X‐ray fluorescence analysis on a group of coins from the ancient roman city of Tridentum (Trento,Italy)

A group of 83 coins, found in the archeological excavations of the ancient Roman city of Tridentum (Trento, Italy), was studied for the determination of their composition, finalized to their classification and cataloging. The coins, mainly made of copper‐based alloys, were minted between the republican period (II century BC) and the last decades of the western empire (V century AD). The X‐Ray Fluorescence archaeometric analysis has allowed a revision of the typological classification of the coins through the identification of six broad groups, each one characterized by a peculiar composition of the coins in the group. A tentative assignation of all the unreadable coins to one of the groups identified was proposed, in a way that could suggest also a possible dating of these coins. Copyright © 2014 John Wiley & Sons, Ltd.     

Micro‐EDXRF investigation of Chalcolithic gold ornaments from Portuguese Estremadura

Chalcolithic gold artefacts assigned to the Bell Beaker Culture in Portuguese Estremadura were analysed by micro‐energy dispersive X‐ray fluorescence spectrometry. These high‐status jewels comprise beads of tubular, spiral and double‐conical type, a spiral ring and a wire fragment. The collection is mainly composed of gold with 8.7–16.3 wt% Ag and <0.04 wt% Cu. Additionally, there is a typologically uncommon double‐conical bead showing a lower Ag content (6.7 wt%). The relative intensity of the Ag‐Kα and Ag‐Lα X‐rays from artefacts established the existence of a surface layer depleted in silver, while the reasonable effective penetration depth of the Ag‐Kα (about 25–30 μm) provided suitable results for such high fineness gold alloys. A uniform Au–Ag composition at the joint indicates that the double‐conical bead was made by joining two sheets without solder. Overall, the collection shows a composition that is similar to known Chalcolithic gold in Portuguese Estremadura but different from coeval gold in Southwestern Iberian Peninsula. The distinct compositional pattern of Chalcolithic gold in Portuguese Estremadura seems to be inconsistent with the natural variability of silver content in alluvial deposits of gold in Iberian Peninsula, thus suggesting a continuous use of particular sources and limited exchange of nuggets and jewels with the neighbouring region. Copyright © 2017 John Wiley & Sons, Ltd.     

Analysis of the Hoard of Beçin using X‐ray‐based techniques

Four hundred and sixteen silver coins stemming from the Ottoman Empire (16th and 17th centuries) were analyzed to confirm the fineness of the coinage as well as to study the provenance of the alloy used for the coins. As most of the coins showed the typical green patina on their surfaces due to corrosion processes that have led to the depletion of copper in the near surface domains of the silver coins in comparison to their core composition, small samples had to be taken, embedded in synthetic resin, and cross sectioned to investigate the true‐heart metal composition. μ‐synchrotron micro X‐ray fluorescence analysis and μ‐proton‐induced X‐ray emission were applied to determine the silver contents as well as the minor and trace elements. The type of the alloy was investigated as well as if coins minted in different locations demonstrated homogeneous traits concerning the predominant impurities (Au and Bi), which could suggest a common ore. Finally, energy‐dispersive microanalysis in a scanning electron microscope was applied to study the homogeneity/heterogeneity of the coins and the presence of surface enrichments and to explain differences between the μ‐synchrotron micro X‐ray fluorescence analysis and μ‐proton‐induced X‐ray emission measurements concerning the main component. In general, the silver content of the analyzed specimen varies between 90 and 95%. These outcomes have not supported the historical interpretations, which predict that during the period studied, a debasement of approximately 44% of the silver content of the coins should have occurred. Copyright © 2012 John Wiley & Sons, Ltd.     

