Monitoring Aging Behavior of Traditional Natural Dye Extracts Using Portable Fourier-Transform Infrared Spectroscopy: A Basis for Future Non-Destructive Analysis of Dyed Cultural Heritage

In this study, a portable Fourier-transform infrared (FT-IR) spectrometer was used to record the spectra of five traditional Korean dye powders, namely, sappan wood, Amur cork tree, indigo, acorn cupule, and gallnut, before and after accelerated aging under three conditions: ultraviolet irradiation, dry heating, and wet heating. Measurement reliability was verified by comparison with a benchtop FT-IR spectrometer. The results revealed that the sappan wood extract exhibited structural changes in carbonyl groups and phenolic substituents during aging, whereas the Amur cork tree extract exhibited variations in C–N skeletal vibrations under all aging conditions. The indigo and acorn cupule extracts exhibited high stability, with negligible spectral changes. In contrast, the gallnut extract exhibited significant structural alterations only during wet thermal aging, demonstrating the hydrolysis of tannin into gallic acid. These findings demonstrate that a portable FT-IR spectrometer can effectively and nondestructively characterize the composition and aging-induced degradation of natural dye powders, providing a foundational spectral reference for future nondestructive investigations of dyed cultural heritage objects. Further research incorporating dyed textile substrates and other dyestuffs is recommended to expand the spectral library and validate its applicability to actual heritage artifacts.