Fig. 1

Experimental set up for the aceramic birch tar making experiments. a Condensation method using several stones simultaneously and the resulting tar (b); c two raised structures during construction. Birch bark rolls are placed on grates bade from fine sticks. The lower chamber is covered by aluminium foil to minimize loss of the tar; d finished raised structure with the sediment covering the bark rolls; e tar produced in one of the raised structures, still adhering to the aluminium foil receptacle