Stone Tool Analysis: Bending initiation

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Bend initiations are formed when the force applied to the edge of the core causes the edge to bend until it breaks.  This starts the crack which then runs down the face of the core. 

A Hertzian cone is not formed in bending initiations, and diagnostic features of conchoidal fracture—such as eraillures, umboes, and points of force application—are not found on bend-initiated flakes.  Bend-initiated flakes lack a true bulb of force, although a subtle bulb-like swelling can occasionally be present.  The mechanics of how this swelling forms in the absence of a Hertzian cone is poorly understood, but the swelling is likely caused by a reorientation of the propagating crack to the core face similar to that seen in conchoidally-initiated flakes.

Platform Lip

A bend initiation creates a lip on the flake where the platform edge is wrenched away from the core edge.  The lip is usually excurvate in plan view, extending the width of the platform, and often curves outward slightly in profile, towards the flake’s ventral surface.  Since a bend-initiated flake lacks a Hertzian cone, the platform will lack a ring crack or umbo, and an eraillure will not be present on the flake’s ventral surface.  It is important not to confuse an umbo with a platform lip.

Biface thinning flake Bletchington

Biface Thinning Flake

'Rolled' Scar Margin

Removal of a bend-initiated flake results in broad and slightly U-shaped notch in the platform edge.  The notch will have a gently curved ‘rolled’ profile corresponding to the curved platform profile of the flake removed from it.  Since a bend-initiated flake lacks a Hertzian cone, an eraillure will never be found adhering to a bend-initiated flake scar.  

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Clovis Point