Corrosion products and microstructure of copper alloy coins from the Byzantine-period Ma'agan Mikhael B shipwreck, Israel

Insight on the deterioration of cultural objects: a multi-analytical approach to characterize degradation products of lead weights from a Steinway & sons piano

The identification of the degradation products in objects of cultural significance, including musical instruments (e.g., a piano), is a key issue for the preservation and valorisation processes of cultural heritage. The aim of this study is to characterize the degradation products of lead weights from an important Steinway & sons piano using a multi-analytical approach that includes ionic chromatography (IC), X-ray diffraction (XRD) and Fourier transform-infrared (FTIR) spectroscopy analyses. These techniques allowed us to identify hydrocerussite as the main degradation product on the superficial layer of lead weights, followed by lead acetate and formate. Moreover, accelerated corrosion experiments in closed environments were performed under acetic and formic acid atmospheres to evaluate the development of lead acetate and formate over time. Exposure of lead weights to formic and acetic acid vapours leads to the prevalent formation of basic lead formate, which promotes the formation of hydrocerussite. These results can help to limit the degradation of these piano components and consequently preserve the sound of the piano itself.

Micro and Nanoscale Structures and Corrosion Patterns in Brass: The Case Study of Ancient Roman Orichalcum Coins

This study investigated the micro and nanoscale structure in Cu-Zn alloy, as well as its corrosion patterns. To achieve this goal, a set of Roman orichalcum coins were analysed using Scanning Electron Microscopy (SEM-EDS), X-ray maps, high resolution field emission scanning electron microscopy (HR-FESEM-EDS) and electron microprobe analyser (EMPA) techniques. The samples showed a high degree of corrosion on their external surfaces, which evolved in depth up to ~1 mm. Micro and sub-micro imaging of the inner metal highlighted the presence of “stressed areas” caused by mechanical processing work, representing the trigger zone of corrosion and causing the loss of material. These images also permitted us to follow the grain-grain interface and selective Zn-dealloying in the examined samples. X-ray maps of Cu and Zn helped us to understand the evolution of the dezincification process, from rim to core. HR-FESEM-EDS imaging investigation highlighted a heterogeneous composition within the strain line structures, confirming that the mechanically stressed areas were active zones for corrosion processes. Cracks and voids also characterised the patina. Conversely, the uncorroded cores of the samples were not affected by dealloying.