Glossary of Pearl Terms I

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I-pearls: Imitation pearls from Izumi, Japan.

Icon pearl: Cultured blister pearl produced in the shape of an iconic object (usually a commercial image or even a trademark logo) by using a nucleus of that shape.

IGI grading system: Cultured pearl grading system developed by the International Gemological Institute in New York in 1993. The system uses twenty-two reference strands to grade color, luster, nacre, shape, and surface according to point values ranging from 1 (lowest) to 30 (highest).

Ikecho-gai: Japanese name for the Biwa pearly mussel, Hyriosis schlegeli. It translates to "pond butterfly shell".

Image pearl: An image pearl, similar to an icon pearl, is a cultured blister pearl in the shape of an image like a Buddha or a dragon; first cultured in Cristaria plicata (cockscomb) mussels in China in the late 1200s.

Imitation pearl: Any material that simulates the appearance of a cultured or natural pearl but does not possess either's physical properties. See Faux Pearls.

Immature pearl: Natural pearl that shows discoloration from a conchiolin core or darkened conchiolin rings.

Imperial golds: South Sea pearls from the gold-lip pearl mollusk (Pinctada maxima) that exhibit deep gold color saturation. Also known as "24K Gold".

Incomparable, The: See Peregrina, La.

Indicator pearl: Small South Sea pearl (also known as a baby pearl) harvested from Pinctada maxima after six to eight months so a larger nucleus can be inserted in the existing pearl sac. The pearls are generally small and have thin nacre. Indonesia is the primary producer.

Infrared spectroscopy: Method of determining the agents used to change the color of a cultured or natural pearl. It is also used to determine the chemical composition of imitation pearls.

Interference: Interference of light by nacre creates the iridescent play of color on the surface of a pearl. Refraction, diffraction and/or thin-film interference occur as light penetrates extremely thin nacre layers.

Iridescence: Play of color over the surface of a pearl as interference divides white light into its component colors.

Irradiation: Exposing a cultured pearl to gamma rays darkens the nacre of a freshwater pearl or the freshwater mussel bead within a cultured saltwater pearl by affecting the manganese each contains.

Ise pearl: Natural white pearl from Ago Bay, Japan. Cultured akoya pearls eclipsed Ise pearls.