achroic Without color; a colorless gemstone.
achromatic As above
adularescence A phenomenal effect;
e.g., the billowing “moonglow” effect in moonstone.
akoya pearl A pearl from the
saltwater akoya-gai oyster (Pinctada martensii); “Japanese
baroque Any pearl that is not
symmetrical, round, or teardrop, oval, or button shaped.
bead nucleation The use of a
shell bead, usually spherical, implanted in the oyster to stimulate
the growth of a cultured pearl, and forming the center of the pearl.
bellied Describing a stone purposely
cut with extra weight around the girdle, yielding a bulbous outline.
bicolor A stone with two distinct,
separate hues, common in tourmaline.
bleed color The loss of saturation
and tone when the viewing environment is shifted between natural
and incandescent lighting.
body color The color of light
transmitted through a gem, as distinguished from key color, the
color of refracted light.
brilliance The total quantity
of light refracted and reflected (from a gemstone) back to the eye
of the viewer.
brilliant cut Usually refers
to a full-cut brilliant of fifty-eight facets, with thirty-two facets
and table above the girdle, twenty-four facets and a culet below;
used almost universally in cutting larger round diamonds.
byewater Off-color; poor color
and transparency; see also water.
“buying the cert”
A purchase based not on an analysis of the beauty of the stone,
but on the language of the grading report (certificate).
cabochon, en cabochon Gem with
a rounded top, without facets. French, “little head.”
carat Unit of weight in gemstones,
one-fifth of a metric gram
cat’s-eye Phenomenal effect
in cabochon cut gemstones resembling the iris of a cat’s eye.
clarity One of the “four
Cs” of quality grading, referring to the presence or absence
of inclusions or flaws.
color See body color, key color.
crown The top half of a
faceted gemstone; the portion above the girdle.
One of the “four Cs” of gem connoisseurship, coined
by author, referring to the transparency and diaphaneity of the
gem. See also water and transparency.
culet The point at the very bottom of the pavilion
of a gemstone.
cut The style in which a gem has been fashioned;
e.g., emerald cut, brilliant cut. Also refers to a gem’s proportions;
e.g., well cut.
daystone A term coined by the author to describe
a gem species or variety or single stone that looks its best in
diaphaneity The property of being transparent
dichroic Of two colors; the characteristic of
a transparent substance to divide refracted white light into two
diffraction The modification of white light as
it breaks up into the color spectrum.
dispersion The division of white light into its
constituent components as in light through a prism; the rainbow
dog A poor quality gemstone in a parcel.
drusy Tiny quartz crystals growing on the surface
of a gemstone.
en cameo Cut in relief. Opposite of cutting intaglio.
enhancement Any process applied to a gemstone
to improve its color or clarity; also heat enhancement, burning,
cooking; see also treatment.
extinction The dark gray to black
portion of a face-up gemstone that does not refract light; usually
caused by off-axis refraction.
eye The finest gemstone in a
eye-clean, eye-flawless Describing
a gem with no inclusions when viewed with the naked eye (assumes
eye-visible Inclusions visible
to the eye without magnification.
face up The view of a gem from
the top or crown.
fancy color In diamond, any color
other than colorless viewed face up; in diamond any color is a fancy
fish-eye A dark gray to black
(achroic) spot at the center of the gem caused by improper proportions
from poor cutting; see also extinction.