Material Symbolism and Ochre Exploitation in Middle Stone Age East-Central Africa Open Access
This dissertation project sought to integrate multiple analytic and experimental methods to study the use of ochre pigments in Middle Stone Age (MSA) Africa. Ochre is a diverse category of iron-containing earth pigments, the appearance of which in MSA archaeological sites broadly coincides with the onset of aspects of modern human behavior. MSA ochre artifacts have long been interpreted as potential, but not conclusive, evidence for the emergence of human symbolic behavior based on the more recent use of ochre for painting rock art, self-adornment, and coloring other material culture objects. The overarching objective of this dissertation was to test whether ochre use in MSA Africa was primarily motivated by symbolic or techno-functional considerations. In order to accomplish this, research was undertaken on geologic sources of ochre in Malawi, Kenya, and Zambia and on ochre artifacts from the site of Twin Rivers Kopje, Zambia.The first phase of this dissertation focused on developing geochemical methods for characterizing the trace element “fingerprint” of ochre artifacts and source samples for the purpose of provenance analysis. Matching ochre artifacts to their source on the landscape can shed light on the preferential exploitation of particularly desirable mineral deposits and on raw material transport distances. First, the ability to distinguish among multiple ochre sources within each study area was tested. Using ochre sources from the Malawi study area it was demonstrated that a minimally destructive variant of Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) is as effective as the gold standard technique, Instrumental Neutron Activation Analysis, at discriminating among sources. LA-ICPMS was then used to distinguish among sources in the Kenyan and Zambian study areas in order to test the effectiveness of this approach on ochre from geologically distinct environments. The second phase of this dissertation entailed using trace element fingerprints to match some of the pigment artifacts from the MSA and Later Stone Age site of Twin Rivers Kopje, Zambia to their sources. This work demonstrated that multiple ochre sources were being exploited during the MSA occupation of the site. Additionally, use-wear and colorimetric analysis of the ochre artifacts from Twin Rivers indicated that a specific type, specular hematite, was preferentially modified by abrasion, likely for the purpose of producing powdered pigment. Although a diverse range of ochre sources may be found near the site, specular hematite yields a striking red-purple color streak significantly different from the other available pigments, suggesting that ochre use was mediated by preferences for specific colors.The final phase of the dissertation was an experimental archaeology project which tested the material properties of ochre-containing hafting adhesives that, based on residues on MSA tools from southern Africa, are implicated in the construction of early compound tools. These experiments indicated that the particle size of ochre loading agents is the major determinant of adhesives toughness. In particular, uniformly fine particle size loading agents yielded tougher adhesives than coarser loading agents or loading agents which included a range of particle sizes. Importantly, non-ochre loading agents like silt and clay-sized quartz were found to produce effective adhesives, suggesting that the use of ochre in MSA glues may have in part been driven by symbolic, decorative motivations rather than purely functional concerns.
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