New materials used for the consolidation of archaeological wood-past attempts, present struggles, and future requirements

Given the perilous state of the Oseberg find from Norway, the Museum of Cultural History and the Department of Chemistry both at the University of Oslo, are looking into new methods for treating archaeological wood. While numerous polymers have been previously tested, most do not stabilise the wood sufficiently, penetrate far enough, or remain stable without producing toxic fumes. A few of the more common examples are: Alum salt, KAl(SO4)(2)center dot 12H(2)O, which was used for treatment earlier but does not penetrate well and leaves the wood very acidic. Poly(oxy ethylene) (POE or Polyethylene glycol [PEG]) is widely used as a consolidant today but this material degrades over time and thus cannot support the finds for a very long time. Melamine-formaldehyde (Kauramin) has also been used and while it is fairly stable, it may also fill the wood and turn it into a 'block' of plastic. Since new consolidants would be advantageous, it is discussed what the requirements of such consolidants are and how material sciences may help procure them. It is proposed that an important requirement for a future stabilising agent is to leave an airy structure in order to allow retreatment in the future. This might be accomplished by foaming a polymer, or by combining nanoparticles with a polymer 'spider web' network to keep them in place. Such particles may help stabilise pH inside the wood by neutralising any acid generated inside treated artefacts. Special attention is given to the field of biomimetics-the discipline of constructing materials inspired by existing natural designs. It may be possible to construct a frame using bio-inspired materials (possibly an 'artificial lignin' mixed with other compounds optimise strength and flexibility) or through biomineralisation (an inorganic 'skeleton'). Tests on biomimetic cellulose and chitosan have begun and the initial evaluation of these materials is given. Chitosan is made from modified chitin (primarily from shrimp and crabs) and may be dissolved in acidic solutions. Crystalline cellulose is interesting in conservation as the individual particles are resistant to acid and not as hygroscopic as the amorphous part of cellulose. The materials and the procedures used in testing are described. It is shown that crystalline cellulose particles usually flocculate when used to treat archaeological wood but that they may be treated with surfactants in order to improve penetration of archaeological finds. (C) 2012 Published by Elsevier Masson SAS.