Ancient Silver Research Articles

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.

First attempt to obtain the bulk composition of ancient silver–copper coins by using XRF and GRT

Archeological silver–copper pieces often show surface enrichments in silver, either intentional or fortuitous. When this happens, non-destructive techniques like PIXE (Proton Induced X-ray Emission) and XRF (X-Ray Fluorescence) are not sufficient to access the whole bulk pieces because their penetration depths are typically of a few tens microns. If the archeological pieces cannot be cut or polished, it is necessary to apply other non-destructive techniques to access the bulk pieces. That way, archeological bronze pieces have been successfully studied combining XRF (or PIXE) with GRT (Gamma-Ray Transmission).In this work, the bulk composition of five silver Roman coins have been indirectly measured by combining XRF and GRT. These results were compared with previous works made by our group using the same coins by direct means of PIXE and XRF, so the accuracy of this indirect method could be tested.

Spectroscopic analyses of an ancient silver fragment of the reliquary bust of St. Leo

A fragment of the silver reliquary bust of St. Leo, made in Messina, Italy, in the last of 1739 and now preserved in the church of SS. Savior of Africo Nuovo, Reggio Calabria, Italy, was investigated with spectroscopic techniques (scanning electron microscopy (SEM)+energy-dispersive X-ray (EDX), X-ray diffraction (XRD)) in order to analyze the composition of the sample in terms of elements and compounds. EDX analysis employs an electron beam that interacts with the sample, leading to the emission of characteristic X-rays as secondary radiation. In the XRD analysis, a Cu Kα X-ray radiation is detected by a Si(Li) solid-state detector after the interaction with the sample. The chemical composition of the bulk allowed to identify the constituting metal alloy, while the detection of surface elements and compounds, closely related to the sample preservation, was useful in order to suggest to restorators the best interventions to minimize the conservation problems that could affect the durability of the precious artefact.

Nondestructive Analysis of Silver Coins Minted in Taras (South Italy) between the V and the III Centuries BC

This work enters in an interdisciplinary research project involving the archaeometrical analysis of ancient silver coins minted in the Greek colony of Taras (the modern south Italian town of Taranto) between the V century BC and the III century BC. In this work, by comparing the results obtained from X-ray microanalysis data acquired from the least corroded surface areas and the cross-section of coins from SEM-EDX and from XRF analysis, we have demonstrated that analysed coins exhibited a corrosion layer no more than 25 μm and that surface silver enrichment was less than 1 wt%. Thus, the data obtained by using X-ray microanalysis from surface may not significantly differ from the original bulk composition. Our results demonstrate that the silver content in the coins decreases considerably ranging from about 97% for the older down to 80% for the ones of 3rd Evans period (300–270 BC), corresponding to the significant social change in the period.

Surface studies of environmental reactive species during exhibition or storage of ancient Ag‐based artefacts

The role played by environmental species affecting the long‐term stability of archaeological Ag‐based artefacts during museum exhibition or storage has been studied by means of the combined use of selected area X‐ray photoelectron spectroscopy, X‐ray diffraction, optical microscopy and scanning electron microscopy + energy dispersive spectrometry. The presence of fine particulate and of aggressive compounds in the museum atmospheres has been investigated by means of an innovative testing methodology based on Ag‐based reference alloys. The procedure has been applied to different areas of some museums in the Mediterranean Basin in order to consider representative environmental conditions of storage and exhibition of Ag‐based artefacts. The case studies of the National Roman Museum in Rome, Italy and of the Egyptian Museum of Cairo, Egypt will be illustrated. Furthermore, the study has been performed as a function of the alloy chemical composition and of the position of the reference specimens. The results of the superficial, micro‐chemical and morphological characterisations of the reference alloys are related to degradation parameters of ancient silver artefacts, as the presence of sulfur dioxide and chloride ions. The chosen methodology can be recommended to investigate the environmental key factors to consider for a safe storage or exhibition of archaeological silver artefacts, ensuring them a long stable life from a chemical–physical point of view. Copyright © 2014 John Wiley & Sons, Ltd.

