Reconstructing hammerstone size flake by flake: an experimental approach.

Understanding force application in flake production is essential for reconstructing hominin behaviour, technological advancements and biomechanics. Extensive research has examined stone tool production, focusing on the intended material outcomes such as the cores, tools and flakes. Analyzing force application in this process requires knowledge of hammerstone selection and use. Despite progress made in understanding hammerstone selection and use, linking specific knapping outcomes to hammerstone use remains challenging. This difficulty stems from the complex relationship between fracture mechanics and material signatures in lithic artifacts. Key variables related to hammerstone use and their influence on flaking outcomes remain poorly understood. We draw on fracture mechanics to explore factors driving flake ring crack size-the circular region where the Hertzian cone, a feature of conchoidal flaking, intersects with the platform. Our experiment systematically examines how hammerstone size, velocity and strike angle-factors influencing strike force-affect ring crack and flake size under controlled conditions. We validate our findings with previously reported controlled and replicative experiments. Results show that flake ring crack size can estimate hammerstone size. Our findings mean that we can reconstruct the flaking process and particularly variability in the application of force at a level of detail previously unavailable.