Glossary

Abraded Culet: A culet that has minor abrasions on it.
Abrasion: Tiny nicks along facet edges, usually caused by contact with other diamonds. Producing white fuzzy lines instead of sharp crisp facet edges.
Acrylic Crystal: Also known as plastic crystals, these were initially introduced in the 1920s.
Adamantine: Refers to the diamond-like luster of a gemstone. Gemstones with a diamond-like luster include diamond (of course), demantoid garnet and sphene.
Age: The age of a diamond ranges between 1 billion to 3.3 billion years.
Alloy: Combination of 2 or more metals.
Alluvial Deposits: Gem deposits found in water after they have been separated from the mother rock.
Alluvial Diamond: A diamond that has been transported by water and deposited in seas, lakes or streambeds.
American Cut: Proportions and facet angles of a diamond that were mathematically calculated by Marcel Tolkowsky to produce maximum brilliancy consistent with a high degree of fire in a round brilliant cut diamond and are considered by many to constitute the “Ideal Cut” diamond. These figures, computed as a percentage of the girdle diameter, are as follows: total depth of 59.3% (without provision for girdle thickness); crown height of 16.2% (table 53% and Crown angle of 34.5 degrees); pavilion depth of 43.1% (pavilion angle of 40.5 degrees).
American Gem Society (AGS): The American Gem Society was established in 1934 by a select group of independent jewelers and Robert M. Shipley, founder of the prestigious school of gemology, the Gemological Institute of America (GIA). It was their vision to create an association dedicated to setting and maintaining the highest possible standards of business ethics and professionalism in the jewelry industry. Today, American Gem Society members continue their dedication to ethics, knowledge and consumer protection.
American Gem Society Laboratory (AGSL): Since 1996, the AGS Laboratories is the world’s premier diamond grading laboratory and the only diamond grading laboratory backed by the jewelry industry’s premier consumer protection agency, the American Gem Society, and the first prominent diamond grading laboratory to offer diamond grading reports with a Diamond Cut Grade for the round brilliant cut diamonds, princess cut, oval brilliant, and emerald cut diamonds.
American Gem Trade Association (AGTA): The American Gem Trade Association and its members are active in all areas, from mines and research labs to wholesale offices, design studios and retail showrooms. As a result, the AGTA is recognized as the voice of the natural colored gemstone and cultured pearl industries. Some of the most significant contributions to the trade have been the creation of the AGTA Code of Ethics and Principles of Fair Business Practices, the Gemstone Enhancement Manual (G.E.M.), along with the opening of the AGTA Gemological Testing Center in New York in October 1998.
Amorphous: Gemstones without a crystal structure are referred to as amorphous. These include gems such as amber, coral, opal and pearl.
Anneal: A treatment process of heating and slow cooling of colored gemstones, color enhanced diamonds, and metals.
Aperture: Some watches contain small openings on the dials, called apertures, that show indications (i.e. numbered date, hour or day of the week).
Appraisal: A written estimate of the value of the item described. They can be used for insurance purposes and should be updated every few years.
Arabic Numerals: The figures on the dial that represent the hours, such as 1,2,3,4, as opposed to Roman Numerals I, II, III, IV.
Arbor: The shaft or axle that a gear rides on. At each end is a narrower segment called the “pivot.”
Arkansas Diamond: An Arkansas diamond is actually a rock Quartz crystal.
Art Deco: Art Deco was a style popular from the mid-1910′s until the late-1920′s. This style originated in Paris, France. Geometric lines and angles, with very few curves, characterize Art Deco pieces. The Asscher Cut diamond and the Emerald Cut diamond were developed and became popular during this period.
Asscher Cut Diamond: A square step cut diamond named after its inventor, Joseph Asscher.
Asscher, Joseph: Joseph Asscher was an eminent diamond cutter who cut the 3,106 carat Cullinan diamond. Asscher worked in Amsterdam. In 1902, his company, the Asscher Diamond Co., developed and patented the Asscher cut, a squarish step cut with an almost octagonal outline. This new cut enhanced the fire and light of the stone; it had a small table, a high crown, wide step facets, a deep pavilion and square culet. This cut became very popular in Art Deco jewelry and was a forerunner of the Emerald Cut diamond.
Asterism: The star effect that you see in star sapphires or rubies, for example. This is usually caused by tiny silk rutile inclusions in the stone. The effect can be four- or six- rayed.
Atmosphere: Used as a measure of the watertightness of a watch case. One atmosphere equals average air pressure at sea level, approximately 14.7 pounds per square inch. Since one atmosphere equals 33.90 feet of water, a 3 ATM water resistant watch is considered water resistant to approximately 100 feet.
Auto Rotor: Rolex patented perpetual movement invented by Emil Borer in 1931
Automatic Winding (also Self Winding): An automatic watch is wound by the movement of the wearer’s wrist. This movement causes a weight inside the watch to rotate backwards and forwards. The weight is connected by a gear train to the barrel arbor, which is hooked to the mainspring, thus winding it and keeping it in constant tension.
Average Girdle Diameter: The average measurement of the minimum and maximum diameter of a Round Brilliant Cut diamond.

Baguette: A long rectangular gemstone shape, somewhat similar in shape to a loaf of French bread, hence the name.
Baguette Watch: A ladies style watch (or movement) featuring a thin rectangular or oval shape.
Bakelite: The transparent acrylic material used on the bezel of early model GMT-Masters in 1954.
Balance: The governor or controller of a watch; it consists of a metal wheel, now commonly made of Invar, a special steel resistant to changes in dimension due to fluctuations of heat or humidity and usually is mounted with a hairspring also of Invar or a similar alloy.
Balance Spring: Also referred to as the “hair spring,” this spring controls the swing of the balance.
Balance Wheel: A portion of the escapement, which divides time into equal sections.
Bar Setting: A diamond setting style that holds each diamond in by a thin bar, shared between the two diamonds.
Barion Cut Diamond: This has a traditional step-cut crown and a modified brilliant-cut pavilion. This is referred to as a mixed cutting style. A square Barion Cut diamond has 61 facets, excluding the culet.
Bark Finish: The finish on some bracelet links that resembles the bark of a tree.
Baroque: Irregular in shape, such as baroque pearls, tumble-polished stones, or freeform shaped gem materials.
Barrel: Often called the “mainspring barrel,” this is a circular box, often connected to a gear, which holds the mainspring, which drives the watch.
Bead: A hollow gemstone, usually round, designed to be strung.
Bearded Girdle: Tiny, numerous, hairlike fractures extending into the diamond. The outermost portion of the diamond, called the girdle, can develop small cracks that resemble whiskers during the shaping process. If a diamond is rounded up too quickly in the shaping process, the surface of the girdle will lack the smoothness and waxy luster of a finely turned girdle. The bearding can sometimes be removed, if not too dramatic, with slight re-polishing, and if the finished weight allows it.
Beat: Measured in either Beats Per Hour (BPH) or Beats Per Second (BPS). This is the number of times per hour or second that the balance wheel goes through a full arc of motion in either direction. The usual number of Beats Per Hour is 18,000. However, current Rolex watches are 28,800 BPH.
Beryllium Treatment: A form of heat treatment for sapphire that adds the element beryllium to the heating process. Beryllium is an element well known in the gem world, since it is an essential constituent in many gemstones, including emerald, beryl, and aquamarine. When sapphires are heated with beryllium, the result is a reduction in blue tones. Thus bright yellow or orange sapphire can be produced from weak yellow or greenish gems. Some stunning colors have been produced using this method.
Bezel: The ring around the crystal on the top portion of a watch. Often, the bezel is made from varying materials (i.e. stainless steel or gold) within a watch line – See also Rotating Bezel, Bi-Directional Rotating Bezel and Uni-Directional Rotating Bezel.
Bezel Facet: On a Round Brilliant Cut diamond, these are eight large kite-shaped facets on the crown, the upper points of which touch the table and the lower points, touch the girdle. Also called top main facet. Some diamond cutters further distinguish four of these as “quoin” or “top-corner” facets.
Bezel Setting: A rim that holds the diamond and completely surrounds the diamond along the area just above the girdle. Bezels can have straight edges, scalloped edges, or can be molded into any shape to accommodate the diamond.
Bi-color: A gemstone exhibiting two color zones, such as ametrine or many tourmalines.
Bi-Directional Rotating Bezel: A bezel which can be rotated either clockwise or counterclockwise, and is used for making calculations.
Birefringence: Some gemstones are singly refractive they have only one refractive index. Other gemstones (in fact, most) are doubly refractive: they have two different refractive indices. When a beam of light enters a doubly refractive gem, it is split into two beams, each travelling at a different speed and on a different path through the crystal. Birefringence is a measurement of the difference between the two refractive indices in gems that are doubly refractive, and it ranges from a low of .003 to a high of .287. Very few gemstones are singly refractive; in fact, the only well-known gems with that property are diamond, spinel and garnet.
Birthstones: Birthstones have their roots in ancient astrology, and there have been many birthstone lists used over the years. The most common one today is based on a list first publicized by the U.S. jewelry industry in the 1950s.
Black Diamond: When a diamond is dark gray, a very dark green, or truly black, it is referred to in the trade as a “black diamond”. Such a stone may be opaque to nearly semi-transparent.
Blemish: Any surface imperfection on the surface of a diamond, such as a nick, knot, scratch, abrasion, minor crack or fissure (cavity), or a poor polish. Also, a natural or an extra facet, visible on or through the crown, usually is considered a blemish.
Blue Diamond: A diamond with a distinctly blue body color, even if it is very light in tone, is a fancy blue diamond. Boron that is present in the crystal structure is responsible for this color. A blue color may also be induced artificially and is referred to as a color enhanced diamond.
Blue White: This is a term that I haven’t heard in many years… actually it was probably last century! It was still commonly used up till the mid 60′s. Federal Trade Commission rulings state that is it an unfair trade practice to apply the term to any diamond having a body color other than blue or bluish. An American Gem Society ruling prohibits the use of the term by its members. Flagrant misuse of this term has made it meaningless and it is no longer used.
Blueground: A miner’s name for “kimberlite”, the rock that contains diamonds in the South African pipe mines.
Body Color: The color of an unmounted diamond as observed when examined under a diffused light against a hueless (colorless) background free from
surrounding reflections. The diffused light eliminates glaring reflections and dispersion, which would otherwise confuse the color determination.
Bombarded Diamond: A diamond that has been subjected to a stream of fast electrons, neutrons, deuterons, etc. The purpose of bombardment is to alter the color of a diamond.
Bort: Industrial grade diamonds.
Bow Tie Effect: An effect caused by a shadowy area visible in some fancy shapes, caused by light leaking out the bottom of the diamond. A large bow-tie in the center of a fancy shaped diamond detracts from beauty and lowers the value. (also ‘Butterfly’)
Boy’s size watch: 2mm smaller than that of a standard men’s size watch.
Brancard: Rolex Prince model with flared ends. From the French word meaning ‘stretcher.’
Breathe: This is the term for the expansion and contraction of the hairspring. When breathing correctly, the spring is working at its optimum efficiency.
Brevet: From the French word Brevette, meaning patented.
Bridge: Any movement plate secured by a minimum of two screws.
Brilliance: The total amount of white light returned to the eye from a diamond or colored stone as the result of internal and external reflections. The major factors that affect the amount of brilliancy in a gem are refractive index, proportions, polish and transparency.
Brilliant Cut: One of three styles of faceting arrangements. In this type of arrangement, all facets appear to radiate out from the center of the diamond toward its outer edges. It is called a brilliant cut because it is designed to maximize brilliance. Round, oval, radiant, princess, heart, marquise, and pear shape diamonds all fall within this category of faceting style.
Brillianteering: The placing and polishing of the 40 remaining facets on a single cut diamond after the 8 main bezel, 8 pavilion main, and the table have been placed and polished. By adding the additional it is now called a “full cut” diamond.
Briolette: A tear or pear-shaped stone cut in triangular facets.
Brown Diamond: Although not as frequently encountered as a yellow body color, brown tints in diamonds are next to yellow in occurrence.
Bruise: Inclusions consisting of surface crumbling, often accompanied by tiny, root-like feathers .
Bubble: Any transparent inclusion in a diamond; e.g., a tiny diamond crystal or a grain of a different mineral. It will look like a bubble.
Bubbleback: Term used to describe the early Rolex Perpetual models, due to the thickness of the case used to house the oversized Auto-Rotor movement.
Burned Facet: This facet may appear whitish, or burnt, as a result of the cutter polishing the facet “against the grain”. The excessive heat of polishing will make the diamond red hot and the surface will actually start to burn. This can also happened if the diamond is not properly protected from exposure to the atmosphere while being heating during repair work. A burnt facet can be re-polished.
Butterfly: Term used to describe the dark area located across a table, sometimes found in fancy shapes.