Microstructures of ancient and modern cast silver–copper alloys

The microstructures of modern cast Sterling silver and of cast silver objects about 2500years old have been compared using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), energy dispersive X-ray microanalysis (EDX) and electron backscatter diffraction (EBSD). Microstructures of both ancient and modern alloys were typified by silver-rich dendrites with a few pools of eutectic and occasional cuprite particles with an oxidised rim on the outer surface. EBSD showed the dendrites to have a complex internal structure, often involving extensive twinning. There was copious intragranular precipitation within the dendrites, in the form of very fine copper-rich rods which TEM, X-ray diffraction (XRD), SEM and STEM suggest to be of a metastable face-centred-cubic (FCC) phase with a cube–cube orientation relationship to the silver-rich matrix but a higher silver content than the copper-rich β in the eutectic. Samples from ancient objects displayed a wider range of microstructures including a fine scale interpenetration of the adjoining grains not seen in the modern material. Although this study found no unambiguous evidence that this resulted from microstructural change produced over archaeological time, the copper supersaturation remaining after intragranular precipitation suggests that such changes, previously proposed for wrought and annealed material, may indeed occur in ancient silver castings.

Diamond-like carbon coatings for the protection of metallic artefacts: effect on the aesthetic appearance

Plasma-enhanced chemical vapour deposition (PECVD) is an environmentally friendly process used to deposit a variety of nano-structured coatings for the protection or the surface modification of metallic artefacts like the SiO2-like films that have been successfully tested on ancient silver, bronze and iron artefacts as barriers against aggressive agents. This paper deals with the preliminary results of a wider investigation aimed to the development of eco-sustainable coatings for the protection of Cu and Ag-based artefacts of archaeological and historic interest. Diamond-like carbon (DLC) coatings have been deposited by PECVD in different experimental conditions, in a capacitively coupled asymmetric plasma reactor, placing the substrates either on electrically powered electrode (cathodic mode) or grounded electrode (anodic mode) with and without hydrogen addition in the gas mixture. The final goal is to develop a coating with good protective effectiveness against aggressive atmospheres and contemporarily with negligible effects on the aesthetic appearance of the artefacts. The evaluation of possible colour changes of the surface patinas, due to coating process, was performed by optical microscopy and colorimetric measurements. Furthermore, to evaluate the reversibility of the thin DLC layer, an etching treatment in oxygen plasma has been successfully carried out and optimized. The chemical-physical characterization of the deposited DLC coatings was performed by means of the combined use of micro-Raman and XPS spectroscopies. The results show that the DLC films obtained in the anodic mode, may be proposed as a viable alternative to polymeric coatings for the protection of metallic ancient objects.

A study of the composition and microstructure of silver hoards from Tel Beth-Shean, Tel Dor, and Tel Miqne, Israel

The chemical composition and microstructure of objects excavated in three hoards from the end of the Late Bronze and Iron Age sites in Israel were studied using energy-dispersive x-ray fluorescence analysis and optical metallography. The objects are industrial in origin (scrap or jewelry pieces) and include differently shaped ingots, mainly so-called hacksilber, in various sizes. The primary composition is Ag with typically several percent of Cu and Au and less than 1 % of Pb. The concentrations of these metals in each hoard differ significantly. The microstructure of the hacksilber ingots shows a typical dendritic as-cast structure and a surface cold work deformation, probably caused by chiseling the ingot piece off a larger cast bar. Relatively high concentrations of Au, as in the above samples, were observed previously in Egyptian ancient silver which differs from the ancient Greek silver that contains a significantly lower Au content.

Changes of microbial properties in (near-) rhizosphere soils after phytoextraction by Sedum alfredii H: A rhizobox approach with an artificial Cd-contaminated soil

The ultimate goal of soil remediation is to restore soil health. Soil microbial parameters are considered to be effective indicators of soil health. The aim of this study was to determine the effects of phytoextraction on microbial properties through the measurement of soil microbial biomass carbon, soil basal respiration and enzyme activities. For this purpose, a pre-stratified rhizobox experiment was conducted with the Cd hyperaccumulator Sedum alfredii H. for phytoextraction Cd from an artificial contaminated soil (15.81mgkg−1) under greenhouse conditions. The plant and soil samples were collected after growing the plant for three and six months with three replications. The results indicated that the ecotype of S. alfredii H. originating from an ancient silver mining site was a Cd-hyperaccumulator as it showed high tolerance to Cd stress, the shoot Cd concentration were as high as 922.6mgkg−1 and 581.9mgkg−1 at the two samplings, and it also showed high BF (58.4 and 36.8 after 3 and 6 months growth), and TF (5.8 and 5.1 after 3 and 6 months growth). The amounts of Cd accumulated in the shoots of S. alfredii reached to an average of 1206μgplant−1 after 6 months growth. Basal respiration, invertase and acid phosphatase activities of the rhizosphere soil separated by the shaking method were significantly higher (P<0.01) than that of the near-rhizosphere soil and the unplanted soil after 3 months growth, so were microbial biomass carbon, urease, invertase and acid phosphatase activities of the rhizosphere soil after 6 months growth. Acid phosphatase activity of the 0–2mm sub-layer rhizosphere soil collected by the pre-stratified method after 3 months growth was significantly higher (P<0.05) than that of other sub-layer rhizosphere soils and bulk soil, and so were microbial biomass carbon, basal respiration, urease, invertase and acid phosphatase activities of the 0–2mm sub-layer rhizosphere soil after 6 months growth. It was concluded that phytoextraction by S. alfredii could improve soil microbial properties, especially in rhizosphere, and this plant poses a great potential for the remediation of Cd contaminated soil.

