**3. Gold Amalgam, Mercury Gilding Process, and Surface Treatment of Metal Buddha Statues**

Gold amalgam, commonly known as gold mud in China, is an alloy product formed by combining gold with metal mercury, which has good chemical activity. Mercury has a shiny silvery color and is present as a heavy liquid at room temperature and pressure. Mercury is copper- and sulfur-loving in nature, so most of it is distributed as mercury sulfide. Natural mercury sulfide was once used as a red pigment by ancient people because of its bright red color. Unearthed wooden bowls from the Hemudu culture period were

coated with substances such as these, suggesting that natural synthetic oils were used in China at least 6000 years ago (Wang and Wang 1999, p. 40). In addition, natural gold also generally contains mercury. Metallic mercury can be obtained through the calcination of mercury sulfide, or the collection of vaporized mercury vapor and condensation, which was the main method of extracting mercury used by ancient people. Gold leaf unearthed in Shuangdun Tomb No. 1 in Bengbu, Anhui Province, in the late spring and autumn periods (770–476 BCE) may be the earliest physical evidence of gold extraction using mercury mixing technology at home and abroad (Qin et al. 2011, pp. 95–96).

The ancient gold amalgam was mainly used as a special coating for the surface treatment of metal objects and was the key material for the invention and application of mercury gilding technology. When using mercury gilding technology, the gold leaf is cut up at first. Under a high temperature of 400 ◦C, the gold leaf is mixed with molten metal mercury to produce gold amalgam. With the gold amalgam wholly or partially coated on the surface of metal objects, through heating, the mercury evaporates when it is heated, while the gold remains on the surface of the objects. Because of the difference between the thickness of the application of gold amalgam and the baking temperature, the surface of each part of the object will appear inconsistently gold. In this case, when the mercury-gilded implement is preliminarily finished, a standard gold color needs to be chosen. Each part is subject to this accordingly. Through repeated mudding and baking a number of times, the mercury-gilded color of the whole object is unified. Finally, an agate knife with a higher hardness is dipped in saponin water and then pressed and polished back and forth evenly on the surface (H. Wang 1984, pp. 57–58). The advantage of this method is that the tiny glume formed by the evaporation of mercury can squeeze out the tiny gap left on the surface, meaning that the gold layer can be firmly combined with the body, increasing the surface brightness and the ability of the mercury-gilded implement to reflect light. The truth is its appearance is almost the same as that of pure gold. The mercury gilding process saves a large amount of gold, which can not only protect the surface of metal objects from oxidation for a long time, but also improve the visual beauty of the objects.

Mercury-gilded implements can only be determined by analyzing the uniformity of the gold amalgam and the heating traces between the gilded gold layers through the detection capabilities of scientific instruments. Under this standard, it could be inferred that Chinese mercury gilding technology had already appeared in the late Warring States period (475–221 BCE) and developed dramatically afterwards (Xu and Yang 2017, p. 72). According to the existing archaeological data, nearly 40,000 mercury-gilded artifacts from the Qin and Han Dynasties (Jiang 2015, pp. 215–16) have been unearthed, mainly including five types of small artifacts, such as human body ornaments, chariot and horse implements, weapons, daily utensils, and utensil components. Beyond that, the world's first gold amalgam was discovered in the Western Han Dynasty (206 BCE–25 CE) Tomb No. 2 in Shuangbao Mountain, Mianyang, Sichuan, China (He et al. 2007, pp. 44–50). The above data apparently prove that China's mercury gilding technology was an indigenous and independent development. The upper nobles once monopolized Chinese ancient mercurygilded technology. Their noble and prominent social status was highlighted through the production of mercury-gilded utensils, in fact. In addition to small mercury-gilded objects, the mercury-gilded bronze horse unearthed in Maoling, Shaanxi Province, and the mercurygilded bronze human-shaped lamp unearthed in the Han Tomb in Mancheng, Hebei Province, both showed that the Western Han Dynasty already had the ability to produce mercury-gilded utensils with a larger size and complex structure (see Figures 3 and 4).

**Figure 3.** Gilded bronze horse from the Western Han Dynasty. Materials: gilt bronze. Dimensions: H. 62 cm x W. 76 cm. Displayed in Maoling Museum, Shanxi Province, China. Photo source: the official website of the Suzhou Museum.8.

**Figure 4.** Gilded bronze human-shaped lamp from the Western Han Dynasty. Displayed in the Museum of Hebei Province. Photograph taken by the author.

During the Eastern Han Dynasty, the Han Dynasty had already made contact with Buddhism. It is recorded in the Annals of the Three Kingdoms: the Biography of Dongyi in the Book of Wei that in the first year of the Yuan Shou (2 BCE) of Emperor Ai (25–1 BCE) of the Han Dynasty, Yicun, an envoy of the Kushan Empire of the Western Regions, came to China and dictated the Pagoda Sutra to Jinglu, an official of the school, in Chang'an, the capital of the Han Dynasty (Treatise on the Three Kingdoms Vol. 12 History of Wei. Dongyi zhuan, S. Chen 1936b, p. 120). Emperor Huan (132–168) cast a gold pagoda, the Laozi statue, covered with a treasure canopy, which was placed in the palace shrine (Kasyapa Matanga 1924–1934, p. 767). This illustrates that gold was used in the imperial court to produce special items for Buddhist sacrifices. According to the Annals of the Three Kingdoms, it was recorded that, from the end of the Eastern Han Dynasty to the Three Kingdoms period (c. 220–265), there was a local despot called Ze Rong (?–195) in Xiapai County

