Cursed By Chemistry

The salvaging of the Vasa in 1961

The salvaging of the Vasa in 1961

Last week I wrote about the ill-fated Swedish battleship Vasa as part of my thoughts on failure. Since writing those words, I have found some more information on what may be the ultimate fate of the Vasa.

It seems that Sweden’s legendary seventeenth-century warship, the Vasa, is cursed. But it is not cursed in the way that the Flying Dutchman, the legendary ghost-ship roaming the world’s seven seas, is cursed. Vasa, in fact, roamed less than a mile in its short vain-glorious life, and it has gone from being the Sunken Swede to the Sewage-Soaked Swede to the Sulfurous Swede. No, the Vasa is cursed by chemistry.

If no way is found to reverse the unpredictable chemistry taking place inside the Vasa’s planks – a ship that survived 333 years at the bottom of Stockholm’s harbor and twenty million visitors as Scandinavia’s leading museum piece – she will eventually, like a cheap paperback novel, crumble into acidic dust.

For the moment, even as a dredged-up wreck, the Vasa is a startling and beautiful sight, its masts almost piercing the museum’s dark ceiling, and its bulk seeming afloat until one gets close enough to look down at the cradle supporting it – and to spot all the telltale red dots pinned on to mark decaying wood.

But for a loser, the Vasa was lucky. It went down in the Baltic Sea, whose isolated, glacier-fed waters are not salty enough to support the ravenous shipworm Teredo navalis. Moreover, it sank in the path of Stockholm’s sewers. The putrid waters nourished sulfur-reducing bacteria whose byproducts penetrated the wood and made it poisonous to underwater fungi and rot.

And there the Vasa lay, the greatest damage being done by the dragging anchors of modern ships, until it was found again in 1956 by a Swedish marine technician and an amateur naval archaeologist named Anders Franzén.

The Vasa underwent an underwater restoration, including the replacement of five thousand rusted iron bolts, some five feet long. On 24 April 1961, The Vasa was raised – an event so thrilling to Swedes that factories closed and newfangled televisions sold out. Inside the hull and scattered on the bottom of the ship and the harbor were fourteen thousand broken-off pieces, a giant jigsaw puzzle that carpenters managed so skillfully that ninety-five percent of the restored ship is original.

For seventeen years, the Vasa was sprayed with a mist of polyethylene glycol, a water-soluble wax, to prevent drying and cracking. This solution makes the ship feel slightly wet and waxy. In 1990, the Vasa was moved to a former dry dock and became Scandinavia’s most visited museum.

Then, after the wet summer of 2000, conservators noticed something new: yellowish stains with crystalline green and white streaks.

Tests showed that some had a pH of 1, more acidic than lemons, and the wood beneath them was crumbling. About seven hundred such spots have been found.

Here is what had happened. The umbrellas and raincoats of visitors had pushed the museum’s humidity up to seventy percent. Deep in the wood, sulfur was reacting with oxygen, catalyzed by the rusting iron bolts, to form sulfuric acid. The moist air speeded up the reaction and drew the acid to the surface and precipitated the streaks of sulfate salts – gypsum, and the iron sulfates, jarosite and melanterite.

Core samples indicated that the ship had three thousand pounds of sulfur locked inside, enough to make five tons of acid.

The process is slow – actual disintegration will take decades – but the crumbling can already be seen, especially on softer pine objects. The sulfur seeps more quickly from them than it does from hard oak sides.

Diagnosis may be easier than treatment, however.

As a first step, the museum has put in a stronger climate-control system to keep humidity near fifty-five percent.

Conservators are now going over every inch of the ship with litmus paper, finding the worst spots. Where it is feasible, they lay down cloth soaked in bicarbonate and soda to neutralize the acid. Compounding the problem is the reactivity between the bolts inserted in the 1950’s and the preservative. The Polyethylene glycol-electrolyte solution (PEG) makes iron bolts rot, and the iron makes the PEG decompose. The solution is to remove a bolt and soak the wood near it with chemicals to draw out the iron. Moreover, there are many hidden surfaces where the bolts are holding planks together, and core samples suggest that there is more sulfur there.

Theoretically, the ideal solution would be to dismantle the ship, soak each piece in a polyethylene glycol bath – this time either heated or treated with hydrogen peroxide or another mild oxidant – to filter out the sulfur and change it into acid quickly. That would be washed away, and the ship would be rebuilt using five thousand new bolts made of nonreactive metal. Titanium would be best.

But this is the Vasa, not NASA, so there is no budget for any of this.

But even the theoretical work may help more recently raised vessels, like the Mary Rose, King Henry VIII’s flagship in Portsmouth, England; the Belle, a supply ship for the French explorer Robert de La Salle, now in Matagorda Bay, Texas; and the Batavia, a Dutch East-Indiaman on display in Fremantle, Australia.

There is sulfur in all of them. Eventually, they will all have acid. Sadly, it appears that chemistry will have the last word.

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