Analysis of the spectacular gold and silver from the Moche tomb ‘Señora de Cao’

On the north coast of present‐day Peru, between the Andes and the Pacific Ocean, approximately between 100 and 600 ad , the Moche civilization prospered. The Moche were very sophisticated artisans and metal smiths, so that they are considered the finest producers of jewels and artifacts of the region. Their metalworking ability was impressively demonstrated by the excavations of the tomb of the ‘Lady of Cao’ (dated around third–fourth century ad ) discovered by Regulo Franco in 2005. Impressive is the beauty of the artifacts, and also the variety of metallurgical solutions, demonstrated by not only the presence of objects composed of gold and silver alloys but also of gilded copper, gilded silver, and tumbaga, a poor gold Cu‐Au alloy subject to depletion gilding. About 100 metal artifacts from the tomb of the Lady of Cao, never before analyzed, were studied by using various portable equipments based on following non‐destructive and non‐invasive methods:

• energy‐dispersive X‐ray fluorescence with completely portable equipments;
• transmission of monenergetic X‐rays;
• radiographic techniques; and
• optical microscopy.

Gold objects and gold areas of nose decorations are characterized by approximately the same composition, that is, Au = (79.5 ± 2.5) %, Ag = (16 ± 3) %, and Cu = (4.5 ± 1.5) %, while silver objects and silver areas of the same nose decorations show completely erratic results, and a systematic high gold concentration. Many gilded copper and tumbaga artifacts were identified and analyzed. Further, soldering gold–silver was specifically studied by radiographs. Additional measurements are needed, particularly because of the suspect that depletion gilding was systematically employed also in the case of some nose decorations. Copyright © 2016 John Wiley & Sons, Ltd.     

Studies on the composition of ancient Indian punch‐marked silver coins

Punch‐marked coins are the oldest known numismatic objects used in ancient India. Seven punch‐marked silver coins were analysed by using the non‐destructive multi‐elemental PIXE technique. A 3 MeV proton beam from a pelletron accelerator was used for irradiation of these samples to obtain the spectral data and GUPIX software was employed to derive the elemental concentrations. The results reveals that silver, copper, gold and lead are significant constituents of the punch‐marked silver coins and there are also traces of elements such as Ti, Cr, Mn, Fe, Co, Ni, As and Y, which seems to imply that PIXE can be used effectively for the non‐destructive quantitative analysis of ancient coins. Copyright © 2004 John Wiley & Sons, Ltd.     

Microchemical investigation on Renaissance coins minted at Gubbio (Central Italy)

The bulk and surface chemical composition of Renaissance coins minted at Gubbio (Central Italy) from 1508 to 1516 and from 1521 to 1538 by Francesco Maria della Rovere is investigated by means of the combined use of different analytical techniques such as scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and optical microscopy (OM). The aim of the work is to determine the bulk chemical composition of these commonly used coins at Gubbio, to ascertain their surface nature and if they were coated by a thin film of silver or other white metals similar to silver.The results indicate that the coins were produced by coating a copper core with a thin film of silver and antimony, and also with lead whose thickness is of a few microns which is now scarcely present because the original silvered surface was almost entirely removed by degradation phenomena. Furthermore, the SEM+EDS results show that the surface content of silver and antimony cannot be attributed to long-term selective corrosion phenomena leaving the coin slightly silver or antimony enriched. Therefore, the presence of silver or apparently silver-like metals i.e. antimony and lead, could be considered as a deliberate surface finishing of the coins obtained via inverse segregation or intentional selective corrosion based on pickling solutions or a combination of them. From a historical point of view the presence of a Ag or Sb film on the surface of the coins discloses the occurrence of a period of economic difficulties. PACS 68.55.Jk; 68.35.Dv; 68.37.Hk; 68.55.Nq; 81.05.Bx     

Combined use of surface and micro-analytical techniques for the study of ancient coins

