Rich mineral resources and lenient policies facilitated the mining and smelting of silver during the Tang dynasty. The record shows that the government allowed private silver mining and more than 58 silver mines were operating under the tax revenue system . Also, large amounts of silver were shipped from different parts of the country to the central government and the imperial family . The analysis of a silver smelting relic found in Hejiacun treasure shows that the percentage of Ag was much low, which indicates that the silversmiths were able to smelt high-quality silver during the Tang dynasty . Figure 6 shows that most of the silver items possess a high percentage of Ag (> 80 wt. %) [8–10, 19–28]. Herein, the composition of the studied silver box and other silver fragments from the pagoda crypt [20–22] are overlapped with most of the data from the places outside the Famen Monastery (Fig. 6). Besides, in addition to the currently studied silver box, the presence of Pb has been reported in the silver objects uncovered from the Shaanxi province, including the tomb of Prince Li Xian, the joint tomb of Yanzhi and his wife, the tomb of Princess Li Chui, the Tang tomb of Yuanzitou site, and tombs in southern suburbs of Xi’an, from Sichuan province, i.e., Zhengkejiaxiang site, and from Xinjiang Uygur Autonomous Region, i.e., gilded silver ornaments collected in Yili Museum [22, 26]. Hence, it can be inferred that the cupellation was commonly used in silver smelting during the Tang dynasty.
Apart from the base composition, Ag, Cu and Zn were identified in the joining area between the box body and ring foot. However, there has been no ancient written record and scientific data on the utilization of silver-based solder during and before the Tang dynasty. Only two fluxes for promoting soldering silver were mentioned, i.e., Hutonglei (a glue gum from Populus diversifolia) and Lusha (NH4Cl) [29, 30]. The historical record and analytical data of silver objects after the Tang dynasty indicate the employment of silver-based solders. At the joining area of a silver artifact of the Liao dynasty (916–1125 CE), Ag–Cu alloy was detected as a solder .
In addition to Ag–Cu alloy, the literature of Qing dynasty (1636–1912 CE) recorded that Ag–Cu–Zn alloy was employed as a solder for copper objects [32, 33]. In modern metallurgy, Ag–Cu–Zn alloy is used to bond silver objects . In the case of currently studied silver box, the content of Zn in the joint was found to be 2.5 wt. %. One should note that the Ag–Cu–Zn alloy has a melting point of ≈ 755 ℃. If the influence of Zn is ignored, the Ag–Cu alloy has a melting point of ≈ 785 ℃ . The small temperature difference of 30 ℃ does not worth the artificially alloying of zinc with Ag–Cu alloy by the Tang silversmiths Therefore, the Ag–Cu alloy should be employed by the ancient artisan to braze silver box and ring foot, and the occasional smelting of copper introduced the Zn impurities.
Remarkably, the repoussé, tracing and fire-gilding were employed to create and decorate the motifs of the box. These techniques were commonly used on the Tang’s silver vessels. The published technical analyses of silver vessels from the Wei family cemetery and Xiaolizhuang site in northern China also demonstrate these techniques. In the Wei family cemetery, a silver cup indicates the utilization of tracing technique to create motifs, a small round silver box applied tracing and partial fire-gilding to create and highlight the motifs, and a three-legged silver pot employed repoussé to shape the pot and tracing and partial fire-gilding to create and decorate the motifs . Moreover, a silver box from the Xiaolizhuang site used repoussé to shape the box, and tracing and all-over fire-gilding to produce and decorate the motifs .
In addition, the ring-matted background was also present on the aforementioned silver vessels. Figure 7 shows the diameter distribution of the rings of the ring-matted backgrounds, which are decorated on the silver cup from the Wei family cemetery, the all-over gilded box of Xiaolizhuang site and the currently studied gilded silver box. The statistical analysis reveals that the ring diameter on three vessels exhibits a small standard deviation, which indicates that the skilled silversmith of the Tang dynasty was able to accurately control the ring size during the rapid tracing process. More strikingly, the ring diameter was closely related to the size of the vessel. To be specific, the gilded silver box of Xiaolizhuang site has the smallest dimensions (3.3 cm in diameter and 1.55 cm in height). It was decorated with a ring-matted background with the smallest diameter of the ring (average diameter: 0.50 mm) , whereas the silver cup from the Wei family cemetery has medium dimensions (5.2 cm in diameter and 4.5 cm in height). It was decorated with a ring-matted background with a medium ring diameter (average diameter: 0.71 mm) . Lastly, the partially gilded silver box has the maximum dimensions (17.3 cm in length, 16.8 cm in width and 11.2 cm in height), and it was decorated with a ring-matted background with the maximum ring diameter (average diameter: 0.87 mm) (Fig. 7). These results indicate that the silversmiths during the Tang dynasty were experienced in choosing the different sizes of chisel for tracing rings according to the dimensions of the artifacts.
