X-ray microtomographic imaging of charcoal

Abstract

We assess the potential of X-ray microtomography as a tool for the non-destructive, three-dimensional examination of the internal structure of charcoal. Microtomographic analysis of a series of charcoals produced by the experimental pyrolysis of pine wood at temperatures from 300 and 600°C in nitrogen only and in nitrogen mixed with 2% oxygen indicates that, despite substantial shrinkage, observed porosity, pore size and pore connectivity are all increased by pyrolysis and also by chemical oxidation. Analysis of a number of altered and unaltered archaeological and geological charcoals has demonstrated the capacity of the technique to identify and map the distribution of authigenic mineral contamination within charcoal fragments. The results are of significance to radiocarbon dating in that they provide insights into the mechanisms by which charcoal can be contaminated by extraneous carbon in the natural environment.