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Diamonds
Abrasion Damage to the culet or facet edges usually caused by contact with other diamonds.
Beard Featherlike inclusions located on the girdle resulting from poor bruting.
Bezel Angled surface located on the crown of a stone between the girdle and table.
Bezel Facet Four sided facets found on the bezel of a brilliant cut.
Boiling Process in which diamonds are placed in heated acid in order to free them of grease and dirt.
Bow Tie Term used to describe the dark area located across a table sometimes found in fancy shapes
(aka ‘ Butterfly’)
Brilliance Intensity of the light reflecting out of the stone through the crown (aka ‘Dispersion’, ‘Fire’).
Brilliant Symmetrical cut with a round girdle outline featuring 56 facets.
Brilliant Cut Collective name for diamond cuts whose lower facets radiate from the centre of the stone towards the girdle, the most common of which is the round cut.
Bruise Crumbled area of the surface of a fashioned diamond, caused by a blow, usually white
(aka ‘Percussion Mark’).
Bruting The process shaping the rough stone into its eventual polished shape along the girdle (aka ‘Girdling’).
Burn Mark Imperfection on the surface of a stone due to overheating during the polishing stage.
Butterfly Term used to describe the dark area located across a table sometimes found in fancy shapes (see ‘Bow Tie’).
Cape (Colour) term used to describe yellow diamonds found in the M to Z range of the colour grading scale.
Carat Standard weight unit for gemstones; 1 carat = .2 grams
Cavity An opening or indentation on the surface of a diamond (see ‘Pit’).
Certificate Document provided by an accreditation laboratory stipulating the stone’s weight, colour, clarity, proportions and finish grade.
Clarity A stone’s relative freedom from inclusions and imperfections. Expressed in a fixed grading scale.
Cleavage A break or fracture in the stone which may be internal or external. These usually occur along the crystal’s growth planes (see also ‘Gletz’ and ‘Feather’).
Cleavage Plane Plane parallel to a possible crystal face.
Cloud A milky area in a stone made up of a multitude of small inclusions. This phenomenon may be local or spread throughout the stone.
Colour This may range from white to brown and is defined y a standard nomenclature (‘grading scale’) mostly ranging from D to M.
Crown The part of the stone located above the girdle.
Crystal Inclusion An impurity within a stone with a geometric, crystal-like shape.
Culet the small facet at the point of the pavilion.
Cut The proportions, make and finish of a polished diamond or the actual shape of the stone.
Dark Centre A dark area visible through the table in a stone of sub-standard make i.e stone is too deep
Dark Inclusion An impurity in the stone which is dark in colour (normally black).
Dead Stone A stone so heavily included that there is no brilliance.
Diamond A carbon based mineral created under extreme pressure and temperature. Diamond is the hardest of all known substances and exists in a variety of colours ranging from white to fancy colours.
Dispersion Intensity of the light reflected out of the stone through the crown (see ‘Brilliance’ and ‘Fire’).
Emerald Cut rectangular or square step cut with diagonally cut corners.
External Characteristics Imperfection located on the surface of a stone.
Extra facet 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.
Facet Flat polished surface on a polished stone.
Faceting The process of polishing facets onto a stone.
Fancy Colour A naturally coloured diamond with varying degrees of rarity.
Fancy Shape Any other shape besides the brilliant cut.
Fashioning The entire process of manufacturing, i.e. designing, cleaving, sawing, bruting and polishing.
Feather A break or fracture in the stone which may be internal or external. These usually along the crystal’s growth planes (see also ‘Gletz’ and ‘Cleavage’).
Finish The quality of the diamond’s finish.
Fire Intensity of the light reflecting out of the stone through the crown (aka ‘Dispersion’, ‘Brilliance’).
Fisheye A diamond whose pavilion is too shallow and as a result a circular reflection of the girdle is seen through the table.
Flat Stone A stone with a shallow crown or pavilion.
Fluorescence A visible light occasionally emitted from diamonds when exposed to ultraviolet light, usually blue in colour.
Four C’s Carat, Cut, Colour and Clarity: the four factors determining the value of a diamond.
Gem / Gemstone Mineral or organic material with sufficient beauty, rarity and durability to be set into jewellery.
Girdle The edge located between the pavilion and the crown which travels around the entire stone.
Girdling The process of shaping the rough stone into its eventual polished shape along the girdle
(aka ‘Bruting’)
Gletz A break or fracture in the stone which may be internal or external. These usually along the crystal’s growth planes (see also ‘Feather’ and ‘Cleavage’).
Goods Generic term used in the diamond business to refer to rough and polished diamonds.
Grain Weight unit equivalent to 0.25 carats. (e.g. a 1.00 ct stone is a four-grainer)
Graining Irregularities in the crystal structure of a stone which show up as faint lines. As these travel throughout the stone they may be internal or external.
Hardness A stone’s resistance to wear and scratching measured on Moh’s hardness scale. Diamond is hardness 10 which is the hardest on the scale.
Heart Shape (H.S) Modified brilliant cut with a heart-shaped girdle outline featuring 56 facets.
Imperfection Blemish located within the stone occasionally reaching the exterior.
Included Clarity grade, referring to eye visible imperfections, existing in I1, I2, I3.
Inclusion See internal characteristic
Industrial Diamonds non-gem quality diamonds used in drills and other tools.
Internal Characteristics Imperfection located within the stone.
Internal Reflection The reflection of a feature within a stone.
Kimberlite Volcanic diamond-bearing rock (also called blueground).
