Provenance, manufacturing and corrosion behavior of Ancient Hellenistic coins from Egypt

Some copper alloy coins of the Ptolemaic period from a private collection, providing valuable evidence for both archaeometric as well as materials science and corrosion studies, have been investigated. The coins were found in the ancient city of Bubastis, known as Tell Basta, in the Nile Delta, Egypt. The coins have been examined by optical microscopy for their metallurgical structure, analysed by X-ray fluorescence and Electron Dispersion Spectroscopy for their composition, and by X-ray diffraction for the characterisation of their corrosion products. An attempt has been made to remove part of their corrosion products by mild chemical cleaning procedures. In some areas the coins are heavily corroded by chlorides, however most of the inscriptions on the coins themselves are still decipherable. Assumptions are made on the coins provenance, the production period, the manufacturing technique and the burial environmental conditions

Raman spectroscopic characterization of corrosion products of archaeological iron

Raman spectroscopy is a versatile analytical technique which allows the detection of different molecules analysing the vibrational modes. As a matter of facts, the vibrational frequencies are typical of a specific chemical bond or of a structural symmetry. In this study, the Raman technique is used for the determination of iron corrosion products, mainly oxides and hydroxides. Metallic artefacts buried in soil are affected, in dependence of their electrochemical nobility, by corrosion phenomena of various entities, which partially modify their chemical composition and their structure. The process may occur both during burial time and after the extraction from the archaeological site, implying the potential loss of information about the metallurgical technology and structure of the object. The study of the corrosion phenomena allows to propose tailored strategies for the restoration and conservation of the artefacts, especially in view of the storage of the artefacts in a museum. This study validates the use of the Raman technique for this purpose, showing its efficiency in the identification of the iron corrosion products in favourable conditions for the analysis of Cultural Heritage artefacts, as the possibility of performing in situ analysis without the need of a previous sample preparation

Environmental monitoring solution for cultural heritage

Environmental monitoring is crucial factor in the safeguard and conservation of the cultural heritage. Unsuitable environmental conditions can easily accelerate the degradation of several materials and, as consequence, damage the stored artifacts. Moreover, environmental conditions can easily change in an unpredictable way and, therefore, the employment of an environmental monitoring system is mandatory in almost all locations, including museums, storage rooms and outdoor exhibitions. This paper tries to explain the main constraints required for environmental monitoring in the cultural heritage field. Moreover, a novel distributed monitoring system, developed at Politecnico di Torino, is described and compared to several solutions that are commercially available. The proposed solution demonstrated excellent characteristics which satisfy the requirements of environmental monitoring in the cultural heritage at a very competitive cost

Corrosion prediction of metallic cultural heritage assets by EIS

Electrochemical Impedance Spectroscopy (EIS) was used to predict corrosion behaviour of metallic Cultural Heritage assets in two monitoring campaigns: 1) an iron bar chain exposed indoor from over 500 years in the Notre Dame Cathedral in Amiens (France); and 2) a large weathering steel sculpture exposed outdoor from tens of years in Ferrara (Italy). The EIS portable instrument employed was battery operated. In situ EIS measurements on the iron chain could be used to investigate the phenomena involved in the electrochemical interfaces among various corrosion products and assess and predict their corrosion behaviour in different areas of the Cathedral. Meanwhile, the sculpture of weathering steel, like most outdoor artefacts, showed rust layers of different chemical composition and colour depending on the orientation of metal plates. The EIS monitoring campaign was carried out on different areas of the artefact surface, allowing assessment of their protective effectiveness. Results of EIS measurements evidenced how employing a simple test that could be performed in situ without damaging the artefacts surface is possible to quickly gain knowledge of the conservation state of an artefact and highlight potential danger conditions

Measurements for restorative dentistry: shrinkage and conversion degree of bulk-fill composites

