ConNext-2021

30 Conserving waterlogged archaeological wooden objects KEYWORDS: conservation, archaeological wood, polyethylene glycol, freeze-drying, degradation. Conserving waterlogged archaeological wooden objects is quite a delicate task. The most common method of treatment for smaller artefacts is a combination of immersing the wood in a solution of polyethylene glycol (PEG) in water, followed by freeze-drying under vacuum. Since there is plenty of research on this topic already, the aim is to break it down into a generally intelligible way. Based on four samples the basic idea of this conservation process is therefore being described, illustrated and compared. Depending on the surrounding conditions in which the archaeological wooden objects are found, the wood may be in various states of degradation. Erosion bacteria, as well as chemical degradation, mostly affect the parts of the wooden cell which contain cellulose. Left behind is the now very weak lignin cell wall, which, as long as it is filled with water, will maintain the former shape (see figure, sample 1). Drying the object without any means of stabilisation however will mean the loss of its outline and therefore any information it may have carried throughout the ages (see sample 2). Polyethylene glycol (PEG) is a water-soluble agent. When the wood is immersed into the solution, the PEG migrates into the damaged cell structure and holds it up from within. Air-drying the object now might still lead to shrinkage (see sample 3), because while drying the water surface tension can force the cell to collapse. The freeze-drying process under vacuum can be broken down to freezing the water within the object and then forcing it to sublimate in a controlled environment. Left behind is only the PEG, bracing the damaged cell structure (see sample 4). The treatment with PEG and freeze-drying under vacuum afterwards may be a time- consuming method of conservation but shows the most satisfying result. Compared to the others, sample 4 kept its former size. When the PEG at the surface is cleaned off, it shows a slightly lighter colour, which in addition gives it a more natural finish. anna ‐ theresa.schwenzer[at ]stud.hawk.de