Laser Cut Using a laser to fashion the diamond’s eventual shape, allowing cuts across the growth plains, thus permitting odd shapes such as letters, horse heads etc.
Laser Inscription Using a laser to engrave identifying text or numerals, most commonly found on the girdle.
Laser sawing Using a laser to divide a crystal (advantageous as it allows the crystal to be divided in any direction regardless of crystal orientation).
Leverage Gauge Tool used to measure the precise dimensions of a mounted or unmounted stone.
Lively Stone A stone with good brilliance and luster.
Loose Goods Polished unmounted diamonds (See goods).
Loupe Small magnifying glass used in the diamond trade to examine diamonds. Magnification may vary but most commonly used is 10X.
Loupe Clean When viewed under magnification 10X, a stone is considered loupe clean if no imperfections are seen.
Lower Girdle Facet Triangular shaped facets, located on the pavilion.
Lower Main Facet Four sided facets of which there are eight meeting at the centre to form the cullet (syn. ‘Pavillion facet’)
Make The quality of the symmetry and finish of a polished stone.
Marking The Process of indicating cleaving and sawing points on a piece of rough diamond using an ink pen.
Marquise Symmetrical boat shaped brilliant cut with pointed ends.
Masterstones/ Colour Samples A set of polished stones which have been colour graded by an accredited laboratory for the purpose of colour grading polished diamonds.
Microscope Magnifying instrument used to determine clarity in gemstones.
Moh Scale used to determine the hardness of minerals. A diamond is the hardest at 10 and talc the softest
at 1.
Natural Original surface on the rough stone left on the polished stone. This is usually found on the girdle.
Nick Small chip on a diamond usually as a result of contact with other stones.
Open Table Inclusion which breaks the surface of the stone and shows a small pit.
Oval Modified brilliant cut with an oval shaped girdle outline.
P.C. Abbreviation for “Per Carat”
Parcel Paper Folded sheets of paper used to contain polished or rough diamonds.
Pavilion The section of the diamond found below the girdle.
Pavilion Facet Four sided facets of which there are eight meeting at the centre to form the culet
(syn. ‘Lower main facet’)
Pear Shape (P.S.) Asymmetrical cut with one pointed and one rounded end with a pear-shaped girdle outline featuring 56 – 58 facets.
Percussion Mark Crumbled area on the surface of a fashioned diamond, caused by a blow, usually white
(aka ‘bruise’)
Pinpoint Inclusion Very small inclusion which may be black or white in colour yet is not distinguishable as a crystal. When clustered together called a group of pinpoints.
Pit Tiny opening on the surface of a polished stone (See ‘Cavity’).
Point Weight unit. One point is 1/100 of a Carat.
Pointer Term used to describe polished stones under a carat.
Polished Diamonds Rough stones that have been faceted to produce a finished stone.
Polishing Lines Small Parallel indentations left on facets during the polishing process.
Polishing Wheel Flat cast iron wheel upon which diamonds are polished (aka ‘Scaife’)
Powder (Diamond-) Powder won during the polishing process on the wheel, also used on the wheel for polishing diamonds.
Princess Modified brilliant cut with a square or rectangular girdle outline featuring 57 facets.
Proportions The relative symmetry of angles and measurements on a polished diamond.
Quality Term used to describe the overall colour, clarity and cut attributes of a stone.
Reflection The bouncing back of light when it strikes an external or internal facet on a polished diamond.
Rejection Polished or rough diamond of very poor quality.
Rough (Stone or Diamond) Diamond of industrial or gem quality before it undergoes any manufacturing process.
Round Cut Round brilliant cut.
Sawing Manufacturing process during which a rough diamond is cut in two along its cleavage plain.
Scaife Flat cast iron wheel upon which diamonds are polished (aka ‘Polishing Wheel’).
Scratch Damage to a polished stone which appears as a faint white line, due to contact with other diamonds.
SI Clarity grade referring to stones that are slightly included, There are two grades in this category:
SI1 and SI2.
Sieve (Diamond-) Round stainless steel plates with perforations which correspond to specified diamond diameters. A quick way to sort small good by size.
Sorting Process of separating rough or polished diamonds into colour, clarity, carat and cut grades.
Star Facet A triangular facet located on the crown of a brilliant cut next to the table, of which there are eight.
Symmetry The accuracy with which the diamond is polished to its perfect proportions.
Synthetic Diamond A non-natural diamond which has been produced by man.
Table Large facet in the centre of the crown on a polished diamond.
Thermal Conductivity The ability of a material to conduct heat. Diamond have the highest conductivity of any material.
Types (diamond type l, ll) Diamonds are split up according to their varying atomic structures.
Ultraviolet Lower end of the light spectrum invisible to the human eye which allows fluorescence to be visible in a diamond.
Upper Girdle Facet Triangular facets located on the lower part of the bezel, right above the girdle.
VS Diamond clarity grade to describe small inclusions under a 10X loupe (very slightly); exists in two grades VS1 and VS2.
VVS Diamond clarity grade to describe very small inclusions under a 10X loupe (very very slightly); exists in two grades VVS1 and VVS2.
Wavy Girdle A girdle which has been improperly polished and does not run evenly.
Weight Diamond weight is measured in carats, subdivided in grains and points.
Well made A well proportioned polished diamond with a good finish.
Wheel See ‘Polishing Wheel’.
White A term to describe goods that are H colour and up.
Yield The total carat weight obtained after polishing from the original rough.
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gem@theassayoffice.co.uk