Tempering-residue on heat-treated silcrete: an experimental perspective and a potential analytical protocol

Combined study of archaeomagnetism and Raman spectroscopy of experimentally burnt limestones from the middle-palaeolithic site of Pinilla del Valle (Madrid, Spain)

“…These studies comprise the analyses of ashes, charred bones, stone implements of diverse lithologies or organic residues through the application of different geoarchaeological techniques such as Mössbauer spectroscopy, x-ray diffraction (XRD), soil micromorphology or Fourier transform infrared spectroscopy (FTIR), among others (e.g. Munayco and Scorzelli, 2013;Reidsma et al, 2016;Schmidt et al, 2013Schmidt et al, , 2015Schmidt et al, , 2017Wadley and Prinsloo 2014). Magnetic methods are very sensitive to detect thermal alterations in archaeological or geological materials.…”

Variance in the response of silcrete to rapid heating complicates assumptions about past heat treatment methods

“…Experimental and ethnographic observations on the heating of other rock types may thus not be relevant to the process as it applies to silcrete. In support of this proposition is evidence for carbonised green wood exudates (residues) on heated silcretes from archaeological sites in southern Africa, along with frequent evidence for heat fracture prior to flaking that, as noted above, is difficult to reconcile with an insulated or 'sand-bath' heating technique (Delagnes et al 2016;Schmidt et al 2015aSchmidt et al , 2017a. It has also been noted that there is no ethnographic evidence that the sandbath approach was ever used during heating of silcrete (Schmidt 2016).…”

“…An alternative 'low-cost' approach suggests that heat treatment can be carried out successfully when silcrete pieces are placed directly in an open fire (Schmidt et al 2015a;2017a). The underpinning principal is that, while slow heating/cooling rates and low maximum temperatures may be required for rocks such as chert and flint, the greater porosity of silcrete enables it to withstand both greater heating/cooling rates and higher maximum temperatures (Schmidt 2014;Schmidt et al 2017b).…”

Pine traces at Star Carr: Evidence from residues on stone tools

“…It might be posited that the tools found to contain Pinaceae resin acids at Star Carr were heat treated in a fire containing embers of Pinaceae wood, and hence diterpenoid compounds from dripping resin could have transferred to the surfaces of the flint. Schmidt et al (2016Schmidt et al ( , 2015 proposed that heat treatment of silcrete was carried out at the Middle Stone Age site of Diepkloof Rock Shelter, South Africa, as evidenced by the similar presence and locations of black heat tempering-residues on both experimental and archaeological tools. Perhaps it is possible that Mesolithic people at Star Carr were heat treating the flint prior to knapping, but again there are no pine macrobotanical remains on site, so no evidence of fires with Pinaceae wood are present.…”

“…Refitting sequences evidence tool manufacture both on and off site (Conneller et al, 2018) , so Pinaceae compounds originating from elsewhere must be considered. Because no macrobotanical pine remains have been securely identified at Star Carr, there are a number of scenarios which are less likely or difficult to support: 1) the tools found to contain Pinaceae resin acids were heat treated on site at Star Carr in a fire with Pinaceae wood embers , and further excavations may recover evidence of the Pinaceae wood, 2) tools were exposed to Pinaceae wood smoke following discard at Star Carr, and further excavations may recover the Pinaceae wood, 3) people made tools off site using a fire treatment with Pinaceae wood , although no heat tempering-residues like those Schmidt et al (2016Schmidt et al ( , 2015 reported were found, or 4) people made tools off site that were exposed to Pinaceae wood smoke that were brought to Star Carr.…”