No abstract

The Oseberg collection includes the most complete ensemble of wooden remains from the Viking Age. However, since many of the wooden objects were treated with alum in the early 1900s, they now suffer from dramatic conservation issues. A multi-analytical approach was adopted to investigate both the organic and the inorganic components of some selected wood fragments, with the aim of fully characterising the materials and their decomposition products. A particular focus was taken on the differences between the surface and the core of the fragments analysed, and on the correlations between the results obtained by the different techniques, in order to disclose possible interactions between the materials during degradation. In addition to differences in alum concentration and wood alteration between the surface and the core, some decomposition/transformation products of alum, such as mercallite (KHSO4), were identified by FTIR and XRD. Contextual interpretation of the results obtained by ICP-OES elemental analysis of inorganic components and Py(HMDS)-GC/MS characterisation of degraded lignocellulosic materials supported some previous observations about potential relationships between specific metals (Al, Fe, Ca) and wood degradation and enabled new correlations to be highlighted. Although similar degradation patterns were revealed in the investigated objects–depletion of holocellulose, oxidation of lignin and some transformation of alum - a notable variability at the molecular level was highlighted. This is an important factor to be taken into account for the planning of re-treatment strategies of these extremely precious artefacts

No abstract

The development of new materials for the consolidation of waterlogged archaeological wood from sustainable sources is an important area of research, as the most widely used consolidant today is petroleum based. Ideally a new consolidant will interact with the existing wood structure, ensuring maximum compatibility. Lignin is often the major component remaining in archaeological wood, as it is less susceptible to degradation than holocellulose. Therefore, in order to maximise the potential for interaction with the wood cells, lignin-like oligomers have been synthesized from isoeugenol using a water soluble copper salen catalyst at pH 10, giving a weight average Mw of 1.6 kDa. Analysis by NMR spectroscopy has shown that the oligomers have a lignin-like structure with β-O-4′, β-β′ and β-5′ connections. A 10 w/w% solution of the oligomers in ethyl acetate was found to thoroughly penetrate 1 cm3 samples of waterlogged archaeological wood (density of 0.146 g/mL, maximum water content of 620%) after 14 days impregnation, as determined by FTIR spectroscopy. No impregnation material could be seen by SEM, suggesting that it coats the cell walls upon drying. This indicates that dehydrogenated polymers penetrate waterlogged archaeological wood well and have the potential to be developed into consolidants.

From the mid-1800s to the late 1950s, conservation by alum salts (aluminum potassium sulfate dodecahydrate)with some variations-was a routine method for treating highly deteriorated waterlogged archaeological wood in many countries, especially in Scandinavia. It was eventually replaced by newer methods in the 1960s, such as that using polyethylene glycol. Accordingly, the signs of deterioration in such collections and the reasons behind them are not well known among current preservation specialists. The research in the Saving Oseberg project (2014-2019) has shed light on the consequences of this treatment and reasons behind the severe deterioration observed today in many objects of the Oseberg Viking Age wooden finds, which were conserved in the early 1900s. Saving Oseberg aims to provide research-based recommendations for the future preservation of the finds, and as such, a large part of the project is aimed at improving our understanding of this complex material. Here the consequences of the method are summarized, drawing on the research to date. Chemical analyses of the Oseberg wood showed its current condition to be highly degraded: little polysaccharide content is left and the lignin is significantly oxidized and extensively depolymerized. The conservation implications are also discussed.