused by lack of care of the wheel (scaife) by the cutter during the polishing process.
grease belt Due to diamond's high affinity for grease, the grease belt is an effective method of separating the rough diamond from the crushed diamond-bearing gravel by washing it across a conveyer belt allowing the diamond to stick.
grease table A slanted rocking table that shakes the diamond-bearing gravel downward, allowing the rough diamond to adhere to the thick layer of grease. Also see grease belt.
GTA See Girdle Thickness Adjustment.
GTL report See GIA report.
GTL See Gem Trade Laboratories.
hand loupe A small hand-held magnification instrument. A folding triplet would be considered a hand loupe.
hardness Diamond is the hardest substance known to man being ten on the Mohs hardness scale. Hardness of gemstones refers to their resistance to scratching.
heart shape A facet layout similar to the round brilliant. The cleft is cut with lasers or a series of saws.
heavily spotted One grade past the I3 clarity grade of the GIA scale if compared side by side to the British clarity scale. Very imperfect.
HPHT High pressure high temperature diamond treatment used for lightening and changing color. GE POL was the innovator and first marketing company to offer this type of treated diamond product.
hue On GIA reports the lab uses up to 31 different hues. Hues are the colors you see in a rainbow or a prism. Red, green, blue, violet, orange, yellow and every combination thereof. Unless you are dealing with fancy colors, hues will not be of great importance very often, since we are dealing with primarily colorless to hues of yellow or brown.
I1 The "I" stands for imperfect in the GIA clarity grading scale. The "1" represents the •rst level of the imperfect range (before I2 and I3).
I2 The "I" stands for imperfect in the GIA clarity grading scale. The "2" represents the second level of the imperfect range before I3 and after I1.
I3 The "I" stands for imperfect in the GIA clarity grading scale. The "3" represents the third level of the imperfect range after I1 and I2.
ideal angle At this writing, the angles agreed upon for the crown are 34.5 degrees and 40.75 degrees for the pavilion (bottom). These angles are measured from the plane of the girdle.
IF Internally flawless. Under 10x magnification no inclusions can be detected. This excludes blemishes which are imperfections on the surface of the diamond.
igneous A volcanic rock as in the diamond bearing kimberlite.
included crystal More than two dozen types of mineral crystals occur in diamond but diamond crystal itself is by far the most common.
inclusion Imperfections located inside the diamond.
indented natural The original skin of the rough diamond that is at least slightly concave in relationship to the surrounding polished facets. It can be considered a blemish depending on its size and location.
independent reports Grading reports done by gem laboratories that are not in the business of selling diamonds or gems.
index plate A pointer fluctuates across the index plate until the counterweights match the weight of the stone in question on a mechanical balance scale.
industrial diamond Generally speaking it is a non-gem quality diamond that is used for tools and abrasives. Some tools require higher clarity or gem quality for better integrity in their applications.
internal containment The modern proportions are designed to capture light by not allowing it to escape until it has entered, reflected, refracted and exited out of the crown facets where it is viewed. Also see critical angles.
internal critical angle See critical angles.
internal fracture A feather that is traveling in a different direction than the cleavage plane.
internal graining See graining lines.
Internally Flawless See IF.
irradiated diamonds Artificially treated to enhance or change the color of a diamond by way of bombardment. These treatments are commonly used on diamonds that have an undesirable tint, to improve their value and salability.
isometric Also commonly called the cubic system. Diamond's crystallographic system with three equal length axes running perpendicular to one another.
JBT directory A reference book of listings of jewelry related businesses for the purposes of information and credit ratings.
JBT See Jewelers Board of Trade
Jewelers Board of Trade It is a credit rating and information agency for the industry.
Kaplan See LKI.
karat Specifically relates to the purity of gold. 24K is pure. Not to be confused with carat, a weight measurement for gems.
kerf A cleaver brutes a groove in diamond with a scratch stick for the purpose of cleaving . The groove or kerf should parallel the direction of the plane in which the cleaver will split the diamond.
kimberlite pipe See pipe.
kimberlite The igneous rock that most rough diamond is found in. Also commonly called blue ground.
