The identification and characterization of hearths is crucial for reconstructing the history of fire use and pyrotechnology. In addition to ashes and charcoals, an active fire will also produce alterations of the underlying substrate to varying degrees. To date, however, few studies have addressed how the characteristics of burned substrates relate to pyrotechnology. Here, we systematize the use of colour to identify burnt sediments by performing quantitative colour measurements in the CIELab system of experimentally heated soils and sediments. The experimental design included different temperatures, different heating durations and substrates with varied chemical and mineralogical compositions, including naturally red soils and sediments with different degrees of pedogenesis. The measured colours were analysed by multivariate statistics for diagnosing whether sediments have been heated or not, and to which temperature. We achieved an accurate identification of heated versus unheated samples independently of their composition. The determination of the temperature of heating required prior knowledge of basic mineralogy and chemical properties in the targeted sediments (silicate or carbonate material, total and secondary Fe, Ca contents and the amount and kind of organic matter). The algorithm developed can be applied to recognize burned layers and estimate burning temperatures in archaeological contexts.
“Simply red? A systematic colour-based method for identifying archaeological fires”