Introducing platform surface interior angle (PSIA) and its role in flake formation, size and shape

Abstract

Four ways archaeologists have tried to gain insights into how flintknapping creates lithic variability are fracture mechanics, controlled experimentation, replication and attribute studies of lithic assemblages. Fracture mechanics has the advantage of drawing more directly on first principles derived from physics and material sciences, but its relevance to controlled experimentation, replication and lithic studies more generally has been limited. Controlled experiments have the advantage of being able to isolate and quantify the contribution of individual variables to knapping outcomes, and the results of these experiments have provided models of flake formation that when applied to the archaeological record of flintknapping have provided insights into past behavior. Here we develop a linkage between fracture mechanics and the results of previous controlled experiments to increase their combined explanatory and predictive power. We do this by documenting the influence of Herztian cone formation, a constant in fracture mechanics, on flake platforms. We find that the platform width is a function of the Hertzian cone constant angle and the geometry of the platform edge. This finding strengthens the foundation of one of the more influential models emerging from the controlled experiments. With additional work, this should make it possible to merge more of the experimental results into a more comprehensive model of flake formation.

The mediating effect of platform width on the size and shape of stone flakes

“…The first being that the configuration of PW is related not only to PD but also the profile shape of the striking platform. We used the concept of PSIA [36] and predicted that flakes made on a triangular ridged platform should exhibit systematically narrower PW (relative to PD) than those made on platforms that are more circular in profile. The results from the glass flakes match our predictions.…”

“…To clarify these issues, it is necessary to look more closely at the way in which PW forms during fracture. In a recent study, McPherron et al [36] noted that the fracture propagating from the point of percussion out towards the exterior platform surface occurs at a more or less constant angle, likely stemming from the Hertzian cone angle. They create a new measure, platform surface interior angle (PSIA), to quantify this observation.…”

Quantifying knapping actions: a method for measuring the angle of blow on flakes

“…The linear model results show that the angle of blow is an important knapping parameter that can help improve our ability to explain flake variation using independent flake variables, such as exterior platform angle and platform depth. The current EPA-PD model of flake formation derived from the controlled experiments by Dibble and colleagues only addresses a portion of the variation in flake size and shape (Dibble and Rezek 2009;Rezek et al 2011;Magnani et al 2014;Leader et al 2017;Dogandžić et al 2020;McPherron et al 2020). The EPA-PD model often performs less well when applied to less controlled experimental replication assemblages and archeological assemblages.…”

“…Knappers need to flexibly apply different manual gestures along the knapping sequence to Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany effectively navigate the changing interactions among different functional parameters, including configurations of the striking platform and various force application variables like the hammer striking speed and angle (Roussel et al 2009;Geribàs et al 2010;Rein et al 2013;Vernooij et al 2015;Baena et al 2017;Cueva-Temprana et al 2019). Some studies of modern knappers suggest that these gestural skills and "know-hows" may be acquired through learning and practice, highlighting the significance of cultural transmission in hominin stone tool making (Lycett 2013;Morgan et al 2015;Lycett et al 2016;Pargeter et al 2019). There are also studies that suggest that the technical "know-how" required for making early stone tools can be acquired via individual learning (Tennie et al 2016(Tennie et al , 2017Snyder et al in press).…”

Another tool in the experimental toolbox: On the use of aluminum as a substitute for chert in North American prehistoric ballistics research and beyond

“…For example, knappers have long used copper pressure flakers or percussion "boppers" as a substitute for antler pressure flakers or billets (Whittaker, 1994(Whittaker, , 2004. Experimenters have used both glass and porcelain as substitutes for conchoidally fractured stone (Dibble and Pelcin, 1995;Dibble and Rezek, 2009;Dogandžic ́et al, 2020;Hecht et al, 2015;Iovita et al, 2014Iovita et al, , 2016Khreisheh et al, 2013;McPherron et al, 2020;Rezek et al, 2011;Speer, 2018;Stout et al, 2015), and foam, plasticine, and even potatoes have been used as substitutes for stone specifically or reductive materials more generally (Clarkson, 2017;Schillinger et al, 2014aSchillinger et al, , 2014bSchillinger et al, , 2015Schillinger et al, , 2016Schillinger et al, , 2017. Some recent experiments have featured conchoidally fracturing stone specimens that were ground into shape with modern lapidary equipment, rather than knapped (e.g.…”