Kimberly Central Mining Company A major diamond mining company in the early diamond history of South Africa. By 1888 after much struggle the Kimberly Central Mining Company was controlled by Cecil Rhodes and Barney Barnato.
knife edge girdle An extremely thin girdle where the crown and pavilion meet with no protective area at all. Very apt to chipping or nicking.
knot An irregularity in the granular structure that can make cutting very dif•cult. Usually invisible until it reaches the surface. Also known as naat.
knot lines A knot that has surfaced during the cutting process exposing the outline. Also see knot.
L/W ratio See length to width ratio.
lab reports An independent report on a diamond or gem determining authenticity, quality and specifications.
lamproite An igneous rock, sometimes containing diamond, that is found in Australia.
laser cutting Light amplification by stimulated emission of radiation. Alaser beam is capable of cutting into and dividing a diamond on any given plane. The advantage of laser cutting is the flexibility of direction since grain does not play a role in this method like it would in sawing.
laser drill hole (LDH) Used to make an inclusion accessible to the surface of the diamond so a strong acid solution can be introduced to lighten or partially remove the darkness.
laser inscription An inscription placed on the girdle of a diamond by laser for identification such as a GIA report number or the identification of a GE POL diamond. Custom lettering is also available.
lattice The geometric arrangement of a crystalline structure on the atomic level.
layout A cutter must lay out or plan the orientation of a piece of rough before giving it to the girdler (bruter).
Lazare Kaplan See LKI.
LDH See laser drill hole.
left hand color deviation Generally, the stone to the left will appear slightly darker than the stone to the right in the process of color grading.
Length to Width Adjustments (LWA) In calculating weight estimation of elongated fancy shapes, the LWA value is inserted in the formula. It varies depending on the length to width ratio.
length to width ratio (L/W ratio) Divide the length by the width of an elongated fancy shape. Used in weight estimation and also to describe the shape of a diamond.
Leveridge Gauge See A.D. Leveridge Gauge.
light carat Between the carat weight of 0.90 and 0.99.
lizard skin Depending on the severity, it can look like a burned area on the surface of the diamond. It is caused by a cutting position that is not perpendicular to a grain. Also see polish marks.
LKI (Lazare Kaplan, Inc.) A well known company specializing in ideal cuts and started by the very famous cutter, Lazare Kaplan. LKI has also teamed up with General Electric in Pegasus Diamonds who specializes in a diamond color lightening treatment.
loose diamond Not mounted. Usually stored in a parcel paper.
loupe A magnification device for the viewing of small objects such as diamonds and gemstones. The standard jeweler's or diamond dealer's loupe is 10x since this is what is required to place a clarity grade on a diamond. Also see triplet.
lower girdle facets Sixteen facets on the pavilion, one on each side of the pavilion mains creating the elongated kite shapes in the finished product. These facets add slightly different angles next to the pavilion mains to create more reflective directions and therefore more brilliance. They can also be referred to as girdle facets (not to be confused with faceted girdle), lower break facets, bottom halves, skew facets, skill facets and cross facets.
luminescence See fluorescence.
LWA See length to width adjustments.
macle A mutation in rough diamond crystal that has grown in two separate directions creating a twinned crystal. The orientation of the twins are 180 degrees in respect to each other. Generally very difficult to polish due to the conflicting grain directions.
main facets See pavilion mains and bezel mains.
make See proportions.
makeable A rough diamond that lays out in such a way that sawing or cleaving is not necessary for maximum weight retention.
marine deposits See alluvial deposits.
marquis cut The marquis is shaped like the outline of an elongated football. The facet placements are similar to the round brilliant. The length to width ratio is an important determining factor in the overall beauty of the finished diamond.
master comparison stones See master stones.
master stones GIA's GTL will do specific reports on master stones for color comparison purposes. GIA's requirements to accept a diamond for a master stone report includes .25 carat or larger size, crown heights 12 to 15 %, thin to slightly thick girdles that are clean, pavilion depth of 42 to 44%, modern cuts only, SI1 or better clarities, and none or faint blue fluorescence is acceptable.
mechanical rocker box A rough diamond recovery method where diamond bearing gravel is first run across a series of screens to separate the larger and smaller chunks. The larger pieces are crushed until they measure approximately 1.5 inches across. The small pieces of kimberlite are then put into a mechanical rocker box and rotating paddles force water to separate the lighter and heavier minerals which settle to the bottom. The lighter materials eventually float off and the heavier are caught at the bottom of the box.
melee A general term used for polished diamonds weighing less than 0.18 carat each. Can also apply to rough diamond and colored stones.
