Assessing the preservation of residues on stone tools from a North African Pleistocene context: the case of Ifri’n Ammar

Since its introduction on the African continent nearly fifteen years ago, optical residue analysis of flaked stone tools has proven to be an effective method for generating high-resolution data that enable the identification of tool use, tool production and hafting technology. The method focuses on the histological identification of all residues adhering to the stone tool surface by using a combination of optical microscopes (stereomicroscope, metallurgical microscope) and lighting techniques (reflected and transmitted light). So far, optical residue analysis has been mainly applied to a limited number of South African assemblages, which may create the impression that residues only preserve in these contexts. While these contexts seem to have excellent preservation conditions, it is essential to evaluate the potential of residue analysis for a wide range of contexts in order to understand the variability in residue preservation between geographical regions and across time. Here, we present the first study of stone tools from a Late Pleistocene Saharan context (Ifri’n Ammar). The study aims at gaining insight into the mechanisms of residue preservation and alteration at the site of Ifri’n Ammar and its implications for assessing the preservation potential of residues in similar contexts. Residues were analysed using a wide range of techniques: stereo-, incident and transmitted light microscopy, biochemical staining and SEM-EDS. Residue interpretations were based on an extensive reference collection available at TraceoLab, University of Liège and the results were confronted with data from use-wear analysis performed by a different analyst