The royal coat of arms on the stern of the Vasa. Image: Yifan Luo

This is Part 2 of A True Tale of Maritime Loss and Redemption. Read Part 1 here.

This post was chosen as an Editor's Selection for ResearchBlogging.org

After the Vasa was salvaged from the bottom of Stockholm harbor nearly intact in 1961 and towed to a dry dock, archaeologists were some of the first people to board the resurrected ship. They squeezed through the Vasa’s cramped quarters and slogged through three-foot-deep mud on the lower decks, searching for artifacts. They quickly began to uncover thousands of objects: coins, bowls, cups, elegant furniture, a board game, a butter cask containing 333-year-old butter. Like a nautical Pompeii, everything was as it had been on the day the Vasa sank. Archaeologists found the ship fully provisioned for a months-long maiden voyage, with casks of salted meat and musket shot stored in the hold. Crew members’ chests, still carefully packed with folded clothes and personal items, were a poignant reminder of the human scale of the tragedy. And as archaeologists sifted through the mud they encountered the calcified skeletons of the crew members themselves who had perished with the ship, some of them still dressed in the shoes and clothes they wore on the last day of their lives. The remains of one unfortunate sailor were found pinned beneath a loose gun carriage.

Together with historical records, the archaeological excavation of the Vasa painted an unpleasant picture of life aboard a 17th-century warship. Most of the Vasa’s crew were conscripts from seaside towns in Sweden. They were poorly paid and were forced to provide most of their own clothing and provisions for their long tours of duty. Sailors lived a meager existence while at sea, subsisting on rations of bread, porridge, salted meat or fish, and ale. Day-to-day life aboard 17th-century, Swedish warships was filled with routine and tedium, but the naval battles of the time were horrific: they often began with hot, smoky artillery barrages and careful maneuvering of the engaged ships, but inevitably progressed to bloody hand-to-hand combat as the crew of one ship boarded the other.

The stern of the Vasa as it appears today. Image: Yifan Luo

As archaeologists excavated the Vasa’s gun deck, where the ship’s 400 sailors would have eaten, slept, socialized, and fought and died in battle, they found homemade clothing, cheap eating utensils, and a small box containing a lock of a woman’s hair. In the admiral’s room and officers’ quarters at the rear of the ship, archaeologists uncovered ornate furniture, painted sculptures, and countless luxury items. The sharp differences between the objects left behind by the ship’s officers and crew illustrate the drastic social inequality present in Swedish society at the time.

While archaeologists excavated the Vasa’s lower decks and hold, a team of conservators began the immense task of reassembling and preserving the Vasa and the objects found within it. The Vasa was mostly complete when it was found, but portions of the ship had collapsed and some of the exterior sculptures had fallen off of the hull. There were no plans or blueprints of the Vasa for conservators to consult as they reconstructed the ship. Instead, they assembled the loose pieces like a giant jigsaw puzzle, using the original nail holes as guides. As fragments were gradually reattached using steel wire, the sculptures and ornaments decorating the Vasa’s exterior became visible in their original context for the first time in over three centuries. After conservators had finished reattaching over 13,500 fragments, the ship was more than 95% complete.

The Vasa's upper deck. Image: Yifan Luo

Because a waterlogged wooden structure as large as the Vasa had never been preserved before, the preservation of the Vasa was a risky, pioneering endeavor. When the Vasa came to rest at the bottom of Stockholm harbor in 1628, it began a centuries-long process of adjusting to its new surroundings. The wooden hull steadily absorbed water until it was saturated; the metal portions of the ship, including the nails that held it together, corroded in the brackish water, while the bright paint covering the ship’s ornate sculptures slowly discolored, cracked, and flaked away. Fortunately for the Vasa, the cold, almost oxygen-free waters of Stockholm harbor are inhospitable to many of the microbes and animals that could have done the most damage to the wreck. In particular the shipworm, which isn’t a worm at all, but a sort of clam that burrows into wooden structures and has been known to make short work of shipwrecks and wooden piers alike, cannot survive in the harbor. Even so, there was enough microbial growth on the sunken ship to degrade the outer 3/4 of an inch of all wooden surfaces. This meant that the Vasa appeared outwardly intact when it was discovered, but was actually incredibly fragile on a microscopic level.