Cabochon Cut: A gem that is cut round without facets into the shape of a smooth polished dome. It lacks the facets that are on most stones.
Calendar Watch: A watch with a mechanism that shows the date, or on the more complex watches, the month, day, moonphase, and even the year. Most calendar watches have to be adjusted manually at the end of the month, but the mechanism of a perpetual calendar watch adjusts itself automatically.
Caliber (or Calibre U.K.): Refers to the size, style, or shape of a watch movement.
Calibrated (size): Many gemstones are sold in calibrated or standard sizes that will fit commercial jewelry settings. Standard sizes are calibrated in millimeters for a number of different gem shapes.
California Dial (Also Roman-Arabic): Dial featuring a combination of Roman & Arabic numerals; Roman on the top half, with Arabic on the bottom. The term “California Dial” refers to a California-based company who became known for reproducing the dial over the years.
Canary Diamond: Fancy color diamonds with an intense yellow hue similar to that of a canary bird. The yellow may be very slightly greenish or slightly orangey.
Cape: An outdated diamond color term referring to diamonds with a yellowish body color. This term originally referred to the Cape of Good Hope, referring to South Africa. The body color of diamonds produced by the South African mines was distinctly more yellow than the average diamond body color of Brazilian diamonds. This term is almost never used anymore because it is very inaccurate.
Carat: A unit of weight for gems. A carat is one fifth of a gram (0.2g)
Carat Weight: The measurement unit for the weight of gemstones. The origin of the word carat is from the seeds of the carob bean that were used to balance scales in ancient times. In the early 1900s the metric carat was standardized as one carat equaling 200 milligrams. When you buy a diamond the weight of a diamond is measured out to the hundredth of a carat (2 places to the right of the decimal point). It is expressed as “ct.” or “Ct.”, for example 1.23ct.
Carbon or Carbon Spots: This is a term used by some people in the jewelry industry to describe the appearance of certain diamond inclusions that appear black… typically a dark included crystal. Diamonds are 99.95% pure carbon; but 25 other different mineral inclusions or small crystals, have been found within diamond as well. These are not carbon spots, but rather small crystals that were trapped within the host diamond as it was forming in nature. Sometimes, they just happen to be dark in color. The most common mineral found within diamond is diamond.
Cat’s Eye: See Chatoyancy.
Cavity: An inclusion consisting of a large or deep opening in the diamond.
Center Seconds (or Centre Seconds U.K.): Also called sweep seconds. Mounted on the center post of the watch for greater visibility and ease in reading.
Center Stone: The main stone in a piece of jewelry with multiple stones. This stone is usually the largest and most prominent.
Certificate or “Cert”: Another term for a Diamond Grading Report. A document produced by a disinterested 3rd party (typically a Gemological laboratory) that describes a diamond’s characteristics. This report should only list the characteristics of the diamond and not refer to any prices.
certified Gemologist: A title awarded by the American Gem Society to qualified members. To qualify, a person must study colored stones and their identification, along with diamond grading and appraising. Also they must prove proficiency with several written examinations and a diamond-grading examination.
Champagne Diamond: A diamond that has a color similar to… you guessed it, champagne!
Channel Setting: Diamonds set into a row where the diamonds are held into place by grooves cut into a strip of metal along the edge of the piece of jewelry. Used quite often for wedding and anniversary bands.
Chanthaburi: The city in southeastern Thailand famous as one of the world centers for gemstone processing and trading. Chanthaburi is also famous for its weekend gemstone market.
Chatoyancy: The cat’s eye effect sometimes seen in gemstones such as chrysoberyl, apatite and tourmaline is known by the technical name of chatoyancy. The effect is caused by tiny parallel inclusions that give the appearance of a narrow line similar to a cat’s eye. Often a gemstone needs to be viewed in natural light to see the chatoyancy effect.
Chip: A chip is a shallow opening on the surface that is the result of damage that occurs after cutting.
Chronograph: A timepiece that, in addition to the normal time telling function, also performs a separate time measuring function such as a stop watch – with a separate seconds hand which can be started, stopped and reset to zero via push-buttons on the side of the case.
Chronometer (or Chronometre U.K.): A highly-precise timepiece which, after rigorous testing, has received a timing certificate from the official Swiss timing bureau Controle Officiel Suisse des Chronometres (COSC). (Greek for Chronos=time/Meter=measure)
Clarity Enhancement: Any process used to improve the apparent clarity of a diamond. This is a relatively complex subject… please refer to the following page on the subject- Clarity Enhanced Diamonds.
Clarity, Diamond Clarity: Diamonds have internal features, called inclusions, and surface irregularities, called blemishes. Together, they’re called clarity characteristics. A diamond clarity grade is determined by the relative absence of clarity characteristics. The Diamond Clarity Grading System was developed by GIA (Gemological Institute of America) in 1953 and is now the common international language when we talk about diamond clarity. The 11 diamond clarity grades are as follows-
Clean: A trade term to refer to a diamond that relatively free of any inclusions… typically a grade of SI1 or higher. It is not a standardized term, so one person’s clean diamond is another person’s not clean diamond. It is a term that is prohibited by the American Gem Society for use by its members. It is also prohibited by the Federal Trade Commission, unless the diamond meets the FTC′s definition of the term perfect. There is another term “Commercially Clean” which would be a grade lower than “Clean”, about SI2 to I1…. again, this is not a standardized term.
Cleavage: The property of some crystalline minerals, such as diamond, to split along certain planes when struck by a blow. These cleavage planes result in a clean flat surface that looks very much like they are a polished facet.
Cleavage Crack: A break parallel to a cleavage plane. It is characterized by a two-dimensional nature; intersections with facets are usually straight lines. It is generally the most dangerous characteristic in a diamond, if it is present, since it could affect the durability as well as the diamond’s beauty.
Closed Culet: A culet, the small facet on the bottom of a diamond, that is too small to be resolved with the unaided eye and that can be seen only with difficulty under 10x magnification.
Closed Table: A trade term used to designate a small table diameter. However, its interpretation and use varies. It may refer to a diameter less than the American cut 53% (of the girdle diameter) or, more frequently, to a table smaller than about 60%, because so many of the stones cut today have tables well over that 60% figure.
Cloud: A group of extremely tiny inclusions that are too small to be distinguishable from one another, even under high magnification. The result is that, under a microscope, this grouping often looks like a soft transparent cloud inside the diamond. Wow…. a cloud inside of your diamond!, cool!
Cluster Setting: A type of diamond setting with many diamonds in a single group.
Coated Diamond: A diamond with a surface coating which masks the true body-color. The coating may be extensive (entire pavilion, for example), but is more often limited to one or two pavilion facets or a spot on the girdle.
Color Change (gemstones) Color change gems change color due to changing light conditions (such as alexandrite or color change sapphire) or when viewed from different angles (such as andalusite or iolite)
Color Grading: Determining the body color of an unmounted (loose) diamond when compared to the known colors of a “master set” of diamonds. This needs to be done under a controlled lightning environment by someone who is trained in the grading system.
Color Origin: A determination of the cause of color in Natural Fancy Color Diamonds. Diamonds that are naturally colored are very rare and expensive. Fancy Diamonds are also available as Color Enhanced Diamonds, where the color has been induced by artifical means. A Gemological Laboritory is able to determine the cause of the color in a Fancy Color Diamond.
Color Used in the evaluation of a gem. The quality of a gem can based on either the presence or the absence of color.
Colored Stone: All natural gemstones other than diamonds.
Comex: A French commercial diving company (COmpagnie Maritime d’Expertise), which in the 1960s, aided in the development of the one-way gas escape valve in the Rolex Sea-Dweller.
Complications: Any additional function the wristwatch performs beyond basic time telling (i.e. hour, minute, and second), such as date, day of the week, moonphase, perpetual calendars or even stop/start chronograph functions.
Concave Cut Traditional gem facets are flat or two-dimensional. Concave cutting creates facets that are curved or three-dimensional. These curved facets refract more of the ambient light and return it to the eye as brilliance. Concave cutting is a recent innovation dating back to the early 1990′s. It requires considerable expertise and results in higher weight loss to the rough stone, since more material must be cut away to create the curved facets.
Concealed Clasp: Clasp used, whereby the buckle is concealed under the bracelet’s links, giving appearance of a continuous flowing bracelet This clasp is found on Modern Rolex President models.
Corundum: A crystalline form of aluminum oxide known in the gemstone world as ruby and sapphire. It is naturally clear, but can have different colors when impurities are present. Corundum is much admired for its hardness (9.0 on the Mohs scale) and brilliance and excellent wearability.
COSC (Controle Officiel Suisse des Chronometres): Official Swiss testing station, whereby watches are tested for the chronometer rating.
Cosmograph: A Rolex trademarked term, which is similar to the chronograph, the cosmetic difference being that the tachymeter scale is printed (or engraved) on the bezel rather than on the outer rim of the dial.
Counterfeit Rolex Parts: Any aftermarket parts that bear illegal, fake or otherwise non-authentic Rolex trademarks, logos or hallmarks. These parts are used with the sole intention of deceiving someone by misrepresenting the watch/parts as authentic Rolex made.
Critical Angle: The largest angle measured from the normal at which light can escape from and optically dense substance, and the smallest angle to the normal at which light is totally reflected within the dense substance. Pretty simple, huh!
Crown: The upper portion of a faceted diamond, which lies above the girdle.
Crown angle: The angle of a diamond’s bezel facets (or, on emerald cut diamonds, the row of concentric facets) as measured from the girdle plane. This gentle slope of the facets that surround the table is what helps to create the dispersion, or fire, in a diamond. White light coming up from the pavilion exits the diamond in the crown area… exiting at different angles which breaks up the white light into its spectral colors, creating a beautiful play of color inside the diamond.
Crown Guards (Also Shoulders): Protective rails protruding from the watch’s case on either side of the crown for the purpose it from damage.
Crown Height: The height of the diamond that is above the girdle. Measuring from the girdle to the table facet.
Crown Height Percentage: The crown height expressed as a percentage of the average girdle diameter of a Round Brilliant Cut diamond or the width of a Fancy Cut diamond.
Cubic System: A crystallographic system, the crystals of which may be described by reference to their axes of equal length, each situated perpendicularly to the plane of the other two. Diamond belongs to this system. Another bit of useful information!
Cubic zirconia: A lab created diamond simulant, often abbreviated as CZ. While CZ is a transparent stone, trace elements can be added to the manufacturing process, producing a wide range of colors. On Mohs scale of hardness, CZ is harder than other gemstones except for diamond, ruby, sapphire and chrysoberyl. Not to be confused with Zircon, a natural gemstone.
Culet: The lowest part of a gemstone. This looks the tip or point of the stone.
Cushion Case: Squared shape with rounder edges, used on older model watch cases.
Cushion Cut Diamond: A square or rectangular shaped brilliant cut diamond with rounded corners. The overall shape is similar to a pillow or cushion. It is a modern version of an Old Mine Cut diamond.
Cut: Cut refers to the angles, symmetry, and proportions a diamond cutter uses in transforming a rough diamond into a polished diamond. One of the 4Cs used to evaluate a diamond, see Diamond C
Cutting Style or Faceting Style: This refers to the shape, size, and arrangement of the facets on a diamond. It can be categorized into the following three basic types.
Cyclops: Glass bubble positioned over the date aperture for the purpose of magnifying the date to be more easily read. First patented on May 1, 1952, and publicly released on the datejust at the Basel fair in 1954.
CZ (Synthetic Cubic Zirconia): A widely used diamond simulant. See Diamond Simulants.