memorandum A short term consignment usually between dealers or a dealer and a jeweler for the purpose of showing a diamond or gemstone and having the option of returning it if a sale is not completed.
methylene iodide A yellowish liquid compound known for its high specific gravity and refraction used to determine refractive indexes and specific gravities of minerals. Also used in the detection of color treatment by the cyclotron method.
metric gram See gram.
metric system A decimal system based on weights and measures. There are five carats in a metric gram.
millimeter A metric measurement of distance. A standard measuring increment in the trade for describing outer dimensions of a diamond. A millimeter is 1/1000 of a meter.
modern cut Generally referring to all cuts that adhere to the acceptable standards of today's diamond cutting. The modern cuts eliminated open culets, short lower girdle facets, steep crown and pavilion angles of the old European and old mine cuts. To capture an acceptable amount of brilliance and dispersion the angles of the modern round brilliant were set at between 30 and 35 degrees for the crown and between 39 and 41 degrees for the pavilion. Many times these angles will be ignored for the purpose of weight retention but still will be considered a modern cut.
modern round brilliant cut See modern cut.
Mohs, Friedrich A German mineralogist who invented the Mohs' scale for classifying the hardness of minerals. Also see Mohs' scale.
Mohs' Scale A hardness scale invented by Friedrich Mohs which is based on diamond (10), the hardest known substance to man. Corundum 9; topaz 8; quartz 7; feldspar 6; apatite 5; fluorite 4; calcite 3; gypsum 2; talc 1.
moissanite A synthetic silicon carbide developed by Moissan. A popular diamond imitation that is harder than corundum (9), but not as hard as diamond (10).
monocular microscope A single lens tube magnification instrument used mainly in science where stereoscopic viewing is not a necessity.
naat See knot.
natural Often a cutter will leave naturals on the finished diamond for the purpose of weight retention. It is the original skin of the rough diamond, which is important to keep enclosed in the girdle or out of view when looking down on the polished diamond under 10x magnification.
needle An elongated included crystal which is a fairly common occurrence in diamond. Can sometimes be confused with laser drill holes.
net price See net.
net The total price of a diamond after calculating the price per carat.
nick A small chip on a diamond which is most common on the girdle especially where extremely thin areas occur. Very common on older cuts.
nitrogen As few as 100 atoms in every one million carbon atoms, in diamond, absorb the blue and violet end of the spectrum, resulting in yellow reflecting back to our eyes.
obtuse angle An angle greater than 90 degrees.
octahedral crystal A well shaped diamond crystal which has a symmetrical layout of eight equilateral triangles. It has the appearance of two pyramids joined at the bases. Also referred to as an octahedron.
octahedral faces The eight triangular faces make up an octahedral crystal. Also see octahedral crystal.
octahedron See octahedral crystal.
off-grain A diamond cutter must polish a diamond perpendicular to a single grain at all times during the faceting process to allow material removal and a high polish. This is referred to as on grain. When the cutting position is not perpendicular it is referred to as off grain.
old cuts Old cuts have particular characteristics that do not adhere to the modern acceptable standards of the modern cut. These would include an open culet and short lower girdle facets. Angles were largely ignored but even in modern cuts they sometimes are for the purpose of weight retention. Old cut terms used are old mine, old miner, old European, modern European (transitional cut), old-English cut, rose cut, old single cut, and some may refer to the single cut as an old style.
on grain See off-grain.
origin of color report A report offered by GIA and other labs to determine the authenticity or irradiation and grade of the color of the diamond in question.
oval cut A similar facet layout to the round brilliant. The length to width ratio is a determining factor in the overall beauty of the finished diamond.
over-graded Due to lack of knowledge or ethic, many dealers assign higher color and clarity grades to their diamonds, which gives the illusion of higher value.
P1 A C.I.B.J.O clarity grade equivalent to GIA's I1, the first level of imperfect. The "P" stands for pique'.
P2 The second level of the imperfect range in the C.I.B.J.O. clarity grading system. It is the equivalent of GIA's I2. The "P" stands for pique'.
