Production Techniques and Microstructures of Copper Granule: Experimental Analysis and Archaeological Case Study

摘要

Granulation is a decorative technique for metalwork where tiny granules are used. Recent discoveries in China confirmed that pure copper granulation was employed as early as the seventh century CE. However, the production techniques for copper granule are still unknown. Herein, a systematic study is carried out to produce pure copper granules by using "pouring method", "heating method", and "crucible method" to investigate possible techniques of ancient times. The results reveal that copper granules can be produced by the same methods for ancient gold and silver granules. Furthermore, the granule rate during the pouring method is mainly influenced by the cooling media. In addition, the cooling rate and oxygen content significantly affect the microstructure of copper beads. Moreover, metallographic analysis of two archaeological granulated copper pieces of the seventh century CE is carried out to compare the microstructure of copper granules by different simulation experiments. The microstructural analysis indicates that the two ancient copper granules were most likely produced by the crucible method, which is also a preferred choice from the viewpoints of mass production and precise control of granule dimensions. The paper provides a point of departure for future research on the utilization of copper granules in ancient times.