Dark Center: A dark area visible through the table in a stone with an inferior cut… the diamond is too deep.
Dark Included Crystal: An inclusion in a diamond which is dark in color. Many times, it is incorrectly referred to as a “carbon spot”.
DCI (Decompression Illness): A condition, especially in divers, caused by the release of nitrogen bubbles in the tissue and blood upon too rapid a return from high pressure to atmospheric pressure —characterized by pains in the joints, cramps, paralysis and possibly death. This condition is often referred to as “the bends.”
De Beers: De Beers and the various companies within the De Beers Family of Companies engage in exploration for diamonds, diamond mining, diamond trading and industrial diamond manufacture. De Beers is active in every category of industrial diamond mining: open-pit, underground, large-scale alluvial, coastal and deep sea. Mining takes place in Botswana, Namibia, South Africa and Canada.
Dead Stone: A diamond so heavily included or so poorly cut that there is no brilliance (life).
Deep Cut: Refers to the angles, symmetry, and proportions a diamond cutter uses in transforming a rough diamond into a faceted diamond. When a diamond is cut too deep, it will leak light through the side or bottom. This results in a diamond that is dark.
Demantoid: is a rare and valuable andradite garnet. It exhibits a range of greens from dull to bright emerald green and on rare occasions displays yellow. On Mohs scale of hardness, demantoid is relatively soft at 6.5. It has an adamantine luster.
Density: The ratio of a gemstone when compared to the weight of an equal volume of water. This means how heavy a gemstone is compared to the same volume of water. Also known as “specific gravity” for solids.
Depth: The height of a diamond from the culet to the table. The depth is measured in millimeters.
Depth Percentage: On a diamond grading report, you will see two different measurements of the diamond’s depth- the actual depth in millimeters and the depth percentage (a percentage in relation to the diameter of a diamond). The (total) depth percentage of a diamond is the sum of the crown height, the girdle thickness, and the pavilion depth. It can give an indication of quality of the cut of the diamond.
Dial: This is the face of the watch, on which the hour markers (or indices) and hands are attached. On date and day-date models, an aperture is cut in the dial to allow the number wheels to be read.
Diameter: The width of a round diamond… used as the reference point for the diamond’s proportions.
Diamond: A form of crystalline carbon, made up of 99.95% pure carbon atoms arranged in an isometric, or cubic, crystal arrangement, singly refractive, a refractive index of 2.417, a dispersion index of 0.44, and a specific gravity of 3.52. It is by far the hardest of all known natural substances (10 on Mohs scale); only manmade Borazon and synthetic diamond are as hard. Now, that is a really romantic description of a diamond!
Diamond Cut: Also known as the Brilliant Cut, the style of cutting a stone with multiple facets to maximize brilliance. Modern round brilliant cuts have 58 facets.
Diamond Cutter: A person engaged in the cutting and polishing of diamonds.
Diamond Cutting: The process by which a rough diamond is transformed into a finished, faceted stone. As a first step, cleaving, sawing, or lasering is used to divide the rough into smaller, more workable pieces that will each eventually become an individual polished stone. Next, bruting grinds away the edges, providing the outline shape (for example, heart, oval or round) of the diamond. Faceting is next done in two steps:
Diamond Gauge: An instrument that is used to measure a diamond’s length, width and depth in millimeters.
Diamond Grading Report: An expert opinion of the quality of a diamond, that contains information on identification, enhancements, carat weight, shape outline, measurements, color, clarity, and cut. Many include diagrams, top and bottom plotting diagrams of the diamond’s clarity characteristics. Usually issued by a disinterested 3rd.party, typically an independent gemological laboratory.
Diamond Saw: A saw used for sawing through diamonds as part of the diamond cutting process.
Diamond Syndicate: In the early days of South African diamond fields, the word “syndicate” was used to refer to various groups of individuals and companies that held controlling interests in diamond production and distribution. In 1890, a syndicate consisting of ten firms offered to produce all of De Beers Company’s diamonds: The term syndicate is no longer meaningful, it is often applied to De Beers Group, because it holds a controlling interesting in a number of diamond-mining companies and in companies that have buying contract with independent producers, including the Diamond Corporation, Ltd.
Diamond Trading Co., Ltd: The organization that markets to the diamond industry the gem diamond it buys from the Diamond Purchasing and Trading Co., Ltd.
Dichroism: A term meaning the ability of some gems to display a second shade of the same color when viewed from a different angle. A dichroscope can see this change, and is used for identifying certain stone.
Dispersion: The spreading of white light into its spectral colors. This typically occurs in the crown area of a diamond. Also referred to as fire.
Divers’ Extension: Used on divers’ watches, a “hinged” extension within the watch’s bracelet allows the bracelet to be lengthened so as to fit over a wet suit.
Dodecahedron: One of the seven basic forms in the highest symmetry (“hexoctahedral”) class of the cubic, or isometric, crystal system. It has 12 rhomb-shaped faces, each of which intersects two of the crystallographic axes and is parallel to the third. This form is uncommon in gem diamonds. Did you understand that?
Double Named Watches (also Co-Branded): Refers to watches that bear more than one company name on the dial (i.e. the manufacturer and retailer).
Double Quick Set: Introduced in late 1990, this feature allows both the day and the date to be rapidly set via the winding crown – See also Quick Set.
Double Refraction: The ability of most gems to split rays of light into two rays.
Doublet: A form of gemstone trickery that was devised to allow inexpensive materials to imitate the more valuable gemstones before modern synthetics were available. A doublet can take several forms but always involves a fake gemstone produced by gluing together two different materials to form an illusion.
Durability: A combination of hardness, toughness and stability that describes a specific gemstone’s ability to resist wear. The durability of a gem depends both on its hardness and “toughness”. It may be quite tough but easily scratched, or it may be exceedingly hard but lack toughness because of easy cleavage. Diamond is highest on the scale of hardness and, despite it rather easily developed octahedral cleavage, it is among the toughest of gemstones.

E: A grade in GIA’s Color Grading System…. in the middle of the “Colorless” category.
Ebauche: A movement blank. Typically, an ebauche does not include a mainspring or balance. These items are added as a movement is completed.
EGL: European Gemological Laboratory, EGL has franchises in a number of cities around the world which grade diamonds and offer other gemological services. EGL USA Group has laboratories in New York City, Los Angeles, Vancouver, and Toronto. EGL USA is not affiliated with any other EGL labs outside North America. Every certificate issued by an EGL USA lab states “A member of the EGL USA Group”. Certificate numbers are preceded by either “US” or “CA” to indicate country of origin and to provide consumers the assurance that their certificate has been issued by a member of the EGL USA Group. Please be careful of diamond grading reports issued by other EGL labs… they have been known to somewhat inaccurate!
Elapsed Time Rotating Bezel: A graduated rotating bezel often found on divers’ models, used to keep track of elapsed time while diving.
Emerald Cut Diamond: A rectangular-shaped diamond with cut corners. On the crown, there are three concentric rows of facets arranged around the table and, on the pavilion, there are three concentric rows arranged around the culet. This type of cut is also known as a Step Cut because its broad, flat planes resemble stair steps.
End Piece: The small (usually hollow) piece of metal, crafted to look like a bracelet link, which allows the bracelet to be attached to the case via tiny spring bars.
Enhancements: An artificial process used to improve the apparent beauty of a gemstone. Common enhancement processes include heating and fracture filling.
Escape Wheel: In a lever escapement, this is the last gear in the train, but does not turn other gears. Instead, it has specially shaped teeth that are alternately locked and unlocked by the motion of the balance and lever to regulate the motion of the watch in a controlled manner.
Escapement: Allows the power stored in the mainspring to be released through the gears in a regular and controlled manner – See also Lever Escapement.
Excellent Cut: A GIA and HRD-CGL grade for the highest cut and polish of diamonds.
External Characteristics: Irregularities located on the surface of a diamond.
Extra Facet: Small facets added to remove clarity characteristics or correct minor cutting discrepancies. Any facet added to the stone which is in excess of the facets normally required to complete the polishing. Usually found along the girdle to remove any imperfections.
Eye Clean: A trade term used to describe a diamond with inclusions or blemishes that can be seen with the unaided eye. It is prohibited by the American Gem Society for use by its members. It is also prohibited by the Federal Trade Commission, unless the stone meets the Commission′s definition of the term perfect. I’ve heard it more used in the colored stone trade than the diamond trade.

