Located in Baofeng County, Henan province, Xiaolizhuang site occupies approximately 1000,000 m2 of land and was listed as one of the national protective heritage sites in 2013. With a 4600 years history, Xiaolizhuang site reserves numerous ancient ruins dating from the Neolithic Age to the Northern and Southern Dynasties (AD 420–589). The first excavation of the site was carried out in 2008 which unearthed various cultural relics including potteries, ceramics, copper wares, iron wares, stone wares, bone artifacts, etc. In 2017, the second excavation was performed jointly by Pingdingshan Bureau of Cultural Relics and University of Zhengzhou. A Tang Dynasty tomb was discovered by coincidence for the first time. It was initially overlooked due to its low status appearance and the difficulty in identifying the female tomb owner due to the damaged epitaph. Only a few potteries, bronze and iron utensils were extracted along with several metal accessories such as hairpins. Among them, a delicate silver artifact which appeared to be a female cosmetics case drew the attentions of the archaeologists. The silver case exhibits a diameter of approximately 3.3 cm and height of 1.55 cm. It consists of two symmetrical pieces of flower-shaped silver and locked by a buckle. The surface is fully decorated with multiple fine carvings which were likely made by experienced silversmith. In the Tang Dynasty, potteries, bronze and iron wares were available to a wide range of people, however, silver objects especially the elaborate ones were reserved for elites to represent their high social status [1]. In other words, the owner of this silver artifact was likely to be a woman of high social status which leaves behind a mystery on the tomb owner’s identity.
Silver is one of the precious metals used by early civilizations to produce ornaments, jewelry and coins, therefore, silver artifacts represent the material cultural heritage of certain periods [2]. Numerous studies of ancient silver artifacts were reported in scientific literatures. The main areas of research are the investigation of provenance [3,4,5], chemical composition and microstructure [6,7,8,9,10] and manufacturing processes [1, 11,12,13]. In ancient China, the sophistication and the technical skills in metalworking of gold and silver artifacts reached its peak in the Tang Dynasty. According to the literatures [14, 15], the various techniques include primarily casting, hammering and annealing, plastic forming, engraving, embossing, granulation, joining techniques and gilding [10, 16, 17]. In general terms, shaping was the basis of metalworking which commonly achieved by utilizing hammering or casting. During the processes of hammering, repeated hammering and annealing were applied to flatten silver metal into desire form [11, 12] and consequent plastic forming was employed to further modify the shape. In addition to hammering, casting was a popular method that involved using a certain mould to form the desired shape of the object. It is believed that the western style hammering was introduced to China in the Tang Dynasty which advanced the local metalworking techniques [18]. Since then hammering presumably became more prevalent than casting in the manufacturing process. After the completion of shape, engraved decorations were subsequently made on the surface of the item by utilizing a set of gravers. To finalize the artifact, gilding was sometimes applied to leave a shiny appearance.
Apart from the written source, numerous silver artifacts were excavated from tombs of the Tang Dynasty over the years. Some limited studies with focusing on the surface design [19,20,21,22,23,24,25] and chemical composition [6] were performed, however, the surface features and manufacturing marks that essential for understanding the metalworking techniques [13] were often overlooked. Tan’s team has done a great job on studying the silver artifacts from the Wei family tomb of the Tang Dynasty [26]. The research provided information on the material features and manufacturing techniques in making those silver wares. However, various metalworking techniques might be used in the Tang Dynasty, it requires more homogeneous studies to reveal the sophisticated skills. In this paper, the microstructural analyses were conducted on the silver artifact excavated from the Tang Dynasty tomb of Xiaolizhuang site. Since sampling is strictly forbidden, the noninvasive approach including microscopic analysis and SEM–EDS analysis was employed to identify both the microstructure of the silver box and the elemental compositions. The metalworking techniques including hammering, plastic forming, engraving and gilding were proved to be used in making the artifact. The results overall provide direct source in understanding the metalworking of silver in the Tang Dynasty.