Earliest use of birch bark tar in Northwest China: evidence from organic residues in prehistoric pottery at the Changning site

The analysis of organic residues in pottery can provide abundant information on the lives of ancient people, including the natural resources consumed, the techniques applied, the functions of pottery, and so on. In this paper, a variety of methods, including FT-IR (Fourier transform infrared spectroscopy), GC–MS (gas chromatography-mass spectrometry), SEM (scanning electron microscopy) and SR-μCT (synchrotron radiation micro-computed tomography), have been employed to characterize the carbonized residues from an amphora, unearthed from the Changning site, Qinghai Province, Northwest China. The pottery residues were identified as birch bark tar, so ancient people in China could have used the particular local plant resources, birch bark, to produce tar as early as the Qijia cultural period (c. 4,000–3,500 bp). The birch bark tar could have been used to make composite tools discovered at the Changning site, and the amphora has probably been used for tar production. This, to our knowledge so far, is the earliest evidence for the use of birch bark tar in China. Due to the special geographical location of the Gansu-Qinghai Region, and the transition of subsistence strategy during the Qijia cultural period, the production and utilization of birch bark tar could not rule out the possibility of western influence, which needs further evidence.