The Mary Rose gets conservation boost from new x-ray technique

The Mary Rose - Henry VIII’s favourite warship whose remains were brought to the surface in a massive salvage operation broadcast to over 60 million people around the world 39 years ago this month - has received a major boost to help conserve the ship for future generations.

A team of researchers, led by Professor Serena Cussen from the University of Sheffield, has used a new x-ray technique available at the European Synchrotron Radiation Facility (ESRF) to discover the presence, location and structure of nanostructured bacterial byproducts lodged within the ship’s wood that could contribute to Mary Rose wood degradation.

The remains of the ship are currently on display in a purpose-built museum at Portsmouth Historic Dockyard, but they are vulnerable to degradation after spending more than 400 years at the bottom of the sea where harmful deposits collected inside the ship’s wooden hull. These deposits originate from degradation of metal fixtures and artefacts after centuries spent under the seabed and the activity of anaerobic sulfur-reducing bacteria and can lead to the formation of harmful acids.

This project, which brings together an international interdisciplinary team of researchers from the University of Sheffield, the University of Copenhagen, Columbia University, the ESRF and the Mary Rose Trust, has applied a new x-ray computed tomography method to unlock detailed information about these deposits. Applying this method also overcomes the additional challenge of studying precious cultural artefacts where care must be taken to avoid damaging the fragile remains as these experiments can be performed without destroying the sample.

Up to now, it has not been possible to obtain detailed information about the structure of harmful deposits within the wood. As Professor Cussen explains: “It is remarkable that this technique, available at the ESRF, allows us not only to image and locate these nanoparticles in Mary Rose wood, but also to evaluate their structure. This is the first time zinc sulfide nanostructures have been observed in Mary Rose wood. This is because it is really challenging to assess the range of material present within archaeological samples.”.

Using the new technique, which combines x-ray computed tomography with pair distribution function analysis (ctPDF), the team has mapped out the location and structure of nanostructured compounds lodged within the ship’s wooden hull. The team have also uncovered the location of organic polymer deposits within the wood, a result of polymer treatments applied to compensate for degradation of the wood. If the polymer starts to breakdown, it would produce degrading acids that could damage the Mary Rose - so knowing where the polymer is within the ship’s wood and tracking it over time is crucial to conserving the artefact.

Professor Serena Cussen added:

“These developments mean that potential threats to the wood can be tracked - a vital step in developing conservation strategies for the future of the Mary Rose. With the insights we have gathered from this experiment we’ve been developing new magnetic nanoparticle-based treatments to target and remove these harmful species from the Mary Rose. This will help us preserve this priceless artefact for years to come. This x-ray method could also be used to inform strategies to preserve other important archaeological discoveries.”

Professor Eleanor Schofield, Deputy Chief Executive Officer at the Mary Rose Trust, said:

“The application of this technique to complex archaeological materials presents a really exciting advancement for the field of heritage science. To be able to look inside a piece of Mary Rose wood and see not only the structure but also the level of degradation, previous conservation treatments and other inclusions from the marine environment, is a fascinating insight. It provides us with a wealth of knowledge which we can use to further understand how the materials will react to certain treatments and environments and from that, devise future conservation strategies to keep them safe for years to come.”

Professor Simon Billinge, Professor at Columbia University, said:

“It was particularly exciting to get a glimpse into the history of the Mary Rose in the years since it sank. The zinc sulfide deposits come from anaerobic bacteria living in the wood as it sat sunk in the seabed, and our results were like a micro-scale archeological dig where by studying the location and composition of the deposits we could see how the bacteria colonised the wood and what they ate.”

Dr. Kirsten M. Ø. Jensen, associate professor at University of Copenhagen, said:

“Analysing the very large X-ray scattering datasets we collected from the Mary Rose wood was like a treasure hunt, where we were looking for signatures of the substances residing in the wood. In the end, our analysis of the data made it possible to obtain very detailed structural information on the zinc-containing nanoparticles, which can now aid in developing new conservation methods.”

Dr Marco Di Michiel, scientist in charge of beamline ID15 at ESRF, said: “This is the first time that we have used the technique of x-ray total scattering with computed tomography to successfully study cultural heritage samples at the nanoscale. This work opens doors to new experiments in the domain of conservation."

More details on the new x-ray technique used by the researchers on the Mary Rose have been published in the journal Matter. For a copy of the paper - Location and characterization of heterogeneous phases within Mary Rose wood - visit: https://www.cell.com/matter/fulltext/S2590-2385(21)00498-7