Some thoughts on bone artefact discolouration at archaeological sites

This paper explores the role of plant enzymes associated with food processing in the discolouration of archaeological bone tools. I present the results of colorimetric analysis aimed at quantifying the range of discolourations produced on bone implements by various food produce (fruits, vegetables and cereals) and compare these data to discolourations produced through above-ground heating events. I show that certain plants, particularly ones with high polyphenol content, produce visible discolourations to the surface of experimental bone tools and, furthermore, that these discolourations are significantly different to the CIE colour values produced on bone surfaces exposed to heating events of longer than 2 min. Although some overlap exists, processing of certain plants produces elevated values primarily on the b* axis with concomitant low L* values relative to heated bone samples. These results are confirmed against FTIR and pXRF analysis. While further research is needed before these results can be applied meaningfully in an archaeological context, this paper highlights the potential of quantifying bone surface discolouration in investigating the probable function of archaeological tools, and that surface discolouration should never be dismissed as a taphonomic alteration.