Conservation-restoration of waterlogged archaeological wood

Archaeological objects discovered during excavations may need to be preserved, so that they can be studied and then displayed in a museum as a testimony to our history.

On the other hand, once extracted from their environment (subaquatic or terrestrial), some of them, in particular wood but also other organic materials not covered in this article (leather, plant fibers...), often present a very altered structure due to the drastic reduction, during their immersion of several centuries, of their biodegradable constituents, hemicelluloses and cellulose.

A new material called "waterlogged wood", whose mechanical properties have been completely altered compared to "modern" wood, can be characterized and described. Its future handling for study and exhibition purposes requires that it first be consolidated: after a brief history of treatments used since the 19th century, the various techniques encountered today are outlined in this article. Following these treatments, the conservation-restoration of archaeological objects, which must respect a certain deontology, always involves compromises in curative conservation and restoration gestures: these are described and illustrated. Finally, the display of these objects, or even their storage in a storeroom, generally requires the design and manufacture of a suitable support or packaging.

The various stages of conservation-restoration have to be constantly adapted to each very particular object, but often encounter certain common difficulties which are mentioned in the article (presence of unstable sulfur salts which can lead to acid production in situ in the object, creep of treated objects over time).

Once all the operations have been completed, the object, ready for storage or display, is still likely to evolve according to the climatic conditions of the environment: it is the role of preventive conservation to give the necessary recommendations for the future good health of the restored object.

Finally, a few additions for special cases, such as "composite" objects (made up of materials of different natures) or very large objects (shipwrecks), appear at the end of the article.

While the conservation-restoration techniques described have been used with some success, progress is expected both in the treatments themselves and in the characterization of these objects, which are difficult to handle and cut! Research and collaboration in these fields are international.