Ancient silver extraction in the Montevecchio mine basin (Sardinia, Italy): micro-chemical study of pyrometallurgical materials

Different pyrometallurgical materials such as slags, refractory materials and thermally treated lead ores likely related to smelting and extractive processes and chronologically related to Punic and Roman periods (IV–III BC) have been found at Bocche di Sciria and Conca e Mosu in the Montevecchio mine basin (south western Sardinia, Italy), where archaeological findings and classical authors locate extractive metallurgy activities since pre-Roman times. By means of the combined use of X-ray diffraction (XRD), scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectrometry (EDS), selected-area X-ray photoelectron spectroscopy (XPS) and optical microscopy (OM), micro-chemical and micro-structural investigations have been carried out in order to identify the nature of the pyrometallurgical materials, to decipher the processes carried out there and their technological steps and to determine the technological level of competence reached by the ancient metallurgists. The results confirm that the findings can be associated with smelting and extractive processes carried out close to the metal ore deposits first for the argentiferous lead production and, then, for the silver recovery via a cupellation process. Finally, the results disclose the high level of technological competence of the ancient metallurgists able to carry out complex high-temperature processes to treat the argentiferous lead ores and to recover low amounts of silver via high-temperature lead-selective oxidation.

Stress corrosion cracking in ancient silver

Six cases of ancient silver embrittlement by corrosion are discussed with respect to evidence for stress corrosion cracking. Both intergranular and transgranular cracking can occur, depending on whether there is retained cold-work in the silver. The severity of cracking is influenced by a combination of factors, including the amount of cold-work in the silver and the burial environment. The burial environment is important for two reasons. Firstly, the soil weight can induce high stresses, particularly in hollow, thin-walled, and incompletely filled-in artefacts. Secondly, grave burials can result in more aggressive soil environments owing to high salinity from body decomposition.

Significance of Discontinuous Precipitation of Copper in Ancient Silver

Discontinuous precipitation of copper has been held responsible for much of the embrittlement of ancient silver objects. The detailed characteristics of this precipitation have been suggested as possible indicators of an object’s age and authenticity. These proposals are considered in the light of metallographic and analytical studies of several embrittled artifacts. These studies indicate that discontinuous precipitation is much less significant for embrittlement than residual stresses due to retained cold-work and externally applied stresses due to burial, and that the precipitation characteristics cannot be used for authentication.

XPS and XRF depth patina profiles of ancient silver coins

Ancient silver coins of different historical periods going from IV cent. B.C. up to recent XIX century, coming from different Mediterranean countries have been investigated with different surface physical analyses. X-ray photoelectron spectroscopy (XPS) analysis has been performed by using electron emission induced by 1.4keV X-rays. X-ray fluorescence (XRF) analysis has been devoted by using 30keV electron beam. Scanning electron microscopy (SEM) has been employed to analyze the surface morphology and the X-ray map distribution by using a 30keV microbeam.Techniques were used to investigate about the patina composition and trace elements as a function of the sample depth obtained coupling XPS to 3keV argon ion sputtering technique.

A Study of ancient Tibetan gold and silver ware

AbstractTibetan gold and silver artworks were recorded in Tang literal documents and enjoyed a great fame throughout the world for their unique and exquisite styles, but their samples have been seldom discovered. Based on a study on the Tibetan gold and silver wares recently unearthed from Tibetan tombs in the Qinghai-Tibetan Plateau and known from collections abroad, this paper believes that both historical records and archaeological discoveries proved the high accomplishments of Tibetan gold and silver crafts. Compared to gold and silver products made in the Central Plains of Tang China as well as in Central and Western Asia, the essence of the Tibetan articles can be said to have been roughly paralleling with those products in technological sense, which indicates that by that time Tibet had become an important production center of gold and silver wares in the East Asia. Tibetan gold and silver wares demonstrate clearly interaction and absorption among the cultural elements of Tibet and those of Tang China’s other regions as well as Sogdiana and Persia. Moreover, they reflect that Tibet in its annexing and expanding procedure came into close relationships with nomadic tribes in the steppes of northern and northwestern China.

