Complementary analytical methods for analysis of Ag-plated cultural heritage objects

Abstract

In a preliminary study of American silver plated cultural heritage objects with the Dallas Museum of Art (DMA), variable plating thickness was observed, which complicates non-destructive characterization of the base metal. Therefore, it is the objective of this study is to compare the effectiveness of three nondestructive complementary analytical methods to characterize both the plating and base metal of a typical silver Ag-plated object and to contrast these results with conventional destructive metallographic methods. An externally purchased sacrificial "Century" fork was chosen for this study and is similar to one found in the DMA's collection. First conventional destructive metallographic methods, where crosssections were taken and then characterized using optical microscopy (OM) and scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS), were employed in order to evaluate the effectiveness of the non-destructive methods. The first non-destructive method, synchrotron radiation X-Ray diffraction (SR-XRD), reveals the plating thickness, texture related to processing methods, and the phases present in both the base metal and plating. The second method , dual beam focused ion beam (FIB) / (SEM) equipped with an (EDS) system, provides elemental composition of both the plating and base metal, as well as imaging of the plating thickness and grain structure, giving some insight into processing methods. The last non-destructive method, handheld X-Ray Fluorescence (XRF) spectroscopy, provides qualitative elemental compositions of both the plating and base metals. Each non-destructive analytical method yields complementary results about the composition, plating thickness, texture, and phases present in the plating and base metals of the Ag-plated "Century" fork and aids in the verification of the results from the other methods. Through these methods, we show that successful characterization of Agplated cultural heritage objects is possible non-destructively, thus maintaining the object's structural, historical and artistic integrity.

Metallurgical investigation on fourth century BCE silver jewellery of two hoards from Samaria

“…EDS is a surface technique; therefore, surface measurements of ancient silver objects may not provide reliable information of the bulk composition, due to tarnish layers, corrosion, oxide layers, conservation treatments, cleaning residues, and silver enrichment of the surface1618192021365354. Therefore, in order to achieve an optimal (relatively quantitative) SEM-EDS chemical analysis that will represent the bulk of the object, it is essential to understand the limitations of the EDS measurements.…”

“…Nevertheless, these limitations do not prevent SEM-EDS from being a functional tool for the study of ancient Ag-Cu alloys. According to these limitations and difficulties associated with EDS tool, it has been suggested by Carl and Young21 to combine SEM-EDS measurements to other techniques such as FIB.…”

“…Hence, numerous studies of ancient silver artefacts exist in the literature, investigating their chemical composition15161718192021, microstructure1517202223, manufacturing processes1524, provenance1617, embrittlement and fracture2223, condition of preservation, corrosion processes and corrosion products142526272829 and their state of conservation2529. These studies normally combine non-destructive testing (NDT) and destructive testing methods, including: metallography, light and scanning electron microscope (SEM) examination including energy-dispersive spectroscopy (EDS) analysis, focused ion beam (FIB) microscopy and micromachining, particle-induced X-ray emission (PIXE) analysis, X-ray fluorescence (XRF) analysis, inductively-coupled plasma (ICP) analysis, X-ray diffraction (XRD), neutron tomography, X-ray photoelectron spectroscopy analysis (XPS), and Raman spectroscopy analysis1516171819202122232526272829303132. Yet, because of the rareness of such ancient artefacts, from the archaeological perspective, the use of NDT methods is always preferred202130.…”

“…These studies normally combine non-destructive testing (NDT) and destructive testing methods, including: metallography, light and scanning electron microscope (SEM) examination including energy-dispersive spectroscopy (EDS) analysis, focused ion beam (FIB) microscopy and micromachining, particle-induced X-ray emission (PIXE) analysis, X-ray fluorescence (XRF) analysis, inductively-coupled plasma (ICP) analysis, X-ray diffraction (XRD), neutron tomography, X-ray photoelectron spectroscopy analysis (XPS), and Raman spectroscopy analysis1516171819202122232526272829303132. Yet, because of the rareness of such ancient artefacts, from the archaeological perspective, the use of NDT methods is always preferred202130.…”

FIB-FESEM and EMPA results on Antoninianus silver coins for manufacturing and corrosion processes

“…Therefore, non-invasive and non-destructive analyses have become almost the exclusive techniques applied in Cultural Heritage fields 28 – 33 . It is clear that surface analyses cannot give proper or complete answers in some critic questions as technologies of manufacturing and post-manufacturing processes, raw materials and provenance 34 . In order to answer to all these questions, it seems necessary to apply a multi-analytical strategy that combines non-invasive, nano-invasive and destructive techniques.…”