Jeweller's Glossary

The four criteria used to assess a diamond: Carat (weight), Clarity, Colour and Cut.

Loss of material on an edge or facet due to friction. On an old-cut diamond, it is usually visible first on the girdle and the pavilion.

Adamantine lustre, the brightest of non-metallic lustres.

Aigrette.

Traditional Japanese saltwater cultured pearls.

Metal alloy. In jewellery, pure gold is alloyed with copper, silver or palladium for hardness and colour.

Omega back.

They are found at each end of a chain or necklace. The first is soldered to the last link at one end. The second, on the other side, is hollow and features an internal spring that allows it to open and close onto the end ring simply by operating a small trigger.

Visually perfect match (shape, colour) of two gems.

Desired optical phenomenon, caused by inclusions forming a mobile 4-, 6- or 12-pointed luminous star. It appears on the surface of a stone, often cut as a cabochon, when illuminated by a direct light source.

Rectangular faceted cut. Used in calibrated sizes, it often serves the design more than the brilliance.

Baroque pearl, due to the caprice of nature.

Long, thin brooch, often in platinum, very popular from 1900 to 1930. Central line or motif of stones or pearls, 4 to 10 cm in length.

Jump ring, mobile or fixed, which connects a pendant to its chain. Its shape or solder can be a clue to transformations.

Round cut with 57 or 58 facets. This is the classic and most popular diamond cut, invented by Marcel Tolkowsky in 1919. It is achieved through mathematical calculations that have optimised the diamond's brilliance and fire.

Also known as tweezers: fine forceps used for safely gripping and handling gemstones.

Polished and rounded stone shape, often used for heavily included or opaque stones. The name comes from «caboche», meaning head, by analogy with the domed shape resembling a bump.

Custom-cut stones to fit the design of the setting precisely, with no gaps between them.

Stone engraved in relief to highlight the variously coloured layers. The subjects vary: animals, scenes, landscapes, profiles of men or women. The cameo can be engraved in a single-coloured material: emerald, amethyst, lapis lazuli, coral, seashell. Worn since antiquity, it experienced a revival during the Renaissance that continued into the 19th century.

French purl.

Unit of weight used for gemstones: 1 carat equals 0.20 g. The word comes from the seed of the carob tree; in antiquity, merchants used these small seeds as a natural counterweight to weigh gold and precious stones.

A functional piece of jewellery that, in its earliest form, held a number of small suspended objects. In the 17th and 18th centuries, it was used mainly for hanging a watch, its key and a seal. Sometimes made of gold, but most often of silver, steel, pinchbeck or gilt brass. At the front, it consists of an ornamental motif formed of one or more articulated elements, sometimes enamelled and set with stones.

Setting.

Chatoyancy.

A choker necklace is made of pearls of the same size, whereas in a graduated necklace, they taper down from the central pearl, which is the largest.

Brooch that appeared at the beginning of the 20th century and was very fashionable between the wars, typical of 1930s jewellery. The clip is remarkable for how it is attached to clothing, thanks to a hinge system that pinches the fabric. Sometimes, two elements joined by an invisible and removable frame formed what were known as «double-clip» brooches.

Plane of least cohesion along which a stone splits cleanly. The diamond has four of these: although it is the hardest mineral in the world to scratch, it exhibits mechanical weakness along these planes.

Bezel setting in which the metal entirely surrounds the stone. The oldest and most protective.

Hoop earrings.

Lower part of a cut stone, below the girdle. Its point may be truncated into a small facet.

Colour variation according to the axis of observation, in birefringent stones. A simple identification test using a polarising loupe.

Small sleeper earrings with a hinged or snap-back clasp, originally designed to be worn overnight without disturbing sleep.

Doublet gemstone.

For gemstones, hardness is resistance to scratching, not to impact. It is measured using the Mohs scale. Diamond is currently considered the hardest gemstone.

Forehead ornament. Originally a thin ribbon of velvet or silk encircling the head, then a gold chain with a stone or pearl fixed at its centre. It owes its name to the most famous of its wearers, «La Belle Ferronnière» painted by Leonardo da Vinci. In the 19th century, between the reigns of Charles X and Louis-Philippe, it accompanied banded hairstyles.

Breakdown of white light into spectral colours by the cut stone. This is what makes a diamond sparkle with coloured reflections.

The ancestor of the brooch, the fibula is a clasp that was used to fasten and hold draped clothing, tunics or capes, from antiquity to the Middle Ages.