F: A grade in GIA’s Color Grading System…. at the end of the “Colorless” category.
Face Up Position: When you view the top of a diamond, perpendicular to the table.
Facet: The smooth, flat faces that are polished on the surface of a diamond. They allow light to both enter a diamond and reflect off its surface at different angle. The way light interacts with these facets affects a diamond’s brilliance and sparkle. A Round Brilliant Cut diamond has 58 facets (or 57 if there is no culet). The shape, quantity, and arrangement of these facets will differ slightly among other fancy shapes.
Faceted Girdle: Sometimes diamond cutters will place facets on the girdle to eliminate noticeable breading, roughness, or to help camouflage a thick girdle.
Fancy Cut: Sometimes used to refer to a gemstone cut in any shape other than the standard round cut, but also used to refer to gemstones that are cut in a shape other than the well known shapes of round, oval, pear, trillion, marquise, etc.
Fancy Diamond or Fancy Color Diamond: Any diamond with a natural body color strong enough to be attractive, rather than “off color”. A body color of light yellow or light brown would need to be beyond the “Z” color grade to be considered a Fancy Color.
Fancy Shape Diamond: Any diamond cut into a shape other than round. Fancy cuts include the Marquise Cut, Asscher, Emerald Cut, Heart Shape, Pear Shape, Keystone, Half Moon, Kite, Triangle, and many others. I’ve even seen them cut into the shape of Christmas Trees, Horse Heads, Tennis Rackets, etc.
Feathers: These are small fractures in a diamond. In some cases the feather both begins and ends within the diamond’s surface and, in other cases, the feather begins inside the diamond and extends to the surface. The term “feather” comes from the fact that, under magnification, these fractures often seem to have an indistinct, feathery shape to them. While the idea of buying a diamond with “fractures” or “cracks” may sound scary, the reality is that, with normal wear and care, most feathers pose no risk to the diamond’s stability. Most diamonds with feathers have survived their growth and their journey to the surface intact… once on the surface, they also survived the mining process, as well as the brutal stresses of the diamond cutting process. Though diamonds are certainly not invulnerable to damage, basic consideration to their care and handling during everyday wear will most likely protect them over the course of several human lifetimes.
Finish: This refers to the quality of how the diamond cutter executed the designing, fashioning, and faceting the diamond. If you look at a diamond’s grading report, you will see its finish graded according to two separate categories: polish and symmetry
Fire: The rainbow or colors that light rays form as they move through a gemstone. This is another word for “dispersion”.
Fisheye: A diamond whose pavilion is exceedingly shallow, producing a glassy appearance (a noticeable lack of brilliancy) and the reflection of the girdle that starts to come into view in the table area.
Fissure: A surface crack on a gemstone. Gems with fissures may be Fracture Filled.
Flat Stone: A Round Brilliant Cut diamond with a very thin crown and pavilion.
Flawless (FL): No blemishes or inclusions when examined by a skilled grader under 10X magnification.
Flip Lock Clasp: Clasp used on special Oyster bracelets, whereas the buckle utilizes a “flip-lock” safety clasp to help prevent accidental loss. These are often found on divers’ models (i.e. Submariner, Sea-Dweller).
Fluorescence: The ability of some gems to appear a different color when viewed under ultraviolet light. If or not a stone has fluorescence is a valuable aid in gem identification.
Foilback: A faceted glass or quartz stone which has a pavilion that is coated with a silver colored paint to reflect light and act like a mirror. It is commonly seen in costume jewelry. Before, modern, highly reflective cuts were developed, even diamonds were foilbacked.
Four C’s: A phrase used to describe the 4 characteristics used to determine a diamond’s value. All the characteristics start with the letter “C”: Cut, Color, Clarity, and Carat weight.
Fracture: An internal or external break or crack in a diamond that is not in the direction of a cleavage plane. Irregular in shape, they usually appear step-like or as a splinter. An internal fracture is also called a feather… a much nicer term to say that you have a feather in your diamond verses having a crack in your diamond!
Fracture Filling or Fracture Filled Diamond: A diamond enhancement process in which a fracture in a diamond is filled with an artificial substance. The fracture that is filled normally reaches the surface of the diamond or it could be laser drilled and then filled. A Diamond Grading Report cannot be issued for a diamond of this type because its clarity characteristics are not considered permanent.
Full Cut: A round-shaped, brilliant-cut gemstone.
Full Cut Diamond: A description of a Round Brilliant Cut diamond with 57 or 58 facets. Consisting of 32 crown facets and a table facet above the girdle and 24 pavilion facets and possibly a culet facet below the girdle.
Fuzzy Girdle: Also called a Bearded Girdle. If a diamond is “rounded up” too quickly in the bruting process, the surface of the girdle will lack the smoothness and waxy luster of a finely turned girdle. As a result, numerous minute, hairline fractures that extend a short distance into the stone. The girdle can be polishing of faceted to remove or minimize the fractures.

G: A grade in GIA’s Color Grading System…. at the beginning of the “Near Colorless” category.
G.M.T: Abbreviation for Greenwich mean time. Time is calculated from the naval observatory at Greenwich, England, which is located at zero degrees longitude.
Gas Escape Valve: A one-way valve used in the Sea-Dweller, by which the helium particles are allowed to escape from the watch’s case during decompression. Sometimes called a helium escape valve.
Gauss: The centimeter-gram-second electromagnetic unit of magnetic flux density, equal to one Maxwell per space centimeter. [After Karl F. Gauss (1777-1855)]. The American Heritage Dictionary, Second College Edition. Copyright 1985 by Houghton Mifflin Company. All rights reserved. Please Note: The Rolex Milgauss gets part of its name from this term (i.e. Mill-Gauss).
Gem / Gemstone: A mineral or organic material with sufficient beauty, rarity, and durability to become desirable enough to be set into items of jewelry.
Gemological Institute of America (GIA): In 1931, Robert M. Shipley founded the Gemological Institute of America in Los Angeles. In the same year, he published his groundbreaking book, Gemology, and by that summer, 250 jewelers had enrolled in his courses. Some would later become instructors and researchers at the Institute. Since that time GIA has become the world’s foremost authority in gemology. GIA’s mission is to ensure the public trust in gems and jewelry by upholding the highest standards of integrity, academics, science, and professionalism through education, research, laboratory services, and instrument development. GIA was responsible for developing and standardizing the diamond grading system that is used today by nearly all other gem labs.
Gemologist / Graduate Gemologist: A person who studies gems…. normally a diploma is associated with this title. If there is no diploma then if a person who has a love of gems could be called a “rock hound” or an “amateur” gemologist. A person who has successfully completed recognized courses of study in gem identification, grading and pricing, as well as diamond grading and appraising is a Gemologist. There are many different institutions that can bestow the title of Gemologist…. a “Graduate Gemologist” is mostly associated with the Gemological Institute of America and a “certified Gemologist” with the American Gem Society. I have the title of GG, so I will show my title as follows- Bud Boland, GG(GIA).
GIA-GTL, Gemological Institute of America’s Gem Trade Lab: The well-respected independent laboratory which grades diamonds and provides other services for the diamond and colored stone trade. GTL has labs in many countries around the world.
Gilt (or Gild): Gold plated, or having a gold color or hue.
Girdle: The widest point in circumference of a gem. This is the point where a gem is usually held by fingers or tweezers for examination.
Girdle Facets: The 32 triangular facets that adjoin the girdle of a Round Brilliant Cut diamond, 16 above and 16 below the girdle. Also called upper and lower girdle facets, upper and lower break facets, top and bottom half facets, skew facets or cross facets. Facets are sometimes placed directly on the girdle, in which case the stone is usually said to have a “faceted girdle”.
Girdle Reflection: When the reflection of the girdle that is viewable inside of the table facet.
Girdle Thickness: The measurement of the girdle and the resulting thickness percentage of the diamond’s average girdle diameter or the diamond’s width. The girdle is not graded, but rather it is described by its appearance at its thinnest and thickest points. The descriptions of girdle thickness range as follows: Extremely Thin, Very Thin, Thin, Slightly Thin, Medium, Slightly Thick, Thick, Very Thick, or Extremely Thick. The girdle should be just thick enough to protect the diamond in setting and normal wear. For a Round Brilliant Cut diamond the girdle should be from Slightly Thin to Medium to Slightly Thick… anything out of this range is the result of trying to retain weight from the diamond rough. A Fancy Shape Diamond should have thicker girdle area at the points of a Marquise Cut or Pear Shape diamond.
Girdling: One of the initial steps of the fashioning process of a diamond in which the stone is given an outline shape. The stone is held in a lathe, or cutting machine, and another diamond, called a sharp, which is affixed to the end of a long dop that is supported by the hands and under an armpit, is brought to bear against the stone behind shaped. An older method consisted merely of rubbing two diamonds together until the desired outline shape was obtained.
Gold: A precious metal which has been used in jewelry for centuries. Gold will never tarnish, rust or corrode. It has also been used as a store of value to build wealth and shield against hard times. Gold used in jewelry is almost always alloyed with other metals since gold in its pure form is very soft and malleable, and would not wear well by itself.
Good Cut: An acceptable, lower priced diamond with adequate proportions.
Grading Report: Sometimes called a “certificate” or a “cert”, although labs do not “certify” diamonds. The grading report, issued by an independent laboratory, should accurately describe the measurements, proportions, weight, color, clarity, symmetry, polish and possible fluorescence seen in the diamond being evaluated. Some labs such as GIA and AGS are felt by many experts to be more consistent and stringent in their grading than some other labs.
Grain and Grainer: A trade term referring to a diamond’s weight. A grain is equivalent to 0.25 carats…. so a 4 grainer = 1.00ct., a 5 grainer = 1.25ct., etc.
Grain Center: A small area of concentrated crystal structure distortion, usually associated with pinpoints.
Graining: A clarity characteristic resulting from irregularities in the growth direction of a diamond crystal. Appears as faint single line or groups of lines. Much like the grain seen in a piece of wood.
Greasy (luster): One of the the technical terms used to refer to the luster of a gemstone. Jadeite is an example of a gem with a greasy luster.
Guilloche: French term meaning ‘engine-turned.’ This term is also used to describe the ‘honeycomb’ textured dial found on some Rolex models

