Birch bark tar production: experimental and biomolecular approaches of a common and widely used prehistoric adhesive
Résumé
Birch bark tar, the oldest adhesive known in Europe, was widely used during Prehistory. This material, produced by a controlled heat treatment of birch bark, is identified in various spheres of activities and provides valuable information on know-how, technical and territorial systems of past societies. This biomaterial can also supply evidence for socio-economic networks and mobility. However, very few is known on the systems of production during Prehistory, even for Neolithic period. The lack of findings in the archaeological record requires the development of an approach that combines experimental archaeology and biomolecular chemistry. We present here (i) the results of experimental production of birch bark tar and (ii) their molecular signatures according to different processes based on the use of ceramic vessels. The key role of bark quality is highlighted for the first time. This study also details direct archaeological inference of the experimental results obtained: a total of 23 samples from the site of Nice-Giribaldi (France, second part of the Vth century BCE) was investigated. Different categories of birch bark tars were identified during Neolithic in the south of France, giving evidence for complex manufacture systems and procurement networks