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Ivory from an XVIIIth century shipwreck is brought to light.

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In the early XVIIIth century, a dutch trade ship sailing close to the coast of Saint-Quay-Portrieux (Britany) sank on his way back from Africa with more than a ton of elephant ivory on board. In 1987, two divers found the shipwreck at the site known as "les Poulins" triggering a series of archaeological investigations in 1991 and 1993 during which dozens of ivory tusks were recovered. After more than three centuries at the bottom of the sea, what remains of the original ivory structure ? At which length scale did the diagenetic process (i.e. the physical and chemical modifications during the "burial" period) occur in this complex, highly hierarchical, composite and nanostructured material ?

To answer those questions, we developed a multiscale characterization approach* on three tusks with very different states of preservation. An original combination of chemical micro- and nano-analysis (μPIXE/PIGE/RBS/EBS), scanning electron microscopy and X-ray scattering and diffraction using synchrotron microbeams now provide a better picture : the collagen, which forms 50 % in volume of ivory, is globally well preserved in those tusks. On the opposite, important modifications of the mineral phase (the remaining 50 %) have been observed with important fluctuations depending on whether or not the tusks were buried in the sand. Contrary to appearances, the buried tusks which surface was better preserved are those for which the chemical composition, the crystalline structure and the mineral nanocrystal organization are most affected.

In addition to the novelty of this analytic approach and to the practical consequences for marine archaeology, our study provides a better understanding of the alteration processes of ivory in sea-water in the early stages of diagenesis. The observation that the collagen degrades at the same time as the mineral phase is subjected to strong changes enables refining fossilization models for much older ivory.

A part of those artifacts are displayed at the Musée d’Art et d’Histoire of St Brieuc.

The published article.