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The effect of heat on keratin and implications for the archaeological record

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Abstract

A horncore feature was encountered during excavations at Border Cave, in Member 2 BSL, dated 60–49 ka. The basal half of the horncore lay towards the centre of a combustion feature and was calcined. The tip half lay on a mat of burnt grass bedding towards the edge of the fireplace. It was covered with a black shiny residue, which was also present on nearby stone tools. The feature was jacketed and excavated later under a microscope in the laboratory. Raman spectroscopy identified the residue only as amorphous carbon, indicating the presence of a heated organic substance. Knowing that variation exists in modern and archaeological glue recipes, we wanted to know if the black residue was melted keratin, and if it was, whether it had been used as a substitute for beeswax or latex for hafting. We set out to test the hypothesis by conducting a heating experiment with a modern sheathed horncore. Experimental results showed that keratin does not transform into viable glue when heated. Instead, it reduces immediately to a glassy brittle residue. Our finding strongly supports a scenario of incidental deposition of residue on the archaeological stone tools. Previous combustion experiments have shown that the sediment below a fire can reach 300+ °C through vertical heat transfer. This implies that horn sheaths in archaeological deposits, separated from overlying combustion features by thousands of years, can transform into a black residue that may deposit on nearby stone and bone tools.

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Data availability

All relevant data are provided in the manuscript. Piece-plotted data taken using a total station theodolite are lodged with the curator of the Border Cave collection, Dr. Bernhard Zipfel, at the University of the Witwatersrand and with the South African Heritage Resource Agency (SAHRA). All finds are housed at the Evolutionary Studies Institute at the University of the Witwatersrand in Johannesburg, South Africa.

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Acknowledgements

The Microscopy and Microanalysis Unit at the University of the Witwatersrand is thanked for the use of the Olympus BX63 microscope and the Raman spectrometer. We are grateful to Christine Steininger for identifying the archaeological and modern horns.

Funding

This research was funded by a National Geographic Explorer grant (NGS-54810R-19) and DSI-NRF Centre of Excellence in Palaeosciences grant (CEOOP2020-1) to LB.

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Authors and Affiliations

  1. Evolutionary Studies Institute, University of the Witwatersrand, Private Bag 3, Wits, Johannesburg, 2050, South Africa

    Lucinda Backwell, Marine Wojcieszak & Lyn Wadley

  2. Instituto Superior de Estudios Sociales (ISES-CONICET), San Lorenzo 429, 4000, Tucuman, Argentina

    Lucinda Backwell

  3. 14C Laboratory, Royal Institute for Cultural Heritage, Parc du Cinquantenaire 1, 1000, Bruxelles, Belgium

    Marine Wojcieszak

Authors
  1. Lucinda Backwell
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  2. Marine Wojcieszak
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  3. Lyn Wadley
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Contributions

Lyn Wadley conceptualized the study and all the authors contributed to the design. Material preparation, data collection and analyses were performed by Lyn Wadley, Marine Wojcieszak and Lucinda Backwell. The first draft of the manuscript was written by Lucinda Backwell, and all the authors commented on previous versions of the manuscript. All the authors read and approved the final manuscript. Funding was acquired by Lucinda Backwell.

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Correspondence to Lucinda Backwell.

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Backwell, L., Wojcieszak, M. & Wadley, L. The effect of heat on keratin and implications for the archaeological record. Archaeol Anthropol Sci 12, 181 (2020). https://doi.org/10.1007/s12520-020-01152-9

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