Shining Light on Dark Matter: Advancing Functional Analysis of Obsidian Tools with Confocal Scanning Microscopy

Over the past decade, confocal microscopy has increasingly been employed to examine changes in stone tool surfaces and has proven to be an accurate technique for quantifying use-wear texture. Promising results have emerged from characterizing Polish formation on experimental and archaeological flint tools. Recent studies also highlighted the potential of confocal microscopy for analyzing tools made from reflective materials, such as quartzite. In this paper, we investigate the capability of confocal microscopy to discriminate use-wear on obsidian quantitatively. We examine whether confocal microscopy and 3D texture analysis can correctly classify several worked materials that are challenging to differentiate using the optical standard method of use-wear analysis. For cutting activities, we include butchery, de-skinning a fresh hide from grease and meaty tissues, cutting tanned leather, harvesting domestic ripe cereals, harvesting semi-green wild cereals, and sawing wet limestone. As for scraping activities, we explore discriminating differences among tools used for working dry hide, dry antler, soaked antler, fresh bone, softwood, fresh reeds, and wet limestone. Our results demonstrate that these worked materials can be confidently identified in experimental tools. While other relevant factors affecting use-wear texture, such as the intensity of use or post-depositional alterations, need to be controlled before employing the method on archaeological materials, our research suggests that the quantitative approach can enhance the standard method of use-wear analysis, providing unprecedented precision for identifying worked materials in obsidian tools.