Insight into the usewear mechanism of archaeological flints by implantation of a marker ion and PIXE analysis of experimental tools

Archaeological flint tools exhibit, after their use, a modification of the original surface as a result of contact with foreign materials. The polish which appears, displays morphological and textural features characteristic of the worked material. These changes at the flint surface are mainly due to residues of the worked matter and therefore contain potential information on the tool use. However it is not clear whether the altered surface stems from a simple coating of soft matter which has filled the original roughness of the cutting edge or whether in addition to that process an erosion of the flint surface by loss of quartz spherules also occurs. An experimental study has been performed to address this issue, which is based on the implantation of Cu ions (energy 100 keV and a dose of 5 x 10(16) cm(-2)) on chipped geological flint samples, mechanical tests simulating the tool use and subsequent PIXE analysis of the edge surface with a 3 MeV proton micro-beam with a rectangular shape (15 x 20 mu m(2)). A beam current of about 1 nA is sufficient to obtain a count rate of 800/min on the Cu K alpha X-ray line. The persistence of the Cu X-ray signal all over the tool edge confirms that the polish is only due to the deposit of external matter. Archaeological implications of usewear are discussed in the light of these new data. (C) 1998 Elsevier Science B.V.