Alluvial Stone – A stone that has been transported by water and deposited in seas, lakes or stream beds. Many gems, including diamonds, are found in alluvial deposits.
Bezel – A smooth metal frame encasing a stone.
Bezel Facets – The eight large, four-sided facets on the crown of a round, brilliant-cut gem, the upper points of which join the table and the lower points join the girdle.
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. Most black diamonds have been treated.
Blemish – Any surface imperfection on a fashioned diamond; e.g., a nick, knot, scratch, abrasion, minor crack or cavity, or 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 though very light in tone, is a fancy diamond. Diamonds that are blue in both daylight and incandescent light are rare, although fluorescence stones that show a blue colour in daylight are comparatively common. A blue colour may also be induced artificially.
Blueground – A miner’s nickname for Kimberlite, the rock that contains diamonds in the South African pipe mines.
Blue White – A term that has been used for many years to refer to a diamond without body colour. However, it is applied frequently, but incorrectly, to stones that have a distinct yellow tint. Federal Trade Commission rulings state that is it an unfair trade practice to apply the term to any stone having a body color in the D,E of F range with a strong blue fluorescence. An American Gem Society ruling prohibits the use of the term by its members. Flagrant misuse has made the term meaningless.
Body Color – The colour of a diamond as observed when examined under a diffused light against a hueless background free from surrounding reflections. The diffused light eliminates glaring reflections and dispersion, which would otherwise confuse the colour determination. This is part of the four C’s.
Bombarded Diamond – A diamond that has been subjected to bombardment by fast electrons, neutrons etc. The purpose of bombardment is to make the colour of the stone more attractive and desirable. Also known as irradiation treatment.
Brillianteering – The placing and polishing of the 40 remaining facets on a brilliant-cut diamond after the main bezel and pavilion facets have been placed and polished.
Brown Diamond – Although not as frequently encountered as a yellow body colour, brown tints in diamonds are next to yellow in occurrence. These stones are also known as top light browns and “cognacs” or “coffees”.
Break Facets or Girdle Facets – The 32 triangular facets that adjoin the girdle of a round brilliant-cut stone, 16 above and 16 below. 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.
Cape – (a) A broad range of diamond colour grades that show a distinct yellow tint face up (except for small stones in the top part of the range). The term originally referred to the Cape of Good Hope, the popular name for the area that later became the Union of South Africa. Since the average colour produced by the South African mines was distinctly more yellow than the Brazilian average, the term “cape” became accepted for strongly yellow-tinted stones. The best grade in the group is variously called “top silver cape”, “top cape”, “light cape”, “fine cape” or “silver cape”, depending on the system used by the grader.
Cavity – An opening on the surface of a fashioned diamond. It may be cause by cleavage, by a blow, or may have been pulled out from the surface during the polishing operation.
Champagne Diamond – A greenish-yellow to yellow-green diamond of a sufficiently pronounced hue to be an asset. Such a stone is called a fancy.
Clarity Grade – The relative position of a diamond on a flawless-to-imperfect scale.
Clean – A term used by some jewelers to mean absence of internal imperfections only, and by others to describe diamonds with slight imperfections. 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.
Cleavage – (a) The tendency of a crystalline mineral to break in certain definite directions, leaving a more or less smooth surface. (b) The act or process of producing such a break. (c) One of the portions of such a mineral resulting from such a break. (d) A term sometimes used for a diamond crystal that requires cleavage before being fashioned. (e) A misshapen diamond crystal, particularly one that is flat and rather elongated. The term is used by diamond cutters to refer to such a crystal, whether or not its form results from cleaving. (f) A grading term used at the mines for broken diamond crystals above one carat, of reasonable thickness, and not twinned. (g) A break within a diamond.
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 damaging kind of imperfection in a diamond, since it affects durability as well as beauty.
Closed Culet – A culet on a diamond that is too small to be resolved with the unaided eye and that can be seen only with difficulty under 10x.
Cloud Texture – A group of tiny white inclusions, composed of minute hollow spaces, or very small patches of tiny crystals or other impurities that produce a cottony or clouded appearance in a n otherwise highly transparent diamond. A cloud may be so minute that it is difficult to see under 10X, or it may be large enough to deprive the entire stone of brilliancy.
Cloudy Texture or Cloud Texture – A group of tiny white inclusions, composed of minute hollow spaces, or very small patches of tiny crystals or other impurities that produce a cottony or clouded appearance in a n otherwise highly transparent diamond. A cloud may be so minute that it is difficult to see under 10X, or it may be large enough to deprive the entire stone of brilliancy.