H: A grade in GIA’s Color Grading System…. in the middle of the “Near Colorless” category.
Hacking: Introduced around 1972, this feature causes the second hand to ‘stop dead’ when the winding crown is pulled out fully to set the time, thus allowing for more easily synchronizing of one or more watches.
Hairspring: See Balance Spring.
Hallmark: A mark or stamp indicating the purity of a metal, or the date and/or country of import.
Hardness: The resistance of a substance to being scratched. Mohs scale of relative hardness consists of 10 minerals, each scratching all those below it in scale and being scratched by all those above it. Diamond is 10 on the Mohs scale of hardness, meaning that the only thing that can scratch a diamond is another diamond. Tests prove that diamond is approximately five to 150 times as hard as corundum, the next hardest mineral.
Harry Winston: A famous Beverley Hills jeweler who is known as the “Jeweler to the Stars”. There are now many Harry Winston store around the world.
Head: The metal basket which holds the diamond in place with prongs. The head is attached to the ring, earrings, pendant, etc.
Heart Shaped Diamond: A fancy diamond cut, which is cut to resemble the popular Valentine’s Day heart shape. It is a modified brilliant cut with a heart-shaped girdle outline that is similar to the Pear Shape Diamond, except that there is a cleft at the top. In fact, often the reason diamond cutters may choose a Heart Shape over a Pear Shape may be that the rough diamond contained an inclusion located in the cleft. The skill of the cutter can make a great difference in the beauty of this cut.
Hearts & Arrows: A Round Brilliant Cut diamond that is cut and polished to ideal proportions with exceptional symmetry and polish which shows eight heart shapes (Pavilion view) and eight arrows (Crown view) when observed through a special viewer called a FireScope. There is no industry standard of diamond proportions.
Heat Treatment: The application of high heat to a gemstone in order to improve its color and clarity.
Hermetic: Completely sealed, expecially against the escape or entry of air and/or dust.
Honeycomb Dial: A Rolex dial model featuring a honeycomb-like texture—See also Guilloche.
Horology: 1 – The science of measuring time. 2 – The art of making timepieces.
HRD: Hoge Raad voor Diamant (HRD). HRD Antwerp (Belgium) operates six services: HRD Diamond Lab, HRD Precious Stones Lab, HRD Education, HRD Graduates Club, HRD Equipment and HRD Research. Certification company Diamond High Council.
Hue: Refers to the position of a color on the color wheel, or the dominant wavelength of color attributed to a gemstone. There are six primary hues: violet, blue, green, yellow, orange, and red. In between these primary hues are secondary hues, such as blue-green. See also tone and s
Hunter Case: A case used on pocket watches and even some early wrist watches, whereas the front and back are protected by hinged covers, which are usually spring loaded.

I: A grade in GIA’s Color Grading System…. in the middle of the “Near Colorless” category.
Ideal Cut: A Round Brilliant Cut diamond that cut to optimal proportions, with optimal polish and symmetry. There is no universally accepted standard for an Ideal Cut. The most commonly mentioned proportions when talking about an Ideal Cut is the proportioning that was mathematically determined by Marcel Tolkowsky in 1919. See Diamond C
IGI: International Gemological Institute. A gemological laboratory which offers a diamond grading reports also written appraisals.
Illusion setting: A head designed to make the diamond that is set into it look larger than it actually is…. hence it is giving the “illusion” of a larger diamond. The metal that surrounds the stone usually has an intricate design.
Incabloc: The best known of the various competing shock absorbers for watches, it is manufactured by Potescap SA and considered an industry standard.
Included (I1,I2,I3): “I” in GIA’s Clarity Grading System… “contain inclusions which are obvious to a trained grader under 10X, can often be easily seen face-up with the unaided eye, seriously affect the stone’s potential durability, or are so numerous they affect transparency and brilliance”. I1 usually has inclusions that are visible to the unaided eye and at the end of the I3 grade the diamond can no longer be considered gem quality.
Included Crystal: A mineral crystal (many times it’s another diamond, but it could also be one of many different minerals) contained inside of a diamond. Include crystals can be almost any size, colored or colorless, and can occur alone or in groups. Dark included crystals are often called “carbon spots” or just “carbon”, but it’s an incorrect term when referring to these diamond inclusions.
Inclusions: Foreign matter that is “included” within a stone. This may be a foreign body such as a crystal, a gas bubble or a pocket of liquid. There are many varieties of inclusions and they are important visual clues for identifying the type of gemstone and for identifying the origin of the stone.
Indices: Another term for the hour markers on a watch’s dial.
Indicolite Blue tourmaline: From bright blue hues to bluish green colors, indicolite tourmaline is one of the rarer tourmaline colors.
Industrial Diamonds: Non-gem quality diamonds used in drills and other tools.
Internal Graining: Internal indications of irregular crystal growth. May appear milky, like faint lines or streaks, or may be colored or reflective.
Internally Flawless (IF): no inclusions when examined by a skilled grader, and only insignificant blemishes under 10X.
Invisible Set Diamonds: A skilled method of setting square gemstones into two rows or more with no metal showing between the rows.
Iridescence Effect: caused by the interference of light on thin films within the gemstone.
Irradiated Diamond: A diamond which has been exposed to a stream of accelerated electrons and then heated in order to alter its color. See Color Enhanced Diamonds.

J: A grade in GIA’s Color Grading System…. at the end of the “Near Colorless” category.
Jewel: A precious stone (usually a synthetic sapphire or ruby) that is used as a bearing for watch gears to reduce friction. The top of the jewel has a depression to hold oil. Jewels are set in the metal plates that support the gears. The pivot (the tip of the gear arbor) goes through a hole in the jewel.
Jump Hour: From Heures Sautantes, a watch where the hour hand is replaced with a tiny aperture at the 12 o’clock position. Through this window one could view a miniature wheel displaying the numbers 1 thru 12. When the minute hand passed the 60-minute mark, the wheel would turn, thus the hour marker jumping into place at the start of each hour.

K: A grade in GIA’s Color Grading System…. at the beginning of the “Faint Yellow” category.
Karat: The measure of purity of gold… 24K gold is 100% pure, 18K gold is 75% pure, 14K gold is 58.5% pure.
Kimberlite: Volcanic diamond bearing rock (also called blueground by the miners). These Kimberlite pipes are the primary source for diamonds. Open pit mines are started at the top of the pipe and vertical shafts are sunk down along the sides and then horizontal tunnels are then dug to access the pipe at greater depths.
Kimberly Process: Also referred to as KPCS- Kimberley Process Certification Scheme. The Kimberley Process (KP) is a joint governments, industry and civil society initiative to stem the flow of conflict diamonds (rough diamonds used by rebel movements to finance wars against legitimate governments). The trade in these illicit stones has fuelled decades of devastating conflicts in countries such as Angola, Cote d’Ivoire, the Democratic Republic of the Congo and Sierra Leone.
Knife-edge Girdle: A girdle of a diamond that is so thin that it can be likened to the edge of a sharp knife. This is a sign of poor cutting since such a girdle is easily chipped.
Knot: An included diamond crystal that is encountered by the saw blade while the diamond rough is being sawn in half. Also an included diamond crystal that is encountered at the surface of a diamond during the polishing operation, and that stands out as a small, raised surface on the finished diamond. This is just like a knot in a piece of wood.

L: A grade in GIA’s Color Grading System…. in the middle of the “Faint Yellow” category.
Lab created: Refers to gemstones created in a laboratory rather than by nature. A lab created gemstone is typically the same material chemically as its natural counterpart, as in the case of corundum produced by flame fusion or quartz grown using the hydrothermal method.
Lady President: This nickname is often used to refer to the ladies ‘Rolex Datejust’ fitted with a President bracelet.
Lapidary: The science and art of cutting and polishing gems to their finished state.
Laser Cutting: Diamond has different directions that it can be cleaved, sawn, and polished. Using a laser to cut the diamond into an unusual shape is now possible. A laser can cut across the growth plains, which makes odd shapes such as letters, Christmas trees, tennis rackets, horse heads, etc. possible.
Laser Drill Hole: A hole is a tiny tunnel drilled into a diamond by a laser beam. The tunnel extends from the surface of a diamond down to a dark included crystal. The diamond is laser drilled in order to lighten a dark included crystal. After the diamond has been drilled the inclusion can be then bleached and become less noticeable. It might improve the clarity grade of the diamond but it usually will make a diamond much more marketable having a lightly colored inclusion verses a much more obvious darker inclusion. GIA’s Gem Trade Lab will issue a diamond grading report on diamonds that have laser drill holes (without any fracture filling) because the holes are permanent features and they will note the laser drill holes under the comments area of the report.
Laser Inscription: An extremely small inscription by a laser along the girdle of a diamond. This can be the diamond grading report number, a logo, a message, or a company’s name.
Length-to-Width Ratio: A ratio of how many times greater the length is in comparison to the width of a fancy shape diamond. Each fancy shape diamond has a range of ratios that are acceptable by most people. There is no “ideal” L to W ratio…. some are considered to be more appealing but it does turn out to be a personal preference.
Lever Escapement: Invented by Thomas Mudge in 1759. It subsequently replaced all other types of watch escapements, and is currently the only type of escapement manufactured for watches. Consisting of an escape wheel, “lever” and a balancing wheel, the lever, when initiated by the balance wheel, locks and unlocks the escape wheel, thus transferring power through the gear train in an even and controlled motion.
Leveridge Gauge: A commonly used device to measure the precise dimensions of a mounted or unmounted gemstones.
Light Yellow: A trade term used by some dealers to cover a wide range of colors in the low end of the diamond color-grading scale. Diamonds with a “touch of warmth”.
Ligne: A pre-metric system of measurement still used in Switzerland to measure watch movements. One ligne (“’) is approximately 2.256 mm.
Lively Stone: A diamond that has a reasonably good cut so that it has good brilliance and luster.
Lot: A large group of diamonds that have been closely matched in clarity, color, cut, and weight…. these diamonds are being offered for sale as an entire group and not piece by piece.
Loupe: A handheld magnifying glass used in the diamond trade to inspect diamonds. Magnification is usually 10X power and is corrected so as not to distort shapes and color. All diamonds are clarity graded under 10X.
Loupe Clean: When viewed under 10X magnification, a diamond is considered loupe clean if no obvious inclusions are immediately seen.
Lower Girdle Facets: These are triangular shaped facets, located on the pavilion just below the girdle.
Lugs: The two pointed edges on either end of the case, by which the bracelet is attached to the case through the end pieces. These are often called the ‘horns.’
Luminova: Organic, non-radioactive, luminous material now used on the hands and hour marker of a watch. It replaced the older (and more dangerous) radioactive material Tritium around 1998.
Luster: The quality and quantity of reflected light from the surface of a gemstone. Because of its hardness, diamond has an “adamantine luster”.

