Non-invasive reflection FTIR characterization of archaeological burnt bones: Reference database and case studies

Abstract To better understand and interpret archaeological bone remains, knowledge of thermally induced changes that can be a consequence of cooking or mortuary practices in past cultures are of extreme importance. Due to the high value of the remains, the methods that require no sampling or no sample manipulation should deserve special attention. For that purpose non-invasive spectroscopic analytical research has been carried out on experimentally heated bones to examine their chemical composition, which may represent a starting point for understanding the conservation status of heated bones and the effects of temperature on the detected chemical changes. Total reflection FTIR spectra collected on experimentally heated bones were due to competition of specular and diffuse reflectance phenomena distorted. In the lower spectral region, where specular reflection prevails, the Kramers–Kronig (KK) operation was applied. Derivative-like bands were successfully corrected with the KK operation. However, the most significant band of νs (PO43−) was inverted by the reststrahlen effect in almost all reflection spectra wherein the KK operation fails. Signals in the spectral region of overtones, combination bands, and OH stretching vibrations were enhanced due to domination of volume reflection and represent additional information about chemical composition and changes that occur during the processes of thermal bone degradation. The created reference database contains crucial information about the chemical composition of heated bones and can represent an important tool for non-invasive characterisation of excavated bone materials. Vibrational characterization of heated bones by means of total reflection FTIR spectroscopy with the KK operation was verified for the first time on cremated human remains excavated from three Slovenian archaeological sites of different chronological age and cultural context.