Award Holder: Margaret-Ashley Veall
University: University of Oxford
Title of Research: ‘Stuck like glue’: Assessing variability in hafting adhesives in the southern African Later Stone Age
My doctoral project centres around the chemical characterisation of organic archaeological materials and their associated trace remains. The tiny fragments of material that are of interest to my thesis research are hafting adhesives, the glues of composite technologies. The wellpreserved assemblages of the Later Stone Age (LSA), spanning roughly the last 40-20 000 years until within the last few hundred years, present a unique opportunity to evaluate the composition of hafting adhesives, as well as assess the relationship between adhesive recipes, tool function, and the raw materials that make up the other components of composite technology. In engaging with these archaeological objects and trace materials through the application of analytical techniques, this investigation will provide insight, broaden our understanding of the composition of these plastic technologies in southern Africa, and contribute to an ongoing discourse of the manufacture and use of these materials by past populations in this region.
In terms of what is known about the sources of hafting adhesives, or mastics, as they are described in the southern African archaeological literature, compositional information comes from a more than 60 000 year long narrative. Evidence from Middle Stone Age and Later Stone Age studies, as well as historic and ethnographic records, has highlighted the use of a range of materials on their own or as mixtures, including plant exudates (resins, gums, and latexes), animal-based materials (fats, beeswax, and proteinaceous substances), and inorganic minerals. The sheer range of possible sources initially proved to be a daunting obstacle to overcome, as each material type is composed of different molecular classes and requires different types of instrumentation, sample processing protocols, and analysis.
To account for this range of variability, I treated each sample as an unknown mixture composed of organic and inorganic materials and employed a multi-method approach to the analyses of material classes, including optical light microscopy to qualitatively characterise the nature of the adhesives, and several analytical techniques aimed at identifying the organic and inorganic components. The analytical suite included: Scanning Electron Microscopy/Energy Dispersive XRay Spectroscopy (SEM/EDS) to obtain high quality images and evaluate the elemental composition; Fourier Transform Infrared Spectroscopy (FTIR), to begin to characterise both the organic and inorganic components; and, a combination of gas chromatography coupled mass spectrometry (GC-MS) and pyrolysis-GC-MS to provide a detailed characterisation of the organic constituents of the adhesive (Figure 1). With an ever-expanding list of plant, animal, mineral, and manufactured (i.e. conifer pitch) reference materials to provide a point of comparison to the archaeological material, it has been possible to identify the plant sources used as adhesives, describe their manufacture process, and identify the types of inorganic minerals present in some samples.
Figure 1. Examples of data output from a multi-method approach to the analysis of a hafting adhesive sample (MHB03). Top Left: Low-powered incident light micrograph. Bottom Right: SEM image. Top Right: FTIR spectra (in percent transmittance). Bottom Right: Total ion current (TIC) chromatograms of the acidic (upper frame) and neutral fractions (lower frame) from GC-MS analysis.
The structural foundations of my research are dichotomous yet complementary, comprising a combination of engaging fieldwork and laboratory analyses. For weeks at a time I found myself in one of two gloriously opposing settings. On the one hand, digging through boxes of material that have not seen daylight in decades; tallying counts of formal tools and raw materials; deciphering Harris matrices and handwritten excavation reports; and, attempting to capture the photograph of an object at just the right angle, all in a wonderful haze of dust. The other, a stark contrast of clean, white lab coats, gloves, and the hum of instruments while analysing the composition of the adhesives used on these millennia old tools.
The support of the Emslie Horniman Scholarship Fund made this project possible from start to finish. It allowed for the opportunity to visit the collections, sort through material, and acquire a sufficient number of samples to conduct analyses. The fieldwork component took place from August to October 2015 in South Africa and involved trips to access and sort through excavation collections housed at the University of the Witswatersrand in Johannesburg, the Albany Museum in Grahamstown, and the University of Cape Town in Cape Town. Sorting through stone tool assemblages, searching for trace remains of adhesives was a time-consuming process and not one that collections managers and curators are able to sacrifice weeks-worth of time to accomplish, given the ongoing demands of their busy schedules. Ideal samples required trace that was at once visible to the naked eye, running opposite to the working edge of the tool, and ideally found on both sides of the piece. It was not uncommon that for every sample I did identify as suitable for further investigation and analysis, hundreds of pieces I examined to ended up tallied in the ‘no’ column, lacking a sufficient presence of adhesive residue. After identifying the material with suitable trace for analysis, it was possible to appreciate the uniqueness of these items and the rarity in which they occur within archaeological assemblages. At the Albany Museum, microscopic analyses were conducted on selected specimens, describing the nature of the adhesives and documenting their characteristics. The micrographs and notes taken from this work provided the foundation of the archaeological adhesive descriptions which have served as the main classification categories for all analysed samples in this research project.
In addition to identifying appropriate samples for analysis, my time in South Africa was highlighted by engaging discussions with archaeologists, botanists, and curators, as well as visits to the Kirstenbosch Botanic Gardens and the Featherbed Nature Reserve. From this I acquired a new perspective on the mosaic of southern Africa’s ecological landscapes, and the sheer variety of resources available for the manufacture of adhesives. This fieldwork has been fundamental to my project and has permitted me to make connections with other researchers in various institutions which enabled the organisation of an additional research trip in support of my project.
