Progress or compromise—technological investigation of the transition zone of metal chaplets in ancient Chinese bronzes

Metal chaplets were frequently used in ancient Chinese bronzes from the Shang Dynasty to the Warring States. The use of chaplets has been regarded as technological progress for a long time; nonetheless, this research shows a transition zone of oxidation between chaplets and metal bodies formed during the solidification of bronzes which negatively impacts these bronzes. To date, the transition zone has attracted very little research attention. The scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM-EDS) analysis on elemental composition and metallographic investigation of the transition zone were carried out in a reconstructed bronze tripod. It was found that the transition zone mainly consisted of copper oxides, which is further demonstrated as cuprous oxide by X-ray diffraction (XRD). It appears to be formed during the solidification process due to the high-temperature and low-oxygen environment. The existence of the transition zone possibly led to preferential corrosion during usage, and thus caused the shedding of chaplets and damage the integrity of bronzes. The existence of this inevitable transition zone indicates the occurrence of inherent defects in the metal chaplet technology. Although this technology can improve the casting success rate and is progress in social production, it can also affect the integrity of bronze and is a compromise of the bronze casting technology itself.