Henry VIII's favorite warship, the Mary Rose, sank to the bottom of the English Channel in 1545 during a French invasion. A team of experts successfully hauled the remains of the Mary Rose out of the ocean in 1982, but 437 years of submersion in saltwater took its toll on the crumbling ship, reports Mindy Weisberger for Live Science.
Since its excavation, scientists have been racing to save the Mary Rose from further degradation, and they've finally pinpointed what's chipping away at the ship: acidic nanoparticles left behind by marine bacteria, a team of scientists reported last week in the journal Matter.
"They are essentially bacteria poop," Simon Billinge, a materials scientists at Columbia University and Brookhaven National Laboratory, tells Jennifer Ouellette for Ars Technica. "Our results were like a microscale archeological dig where, by studying the location and composition of the deposits, we could see how the bacteria colonized the wood and what they ate."
Metal sulfides left behind by anaerobic bacteria and the breakdown of iron artifacts were sopped by the wood while the ship was submerged. Now that the ship is out of water, those nanoparticles—namely zinc sulfide—are oxidizing and becoming acidic, reports Ars Technica.
To look at what's happening within the ship's wooden beams, the team combined X-ray analysis with a technique commonly used to study batteries, reports Ars Technica. It allowed them to take detailed images—down to the millimeter scale—while "obtaining atomic-scale structural information," according to the paper. Not only did this allow them to map out where the nanostructures were found in the wood, but it also revealed the structure.
"This is the first time zinc sulfide nanostructures—the bacterial byproducts—have been observed in Mary Rose wood," Serena Cussen, a materials scientist at the University of Sheffield in the United Kingdom, says in a press release.
In addition to identifying the harmful bacteria poop, the team found that polyethylene glycol (PEG), a compound that prevents wood from shrinking as it dries, is also contributing to the damage. When the ship was excavated, it was sprayed down with water regularly so that it wouldn't dry out. Without the water, the ship could've shrunk to half its size. Then, the team sprayed the hull with PEG to replace the support that the water provided and dried it out, according to the Mary Rose Trust.
Per Live Science, this study reveals that PEG can also become acidic when it breaks down—a concerning result for other conservators working to preserve ancient artifacts.
"What our results have done is alert conservators to these previously unknown deposits and expand the study of degradation-inducing materials," Cussen says in the press release. "Knowing the structure of these potentially harmful species also allows us to design targeted treatments for their future removal."