A
AGS
The American Gem Society, or AGS. This group is recognized by the jewelry industry as an authority for grading gemstones.
AGTA
The American Gem Trade Association is recognized in the jewelry industry as an authority for grading gemstones.
Akoya Pearls
A type of cultured pearl grown primarily in Japan.
Anneal
A term used by the Independent Gemological Laboratories to describe a heating enhancement process used with color gemstones.
B
Bar Channel Setting
Individual metal bars separate the gemstones. The metal is molded around a gem to lock it in place.
Baroque Pearl
A shape of pearl. The shape is not round but is symmetrical, having similar characteristics on opposite sides.
Bezel Setting
A metal rim gently secures a gemstone in place by the girdle. The bezel setting guards the gem from damage, yet does not block light from creating brilliance.
Blemish
A flaw (blister or spot) on the surface of a gem.
Brilliance
White light reflected up through the surface of a diamond. Brilliance is maximized by cutting a diamond to the correct proportions.
Brilliant Cut
Any cut with 58 facets. A brilliant cut can have several shapes: round, oval, radiant (basically square), as well as pear-shaped or heart-shaped.
Birthstone
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.
C
Cameo
A style of carving in which the design motif is left and the surrounding surface is cut away leaving the design in relief. Cameos in jewelry are often made of shell, although hard stone cameos such as sardonyx are more valuable. Cameos have been carved from ancient times, and ancient motifs such as the goddess Athena or a Baccante or follower of Bacchus were popular cameo subjects in Victorian times, through the 1930's. Cameos are still being made today in Italy. A cameo habille is one in which "jewelry" such as a miniature diamond pendant is actually attached to the carving.
Cabochon
A gemstone shape resembling a dome. Onyx is commonly cut in a cabochon shape, as are star sapphires.
Carat
A unit of weight for a diamond, equivalent to 200 milligrams, or 0.2 gram.
Center Stone
The central, dominant stone in a piece of jewelry set with multiple stones. In a ring set with one stone, the center stone is also called the solitaire.
Chemistry
It is the chemistry of a gem material which is ultimately responsible for all of its physical properties. Chemistry determines color which in turn determines value. Heat treatment is a chemical modification of a gem material to improve its color and value.
Channel Setting
Ridges in the metal create a channel that holds gemstones in place.
Choker
A pearl necklace 16 inches long.
Clarity
The clarity scale is used to describe how few inclusions a gemstone has. For diamonds, the clarity scale ranges from flawless (FL), meaning a gemstone has no internal or external flaws, to severely included (I3), meaning there are many flaws clearly visible to the unaided eye.
Cloud
A cluster of small inclusions inside a gemstone.
Color
The color scale is used to describe the color tones of a gemstone. For diamonds, the color scale ranges from D, meaning completely colorless, to Z, which indicates a distinct yellow cast. As the scale moves from D to Z, it indicates increasing levels of yellow and brown tone. For color gemstones, the color is measured by tone and hue. Color is the most important criteria in determining the value a colored gemstone. More important than clarity and cut, even subtle differences in hue can correspond with marked variations in valuations
Comfort fit
The rounded finish on the inside of a ring's band. This design does not pinch the skin of the finger as much as other ring bands and provides comfort for constant wear.
Corundum
A hard mineral that exists in the form of colored crystals, such as rubies and sapphires.
Crown
The edges of a gemstone above the girdle and surrounding the table. Colored light escapes through the crown in the form of fire.
Crystal
The protective clear cover that fits over the watch dial. It can be made of mineral, synthetic sapphire, plastic, or acrylic material. The sapphire crystal is the most durable, as only a diamond can scratch its surface.
Crystal System (Group)
Crystals are divided in to 7 systems, each corresponding to a specific set of angular, geometrical, and symmetrical specifications. Every gem group can be classified according to its crystallization. The study of crystallization is invaluable in the determination and identification of rough gem materials.
Culet
The facet at the tip of the pavilion of a gemstone. The culets of older, European-cut diamonds can be seen through the table of the diamond and appear as round, glassy disks. The preferred culet is visible only as a tiny focal point where the facets of the pavilion converge.
Cultured Pearl
A pearl cultivated by artificial insertion of a small irritant (often a bead made of mother-of-pearl and mantle tissue taken from a particular species of oyster found on the Mississippi River) into an oyster or other bivalve mollusk. The method of culturing pearls was patented by Kokichi Mikimoto in 1916.
Cut
Refers to the geometric proportions of a gemstone. The cut of a gemstone is one of the most important factors in determining how much sparkle a gemstone produces.
Cut, Ideal
A diamond cut of perfect proportions, having depth percentages and table percentages that maximize fire and brilliance.
Cut, Very Good
A grade of diamond cut that fits very strict requirements for depth percentage and table percentage. These specific proportions maximize fire and brilliance in a diamond.
Cut, Good
The cut grade assigned to diamonds with acceptable proportions. These diamonds generally have very good brilliance and fire and they are also are beautiful in jewelry.
Cut, Fair
The cut used to maximize the weight of a diamond, generally at the expense of fire and brilliance. Diamonds with this cut are less expensive than diamonds having good and very good cuts, and they lack the sparkle people expect from a diamond.
Cut, Poor
This cut makes diamonds appear lifeless. These diamonds are not recommended for fine jewelry.
Cut, European
The style of diamond cutting popular from approximately 1890 to the 1930s. Unlike the old mine cut preceding it, the European cut has a round girdle (perimeter) made possible by the introduction of the power bruting machine (Bruting is the term for shaping the girdle of a diamond, the first step in the cutting process). The European cut can be distinguished by the size of the table (the top, flat facet) in relation to the diameter of the stone. In a European cut, the table is smaller in relation to the diameter of the stone. Also, the culet (the bottom facet, is often large, often appearing to create a hole at the bottom of the diamond, when viewed from the top, since the large culet lets light escape instead of reflecting back to the viewer.
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