Effect of rust due to freshwater on the provenance determination of unearthed iron artifacts using nondestructive X-ray fluorescence spectrometry.

We examined the effect of rust due to freshwater on the provenance determination of iron artifacts, which is typically conducted based on elemental concentrations determined using nondestructive X-ray fluorescence (XRF) spectrometry. This was achieved by comparing a rusted iron sickle collected from farmland in Fukuoka, Japan before and after rust removal. The data were collected at 30 positions on the surface of the sample using nondestructive XRF spectrometry before and after rust removal. The concentration distributions of all elements in the sample before and after rust removal were considerably different. The escape depths of the fluorescent X-rays were calculated based on the median chemical composition of the rusted sample and then compared, and the rust thickness was estimated based on the sample thickness before and after rust removal. The fluorescent X-rays emitted from the sample, except Ba Kα, reflected only information from the rusted part not the uncorroded metal part. The As/Sb scatter plots, which are often used in provenance determination of iron artifacts, were created to compare the sample before and after rust removal. The As/Sb values measured at 30 positions after rust removal were normally distributed, whereas those measured before rust removal were not. Similarly, the scatter plots obtained in both cases exhibited different distributions. Therefore, the provenance determination of ironware using nondestructive XRF spectrometry would be affected by its rusting due to freshwater.