Charred bone: Physical and chemical changes during laboratory simulated heating under reducing conditions and its relevance for the study of fire use in archaeology

In order to gain insight into the timing and nature of hominin fire use, the effect of heat on the physical and chemical properties of the materials entering the archaeological record needs to be understood. The present study concerns the fire proxy heated bone. Two types of heating can be distinguished: combustion (or burning, with oxygen) and charring (without oxygen), for both of which the formation of char is the first step. We performed a series of controlled laboratory-based heating experiments, in reducing conditions (i.e. charring), covering a broad temperature range (20-900 °C), and applied a variety of different analytical techniques. Results indicate that charred bone shows a distinctly different thermal alteration trajectory than combusted bone, which has implications for the suitability of the different analytical techniques when identifying and determining past heating conditions (charring vs. combustion; temperature) of heated bone from archaeological contexts. Combined, the reference data and techniques presented in this study can be used as a robust toolkit for the characterisation of archaeological charred bone from various ages and contexts.