At the base of this project are several underlying questions related to the inherent value of this work, and the application of multiple analytical techniques to archaeological questions and materials of this kind. Perhaps at its most basic, is the value of these datasets to provide insight into our understanding of the composition of plastic technologies in southern Africa. Nearly sixty years ago, J. Desmond Clark (1958) stipulated that adhesives from Later Stone Age assemblages in southern Africa must have varied from region to region depending on the changes in vegetation patterns. This stands to reason given the ecological diversity of southern Africa, however, Clark did not postulate as to the nature of adhesive composition. My research is the first large-scale, multi-site study in this region and aims to comprehensively characterise
both organic and inorganic materials that make up hafting adhesives, providing a sufficient sample size to fully test Clark’s long-standing hypothesis. At this stage of the analysis, the results from adhesives found in the Holocene layers of the Later Stone Age at Melkhoutboom Cave and from two hafted implements provide evidence of a longstanding manufacture of plant products for use as adhesives. These findings, and this research as a whole, contributes to an ongoing discourse expanding our impressions of past populations as competent engineers and chemists (Wadley et al. 2009; Charrié-Duhaut et al. 2013). However, it is my hope that in conducting research centred around these well-preserved malleable materials, that it may be possible to shift focus toward the role these largely organic components of tools play in discussions of the adaptive strategies associated with tool design and function, and the economic costs and benefits of producing these materials.
The contribution of this project to discourse in southern African archaeology is not the only value of this research. This became especially apparent after a thorough consideration of the opportunities to engage with the biographies of objects, and what this means to the contribution to an object’s history from the perspective of an archaeological scientist. This is perhaps best exemplified in the narrative of the hafted implement A1543 from the Albany Museum (Figure 2). First acquired by the museum in 1908, this “stone implement fixed by means of resin to a wooden handle” was recovered from a grave in cave near Plettenberg Bay (Deacon 1966; Binneman 1983). The historic timing and nature of its recovery means that it is lacking provenience and direct association to any cultural technocomplex. Studies have described the structural alterations made to the object after its acquisition (Hewitt 1912; Deacon 1966); the possible function of the object (Binneman 1983); and, have attempt to explain its reddish appearance (Deacon 1966; Lombard 2007). Beyond this, however, it is difficult to place this object within the context of the stone age sequences of southern Africa, limiting the contribution of this object to little beyond its value as a singular item and a potential analogue for tool design or appearance. Personally, the moment of viewing an object for the first time that has been sketched and described in academic literature for over one hundred years is a humbling one; and, to be given the opportunity to contribute to a body of literature that narrates the life-history of a specimen is one that will never be forgotten. In revisiting A1543 to conduct chemical analyses, I have been able to determine the composition of the resinous adhesive from this piece. The well-preserved markers from this material not only provided a baseline to assess the preservation of the other archaeological assemblages, but the constituents of this material now places A1543 into a larger narrative of the use of manufactured plant products across the southernmost coastline of South Africa.
Figure 2. Photographs of the hafted implement A1543, taken in September 2015 at the Albany Museum (M. Veall). Left: Implement and rhinoceros horn handle. Right: Macro-image of the proximal end of the adhesive.
All cultural heritage objects have life-histories; the story of their creation, use, and death. These biographies, however, extend beyond their purposeful lives which are book-ended by the manufacture of an object and their eventual disuse, discard, and deposition (Holtorf 1998; Joy 2009) and represent the varying relationships between objects and people depending on cultural context (Gosden and Marshall 1999). Indeed, the appearance of objects in museum exhibitions, in accession catalogues, and excavation reports; as interconnected components leading to a body of research, and their depiction in the inevitable write-up process that is to follow is a testament to the extended lives of objects and their contextually dependent value. The application of analytical techniques to better understand the composition of objects, especially those that are organic in composition, not only provides the opportunity to contribute to its life history, but also sparks the potential to re-engage with objects and reestablish their value to past users, current researchers and future audiences.
References Cited:
Binneman, J., 1983, Microscopic Examination of a Hafted Tool, The South African Archaeological Bulletin, 38(138), 93–5.
Charrié-Duhaut, A., Porraz, G., Cartwright, C. R., Igreja, M., Connan, J., Poggenpoel, C., and Texier, P.-J., 2013, First molecular identification of a hafting adhesive in the Late Howiesons Poort at Diepkloof Rock Shelter (Western Cape, South Africa), Journal of Archaeological Science, 40(9), 3506–18.
Clark, J. D., 1958, Some Stone Age Woodworking Tools in Southern Africa, The South African Archaeological Bulletin, 13(52), 144–52.
Deacon, H. J., 1966, Note on the X-Ray of Two Mounted Implements from South Africa, Man, 1(1), 87–90.
Gosden, C., and Marshall, Y., 1999, The Cultural Biography of Objects, World Archaeology, 31(2), 169–78.
Hewitt, J., 1912, Notes on Two Remarkable Implements, presumably of Strandlooper origin, Records of the Albany Museum, 11(4).
Holtorf, C. J., 1998, The life-histories of megaliths in Mecklenburg-Vorpommern (Germany), World Archaeology, 30(1), 23–38.
Joy, J., 2009, Reinvigorating Object Biography: Reproducing the Drama of Object Lives, World Archaeology, 41(4), 540–56.
Lombard, M., 2007, The gripping nature of ochre: The association of ochre with Howiesons Poort adhesives and Later Stone Age mastics from South Africa, Journal of Human Evolution, 53(4), 406–19.
Wadley, L., Hodgskiss, T., and Grant, M., 2009, Implications for complex cognition from the hafting of tools with compound adhesives in the Middle Stone Age, South Africa, Proceedings of the National Academy of Sciences, 106(24), 9590–4.