Archaeological fresh and fossil plant exudates and tars: chemistry, manufacture and uses – EXSUDARCH

a methodology at the interface of archeology, chemistry and archaeobotany was developed. From a methodological point of view, the advances were of several kinds:
• Development of a database combining chemical, archaeological and archaeobotanical;
• Implementation of innovative non-destructive analytical strategies based on vibrational spectroscopy and mass spectrometry;
• Isolation of molecular biomarkers of interest by preparative chromatographic techniques;
• Establishment of experimental methods for making birch bark tar under controlled conditions in the laboratory and outdoors;
• Construction of a platform for experimental shots to determine the mechanical properties of adhesives used in hunting activities;
• Development of a method for assessing cost-distance to understand the supply networks in birch bark.

Thus, through this ANR, we now have tools and methods that will allow us in the future to effectively understand production systems and plant exudates tar in all their dimensions, i.e. archaeological, chemical and regarding relations Men - environments.

The results of the project were obtained in complementary fileds of archaeology, analytical methodology and archaeobotany.
In archaeological terms, we confirmed the massive and almost exclusive exploitation of birch bark tar up to the borders of Western Europe during the Neolithic but also in the Mediterranean area. We also studied the evolution of crafts between the Neolithic and the end of the protohistory / early antiquity; We have thus demonstrated that during the first Iron Age in Corsica, birch bark tar was used in combination with pine resin and beeswax; we also showed for the first time that birch bark tar was still in use after the Roman conquest in Frejus.
At the methodological level, progress has been made on (i) the micro- or non-destructive characterization of micro-residues; (ii) the experimental protocols for making birch bark tar; (iii) isolation of some biomarkers in different plant exudates to determine their molecular structure accurately.
Finally, in the field of archaeobotany, we have compared the data from the characterization of materials with archaeobotanical data and implemented a cost-distance model. This helped to determine acquisition systems on some sites, for example highlight a differentiated plant resources for their timber and timber products (resin and tar) operations.
Research in the Arabian Peninsula, based on archaeological data and the study of textual sources, were developed to study the evolution of frankincense trade over time (ca. fourth to sixteenth centuries AD). They highlighted (i ) the complexity of networks and the role of rotating plate of this region in the spices trade between the Indian Ocean and the Mediterranean world ; ( ii) the continuity of the trade until the medieval period in the Middle East, a period generally omitted in the literature ; ( iii) the diversity of products that were circulating at the time.

There are many opportunities: expansion of archaeological sites studied, analytical developments and synthesis of the results which are not all still counted. Furthermore , it is conceivable that the extension of this research beyond the chrono- cultural areas considered in this project could lead, once all the data from this project have been published,to the development of a European project .

The scientific output of the project is characterized by its interdisciplinary nature. Scientific articles have been published in international journals of Chemistry (Analytical methods, Talanta) and Archaeometry (Archaeometry) and have been published in book chapters archaeometry (book edited by Ph. Dillmann and L-Bellot Gurlet). The data were also published in conference proceedings chapters or monographs. Finally, the results of the last year of the ANR are being finalized and will be collected to be published in international journals of archeology, biogeography and archaeobotany.
In total, there are currently 13 items / conference proceedings / book chapters that have been published, are in press or accepted and six others are in preparation. The ANR will have resulted in a score of publications, which must be added 14 papers in national and international conferences, 11 poster communications, 12 thematic interventions in schools or seminars and public interventions.
Six PhD theses were also developed in relation with this ANR.

Among materials that have been exploited over time, natural substances are probably the most challenging to study. Issued from organic biomaterials such as resins, beeswax, animal fats or vegetal oils, they are preserved at low amount as amorphous organic residues and are often difficult to detect at the archaeological field. They give evidence for the use of animal, plant and fossil products that were of great importance for various aspects of human life, including diet, medicine, funerary rituals, economic and technical activities. Because they lack recognisable morphological attributes, the only way to determine their nature and origin relies on the development of analytical strategies that allow elucidation of their chemical composition.
This proposal is focused on the study of the exploitation of fresh and fossil plant exsudates and tars. All these substances share common features in the field of archaeology and chemistry: they are made of complex molecular mixtures, they contain terpenoid components, they are often preserved at low amount and they were used for common purposes (hafting lithic and bone tools; mending, decorating or waterproofing ceramic vessels, etc.). In some cases, these materials were mixed with various adjuvants such as beeswax, vegetal oils, animal fats, clay, ochre, …, that will also be considered in this project.
Surprisingly, despite the first interest of researchers for bitumen, vegetal resins and tars as early as the 19th century, no systematic study was carried out on such materials. While these substances are of prime importance in ancient societies due to their role in subsistence strategies, medicine and rituals, only partial and occasional data are thus available.
This is why we decided to develop the present interdisciplinary research programme based upon complementary approaches including archaeology, analytical chemistry and archaeobotany.
At this stage of the research, it would be a non-sense to focus on a narrow chronological and / or geographic area. Indeed, the study of such remains is still quite young and before developing detailed research on specific points, we first need to gain an overview of the sites in which plant amorphous remains are preserved and, of the diversity of materials exploited. We will first proceed to the inventory of samples issued from a large geo-chronological zone, from western Europe to eastern mediterranean region, from Neolithic to recent periods, and we will then focus on geo-chronological windows for which numerous series of samples are available and specific archaeological questions have to be addressed.
Our purpose is to better understand the socio-economic systems of production, from acquisition to utilisations, of fresh and fossil plant exudates / tars and their evolution over time. The putative causes of this evolution will also be considered (climatic changes, cultural evolution, change of trade/exchange networks, etc.), as well as strategies of plant management. The most striking aspect of this project is the development of a multi-sided methodology that allows overcoming the physico-chemical characterisation of the materials studied to reach socio-economic information on the systems of exploitation of plant substances over time, by combining chemical and archaeobotanical data. At the end of this project, we hope that we could pass from a fragmentary knowledge to an extended overview of plant exudates and tars exploitation. The choice of diachronic study will highlight the continuity and discontinuity of use of the materials identified and the evolution of their modes of production.