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

摘要

Artificial color treatment techniques have been applied to pearls of less appealing colors to improve their appearances and to increase their commercial values. In addition, separation of various types of pearls could be challenging due to similar characteristics among several closely related mollusk species. Currently gemological laboratories use various spectroscopic and imaging techniques in tandem, including x-ray imaging, microscopic observation, ultra-violet to visible reflectance spectroscopy, and Raman spectroscopy for various identification purposes. Due to the complexity of the protocol, there is a strong demand for a fast and simple identification method designed for gemological laboratories or users without advanced equipment or expertise, such as pearl dealers and jewelry manufacturers. We demonstrate a fluorescence detection system for pearl's color treatment identification and species classification. A photoluminescence excitation spectroscopy was used to select the proper excitation wavelengths. Multiple light emitting diodes were selected as the sources: and spectrometers were used to monitor ultra-violet to visible fluorescence. The system can noninvasively analyze both loose pearls and mounted pearl jewelries under normal office lighting condition. Spectral analysis protocols were used to localize the trace of treatments and classify fluorescence features between different pearl types. The primary purpose of this device is to detect commonly used color treatments. Additionally, it may also classify pearls between the most common types in seconds, as suggested by preliminary study.