The Last Stand
She was the warship of her time, but met a rather inglorious end. Today a new battle for the carrack "Mary Rose" has to be fought. The enemies now: sulfur and iron.
"Britannia, rule the waves: Britons never shall be slaves", sounds the final song of Thomas Arne's opera "Alfred" from 1740 - commonly understood as the unofficial national anthem of the British kingdom. In order to substantiate and maintain this claim, the Empire always relied on a dominant fleet, which, for example, taught the Spanish Armada in 1588 to do more and kept the Prussian or German Navy constantly in check.
One of the first prides of English seafaring was the "Mary Rose" - commissioned by Henry VIII.and named after his sister and the coat of arms of her Tudor lineage. Built between 1509 and 1510, she served her admirals faithfully and emerged victorious in several naval battles. However, since there was already a permanent arms race between the European superpowers at that time, the ship was rebuilt and enlarged in 1528 and 1536 so that it ultimately weighed 700 tons and could carry 91 cannons.
But this already contained the germ for the later fate of the "Mary Rose": She was now very top-heavy, her center of gravity was well above sea level. In the important naval battle to repel a French invasion in 1545, she was flooded by her own sailors through an unfortunate turning maneuver. The ship tipped over and sank headfirst into the waters of the Solent Canal between Hampshire and the Isle of Wight - only 35 of the more than 400 soldiers on board survived.
The carrack was then forgotten for more than 400 years until it was finally raised again in 1982 and was to be conserved for posterity. After a long period of passive protection and turning the ship, restorers have been spraying the wreck with polyethylene glycols (PEG) since 1994 as an active measure to replace the moisture in the planks with wax. But in the woods also lurk more treacherous enemies than French cannons or nagging sea shells: sulfur and iron.
These elements and even more their derivatives such as thiol, disulphides, sulphates or pyrite decompose it slowly but steadily, because they oxidize in the air or bind with water to form sulfuric acid, which in turn breaks down the wood fibers and thus the residues break up the ship. After the moisture has been removed, the compounds can also crystallize out as s alts and mechanically blast the planks of the former destroyer - a fate that also threatens Sweden's former marine pride, the "Vasa"
However, before measures can be taken against acid damage and s alt pressure, the archaeologists first have to know where the devil's stuff is hidden. Therefore, chemists around Magnus Sandström from the University of Stockholm - he already tracked down "Vasa's" molecular nemesis - measured the sulfur and iron contents of wood samples from the distressed vessel using X-ray diffractometers and X-ray fluorescence analyzes as well as photoelectronic spectroscopy.
What they found was both worrying and hopeful: in all, about two tons of sulfur are hidden in the Mary Rose's 280 remaining tons, but they are fairly evenly distributed throughout the wreck's timbers. In the "vasa", on the other hand, they are concentrated in the outer layer of the building material because they have been enriched by bacteria there. The relics there are correspondingly dilapidated. Iron compounds - they catalyze the reactions leading to sulfuric acid - are found in the "Mary Rose" only inconsistently, but they accumulate in the environment of long since decomposed nails, bolts and fittings.
The researchers were able to identify the highest sulfur content in the lignin-containing areas between the cells of the wood, which probably also protected the sunken ship from faster decay in the oxygen-free atmosphere below a dense layer of clay. However, in addition to the thiols and disulfides, there are also pyrite and other iron-sulphur compounds that become a problem when the environment becomes too oxygen-rich. They then oxidize and become the main source of sulfuric acid in the PEG-impregnated timbers - accelerating the wreck's chemical decline.
To prevent this, the restorers kept soaking the "Mary Rose" in sodium bicarbonate, washing out the acid and keeping the environment in the wood neutral. But as long as iron impurities are still found in it, this remains a Sisyphean task, because they not only facilitate the formation of sulfuric acids, but also promote the oxidative degradation of cellulose. And, to complicate matters, they even facilitate attack on the preservative PEG polymers by producing hydroxyl radicals-so iron is the ticking time bomb in wet wrecks that needs to be defuse in the first place.
However, acids and iron cannot be removed from the plank, keel and mast at the same time, since the trivalent iron hydroxides that are usually present precipitate at low pH values and remain in the wood. The hope is therefore now resting on a compound with the euphonious name ethylenediamine monoacetate, which encloses the iron atoms like in a cage and thus renders them harmless. But all these treatments must last at least another twenty years: It will be the longest battle of the "Mary Rose".
