Thomas Jewelers

A
abraded culet	A chipped or scratched culet. Can be caused by contact with another diamond.
abrasion	A bruise or scratch on the surface of a stone.
AGS	American Gem Society. Professional organization formed in 1934 by several independent jewelers and the founder of the Gemological Institute of America (GIA). The AGS is dedicated to setting and maintaining ethical standards and practices within the industry.
Antwerp	Perhaps the most noteworthy and versatile diamond-cutting center in the world. All sizes and shapes of rough diamonds are cut in Antwerp.
appraisal	A monetary evaluation, usually performed for insurance purposes by a gemologist. Appraisals should describe the piece in detail, including color, clarity, proportions, stone sizes, flaws and other distinguishing characteristics.
B
baguette	A rectangular cut stone with squared corners.
bearding	Small feather-like cracks along the girdle of a diamond.
bezel	Outer ring of a watch case, usually designed to hold the crystal, that may also be used for advanced functions like diving timers.
bezel setting	Holds a gemstone in place on all sides at the girdle, creating a smooth, metal halo flush with the stone's crown. Bezel settings often give the impression of a larger stone.
blemish	A flaw, spot or scratch on the surface of a gemstone.
brilliance	The intensity and amount of light reflecting from inside a diamond or gemstone.
brilliant cut	The most common style of cutting for diamonds and colored stones. Brilliant cuts may be round or fancy and must have 57 or 58 facet cuts.
C
cabochon	A gemstone cut that creates a dome shape with no facets.
caliper	Instrument for determining the thickness or diameter of a gemstone.
carat	One of the "Four Cs". Metric unit of weight for diamonds and gemstones. One carat equals 200 milligrams or 0.2 grams.
clarity	One of the "Four Cs". Measures the degree to which a gemstone is free from flaws. A clarity scale is used to grade flaws in gemstones. The scale ranges from FL (Flawless) where there are no visible internal or external flaws to I3, where many imperfections are visible to the naked eye.
cleavage	Tendency of a crystalline material to break in certain directions, often along a grain or crystal face.
cloud	Group of tiny white inclusions in a diamond.
color	One of the "Four Cs". In diamonds, the color scale ranges from D (colorless) to Z (yellow). In colored gemstones, the grading scale differs widely depending on the type of stone.
comfort fit	Ring design in which the edges of the shank are rounded for maximum comfort.
crown	The facets or portions of a gemstone located above the girdle.
culet	A small polished facet located at the sharp point or base of a faceted diamond or gemstone.
cultured pearl	Pearls created by the artificial introduction of a mother-of-pearl irritant into an oyster or other mollusk. Cultured pearls generally have thinner nacre and lack the luster of a natural pearl.
cut	One of the "Four Cs". Perhaps the most important factor in determining the value of a diamond or gemstone. The cut refers to the geometric proportion that dictates the reflection and refraction of light within a stone.
D
depth	The distance from a gemstone's table to its culet (top to bottom).
depth percentage	The measurement of a gemstone's depth (top to bottom) in relation to its diameter. Depth percentage is primarily responsible for refraction, which produces the fire or sparkle in a gemstone.
Diamond Gauge	A mechanical device used to determine the precise measurements of a gemstone.
DiamondLite	Instrument for color grading diamonds using visual comparisons to master diamonds. Trademark, Gemological Institute of America.
dispersion	The separation of white light into the full color spectrum. Often described as the "fire" or sparkle when discussing diamonds.
E
emerald cut	Step cut gemstone (most often rectangular) whose corners have been cut off.
extinction	Dark or black spots in colored stone.
eye-clean	Gemstone in which the flaws cannot be seen without a 10x loupe.
F
facet	Flat, polished surface or plane on a gemstone.
faceted girdle	Girdle that has been cut with facets.
fancy shapes	A gemstone shape other than round.
feather	Internal flaw (inclusion) that has a feathery appearance.
findings	Small, pre-fabricated parts of jewelry such as clasps, settings, etc.
fire	The sparkles of flashes of spectral colors emitted from diamonds and other gemstones.
flaw	General term used to refer to internal or external characteristics of a gemstone (i.e., inclusion, fracture, etc)
flawless	Term used to describe a gemstone that lacks discernable internal or external blemishes when viewed by a gemologist using no less than 10x magnification.
fluorescence	Luminescence that appears when certain diamonds are exposed to ultraviolet light.
fracture	Cracks, feathers or chips in a gemstone.
full cut	Gemstone with 58 facets.
