Combined use of vibrational spectroscopy and GC–MS methods in the characterization of archaeological pastes from Patagonia

Two samples of ochre painting residues (crayons) obtained from the archaeological site Cave Loncomán (Río Negro, Argentina) were analysed by ATR-IR and FT-Raman spectroscopy revealing the presence of haematite as the red pigment. Further analysis by FTIR of the chloroform/methanol extracts from both archaeological pastes showed the presence of carboxylic acids, indicative of hydrolysis of triacylglycerols in the pastes. Analysis by GC and GC/MS indicated that the main organic constituents of both pastes were saturated (C16:0 and C18:0) and unsaturated (C16:1 and C18:1) fatty acids. Our results show that the combined FTIR and Raman spectroscopic evaluation of archaeological pastes and their organic extracts provides a very useful and simple methodology to characterize the inorganic pigment and the presence of organic binders in an archaeological sample.