Stabilisation of waterlogged archaeological wood: the analysis of structural and dimensional changes of different conservation methods using magnetic resonance imaging and X-ray micro-computed tomography

Waterlogged archaeological wood can be preserved for many years in the absence of air, as decomposition is substantially slowed down. After excavation, conservation is necessary to prevent damage of objects due to uncontrolled drying. In this study, the following conservation methods were tested to investigate their ability to stabilise the objects: alcohol-ether resin, melamine-formaldehyde (Kauramin 800), lactitol/trehalose, saccharose, polyethylene glycol (PEG 2000 with air-drying and PEG 2000 or 400 and 4000 with subsequent freeze-drying). In order to precisely understand the changes caused by conservation and drying, 40 samples each of pine wood and oak wood were documented using magnetic resonance imaging and X-ray micro-computed tomography before and after conservation. This imaging made it possible to quantitatively record changes in the wood structure, for example due to shrinkage, collapse and cracks, which could not be prevented by conservation. The alcohol-ether-resin method with solvent drying had the best stabilizing effect and no damage of the wood structure was visible. The two PEG treatments followed by freeze drying showed effective volume stabilisation. In both cases, however, the treatment led to cracks in the wood structure, which occurred less frequently when the cryoprotectant PEG 400 was used. In comparison, the other methods with air drying did not show consistently good results in stabilizing the volume or wood structure.