Nuclear magnetic resonance imaging of waterlogged wood

Abstract

The authors evaluate the usefulness of nuclear magnetic resonance (NMR) imaging to conservation research, and assess the ability of the technique to obtain non-destructive images from waterlogged wood samples, both prior to conservation and during consolidation. In the absence of iron salts, very high-quality images of internal wood structures, with a resolution of 25μm, can be obtained; this resolution would be adequate to carry out non-destructive dendrochronological studies. However, the maximum size of sample which can be imaged at this resolution is limited by the field strength of the magnets required. Paramagnetic salts, of which iron II and III are the most common, make NMR studies of any sort very difficult. As these contaminants are quite common in waterlogged wood, particularly oak, high-quality imaging cannot be carried out on all samples. This apparent drawback can be turned to advantage as a diagnostic probe for the presence of iron in the sample being conserved, and it can monitor the effectiveness of procedures adopted to remove the iron. Polymer ingress into wood samples could not be monitored directly, due to poor peak resolution. However, if some or all of the proton signal from the water were masked by deuterium substitution, then good polymer-selective images could be obtained, as is demonstrated by studies on modern balsawood model systems. The authors conclude that NMR imaging can be used as an experimental technique for studying many of the processes important to wood conservation.