Quantifying 3D micro-surface changes on experimental stones used to break bones and their implications for the analysis of Early Stone Age pounding tools

Abstract

We present a new method to assess use-wear formation processes of pounding tools used to break bones based on a combination of conventional microscopy, optical 3D surface measurements obtained with a confocal microscope and GIS analysis. The method involves 3D alignment and 3D surface change inspection techniques along with a surface morphometric characterization and 2D spatial pattern analysis, to measure the spatital distribution of significant changes in surface topography of pounding tools. Our results show that microscopic changes can be detected in the surfaces of hammers and anvils after bone breakage activities are performed. Use-wear on the active elements (hammers made on basalt and quartzite) occurred over a larger area than was observed on the passive element (quartzite anvil), but the latter often exhibited deeper modifications. Tool surfaces generally developed smoother topography with increased use, but grain microfracture also appeared with greater frequency over time. This methodology offers highly accurate and statistically robust analyses of microscopic use-wear traces that can be applied to the analysis of archaeological pounding tools.