P3 The third level of the imperfect range in the C.I.B.J.O. clarity grading system. It is the equivalent of GIA's I3. The "P" stands for pique'.
pavilion angle The optimum pavilion angle is 40.75 degrees which is measured off of the girdle plane (or the table which is parallel). The eight main facets (elongated kite shapes) are where the measured pavilion angles would occur.
pavilion depth A 43% pavilion depth is indicative of 40.75 degrees angles which is optimum for internal light reflection. The pavilion depth is measured from just below the girdle to the culet. This figure is divided by the diameter of the diamond and is expressed in percentages.
pavilion main method A crown angle estimation procedure relying on diamond's refraction to distort the pavilion mains as their images pass under the crown mains. The crown angles determine the amount of distortion of the pavilion mains.
pavilion mains The eight primary facets on the bottom of the brilliant cuts or most of the old cuts. Once the lower girdle facets have been polished into place the pavilion mains are elongated kite shapes in appearance.
pavilion The bottom or lower portion of the polished diamond. All facets below the girdle would be considered pavilion facets.
pear shape A tear drop shaped cut that may have fifty-five to fifty eight facets depending on the presence of a culet and the absence of the pavilion main facets. Some of the most famous diamonds in the world were cut into pear shapes.
Pegasus See Bellataire.
pennyweight Abbreviated DWT. It is a measurement of weight generally used for precious metal. It is equal to 1/20 of a troy ounce.
peridot A deep yellowish green semi-precious gem that occasionally occurs in diamond as an inclusion.
perpendicular Exactly vertical or upright to the base of the angle. 90 degrees.
pinpoints Tiny included crystals. Also see included crystals.
pipe A term for the description of a volcanic column of cooled igneous rock. When kimberlite is present it might be referred to as a kimberlite pipe in which the presence of diamond is possible.
pique' French word meaning pricked. The term was originally used to describe high clarity stones. In today's usage it is an old fashioned term meaning imperfect. P1, P2 and P3 are the loose equivalents of the GIA's I1, I2 and I3 for imperfects.
pits Very small openings on the surface of a diamond most commonly caused by included crystals that have surfaced during the cutting process.
plastic template gauge See template gauge.
point-cuts A very early style in diamond cuts where the cutter cleaved away the triangular octahedral faces leaving smooth, facet like faces. The finished cut would still look like an octahedron crystal.
points There are 100 points in a carat, a weight measurement for diamonds and gemstones.
POL (Pegasus Overseas Limited) See Pegasus.
polish mark If the cutter polishes in a position that is not perpendicular to the grain there will most likely be polish marks on the surface. Waves and/or grooves can appear which are very easy to spot given the reflection of light off the surface of the facet in question. Sometimes the raised areas are partially surrounded with trailing lines or tails. Sometimes referred to as lizard skin.
polisher A general reference to a diamond cutter that does the faceting stage of the cutting process.
polishing lines The fainter the polishing lines on the surface of the finished diamond the better the polish is. Caused by cutting off-grain or a smoothing ring on the cutting wheel (scaife), that has not been properly cared for. Even in excellent polishes at least very faint lines will likely be detected under 10x magnification.
polishing The faceting of a diamond.
pot A cup-like or platform piece that is inserted into the dop which clamps or holds the diamond in place during the polishing process. An assortment of pots are used by the cutter for different shapes and sizes of the re-cut or rough diamond being polished.
PPC See price per carat.
price per carat The diamond trade generally prices diamonds, polished or rough, in a price per carat format. The only time the price per carat and the total or net price is equal is when the diamond in question is a 1.00 carat even. The Rapaport Diamond Report lists all diamonds in price per carat.
primary deposits Rough diamonds that have been found in kimberlite forced near the surface by volcanic action are considered primary deposits. Also see alluvial deposits.
proportions Ageneral reference referring to the angles, depth and table percentages and girdle thickness of a polished diamond. Commonly called "make" also.
proportionscope First designed and manufactured by GIA in 1967. It is an instrument that casts a silhouetted image of a diamond that allows us to check the exact proportions of the subject.
quartz Number 7 on the Mohs' hardness scale.