(now Xuzhou, Jiangsu Province). He "established Fu Tu Temple. The statue was made of bronze and painted with gold" (Treatise on the Three Kingdoms, Vol. 17 History of Wu. Liuyao zhuan, S. Chen 1936a, p. 5). This was the earliest record of a mercury-gilded bronze Buddha statue in ancient Chinese literature and might also be the earliest use of local, mature mercury gilding technology to treat the surface of a metal Buddha statue. In 1902, Tatsunobu Watanabe et al. of the Japanese Otani expedition team found several broken mercury-gilded statues in a temple in Hotan Prefecture, Xinjiang, China (Seiko 2014, p. 146). One of the mercury-gilded bronze Buddha heads, with a height of 13.7 cm, was believed to have been an imitation of the Gandhara style by local artisans in the second half of the 3rd century. Indeed, this place was an important area of ancient Buddhism in its spreading east, named Khotan, where mercury-gilded Buddha statues possibly entered the Central Plains. In the Sixteen Kingdoms of the Wei and Jin Dynasties (220–439), small standing or seated mercury-gilded Buddha statues gradually appeared in the Central Plains, which were either imported from the western regions or imitations from the Han region. There are presently about 40 representative works in existence (F. Zhang 2018, p. 98). Among them, in San Francisco, United States of America, is the mercury-gilded bronze Buddha statue produced in the Later Zhao Regime (319–351), the fourth year of Jianwu (338), displayed in the Asian Art Museum; it is 39.7 cm high and the earliest Buddha statue in China (see Figure 5). From the literature and existing objects, it can be confirmed that gilded Buddha statues were a common decoration technology in the eastward spread of Buddhism.

**Figure 5.** Gilded bronze Buddha from the Later Zhao Dynasty. Materials: gilt bronze. Dimensions: H. 39.7 cm × W. 24.1 cm × D. 13.3 cm. Displayed in the Asian Art Museum of San Francisco, San Francisco, United States of America. Photo source: the official website of the Asian Art Museum of San Francisco9.

In the Northern and Southern dynasties, when Buddhism was constantly communicating, absorbing, and digesting, the production of mercury-gilded Buddha statues began to flourish, and it has been prevailing and continuing to this day, occupying the mainstream position of mercury-gilded utensils for a long time. The invention of mercury gilding technology is actually an innovation of the surface treatment technology for metal implements, which balances the relationship between the surface treatment of implements and the efficient utilization of gold materials. However, with the prosperity of Buddhism in China, devout believers, especially the emperor, who possessed metal resources, also joined the ranks of those producing Buddha statues, and the number and volume of metal Buddha statues continued to increase. According to historical records, the Ming Emperor

of the Song Dynasty in the Southern Dynasty (420–589) produced a fourteen-foot gilded Buddha statue (Biography of Eminent Monks, Shi 1992, p. 493), while Emperor Xianwen of the Northern Wei produced a giant standing statue of Sakya, "with 100 thousand jin of bronze and 600 jin of gold" (History of the Wei Dynasty, vol. 114. Shi Laozhi, Wei 1997, pp. 3037–38). In the book "*A Record of Buddhist Monasteries in Luo-Yang*" from the Northern Wei Dynasty, there were more than 1000 temples in the city of Luoyang. In the largest Yongning Temple, there were over 40 gilded bronze Buddha statues (Yang 2006, pp. 1–2, 124–25). Moreover, the Buddha statues of the Southern Dynasty flourished during the reign of Emperor Wudi (464–549) of the Liang Dynasty (502–557). During his forty-eight-year reign, it could be said that the emperor ruled the country with Buddhism, with numerous Buddha statues made of gold, silver, and bronze (Tang 1997, pp. 384–85). The mercurygilded bronze Buddha Maitreya statue of the tenth year of Taihe (486) from the Northern Wei Dynasty is displayed in the Metropolitan Museum of Art, New York, USA. It is 140.3 cm high and known as the biggest statue of its kind at present (see Figure 6). Casting a large metal Buddha statue in ancient times, whether using the casting method or the lost-wax method, was an extremely expensive and complex project in terms of labor and material. This, in turn, increased the consumption of gold, mercury, and metals such as bronze and iron. Before the introduction of Buddhism to China, the main users of mercury gilding technology were members of royalty, which then changed to Buddhist temples. At the same time, the main objects of decoration also changed, from five types of small artifacts, such as human body ornaments, chariot and horse implements, weapons, daily utensils, and utensil components, to medium- and large-sized Buddhist statues10. This reflects the influence of the introduction of Buddhism on the application of metal processing technology in China and the distribution of social metal resources.

**Figure 6.** Gilded bronze Buddha Maitreya from the Northern Wei Dynasty, 10th year of Taihe reign. Materials: gilt bronze. Dimensions: H. 140.3 cm × W. 62.2 cm × D. 48.9 cm. Displayed in the Metropolitan Museum of Art, New York, United States of America. Photo source: the official website of the Metropolitan Museum of Art (Leidy and Strahan 2010, p. 59).
