types of instruments are used in the laboratory for examining gemstones
and other valuables. The terms expressed in the documents created
at the laboratory may be perplexing to clients. We've created a
tutorial to explain the equipment used at Guild Laboratories and
some terms which appear often in the documents we create.
Appraisal An evaluation of jewelry, gemstones
or other valuables, expressed in dollars (or other monetary values)
to be used for insurance, estate or other purposes. The appraisal
is a researched estimate of retail replacement value, or for another
appropriate market. A properly prepared appraisal conducted by a
qualified appraiser affords protection in the event of loss or damage
and is critical for settling probate, estate and other types of
Binocular Microscope A critical piece of magnifying
equipment in a professional laboratory. The gemological microscope
has twin objectives & oculars which provides three dimensional
viewing, various magnification lens, plus variable illumination
sources to examine the exterior and interior of an object.
Branded Gemstone or Diamond A proprietary, often
patented gemstone cut making the stone recognizable as a unique
shape. Branded cut stones may also bear identifying laser inscriptions
on the girdle (circumference).
Carat Weight A measure of weight,
rather than the size of a gemstone or diamond as expressed by carats.
Certificate A written report describing the results
of examination of a gemstone, diamond or other valuables detailing
the weight, proportions, color and clarity grades, and any other
variables pertaining to its identity and quality.
Chelsea Filter A small handheld
device assists in discriminating between natural green emerald and
other green gems, glass or gem simulants.
Clarity Grade A method of expressing relative
levels of clarity in a diamond. Gemological Institute of America
(GIA) has developed the most widely accepted grading scale ranging
from highest, Flawless (FL) to Included 3rd level (I3), or lowest.
Color Grading Scale (GIA) Colorless
diamonds are graded on a scale beginning with the letter D and continue
to the end of the alphabet.
N O-P-Q R||Very
Diamond A unique gem-mineral composed essentially
of only one element: carbon. It is the hardest of all known natural
substances ranking10 on the Mohs scale. It occurs in colorless
form, called "white" diamonds,
but also occurs naturally in a wide range of colors.
Dichroscope A small and very portable
laboratory instrument also used in the field to test for pleochroism--
a trait observed by a gem changing colors when viewed through its
lens while being turned. This is one test for gem identification.
Dispersion. The term used to express a transparent
gem or diamond's ability to separate white light into the spectral
colors; also referred to as fire.
Facet A polished surface placed on a diamond or
Face-up Color Apparent color observed in
a diamond or gem viewed in a direction perpendicular to the table
or how it would appear in its setting.
Fancy Cut Any gemstone shape or cutting style other than
a Round Brilliant cut. This includes pear, heart, emerald cut, marquise,
princess, trillion, cushion etc.
Fancy Color A diamond with an attractive natural
body color other than very light yellow. This includes pink, blue,
brown, fancy yellow (canary) and other rare colors. Any color sapphire
other than blue is called Fancy Color sapphire.
Fire See Dispersion.
Flaw A catch-all term referring to any internal
or external characteristics on a cut diamond or gemstone, also called
imperfections or inclusions.
Flawless (Fl) A diamond or gem with no internal
or external flaws or blemishes when viewed under 10X magnification.
Fluorescence The emission of light from a diamond
under a source of controlled ultraviolet lighting. This is part
of an identifying test performed on some diamonds.
Four Cs An easy to remember quality assessment
for diamonds: Carat weight, Color, Clarity and Cut.
Fracture-Filled Stone An enhancement technique
using materials which fill surface-reaching fractures. This process
is not considered permanent, and a full disclosure of these treatments
by the seller must be made to the consumer.
Full Cut (or Brilliant Cut) A round cut diamond
with the total of 58 facets.
Gem A cut and polished stone that possesses the
necessary rarity, beauty, utility and durability for use in jewelry
or for a collection.
Gem Identification A series of systematic tests
performed in a laboratory or other setting as allowed until an absolute
separation (identification) is made of the stone in question.
Institute of America (GIA) An
educational institute dedicated to research in the field of gemology;
considered the global leader in gem education for the benefit of
the industry and the public.
Gemology The science and study of all issues relating
to gemstones including their identification, description, origin,
Graduate Gemologist or GG One who holds a Graduate
Gemologist Diploma from the Gemological Institute of America (GIA).
Gram The weight in grams of metal used in jewelry
or decorative items. 28.35 grams = 1 ounce Avoirdupois
Hardness A relative ranking of a mineral's resistance
to being scratched. The Mohs scale developed in the 19th century
is the most accepted method for comparison of relative hardness.
Diamond, the hardest known substance is rated 10 on the Mohs scale,
and talc is the least hard mineral, ranking 1 on the Mohs scale.
Imperfection Any internal or external flaw or blemish
on a polished diamond or gemstone, also called an inclusion.
Irradiated Diamond A diamond that has been treated
with safe irradiation and annealing to increase its attractiveness
Karat A measure of gold purity or fineness, usually
stamped on a piece of jewelry with the mark K or KT after a number.
It represents the relationship of pure gold to the total metal alloy.
24K means pure gold. 14K equals 58.5% pure gold in the total metal.
Leveridge gauge A millimeter dial micrometer that
measures mounted and loose diamonds and gemstones of any shape and
Loupe A handheld 10X optical device, corrected
for spherical & chromatic aberration used for examining gemstones.
Microscope See Binocular Microscope
Millimeter (mm) Metric system unit of 1mm = 0.001
meter. 6 mm measures nearly 1/4 inch.
Millimeter Gauge A precision tool used for accurately
measuring (to 0.01mm) the overall dimensions of gemstones or of
jewelry in millimeters.
Mohs Scale See Hardness
Old European Cut Describes the earliest form of
circular shaped full brilliant cut diamonds. It is distinguished
by a small table, a high crown and great overall depth contrasted
to modern round cuts.
Old Mine Cut A term for an early form of brilliant
cut diamonds featuring a square-like or cushion-shaped outline.
Polariscope An optical instrument used to identify
a gemstone as having single or double light refraction; one of several
tests used in gemstone identification.
Refraction This is how a gemstone handles light
rays entering it, and is expressed in a stones' RI or Refractive
Refractive Index (R.I.) A measurement of how light
rays change direction (related to speed) as they enter or exit a
gemstone. There is a direct correlation between the higher
RI's and a stones' brilliance.
Refractometer An optical instrument used in the
laboratory for measuring the refractive index of a gemstone.
Rough Diamond A diamond crystal in its natural
state as found in the earth.
Slightly Included (SI) A clarity grade in a diamond,
which shows more inclusions than VVS or VS but less than Included.
Diamonds of this grade are usually very attractive to the naked
Specific Gravity A way to measure and articulate
the relative density of gemstones to that of water.
optical instrument reveals the unique absorption spectrum of gemstones,
and is used for identification and separation of natural and synthetic
Treated (Enhanced) Diamond A natural diamond that
has been coated, filled, laser drilled or otherwise treated to improve,
change its color, or its appearance.
Ultraviolet Light Electromagnetic
wave lengths shorter than that of visible light. The use of ultraviolet
light is important in the study of diamonds and colored gems because
of the (identifying) fluorescent effects seen in some gems.
Very Slightly Included (VS) and Very Very Slightly Included
(VVS) These grades identify imperfections in a diamond
which are few, small and very difficult to see even with the aided
eye at 10X magnification.
X-Ray Fluorescence Some diamonds fluoresce from
exposure to X-rays; usually in varying intensities of blue.
Zirconia cubic (CZ) A created material
without a natural counterpart that is often used as an inexpensive