Pyrotechnology and lipid biomarker variability in pine tar production

Tar or pitch produced from pine resin and wood played an important role in the past as an adhesive, waterproofing and medicinal product. However, the formation and biomolecular composition of pine tar produced only from resin under different combustion conditions (i.e., temperature and oxygen availability during heating) has not been as widely investigated as pine tar produced by dry distillation of wood or birch bark tar, for which an extensive literature is available. This lack of information hampers technological interpretations of biomolecular data obtained from organic residue analyses of archaeological pine tar products. In this study, we performed controlled laboratory heating sequences with pine resin ( Pinus canariensis ) at 150, 250, 350 and 450 ºC under both oxygenated and oxygen-limited conditions, and analyzed the products using gas chromatography-mass spectrometry (GC-MS). A control unheated resin sample was also analysed. We found that the formation of pine tar from resin occurs around 250–350 ºC under both oxygenated and oxygen-limited atmospheres. We also present and discuss the lipid biomarkers of pine resin and its combustion products according to changes in temperature and oxygen availability. Our reference data provide new information for the biomolecular identification of archaeological pine tar products and show potential for shedding light on the conditions in which tar was manufactured by ancient populations in different contexts.