By means of the combined use of surface and micro-analytical techniques the surface chemical composition of ancient coins and some aspects of their manufacturing techniques and of degradation mechanisms have been elucidated. Two case histories are described concerning silver Roman Republican coins and some coins plated with thin films of silver and gold. In particular, the coinage methods, the silvering and gilding techniques and the origin of the embrittlement of these selected Roman coins have been studied by means of the combined use of selected-area X-ray photoelectron spectroscopy (SA-XPS) and scanning electron microscopy and energy-dispersive spectrometry (SEM+EDS). This innovative approach has been utilised in order to gain further insight into the microchemical structure of the external regions of the coins as well as of the bulk features. The results show the use of mercury to coat a copper or silver core with a thin film of precious metals that could be considered the most important advance in the technology of gilding to be made in antiquity. Furthermore, the microchemical investigation of brittle Roman silver coins has allowed us to identify the origin of this troublesome problem. The microchemical results indicate that brittleness is induced by the presence of a low amount of lead that is retained in supersaturated solution when the cast blank was produced. This latter element segregates at the grain boundaries during the coin production and the subsequent long-term ageing at room temperature, thus inducing the alloy fracturing along the weakened grain boundaries. PACS 68.55.Jk; 68.35.Dv; 68.37.Hk; 68.55.Nq; 81.05.Bx     

Micro‐Raman investigations of early stage silver corrosion products occurring in sulfur containing atmospheres

Silver is a soft, lustrous metal with the highest electrical and thermal conductivity. Due to these properties, it has many applications as a precious material both in pure and alloy form (ornaments, jewellery, utensils, coins), but also in several technological fields, considering silver compounds (e.g. photography, electric and electronic industry). As a consequence of this, silver and its by‐products are regularly exposed to different atmospheres where a wide spectrum of agents (e.g. moisture, temperature, air pollutants, UV light) may cause metal corrosion and alteration of their surface characteristics and properties. The aim of this research is to deepen the potential and applicability of micro‐Raman spectroscopy as a surface‐sensitive technique to investigate the initial steps of atmospheric corrosion throughout the identification of surface chemical reactions and corrosion products formed on silver substrates. In a previous study, micro‐Raman analysis was carried out on pure silver powder compounds, selected among the most expected corrosion products occurring on silver substrates, in order to optimize experimental conditions and to obtain reference spectra ^[1]. Subsequently highly pure silver samples were exposed for 24 h to different controlled laboratory atmospheres (synthetic air, relative humidity, SO₂, H₂S), particularly focusing on sulfur containing gases, and the resulting surface reactions. The experiments highlight micro‐Raman spectroscopy as a highly surface‐sensitive technique enabling to detect both adsorbed chemical species and crystalline corrosion products of only several monolayers of thickness. Furthermore, these investigations could show the trends of primary and secondary corrosion mechanisms and their mutual interaction occurring on silver substrates. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of the provenance of medieval silver coins: potential and limitations of x‐ray analysis using photons,electrons or protons

One hundred and fifty seven ‘Tiroler Kreuzer’, a medieval currency from the county of Tyrol/Austria, were analysed in order to determine their place of mintage. The silver coins were produced during the 15th century in the mints of Merano (South Tyrol) and Hall (North Tyrol) but they have no marks or punches which would allow a clear distinction. Energy‐dispersive x‐ray fluorescence analysis (EDXRF) was applied without sampling in order to determine the silver contents and also minor (Cu, Pb, Bi) and trace elements (Fe, Au, Hg, Ni). Owing to corrosion processes, which changed the chemical composition of the surfaces of the coins, investigations of cross‐sections were necessary using energy‐dispersive x‐ray microanalysis in a scanning electron microscope (SEM/EDX) to determine the stage of corrosion and the Ag concentration of the core of the coins. The results showed differences of up to 50% between the composition of the core and the surface. Finally, proton‐induced x‐ray emission (PIXE) at an external proton beam was applied, in order to detect also Ni, an element which could not be measured by either EDXRF or SEM/EDX in the ppm range. The data show a clear difference in the Ni content between the coins from Merano (～0.1% Ni) and Hall (～0.01% Ni). Copyright © 2003 John Wiley & Sons, Ltd.     

