Recently, GIA’s Mumbai laboratory received a five-strand necklace for identification, consisting of light cream and cream pearls (figure 1, left). The pearls varied in shape from near-button to near-oval, with diameters ranging from 3.27 to 4.80 mm, providing an overall well-matched appearance. Real-time X-ray microradiography (RTX) revealed that the majority of pearls were natural, showing different-sized cores surrounded by concentric growth arcs, while some displayed minimal structures. However, eight pearls exhibited suspicious internal structures, with some showing unclear demarcations. These were difficult to conclusively identify in their strung condition and were removed for further analysis (figure 1, right).
The eight removed pearls weighed between 0.51 and 0.68 ct, with sizes ranging from 4.45 × 4.33 × 3.53 mm to 5.30 × 4.22 × 3.98 mm. Energy-dispersive X-ray fluorescence revealed no traces of manganese, with strontium levels ranging from 981 to 1270 ppm, indicating a saltwater growth environment. However, when exposed to X-rays, some of the pearls showed a very weak yellowish green fluorescence and a stronger fluorescence in their drill holes. While saltwater pearls are usually inert to X-ray fluorescence, saltwater bead cultured pearls with freshwater shell nuclei tend to fluoresce with a weak to moderate yellowish green reaction (Fall 2023 Lab Notes, pp. 365–366). The weak fluorescence observed in these saltwater pearls, along with stronger fluorescence in the drill holes, indicated the potential presence of a freshwater nucleus within each pearl.
Detailed analysis of the internal structures via RTX and X-ray computed microtomography (μ-CT) confirmed that each of the eight pearls had a nucleus and boundary structure (figure 2). These nuclei appeared slightly more radiopaque than the surrounding nacre, were asymmetrical in shape, and lacked the growth structure present in the nacre surrounding them. In general, traditional bead cultured pearls are produced with spherical freshwater shell beads, which are easily identifiable through RTX analysis. When these freshwater shell beads are cut into differing shapes, or any other materials are used as nuclei, the resulting pearls are classified as atypical bead cultured (aBC) pearls.
The identification of this type of aBC pearl with an irregularly shaped shell bead presents significant challenges due to its deceptive similarities to the external appearance of natural pearls. Their irregular shape, characterized by asymmetrical and non-traditional nucleation, can mislead both gemologists and consumers alike. This necklace is particularly noteworthy as it marks the first time GIA’s Mumbai laboratory has encountered numerous relatively small aBC pearls of this type, drilled and strung alongside natural pearls. As cultivation techniques continue to evolve, the challenges associated with pearl identification will only increase. Therefore, it is essential for gemologists to accurately identify cultured pearls when intermixed with natural pearls of similar appearance.
Nishka Vaz is a senior gemologist, and Karan Rajguru is a gemologist, at GIA in Mumbai. Abeer Al-Alawi is a consultant to GIA.
Recently, GIA’s Mumbai laboratory received a five-strand necklace for identification, consisting of light cream and cream pearls (figure 1, left). The pearls varied in shape from near-button to near-oval, with diameters ranging from 3.27 to 4.80 mm, providing an overall well-matched appearance. Real-time X-ray microradiography (RTX) revealed that the majority of pearls were natural, showing different-sized cores surrounded by concentric growth arcs, while some displayed minimal structures. However, eight pearls exhibited suspicious internal structures, with some showing unclear demarcations. These were difficult to conclusively identify in their strung condition and were removed for further analysis (figure 1, right).
The eight removed pearls weighed between 0.51 and 0.68 ct, with sizes ranging from 4.45 × 4.33 × 3.53 mm to 5.30 × 4.22 × 3.98 mm. Energy-dispersive X-ray fluorescence revealed no traces of manganese, with strontium levels ranging from 981 to 1270 ppm, indicating a saltwater growth environment. However, when exposed to X-rays, some of the pearls showed a very weak yellowish green fluorescence and a stronger fluorescence in their drill holes. While saltwater pearls are usually inert to X-ray fluorescence, saltwater bead cultured pearls with freshwater shell nuclei tend to fluoresce with a weak to moderate yellowish green reaction (Fall 2023 Lab Notes, pp. 365–366). The weak fluorescence observed in these saltwater pearls, along with stronger fluorescence in the drill holes, indicated the potential presence of a freshwater nucleus within each pearl.
Detailed analysis of the internal structures via RTX and X-ray computed microtomography (μ-CT) confirmed that each of the eight pearls had a nucleus and boundary structure (figure 2). These nuclei appeared slightly more radiopaque than the surrounding nacre, were asymmetrical in shape, and lacked the growth structure present in the nacre surrounding them. In general, traditional bead cultured pearls are produced with spherical freshwater shell beads, which are easily identifiable through RTX analysis. When these freshwater shell beads are cut into differing shapes, or any other materials are used as nuclei, the resulting pearls are classified as atypical bead cultured (aBC) pearls.
The identification of this type of aBC pearl with an irregularly shaped shell bead presents significant challenges due to its deceptive similarities to the external appearance of natural pearls. Their irregular shape, characterized by asymmetrical and non-traditional nucleation, can mislead both gemologists and consumers alike. This necklace is particularly noteworthy as it marks the first time GIA’s Mumbai laboratory has encountered numerous relatively small aBC pearls of this type, drilled and strung alongside natural pearls. As cultivation techniques continue to evolve, the challenges associated with pearl identification will only increase. Therefore, it is essential for gemologists to accurately identify cultured pearls when intermixed with natural pearls of similar appearance.
Nishka Vaz is a senior gemologist, and Karan Rajguru is a gemologist, at GIA in Mumbai. Abeer Al-Alawi is a consultant to GIA.
