Research into the chemical processes that cause wood to degrade over time has uncovered new information vital to the conservation of the wreck of the Mary Rose.
Henry VIII’s flagship sank in the Solent on 19 July 1545, where it remained for 400 years until the hull was raised from the seabed in 1982 (see CA 85). The newly salvaged wreck was sprayed with cold water and received a series of polyethylene glycol spray treatments to prevent the wood from drying out, shrinking, and collapsing. The last of these treatments was completed in April 2013, and the hull was then left to dry in controlled conditions.
The recovery of the Mary Rose was a significant achievement, offering an unprecedented view into Tudor life, but moving the remains of the ship from the anoxic (oxygen-free) conditions on the seabed to an oxygen-containing environment on land posed some issues. One of the main threats was acid-generating sulphur-based compounds, which form within the wood structure and can cause it to degrade.
Previous research conducted to determine the best methods of conservation for the Mary Rose (see CA 272) suggested that exposure to an environment where oxygen was present could cause up to two tons of acidic sulphur to develop in the wood. However, none of these studies focused specifically on the sulphur-based compounds that are produced as the wood dries out and the way in which they affect its degradation.
A new study, recently published in the journal ChemPlusChem (https://doi.org/10.1002/cplu.202000160), took samples from six locations around the hull, then used a combination of techniques to identify the acidic sulphur species present and assess the state of the wood itself. This research determined that oxidised sulphur, iron, and zinc deposits were all found together in the areas with the highest levels of degradation, demonstrating that they may play a role in the deterioration of the waterlogged wood.
This new understanding of acidic sulphur-based compounds in marine archaeological wood and how they evolve during the drying process can now be used to help develop strategies to protect the Mary Rose from further harm.
This news article appears in issue 366 of Current Archaeology. To find out more about subscribing to the magazine, click here.