Thickness and composition of gold and silver alloys determined by combining EDXRF‐analysis and transmission measurements

Energy‐dispersive X‐ray fluorescence (EDXRF)‐analysis is a technique which in the case of metals analyzes thin surface layers. For example, when gold and silver alloys are analyzed, it typically interests a depth of microns up to a maximum of tens of microns. Therefore, it can give wrong results or be affected by a large indetermination when the sample composition is altered because of surface processes, as often happens when silver alloys are oxidated, and sometimes in the case of gold alloys rich on copper or silver. A complementary technique was therefore developed, of bulk analysis, which uses the same equipment employed for EDXRF‐analysis; the X‐ray beam from the X‐ray tube is monochromatized by means of a tin secondary target, which K lines bracket the silver‐K discontinuity. The sample to be analyzed is positioned between the secondary target and the detector. This technique is able to determine (by measuring the attenuation of tin‐K rays) thickness and/or composition of gold and silver alloys having a thickness of less than about 120 µm for gold and about 0.7 mm for silver. The method was tested with Au–Ag–Cu alloys of known composition and thickness and then applied to gold and silver artifacts from the tomb of the Lady of Cao, which belongs to the Moche pre‐hispanic culture from the North of Peru, and dates about 300 A.D. Copyright © 2014 John Wiley & Sons, Ltd.     

Microchemical investigation of Greek and Roman silver and gold plated coins: coating techniques and corrosion mechanisms

Within the framework of a project financially supported by the European Commission (contract Nr. 509126, acronym PROMET) the metallurgical techniques used by Romans and Greeks for coating the copper core of coins with a thin or thick layer of gold or silver are studied by means of the combined use of scanning electron microscopy combined with energy dispersive spectrometry (SEM-EDS) and optical microscopy (OM) techniques.This approach is utilised to gain further insight into the micro-chemical structure of the external regions of the coins as well as into the bulk metallurgical features. The results indicate that several methods were used by the Greek and Roman craftsmen including the mechanical application of a thin malleable gold or silver foils to be welded via thermal treatment. The analytical approach is also used for investigating the corrosion products grown on the coins during the long-term burial and for identifying degradation mechanisms.PACS 68.55Jk; 68.35 Dv; 68.37Hk; 68.55 Nq; 81.05 Bx     

Celtic gold coins in the light of Mössbauer spectroscopy, electron microprobe analysis and X-ray diffraction

Celtic gold coins found in Southern Germany were studied by Mössbauer spectroscopy, electron microprobe analysis and X-ray diffraction with special attention to coins rich in silver and copper. In such coins the electron microprobe analyses reveal a gold enrichment in a surface layer of more than 100 μm thickness. ¹⁹⁷Au conversion electron Mössbauer spectroscopy also shows that the surface of the coins consists of two phases, one of which is strongly enriched in gold compared to the bulk composition. In comparison with laboratory experiments the observed phenomena suggest that coin production in Celtic times may have involved deliberate heating and etching steps to enrich the surface layer in gold by depleting it of silver and copper.     

Microchemical investigations of historical coins

Microchemical investigations were carried out on ancient silver coins originated from the same country but of different historical periods between the fifth and the second centuries B.C. Energy-Dispersive X-ray microanalysis in a Scanning Electron Microscope (SEM-EDX) was employed to obtain qualitative and semi-quantitative information about the chemical composition of these coins. SEM-EDX analyses employ an electron beam of 20?keV, which interacts with the sample leading to the emission of characteristic X-rays, to determine elements present in the surface patina, closely related to the sample preservation. In the X-ray photoelectron spectroscopy (XPS) analysis a monochromatic Al Kα radiation (1486.6?eV) interacts with the sample and photoelectrons are detected as secondary radiation, to investigate about coins elemental composition. Moreover a beam of Ar⁺ ions with an energy of 3?keV was used for the sputtering procedure in order to perform depth profile measurements, from the surface (patina composition) down to deeper layers. Useful information about production, chronological period and utilization places of coins are obtained to support a correct dating of these samples.     

