Gribshunden (or Griffen), sunk in 1495, is possibly the best preserved 15th century warship in the world. Probably built in the Netherlands with timber from France, used by the Danish king on travels to England, Norway and Sweden, it is truly an international shipwreck. Since it is carvel built, it can also give important clues to the ship building techniques used by the great explorers, Columbus and Vasco da Gama.

A Gribshunden seminar took place in Ronneby, Sweden in November 2015. The aim of the seminar was to present current stage of investigation of the shipwreck. Blekinge museum and the county administrative board of Blekinge invited researchers, conservators and archaeologists from different parts of Europe to share their research and their view on Gribshunden.

Conservation of waterlogged objects – Kristiane Strætkvern

A waterlogged archaeological object needs a lot of consideration from the first lift from the water. Even in an environment with the absence of oxygen, wooden objects go through some process of degradation. The inner parts of the cells are infected by fungal and bacterial decay while the outer walls are left. The cells then fill with water which help support and preserve the shape of the wood. However, once the object is removed from the sea or lake, the water inside the cells starts to evaporate. When this happens, the structure of the wood shrinks and collapse, a process that is irreversible.
Before conservation, the condition of the object needs to be evaluated. The assessment is based on the physical properties of the wood and the overall degradation pattern. It’s on the surface, the outermost part of the wood that the decay starts. This part is also the one most interesting for research purposes.
There are different ways to map the degradation patterns. Two machines are preferred for this investigation, The wood profile recorder and The X-Ray fluorescence spectroscopy. Both of them generate different type of information, e.g. localize collapsible zones, which will help design a conservation plan. They are preferable since they don’t require any sampling from the wood.
In Scandinavia, the most common method of conservation of waterlogged material is freeze-drying. This method in combination with impregnation PEG 2000 prevents collapse during the drying process. Free water in the cell lumen is removed by sublimation, and as such this maintains the structure of the wood. The estimated time for impregnation depends on factors such as the volume of the object and the degree of degradation. Some post-drying treatments are usually necessary, e.g. removing excess PEG or preparing for exhibitions. Although, once the object is placed in the museum it can be exhibited in normal and stable museum climate.