Research on the micro-structure and water effect of excavated ivory from sacrificial pit No.7 at the Sanxingdui Ruins

Abstract The excavation of ivory and other artifacts from the Sanxingdui Ruins holds profound research significance in tracing of both the ancient Shu and Chinese civilizations. After being unearthed, a large quantity of ivory encountered issues such as dehydration, pulverization, and cracking, resulting from poor preservation conditions. To establish effective long-term conservation strategies for the excavated ivory, this paper takes the dentin of excavated ivory from the No.7 Sacrificial Pit (K7) at the Sanxingdui Ruins as the research object, focusing on the primary correlation between its microscopic porous structure and moisture states. The results show that the organic collagen protein component of the excavated ivory has already undergone basically diagenetic degradation. The remaining main mineral phases are hydroxyapatite and carbonated hydroxyapatite, exhibiting a mixed crystal structure with mainly needle-like and secondary lamellar. The porosity of the excavated ivory, as measured by dry and wet methods, is approximately 62 and 60%, respectively. The pore size distributions are primarily concentrated in the ranges of 5–100 nm for the dry method and 10–200 nm for the wet method. These diverse and heterogeneous pore structures store approximately 35–38% of water as free water and adsorbed water. Free water is primarily found in dentinal tubules, interlayer gaps and cracks, providing volume support and stabilizing equilibrium with the external environment. Adsorbed water is mainly present in the pores (d < 100 nm), providing support function through intermolecular forces and hydrogen bonding. The deterioration of excavated ivory is positively correlated with the loss of moisture. This is due to irreversible structural damage caused by the loss of water’s supportive, bonding, and stabilizing effects. Among them, the rapid migration and evaporation of free water affect the expansion of cracks and the formation of new fissures. This study offer a robust scientific basis and valuable insights for the subsequent conservation of excavated ivory, and also provide guidance for the research of other fragile bone and horn relics.