The experiment was carried out in the BioArCh Facility laboratory, University of York, on 15 May 2014, and used flakes were buried on 19 May. Each flake was removed from its bag and handled with a new set of powder-free nitrile gloves during the experiment and laid on a clean surface of PVC cling film (Figure 2).
Based on the presence of human-made cut marks, we know that mammals with hair were butchered by people at Star Carr, including red and roe deer (Cervus elaphus and Capreolus capreolus), elk (Alces alces), aurochs (Bos taurus primigenius), beaver (Castor fiber) and wild boar (Sus scrofa), as well as birds with feathers, including cranes (Grus grus) (Fraser and King 1954; Legge and Rowley-Conwy 1988). Also recently discovered at Star Carr were fourteen fish remains from pike (Esox lucius, Esox lucius/Salmonidae), perch (Perca fluviatilis), and Cyprinids in the form of teeth, vertebrae, a premaxilla, a rib, and a scale, and it is likely people used stone tools to process these resources (Robson et al. 2016). Therefore, the contact materials used in the experiment were chosen as proxies to reflect the animal, botanical, and mineral materials likely to have been used by ancient hunter-gatherers at Star Carr.
The species used in the experiment (see Table 2) are native and non-native to Britain, and are generally comparable with wild Mesolithic resources. Residues found on stone tools by the use of VLM reported in the literature, such as hair (Hardy 2004; Hardy et al. 2001; 2008; 2013; Hardy and Moncel 2011), blood (Lombard 2008; 2011; 2014; Loy 1983; Loy and Dixon 1998; Loy and Hardy 1992; Robertson et al. 2009; Williamson 2004), feathers (Hardy et al. 2001; 2008; 2013), and starch (Atchison and Fullagar 1998; Barton et al. 1998; Piperno et al. 2000; 2004; Piperno and Holst 1998; Revedin et al. 2010; Yang et al. 2009; Zarrillo and Kooyman 2006), were also specifically used to assess the likelihood of encountering them microscopically on stone tools from Star Carr.
American grey squirrel (Sciurus carolinensis) was used in the experiment instead of the native red squirrel (Sciurus vulgaris), as the latter species is in decline. The cow bone and muscle are from the same genus as extinct aurochs (Bos taurus primigenius). Although not a native species, potato starch was used since it has distinctive starch granules, making it easy to track in the experiment. Starch was included in the experiment since geophytes with underground storage organs and seeds available to Mesolithic people at Star Carr, such as yellow and white water lily rhizomes and seeds (Nuphar lutea and Nymphaea alba), Reedmace rhizome (Typha sp.), bogbean rhizome (Menyanthes trifoliate), goosefoot seeds (Chenopodium spp.), and knotweed seeds (Polygonum spp.) (Taylor 2012; Walker 1954, 58) were probably exploited, thus it is plausible their remains could be found on tools at the site. Additionally, processing of starch-containing plant parts such as leaves, bark, and roots for cordage, mats, baskets, and other perishable technologies are also possible starch pathways (Beck and Torrence 2006, 61–63; Essiamah and Eschrich 1985).
The fish, bird, and squirrel were unfortunately frozen and then thawed prior to being used in the experiment. As a result, no intact cells were located owing to lysis of the cell membranes.
Blank control flakes were added to each group of used flakes in order to: 1) examine the variation in the morphology of the raw stone substrate, 2) observe any possible transfer of soil material to the blank flakes that might be mistaken for a residue, and 3) document changes to the flint due to burial condition, independent of the presence of residues. No residues were applied to the controls, but they were otherwise treated identically to the experimentally used flakes.
| Material | Taxon | Motion | Expected residue composition |
|---|---|---|---|
| Bone | Bos taurus | Fresh cow bone including periosteum tissue cut in a sawing motion, creating grooves both parallel and transverse to the long axis of the bone | Bone (compact), fat, fibrous periosteum tissue |
| Antler | Cervus elaphus | A small amount of ultrapure water was added to dry antler with only the brown colour remaining as a remnant velvet, then cut in a sawing motion, creating grooves with the grain and transverse cuts | Bone (compact), trace brown velvet epidermis |
| Muscle | Bos taurus | Cutting motion was used on a piece of fresh beef steak | Muscle (striated), fat, blood |
| Fish | Family Cyprinidae | Cutting motion through skin and scraping against the few large scales present on the body. Note: scales did not easily stick to flint surfaces during use of the tools | Scales, muscle, skin, fat, blood |
| Bird | Anser anser | Cutting through goose skin, feathers and muscle | Feathers, muscle, skin, fat, blood |
| Squirrel | Sciurus carolinensis | Cutting motion through animal skin, hair, and tissues | Hair, blood, muscle, skin |
| Potato | Solanum tuberosum | Slicing motion through the peel and centre of the potato | Starch granules, epidermal tissue |
| Reeds | Iris pseudacorus | Leaves were sliced and scraped | Cell walls, epidermal tissue, parenchyma, vascular tissue |
| Softwood | Picea sp.; cf. Picea abies | Conifer branches with bark were cut and scraped | Tracheids |
| Hardwood | Salix alba | Branches were cut and scraped | Vessel elements, tracheids, fibres |
| Resin | Pinus thunbergii | Natural unmodified pine resin was applied with gloved hands to the non-cutting edge of flakes at the proximal end | Resin, perhaps wood fragments |
| Red ochre | Contains Fe2O3 | Natural red ochre pigment powder was obtained from an art supplier. According to the supplier, it had no additives, and contained 20-70% iron oxide. The ochre was heavily applied with gloved hands all over flint pieces | Granular red powder |
An acute-angled edge of each flake was used to cut into each contact material until residue was visible on the surface. The used flakes were placed on trays lined with PVC film. Residues were left for three days to dry on the surfaces of the flakes in order to ensure that they adhered to the stone substrate. The trays were kept in a lab space with no opening windows and away from air vents to avoid air particulate accumulation. After the three days, each flake was placed in its own zip-lock bag prior to burial, with new gloves used for every flake.
To avoid directly marking or labelling the flint flakes and potentially contaminating or obscuring residues, a laminated label was created for each specimen, which stayed with each specimen throughout the experiment. Each label contained a unique number, the residue type, and duration of burial.
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