Commercially Clean – The common meaning of this refers to a stone reasonably free from inclusions. If a diamond were without flaws or blemishes, logically, it would be called flawless. Sometimes, highly flawed stones are represented as “commercially clean”. The obvious misleading nature of the term has led the American Gem Society to prohibit its use by Society members. It is also prohibited by the Federal Trade Commission, unless the stone meets the Commission’s definition of the term “perfect”.
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.
Cube – One of the seven basic forms in the highest symmetry (hexoctahedral) class of the cubic, or isometric, crystal system. It has six square faces that make 90Â° angles with one another, each of which intersects one crystallographic axis and is parallel to the other two. Gem-quality cube-shaped diamond crystals are so rare as to be regarded as collector’s items.
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.
Cushion Cut – The older form of the brilliant cut, having a girdle outline approaching a square with rounded corners. Essentially an old-mine cut. Modern cushion cuts have different crown angles and larger tables and can be square-ish or rectangle.
De Beers Consolidated Mines – This company is the major factor in the diamond industry, because it holds a controlling interest in a number of diamond-mining companies and in companies having buying contracts with independent producers. It owns or controls all of the important pipe mines in South Africa and Consolidated Diamond Mines of South-West Africa, Ltd. Williamson Diamonds, in Tanzania, is owned by De Beers and the government of that country on an equal basis.
Diamond Cut – A name sometimes used in the coloured-stone trade for brilliant cut.
Diamond Cutter – (a) Any workman engaged in the cutting and polishing of diamonds. (b) One who rounds up rough diamonds as a step in the fashioning of brilliants.
Diamond Saw – (a) A saw used for dividing or separating diamonds. (b) A diamond-charged blade used as a cutting edge in fashioning colored stones or in various applications in industry.
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.
Draw Color – When several diamonds are placed together in a diamond paper and light passes through one stone after another, each stone tends to intensify the slight color of the other. The group of stones is then said to draw color. The term is also used to describe an individual diamond with a visible body color.
Durability – 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.
Emerald Cut – A form of step cutting. It usually is rectangular but sometimes is square, in which case it is known as a square emerald cut. It has rows (steps) of elongated facets on the crown and pavilion, parallel to the girdle, with sets on each of four sides and at the corners. The number of rows, or steps, may vary, although the usual number is three on the crown and three on the pavilion. The emerald cut is seldom used for diamonds in the intermediate color grades, since it tends to emphasize color. It is excellent, however, for colorless stones and when it is desirable to emphasize the color of fancy colors. This stone traditionally has 58 facets, just like the rounds.
European Cut – Obsolete term for diamond brilliant whose proportions were worked out mathematically for light falling perpendicularly on the crown. It was never adopted as a common form of cutting. The angle of the pavilion facets to the girdle is 38-40 degrees; of the bezel facets, 41 degrees. The table is 56% of the girdle diameter or smaller; crown depth, 19%; and pavilion depth, 40%. It is not to be confused with the Old European cut.
Facet – A plane, polished surface on a diamond or other gemstone.
Faceting – The operation of placing facets on a diamond or other gem.
Feather – When the plane of cleavage or fracture in a diamond is viewed at right angle to it, the appearance is often reminiscent of a feather. Thus, cleavage and fractures are often called feathers.
Fire – Flashes of different spectrum colours seen in diamonds and other gemstones as the result of dispersion.
Fissure – An elongated cavity in a diamond’s surface. It may or may not have occurred along the line where a cleavage reached the surface.
Flaw – Any external or internal imperfection on a fashioned diamond; e.g., a feather, fissure, included crystals, knot, etc. Some limit its use to internal faults only, using the term blemish for surface faults. The terms “flaw” and “imperfection” are usually used interchangeably.
FL or Flawless – The recommended term for a diamond without external or internal flaws or blemishes of any description when viewed by a trained eye under efficient illumination and under a corrected magnifier of not less than ten power; binocular magnification under dark-field illumination is preferred. The American Gem Society advocates the use of the term “flawless” by its members, while at the same time denying them the use of the term perfect. The Federal Trade Commission permits the use of the term “flawless” but only if a stone conforms to its definition of the word perfect, without reference to make or color.
Fluorescence – The property of changing the wavelength of radiation to one in the visible range; for example, the visible wavelengths emitted by a material when excited by invisible radiation (such as X-rays, ultraviolet rays or cathode rays), as well as by certain visible wavelengths. It is exhibited by a variety of stones including diamond.
