Studying archaeological iron corrosion in the ground – Sample handling to avoid undesirable changes

Abstract

This paper evaluates sampling and storage methods for the study of iron archaeological artifacts, aiming to minimize unwanted changes. The selected methods will be used to handle samples in multiple studies utilizing neutron and X-ray computed tomography (NX-CT) to monitor 3D transformations in artifacts during time series experiments. It is thus important to keep full control of the parameters that could induce such changes.

Two main approaches were tested: 1. imaging iron nails with their surrounding soil to maintain quasi-in-situ conditions and 2. imaging iron nails with a limited amount of soil to improve imaging resolution, also applicable for fully excavated nails. The highly variable soil moisture levels caused option 1 to be discarded, due to difficulties in reconstructing the tomograms. For the nails from setup 2, image reconstruction was successful. Additionally, to prevent unwanted changes occurring during storage, various short-term anoxic storage options were tested. Results showed that keeping the samples in Intercept® bags with RP-K oxygen scavengers and shortening the waiting time between experiments effectively minimized alterations like moisture loss, microcracks, and material displacement. In contrast, prolonged storage in the imaging sample holder caused noticeable unwanted changes.

The findings emphasize the importance of optimized handling and storage to distinguish changes caused by external factors of interest. These protocols ensure accurate assessments of post-excavation conditions and conservation treatments, providing valuable insights into the preservation of archaeological iron artifacts and advancing the study of long-term corrosion processes.