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Glossary of Terms
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
bruting See bruted girdle.
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.
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.
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 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.
CSO See Central Selling Organization.
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.
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.
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 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.
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 cleavage See cleavage.
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.
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.
DPA See Diamond Producers'Association.
DTC See Diamond Trading Company, Ltd.
DWT See pennyweight.
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.
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 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.
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.
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.
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.
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 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.
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.
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 reflection See fish-eye.
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.
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.
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.
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.
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.
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.
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 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.
JBT See Jewelers Board of Trade
Kaplan See LKI.
kimberlite pipe See pipe.
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.
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.
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 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.
Lazare Kaplan See LKI.
LDH See laser drill hole.
Leveridge Gauge See A.D. Leveridge Gauge.
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.
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.
make See proportions.
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.
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.
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' 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.
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.
net price See net.
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.
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.
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.
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.
pinpoints Tiny included crystals. Also see included crystals.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 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.
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.
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.
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.
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.
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.