M: A grade in GIA’s Color Grading System… at the end of the “Faint Yellow” category.
Main Facets: The 8 crown and the 8 pavilion facets of a Brilliant Cut diamond. These are the facets where the angles are measured in order to determine a diamonds proportions.
Mainspring: The principal spring of a watch that supplies the force of motion to the gear trains.
Make: A trade term referring to the proportions, symmetry, and polish of a diamond. Commonly stated as a “good make”, “well made”, a “poor make”, etc.
Marquise: The marquise shape is an elongated oval with points on both ends. Said to be named after the Marquise de Pompadour, the mistress of King Louis XV.
Marquise Cut Diamond: A Fancy Shape diamond which is “boat shaped”, elongated with points at each end. The term “Marquise” came from a story about the origins of the shape. The French “le Roi Soleil”, Louis XIV wanted a diamond to be polished into the shape of the mouth of the Marquise of Pompadour.
Master Stones: A set of diamonds of known color that are used to decide the body color of other diamonds that are compared to this set of master diamonds. A set of master stones must have very exacting specifications in order to be used.
Mechanical: Movement used on traditional timepieces, whereas the watch uses a main spring for its power source and must be hand wound.
Melee: A French word meaning confused mass. A trade term that is used to describe small diamonds. They are usually side diamonds or accent diamonds in a piece of jewelry.
Mercedes Hands: Nickname used to describe a style of hands used on some sports model watches. The name comes from the hour hand which features a round emblem which resembles the logo of the German automobile manufacturer Mercedes Benz. Rolex refers to these hands as skelette or skeleton hands.
Metallic (luster): One of the technical terms used to refer to the luster of a gemstone. A gemstone that is reflective like polished metal is said to have a metallic luster. Hematite is one of the rare examples.
Micro-Stella: Tiny screws used for adjustment of the balance.
Mid-sized Watches: Refers to Rolex models that are 80% of the size of a standard men’s watch.
Milled Edge: Having a grooved or coined edge. First used on watch cases by the Dennison Watch Case Company in the early 1900s, and is still featured on the back of all Rolex Oyster cases.
Mixed Cut: This faceting style has both step-cut (crown, top) and brilliant-cut (pavilion, bottom) facets.
Mohs Scale: In 1812, a scale of mineral hardness was devised by the German mineralogist Friedrich Mohs, who selected the ten minerals because they were common or readily available. The scale is not a linear scale, but somewhat arbitrary. The scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material.
Moissanite: A lab-created diamond simulant based on the structure of natural moissanite. On Mohs’ scale of hardness, moissanite is 9.5. It has more brilliance, fire and luster than any hard jewel on earth, including diamond.
Moon Phase: A type of dial showing the changes in the moon’s phases, or lunar cycles.
Mounting: Trade term for a piece of jewelry in which a gem or other object is set.
Movement: The machinery of any time piece.

N: A grade in GIA’s Color Grading System…. at the beginning of the “Very Light Yellow” category.
Natural: A portion of the original “skin” of a rough diamond that is left by the diamond cutter on a faceted diamond. Naturals are usually found along the girdle. In many cases, naturals do not affect the clarity grade.
Navette: A French word meaning “little boat”. A Marquise Cut diamond.
Near Colorless: A general term for diamonds in the G-to-J color range.
Needle: A long, thin included crystal which looks like a…. needle.
Nick: A minor chip out of the surface of a fashioned diamond, usually caused by a light blow. Could be found along the girdle or facet junctions.
Nitrogen Narcosis: This alcohol-like effect is often called ‘rapture of the deep’, whereas the body absorbs a toxic level of nitrogen, which in some cases can cause death.

O: A grade in GIA’s Color Grading System…. at the beginning of the “Very Light Yellow” category.
Octagon Case: A watch case having eight sides, shaped similar to that of a stop-sign.
Oersted: The centimeter-gram-second electromagnetic unit of magnetic intensity, equal to the magnetic intensity one centimeter from a unit magnetic pole. [After Hans Christian Oersted (1777-1851)]. The American Heritage Dictionary, Second College Edition. Copyright 1985 by Houghton Mifflin Company. All rights reserved.
Off Center Culet: This is a problem with the symmetry of a diamond… the culet is not lined up with the center of the table. The culet has been pushed over to one side of the diamond. It was intentionally done in order to repair damage to a previously polished diamond or from attempting to retain maximum weight from a distorted piece of diamond rough.
Off Make: A trade term for a poorly proportioned Diamond.
Officially certified Chronometer: Around 1949, Rolex introduced this wording on the dials of their chronometer–rated models.
Oiling: Oiling infuses colorless oils, resins or waxes into tiny surface-breaking fissures to hide them and give certain gemstones a cleaner appearance. This long-practiced clarity enhancement is used mainly for emerald and jade. The oils used are either natural or have a natural counterpart. If coloring agents are added to the oil, the stones are classified as dyed rather than oiled.
Old European Cut: An early form of the Round Brilliant Cut diamond characterized by a small table, a high crown, deeper pavilion, and a large culet. Contrary to what you initially might have thought, it is not a diamond that was cut by an old European.
Old Mine Cut: A diamond cut that pre-dates the Old European Cut with the primary difference being the overall shape of the diamond was squarish…. similar to today’s Cushion Cut diamond.
Opaque: A term used for gemstones that you cannot see any light passing through the gem. Lapis and malachite are an example of this.
Open Table: A term that is sometimes used to refer to a diamond with a table of 65% or more.
Organic (gemstone): Most gemstones are minerals with a crystal structure but some gems, such as amber and pearl, are organic rather than mineral, being formed by plants and animals. See also Amorphous gemstones.
Oval Cut: The famous diamond cutting house of Lazare Kaplan developed the Oval Shape Diamond in the early 1960′s. This is a brilliant style of faceting and is an elliptical variation of the traditional round brilliant cut.
Ovettone (or Ovetto, or Ovitone): Italian for ‘little egg’, this nickname was associated with the Bubbleback models due to their rounded shape.

P: A grade in GIA’s Color Grading System…. in the middle of the “Very Light Yellow” category.
Padparadscha: Derived from the Sinhalese term for “lotus flower,” padparadscha refers to a lush pink and orange sapphire resembling the color of the lotus. Padparadscha is also sometimes used to refer to other types of gemstones, such as topaz and tourmaline, with this unique coloration.
Paraiba: A rare copper-bearing tourmaline with an intense blue or blue-green color, first found in the state of Paraiba in Brazil in 1989. There have been recent finds in Nigeria and Mozambique of similar material, and the term “paraiba” is now used to refer to all examples of this copper-bearing tourmaline. See also Copper-bearing.
Parcel Paper: Also called diamond papers. Folded sheets of paper used to contain polished or rough diamonds. On the outside of the paper are many different numbers- such as stock number, clarity, color, carat weight, shape, supplier, cost, etc. Contrary to what you see in the movies…. diamonds are not kept in big piles in boxes and trays… they are kept in papers.
Paste: A term for glass imitation gemstones.
Patina: A sheen which develops on the surface of platinum jewelry through continued wear.
Pave: (pah-VAY) A style of setting small stones very tightly together, as in a pavement or paved with diamonds. Most commonly seen with diamonds, but may be used with any stone.
Pavilion: The lower portion of a gemstone that begins just below the girdle.
Pavilion Angle: The angle measured between the girdle plane and the pavilion main facet.
Pavilion Main Facet: Eight, four sided facets of a Round Brilliant Cut diamond that meet at a point to form the culet.
pc: Abbreviation for “per carat” pricing…. expressed as $750pc.
Pear Cut: Resembling a pear or teardrop, this fancy cut is rounded on one end and pointed on the other.
Pedometer: The first self-winding pocket watch design, invented by Abraham-Louis Perrelet in 1770. Thus named after the source of its power (i.e. a weighted lever that jerks as a man walks)
Perfect: This term has been so flagrantly misused in the sale of diamonds that many jewelers avoid its use entirely. The American Gem Society also prohibits its use by its members. The Federal Trade Commission considers it an unfair trade practice to use the word “perfect”, or any other word, expression or representation of similar import, as descriptive of any diamond that discloses flaws, cracks, carbon spots, clouds or other blemishes or imperfections of any kind, including inferior color and make, when examined by a trained eye under a corrected diamond eye loupe or other equal magnifier of not less than ten power.
Perpetual Movement: Another term for an automatic or self-winding movement with a winding rotor that travels a full 360 degrees.
Phenomenal Gems: Gems that display unusual optical properties such as color change, chatoyancy, asterism or iridescence.
Pigeon’s Blood: Refers to the most prized color of red in rubies. Pigeon’s blood red is thought to be a pure red with a hint of blue. It is associated most with rubies from Burma, though any ruby could be this color.
Pinpoint: A pinpoint is a extremely small included crystal inside of a diamond. A grouping of pinpoints is called a “cloud”. A cloud can appear as a hazy area in the diamond. A single pinpoint can change a diamond clarity grade from an Internally Flawless to a VVS1.
Pipe: The remains of an ancient volcano. Diamond bearing magma (kimberlite) had made its way to the surface via a weak spot in the earth’s crust. The volcanic mountain that was formed is then eroded away from rain and all that is left is the pipe. Open pit mining is done on top of the pipe and a vertical shaft is sunk next to the pipe with horizontal tunnels dug into the pipe. Kimberlite pipes have been found in Africa, Canada, Russia, Arkansas, Australia, and elsewhere.
Pit: A tiny opening on the surface of a diamond, often looking like a white dot.
Pivot: The turned down part of an arbor. This part commonly projects through the hole in watch jewels.
Plate: The portion of the movement which supports the bridges and other plates.
Platinum: A rare precious metal used in jewelry. Platinum is naturally white and is favored for many ring settings because of its durability.
Pleochroism: The ability of certain gems to display two or more colors when viewed from different angles. This is a term also used for Dichroism and trichroism.
Plotting Diagram: A diagram used on some Diamond Grading Reports that illustrates the facets of a diamond and the approximate location and type of internal and external characteristics.
Point: A trade term used to describe the weight of diamonds. One point is equivalent to one-hundredth of a carat. For example, a 1/4 carat diamond, equals 0.25ct., equals 25 points.
Pointer: Term used to describe polished stones under a carat. For example, a 37 pointer (0.37ct.
Polish: The smoothness of the surface of a diamond which shows no visible wheel or burn marks. Polish is regarded as one of the indicators of the quality of as diamond’s cut; it is graded as either Ideal, Excellent, Very Good, Good, Fair, or Poor.
Polish Lines: Tiny parallel lines left by irregularities in the diamond cutting wheeel’s surface.
Polish Mark: Surface clouding caused by excessive heat (also called burn mark, or burned facet), or uneven polished surface resulting from structural irregularities.
Polished Girdle: A girdle that has been lapped or polished to yield a uniform, highly reflective surface.
Polishing: In diamond fashioning, it is used to include both lapping, or blocking, and brillianteering, as well as the production of any facet; the final operation in fashioning a diamond, usually done with diamond powder on a horizontal disc, or lap, against which the diamond is held in a dop.
Poor Cut: A inferior cut diamond that can be either cut too deep or too shallow which will lose or leak light through the side or bottom resulting in less brilliance and value.
Precision: Term used by Rolex to describe their watch movements which had not received a timing certificate, thus were not rated as chronometers.
President: This nickname is often used to describe the Rolex Day-Date models, since one was given to then President Dwight D. Eisenhower in 1956 to celebrate his re-election, and nearly every President since Franklin D. Roosevelt has worn one. However, the name ‘President’ is officially only used to describe the bracelet style featured on the Day-Date model.
Princess Cut: A square or rectangular-shaped modified brilliant cut diamond.
Prong or Claw Setting: A setting style that uses 4 or 6 small fingers of metal that hold a diamond in place. Each metal prong is individually pushed into place to hold the diamond securely.
Proportion: The proportions of a diamond are very important, so that the maximum amount of light be reflected off and out of a stone. Proportion is the relationship between the angles of the facets of the crown and pavillion.
Proportion Scope: A device that combines lenses and movable mirrors to project the silhouette of a diamond onto a screen. Diagrams and scales are printed on the screen which facilitates the analyzation of the proportions of round brilliant cut diamonds, as well as fancy shaped diamonds.

