Quantification of microwear on experimental shell tools: First results using focus variation microscopy, surface roughness, and multiscale geometric analyses

Abstract

Archaeologists have increasingly adopted approaches from engineering and materials sciences to quantify the surfaces of artifacts and ecofacts. Different microscope systems and surface texture/roughness parameters have been employed with various degrees of success. Although most studies have focused on chipped stone tools and animal bones, to date there has been no attempt to quantify microwear on shell tools. In this study, focus variation microscopy was used to mathematically document the surfaces on the edges of twelve little neck clam shells in both unused and used conditions. The clam shells were used to scrape a variety of materials, including fresh, greasy bone, untanned leather, and sweet potato (hard vegetable). Microwear was calculated from the surface measurements taken on the used and unused shell edges using multiple ISO parameters, including conventional height parameters and multiscale geometric analysis (relative area; area-scale complexity). The results of this experiment indicate that the quantification of microwear on shell tools is possible and that shell, as a raw material, may present challenges in terms of surface texture/roughness documentation. Discussion of the results includes an assessment of which parameters may be best for distinguishing used from unused shell tool surfaces and the surfaces of shell tools used on different contact materials, and possible problems resulting from post-depositional processes.