Rapaport Diamond Report A diamond price index publication by Martin Rapaport. The index is also available on the internet with a paid subscription.
re-cutting Many times an old style cut such as the old European or old mine cut will be re-cut (re-fashioned) to improve upon its beauty, salability and value. If a diamond is chipped a full re-cut may be required to improve its salability. Also see repair.
re-fashioning See re-cutting.
reflected light Light beams that bounce off the surface of the diamond versus transmitted light that enters the diamond. Also see angle of reflection, angle of incidence and critical angles.
refractive index Diamond's refractive index is 2.417. The ratio between the speeds of light traveling through air versus the subject at hand. As light enters diamond it is refracted or bent exposing the array of spectral colors in white light. Refraction is critical to dispersion. Also see dispersion.
reject Extremely imperfect. In the Britain clarity scale it is below "heavily spotted". The equivalent of two grades below GIA's I3. By GIA's standard it would be considered off the scale.
repair Many times the diamond dealer/cutter will opt to repair a diamond instead of a full re-cut, to maximize weight retention. Only a portion of the diamond's facets are affected around the area of the chip or nick. A repair versus a re-cut will usually have a negative impact on the symmetry of the finished diamond.
Rhodes, Cecil An Englishman who moved to S. Africa for health reasons. He joined his brother in diamond prospecting and they soon became very successful in the diamond rush. He collected several claims and eventually formed the De Beers Mining Co. Rhodesia was named after him for his positive influence on the region. He was the first appointed chairman of De Beers and held that position until his death in 1902.
RI See refractive index.
rough girdle A girdler will sometimes apply too much pressure in the girdling (rounding) process and as a result leave a rough girdle which gives a granular appearance under 10x magnification. Similar to a bearded girdle but the tiny feathers are absent behind the pitting or granular surface. A rough girdle would be considered a blemish. Also see bearding.
rough A common term when referring to uncut diamonds.
round brilliant By far the most popular shape of all the shapes. Its popularity is due to its unsurpassed brilliance and dispersion caused by the consistent angles all the way around the finished diamond. The round brilliant has fifty-eight facets or fifty seven without a faceted culet. Many of these stones may be modified for the purpose of maximum weight retention sacrificing brilliance and dispersion.
saturation It is the intensity or strength of the hue. For example a fancy yellow with added saturation might be considered an intense fancy yellow.
saw plane The area or imaginary plane the diamond sawyer has chosen in order to saw the rough diamond into two pieces. The grain is of much importance in the limitations as to where the saw plane may exist. Many times the sawyer will choose an off center saw plane to get two different sizes in the final products.
sawing A large portion of the rough diamonds mined today are sawed into two pieces for the purpose of weight retention. Sawing is generally done on well formed octahedron crystals which leaves two pieces that generally yield 50 to 55% in the finished product. The disadvantage of sawing is the limited directions in which the rough can be divided, due to the rules of cutting on grain. Also see saw plane.
sawyer A person who specializes in the sawing of diamonds.
scaife The cast iron wheel used for the polishing of diamond. Most cutters still use the bare scoured wheel (adding a diamond-dust-oil mixture onto the surface by hand) versus the diamond-imbedded scaife. The scaife typically spins at approximately 2600 RPMs, driven by an electric motor and held by different styles of spindles.
scalloped girdle Sometimes the cutter will facet the upper and/or lower girdle facets deep into the girdle to thin it down. This gives an unpleasant appearance with a less uniform girdle in the finished diamond.
scintillation It is the movement of the reflections (brilliance) and dispersion (spectral colors), as the diamond (or other gemstone) is rotated or tilted before the viewer's eyes.
scratch A blemish that appears as an elongated, whitish to grayish, shallow line on the surface of the diamond. Caused by contact with another diamond.
secondary deposits See alluvial deposits.
secondary market The secondhand market is considered anything that has been resold by an end user. Pawn shops and businesses established for the purpose of buying from the public or other pawn shops and secondhand buyers would be considered part of the secondary market.
semi-automatic tang As it relates to diamond cutting, the holding device for the dop. It is a clamp like tool that holds the diamond in place during the polishing process. The semi-automatic tang replaced (or was added to) the copper stalk style of cutting by adding cheaters or knobs that are turned by hand for the adjustment of the straightness and angle of the facet. It still takes extreme skill to operate a semi-automatic tang effectively. Fully automatic tangs or faceting machines take much less skill by the cutter to operate.
shape Refers to the layout or outline in the finished diamond. Examples: heart shape; pear shape; round; etc.
SI1 The first level or better of the two "slightly imperfect" levels in GIA's clarity grading scale. Two grades within the eye- clean range.