X-ray Fluorescence analytical criteria to assess the fineness of ancient silver coins: Application on Ptolemaic coinage

The application of X-ray Fluorescence (XRF) analysis in a non-invasive manner on ancient silver coins may not provide reliable bulk compositional data due to possible presence of a surface, silver enriched layer. The present work proposes a set of three complementary analytical methodologies to assess and improve the reliability of XRF data in such cases: a) comparison of XRF data on original and cleaned micro-spots on coin surface, b) Ag K/L ratio test and c) comparison of experimental and theoretically simulated intensities of the Rayleigh characteristic radiation emitted from the anode. The proposed methodology was applied on 82 silver coins from the collection of Ioannes Demetriou, donated to the Numismatic Museum of Athens in the 1890s. The coins originate from different mints and are attributed to the first five Ptolemaic kings' reign (321–180 B.C.). They were analyzed in-situ by using a milli-probe XRF spectrometer. The presence of an Ag-enriched layer was excluded for the majority of them. The silver fineness was found to be high, with very low concentrations of copper and lead. The composition data provide important information about possible sources of silver during the Ptolemaic period and indications of a gradual coinage debasement after 270 B.C. due to economic or technical reasons.

A Late Antique Silver Reliquary in Toronto

A previously unpublished casket now in Toronto shares some formal and compositional features with the small corpus of known silver reliquaries produced in the eastern Mediterranean during Late Antiquity; at the same time, it differs from these in iconographic (and orthographic) particulars and in style. Investigation of a wide range of comparanda in diverse media reveals that the principal message of the reliquary’s decoration is the adoration of the cross on Golgotha, conflated with the baptism of Christ to symbolize the source of life. It was likely made in Palestine during the reign of Heraclius and perhaps can be associated with that emperor’s restoration of the True Cross to Jerusalem. As the first attested silver reliquary with figural decoration from that region, it significantly expands our knowledge of artistic production in Palestine in the early seventh century.

Case Histories of Ancient Silver Embrittlement

This article discusses six cases of ancient silver embrittlement. The diagnostic techniques and results are surveyed, followed by the most likely explanations of embrittlement. There are two basic types of embrittlement: corrosion-induced, and microstructurally induced, which can act synergistically. Corrosion-induced embrittlement takes several forms, including what appears to be intergranular and transgranular stress corrosion cracking. The main intrinsic factor facilitating corrosion-induced embrittlement is retained cold-work in the silver. Microstructural embrittlement is characterized by intergranular fracture, most probably due to low-temperature segregation of lead to the grain boundaries. Knowledge of the details of embrittlement can be essential for optimizing the restoration and conservation of damaged artifacts.

Experimental results of UV laser cleaning on a silver Carlino coin

Silver artefacts and particularly ancient silver artefacts present the serious problem of turning black due to ambient contamination. The black colour is the consequence of a layer forming on the surface made of acanthite and jalpaite; both compounds are sulphur composts. Recently, a UV laser cleaning technique has demonstrated to be very promising in the processing of cultural artefacts. To operate on artefacts without contaminating the bulk, we first determined the laser fluence threshold of the bulk; second, we controlled the surface compounds, and finally we operated the laser irradiation. In this work, we utilised certified silver and silver/copper samples in order to perform preliminary studies. The threshold fluences we found were 780 and 510 mJ/cm2 for the pure Ag and for the Ag/Cu alloy, respectively. The jalpaite concentration on the Ag/Cu sample increased after a laser dose of 25 J/cm2, whereas for a higher laser dose its value lowered, pointing out that complex processes take part during the laser application. We successfully applied the technique on a Carlino coin made of silver coined in 1689 under King Carlo II. The analyses were performed by two different techniques that are able to find the percentage of elements and the chemical compounds: the energy dispersive X-ray fluorescence and the X-ray diffractometer spectrometer. We found that the sulphur concentration decreased upon the increase of the laser dose. Operating on the coin up to a dose of 280 J/cm2, the sulphur concentration deceased by up to 20%, while the coin looks clearer just after 50 J/cm2.

Museum Laboratories: Where Art Meets Science

Museum Laboratories: Where Art Meets Science

Embrittled Ancient Silver and Iron Objects and Their Conservation

Abstract Embrittlement of ancient metals is often complex. The details of embrittlement should be investigated in order to select the best remedial measures for restoration and conservation. This article surveys the techniques used for investigating several ancient embrittled silver artifacts and an iron pile-shoe from a Roman bridge. The possibilities for preserving such objects are also discussed.