Emission of light under ultraviolet radiation. On the diamond, it is frequent and has no impact on its durability.

Also known as ice: a cleavage plane induced in a stone by a crystal defect or a shock, sustained for example during extraction or polishing, which creates a sort of translucent white spot or band within it.

The art of engraving fine or hard stones. It is divided into two techniques: relief engraving, the cameo, and intaglio engraving.

Rounded and elongated raised motif, worked in repoussé or cast. Used to add volume.

Small bead of metal raised with a graver to hold a stone. Bead setting requires a very steady hand.

Metal prong folded over the stone. Four to six claws depending on the size; their position exposes or protects the table.

Impregnation of the fissures of an emerald with a natural colourless oil. Old treatment.

Foreign element, crystal or fissure, present inside a gemstone. In the case of the emerald, it is known as a garden.

Intaglio engraving work carried out on the surface of a stone. The subjects depicted vary: faces, animals, monograms, mythological scenes. Intaglio stones generally adorn rings or signets used to stamp a personalised impression into wax. Whilst most were made from opaque hardstones, transparent stones (rock crystal, aquamarine, amethyst) were also used.

All the inclusions within an emerald. Its appearance is as much an indicator of geographic origin as it is a criterion of purity. Three-phase inclusions are characteristic of Colombian emeralds.

Quality of the reflection on the surface of a pearl. First criterion of value, before size and shape.

Organo-mineral layer secreted by the mollusc. Its thickness determines the durability and depth of the lustre.

Irisation specific to nacre, produced by diffraction between its layers. Distinct from lustre, which is a surface reflection.

Naturally white, rare metal of the platinum family that does not oxidise. Being very expensive, it is rarely used pure, but as an alloy in metals, for 750-thousandths white gold, for example.

Diamond of exceptional purity and water, with no visible flaws. The term formerly referred to stones of over one hundred carats.

Lower part of a cut stone, between the girdle and the pavilion. Its proportions control the return of light to the eye.

Coarse-grained rock, commonly of granitic composition (feldspar, quartz and micas), which can contain numerous gemstones such as tourmalines, topaz or beryl.

Cultured pearl.

Natural pearl, an organic gem that forms within a mollusc without any human intervention.

Traditional paper packet, sometimes lined and folded to securely hold and transport properly identified gemstones.

Hallmark.

Maker's mark of a craftsperson, jeweller or workshop, stamped onto a precious metal object.

Polishing.

Rhodium bath which makes silver or white gold brighter and whiter.

A fashionable type of necklace in the 18th century, when its effect by candlelight was adored. The rivière is a flexible necklace, in which diamonds are set in continuous collets: in silver enhanced with gold, then in platinum and white gold. By extension, any necklaces and bracelets where stones are mounted in a line are called a rivière.

Girdle of the cut stone, at the junction of the crown and the pavilion. This is where the diameter is taken, and where the first signs of wear can be seen.

Old-cut with a flat base and faceted pointed top, without a pavilion. It illuminated 17th- to 19th-century jewellery by candlelight.

Traditional turban ornament from Mughal India. Worn by maharajas, the sarpech is set with precious stones.

Stone setting is the meticulous process by which the setter embeds a stone into its mounting.

Upper, widest facet of a cut gemstone. Its proportion directly influences brilliance.

Diamond cut with a table that is often smaller, with little or no facet symmetry, often very irregular.

Proportion of pure metal contained in an alloy, which has been compulsory to express in thousandths in France and Europe since 1995. 750 ‰ for 18-carat gold: 75 % of pure gold and 25 % of metal alloy (silver, copper, palladium) depending on the colour of the gold.

Originally, the Toi et Moi ring was made up of a pearl and a gemstone, mounted on a crossed band. By extension, any ring featuring two stones facing each other bears this name, which is laden with promising messages.

Torcs or bracelets of Celtic origin, characterised by their massive and rigid appearance. They consist of an open ring, with each end terminating in a larger decorative motif that is either abstract (a disc or ball) or figurative, such as an animal's head. While authentic Celtic jewellery can no longer be found, modern jewellery has retained both their shape and name.

Treated (said of a gemstone whose colour or clarity has been modified: heating, diffusion, irradiation, fracture filling. Disclosure is mandatory.).

Jewellery whose setting vibrates at the slightest movement. The signature of 19th-century parures.

Tapered mandrel used for measuring the diameter of rings.

Silver coated with a layer of gold of at least five microns. Regulated, it must not be presented as gold.