Rapid detection of color-treated pearls and separation of pearl types using fluorescence analysis.

Abstract

Pearl identification plays a key role to maintain transparency in the gem industry by disclosing potential color treatments and classifying pearl species. Current techniques for pearl identification have been limited by expensive instrumentations and long measurement time, severely restricting their use outside of major gemological laboratories. There is a strong demand for simple and inexpensive identification instruments designed for non-specialized users and small-scale gemological laboratories. For this purpose, we demonstrate a portable fluorescence spectroscopy for pearl treatment detection and species classification based on pearl's nacre fluorescence detection. This device can be used to rapidly separate naturally colored pearls from treated colored pearls, detect potential treatments applied to white colored pearls, and separate pearls between certain species in seconds, based on their differences in nacre fluorescence intensity. The system enables noninvasive testing of loose pearls, pearl strands, and mounted pearl jewelry under normal office lighting conditions. The experimental prototype demonstrates high accuracy for automatic pearl color treatment screening, referring 100% of the treated colored pearls. Furthermore, similar protocols can be applied to evaluate popular pearl enhancements such as bleaching and to extend its application to separate akoya pearls and their South Sea counterparts.