SI2 The second level or the worse of the two "slightly imperfect" levels in GIA's clarity grading scale. The last or the lowest eye-clean grade.
singly refractive Diamond is singly refractive since the light traveling through it has a consistent refractive index regardless of the direction it enters. Moissanite, the popular diamond imitation, is doubly refractive due to its anisotropic crystalline structure.
size categories Weight categories is a more accurate term. Starting at fifth carats (.18-.22 carat); quarter carats (.23-.29 carat); third carats (.30-.37 carat); three eighths carats (.38-.45 carat); light half carats (.46-.49 carats); half carats-five eighth carats (.50-.69); three quarter carats (.70-.89 carat); light carats (.90-.99 carats) one carats (1.00+) etc.
skew facets They can also be referred to as upper and lower girdle facets, (not to be confused with faceted girdle), lower break facets, top and bottom halves, skill facets and cross facets. Also see upper girdle facets, lower girdle facets.
skill facets See upper girdle facets, lower girdle facets.
skin The surface of a rough diamond. This skin may be very transparent or very opaque. Naturals on a polished diamond are the remaining skin of the rough.
smoothing ring One of three cutting rings on the diamond cutting scaife. The smoothing ring is the widest and the last to be used to give the diamond its final polish.
soft stones A general term for gemstones that are non-diamond. Colored stones.
South Africa A major diamond producing country on the African continent. The diamond rush in the late nineteenth century started in South Africa. De Beers Consolidated was initiated in South Africa.
spectrum When the spectrum of white light is exposed via refraction, the colors are in order of their wave lengths with the shortest first: red, orange, yellow, green, blue and violet.
spherical aberration The failure of the lens in a loupe to bring light into a consistent focus due to its shape. Also see chromatic aberration; triplet.
spotted In the "Britain" clarity scale it is the equivalent clarity to GIA's I3, the last and worst in the imperfect range before going off the scale.
stability field Scientific study of temperature and pressure conditions, synthetic diamond testing and production, volcanic activity and inclusion analysis has given us strong evidence of the diamond stability field. The stability field is the conditions required so that carbon can crystallize into diamond.
star facets The eight triangular facets forming the final shape of the brilliant cuts.
star gauge A measuring device used by a diamond cutter to determine the crown angles.
Star of South Africa The 83.50 carat diamond crystal now known as the Star of South Africa, started the international diamond rush in South Africa in 1868.
steamer A machine that heats and pressurizes water that can then be used for the cleaning and rinsing of diamonds and jewelry.
step-cut Step cuts are polished in a parallel-horizontal facet arrangement as in the emerald cut and baguette.
stereoscopic viewing Dual eye-pieces on the gem microscope allows three dimensional viewing. This increases the ability of your eyes to detect depth of an inclusion.
stereoscopic vision See stereoscopic viewing.
strong blue fluorescence See fluorescence.
surface graining An irregularity of the crystal structure of the diamond. It appears as a line traveling across one or more facets, which can be mistaken as polishing lines, especially when occurring in a multiple pattern. Grain lines will be more obvious than polishing lines and polishing lines will be in larger numbers running close together. A single grain line can run across several facets in a continuous line, whereas polishing lines will at least change directions slightly from one facet to the next.
symmetry Facets on a diamond should be a mirror image of each of their opposites. The kite-shaped mains on both the crown and pavilion should all look the same. If the culet or table of the diamond is off center, this will have a negative affect on the symmetry.
synthetic diamond A synthetic is a copy of nature down to the molecular structure of the substance. Synthetic diamond has the same atomic structure as natural diamond and retains the same properties.
table gauge This is a small transparent plastic ruler in increments of tenths of a millimeter (0.1 mm) for the purpose of measuring the table size under magnification.
table percentage bowing method With properly cut star facets, a 60% table forms a perfect square. When the lines of the square bow inward you know the table is smaller than 60% and when the lines bow outward you know the table is larger than 60%.
table percentage value The size of the table which is expressed as the percentage of the average girdle diameter.
table reflection method A method for determining the depth of the pavilion. The size of the reflection of the table which is viewed through the table and is located around the culet, determines the depth of the pavilion in question. In the ideal 43%, the shadow or reflection covers about 1/3 of the distance between the culet and the edge of the table where two stars join. With the reflection reaching 1/2 of the distance the depth is approximately 44.5% (too deep). As the reflection gets smaller the depth is shallower and with a greater depth the reflection is larger. Easy to remember larger is deeper, smaller is shallower. Again the ideal marker is the 43% depth (40.75 degrees) with the reflection extending 1/3 of the way between the culet and the table corner (where stars join).
