Revealing the manufacturing and corrosion characteristics of Chinese archaeological metal arrows by non-destructive neutron techniques

The manufacturing and corrosion properties of metal artefacts are significant for archaeologists and conservators. In this study, non-destructive neutron-based techniques are applied on ancient copper-iron arrows. The archaeological samples were excavated from a Western Han tomb (202 BC - AD 8) near the Han Chang'an city site (the capital of Western Han dynasty) in China. This is the first time that the combination of neutron resonance capture analysis, neutron diffraction, neutron tomography, and Raman spectroscopy has been used in Chinese cultural heritage to obtain useful information about the arrows. The results indicate that one arrowhead is made of low-Sn, high-Pb bronze, while the other is composed of high-Sn, low-Pb bronze. These analyses also reveal the production method of these arrows, with the iron tangs likely being cast first and then connected to bronze arrowheads through casting. Furthermore, due to the variations in materials used, certain parts of the arrows were more susceptible to corrosion than others; specifically, those made of pure iron were more prone to corrosion than their bronze counterparts. Additionally, it is confirmed that the iron inside the arrowhead corroded less than the visible iron tang at its base. The corrosion products include cuprite, goethite, hematite, magnetite, cerussite, azurite, malachite and lepidocrocite. These findings are highly beneficial for understanding the making techniques, as well as conservation state and corrosion products associated with archaeological arrows.