Four C’s – A phrase coined for advertising purposes that sums up the numerous factors affecting diamond value into four categories: colour, clarity, cutting, and carat weight.
Fracture – The breaking or chipping of a stone along a direction other than a cleavage plane.
Girdle Facets – The 32 triangular facets that adjoin the girdle of a round brilliant-cut stone, 16 above and 16 below. 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 Thickness – The width of the outer edge, or periphery, of a fashioned diamond or other gemstone. In a rounded style of cutting, such as the round brilliant or pear shape, the girdle edges, when viewed parallel to the girdle plane, consist of undulating lines caused by the intersection of the flat facets with the curved girdle. In such stones, the girdle thickness is measured across the midpoints of opposing upper- and lower-girdle facets.
Girdling – The step in the fashioning process of a diamond in which the stone is given a circular 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.
Hardness – The resistance of a substance to being scratched. Diamond is 10 in Mohs scale of hardness. Tests prove that diamond is approximately five to 150 times as hard as corundum, the next hardest mineral. The variation stems not only from the differences obtained from different hardness-testing methods, but also from the fact that various directions on a given stone’s surface show a considerable variation in resistance to abrasion. The hardest direction in diamond is parallel to the faces of the octahedron.
Heart-shaped Brilliant – A heart-shaped variation of the brilliant cut. The round end is flattened and indented and the girdle widened until the length is approximately equal to the width.
Imperfect – The diamond imperfection grade at the low end of the flawless-to-imperfect scale. An imperfect diamond contains imperfections that are visible face up to the unaided eye or that have a serious effect on the stone’s durability. The Gemological Institute of America recognizes three grades in the imperfect category.
Inclusion – A general term used to refer to any external blemish or internal inclusion or flaw on or in a fashioned diamond; e.g., a feather, included crystal, knot, fissure, scratch, natural, etc.
Knife-edge Girdle – A girdle of a diamond that is so thin that it can be likened to the edge of a sharp knife. Since such a girdle is easily chipped, an ideal girdle has an appreciable thickness.
Knot – (a) An included diamond crystal that is encountered at the surface of a stone during the polishing operation, and that stands out as a small, raised surface on the finished stone. (b) An included diamond crystal that is encountered by the saw blade. Since the softest directions available for sawing and polishing are used by the cutter, and since included crystals have a different orientation from the surrounding mass, they almost always have a harder direction than that being exploited. (c) A small section of a twinned stone in which the grain differs from the main mass.
Main Facets – The large crown and pavilion facets of a brilliant-cut diamond or other gemstone; on step-cut stones, the center row of facets on the pavilion.
Natural – A trade term for a portion of the original surface of a rough diamond that is usually left by the cutter on a fashioned stone, usually on the girdle. The excuse for leaving naturals is to show that there was no unnecessary weight loss in the rounding-up and polishing operations. The American Gem Society considers that naturals that do not flatten the girdle outline nor extend beyond the width of a medium girdle should not be regarded as blemishes.
Nick – A minor chip out of the surface of a fashioned diamond, usually caused by a light blow. It is more likely to be found along the girdle than elsewhere, although it may also appear on a facet junction or on a facet.
Off-center Culet – A culet that, due to differences in the angles of the opposite pavilion facets, is off center with respect to the girdle outline. It usually results from repairing or repolishing a portion of the pavilion or from attempting to retain maximum weight from a distorted piece of rough.
Old-European Cut – A term applied to the earliest form of circular-girdled full brilliant. It is characterized by a very small table, a heavy crown, and usually great overall depth. Often improperly referred to as an old-mine cut.
Old-mine Cut – (a) An early form of brilliant cut with a nearly square girdle outline. (b) Incorrectly applied to a somewhat more modern style of brilliant cut that also has a much higher crown and smaller table than the modern brilliant cut, but whose girdle outline is circular or approximately circular; a style of cutting that is more properly called a “lumpy stone” or and old-European cut.
Oval Cut – A brilliant style of cutting in which the girdle outline is elliptical; i.e., a rounded oblong. Also called the oval brilliant cut.
Perfect – 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. Because of flagrant misuse of this term in the sale of diamonds that do not fit this description, many jewelers avoid it use. The American Gem Society also prohibits its use by its members.
Pink Diamond – A term often used loosely in the trade to describe any diamond of pale reddish, purplish-red, purplish or violetish hue. Diamonds of colors other than pale reddish are sometimes described as rose pink, rose colored, peach blossom, heliotrope and similar terms. Such a diamond is called a “fancy”.