Gemstones and noble metals adorning the sceptre of the Faculty of Science of Charles University in Prague: integrated analysis by Raman and XRF handheld instruments

A commonly marketed handheld Raman spectrometer showed excellent possibilities in being used as a key instrument for unambiguous identification of gemstones mounted in the sceptre of the Faculty of Science of Charles University in Prague from the mid‐20s of the 20th century. Numerous SiO₂ forms including chalcedonies intermixed with moganites (e.g. moss agates and carnelians), amethysts, citrines as well as garnets (pyrope–almandines) were identified. The estimation of the garnet type was based on obtained Raman parameters. The individual minerals constituting the lapis lazulis could not be discerned because of very high fluorescence they exhibited in the fingerprint region of the Raman spectrum, nevertheless the positions of the observed peaks in the 1000–2000 cm^–1 area were in very good agreement with the values of commercially available lapis lazuli pigment. The noble metals of the sceptre were studied by means of X‐ray fluorescence analysis, which confirmed the presence of silver alloys and gilding. The comparison of silver alloys' semiquantitative analysis with the expected fineness, denoted by the hallmarks, indicated silvering. This has been later confirmed by the newly discovered restoration documentation. Portable handheld Raman and X‐ray fluorescence instruments represent an ideal tool for studying historical artefacts, where an in situ investigation in museums or similar sites is obligatory. Copyright © 2012 John Wiley & Sons, Ltd.     

Micro‐Raman innovative methodology to identify Ag–Cu mixed sulphides as tarnishing corrosion products

Mixed Cu–Ag alloys with different compositions have been produced and subjected to an accelerated sulphidation process which causes the development of a mixed sulphide‐rich corroded film on their surface. It was called tarnishing, that is, the formation of a blue‐brownish patina when Cu–Ag alloys are exposed in a sulfur‐containing atmosphere. The structures of the pristine alloys have been determined by the combined analytical techniques as scanning electron microscopy energy dispersive X‐ray microanalysis and X‐ray diffraction. The experimental conclusions confirmed the occurrence of micro phase separation with the formation of different dendritic domains of about 10 µm in width. The sulphidized samples were firstly investigated by optical microscopy and X‐ray diffraction in order to verify the homogeneity of the patina and to identify the different AgCuS phases appearing on the alloy surfaces. It was observed that, despite the inherent micro‐heterogeneity of the alloys, the sulphide layer was throughout uniform in composition at the micro‐scale. The complex scenario of the relative stability of all the various mixed sulphides involved was then explored by micro‐Raman spectroscopy (μ‐RS), pointing out that the Cu‐for‐Ag substitution in the crystal lattice of the mixed Ag–Cu sulphides caused a monotonous blue shift of the vibrational wavenumbers in Raman spectra. This study has unveiled microscopic details of the tarnishing process, furnishing an innovative, cheap and non‐destructive methodology based on μ‐Raman spectroscopy for the evaluation of the silver‐copper artefacts via the compositions of their corroded products. Copyright © 2016 John Wiley & Sons, Ltd.     

In situ nucleation and growth of silver nanoparticles in membrane materials: a controllable roughened SERS substrate with high reproducibility

A controllable roughened silver surface with high surface‐enhanced Raman scattering (SERS) activity and high reproducibility has been developed in this study. This silver surface was prepared by silver nucleation in polyelectrolyte multilayers (PEMs) and silver‐enlarged growth. First, the small Ag nuclei were synthesized by NaBH₄ in situ reduction of Ag ions on a surface of PEMs. Then the small Ag nuclei formed were effectively enlarged by using a mixture of commercially available reagents named Li Silver . The optical properties and morphologies of the silver substrates have been investigated by ultraviolet–visible (UV–vis) spectroscopy and atomic force microscopy (AFM). The UV–vis and AFM results revealed that the small Ag nuclei separately appeared on the PEMs after NaBH₄ in situ reduction. The size of the enlarged Ag nanoparticles can be easily controlled with the immersing cycle in Li Silver. 4‐Mercaptopyridine (4‐MPY) and Rhodamine 6G (R6G) have been used as Raman probes to evaluate the properties of the new SERS substrates. It has been found that the enhancement factor of R6G reached ∼10⁹ after treatment in Li Silver. Reproducibility has been investigated using the SERS signal intensity at 1094 cm⁻¹ of 4‐MPY. Signals collected over multiple spots within the same substrate resulted in a relative standard deviation (RSD) of 6.38%, while an RSD of 10.33% was measured in signals collected from different substrates. Copyright © 2008 John Wiley & Sons, Ltd.     

