The Effects of Fire on Archaeological Soils and Sediments: Temperature and Colour Relationships.

Although fire is a fundamental building block of interpretation, details of its effect on archaeological substrates are still poorly understood. The key questions, from an interpretative point of view, are the level of heating produced in the soil underneath different fires and the degree of reddening preserved in the final stratigraphy. This paper explores these questions by examination of previous studies and through a series of instrumented experimental fires. We conclude that, although there is some variation, temperatures beneath most surface-built fires remain below 500° C and reddening of the soil happens only rarely. These two generalisations are, however, linked in a complex way which is not fully clarified. Some sediments redden dramatically at temperatures commonly found under the experimental fires and in the literature on soil heating, while others fail to redden even at significantly higher temperatures. These ‘anomalies’ could relate to either organic matter content or chemical variations affecting the progress of the iron oxide transformations that lead to soil reddening.