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.
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.
