An international team of researchers has analysed the sulphurand iron composition in the wooden timbers of the Mary Rose, an Englishwarship wrecked in 1545, which was salvaged two decades ago. The teamused synchrotron X-rays from the Stanford Synchrotron RadiationLaboratory (USA) and the European Synchrotron Radiation Facility(France) in order to determine the chemical state of the surprisinglylarge quantities of sulphur and iron found in the ship. These newresults provide insight to the state of this historic vessel and shouldaid preservation efforts. They are published this week in theProceedings of the National Academy of Sciences Early Edition.
TheMary Rose served as English King Henry VIII's principal warship for 35years until she went down outside of Portsmouth in 1545. In 1982 thehull was recovered from the sea and is currently undergoing aconservation process. The first author of the publication, MagnusSandström, and his colleagues showed recently that the accumulation ofsulphur within shipwrecks preserved in seawater is common by studyingthe Swedish warship Vasa, which remained on the seabed for 333 years.Their research concluded that sulphur in contact with oxygen could poseconservation problems. Over time, sulphur can convert to sulphuricacid, which slowly degrades the wood until the hull's stability is lost.
Theauthors examined the Mary Rose to determine the potential threat andfound about 2 tons of sulphur in different compounds rather uniformlydistributed within the 280-ton hull. To determine the sulphur speciespresent in the wood, researchers first carried out experiments at SSRL.The team needed to obtain complimentary information in order to knowthe precise location of sulphur species at the micron scale and theythen came to the ESRF. By studying thin wood slices perpendicularly cutto the cell walls at X-ray microscopy beamline ID21, they found highconcentrations of organo-sulphur compounds in the lignin-rich areasbetween the cells, which may have helped preserve the ship while it wassubmerged in the seawater. This helped to understand how accessible andreactive the different sulphur compounds found are to acid-producingoxidation.
Plenty of iron and pyrite is also present in the MaryRose, which is a concern, since in the moist wood iron ions cancatalyse the conversion of sulphur to sulphuric acid in the presence ofoxygen. The authors suggest that chemical treatments to remove orstabilize the remaining iron and sulphur compounds, and reducinghumidity and oxygen access, are requirements for long-term preservation.
Atthe Mary Rose Trust they are already investigating new treatments toprevent new acid formation. For slowing down the organo-sulphuroxidation reaction and prevent new acid formation, wood samples fromthe Mary Rose are being treated with antioxidants in combination withlow and high grade polyethylene glycol (PEG). Another approach to slowdown acid formation in PEG treated conserved archaeological wood is tomaintain it in a stable climate. It is hoped that keeping a constantlow humidity of 50-55% without variations of temperature will stopchanges in sulphur speciation. To maintain a stable microclimate withinthe wood structure a surface coating offers a possible solution,although the effectiveness of this approach has yet to be tested. “Thisongoing research is considered to be an important step forward indevising improvements to the current Mary Rose hull treatmentprogramme”, explains Mark Jones, curator of the Mary Rose.
Reference:Magnus Sandström, Farideh Jalilehvand, Emiliana Damian, Yvonne Fors,Ulrik Gelius, Mark Jones and Murielle Salomé. Sulphur accumulation inthe timbers of King Henry VIII's warship Mary Rose: a pathway in thesulphur cycle of conservation concern, PNAS, Proc. Natl. Acad. Sci. USApublished 26 September 2005, 10.1073/pnas.0504490102.
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