Tabea Joanna Koch

Explorer les chaînes opératoires des adhésifs préhistoriques au cours de l'Holocène (du Mésolithique à l'Âge du Fer): Les adhésifs jouent un rôle important dans les premières innovations technologiques de l'humanité. Les hommes préhistoriques utilisaient des résines d'arbres naturellement disponibles, le bitume, ou des colles synthétiques telles que le brai de bouleau, pour fabriquer, réparer, décorer et imperméabiliser leurs objets. Les recherches antérieures se sont concentrées sur l'identification chimique des adhésifs, la reproduction expérimentale et les tests sur les propriétés mécaniques, ce qui nous a permis de mieux comprendre les choix de matériaux et le savoir-faire technologique de l'époque. Les découvertes d'adhésifs sont encore rares par rapport à d'autres types d'artefacts, ce qui limite notre capacité à documenter les techniques de production d'adhésifs, la diversité des matériaux et leur fonctionnalité.Cette thèse s'organise autour de cinq axes d'études principaux qui ont pour objectif de pallier les lacunes sur les adhésifs en Europe, en explorant des contextes géographiques et chrono-culturels variés. La première étude vise à corréler les techniques de production de brai de bouleau en contexte acéramique avec des artefacts mésolithiques, afin de comprendre l'utilisation de l'adhésif pour l'emmanchement et la décoration. La seconde étude porte sur l'utilisation du brai de bouleau pour ses propriétés hydrophobes dans les équipements de pêche néolithiques. Une enquête à grande échelle sur des objets de l'âge du Fer vise à identifier les variations de composition des brais de bouleau trouvés sur les céramiques. Une étude supplémentaire explore la diversité et la fonction des adhésifs sur des objets métalliques. Enfin, une étude transdisciplinaire, associant la caractérisation moléculaire et l'analyse ADN, met en avant le potentiel de ces disciplines pour documenter les chaînes opératoires et les pratiques culturelles passées.Ce travail confirme l'utilisation courante du brai de bouleau comme adhésif du Mésolithique à l'âge du Fer en Europe, ainsi que les différences de composition des brais, résultant probablement d'une production ou d'un traitement spécifique aux fonctions de l'adhésif. La gamme de matériaux adhésifs utilisés se diversifie au cours du temps pour inclure plus fréquemment les résines de conifères, la cire d'abeille et le bitume. Les résultats suggèrent que la fonctionnalité des adhésifs a évolué avec l'émergence de nouvelles technologies, témoignant de leur adaptation aux exigences changeantes des outils en pierre, de la céramique et de la métallurgie. Cela ouvre de nouvelles perspectives et orientations pour la recherche future afin d'utiliser des approches expérimentales et biomoléculaires pour étudier les adhésifs anciens.

Birch bark tar was widely used throughout prehistoric Europe for hafting stone tools as well as various other purposes. While previous research has mainly focused on the identification and production of birch bark tar, its diverse uses remain to be fully explored. In this study, we combined ancient DNA with organic residue analysis to analyse 30 birch tar artefacts from nine Neolithic sites in and around the Alps. We identified birch tar as the main component, with some samples also containing conifer resin or tar, possibly added to modify its properties. Degradation markers indicate that tar used for ceramic repair was heated repeatedly, probably during cooking. Additionally, the presence of human and oral microbial DNA in some of the samples suggests the tar was chewed, in some cases by multiple individuals. The human DNA also enables us to determine the sex of those who chewed the tar, offering insights into gendered practices in the past, while plant and animal DNA shed light on past diets and the possible use of additives. This study underscores the value of integrating organic residue and ancient DNA analysis of archaeological artefacts to deepen our understanding of past cultural practices.

Birch tar was the first substance made by humans that is otherwise not available in nature. The oldest artefacts date to ~ 200 thousand years ago in Europe but birch tar becomes more frequent around 45 thousand years ago and even more so from the Mesolithic onwards. Their study has important implication for our understanding of evolutionary processes such as cognitive capacity and cultural evolution. What remains unknown is the overall molecular composition of birch tar. Several approaches based on gas chromatography-mass spectrometry have shown the potential of studying solvent soluble molecules to understand the botanical origin of different tars, their manufacturing techniques and their post-depositional alteration mechanisms. However, birch tar’s soluble fraction cannot shed light on its mechanical properties. In this study, we conduct gas chromatography-mass spectrometry and spectroscopic analysis of seven bulk birch tar samples, including infrared band assignment and structural refinement of organic molecules in the insoluble fraction. We find that the overall proportion that cannot be analysed by gas chromatography accounts for 85–90% in birch tar. This phase consists of polymerised molecules with a structure analogous to asphaltenes but containing a significantly greater amount of oxygen-related functional groups. Our findings have implications for understanding the viscosity, adhesiveness and stiffness of birch tar and they call for caution in applying analytical techniques that only target soluble molecules in birch tar.