Q: A grade in GIA’s Color Grading System…. at the end of the “Very Light Yellow” category.
Quality: Term used to describe the degree of excellence of a diamond by its weight, color, clarity, and perfection of cut.
Quartz Movement: Quartz watches use a tiny energy cell (or battery) to replace the mainspring as the power source. The oscillating mass is replaced by a tiny piece of shaped quartz crystal, which is tuned to a frequency of 32,768 Hz (cycles per second) – this is often called the piezoelectric effect and is similar to that of a tuning fork. A system of integrated circuits then divides the frequency into one-second pulses to drive a tiny motor, which in turn drives the hands.
Quick Set: Introduced in late 1970, this feature allows the date to be rapidly set via the winding crown, without having the hour hand pass over the ‘midnight’ position – See also Double Quick Set.

R: A grade in GIA’s Color Grading System…. at the end of the “Very Light Yellow” category.
Radiant Cut: A brilliant cut fancy shape that has a square shape with the corners cut off. It might have a step cut or a scissor cut on the crown and a brilliant faceting style on the pavilion.
Radium: Radioactive luminous material first used on the hands of watches around 1913. This material was subsequently replaced by Tritium around 1950.
Reference Number: The case or model number of a watch, usually engraved between the lugs, and/or inside/outside the case back.
Reflection: The bouncing back of light when it strikes an external or internal facet on a polished diamond.
Refraction: The change in direction of a ray of light as it passes obliquely from a medium of one optical density to a medium of a different optical density, as from air into water or from air into a gemstone. This means that the light bends as it enters a diamond because the light travels through air and the diamond at different speeds.
Refractive Index: A process using a refractometer to measure the speed and angle of light entering a gemstone. Very important for gem identification.
Registers: Term used to describe the subsidiary ‘extra-function’ dials positioned on the face of a chronograph watch.
Rhinestone: A facetted piece of glass or quartz that has a foil backing in order to imitate a diamond.
Rhodium Plating: Rhodium is metal that is part of the platinum family. White gold is commonly rhodium plated in order to give it a very white finished color because white gold is not purely white but instead has a yellowish tint It is also used on silver to prevent it from oxidizing.
Rolesium: A Rolex term used to describe the case metal mixture of stainless steel and platinum, trade-marked on May 21, 1932. This configuration is currently seen on the Rolex Yacht-Master.
Rollesor: A Rolex term used to describe the case metal mixture of stainless steel and gold, trademarked on April 1, 1933.
Roman-Arabic Dial: See also California Dial.
Rose Cut: An early style of cutting that is thought to have originated in India and to have been brought to Europe by the Venetians. In its most usual form, it has a flat, unfaceted base and a somewhat dome-shaped top that is covered with a varied number of triangular facets and terminates in a point. The rose cut diamonds are very seldom used today but may be seen in antique pieces.
Rotating Bezel: Often used on sports watches like divers’ or aviator models, it is used to perform an additional function, such as checking decompression times, or telling the time in different time-zones – See also Bi-Directional Rotating Bezel and Uni-Directional Rotating Bezel.
Rotor: The oscillating weight used in an automatic movement.
Rough: In gemology, this refers to the raw, natural state in which gems are found, before they are cut.
Rough Girdle: When a diamond outer shape is formed in the cutting process it is done by grinding one diamond against another. This should leave the surface of the girdle with a smooth and waxy luster. If a diamond is rounded up too quickly in the fashioning process it will leave it grainy or pitted. It may also be accompanied by numerous hair like fractures extending into the stone, which is called a bearded or fuzzy girdle.
Round Brilliant Cut: This is the most common cut for a diamond. The standard round brilliant “full cut” diamond consists of a total of 58 facets: 1 table, 8 bezel facets, 8 star facets and 16 upper-girdle facets on the crown; and 8 pavilion facets, 16 lower-girdle facets, and usually a culet on the pavilion.
Rounding Up or Girdling: The step in the fashioning process of a diamond in which the stone is given its overall shape. The stone is held in a lathe, or cutting machine, and another diamond, called a sharp, which is affixed to the end of a long dop that is supported by the hands and under an armpit, is brought to bear against the stone behind shaped. An older method consisted merely of rubbing two diamonds together until the desired shape was obtained.
Rubellite: Used to refer to the red variety of tourmaline, including the color range from pink to red. More of a marketing than a gemological term; these days gemologists tend to use simply “red tourmaline.”
Ruby: See Jewel.
Rutiles: Needle-like inclusions (or foreign matter) within stones. These can produce some gem phenomena as an asterism (star) or cat’s eye (chatoyancy.

S: A grade in GIA’s Color Grading System…. at the beginning of the “Light Yellow” category.
Sapphire Crystal: First introduced in 1970, on the Rolex Quartz, these synthetic crystals are now used in most watches, due to the fact that they are highly scratch resistant.
Saturation: Saturation is one of three characteristics used to describe the appearance of color. Saturation (also known as intensity) refers to the brightness or vividness of a color. See also hue and tone.
Sawable: These are rough diamonds that can be divided by sawing.
Sawyer: A person who has the job of sawing diamonds.
Scaife: The horizontal cutting wheel on which a diamond is polished… also spelled scaive or scaif.
Scintillation: The flashes of light reflected off of the facets of a diamond when the diamond or the eye of the viewer moves. This is the bling factor! The number, the size, and the quality of the polish of the facets are all factors in the scintillation.
Scratch: A fine white line, curved or straight on the surface of a diamond. A scratch would be considered during the clarity grading process. A scratch can be polished away.
Self Winding: See also Automatic Winding.
Semi-mount: A jewelry setting that has the side stones already mounted, but which contains an empty set of prongs which are intended to mount a diamond center stone.
Semi-precious (gemstone): Traditionally, the four precious gemstones are diamond, ruby, sapphire and emerald. Semi-precious gemstones include everything else. But other gems have also been labelled precious at times, including opal, amethyst and pearl. Today, the distinction between precious and semi-precious gems has been rejected by some gem trade associations. See also Precious gemstones.
Serial Number: An identification number of a watch, usually engraved between the lugs, and/or inside/outside the case back. This number can often be used to date the production of the watch.
Set: How a diamond is held into a piece of jewelry. For example… bead set, pave set, channel set, prong set, etc.
Setting: A metal holder for the diamond.
Sheen: This effect resembles luster, and is caused by light reflection from inclusions or texture inside the gem. Luster is light reflected from the surface of the gem and sheen is reflection from inside the gemstone.
Shock Absorber: A system where the jewels on the balance staff are spring mounted, thereby protecting the balance staff from damage, in the event that the watch is dropped.
Side Stone: Side stones are set around or beside the center stone in a jewelry setting.
Single Cut: A round diamond with only 17 or 18 facets, instead of the normal 57 or 58 facets of a full cut diamond.
Single Refraction: Most gemstones are doubly refractive — they have 2 refractive indices. Only a few gemstones have a single refractive index, specifically diamond, spinel and garnet. See also Birefringence.
Skeleton Case: Also known as a ‘clear back’ model. It features a transparent front or back, thus permitting a view of the internal workings of the watch.
Skeleton Hands (or Skellete): Term used by Rolex to describe the hands on a watch that are ‘cut-out’ so they only feature an outline of the hands. Some of these hands are nicknamed Mercedes-style.
Skin: The surface of an unpolished diamond.
Slightly Included (SI1 and SI2): Contain noticeable inclusions which are easy (SI1) or very easy (SI2) to see under 10X. In some SIs, inclusions can be seen with the unaided eye.
Solitaire: A solitaire, often found in rings and pendants, is a single stone in a simple setting. Compare Center Stone and Side Stone.
Sorter: The person who separates rough diamonds into sizes and grades of quality by shape, color, and clarity.
Species: The term used to designate a family of gemstones. For example, corundum is a species that contains the varieties sapphire and ruby. The Quartz family contains amethyst, citrine, and chalcedony, to name a few.
Speleology: The study and exploration of caves. It was for these ‘cave dwellers’ (or speleologists) that the Rolex Explorer II was designed, whereby one could distinguish day from night with the use of a special 24-hour hand and bezel.
Spread Stone: A diamond with a large table.
Spring Bar: A small spring-loaded pushpin, which passes through the end piece into either side of the lugs, thus holding the bracelet onto the case.
Star Facets: The eight triangular facets around the table of a diamond that make it star-shaped.
Step Cut: Broad, flat facets that resemble stair steps. Emerald Cut or Asscher Cut Diamonds are cut in this style.
Subsidiary Seconds (or Sunk Seconds): The small seconds dial, usually positioned at the 6 o’clock and is sunken so as not to impede the hour and minute hand.
Super Balance: Balance wheel design for the Auto Rotor Perpetual movement, patented by Rolex in 1935.
Superlative Chronometer Officially certified: Starting in 1957, Rolex introduced this wording to replace ‘Officially certified Chronometer’ on the dials of their chronometer-rated models, and it is still used to this day.
Surface Graining: An area of crystal growth irregularity that does not polish the same direction as the surrounding area. Much the same as grain in wood.
Sweeping Movement: Also known as the ‘step’ or ‘action.’ Sweep refers to the movement of the second hand quickly ‘ticking’ at approximately 58 times per second, thus giving the illusion of sweeping.
Swiss Cut: A gem cut consisting of thirty-three facets.
Symmetry: The misalignment of facets or facets that fail to point correctly to the girdle. Symmetry is regarded as an indicator of the quality of the Diamond Cutter’s care and skill in fashioning the diamond. It is graded as either Ideal, Excellent, Very Good, Good, Fair or Poor.
Synthetic (gemstone): A synthetic gemstone is man-made rather than mined from the earth. Natural gemstones which are treated by industry-accepted methods such as heat or irradiation are not classified as synthetic.

