Octahedral: A geometric object with eight
plane surfaces.
Oiling: The process of applying mineral oil to
a stone, such as an emerald, to mask
inclusions and enhance the color.
Old European Cut: A
round Brilliant cut with 58 facets, similar to the old mine
cut, first appearing in around the 1880's. It is characterized by a deep
pavilion, high
crown, and an open
culet.
Old mine cut: See Mine Cut.
Oligoclase: (Also called Plagioclase) A
triclinic
feldspar made of
soda-lime.
Olivelia Shells: A kind of
seashell used for
Heishi
necklaces.
Olivine: See
Chrysolite and
Peridot.
Omega chain: Unlike most
chains which are a series of linked rings,
an Omega chain is made up of rectangular smooth rounded
metal plates set side by side and crimped
along the ends onto a strip of metal
mesh. The end result is a fairly stiff, yet
flexible, circle which needs to be worn high around the neck since it is not
nearly as attractive when viewed from the edges.
Omega back: These work a bit like
lever back earrings, in that they have a hinged lever on the back of the
earring near the bottom, but in this case the lever ends in an O shape that
closes over a post in place of a clutch to
secure the earring to a pierced ear.
Onyx: A
semiprecious variety of chalcedony
quartz that is a used often in
jewelry. See Onyx Rings: When
chalcedony is variegated with with
spots or figures, or arranged in differently colored layers, it is called
agate; and if by reason of the thickness,
color, and arrangement of the layers it is suitable for being carved into
cameos, it is called onyx. White Onyx, a
semi-translucent white to slightly
yellowish-white stone, was often used as a background in
Victorian
jewelry, especially for
cameos. Black Onyx can appear
opaque or
translucent. Although it occurs naturally in black, it is generally dyed
black to improve its color. It has a hardness of between 6.5- 7 on the
Mohs scale. In India, onyx
necklaces are thought to cool feelings
of love.
Opal: An amorphous non-crystalline variety of
silica which is softer and less dense than
quartz. Opals are known for their
distinctive iridescent luminous
qualities which are actually inclusions
that can refract light in a rainbow of colors, called "fire",
that change with the angle of observation (Dichroism).
Opals contain a large amount of water and susceptible to cracking. Opal is the
birthstone for October.
Opaque: A substance which is not
transparent or
translucent. i.e. a substance that
does not allow light to pass through it.
Open-work: A setting that has open areas similar
to filigree cut which may allow for
viewing of the bottom of a stone. See Basket.
Opera Length: A
necklace which is 48 to 90 inches long.
Optical Properties: A
gemstone's inherent ability to interact
with light. Color,
dispersion and
fluorescense are all optical
properties.
Orb: A part of coronation regalia placed in the
left hand of the Sovereign during the coronation as a symbol of Kingly power.
It is a globe of gold encircled by a band
edged with pearls and set with
rubies,
emeralds and sapphires, joined by a
perpendicular band and surmounted by large
amethyst above which is a jeweled cross.
Ore: A metal
bearing mineral from which
metal can be profitably mined or extracted.
Oriental Pearl: A
pearl that has formed naturally with no
human intervention.
Ormolu: A term referring to gilded
bronze or
brass mounts. From the French for "ground
gold"
Orthoclase: A variety of
feldspar, composed of
potassium
aluminum
silicate, characterized by a
monoclinic crystalline structure and
found in igneous or
granitic rock. Also called
potash
feldspar.
Ouvarovite: See
uvarovite.
Oval Cut: A "fancy
cut" diamond or stone in an
elliptical shape like an oval.
Overlay: The upper layer of an
overlay technique. The layer with the design.
Overlay Technique: A decorative technique involve two flat pieces of
silver, or other
metal. The top piece has a design cut out
of it and is highly polished. The bottom layer is darkened with
oxidation to provide good contrast to the design on
the top piece when the two pieces are
soldered together.
Oxidation: A chemical process in which a
metal, such as
silver, is blackened as a reaction to
oxygen.
Oxide: A compound containing one
oxygen atom per molecule. See also
dioxide.
Oxidize: The act of combining with
oxygen to make an oxide.Oxidized
metal is rusted.
Oxygen: A
nonmetallic element that is normally
a colorless, odorless, tasteless gas that constitutes 28 percent of the
Earth's atmosphere. Oxygen combines with many other
elements easily. These compounds are
called oxides and make up about half the solid matter on
Earth, making oxygen the most abundant
element present in the Earth's crust.
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