Glossary of Pearl Terms O

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Occidental pearls: Historical term used to describe natural pearls from Mexico, dates to the 16th century but fell from usage after 1930.

Oil pearls: Imitation pearls worked from the columella (see) of the Trochus and Turbo snails.

Oiling: Process of soaking a natural or cultured pearl in warm oil to diminish the visibility of cracks.

Opera necklace: Pearl necklace measuring 28 to 35 inches (70-90 cm).

Operculum: Shell-like cover that closes the opening of some marine gastropod shells.

Orama Pearls: Trade name for cultured blister pearls sold to tourists on Rarotonga in the Cook Islands.

Organic dyes: Used to change the color of natural and cultured pearls.

Orient: Optical phenomenon that produces iridescent colors on the surface of some natural and cultured pearls. These factors help create orient: reflection, refraction, diffraction, and thin-film interference.

Oriental pearls: Historical commercial term for natural marine pearls from the Persian Gulf and the Red Sea.

Osmena pearl: Also called Osmend Osmeña, or Osmenda pearl. Imitation pearl worked from the inner coil of the Nautilus pompilius shell.

Ostracum: Central, prismatic layer of a bivalve mollusk shell.

Ounce pearls: Historical trade term describing small natural pearls offered in lots.

Oval: Natural or cultured pearl in an oval or egg shape.

Overtone: Secondary color(s) on the surface of a natural or cultured pearl. It is created by nacre layers interfering with white light and splitting it into its component colors.

Oyster: Common name correctly applied to some bivalve mollusks and incorrectly to others. No bivalve mollusk that produces nacreous natural or cultured pearls is a true oyster. It accurately refers to "Edible Oysters" of the Ostreidae family.

Oyster pearls: Chalk-like natural concretions produced by edible oysters (Family Ostreidae), of low to no commercial value.