Archaeological Bronze Artefacts Research Articles

Micro-structural and micro-chemical investigation of Samnite high-tin bronze cuirass discs: ancient metallurgy in central Italy

In the present study, micro-structural and micro-chemical investigation of archaeological bronze artefacts provided new insight about the metallurgical manufacture of defensive weapons by the Samnite’s metalsmiths in central Italy from the archaic necropolis of Barrea (AQ) and Torrebruna (CH). In particular, the metallurgical features, the chemical composition and the manufacturing process of Cu-based high-tin alloys used to produce cuirass discs were investigated. These artifacts were used to protect the warrior’s heart (i.e. the kardiophylaches) but were also and more importantly a distinctive sign of rank and role of warriors of the archaic age (VI BC). The Samnite cuirass discs are multi-material artifacts made of a decorated bronze central part with a complex metallurgical structure, due to the presence of different Cu-Sn phases, and a surrounding iron cladding to support the disk. These discs were studied by different surface and bulk techniques, namely Optical Microscopy (OM), Field Emission Scanning Electron Microscopy coupled with energy dispersive X-ray microanalysis (FE-SEM-EDS), X-ray Diffraction (XRD) and Infrared Spectroscopy (FTIR). The combined use of these techniques proved the high technological level of the Samnite metallurgists. In fact, their particular composition, having an uncommon high content of tin, made their manufacturing process difficult because of the intrinsic brittleness of the alloy. This work disclose the ability of Samnites people to successfully manipulate fragile high tin bronze alloys by inducing temporary phase changes and, thus, facilitating the mechanical shaping of the artifact.

Application of µ-Raman spectroscopy to the study of the corrosion products of archaeological coins

<p>In this paper, a study of the corrosion products formed on archaeological bronze artefacts excavated in Tharros (Sardinia, Italy) is presented. The investigation was carried out by means of the combination of different analytical techniques, including optical microscopy, micro-Raman spectroscopy (µ-RS), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction. The artefacts under study are three bronze coins from the Phoenician–Punic period that are deeply corroded due to the chloride-rich soil of the Tharros excavation site. µ-Raman spectroscopy was chosen to investigate the corroded surfaces of the artefacts because it is a non-destructive technique, it has high spatial resolution, and it makes it possible to discriminate between polymorphs and correlate colour and chemical composition. Through µ-RS, it was possible to identify different mineralogical phases and different polymorphs, such as cuprite (Cu<sub>2</sub>O), copper trihydroxychloride [Cu<sub>2</sub>Cl(OH)<sub>3</sub>] polymorphs, hydroxy lead chloride laurionite [PbCl(OH)] and calcium carbonate polymorph aragonite. The experimental findings highlight that micro-Raman spectroscopy can be used to provide further knowledge regarding the environmental factors that may cause the degradation of archaeological bronzes in soil.</p>

Quantitative determination of antimony in archaeological bronze artefacts by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a reliable, fast and micro-destructive diagnostic method for qualitative and quantitative analysis of a variety of materials. In this paper, we report the results of quantitative determination of antimony in four archaeological bronze artefacts analyzed by means of LIBS. For the purpose of this study, an approach of multi-elemental quantitative LIBS analysis is proposed, based on the use of an element with known concentration as an internal standard and measurement of the spectral lines intensities of the internal standard and the element with unknown concentration. An important plasma parameter which is included in the quantitative analysis is the excitation temperature as determined by the Boltzmann plot method. The quantity of antimony in the bronze artefacts obtained by means of the proposed LIBS approach is between 1.49% and 3.13%.

