Saltwater pearl with barium

by Dr. M.S. Krzemnicki, first published in Facette 28 (May 2023)

Figure 1: Antique pearl necklace with a “pearl” in the centre, assembled from a blister with a polished piece of shell at the base. Photo: A. Chalain, SSEF.
Recently, the SSEF received a button-shaped pearl of 7.5 ct for testing. Based on X-ray radiography and a UV-Vis-NIR reflectance spectrum, the pearl was easily identified as a saltwater natural pearl from the species Pinctada margaritifera. Strangely enough however, this pearl showed a distinct concentration of barium (approx. 350 ppm), an element commonly found in freshwater pearls but only at very low trace levels (about 1 ppm or below) in saltwater pearls. We assume that the presence of barium in this specific pearl might be a residue from a former X-ray radiography performed with an X-ray absorber liquid containing barium. The admixture of barium sulfate to water is applied in medical X-ray radiography since many years with the aim to increase the visibility of internal features.

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