Time-Gated Raman Spectroscopy Decodes Degradation Pathways in 3,000-Year-Old Ivories: A Fluorescence-Free Approach to Heritage Science

Archaeological ivories are of great cultural significance but pose analytical challenges due to heterogeneous surface composition and intense fluorescence. In this study, 532 nm time-gated Raman spectroscopy was employed to overcome these limitations, enabling high spatial resolution and effective fluorescence suppression for detailed compositional analysis. Four ivory samples from Sacrificial Pits No. 3 (K3) and No. 7 (K7) exhibited markedly different preservation states. K3 samples showed evidence of copper corrosion, lower fluorescence intensity, and greater calcium loss, while K7 samples suffered from more severe sulfate-driven hydroxyapatite degradation. Sulfate substitution was found closely associated with phosphate peak broadening and surface discoloration, identifying it as a key indicator of mineral deterioration. Residual protein was detected in all specimens, with K3 samples retaining higher nitrogen content. These results demonstrate the strength of time-gated Raman spectroscopy for nondestructive, spatially resolved analysis of ancient ivory and reveal degradation pathways shaped by burial microenvironments─offering essential insights for the scientific conservation of archeological ivory.