• The Korean Journal of Malacology
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• v.24 no.3
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• pp.243-251
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• 2008

Analyses of UV-Vis spectrum and reflectance are useful tools to identify pearls of which color was naturally made or chemically changed. Contents of some trace elements of pearls by using ED-XRF may give us the information that the pearls were originated from marine shells or freshwater shells, and may give us whether the pearls were chemically treated or not. Three types of chemically untreated pearls, freshwater cultured, Akoya cultured and Tahitian cultured, were treated with silver nitrate. UV-Vis absorbance spectrum of Ag was changed after treatment, and reflectance of pearls was decreased. Absorbance of natural black colored Tahitian cultured pearls at 400, 500 and 700 nm was observed. Natural black colored freshwater cultured pearls showed two characteristic absorption patterns in UV-Vis spectra at 380-400, 480-500 nm. Unlike naturally black colored Tahitian cultured pearls, the absorption spectrum at 700 nm could not be found from black freshwater cultured pearls. Manganese was not detected in the pearls from marine shells, and strontium content of the pearls from marine cultured shells was higher than that from freshwater cultured shells. According to ED-XRF analysis, Ag contents of silver nitrate treated pearls increased as more time passed, because silver ion invaded to nacre layer of the pearls. Since Ag content of the black pearls known as untreated ranged under 0.1%, analysis of Ag content may used to distinguish the black pearls are treated or not in marketplace.