table The largest and perhaps the most important single facet on a modern cut diamond. It is the crown facet that parallels the girdle that regulates the amount of important light that enters the diamond. On the round brilliant it is octagon in shape.
talc An extremely soft mineral representing #1 on the Mohs Scale for hardness.
tang The tool used by a diamond cutter in holding or clamping the dop which, in turn, holds or clamps the diamond in place while it is being polished.
template gauge A plastic sheet with illustrations of black lines to lie over the diamond in question to determine approximate weight.
TLB See top light brown.
tone It refers to the darkness or shade of color. The darker a diamond is the stronger the tone. Tone and saturation are two completely different elements. A vivid fancy yellow has high saturation and a dark tone. Add a little gray or brown to the yellow and it diminishes the saturation of yellow but maintains or strengthens the tone.
top halves See upper girdle facets.
top light brown (TLB) A term used to describe a very light brown diamond that would be the approximate equivalent of J to K color on the GIA scale.
top top light brown (TTLB) A very, very light brown diamond that is the approximate equivalent of I to J color on the GIA scale.
topaz A gemstone representing #8 on the Mohs Scale of hardness.
toughness It is the resistance of breakage, powdering or the lack of ability to flatten during repeated pounding.
transmitted light It is the light that enters the diamond especially through the table. Also see reflected light.
trigon Triangular shaped impressions on the skin of the rough or a natural on a finished diamond which also indicate granular orientation for the cutter.
triplet A magnifying instrument for the viewing of small objects, especially gemstones. The three lenses are designed to correct for spherical and chromatic aberrations (distortions).
TTLB See top top light brown.
twinning lines See graining lines.
U.L. rated safe Underwriters Laboratories tests safes (among many other products) for their resistance to tools and torches. Insurance companies will require a U.L.rated safe along with a U.L. rated alarm system.
ultrasonic cleaner A cleaning unit that vibrates the jewelry in a cleaning solution and water. Some models come with heaters and timers.
underground mining Consists of a large vertical shaft running next to the pipe to use as a pathway to the many horizontal tunnels that lead into the kimberlite. Diamond bearing rock is blasted loose, hauled to the surface and processed. Sometimes tons of rock, gravel or sand have to be processed to retrieve one carat of rough diamond.
uneven fracture Diamond's fracture is classified as uneven due to its typical step like surface of a chip.
upper girdle facets Sixteen facets on the crown, one on each side of the crown mains creating the kite shapes in the finished product. These facets add slightly different angles next to the crown mains to create more reflective directions and therefore more brilliance. They can also be referred to as girdle facets (not to be confused with faceted girdle), lower break facets, bottom halves, skew facets, skill facets and cross facets.
Van de Graff generator method Depending on the original color this method of color treatment irradiation is capable of producing bluish hues. The common cape (yellow) diamonds used in this process change to a bluish-green or greenish-blue.
vivid fancy color The best and most valuable of the yellow fancy colors. It possesses very high yellow saturation and a pure yellow tone.
VS1 A clarity grade on the GIA scale which stands for very slight (imperfections). One clarity grade better than VS2.
VS2 A clarity grade on the GIA scale which stands for very slight (imperfections). One clarity grade better than SI1.
VVS1 A clarity grade on the GIA scale which stands for very very slight (imperfections). One clarity grade better than VVS2.
VVS2 A clarity grade on the GIA scale which stands for very very slight (imperfections). One clarity grade better than VS1.
weight retention On a piece of rough or a diamond recut or repair, weight retention is always an important consideration in value. It is the preservation of weight or the lack of weight loss during the cutting process.
window Sometimes dead spots in polished diamonds are referred to as windows. Many times the skin of a rough diamond is too opaque for the cutter to locate inclusions which may affect the layout of the diamond. A window will be polished on the rough, removing the skin so that a view of the internal clarity is permitted.
wisps See graining lines.
X-ray separation system In 1958 Soviet scientists invented the X-ray separation system. Relying on the fact that diamonds fluoresce under X-rays the prepared gravel would pass through X-ray beams and when fluorescence occurred it triggered a concentrated air stream directing the diamonds into a separate area.