Pipe – The common name for a vertical, columnar mass of rock that cooled and solidified in the neck of a volcano. When these rock masses consist of Kimberlite, they often contain diamonds. They occur in Africa, India, Russia, Arkansas and elsewhere.
Polish – The relative smoothness of a surface, or the degree to which the finish of the surface approaches optical perfection. A well-polished diamond shows no wheel marks or burn marks under 10X.
Polished Girdle – A girdle that has been lapped to yield either a lustrous, curved surface or a series of flat, polished surfaces (facets).
Polishing – The reduction of a rough or irregular surface to a smooth flatness or curvature. 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.
Proportions – A term that meant originally the distribution of the mass of a fashioned diamond above and below the girdle. Its meaning has broadened to include the major factors that determine cutting quality; i.e., total depth as a percentage of the girdle diameter, table diameter, girdle thickness, facet angles, symmetry, and even details of finish.
Proportionscope – The Proportion Scope combines lenses and movable mirrors to project the silhouette of a diamond on a screen. Diagrams and scales on the screen, as well as a zoom range, enable the instrument to analyze the proportions of round brilliant-cut diamonds, as well as fancy-cut diamonds.
Round Cut or Brilliant Cut – The most common style of cutting for both diamonds and colored stones. The standard round brilliant 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, or base. Although the brilliant style was devised to give maximum brilliancy and fire, many stones cut in this fashion do not have ideal proportions or angles for that purpose. Modifications of the round brilliant include such fancy shapes as the marquise, half moon, pear shape and many others.
Red Diamond – The rarest of all fancy-coloured diamonds. However, the term is often used to mean red-brown or rose-colored stones. Diamonds of an intense red color approaching that of ruby are excessively rare.
Refraction – The bending of light rays. The deflection from a straight path suffered by 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. The degree of bending is related to the change in velocity of light and the angel at which the light impinges.
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 is now used primarily on small diamonds.
Rough Girdle – If a diamond is rounded up too quickly in the fashioning process, the surface of the girdle, instead of having the smoothness and waxy luster of a finely turned girdle, will be rough or granular. This condition may also be accompanied by numerous hair like fractures extending into the stone, in which case the term bearded (or fuzzy) girdle is applied.
Scintillation – The display of reflections from the polished facets of a gemstone seen by the observer when the light source, the gemstone or the observer is in motion; a flashing or twinkling of light from the facets.
Scratches – Narrow, shallow, elongated, rough-edged depressions on the surface of a fashioned diamond, usually appearing as faint white lines under magnification.
Slightly Imperfect – A grade of relative imperfection in a diamond. It signifies a more flawed condition than very slightly imperfect but less than imperfect. In general, stones are called slightly imperfect only if the flaws they contain are not visible face up to the unaided eye of a trained observer.
Spread Stone – A term that is used frequently in the diamond trade to refer to a stone that has been cut with a large table and a thin crown, to retain greater weight from the two sawn pieces of an octahedron than is possible by using ideal proportions. In a strict sense, any increase in table diameter over the ideal 53% constitutes spreading; however, it is a general trade practice to apply the term only to those stones with tables that measure in excess of about 64%
Square Emerald Cut – A form of step cutting with a square girdle outline but modified by corner facets.
Symmetry – The exactness of placement and shaping of opposed facets and other portions of a diamond. Symmetry is judged on the basis of the degree to which these opposed features yield exact mirror images.
Table – The large facet that caps the crown of a faceted gemstone. In the standard round brilliant, it is octagonal in shape and is bounded by eight star facets.
Table Size – The size of the table of a fashioned diamond, expressed as a percentage of the stone’s narrow-girdle diameter, is a dimension used in proportion analysis. On a round brilliant, it is measured from corner to opposite corner, rather than from flat side to flat side.
Top Cape – An early trade term still used by some dealers to designate the diamond colour grade between crystal and cape in the river-to-light-yellow system. Small stones in this range will face up colourless when mounted, but larger stones will have a yellow tint.
Trigon – A triangular indentation occurring as a growth mark on diamond octahedron faces. The sides of the trigon are reversed with respect to the face on which it occurs.
Twinning Lines or Wisps – Visible line on or with in a fashioned diamond, caused by twinning in the crystal. Since the orientation on one side of a twin plane differs from that on the other, the best polishing direction for one is a poorer one for the other; as a result, a line remains at the surface. Also called knot lines.
Yantz Bradbury Associates
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Rockville, Maryland 20850
Office: (301) 335-6687
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