The formation conditions of birch tar in oxygen-depleted environments

Tabea J Koch,Patrick Schmidt

doi:10.1007/s12520-021-01352-x

Tabea J Koch, Patrick Schmidt

Open Access

https://doi.org/10.1007/s12520-021-01352-x

Copy DOI

Abstract

Birch tar is the oldest manmade adhesive dating back to the European Middle Palaeolithic. Its study is of importance for understanding the cognitive capacities and technical skills of Neanderthals and the aceramic production systems employed in the European Palaeolithic and Mesolithic. Several methods may have been used to make birch tar, the most common proposition being dry distillation in oxygen-depleted atmospheres. One of the major impediments for our understanding of the conditions employed to make Neanderthal birch tar, and ultimately the technique used, is that it remains unknown at which temperatures exactly birch tar forms. The relationship between heating duration and tar formation is also unknown. To address these questions, we conduct a laboratory heating experiment, using sealed glass tubes and an electric furnace. We found that birch tar is only produced at a narrow temperature interval (350 °C and 400 °C). Heating times longer than 15 min have no effect on the quantity of tar produced. These findings, notwithstanding previous propositions of necessarily long heating times and larger tolerances for temperature, have important implications for our understanding of the investment in time needed for Palaeolithic birch tar making.

Highlights

Birch tar is the oldest manmade adhesive, dating back to the European Middle Palaeolithic (Mazza et al 2006). It has recently attracted the attention of archaeologists because of its potential to yield information about the cognitive capacities and skills of Neanderthals and the technical knowledge employed to make birch tar in the European Palaeolithic and Mesolithic (e.g. Kozowyk et al 2017; Niekus et al 2019; Schmidt et al 2019)
Sieves were inserted into the test tubes to create a barrier for ash not to fall into the birch tar accumulating at the bottom of the tubes
A rack was built from copper wires to hold five test tubes at a time in a tilted position in the electric furnace that was used for heating

Summary

Introduction

Birch tar is the oldest manmade adhesive, dating back to the European Middle Palaeolithic (Mazza et al 2006). It has recently attracted the attention of archaeologists because of its potential to yield information about the cognitive capacities and skills of Neanderthals and the technical knowledge employed to make birch tar in the European Palaeolithic and Mesolithic (e.g. Kozowyk et al 2017; Niekus et al 2019; Schmidt et al 2019). Production pathways that could potentially have been used by Neanderthals in the Middle Palaeolithic include above-ground heating with the condensation method (Schmidt et al 2019), heat treatment in earth-pits and/or under embers (Kozowyk et al 2017) and specially built earthen raised structures (Osipowicz 2005). Except the condensation method, rely on the creation 92 Page 2 of 5

Methods

Results

Conclusion