Though the silver vessels from northern and southern regions were prepared with the same techniques and decorative elements, the comparison of their technical details suggests that the southern-origin silver box from the pagoda crypt of Famen Monastery employed more sophisticated technology. The ring-matted backgrounds on the silver box and pot from the Wei family cemetery and the silver box from the Xiaolizhuang site were quite rough and the rings were overlapped under the microscope. One should note that the rings overlapping was so severe, especially the rings on the small round box, that the single ring was difficult to be recognized [8, 9]. Besides, the silver cup of the Wei family cemetery and the currently studied silver box (Fig. 4d and e) do possess distinct ring-matted backgrounds, however, the latter contains a more regular ring arrangement . In addition to the ring-matted background, the details of the traced motifs also reflect different technical skills. In the case of silver vessels from the Wei family cemetery, the triangular tracing marks on the silver cup are deep, however, the lines made up of isosceles triangles are unsmooth and these triangles are unevenly spaced. The tracing marks of main motifs on the three-legged pot are also different, while the tracing marks of other motifs are blurred. In addition, the triangular tracing marks on the small round box could be recognized in the main motifs, but the traced line on the rim is indistinct and unfinished . With respect to the silver box of the Xiaolizhuang site, the traced marks are shallow and some are even out of shape . In the case of partially-gilded silver box from the Famen Monastery, the tracing lines are smooth and triangular marks are clear and deep (Fig. 4a, d, and f).
According to the inscription and inked Neiku on the Famen gilded silver box, it could be speculated that the box was first produced in Jiangnanxidao and, then, it was presented by official Li to the Emperor for the Yanqing Festival and collected in Neiku. Finally, along with other treasures, the box was donated to the true body relic in Famen Monastery. Therefore, it is reasonable to assume that the silver box was made by the most experienced silversmith in the southern region. Overall, these observations confirm that the silver technology in the southern areas of the Tang dynasty was well developed.
Perspective on the manufacturing of southern-origin silver box of the Famen Monastery
Based on the above discussion, it can be concluded that same techniques were employed in the southern-origin silver box and the northern-origin silver vessels, however, the former demonstrated more exquisite decorations in terms of technical details. It is undeniable that the lions’ decorated box must be made by the most skilled silversmith in the southern region as a gift for the Emperor, however, it is also true that the southern vessels of the late Tang dynasty must be exquisite enough and even more delicate than the northern silver vessels to be loved by the Emperor. The appearance and rise of the most sophisticated southern-origin silver vessels derive from the political and social backgrounds.
Before the mid-8th century CE, frequent interactions with the west strongly influenced the design and manufacturing of silver vessels in China, especially Persia, Sassanian and Sogdian . During the early Tang dynasty, silver was partially imported and processed by foreign metalsmiths living in China . The members of the Royal family and nobles were the major customers of these delicate silver artifacts. Therefore, the Chang’an region is considered as the manufacturing center of silver artifacts during the early Tang dynasty. Subsequently, the raw silver was shipped to the Chang’an region from different suppliers and the skilled craftsmen congregated here to utilize their talent . The silversmiths of this period employed the foreign techniques and further developed them to the greater perfection, resulting in some innovative forms due to the combination of foreign and traditional methods , such as the treasures of Hejiacun hoard in Xi’an .
However, the situation changed after the mid-8th century CE. The political and economic downfall in northern China due to the An Lushan rebellion resulted in the migration of businessmen and official artisans towards the south . It is worth noting that the south contained abundant gold, silver and lead resources, which are the major raw materials for the production of gold and silver vessels. Gold production accounted for 92 %, whereas silver production accounted for 94 % during the Tang dynasty [1, 39]. The increase in commercial activities shifted the manufacturing center of gold and silver from the north to south . The written record shows that five regions in the south, including Jiangnanxidao, frequently presented gold and silver artifacts to the imperial court . In terms of decorations on silver artifacts, some southern-origin silver vessels after the mid-8th century CE have very similar decorative styles to the silver vessels recovered in the north before the mid-8th century CE, e.g., ring-matted background.
On the other hand, the northern-origin silver vessels after the mid-8th century CE contained simple decorations. For instance, the silver vessels produced by the Wensiyuan were without decoration or with gilded motifs on a smooth background . However, from a technological perspective, the same motif expressions were utilized by silversmiths in both north and south regions, where the main motifs were highlighted by a combination of repoussé and gilding techniques. In summary, the manufacturing of southern-origin silver vessels after the mid-8th century CE was far more delicate and diverse, inheriting the decorative techniques of the northern-origin silver vessels before the mid-8th century CE.