Stone Tool Analysis: Hinge termination
As the crack grows and starts to lose compression energy, the force angle can become too large to maintain the balance between compression and shearing forces. The stiffness of the flake is overcome by the shearing force and the crack curves abruptly to exit the face of the core. This creates a distinctive curved ‘hinge’ profile at the termination end of the flake and a corresponding profile on the flake scar.
Flakes struck too close to a hinge-terminated scar will also end in hinge terminations. Because hinge terminations can disrupt the smooth surface of the core, they are generally considered a stoneworking mistake. However, experienced flintknappers have techniques for removing hinge scars from the faces of cores, such as by removing additional flakes that eliminate the hinges by travelling under them. In Australia, hinge-terminated flakes were retouched so that the curved profile could be used to carve grooves with U-shaped profiles in wood objects.