Changes in the composition and surface structure of alloys in regions with varying deformation

The change in the structure and composition of deformed regions hidden beneath the surface of samples are studied experimentally upon their identification by the method of successive processes of polishing and sputtering. Two present-day steel coins coated with different binary alloys, a 1-ruble coin (coated with the alloy Ni1%Fe) and a 50-kopeck coin (coated with the tompak alloy Cu10%Zn), and also a 5-kopeck coin minted in 1990 consisting of brass L60 are used as the samples. It is found that a change in the surface structure (different for the studied coins) and an increase in the light-component concentration take place in the region of increased deformation by pressing due to its diffusion to the side of greater deformation. The obtained results can be used for improving the means of determining hidden deformed regions using sputtering and stage-like analysis of the surface composition.     

Raman spectra of benzoic acid enhanced by the silver nanoparticles of various sizes

Using sodium borohydride as the reducing agent and polyvinyl pyrrolidone (PVP, MW = 10 000) as the stabilizer, we obtained silver nanoparticles of various diameters (8–78 nm) from silver nitrate aqueous solutions in the concentration range from 0.001 to 0.1 M. The surface‐enhanced Raman scattering (SERS) from benzoic acid's ring‐breathing mode at 1003 cm⁻¹ was detected from its dilute solutions (∼10⁻² M) doped with these silver nanoparticles under 488‐nm laser excitation. The observed size dependences of SERS intensities fit quite well with those calculated by Schatz's theoretical model for spherical silver nanoparticles. The only exception occurred with the smallest particles (8 nm), possibly due to the failure of Maxwell's electromagnetic theory used in this model. Copyright © 2009 John Wiley & Sons, Ltd.     

pH‐dependent surface‐enhanced Raman scattering studies of N‐acetylalanine monolayers self‐assembled on a silver surface

Monolayers of N‐acetylalanine on a metallic surface can serve as a biocompatible functional interface to construct biosensors. In the present paper, the surface‐enhanced Raman scattering (SERS) spectra of N‐acetylalanine monolayers self‐assembled on a silver surface under different pH were recorded. Assignments of the obtained spectra were carried out by density functional theory (DFT) calculations (BLYP/6‐311G). On the basis of the SERS effect, the nature of adsorption of N‐acetylalanine on a silver surface was deduced. It can be concluded that the fully protonated N‐acetylalanine is adsorbed on the silver surface via the imine group together with the carboxylate group, while it anchored onto the surface not only through both the imine and the carboxylate groups but also through the amide group after being completely deprotonated in the basic solution. Copyright © 2007 John Wiley & Sons, Ltd.     

On the interaction mechanisms between a high-power diode laser source and silver alloys: The case of aesthetic welding

Welding process is generally considered as a crucial stage in the manufacturing of decorative items in silver alloys. It is mostly hand-made by using oxy-fuel torch and the final performance of the manufactured goods is too strongly related to the capability of skilled technicians and to the settings of factors often unpredictable. Further, spreading and out-of-control oxidative phenomena, troublesome reprocessing of the welded parts and unsafe operational conditions are determining a progressively growing demand for alternative welding technologies.The matter of the present investigation is therefore to evaluate the suitability of a high-power diode laser source in automatic butt-welding of sheets in ‘800/1000’ and ‘925/1000’ silver alloys. Interaction mechanisms between laser beam and underlying silver substrates in a chemical active environment were studied. A ‘first approximation’ oxidation model and, accordingly, simple tools for monitoring and control of the welding process was then proposed. Finally, butt-welding of thin silver sheets was successfully experimented.