A new Danish research project is examining how Viking ships can be preserved for generations to come while reducing the considerable amount of energy museums use to protect ancient wooden vessels.
The four-year project has received DKK 4.5 million (appox 700,000 USD) from the Augustinus Foundation and will bring together researchers from the Royal Danish Academy’s Institute of Conservation, the National Museum of Denmark, the University of Copenhagen, the Viking Ship Museum in Roskilde and Museum Vestsjælland.
At the centre of the research is a difficult problem in archaeological conservation. Ancient oak can survive for centuries when buried in wet, oxygen-poor environments, but once the wood is excavated it must be conserved and subsequently kept under stable environmental conditions.
Maintaining those conditions in museums can require considerable energy. Researchers therefore want to establish more precisely how conserved ship timbers respond to changes in temperature and humidity, and whether some of the strict climatic requirements currently followed by museums could safely be relaxed.
Over the next four years, the researchers will analyse original vessels, including the Gislinge Boat, now displayed at Holbæk Museum in Denmark. They will examine how the condition of the wood and the methods used to conserve it influence its long-term stability under different environmental conditions. The goal is to develop new recommendations that reduce museums’ energy consumption without compromising the long-term preservation of the ships.
The Gislinge Boat
The Gislinge boat when it was discovered in 1993. Photo: National Museum of Denmark
The Gislinge Boat offers the researchers an important case study because its preservation has already been a decades-long process. The remains were discovered during drainage work near the village of Gislinge on the Danish island of Zealand in 1993. Today the surrounding Lammefjord is largely agricultural land, but in the Middle Ages it was an extensive body of water connected to the Isefjord.
Despite spending centuries beneath layers of silt and sand, much of the hull remained remarkably well preserved. The vessel was clinker-built, with overlapping oak planks and frames fastened using iron rivets and wooden treenails.
Its construction initially suggested a Viking Age date. Tree-ring dating later showed that the boat had been built around 1130, shortly after the conventional end of the Viking Age. However, its construction continued Viking shipbuilding traditions, including clinker-built planking and distinctive stepped stems.
The Gislinge boat from excavation in 1993. Photo and copyright: Viking Ship Museum in Roskilde
The surviving boat is about 7.7 metres long and 1.5 metres wide, with a shallow draught of only about 25 to 30 centimetres. Rather than being a warship or long-distance trading vessel, it appears to have been an everyday boat suited to the shallow waters of the Lammefjord.
It could carry approximately one tonne, making it useful for moving people and goods through the region’s waterways. The Viking Ship Museum has suggested that cargoes could have included grain, wool, dried fish, meat, rope and furs.
The vessel had also seen considerable use. Its hull was worn and several cracks had been repaired with pieces of beech. Archaeologists believe it may have remained in service for approximately 50 years before being abandoned.
Twenty Years in Conservation Tanks
The Gislinge boat as preserved. Photo: National Museum of Denmark
Excavating the Gislinge Boat created a new challenge: how to prevent wood that had survived underground for more than eight centuries from deteriorating once removed from its waterlogged environment.
After excavation, the timbers were sent to the National Museum’s conservation department. There they underwent treatment with polyethylene glycol, better known as PEG, whuch is used to stabilise waterlogged archaeological wood by replacing water within its cellular structure with a wax-like substance. Without such treatment, ancient timbers can shrink, warp or collapse as they dry.
For the Gislinge Boat, this was an exceptionally lengthy process. Its timbers remained in impregnation tanks for almost 20 years before they were ready for freeze-drying.
The freeze-drying itself took several months at very low temperatures. Individual planks were secured in specially constructed moulds during the process so that they retained their original shapes. After drying, each plank and frame was cleaned and surviving fragments were carefully reassembled.
The Gislinge Boat on display at Holbæk Museum. Photo courtesy Museum Vestsjælland
The result allowed much of the original vessel to be displayed. After more than two decades of conservation, the boat was returned to the Holbæk area in 2024 and subsequently installed at Holbæk Museum.
Its preservation did not end there. The surviving pieces were mounted on a specially designed steel frame inside a large secured glass display case, where environmental conditions can be controlled.
Finding a More Sustainable Way to Preserve Viking Ships
It is this need for continued environmental control that the new project will investigate. Researchers want to understand exactly how sensitive conserved archaeological wood is to changes in relative humidity and temperature. This could determine whether museums need to maintain such narrow environmental ranges around the clock or whether carefully controlled fluctuations can occur without damaging the objects.
The project will examine the relationship between the present condition of the wood, the conservation methods previously applied to it and its response to changes in the surrounding environment.
If museums can safely broaden their permitted climatic ranges, they could potentially reduce the energy required to heat, cool, humidify and dehumidify exhibition and storage areas. The Gislinge Boat will therefore serve not only as an archaeological object but also as evidence for determining how ancient ships can best be cared for in the future.
“The wood from which the Gislinge Boat is made gives us today a direct insight into the techniques and skills of the boat builders of the time,” says Jonas Abkjær Andersen, research coordinator at Museum Vestsjælland. “We are therefore looking forward to the new research project, which will give us even more knowledge about how we can best preserve this unique cultural heritage.”
The project could ultimately have implications beyond the Gislinge Boat. Other original vessels, including the Skuldelev and Roskilde ships, are also expected to be studied as researchers work towards new energy-saving recommendations for the preservation of Denmark’s surviving Viking ships.
