Infrared reflectance spectroscopy as an analytical technique for the study of residues on stone tools: Potential and challenges

FTIR (Fourier transform infrared) spectroscopy is a non-destructive analytical method that has been used successfully to analyse both inorganic and organic archaeological material. Using a microscope attachment has the additional benefit of analysing very small spots (diameter 100μm) directly on an artefact without sample preparation or destruction. It is therefore a suitable method to study residues on prehistoric stone tools. However, using a microscope without an ATR (attenuated total reflection) microscope objective, results in a combination of reflection and transmission/absorbance FTIR spectra, which is not always as easy to interpret as directly measured transmission/absorbance spectra. In order to improve the interpretation of spectra recorded on archaeological samples, the method was tested with replicated Middle Stone Age stone points used during hunting and butchery experiments on parts of a blue wildebeest (Connochaetes taurinus) published in 2004 (Lombard etal., 2004). In this case, the residues on the tools were known and post-depositional contamination was eliminated. Additional samples of the organic materials, and the minerals from which the tools were made were also available. Therefore, we could assess the viability of FTIR reflectance spectra for distinguishing between bone, fat and protein residues.