Microstructural characteristics and formation of the gilded artifacts excavated from Han Tomb situated in Qufu, Shandong, China

This study aims to investigate the metallurgical techniques of the gilded artifacts excavated in Tomb M3 of King Lu, a ruler in China's Western Han Dynasty. The 14 samples were examined by metallurgical microscopy, SEM-EDS, and FIB-SEM-EDS. The analysis of elemental composition and microscopic morphology confirms that all 14 artifacts were coated with mercury gilding. The thin cross-section of the gilded layer displays a three-tiered structure. The lower layer, adjacent to the copper substrate and consisting of nanoscale grains, is hypothesized to be composed of the intermetallic compound AuCu. The upper layer is constituted of nanoscale grains. The middle layer exhibits coarse, equiaxed, and twinned crystal grains. It is conjectured that the principal phases of the upper and middle layers are the FCC structured terminal substitutional solid solution of gold, Au (Hg). The 14 samples can be classified into three categories, epitomizing diverse gilding techniques and varying skill levels.