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.