The paper deals with a measuring approach based on Raman Spectroscopy and micro-CT imaging for correlating the degree of conversion of bulk-fill composites to the contraction shrinkage and consequently to the internal gap formation in high c-factor dental cavities. The developed study was performed on extracted molars in which a first-class cavity was prepared. A micro-CT scan was performed before and after composite lightcuring to tridimensionally measure the interfacial gap between the composite material and the cavity walls. After the complete polymerization of the composite, each sample was sectioned vertically to expose the lateral surface of the restorative material. Raman Spectroscopy measurements were performed along the cross-section of the cavity filled with the restorative material, every 0.5 mm from the occlusal surface. The obtained results showed a minimal gap opening after light-curing and a degree of conversion which was not affected by the bulk-fill composite thickness. Thanks to the 3D rendering, it should be observed that gaps were mostly concentrated at the cavity floor and despite the reduction in the degree of conversion detected in the deeper portions of the restoration, a three-dimensional opening of an interfacial gap was not observed. Therefore, it is possible to assume the presence of a correlation between the degree of conversion and the volumetric interfacial gap could. Further studies are actually in progress to compare these preliminary results with those obtained on other dental composite materials

Atmospheric corrosion of outdoor bronze artefacts: The case study of 'Katarsis', by Magdalena Abakanowicz

The conservation of cultural heritage metallic items is deeply connected to the investigation of the corrosion phenomena affecting the metallic surface and to the study of the influence of the surrounding environmental parameters. This paper describes the case study regarding the metallic artwork 'Katarsis' of the Gori Art Collection at Fattoria di Celle (Pistoia, Italy), created by the artist Magdalena Abakanowicz. An in-situ multi-analytical approach was employed in order to assess the conservation state of the statues and to ensure their long-lasting preservation. In particular, X-rays fluorescence (XRF), Raman spectroscopy (RS), and X-Rays diffraction (XRD) were used for the identification of the corrosion products, mainly sulphates, and to identify the employed alloy. In this paper, the preliminary results will be presented and discussed

ToF-SIMS and -Raman measurements on laser cleaned bronze archaeological artefacts

n this study, ToF-SIMS and -Raman analyses have been employed to assess the feasibility of laser treatments as a selective, non invasive cleaning methodology for archaeological metallic artefacts. A Q-switched Yb:YAG fibre laser, operating at 1064 nm, has been used for the cleaning treatments, carried out in air and 18O rich atmosphere on an ancient bronze coin. The preliminary results show that laser cleaning treatment selectively removes the dangerous oxyhydroxy chlorides corrosion products without affecting the cuprite protective patina grown directly in contact with the metallic surface

MA-XRF measurement for corrosion assessment on bronze artefacts

In this study, an innovative portable macro X-Ray Fluorescence (MA-XRF) scanner prototype has been employed in order to gain information on composition and distribution of corrosion products artificially grown on Cu-based coupons. First results have shown the importance of using artificially corroded reference samples before any assessment on archaeological artefacts. Moreover, the prototype used demonstrated to be a powerful tool for understanding complex corrosion processes which might occur on Cu-based alloys. The scanner was able to detect light elements as S and Cl, essential for studying the distribution of specific corrosion compounds. Using imaging techniques, it was possible to observe a gradient in Cu elemental maps intensity caused by the overlapping of a thicker corrosion product layer

Electrochemical characterization of innovative hybrid coatings for metallic artefacts

In this paper, an electrochemical characterization of two different hybrid coatings is presented, with the specific aim of studying their corrosion protection behavior and better understanding their possible application in the cultural heritage field. The two formulations under study were epoxy resin containing silica nanoparticles and epoxy resin containing graphene oxide. Electrochemical Impedance Spectroscopy (EIS) and Scanning ElectroChemical Microscopy (SECM) were used to compare the electrochemical behavior of the two coatings and highlight their failure mechanism when immersed in an electrolytic solution containing chlorides. The investigation highlighted the good corrosion protective properties of both coatings; and moreover, thanks to the joined use of the two described analytical techniques, the different water uptake of the two solutions was studied, together with the different evolution of the coating surface morphology when immersed in the electrolytic solution

MA-XRF measurement for corrosion assessment on bronze artefacts

In this study, an innovative portable macro X-Ray Fluorescence (MA-XRF) scanner prototype has been employed in order to gain information on composition and distribution of corrosion products artificially grown on Cu-based coupons. First results have shown the importance of using artificially corroded reference samples before any assessment on archaeological artefacts. Moreover, the prototype used demonstrated to be a powerful tool for understanding complex corrosion processes which might occur on Cu-based alloys. The scanner was able to detect light elements as S and Cl, essential for studying the distribution of specific corrosion compounds. Using imaging techniques, it was possible to observe a gradient in Cu elemental maps intensity caused by the overlapping of a thicker corrosion product layer