2023

Queen Mary pearl: age dating & DNA fingerprinting

by Dr. A. Sato & Dr. L.E. Cartier, first published in Facette 28 (May 2023)

Figure 1: The Queen Mary Pearl set as a pendant in a necklace. This pearl of 41 ct exhibits a delicate slightly grey colour and a very fine and smooth pearl lustre. Photo: L. Phan, SSEF.
Similar to gemstones which are re-polished over time and thus need an updated SSEF report, we also occasionally receive pearls a second or third time for a new report, for example when the pearl is set in a new jewellery design. This is specifically the case when a pearl is important and/or of historical provenance. An excellent example for such an update is the Queen Mary Pearl (Figure 1). This beautiful drop-shaped saltwater natural pearl of 41 ct was tested by SSEF already many years ago as an unmounted loose pearl and then later in 2019 after being set as a pendant in a necklace (see also SSEF Facette 2020, No. 26, page 34). Based on the provided documentation, the Queen Mary Pearl belonged originally to Queen Mary (1867-1953), wife of King George V of England (1865-1936). This important pearl was then passed on to the following generations within the royal family until it was eventually sold some years ago. Last year, we were lucky enough to be able to analyse this pearl a third time, as the saying goes “all good things come in threes”. This time, however, the client was specifically keen to know more about the historical background of this pearl, i.e. the species of the pearl-oyster producing this pearl, its habitat, and its age.
Figure 2: X-ray tomographic section of the Queen Mary Pearl, exhibiting a (half) drill-hole partially with some residues from the former jewellery setting, and several ring structures as is characteristic for natural pearls. Figure: J. Braun, SSEF.

As it was submitted as an unmounted loose pearl, we were not only able to do a full X-ray tomographic study of the internal structures of this historic pearl (Figure 2), but also to take minute nacre powder samples (about 20 mg in total) from within the pre-existing drill-hole for DNA fingerprinting and radiocarbon age dating analyses. Radiocarbon dating is a scientific method used to determine the age of materials containing 14C, an unstable isotope of carbon. This method was developed in the late 1940s by Willard F. Libby, who received the Nobel Prize in Chemistry in 1960 for his ground-breaking research on radiocarbon dating. Since then, this method has become a standard tool for archaeologists, historians, and geoscientists and is offered by SSEF as a service to our clients since many years. The results of the radiocarbon dating performed at a specialised research laboratory of the Swiss Federal Institute of Technology in Zurich reveals a historic age for the analysed pearl. As it is often the case with radiocarbon dating, the determined age indicates a period in history rather than a precise date. Based on our data, the pearl probably formed between 1707 and 1876 A.D. in coastal waters along the Paci c coast of Mesoamerica. A recent formation in the mid to late 20th or early 21st century, however, can be excluded. In addition, the Swiss Gemmological Institute SSEF in collaboration with the forensic Institute of the University Zurich carried out DNA fingerprinting on the pearl to determine its species, using a method first developed by SSEF for pearls (Meyer et al., 2013) and precious corals (Lendvay et al., 2020). The resulting DNA analysis unambiguously revealed that the Queen Mary Pearl belongs to the Pinctada mazatlanica species, commonly known also by the name Panama pearl oyster or La Paz pearl oyster. This species is found o the Paci c coast of Mesoamerica from the Baja California (Mexico) to Ecuador and northern Peru (Figure 3).

Figure 3: Map indicating where Pinctada mazatlanica is commonly found. Figure: SSEF.

Pearl oyster fishing of Pinctada mazatlanica began in the Americas long before the arrival of the Spanish in the 15th century, as local indigenous cultures already collected these pearls and oyster shells. Traded and treasured also by European royal courts, these pearls became quickly very fashionable. They were set in historic noble and royal jewellery and remain highly appreciated in the pearl and jewellery trade until today. Having been able to not only investigate in detail the nature of this important pearl scientifically, but actually contributing and confirming the historical provenance of the Queen Mary Pearl has been a fascinating venture and voyage in time.

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