Ahmad N. Abu-Baker – The use of MiCorr application to diagnose the corrosion of archaeological brass artefacts from Jordan
Host: Haute Ecole Arc Conservation-restauration, Neuchâtel, Switzerland
June 1 to 9, 2023
In this STSM, the computer-based Decision Support System (DSS) MiCorr tool was used to create stratigraphic representations of the corrosion structures of two copper-alloy artefacts from Jordan, a buckle and a button. They are part of a metal artefacts collection excavated in 1996 from the Byzantine cemetery at the Khirbet Yajuz archaeological site in Jordan, and currently stored in the storage area of the University of Jordan Archaeological Museum (UJAM) in Amman.
The process included six steps; the first was determining the study areas of each artefact for the non-invasive and invasive analytical techniques. The second step included observing the artefacts and their corrosion forms with the aid of a binocular microscope and creating a conceptual representation of their corrosion stratigraphy. The third step was creating a digital representation of the corrosion products (CP) strata from the binocular observation using the MiCorr modelling programme. Then, in the fourth step, the two artefacts and the prepared and polished cross-section samples taken from them were analysed. The non-invasive X-ray fluorescence (XRF) analysis was carried out on the surface of the artefacts, and the invasive optical microscopy (OM) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) were conducted on the cross-sections of the artefacts to reveal their composition, microstructure, corrosion characteristics, and elemental distribution in the corrosion layers and original alloys. The XRF and SEM-EDS results showed that the buckle is a quaternary alloy of Cu-Zn-Sn-Pb, while the button is a brass alloy (Cu-Zn). The OM examination results of the etched cross-sections showed an as-cast dendritic microstructure for the buckle with strain lines, suggesting that it was cold-worked without annealing, while the button was annealed as indicated by its recrystallized microstructure and annealing twins. The SEM-EDS, EDS elemental mapping and OM investigation of the corrosion stratigraphy of the two artefacts showed the presence of an external soil layer (S1) containing elements of soil deposits such as Si, Al, and Ca. This is followed by the CP1 layer with Cu, Zn, Pb, C, O, P, and Cl containing corrosion products, then the CP2 layer with Cu and O, and finally the CP3 layer containing Cu and Cl, and suffering from a selective leaching of Zn, i.e. dezincification. This corrosion phenomenon is prominent in the button as it has a higher zinc content. In the fifth step, a digital representation of the corrosion stratigraphy from the cross-section examination was created using the MiCorr modelling programme. Finally, the sixth step included Synthesising the binocular/ cross-section examination of the corrosion structure for the two artefacts.
These corrosion stratigraphy representations and accompanying information will form two new files, which will be added to the MiCorr database and made available to other users.
The STSM also allowed the grant recipient to have basic training on Pleco and DiscoveryMat analytical tools. It also offered access to the Haute Ecole Arc Conservation-Restauration laboratories, where the training and use of the tools took place. The knowledge obtained on MiCorr application and applied on two archaeological artefacts will be applied on more artefacts in the future, and the information on the tool will be passed on to other professional colleagues and students. In addition, the STSM will open venues for networking and fostering research collaboration with the host, project team and fellow STSM grant recipients in the future.
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