G
gemologist	Gemstone specialist trained in gem identification, grading and appraising.
gemology	Science and study of gemstones.
GIA	Gemological Institute of America. Non-profit organization specializing in grading diamonds and gemstones. Widely held as the premier laboratory for gemological grading.
girdle	The narrow rim around a gemstone separating the crown from the pavilion.
gold filled	Metal covered by a thin layer of gold that is at least 10k and 1/20th of the total weight of the piece
gold plated	Virtually the same as gold filled, except gold plated items may have a layer of gold that is less than 1/20th of the total weight of the piece
grading	Valuing a diamond using master stones.
H
head	Portion of a jewelry item that holds the stone.
I
IJO
imperfection	General term used to refer to internal or external characteristics of a gemstone (i.e., inclusion, fracture, etc)
inclusion	Visible internal flaws in a gemstone, including fractures, crystalling abnormalities, and foreign objects.
irradiation	Treatment performed on gemstones and even pearls to enhance color.
K
karat	Standard measure of gold purity. One karat is 1/24th pure.
L
laser drilling	Technique used to enhance a stone's clarity by allowing for the introduction of bleaching agents or other enhancing agents.
leakage	Light leaving, or escaping, through the facets of fashioned gemstone.
Leveridge gauge	A millimeter gauge used to measure both mounted and unmounted stones.
loupe	Small magnifying glass, often held in the eye socket, used for analyzing gemstones.
luster	The appearance of a material's surface, as determined by the quantity and quality of light reflected.
M
marquise	Oval shaped gemstone with ends sharpened to points.
master stones	A set of diamonds used to grade the color of other diamonds.
milgrain	Tiny beads of metal used to decorate bands of metal
Moh's Scale	Scale used to measure gemstone hardness. Scale ranges from 1 to 10.
mounting	Method of holding gemstones in place (i.e., prongs, bezels, etc)
N
nacre	Crystalline substance that forms a pearl when secreted by a mollusk in response to an irritant.
O
off color	A stone presenting any semblance of undesirable color.
oiling	Temporary treatment used to enhance the color of a gemstone.
opera	A strand of pearls 32 inches in length.
P
pave (pah-vay') setting	Style of setting small stones as close together as possible. Stones are set into drilled holes and metal beads are pushed over to hold the stone.
pavilion	The portion of a gemstone located below the girdle.
percussion mark	Indentation or bruise on the surface of a gemstone caused by contact from a pointed object.
pit	Indentation on the surface of a diamond or gemstone.
platinum	Precious metal that is far harder than gold. Platinum does not tarnish and is hypo-allergenic.
plot	Diagram of a gemstone's clarity characteristics. Generally performed during an appraisal using magnification.
point	One-one hundredth (0.01) of a carat.
princess	A strand of pearls 18 inches in length.
princess cut	Square cut, brilliant gemstone.
prong	Metal "finger" bent around the girdle of a gemstone to hold it securely in place.
proportion	Mathematical representation of a gemstone's overall symmetry.
R
recutting	Refinishing a polished stone in order to improve the stone's clarity, proportion or other imperfection.
reflection	Light rebounding off the polished surfaces of a gemstone.
refraction	Bending of light waves. When white light is refracted, a full spectrum of color appears, as in a prism.
rope	A strand of pearls 40 inches in length.
rough	An uncut or unpolished diamond or gemstone.
S
setting	Method of holding gemstones in place (i.e., prongs, bezels, etc)
shank	Part of the ring that encircles the finger.
single cut	A simple form of cutting that has a table, approximately 16 facets and rarely a culet.
solitaire	Ring containing a single diamond or gemstone.
symmetry	Uniformity of a gemstone's cut, including the shape and placement of facets.
synthetic stone	"Man-made" gemstone grown in a lab.
T
table	Largest facet on a gemstone. The table sits atop the crown and allows light to enter and exit, creating the stone's brilliance.
table percentage	Diameter of a gemstone divided by the size of the table.
Tolkowsky, Marcel	Mathematician that defined the proportions necessary for maximum brilliance from a round diamond brilliant cut
U
ultrasonic	Cleaning device for jewelry that removes dirt through the use of ultrasonic waves. Note: Certain gemstones may be damaged by an ultrasonic cleaner.