Scientists from the Mary Rose Trust are using magnetic nanoparticles to remove corrosive ions from inside the hull of the Tudor warship.
Sunk off the south coast of England in 1545, the Mary Rose was raised in 1982, bringing with it a veritable bounty of archaeological treasure from the time of Henry VIII. Around 19,000 artefacts were recovered, including timber making up approximately 40 per cent of the hull.
While on the seabed, this collection of timber, leather and other textiles became colonised by sulphur-reducing marine bacteria that produced hydrogen sulphide. This gas reacted with iron ions from corroded fixtures like cannons to form iron sulphides. Although stable in low-oxygen environments, sulphur rapidly oxidises in regular air in the presence of iron to form destructive acids. The goal of the team at the Mary Rose Trust was to devise a method to remove the free iron ions and prevent further decomposition of the hull and its contents.
“This project began over a glass of wine with Dr Eleanor Schofield, who is head of conservation at the Mary Rose Trust,” said Serena Corr, PhD, the project’s principal investigator. “She was working on techniques to preserve the wood hull and assorted artefacts and needed a way to direct the treatment into the wood. We had been working with functional magnetic nanomaterials for applications in imaging, and we thought we might be able to apply this technology to the Mary Rose.”
Since being raised, the Mary Rose has been preserved by periodically spraying the structure first with cold water, then solutions of polyethylene glycol (PEG-200 and PEG-2000) as the timber dried. Initially, the team used synchrotron techniques to probe the nature of the sulphur species periodically during this drying process. This was the first real-time experiment to closely examine the evolution of oxidised sulphur and iron species, and it helped inform efforts to design new targeted treatments for the removal of these harmful species.
The next step will involve a nanocomposite based on core magnetic iron oxide nanoparticles that include agents on their surfaces to remove the ions. The nanoparticles can be directly applied to the porous wood structure and guided to particular areas using external magnetic fields, a technique sometimes employed for nanoparticle drug delivery. Encompassed in a heat-responsive polymer, the nanoparticles are protected and can be safely delivered to and from the surface of the wood.
“Conservators will have, for the first time, a state-of-the-art quantitative and restorative method for the safe and rapid treatment of wooden artefacts,” said Corr. “We plan to then transfer this technology to other materials recovered from the Mary Rose, such as textiles and leather.”