After the Vasa was removed from the cold harbor waters, it immediately began to dry out. If it dried too quickly conservators knew that the timbers of the hull could shrink and crack and that degraded areas of wood could collapse. In order to preserve the structural integrity of the ship as it dried, they needed to replace the mass and volume of the lost water with a more stable substance. They chose a synthetic wax called polyethylene glycol. For 17 years the Vasa sat in a dark warehouse where it was sprayed almost continuously with increasingly concentrated solutions of polyethylene glycol, which gradually soaked into the hull, displacing the seawater. After the polyethylene glycol had displaced hundreds of tons of water from the ship, the relative humidity in the storage warehouse was slowly decreased, allowing the Vasa to gradually dry over a period of nine years.

By the late 1980’s the Vasa was stable enough to be moved to a new museum where it could be displayed permanently. In 1988, it was towed into a flooded dry dock and the new Vasa museum was built around it. The museum was completed and opened to the public in 1990. Although conservators had addressed the immediate danger of the Vasa cracking or collapsing as it dried, the ship’s long-term, public display presented them with new challenges. By the time the Vasa was first moved to the museum, it had dried out quite a bit, but the water content of the wood was still high. In order to prevent further degradation and to minimize mold and bacterial growth on the damp ship, it needed to be stored at a very specific temperature and relative humidity. To meet this need, the Vasa museum was designed as a giant, carefully controlled display case that visitors enter through air locks.

The exterior of the Vasa Museum. Image: Yifan Luo

During the unusually humid summer of 2000, museum conservators were startled to suddenly find patches of yellowy-white powder emerging from many wooden surfaces on the Vasa, as though the ship had come down with an unpleasant skin condition. Chemical analysis of the powder revealed that it was made up of a variety of sulfur-containing salts, mostly sulfates. Where did this sulfur come from? For most of the 333 years that the Vasa spent underwater, Stockholm harbor was so polluted that the ship absorbed a significant amount of sulfides from the water. After the Vasa was salvaged, these sulfides reacted with oxygen and moisture in the air, as well as iron that had leeched into the the wood as the original nails and bolts corroded, to form large quantities of sulfuric acid and yellow-white iron sulfate salts. If sulfuric acid continued to form unabated, it threatened to liquify portions of the Vasa and some of the wooden objects found within it. Conservators chose to manage this problem by carefully controlling the environment surrounding the ship. Sensors in and around the ship showed that the museum’s temperature and humidity had varied beyond the predetermined range during the summer of 2000 which triggered the formation of sulfates and acid. So, the museum’s elaborate climate control system was upgraded in 2004 to ensure that it could maintain the optimal temperature and humidity levels even as thousands of warm, breathing visitors enter the museum every day. By managing the temperature and relative humidity of the museum, conservators were able to reduce the formation of acid, but the ship’s high acid content is still a major concern today.

The preservation and display of the Vasa remains one of the largest, ongoing conservation projects in the world. Today it’s one of Sweden’s most treasured pieces of cultural heritage. It draws thousands of tourists to Sweden every year, and for Swedes it recalls an era of Swedish regional dominance and a romanticized past. When the Vasa was completed 383 years ago, it was a potent symbol of Swedish nationalism, and its loss was deeply damaging to Sweden’s national pride. It took well over three centuries, but, fittingly, the Vasa has reassumed its original position as a symbol of national pride.

References and Further Reading

Learn more about the Vasa, and how to visit it if you ever find yourself in Stockholm, at the Vasa Museum website.

This past summer divers located what they believe is the shipwreck of Mars, a 16th century Swedish warship and the Vasa’s predecessor. Mars sank in 1564 during a naval battle with Denmark in the Baltic Sea.

Matz, Erling. Vasa. Published by the Vasa Museum. 2009

Hocker, Emma (2010). Maintaining a Stable Environment: “Vasa’s” New Climate-Control System Association for Preservation Technology International Bulletin, 41 (2/3), 3-9

Special thanks to Yifan Luo for providing the images for this post, and to Gregory Bailey for providing information and sources about the conservation of the Vasa.

  2 Responses to “Part 2: The Vasa Resurrected”

  1. [...] Smells Like Science, Dan Bailey has a fascinating account of the preservation of The Vasa, a warship that sat at the bottom of Stockholm harbor for three centuries. Bailey recounts how it [...]

  2. In case you missed it, the proceedings of the 2011 conference, ‘Shipwrecks’, includes some interesting updates on the conservation of the Vasa, including information on the development of cellulose and chitosan polymers for use as consolidants in water-logged wood– a potentially revolutionary approach to the conservation of archeological wood from marine contexts:

    http://issuu.com/marcus.blom/docs/shipwrecks2011-proceedings

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