Controlled comparative tensile tests of backed versus non-backed edges’ adhesion: Inferences into stone tool functional properties

Backing is a procedure for retouching a stone tool edge to an angle of or near 90°. Archaeologists have recorded backed lithic specimens in the Pleistocene and Holocene around the world. One prominent hypothesis for the occurrence of backing is that it increases a stone tool's adhesion relative to what it would have otherwise been with unmodified, sharp edges. We conducted a highly controlled semi-static tensile test in which we assessed lithic specimens that possessed both a backed and a non-backed edge, opposing each other. We hafted each specimen's backed and non-backed edges to wood, and the bi-hafted stone implement was then pulled apart using an Universal Instron Materials Tester, allowing for a direct ‘head-to-head’ comparison of the two edge types’ adhesive properties. Our tensile test results suggested no significant difference between backed and non-backed edges in terms of adhesion, which does not support the hypothesis that backing increases a lithic specimen's adhesion.