Color Me Heated? A Comparison of Potential Methods to Quantify Color Change in Thermally-Altered Rocks

ABSTRACT

This study investigates and compares methods to quantify color changes in quartzite rocks after repeated heating episodes. We collected quartzite samples from the southern Cape coast, South Africa, and heated them three times in experimental fires. We recorded the colors of the samples before and after heating using visual observation, Munsell color notations, Munsell color notations converted to RGB values, and digital image analysis. The methods are also tested on potentially heated and potentially unheated archaeological samples from Klasies River main site, South Africa. It was possible to distinguish between unheated and repeatedly experimentally heated quartzite using visual observation and Munsell color notation, but a large proportion of repeatedly heated samples appeared unaffected by the heat. The digitally-captured color values best discriminated color changes after heating. Color values of repeatedly heated experimental samples overlap with color values of potentially heated archaeological samples.

KEYWORDS:

• thermally-altered rocks
• color
• quartzite
• experimental archaeology
• Middle Stone Age
• Klasies River

Acknowledgements

This work was supported by the National Research Foundation (NRF), reference AOP150909141975, Grant No: 98826, Wits postdoctoral contract F14/25 funded by the NRF and the Claude Leon Foundation and partly by Postdoctoral Fellowship Grant No. PD2015/02SB from the DST/NRF Centre of Excellence in Palaeosciences (CoE-Pal). Any opinion, finding and conclusion or recommendation expressed in this material is that of the author(s) and the funding bodies does not accept any liability in this regard, nor do the opinions, findings, conclusions or recommendations in this material necessarily represent the views of the funding bodies. We thank the Klasies River excavation team and everyone who helped collect and carry rocks for this study. Special thanks to Liezl van Pletzen-Vos for help with Figure 4.

Disclosure Statement

No potential conflict of interest was reported by the author(s).

Notes on Contributors

Silje Evjenth Bentsen (Ph.D. 2014, University of the Witwatersrand) is a postdoctoral research fellow at SapienCE, University of Bergen, Norway. She conducted this research as a Claude Leon Postdoctoral Fellow in archaeology at the University of the Witwatersrand. Her main research interests are combustion features and fire-related behavior among hunter/gatherers/fishers. She currently investigates the use of fire and site formation processes at the Klasies River main site and incorporates experimental archaeology and geochemistry in her research.

Sarah Wurz (Ph.D. 2000, University of Stellenbosch) is Associate Professor at both the School of Geography, Archaeology and Environmental Studies, University of the Witwatersrand and the Centre of Excellence on Early Sapience Behaviour at the University of Bergen. She is the director for excavations and research at Klasies River, a key site for understanding the origins of modern humans. Her research on the Middle Stone Age and the Klasies River sequence led to new insights into the complexity of lithic technological and related behaviors. Her background and expertise that includes musicology provide the multidisciplinary context from which she investigates past behavior and cognition

ORCID

Silje Evjenth Bentsen http://orcid.org/0000-0001-6394-4437

Sarah Wurz http://orcid.org/0000-0002-0949-5391