From bone to ash: Compositional and structural changes in burned modern and archaeological bone

• FTIR-ATR analysis of experimentally burned and archaeological cremated bone showed that
• Both time and temperature have an impact on the degree of cremation
• Once fully calcined, however, only time impacts on its composition and structure
• A combination of IRSF and proportion of carbonates indicates the heating conditions
• Archaeological calcined bone differs in composition from modern calcined bone

The composition and structure of experimentally heated modern bone and cremated bone fragments from various archaeological sites were analysed by Fourier Transform Infrared Spectroscopy (FTIR) in Attenuated Total Reflectance (ATR) mode before and after pre-treatment with acetic acid. The results confirm that time and temperature have an impact on the degree of calcination but also highlight that, once fully calcined, the final composition and structure of bone are influenced by temperature alone. A combination of several infrared indices makes it possible to discriminate between bones cremated under different conditions. The study of archaeological samples revealed that their carbonate composition is quite different to modern calcined bone and that some samples, originating from high-carbonate geological contexts, have significantly higher carbonate concentration compared to modern specimens, even after pre-treatment. The results suggest that FTIR yields information on not just the structure of burned bone, but also potentially about the modes of burning, including cremation, and the depositional conditions.