The financial support for this research project by the Thailand Research Fund (TRF) and Office of the National Research Council of Thailand (NRCT) is gratefully acknowledged. The authors would like to thank The Gem and Jewelry Institute of Thailand (Public Organization) for enabling access to the ICP facilities and Assistant Prof. Dr. Anansawake Haewsungjarern for the X- Rite handheld Spectrophotometers.