Non-destructive Dendrochronology: The Effect of Conservation Agents on Tree-ring Measurements in Archaeological Oak with Micro-computed Tomography

Abstract

ABSTRACT The effect of different conservation methods on non-destructive dendrochronology with micro-computed tomography (μCT) of waterlogged archaeological wood (WAW) was assessed. To this end, oak samples were conserved with alcohol-ether-resin, Kauramin 800®, lactitol/trehalose, saccharose, silicone oil and different polyethylene glycol (PEG) treatments with subsequent freeze-drying. Tree-ring measurements were compared with respect to the number of rings and the mean ring width using (a) an analog linear measuring table and (b) the digital μCT. Overall, the measurements in the μCT data agreed very well with the corresponding microscopic measurements. It was possible in all cases to recognize the rings in the samples with μCT. A dendrochronological cross dating with regional absolutely dated oak ring width chronologies was successful. However, the varying influence of conservation agents on the quality of the μCT data were also evident. To quantify this influence, the contrast in the μCT data were calculated using gray-scale profiles. An influence on the contrast in the μCT data were detectable for all conservation agents. The contrast is especially reduced due to conservation methods using lactitol/trehalose, PEG, saccharose and silicone oil. Overall, the experiments confirm, though, that μCT is a powerful and accurate tool for dendrochronology of conserved archaeological oak objects.