Glossary of Jewellery Terms

Here is a few of the terms that jewellers and gemmologists use, and their meanings:

• A jour: a type of setting which allows light to enter the pavilion of a faceted stone

• Adularescence: The appearance of a floaty, billowy light in cabochon gemstones, or a stationary sheen on the flat surface of a stone

• Ajouré: Pierced or openwork in metal

• Amethystine: The colour violet to purple in gemstones

• Angle of refraction: The angle at which a reflected ray of light leaves a surface as measured from the normal

• Anisotropic: The gemological term for double refraction

• Annealing: Toughening and softening a metal by heating

• Artificial stone: A man made imitation or synthetic gem

• Assembled stone: A gem constructed of two or more ports

• Asterism: The appearance of a rayed figure or a star in a gemstone, caused from the reflection of light from minute inclusions

• Aventurescence: A glittery appearance on the surface of a gemstone

• Birefrengence: The numerical measurement of double refraction

• Black onyx: A common misnomer for black chalcedony

• Body colour: The dominant hue in a gemstone

• Brilliancy: The total amount of white light returned to the viewer of a gemstone

• Bruting: A method of shaping a rough diamond, by rubbing one diamond against another

• Cabochon: A gemstone with an unfaceted dome shape

• Calibré cut: Small gem material used for pavé settings, or small stones cut to a particular shape and size

• Cameo: A gem or shell material with two distinct colour layers, carved in relief with the lower layer as a contrasting background

• Carat: A measurement of weight, equal to one fifth of a gram

• Chatoyancy: The appearance of streaks of light across the surface of a gemstone; may appear as a single band of series of bands

• Cleavage: A smooth break or separation of a gemstone along the direction of it’s crystal structure

• Cloud: A small group of white inclusions in a diamond

• Colour Zoning: Uneven colour in a gemstone

• Coloured stones: A gemstone other than a diamond

• Critical angle: The greatest angle measured from normal at which light can be refracted out from a stone

• Crown: The part of a faceted gem above the girdle

• Crystal system: The classification of minerals according to the geometric form of their crystals

• Culet: A small polished surface, at the point of ridge of a gemstone, used to reduce chipping

• Dichroism: The transmission of two different colours from a gemstone (best viewed with a dichroscope)

• Dispersion: The separation of light into its spectral colours as it passes through a gemstone

• Double refraction: The separation of light into two separate beams in a gemstone.

• Doublet: An assembled stone of two parts

• Durability: A combination of hardness, toughness and stability

• Facet: A planear surface polished on a gemstone

• Fancy diamond: A diamond with a strong body colour

• Feather: An inclusion within a gem, often with a white irregular look

• Fingerprint inclusion: Liquid or gas inclusions on a gemstone, aligned in the form of a human fingerprint

• Fire: The play of colour on or within a gemstone as a result of dispersion

• Flaw: A visible inclusion in a gemstone

• Fluorescence: The emission of visible light when a gemstone is exposed to ultraviolet light

• Foilbacked: The addition of a metallic foil to the pavilion of a gemstone to improve its face-up colour

• Fracture: A break or chip in a gemstone along anything other than a cleavage plane

• Girdle: The outer edge of a gemstone

• Grisaille: An enameling technique of built-up layers of black and white enamel

• Hardness: A gemstone’s ability to resist scratching

• Heat treatment: Altering or improving a gem’s appearance by heating

• Incandescence: The emission of light caused by heating

• Inclusion: A visible irregularity in a gemstone

• Intaglio: A design carved on the surface of a gemstone (the opposite of a cameo)

• Iridescence: Spectral colours observed on a gemstone (Similar to the sheen on the surface of bubbles)

• Matrix: The rock in which a gem is found

• Millegrain: A style of setting in which there is a tiny rows of beads along the edge of the setting

• Natural pearl: A pearl which occurs without the aid of man

• Normal: In the study of light, an imaginary line perpendicular to a surface

• Opalescence: Milky or pearly appearance

• Optic character: The effect a gemstone has on the transmission of light

• Overtone: A tint of colour on the body of a pearl

• Parting: Flat, smooth breakage of a mineral along planes os twinning

• Pavilion: The portion of a faceted gemstone below the girdle

• Phenomenon: An optical effect in gemstones, often enhanced by proper cutting

• Phosphorescence: A continuing glow emitted after the light source has been removed

• Play of colour: Prismatic flashed of colour seen in a gemstone

• Refraction: The change of velocity of light and subsequent bending of it

• Refractive index: The ratio of the speed of light in air to the speed of light within a substance

• Refractometer: A device to measure the refractive index of a gemstone

• Rough: An uncut of unfashioned gemstone

• Scintillation: Reflections from a polished surface as its position relative to the viewer or the source of illumination changes

• Stability: The resistance of a gemstone to deterioration

• Table: The flat horisontal surface on the crown of a faceted gemstone

• Toughness: Resistance to chipping or breaking

• Trichroism: The transmission of three different colours in three optical planes as light passes through a gemstone