T: A grade in GIA’s Color Grading System…. at the beginning of the “Light Yellow” category.
Table: The large facet on the top of the diamond’s crown.Table – The flat facet on the top of the diamond. It is the largest facet on a cut diamond.Table: The flat facet on the top of the diamond. It is the largest facet on a cut diamond.
Table Percentage: The relationship of the table as compared to the average diameter of a round brilliant cut or the width of a fancy shape diamond. So, a diamond with a 60% table has a table which is 60% as wide as the diamond’s outline.
Tachymeter (or Tachometer): A special scale printed on the outside of a chronograph, used to calculate the average speed traveled over a measured distance. Frequently used in auto racing to determine ‘lap times.’.
Telemeter: A special scale printed on the outside of a chronograph, used to determine the distance of an object from the wearer by measuring how long it takes sound to travel that distance.
Thunderbird Bezel: Also called the Turn-O-Graph bezel in the U.K., thus named after the Turn-O-Graph watch where it was first introduced. The bezel is now fitted to select Rolex Datejust models.
Tone: One of 3 characteristics used to describe the appearance of color. Tone refers to the lightness or value of the lightness in a particular stone. See also Saturation and Hue.
Tonnueau Case: Barrel-shaped case, whereas the ends are squared and the sides bow out in a rounded convex shape.
Tool Watch: This concept refers to watches created for use in specific sports or professional activities.
Translucent: A quality of a gemstone transmitting light imperfectly so that one cannot see through the stone clearly. Star sapphire is an example of this quality.
Transparent: There are several ways a light travels through a stone. In a transparent stone, the light travels through stone with virtually no distortion. Transparent stones are clear and easy to see through. See also Translucent and Opaque.
Travel Clock: Also called portfolio or purse watches. This refers to early covered, folding or protected clocks, some of which were carried in women’s purses around the early 1900s.
Treated Diamond: Describes a polished diamond that has been altered to change its appearance, (e.g., by artificial coloration, that is, irradiation).
Treated stone: A stone that has been heated, dyed, irradiated, or stained in order to improve the color or the clarity. Also pertains to gems that have their cracks or fractures concealed by filling the material.
Trichroism: A property of a stone that will show three colors or shades of the same color when the stone is viewed through a dichroscope.
Trillion Cut: A faceted cut in a triangular shape with 44 facets.
Triplock: Rolex screw-down crown, which features a triple seal against water and dust. First patented on July 22, 19652, it features the Rolex crown underscored with three ‘dots.’.
Tritium: Luminous material used on the hands and hour markers of a watch since the 1950s. This radioactive material was discontinued by Rolex around 1998, in favor of a safer material LumiNova. Modern watches containing Tritium will be marked “T”, “T25”, or “T<25” on the bottom of the dial. (Please Note: The radiation content is extremely small and is not a direct hazard to the wearer).
Twinlock: Rolex screw-down crown, which features a twin seal against water and dust. First patented on April 20, 1953, it features the Rolex crown underscored with a single horizontal ‘line.”.
Twinning Wisp: A cloudy area produced by crystal structure distortion, usually associated with twinning planes.
Two-Tone (also 2-Tone or Tu-Tone): Refers to a watch case featuring two different metals (e.g. stainless steel and yellow gold).

U: A grade in GIA’s Color Grading System…. at the beginning of the “Light Yellow” category.
Ultraviolet Fluorescence: The property in diamonds that makes them glow in ultraviolet light. Also known as photoluminescence. Ultraviolet light is high frequency, short wavelength electromagnetic radiation, between visible light and X-rays.
Uncut or Unpolished Diamonds: Diamonds that are usually referred to as “rough” or “diamond rough”… diamonds are they are found in the earth. It applies to all diamonds that have not been cut and polished yet.
Uni-Directional Rotating Bezel: Introduced in the 1980s, this elapse time bezel is often found on divers’ models, and only moves in the counterclockwise direction. Thus, protecting the diver from an erroneous (and potentially dangerous) reading when measuring decompression times, since any accidental movement could only err on the side of safety.
Unmounted: A faceted diamond which is loose, not set into a piece of jewelry.
Upper Girdle Facets: These are 16 triangular shaped facets, that are located on the crown just above the girdle.

V: A grade in GIA’s Color Grading System…. in the middle of the “Light Yellow” category.
Very Slightly Included (VS1 and VS2): Contain minor inclusions ranging from difficult (VS1) to somewhat easy (VS2) for a trained grader to see under 10X.
Very Very Slightly Included (VVS1 and VVS2): Contain minute inclusions that are difficult for even a skilled grader to locate under 10X. VVS1: extremely difficult to see, visible only from the pavilion or small and shallow enough to be removed by minor repolishing. VVS2: very difficult to see.
Vitreous: A technical term referring to the luster of a gemstone. Gemstones with a vitreous or glassy luster are by far the most common in the gems world.
Vivid: Used on color grading of fancy colored diamonds to denote the most intensely colored stones, not the darkest.
VS1, VS2: Clarity grades for diamonds developed by the Gemological Institute of America, just below Very Very Slightly Included (VVS). VS- Very Slightly Included, contain minor inclusions ranging from difficult (VS1) to somewhat easy (VS2) for a trained grader to see under 10X.
VVS1, VVS2: Clarity grades for diamonds developed by the Gemological Institute of America, just below Internally Flawless (IF). VVS- Very Very Slightly Included, contain minute inclusions that are difficult for even a skilled grader to locate under 10X. VVS1: extremely difficult to see, visible only from the pavilion or small and shallow enough to be removed by minor repolishing. VVS2: very difficult to see.

W: A grade in GIA’s Color Grading System…. in the middle of the “Light Yellow” category.
Waxy: One of the technical terms used to refer to the luster of a gemstone. Turquoise is an example of a gem with a waxy luster.
West 47th Street: “Diamond Jewelry Way” is the central location of the diamond industry in New York.
Wetability: Diamond is highly resistant to wetting by water.
White: A term that refers to a colorless diamond. Actually it is a colorless diamond so it technically can’t be w
White Light: Light containing a balanced full spectrum of colors, so that it appears colorless. Traditionally, in the North Hemisphere it has been light coming in a window that faces north (in the Southern Hemisphere would be the south) this light source would be considered balanced enough for good consistent results. Today it is possible to have color balanced fluorescent lights that make it possible to have this balance white light that is important for diamond color grading.
Winding Stem: Shaft on which the crown is fixed on an end.
Window: A small facet polished on a rough diamond, through its skin, to allow a diamanteer to observe and map any internal features of the diamond prior to cutting. Also an area of a gemstone which “leaks” light or color usually due to poor, often shallow, cutting.
Windowing Out: A trade term describing when the viewer is able to see through a gemstone as it is tilted to the side. The pavilion should act like a mirror and not like a window.
Wisp: An clarity feature due to twinning which is an irregularity in the crystal growth.

X: A grade in GIA’s Color Grading System…. at the end of the “Light Yellow” category.
X-ray Fluorescence: The property in diamonds that makes them glow when exposed to X-rays. All diamonds will fluoresce when exposed to X-rays and this property is used during the mining process to separate rough diamonds from ore.

Y: A grade in GIA’s Color Grading System…. at the end of the “Light Yellow” category.
YAG: Yttrium Aluminium Garnet, used as a somewhat unconvincing diamond simulant before Cubic Zirconia.
Yellow: Most diamonds contain nitrogen which gives them a slight yellow, “touch of warmth”.
Yellow Ground: The usual diamond bearing rock in which diamonds are found is called Kimberlite or blue ground. As this rock is exposed to sunlight and the weather elements is begins to decompose and its color changes from blue to yellow. This yellow ground is easier to break apart in the search for diamond rough.

Z: A grade in GIA’s Color Grading System…. at the end of the “Light Yellow” category. The next color grade for a yellow diamond will put it into the “Fancy (Color) Diamond” category and the price will begin to rise.
Zaire: The former name of the Democratic Republic of the Congo used from 1965 to 1997. Produces a large proportion of the world production of industrial grade diamonds.
Zirconia: Zirconium Oxide, or more accurately Zirconium Dioxide, also called zirconia, when crystallised in cubic system, it is known as Cubic Zirconia. Although this is found in nature, most Cubic Zirconia is made in the lab… hence it is should be more correctly called Synthetic Cubic Zirconia.
Zoning (color zoning): A term that describes the uneven distribution of color in a gemstone. Zoning is best seen when looking at the stone through the top table facet.

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