Hidden in plain sight: A microanalytical study of a Middle Stone Age ochre piece trapped inside a micromorphological block sample. Issue 2 (15th December 2020) - Haaland, Magnus M.
Abstract: A complete Middle Stone Age ochre piece was unintentionally collected and fully preserved within a micromorphological block sample intended to characterise a 74 ± 3 ka occupation horizon at Blombos Cave, South Africa. Previously recovered ochre pieces from the same stratigraphic context (Still Bay) have displayed intricate modification patterns with significant behavioural implications. Yet, in the case of the trapped ochre, a direct visual assessment of its surfaces was impossible due to its impregnated state. In this study, we demonstrate how we successfully reconstructed three‐dimensionally and characterised the block‐sampled ochre piece using high‐resolution microcomputed tomography scanning coupled with a range of microanalytical techniques, including optical petrography, micro‐Fourier transform infra‐red spectroscopy, micro‐X‐ray fluorescence and micro‐Raman spectroscopy. Through a morphometric analysis of the score marks present on the trapped ochre's reconstructed surface, we were able to assess the types of modifications and the nature of the actions that created them. Our results show that a block sample‐based study of archaeological artefacts allows for a comprehensive assessment of their depositional and microcontextual setting, their external morphology and microtopography, as well as their internal texture and geochemical properties. We suggest that this type of context‐sensitive, multiscalar and multidisciplinary investigation may also prove beneficial in the study of conventionally recovered archaeological artefacts. Graphical Abstract: 3D reconstruction of a Middle Stone Age ochre piece trapped inside a micromorphological block sample.