Breaking Free from the Constraints of Strength: Rethinking the Role of Archaeological Adhesives in Prehistoric Hafting Systems

This study explores the impact of lithic substrate variability on joint design, aiming to enhance the understanding of archaeological adhesives through mechanical testing. While previous research has shown that adhesive shear strength can vary with different recipes, few studies have examined the behaviour of adhesives on irregular, knapped lithic substrates typical of archaeological contexts. To address this, we conducted lap shear tests using these authentic materials to bridge the gap between controlled laboratory experiments and real-world archaeological conditions. Our findings suggest that joint design and the axialapplication of force significantly influence bond performance, posing challenges when using uneven lithic substrates. This highlights the need to reconsider whether current testing methods fully capture the behaviour of adhesives under such conditions. Mechanical tests can provide insights into certain material properties, but they should be used selectively to address specific questions, avoiding direct and potentially inappropriate extrapolations to prehistoric or archaeological contexts. While often a focus in modern testing, shear strength may not have been the primary function of many adhesives. Instead, these adhesives likely played non-structural roles, such as sealing, stabilising, or moulding, suggesting the need to complement current testing approaches with alternative methods that better reflect their intended uses. By rethinking adhesive categorisation and function, future research can build on existing methods to gain a more comprehensive understanding of the diverse properties of archaeological adhesives.