An Experimental Study of Hafting Adhesives and the Implications for Compound Tool Technology

Abstract

Experimental studies of hafting adhesives and modifications to compound tool components can demonstrate the extent to which human ancestors understood and exploited material properties only formally defined by science within the last century. Discoveries of Stone Age hafting adhesives at archaeological sites in Europe, the Middle East, and Africa have spurred experiments that sought to replicate or create models of such adhesives. Most of these studies, however, have been actualistic in design, focusing on replicating ancient applications of adhesive technology. In contrast, this study tested several glues based on Acacia resin within a materials science framework to better understand the effect of each adhesive ingredient on compound tool durability. Using an overlap joint as a model for a compound tool, adhesives formulated with loading agents from a range of particle sizes and mineral compositions were tested for toughness on smooth and rough substrates. Our results indicated that overlap joint toughness is significantly increased by using a roughened joint surface. Contrary to some previous studies, there was no evidence that particle size diversity in a loading agent improved adhesive effectiveness. Generally, glues containing quartz or ochre loading agents in the silt and clay-sized particle class yielded the toughest overlap joints, with the effect of particle size found to be more significant for rough rather than smooth substrate joints. Additionally, no particular ochre mineral or mineral mixture was found to be a clearly superior loading agent. These two points taken together suggest that Paleolithic use of ochre-loaded adhesives and the criteria used to select ochres for this purpose may have been mediated by visual and symbolic considerations rather than purely functional concerns.

Laboratory strength testing of pine wood and birch bark adhesives: A first study of the material properties of pitch

“…Of these standards, we selected two tests: lap hear and impact, D-1002 and D-950 [61,62]. Lap shear tests are widely used as adhesive joint strength tests because they are easy to conduct and closely resemble the geometry of many practical joints, including the cleft haft [28,63]. The ASTM D1002 test standard was therefore selected for the quasi-static shear strength (or low load rate) of a single-lap joint.…”

“…Adhesives are used as a proxy to understand the technological and cognitive abilities of hominins [2,3,6,25, but see also 26]. This research has been dominated by compound resin/gum-ochre adhesives made by anatomically modern humans in Africa [5][6][7][8][27][28][29]. In this scenario, it is hypothesised that the production and application of compound glues require advanced working memory, the ability to multitask, an understanding of abstract terms (e.g.…”

Those marvellous millennia: the Middle Stone Age of Southern Africa

“…Furthermore, at MSA sites like Sibudu, Umhlatuzana and Rose Cottage ochre powder was employed in the manufacture of compound adhesives used for stone tips to handles or shafts (Gibson et al 2004;Lombard 2007;Wadley et al 2009). Experimental replications show that ochre acts as a successful loading agent when mixed with ingredients such as plant gum and/or fat or wax (Wadley 2005a;Wadley et al 2009;Zipkin et al 2014). Zipkin and colleagues (2014) have demonstrated that ground quartz can also act as a reliable loading agent and they suggest that the occasional use of ochre for this purpose may, then, have been mediated by a desire to use ochre symbolically.…”

Landscape variability in tool-use and edge damage formation in South African Middle Stone Age lithic assemblages

“…In addition to unhafted involve the fewest techno-units (Oswalt, 1976), are well known from the ethno-historic record, and serve as a starting point for the assemblage edge damage method. The powdered resin was mixed with water over low heat on a stove using an initial ratio of 2.5g resin, 2.5g water, and 1g sand, following the recipe provided by Zipkin et al (2014). The mixture was allowed to air dry until tacky, then applied to stone tools.…”