Pinctada radiata Atypical Bead Cultured Pearls from the UAE
Pearling is embedded in the culture and traditions of everyday life in the United Arab Emirates (UAE), especially in the trading center of Julfar. Abdulla Al Suwaidi, grandson of one of the last traditional pearl divers in the UAE, took on the challenge of reviving the country’s pearling industry. He succeeded in establishing the Suwaidi Pearl Farm in Al Rams, Ras Al Khaimah (RAK), in 2005. Suwaidi’s cultured pearl farm is recognized as the first of its kind in the Arabian (Persian) Gulf region.
GIA’s Mumbai laboratory recently examined a quantity of cultured pearls obtained from the farm. The parcel contained variously shaped white to cream-colored pearls. Examination by real-time microradiography (RTX) showed a variety of different internal structures including bead and non-bead cultured pearls, but two pearls in particular (figure 1) revealed very interesting structures and were confirmed to be samples from atypical “bead” culturing experiments conducted by the farm. Pearl A was light cream and near-round, weighing 0.87 ct and measuring 5.13 × 4.93 mm, while pearl B was cream and button shaped, weighing 0.94 ct and measuring 5.42 × 5.12 × 4.93 mm. When viewed under 40× magnification, both pearls exhibited a smooth surface and possessed typical nacreous overlapping aragonite platelets.
Additional RTX and X-ray computed microtomography (μ-CT) analyses were conducted to further study the internal structures. RTX imaging of pearl A revealed a non-bead cultured pearl used as a “bead” nucleus (figure 2). A light gray core surrounded by organic-rich concentric growth structures followed by finer growth arcs was visible. An obvious demarcation with a small organic tail-like feature just below the surface overgrown with cultured nacre was also apparent. The lack of growth arcs in the nacreous layers was due to rapid growth during the culturing process (“Atypical ‘beading’ in the production of cultured pearls from Australian Pinctada maxima,” GIA Research News, February 13, 2017). Similarly, pearl B revealed a natural pearl used as a “bead” nucleus (figure 3), with a very small but clearly visible dark gray core surrounded by faint growth arcs. As with pearl A, a distinct demarcation with organic-rich areas and a small organic tail-like feature were evident just below the surface overgrown with cultured nacre. X-ray computed microtomography analysis of both samples revealed clearer images of the demarcation between the “bead” pearls used as nuclei and the cultured nacre overgrowths.
Optical X-ray fluorescence examination did not show any fluorescence in either sample. Energy-dispersive X-ray fluorescence spectrometry revealed manganese levels below detection limits and strontium levels of 1130 ppm for pearl A and 1446 ppm for pearl B. The results from both testing methods were consistent with a saltwater growth environment. The ultraviolet/visible reflectance spectra collected for both pearls showed features around 435 and 460 nm and an additional weak band at 495 nm. These features are similar to spectral observations previously recorded for natural Pinctada radiata pearls (A. Al-Alawi et al., “Saltwater cultured pearls from Pinctada radiata in Abu Dhabi (United Arab Emirates),” Journal of Gemmology, Vol. 37, No. 2, 2020, pp. 164–179). Raman analysis using 514 nm laser excitation was carried out on the surfaces of both pearls, and a doublet at 704/705 cm–1 as well as a peak at 1085 cm–1, indicative of aragonite, were observed. Weak polyenic pigment-related peaks at 1130 and 1540 cm–1 were only observed for pearl B and were associated with its cream coloration. The photoluminescence spectra were also consistent with the Raman results and displayed high fluorescence together with the aragonite peaks, typical of most nacreous pearls.
Using lower-quality pearls (both nacreous and non-nacreous), gemstones, and other materials as “bead” nuclei has been a known practice for the last decade (“Chasing cultured pearls at SSEF: Cultured pearls using a natural pearl as a bead,” 2020, https://www.ssef.ch/chasing-cultured-pearls-at-ssef-cultured-pearls-using-a-natural-pearl-as-a-bead/). Although not seen on a regular basis, atypical “bead” cultured pearls (aBCPs) are encountered in laboratories from time to time and can be very challenging to separate from some natural pearls. This would be especially true of the two samples featured in this report: If either of them were drilled and mixed in strands with natural Gulf pearls, an experienced gemologist would find it difficult to separate them from the other pearls. The authors have encountered natural pearls with similar distinct boundaries. It should also be noted that the aBCPs produced at the Suwaidi farm are the result of successful experiments, and they are not commercially available at the time of this writing. The farm continues to conduct various experiments and aims to restore the UAE’s place in the global market by producing the finest Pinctada radiata cultured pearls available.
