The Palace Museum houses seven Qing Dynasty copper statues of immortals, six of which are covered with an unusual black substance rarely observed on the surface of copper artifacts. In this study, a statue of an immortal holding a Yuanbao and riding a Qilin was selected as the research object. The black substance on its surface was analyzed using a range of analytical techniques. The results indicate that the black substance is a mixture of carbon black, natural waxes (insect wax and beeswax) and natural resins (shellac and rosin), suggesting that it represents an intentionally applied decorative and protective surface layer. Based on the historical use and physicochemical properties of these four natural substances, it is proposed that shellac and rosin functioned as adhesive components, beeswax represented the molding material from the lost-wax casting process remaining on the artifact surface, and insect wax was applied to enhance the luster of the black layer. In addition, the preservation status of the artifacts was evaluated, the causes of localized corrosion were analyzed, and corresponding suggestions for the preventive conservation of similar artifacts are proposed.