The Mary Rose project leads the way in techniques to conserve archaeological finds.
After recovery, artefacts were placed in ‘passive’ storage, to stop any immediate deterioration before the team actively conserved them.
The passive storage used depended on what an object was made of.
For instance, small wooden objects could simply be sealed in polyethylene bags to preserve their moisture, while timbers were stored in unsealed water tanks.
Leather, skin and textiles were also put in passive storage, kept moist in tanks or sealed plastic containers. Bone and ivory were desalinated to stop any damage from salt crystallisation, as was glass, ceramic and stone.
Alloys of lead and pewter are inherently stable in the atmosphere and don’t normally need any special treatment.
Without spraying, the wood would have shrunk by anything up to 50%, warping and cracking as the water evaporated from its cellular structure.
The conservation team then sprayed the hull with polyethylene glycol (PEG) to replace the water in the cellular structure of the wood. There were three distinct phases, with a low molecular weight PEG to begin with, then a higher weight to strengthen the outer layer of wood.
Finally the hull was carefully air dried.
The acid originates from sulphur species incorporating into the wood whilst on the seabed which eventually can transform to acid when exposed to oxygen.
This is particularly a problem in artefacts which originally contained iron, as the corroded iron has migrated into the wood and drives the sulphur reaction to form acid.
Therefore, a way to inhibit acid production is to remove the iron by reacting the wood with a suitable complexing agent. This method has been used extensively at the Trust as a surface treatment and it is now being explored as a submersion treatment for entire artefacts.
Application of Strontium carbonate treatments to artefacts which are showing the presence of sulphate salts.
Many of the waterlogged archaeological wooden artefacts have the potential to form acids due to the presence of iron and sulphur. The sulphur originates from biological reactions which occurred on the seabed and the iron is present due to the corrosion of original fixtures. While they were exposed to limited oxygen on the seabed these posed little threat but can form acid when exposed to oxygen for extended periods of time. Removal of iron is one way of treating this problem and is explored in another section. Another route is to neutralize the products. At the Mary Rose, a treatment of Strontium carbonate is being pioneered to neutralise acids and elements which have the potential to form acids if left unattended. A stable product is formed which can remain in the wood.