Radiocarbon age dating of pearls

Cyril Roger Brossard

Well-known member
Aug 30, 2012
As seen in the FACETTE of 2013.

Apart from constantly updating our equipment for our scientific pearl testing procedure, we also invest much effort evaluating new scientific approaches for pearl characterisation and testing.

In this context, we started a research project a few years ago in collaboration with Dr. Irka Hajdas (ETH Zurich) to investigate the possibilities of radiocarbon age dating of pearls. This method uses naturally occurring isotope 14C to determine the age of carbonaceous materials up to 60?000 years.
Last year saw some interesting developments, as we were able to analyse a batch of pearls that spanned from the 18th century to today. The results of this research were presented by M.S. Krzemnicki at the 21st International Radiocarbon Conference, held in the prestigious UNESCO building in Paris (9-13th July 2012).
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Pearls - being calcium carbonate (CaCO3) concretions formed by biomineralization in molluscs - contain traces of radiogenic 14C. Similar to age dating of bones or tissues or other artefacts, a tiny amount of pearl nacre (ca. 8 mg) was scratched/peeled off from the surface of the pearls and investigated using the ultra-sensitive Accelerator Mass Spectrometry (AMS) technique at the Laboratory of Ion Beam Physics, Swiss Federal Institute of Technology (ETH Zurich) in Zurich. A general problem of our data is that marine reservoir ages may strongly affect the resulting radiocarbon ages of shells, and consequently also pearls, especially in areas with upwelling of ?old? seawater. As could be shown, it is usually not possible to gain a reasonable radiocarbon age for freshwater pearls (and shells). This is due to the incorporation of sedimentary limestone into the biomineralized calcium carbonate (socalled ?hard-water effect?), which then may strongly affect the resulting data (Bezzerra et al. 2000). However, for suspension-feeding saltwater molluscs (e.g. oysters), such as our studied samples from Pinctada maxima and Pinctada radiata, which live in coastal marine habitats with known upwelling and carbon isotope ratios, the analyses should result in more or less reliable radiocarbon ages (Taylor & Slota 1979, Bezzerra et al. 2000, Rick et al. 2005).
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The most important feature for pearl age testing is the so-called bomb peak calibration curve, a major and sudden increase in 14C ratio around 1965, followed by an exponential decreasing tail, as a consequence of the atmospheric nuclear bomb testing in the 50s and 60s of the 20th century. By superposing the bomb peak to the progress of the cultured pearl industry, we were able to separate our saltwater pearl samples into two main categories: pearls which are distinctly older than the bomb peak (before 20th century), and which therefore are most likely to be natural pearls, and pearls whose age is close to or later than the bomb peak. Pearls from the second category are either natural or cultured. Finally, an identification of the nature (natural vs. cultured) of these pearls is still based on the ?classical? approach using radiography and μ-tomography.
Based on these promising results, a further study with more pearls is planned for the near future. Although there are many factors which may influence radiocarbon data of pearls and which are not well understood so far, it will be of strong interest for us to study further well-documented pearls of historic or recent age. This will give us a better picture about possibilities and restrictions of this method. Though this is so far not intended as a commercial service fo our clients, we will inform our members as soon as such a testing service is feasible.
Any reader who would like to contribute to this research by supplying well-documented pearls is highly welcome to contact Dr. Michael S. Krzemnicki at SSEF. An article about our findings has been submitted to the Radiocarbon Journal and will be published soon...
A general problem of our data is that marine reservoir ages may strongly affect the resulting radiocarbon ages of shells, and consequently also pearls, especially in areas with upwelling of “old” seawater.

The marine reservoir refers to the 400 year old layer in the top of the oceans?
thank you. I learned about that during my pearl of Allah story too. It was regarding the actual age of the pearl as opposed to the age claimed in a so-called appraisal.
If the technology becomes widespread within GIA and other renown laboratories and if there is a will to date some famous jewels then yes it would be most interesting to try to check how old they really are. The thing is dating is more accurate for terrestrial samples as you understood it (reservoir).