Conservation process of archaeological waterlogged wood studied by spectroscopy and gradient NMR methods

Joanna Kowalczuk,Jadwiga Tritt-Goc,Adam Rachocki,Graham A Ormondroyd,Magdalena Broda,Bartłomiej Mazela

doi:10.1007/s00226-019-01129-5

Abstract

The properties of methyltrimethoxysilane-treated, waterlogged archeological elm wood were studied by magnetic resonance imaging and nuclear magnetic resonance (NMR) methods. The spatially resolved proton density images, spin–spin relaxation profiles, proton NMR spectra, and self-diffusion coefficients of the preservative agents were measured during drying. The resolution of the data allowed for the differentiation between the early and late wood areas of the elm wood and determination of the shrinkage of the sample in the tangential and radial directions, and it showed the different dynamics of methyltrimethoxysilane (MTMS) in the lumen cells of both early and late woods. The NMR spectra indicated that the MTMS, after rapid evaporation of ethanol, is bound to the wood. Identical measurements were also taken for the archeological elm wood treated with polyethylene glycol (PEG) and for an untreated wood sample. From the results, it can be concluded that MTMS showed significantly higher stability against shrinkage when compared to PEG. Therefore, it may be considered as an alternative preservative for archeological wood.

Highlights

Waterlogged archaeological wood is most often characterized by a high degree of degradation, but it retains its shape and dimensions due to the presence of water that fills cell lumen and voids within the wood tissue
The signal intensity of water (Fig. 1a), polyethylene glycol (PEG) (Fig. 1b), and MTMS solution (Fig. 1c) in early wood areas of saturated samples is considerably higher compared to late wood
Larger cavities of early wood contain more solvent in comparison with late wood, which results in a higher Magnetic resonance imaging (MRI) signal

Summary

Introduction

Waterlogged archaeological wood is most often characterized by a high degree of degradation, but it retains its shape and dimensions due to the presence of water that fills cell lumen and voids within the wood tissue. The only way to save waterlogged wooden objects is their proper conservation immediately after excavation from the wet environment. This involves the exchange of the water that fills the wood tissue for an appropriate chemical that will strengthen the wood structure and prevent its distortion, but unlike water, will not evaporate from the wood when exposed to air. The results of previous research indicate that MTMS can effectively stabilize the dimensions of archaeological waterlogged wood differing in the degree of degradation (Broda and Mazela 2017; Broda et al 2018)

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Conclusion