The Chemistry of Wood Degradation in a 16th Century Shipwreck

The Chemistry of Wood Degradation in a 16th Century Shipwreck

Author: Janina Tolks

The Mary Rose, an English warship of the Tudor era, sank during a battle in the 16th century. It was salvaged in 1982, after more than 400 years at the bottom of the sea. To preserve this historical heritage, the development of effective conservation strategies is crucial. In order to prevent the ship’s wooden hull from degrading, it is important to understand the chemical processes that take place within the wood and contribute to its degradation. Especially during the drying procedure of the wooden hull in a controlled environment, the formation of oxidized sulfur compounds turned out to be a significant threat to the integrity of the ship.

Eleanor J. Schofield, The Mary Rose Trust in Portsmouth, UK, and colleagues have investigated the contribution of sulfur and metal species to wood deterioration, as well as the evolution of sulfur-containing compounds as a function of the depth and drying time of the wood. Atmospheric, oxygen-rich conditions can lead to the formation of acidic sulfur compounds that degrade the wood. Iron ions, for example, can catalyze the breakdown of the wood via Fenton-like oxidative processes.

The researchers used synchrotron-based techniques to analyze the sulfur compounds using wood samples from different locations of the hull. X-ray absorption near-edge spectroscopy (XANES) provided insight into the oxidation state and coordination environment of the sulfur species. Linear combination fitting (LCF) of the XANES data with spectra of standard sulfur compounds resulted in a quantitative overview of the reduced and oxidized sulfur species in the wood. The team found that the amount of oxidized sulfur species had increased after five months of drying, both on the surface and inside the wood in all studied locations of the wreck.

Fourier-transform infrared spectroscopy (FTIR) measurements of the wood indicate an increased degradation of (hemi)cellulose as the main cause for the deterioration of the wood. The lignin component of the wood was less susceptible to degradation.

The team also investigated the influence of metal deposits. X-ray fluorescence (XRF) line scans showed that significant amounts of iron and  zinc are present in the most degraded wood regions, both at the surface and in greater depth within the wood. This indicates that these metals contribute to the degradation process. Overall, the work contributes to the understanding of wood degradation and the development of effective conservation techniques to protect unique pieces of cultural heritage such as the Mary Rose.


 

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