Birch bark tar is the most widely documented adhesive in prehistoric Europe. More recent periods attest to a diversification in terms of the materials used as adhesives and their application. Some studies have shown that conifer resins and beeswax were added to produce compound adhesives. For the Iron Age, no comparative large-scale studies have been conducted to provide a wider perspective on adhesive technologies. To address this issue, we identify adhesive substances from the Iron Age in north-eastern France. We applied organic residue analysis to 65 samples from 16 archaeological sites. This included residues adhering to ceramics, from vessel surface coatings, repaired ceramics, vessel contents, and adhesive lumps. Our findings show that, even during the Iron Age in north-eastern France, birch bark tar is one of the best-preserved adhesive substances, used for at least 400 years. To a lesser extent, Pinaceae resin and beeswax were also identified. Through statistical analyses, we show that molecular composition differs in samples, correlating with adhesive function. This has implications for our understanding of birch bark tar production, processing and mode of use during the Iron Age in France and beyond.

Birch tar has been identified as the predominant adhesive used for hafting purposes in the European Mesolithic and Neolithic. Its role in the manufacture of composite tools and weapons comprising wooden, bone and flint components attests its importance during these periods. The discovery of birch tar lumps, some bearing tooth imprints, suggests a broader range of functions beyond its adhesive properties. In this study, we present an analysis of five residues from two sites (Syltholm II and Strandholm I) that have been excavated through the Femern project, with the aim to shed light on the adhesives used in relation to their functions. Through chemical analyses, we show that birch tar constitutes the main component of two lumps and one chewed piece. We also found that birch tar served to haft a bone point within leister prongs, providing new information on its previously unknown role in composite fishing tool technology. These findings have significant implications for our understanding of the functional role and performance of birch tar in aquatic environments.

Birch tar is the oldest synthetic substance made by early humans. The earliest such artefacts are associated with Neanderthals. According to traditional interpretations, their study allows understanding Neanderthal tool behaviours, skills and cultural evolution. However, recent work has found that birch tar can also be produced with simple processes, or even result from fortuitous accidents. Even though these findings suggest that birch tar per se is not a proxy for cognition, they do not shed light on the process by which Neanderthals produced it, and, therefore, cannot evaluate the implications of that behaviour. Here, we address the question of how tar was made by Neanderthals. Through a comparative chemical analysis of the two exceptional birch tar pieces from Königsaue (Germany) and a large reference birch tar collection made with Stone Age techniques, we found that Neanderthals did not use the simplest method to make tar. Rather, they distilled tar in an intentionally created underground environment that restricted oxygen flow and remained invisible during the process. This degree of complexity is unlikely to have been invented spontaneously. Our results suggest that Neanderthals invented or developed this process based on previous simpler methods and constitute one of the clearest indicators of cumulative cultural evolution in the European Middle Palaeolithic.

Birch tar is the earliest adhesive produced by Neanderthals in the European Palaeolithic. Experimental studies have proposed a number of aceramic (i.e. without the use of ceramics) birch tar–making techniques, but to date, no archaeological evidence for any of these techniques has been brought forward. The likelihood of one of those methods being actually used in the Stone Age may be investigated by evaluating the method’s complexity, efficiency and the performance of the tar obtained. In this study, we experimentally produce birch tar with four common experimental aceramic techniques. These tars are tested for their mechanical properties using lap-shear tests. We found that tar made with the aboveground condensation method is strongest in terms of its adhesive strength. The tar also shows the most consistent behaviour throughout our test series. The weakest adhesive was observed in tar made with an underground (i.e. oxygen-depleted) technique resembling double-pot distillation (raised structure). Two supplementary methods yielded intermediate values: the recently proposed cobble-groove method produces tar with plastic behaviour. Tar made with another underground technique (pit roll) is almost as strong as condensation method tar. This study adds to our understanding of adhesive performance of birch tar made with different aceramic techniques. It also allows understanding the potential use of one method instead of another.