Historical warship under threat
In the 17th century the kingdom of Sweden embarked on the construction of the most expensive and ornamented warship of its time. Taking three years to build, it involved the work of carpenters and sail-makers, as well as sculptures and painters to work on carving and painting the intricate woodwork motifs and decorations that adorn this ship. Unfortunately the ship sank on its maiden voyage. The king's misfortune however turned out to be our good fortune as it has been a vital resource for historians, giving us valuable insight into the times. Now the royal warship Vasa is facing a battle for its life as it is under threat from its own iron armoury.
Since early 2000, scientists have noticed certain changes taking place in the wood of the ship: changes that threaten the very stability and life of the ship. Now a team of experts working on Vasa have been able to identify the culprit that was threatening the ship: iron.
On August 10, 1628, Vasa, built for King Gustav Adolphus of Sweden set sail on her maiden voyage. At the time of her construction she was a feat of military engineering; while not the largest ship ever built she was the most powerful, boasting the capability of firing the most destructive broadside ever. However, her guns were never fired as she sank less than one nautical mile into her maiden voyage, after encountering her first gust of wind in the open sea. Early attempts to raise the ship floundered, after which the ship's location was forgotten.
It wasn’t until the 1950s that the ship was once again relocated and eventually raised to the surface in 1959. At the time it was a major challenge for archaeologists to preserve the ship. Experts recognise that the wooden hull of the Vasa had been seriously affected during its exposure to the biological and chemical processes under water, from the time of its sinking in 1628 to 1961 when it was raised. Again there were some adverse affects noticed during its conservation period between 1962 and 1989, and subsequently in its modern museum setting.
Scientists first noticed something going wrong during a particularly humid summer back in 2000. It was during this season that white and yellow precipitates were discovered on the ship. These deposits turned out to be acidic sulphur and iron compounds, and it was concluded that sulphur in the wood had been converted into sulphuric acid. This spurred further investigation into the cause of the deterioration.
At first scientists thought that the conversion of sulphur to sulphuric acid was causing the deterioration of the wood. Now however, the most likely culprit is the iron from the ship’s rusted bolts and cannonballs.
A source of sulphur comes from the degradation of Stockholm’s un-purified sewage on the oxygen-free bottom, while the iron primarily comes from the bolts that held together the hull and other iron objects onboard, such as cannonballs. This is the conclusion of research conducted by Gunnar Almkvist and his colleagues. Together they completed a thorough examination of the chemical degradation processes in the wood.
Currently the most serious problem is that the level of degradation in the wood has also affected the conservation agent that protects the ship. During its long history, Vasa has also suffered at the hands of humans.
During initial salvage operations to recover the expensive canons, much of the planking on the weather deck was removed. Also removed were some of the sculptures which adorned the ship including a life-size human sculpture of the Roman soldier Septimus Severus. Traces of anchors that had caught the ship and had to be violently forced free of the ship were found as well.