For vessels that have already survived beneath the ground or water for close to a millennium, the research aims to determine how museums can give them the best chance of surviving for centuries more.
A new Danish research project is examining how Viking ships can be preserved for generations to come while reducing the considerable amount of energy museums use to protect ancient wooden vessels.
The four-year project has received DKK 4.5 million (appox 700,000 USD) from the Augustinus Foundation and will bring together researchers from the Royal Danish Academy’s Institute of Conservation, the National Museum of Denmark, the University of Copenhagen, the Viking Ship Museum in Roskilde and Museum Vestsjælland.
At the centre of the research is a difficult problem in archaeological conservation. Ancient oak can survive for centuries when buried in wet, oxygen-poor environments, but once the wood is excavated it must be conserved and subsequently kept under stable environmental conditions.
Maintaining those conditions in museums can require considerable energy. Researchers therefore want to establish more precisely how conserved ship timbers respond to changes in temperature and humidity, and whether some of the strict climatic requirements currently followed by museums could safely be relaxed.
Over the next four years, the researchers will analyse original vessels, including the Gislinge Boat, now displayed at Holbæk Museum in Denmark. They will examine how the condition of the wood and the methods used to conserve it influence its long-term stability under different environmental conditions. The goal is to develop new recommendations that reduce museums’ energy consumption without compromising the long-term preservation of the ships.
The Gislinge Boat
The Gislinge Boat offers the researchers an important case study because its preservation has already been a decades-long process. The remains were discovered during drainage work near the village of Gislinge on the Danish island of Zealand in 1993. Today the surrounding Lammefjord is largely agricultural land, but in the Middle Ages it was an extensive body of water connected to the Isefjord.
Despite spending centuries beneath layers of silt and sand, much of the hull remained remarkably well preserved. The vessel was clinker-built, with overlapping oak planks and frames fastened using iron rivets and wooden treenails.
Its construction initially suggested a Viking Age date. Tree-ring dating later showed that the boat had been built around 1130, shortly after the conventional end of the Viking Age. However, its construction continued Viking shipbuilding traditions, including clinker-built planking and distinctive stepped stems.
The surviving boat is about 7.7 metres long and 1.5 metres wide, with a shallow draught of only about 25 to 30 centimetres. Rather than being a warship or long-distance trading vessel, it appears to have been an everyday boat suited to the shallow waters of the Lammefjord.
It could carry approximately one tonne, making it useful for moving people and goods through the region’s waterways. The Viking Ship Museum has suggested that cargoes could have included grain, wool, dried fish, meat, rope and furs.
The vessel had also seen considerable use. Its hull was worn and several cracks had been repaired with pieces of beech. Archaeologists believe it may have remained in service for approximately 50 years before being abandoned.
Twenty Years in Conservation Tanks
Excavating the Gislinge Boat created a new challenge: how to prevent wood that had survived underground for more than eight centuries from deteriorating once removed from its waterlogged environment.
After excavation, the timbers were sent to the National Museum’s conservation department. There they underwent treatment with polyethylene glycol, better known as PEG, whuch is used to stabilise waterlogged archaeological wood by replacing water within its cellular structure with a wax-like substance. Without such treatment, ancient timbers can shrink, warp or collapse as they dry.
For the Gislinge Boat, this was an exceptionally lengthy process. Its timbers remained in impregnation tanks for almost 20 years before they were ready for freeze-drying.
The freeze-drying itself took several months at very low temperatures. Individual planks were secured in specially constructed moulds during the process so that they retained their original shapes. After drying, each plank and frame was cleaned and surviving fragments were carefully reassembled.
The result allowed much of the original vessel to be displayed. After more than two decades of conservation, the boat was returned to the Holbæk area in 2024 and subsequently installed at Holbæk Museum.
Its preservation did not end there. The surviving pieces were mounted on a specially designed steel frame inside a large secured glass display case, where environmental conditions can be controlled.
Finding a More Sustainable Way to Preserve Viking Ships
It is this need for continued environmental control that the new project will investigate. Researchers want to understand exactly how sensitive conserved archaeological wood is to changes in relative humidity and temperature. This could determine whether museums need to maintain such narrow environmental ranges around the clock or whether carefully controlled fluctuations can occur without damaging the objects.
The project will examine the relationship between the present condition of the wood, the conservation methods previously applied to it and its response to changes in the surrounding environment.
If museums can safely broaden their permitted climatic ranges, they could potentially reduce the energy required to heat, cool, humidify and dehumidify exhibition and storage areas. The Gislinge Boat will therefore serve not only as an archaeological object but also as evidence for determining how ancient ships can best be cared for in the future.
“The wood from which the Gislinge Boat is made gives us today a direct insight into the techniques and skills of the boat builders of the time,” says Jonas Abkjær Andersen, research coordinator at Museum Vestsjælland. “We are therefore looking forward to the new research project, which will give us even more knowledge about how we can best preserve this unique cultural heritage.”
The project could ultimately have implications beyond the Gislinge Boat. Other original vessels, including the Skuldelev and Roskilde ships, are also expected to be studied as researchers work towards new energy-saving recommendations for the preservation of Denmark’s surviving Viking ships.
For vessels that have already survived beneath the ground or water for close to a millennium, the research aims to determine how museums can give them the best chance of surviving for centuries more.
Click here to learn more about the Gislinge Boat exhibition at the Holbæk Museum
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