Assessing the Function of Palaeolithic Hearths: Experiments on Intensity of Luminosity and Radiative Heat Outputs from Different Fuel Sources

Assessing the function of Palaeolithic hearths is a key research issue that can benefit from the application of experimental archaeology when examining whether the behaviourally related purposes of fire, e.g. heat, light and cooking, could be correlated with combustion features in the archaeological record. Not all species of wood and types of fuel burn the same way. Variability exists in the amount of ash and smoke produced, along with differences in speed of burning and outgoing light and heat. This paper examined the light and heat properties of nine different types of fuels (eight individual species of wood and fresh bone) by assessing intensity of luminosity and radiative heat outputs using a lux metre and thermal imaging camera. Results show that there is considerable variation between bone and wood in terms of light and heat output and between the individual species of wood. In order to assess whether heat efficiency may vary seasonally, experiments were performed overnight and repeated at ambient air temperature ranges of 11 to 13 and 0 to 3 °C. Results show that in the current data set fuels that emit lower to intermediate heat outputs could be more efficient at colder temperatures in terms of warmth. This represents a preliminary step forward towards attributing behaviourally relevant functions such as light and heat to Palaeolithic combustion features with regard to fuel selectivity.