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Glossary of Pearl Terms O

Glossary of Pearl Terms O

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. One or more of these factors creates 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 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 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.

oyster pearls: Chalk-like natural pearls produced by edible oysters (Family Ostreidae), low in commercial value.