Stone Tool Analysis: Termination
In stone flaking, a crack is initiated and then propagates through the material. The crack then exits the stone and the flake is detached from the core. This is referred to as the ‘termination’ phase of fracture. The way the flake terminates depends on the balance of forces that drove the propagating crack through the stone.
Compression force operates down the length of the flake, stiffening it, and shearing force separates the flake from the core; these two forces operate at right angles to each other, and when approximately balanced, the crack travels parallel to the core face. In this case, the ‘force angle’ driving the crack is aligned with the face of the core. With feather terminations, the fracture front remains in balance until it cleanly exits the stone, thus creating the sharp edge that makes the flake so useful as a cutting tool.
Most stoneworking strategies aim to produce flakes with feather terminations or flake scars that end in feather terminations. The lateral margins of a flake almost always feather onto the core surface.
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.
If the force applied to the stone is insufficient, the crack can stop entirely. Since the indentor is moving away from the core face, pulling the platform away with it, the proximal end of the stalled flake will bend and then break transversely, detaching from the core and creating an abrupt shelf called a ‘step’ termination.
The bend-snap usually occurs a short distance up from the end of the stalled crack, and the distal end of the flake is left attached to the core. The crack defining the distal end can often be seen continuing into the core. Importantly, the transverse bend fracture that breaks off the flake is morphologically identical to the transverse bend fractures that can occur when fully-formed flakes break, either during detachment or afterwards. For this reason, it is not possible to reliably identify step terminations on flakes without conjoining them back to their scars. It is possibly, however, to identify step terminations on cores, and most cores have them.
As with hinge terminations, flakes struck too close to a step-terminated scar will also end in step terminations. Because step terminations can disrupt the smooth surface of the core, they are generally considered a stoneworking mistake. However, experienced flintknappers have techniques for removing step scars from the faces of cores, such as by removing additional flakes that eliminate the steps by travelling under them. Another technique is to strike a punch resting on the step termination—or to replace the broken-off proximal end of the flake and strike it again—in the hope that the embedded crack will initiate again and exit the core.
In Australia, step-terminated flake scars were the deliberate result of maintaining the mass of horsehoof cores; the series of step terminations were then eliminated by striking a flake that propagated under them. Quina ‘scalar’ retouch, associated with Neanderthals in Europe, was a strategy of scraper resharpening that involved striking off flakes that ended in step or hinge terminations.
A finial is sometimes formed on flakes ending in hinge terminations. An inflexed finial is formed when the crack, just as it exits the core, curves back in the opposite direction it was originally travelling, creating a thin, sharp overhanging edge on the hinge-terminated flake scar. A large hinge-terminated flake scar with an inflexed finial is often ideal for scraping wood.
A retroflexed finial is formed when the crack hinges but then resumes in the same direction it was originally travelling. This creates a thin, sharp projection on the flake at the end of the hinge termination.
The bending fracture on a snapped flake or core can sometimes ‘roll over’ onto the other half before terminating, creating a finial. Finials like this are often seen on flakes split by siret fracture.
As the crack grows and starts to lose energy, the force angle can become too small, resulting in an imbalance between compression and shearing forces. The stiffness of the flake causes the crack to curve towards the interior of the core, lopping off the core’s base. This is referred to as an overstruck, overshot, outrepassé, or reverse-hinge termination.
Overstruck terminations are generally considered a stoneworking mistake. This is particularly true in blade-making because it can dramatically shorten the core. Overstriking is overcome by using strong core support to ensure that the compression force maintains the crack straight to the bottom of the core. Careful use of the indirect percussion technique—which can increase the shearing force relative to the compression force—can achieve a similar effect without using core support. In sophisticated biface manufacture, just barely lopping off the opposite edge of the biface (in effect, the core base) is considered a demonstration of a flintknapper’s skill.