N
Natural pearl
A pearl that forms naturally when a grain of sand or other small object enters the pearl. If the oyster is unable to eject the object, the oyster will coat the object with layers of nacre to form a pearl. There is no way to determine if an oyster contains a pearl, so to create a dependable pearl supply, the culturing process was invented.
NGL
The Northwest Gemological Laboratories, or NGL, are recognized authorities on grading gemstones.
O
Opaque
Description of a gemstone that is so thick with inclusions or flaws that light is blocked from passing through the gemstone.
Opera Length
A pearl necklace 32 inches long.
Orient
P
Pearl
A natural gemstone formed when a oyster is irritated by a substance that gets into its shell. If the irritation is a naturally occurring grain of sand, it is an Oriental pearl. If it is produced by purposefully inserting a mother-of-pearl bead, a cultured pearl is formed.
•Baroque – an irregularly shaped pearl, can be natural or cultured.
•Blister – pearl taken from the shell where an irritant has lodged and been covered with layers of nacre, usually hollow.
•Cultured – artificially produced pearl made by placing an irritant inside the oyster where it is covered with layers of nacre. First available in the 1920's.
•Freshwater – pearls produced in freshwater mussels.
•Mabe – (pronounced mah-bay) a cultured pearl usually of teardrop shape, flat on one side.
•Natural – pearls that have occurred naturally, usually found now only in antique jewelry.
Pear-shaped
Description of a shape of gems and pearl rounded on one end and tapered on the other.
Pearl Shape
An important characteristic in determining the value of a pearl. Shape is classified by various degrees of roundness, symmetry, or irregularity.
Pearl Size
The diameter of a pearl measured in millimeters. The most important characteristic in determining price.
Peg setting
A tiny hole is drilled halfway into the pearl and a metal bar is inserted and secured with adhesive.
Point
A weight measure equal to 0.01 carat. (A 0.50-carat diamond is said to weigh 50 points.)
Polish
Polish describes how smoothly the facets of a diamond have been polished, whether any marks are visible from the polishing wheel, and how defined the edges of each facet are. Since these characteristics are rarely visible to the unaided eye, for an excellent value, look for a polish grade of very good or good, though the higher grades of ideal and excellent are also recommended. Avoid diamonds with polish grades of fair or poor, as the quality of their polish may affect the brilliance of the diamond.
Princess Length
A pearl necklace 18 inches long.
Paste
A term for imitation gemstones. Fine jewelry was often imitated in finely made copies to protect the wearer from theft, and these were referred to as "paste".
Pave’
(pah-VAY) a gem setting technique in which the stones are set low and very closely spaced, so that the surface appears to be paved with gemstones. Most commonly seen with diamonds, but may be used with any stone.
Pleochroism
(from Greek pleion, "more," and chros, "colour"), in optics, the selective absorption in crystals of light vibrating in different planes. Pleochroism is the general term for both dichroism, which is found in uniaxial crystals (crystals with a single optic axis), and trichroism, found in biaxial crystals (two optic axes). It can be observed only in coloured, doubly refracting crystals.
R
Refractive Index
The ratio of the velocity of light in air to its velocity in the new substance is known as the refractive index of that substance. Almost every gem material has it's own unique specific refractive index (R.I.). Determination of the RI is probably the most conclusive measurement available to gemologists.
Rope
A pearl necklace 40 or more inches long.
S
Saturation
This term refers to the color purity, or the degree to which the gem color is free from brown or gray hues. The most desirable gemstones, which show little gray or brown, are often described as having vivid or strong color saturation.
Shape
The geometrical form a gemstone takes on after it has been cut and polished. The most common shapes of gemstones are round, oval, radiant, princess, square, as well as pear-shaped or heart-shaped.
Seed Pearl
Refers to a very small round pearl. These were strung on horsehair and used in intricately woven jewelry during the early-mid Victorian period. In the late Victorian period accents set into gold jewelry. During the Edwardian period, they were sometimes woven into long fringed necklaces called sautoirs.
Side Stone
A gemstone set alongside, or as part of a group of gemstones encircling a center stone.
Sparkle
The combination of fire and brilliance; the amount of light reflected from a diamond.
Spherical
Round in shape.
Symmetrical
A pearl with similar characteristics on opposite sides.
Symmetry
Symmetry refers to the alignment of the diamond facets - whether they are the same size on each side, and whether or not the facets on the pavilion are directly below the facets on the crown.
T
Table
The largest facet of a gemstone, located on the top of the gemstone, through which refracted light escapes as brilliance.
Table percentage
The width of the table divided by the diameter of the gemstone. The table percentage is critical to creating sparkle in a gemstone; a gemstone with a table percentage too low or too high will lack sparkle.
Tone
A classification scale, ranging from light to dark, which indicates color intensity.
U
Uniformity
The grading system used to denote how well pearls in a piece of jewelry match one another. Uniformity can be excellent, good, or fair.
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