Wood Tar Production Without the Use of Ceramic Vessels: Experimental Archaeology in Grodzisko Żmijowiska

Abstract

Several pits, the remains of wood tar production using the so-called ‘vessel-less method’, were discovered in the Lublin region. They contained objects related to the early Middle Ages. These discoveries were used as the base for experiments run in 2013 in the experimental archaeology centre at Grodzisko Żmijowiska. The first experiment involved the acquisition of wood tar from birch bark, while the other attempts were aimed at extracting tar from pine stumpwood. The experiments were conducted in a shallow pit that was plastered with clay and had a small depression at its bottom used as a container for the tar, separated from the pit by a clay strainer. The raw material gathered in the pit was covered with a clay dome. When the dome was dry, it was slowly heated up with burning wood to the right temperature which was checked inside the dome with a thermocouple. Both processes were conducted successfully. The results were compared with experiments focused on the production of wood tar using the two-vessel method known in the early Middle Ages. The comparison showed that the vessel-less method is less economical due to the amount of fuel used and almost three times less efficient in terms of the raw material to final product ratio. However, it is very simple technically and allows the effective production of wood tar.