Investigating experimental knapping damage on an antler hammer: a pilot-study using high-resolution imaging and analytical techniques
Introduction
In recent years, new and increasingly sophisticated imaging and analytical techniques have been applied to the study of past human behaviour: optical and laser microscope, X-ray, CT and Micro-CT scans, just to mention a few (e.g. Abel et al., 2012, Bello et al., 2013, Boschin and Crezzini, 2012, Evans and Donahue, 2008, Le Bourdonnec et al., 2010). The use of soft (bone, antler, wood) hammers and retouchers was a key innovation in early stone tool technology, first recorded in the archaeological record during Lower Palaeolithic (Acheulian of Boxgrove, UK ∼500 kya; Wenban-Smith, 1985, Wenban-Smith, 1999). The use of antlers as soft hammers can be identified from characteristic damage on the working area in form of micro-fractures. These have been described and recognized since the beginning of the 20th century (e.g. Bourlon, 1907, Girod and Massenat, 1900, Henri-Martin, 1907-1910). However it is the presence of small flint chips embedded in the surface of an antler that can ultimately confirm the use of an antler as a tool-maker. These small flint residues can be observed using a hand lens and binocular microscope at low magnification, but more informative results can be obtained using higher magnification photography and scanning electron microscopy (Bordes, 1974, Mallye et al., 2012, Olsen, 1989).
Several experimental studies have explored the use of bones as soft-hammers and retouchers, either as percussors or pressure flakers (e.g. Karavanić and Šokec, 2003, Mallye et al., 2012, Newcomer, 1971, Rosell et al., 2011, Semenov, 1964, Wenban-Smith, 1985, Wenban-Smith, 1999), however, antler knapping-hammers have received little systematic attention (Lyman, 1994; but see Bordes, 1974, Olsen, 1989, Shipman and Rose, 1983). This is surprising as antler is the preferred soft-hammer for thinning and finishing of experimental handaxes, Mousterian scrapers and Upper Palaeolithic blades (Bordes, 1974, Crabtree, 1970, Flenniken, 1984, Johnson, 1978, Knowles, 1953, Newcomer, 1971, Ohnuma and Bergman, 1982, Whittaker, 1994, Wymer, 1968). The lack of detailed documentation and description of traces of use on antler knapping-percussors presents a major stumbling block to identifying fragmentary (Jéquier et al., 2012), poorly preserved, sediment-encrusted (Kuhn et al., 2008) or contentious archaeological examples (Goren-Inbar, 2011).
This paper presents the results of a preliminary analysis to document use-damage on an experimental knapping hammer using a range of analytical and imaging techniques (i.e. micro-computed tomography, focus variation microscopy, variable pressure scanning electron microscopy and energy dispersive X-ray spectroscopy). The strength and weakness of each technique have been highlighted. We illustrate microscopic use-wear features that are diagnostic of antler knapping hammers and propose a protocol for their analysing.
Section snippets
Material
The soft hammer used in the experimental study (Fig. 1A) was cut from the beam of an antler of a whitetail deer (Odocoileus virginianus) using a metal saw. Although cuts are still visible at the base (‘handle’) of the hammer, extensive use-damage has removed all but a vestige of the saw-marks at the ‘apical’ end (Fig. 1B). The hammer was part of the tool-kit used during flint-knapping experiments conducted at Boxgrove between 1995 and 1996. These experiments replicated sharp ovate handaxes
Methods
The antler was examined initially with a variable magnification binocular and observations were aided by illumination from a fibre-optic light source. Drawings were used to record the location and intensity of damage, and to indicate the position of the flint chips. An un-modified area of the antler used as a control for surface texture was also analysed. This corresponds to its central basal portion, where the hammer was held (Fig. 1F). Comparisons were also made with natural surface
Results
The surface of the antler used for hammering displays extensive modification, with the most concentrated damage near the apical end covering an area of about 240 mm2. The intensity of use is visible on the CT sections (Fig. 1B–C), which illustrate attritional loss of the outer cortical surface towards the apex. In this area, the cortical bone has been penetrated and the internal trabecular tissue exposed (Fig. 1C – Cross-sectional profile 1, CS1). The CT sections also show increased density of
Discussion
The different techniques employed illustrate microscopic features that are diagnostic of antler knapping hammers. Each technique has advantages and limitations for this type of analyses. Micro-CT scanning, as well as recording the gross 3D surface morphology (Fig. 1), revealed the extent of the attritional loss of the outer cortical surface and the density differences associated with compaction due to repeated hammering (Figs. 1 and 4). Both cortical loss and compression provide new
Conclusion
Different non-destructive imaging and analytic techniques were used to study and quantify the macroscopic and microscopic use-wear modifications on an experimental antler hammer. These techniques are applicable to fragile archaeological specimens, including those encrusted by sediment or encased in matrix. Previous studies have identified pitting and the occasional presence of associated embedded flint flakes as the main features for recognizing archaeological bone and antler percussors (
Acknowledgements
This work was part of the Ancient Human Occupation of Britain project, funded by the Leverhulme Trust and the Human Behaviour in 3D project funded by the Calleva Foundation. We are grateful to the flint-knappers who participate in the experiments at Boxgrove and to Lady Maude of Redvins for procuring the antler hammer described in this paper. We thank Alex Ball, Thomasz Goral and Anton Kearsley for their help while conducting SEM analyses.
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