NOTES & NEW TECHNIQUES

Irradiated South Sea cultured pearls (SSCPs) from the Pinctada maximamollusk typically show col- ors from light gray to silver. It is difficult to identify gamma-ray irradiation of SSCPs using standard gemological methods because of their thick nacre. Therefore, an advanced analytical tech- nique such as electron spin resonance (ESR) spectroscopy is needed to detect the treatment. ESR measurements of minute amounts of SSCP powders revealed the formation of CO 2 - radicals, and the parameter known as the g-factor was measured at 2.0015 ± 0.0005. Higher levels of CO 2 - radicals were detected in the pearl nacre than in the nucleus. Therefore, the existence of CO 2 - radicals is an indicator of irradiated SSCPs.