There are very few examples of experiments that have aimed to interpret microscopic lithic residues that have undergone diagenesis (Table 1). To date, the only large-scale lithic residue preservation study is that of Langejans (2009; 2010) (~370 experimental pieces); although other researchers currently have residue diagenesis experiments in progress. Other, smaller scale, studies have included residues that were experimentally degraded by burial, exposure on the soil surface, or treatment with chemicals: Anderson (1980), 23 experimental pieces, chemical treatment; Jahren et al. (1997), six experimental pieces, chemical treatment; Hortolà (2001), two experimental pieces, one that was exposed outdoors, then exposed indoors, the other was buried; Wadley et al. (2004), ten experimental pieces, buried; Barton (2009), eight experimental pieces, half exposed on soil surface and half buried; and Rots et al. (2016), three experimental pieces, buried.
| Reference | Total number of pieces (including blanks, replication, and pieces lost during experiment) | Substrate type(s) | Residues applied | Diagenesis treatment(s) | Duration of treatment |
|---|---|---|---|---|---|
| Anderson 1980 | 23 | flint tools | wood, grass, cartilage, fresh and cooked bone, soaked antler, dry hide | Chemical: hydrogen peroxide and hydrochloric acid, sulfuric acid, sodium hydroxide, alcohol, and ether | unknown |
| Jahren et al. 1997 | 6 | chert flakes | bamboo, bone | Chemical: 35% hydrogen peroxide | one day |
| Hortolà 2001 | 2 | stone tools: knife, projectile point | blood | Exposure outdoors (1 week), exposure indoors, burial | 1 year |
| Wadley et al. 2004 | 10 | flakes of hornfels, chert, dolerite, chalcedony | raw muscle, raw fat, raw blood, raw bone, cooked fat, cooked and uncooked starch, tree bark, and tree exudates | Burial and outdoor exposure. Buried in a bag with compost for 30 or 60(?) days indoors. Thereafter tools mistakenly scattered outdoors in a garden where they were watered daily for a period of three days. Tools subsequently sun-dried and examined | 63 days(?) |
| Barton 2009 | 8 | silcrete and silicified tuff flakes | starch | Burial and outdoor exposure at soil surface | 4 months, 2 years |
| Langejans 2009; 2010 | ~ 370 | flakes of hornfels, chert, quartzite, Meuse flint; microscope slides with 3 grades of sandpaper | bone, fat, blood, muscle tissue, starch, woody tissue | Burial and outdoor exposure at soil surface, covered or outside caves, microscope slides buried facing up or down | 4 weeks, 1 year |
| Rots et al. 2016 | 3 | flint tools: blades and an endscraper | wood, bone, meat | Burial | 2 months |
Microscopic residue analysis typically relies on visual observations to interpret archaeological residues. However, insufficient attention has been paid to 1) the degree to which residues are visually identifiable after undergoing diagenesis, and 2) the issue of contamination, originating within the archaeological context or during the process of artefact recovery and analysis. Furthermore, blind tests by Monnier et al. (2012) demonstrated that even modern residues that have undergone no diagenetic alterations can be ambiguous and difficult to identify, indicating that interpretation of degraded archaeological residues is complex and requires due caution. Thus, foundational experiments to assess the reliability of archaeological residue analysis from varied burial environments are still very much needed. Compiling a 'significant body of results' (Haslam 2006a, 408; Langejans 2009, 15) is required to form a reference base for residue analysis as a discipline, in terms of establishing both a descriptive and micrographic archive. Such a body of results will ultimately enable examination of broader issues, such as resource exploitation and social changes (Haslam 2006a, 408).
It is hoped that the experiment reported here will represent a step forward in the discipline. There are several key ways in which this research differs from previous residue burial experiments. First, the experimental pieces containing residues were buried in archaeological contexts – a decision made on the basis that it was important to expose experimental residues to chemical soil processes as similar as possible to the soil conditions experienced by archaeological residues. Second, the experimental conditions were repeated in their entirety and buried at an off-site control location. Thirdly, the same stone material type (Wolds flint) was used throughout the experiment. In this way, the substrate to which residues were applied was controlled. Fourth, no marks or labels were applied to the flint flakes. Rather, a sample number on a separate waterproof label was buried alongside each flake, so as to avoid unnecessary contamination and interference with subsequent interpretation of the applied residues. Fifth, during the experiment, there was no disturbance to the used flakes in any of the locations from digging animals, ploughing, or human interference. Sixth, soil samples were collected directly underneath each flake in the experiment at the time of recovery. These soil samples were mounted and examined to assess the extent of downward movement of residues. Finally, all experimental pieces originally buried were recovered; in other words sample recovery was 100%.
This study produces three contributions to lithic residue analysis: 1) an assessment of residue preservation over time in varied burial environments (archaeological soils at Star Carr and non-archaeological soils at Manor Farm), 2) an assessment of the extent to which residues can be characterised with reflected VLM, 3) a comparison of microscopic techniques for residue identification: reflected VLM versus SEM.
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