Corrosion inhibition of bronze alloy B66 by 4-amino-3-methyl-1,2,4-triazole-5-thione in 3 per cent NaCl solution

Purpose – The purpose of this study is to study corrosion inhibition of Bronze alloy B66 by 4-amino-3-methyl-1,2,4-triazole-5-thione (MTSNH) in 3 per cent NaCl solution. Archaeological bronze artefacts often are stored or displayed in uncontrolled conditions and may suffer from dangerous active corrosion processes that can lead to their destruction. The most dangerous form of archaeological bronze degradation is due to a cyclic reaction that involves copper from the pure alloy and chlorine as a pathogenic agent. A protection treatment can be used to protect them from the corrosion environment and stabilise them to avoid further degradation during exhibition or storage. Starting from its initial assessment as a corrosion inhibitor for pure copper, nowadays benzotriazole (BTA) is in widespread use for the conservation of copper-based artefacts, but unfortunately, BTA is toxic and a suspected carcinogen. The development of new and safe protection systems would offer a choice of alternative products to conservation-restoration professionals for the effective and safe stabilization and protection of metal artefacts. In this investigation, a new organic compound, namely, MTSNH, was synthesized, characterized and tested as a corrosion inhibitor for Bronze B66 (similar to archaeological bronze) in 3 per cent NaCl solution using potentiodynamic polarization studies and electrochemical impedance spectroscopy (EIS) at room temperature. It has been observed from the corrosion rate that the inhibition efficiency increased with increasing concentration of MTSNH. Potentiodynamic polarisation results revealed that the compound acted as a mixed-type inhibitor. Impedance studies indicated that protection occurs through adsorption of the inhibitor on the metal surface, with important modification to the mechanism of corrosion. Surface analysis was carried out using scanning electron microscopy scanning electron microscopy (SEM)/energy dispersive spectrometry (EDX) techniques to verify the electrochemical results. Design/methodology/approach – The inhibition efficiency of MTSNH is investigated by potentiodynamic polarization, EIS and surface analysis. Findings – The synthesized MTSNH act a good inhibitor in 3 per cent NaCl and inhibition efficiency increases with inhibitor concentration. Polarisation curves showed that the inhibitor is mixed. The EIS measurements showed that the inhibitor acted throughout the formation of film at the bronze surface. The surface analysis confirms this result. Originality/value – The adsorption of the MTSNH on the metal surface can markedly change the corrosion resisting property of metal. Therefore, the study of the relation between adsorption and corrosion inhibiting is of a great importance.

Unusual surface degradation products grown on archaeological bronze artefacts

Within the framework of the EFESTUS project funded by the European Commission a large number of Cu-based archaeological artefacts from the Mediterranean basin have been studied to investigate their chemical composition, metallurgical features and corrosion products nature (i.e. the patina). By means of the combined use of X-ray photoelectron spectroscopy (XPS), optical microscopy (OM), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS) and X-ray diffraction (XRD) the bronze artefacts have been studied for the detailed identification of the corrosion products and their micro-chemical structure in order to achieve information about degradation agents and mechanisms. In the present work, some examples of unusual corrosion products formed on the objects during the long-term burial are presented and related to the peculiar local context revealing the strong interaction between the bronze artefact and the chemical components found in the archaeological site.

Analytical methodologies for the investigation of soil‐induced degradation of Cu‐based archaeological artefacts

Archaeological bronze artefacts are covered with corrosion products, that is, the patinas, whose nature depends on different degradation processes occurring during long‐term burial. As a consequence of the corrosion phenomenon, surfaces of archaeological metal objects are composed of a complex structure. By means of the combined use of different analytical techniques such as XPS, scanning electron microscopy combined with energy dispersive X‐ray spectroscopy, optical microscopy and X‐ray diffraction, some typical patinas grown on Roman and Punic archaeological bronze artefacts have been studied in details by selecting a suitable methodological approach to acquire micro‐chemical, morphological and structural information. The XPS measurements of Cu 2p, Cu LMM and valence band spectra of archaeological objects and reference samples such as CuCl2, CuCl, Cu2Cl(OH)3, Cu2O and CuO allowed us to identify the different copper oxidation states and crystallographic phases present in a patina. Moreover, the XPS elemental concentration depth profiles have yielded information about the stratified outermost layers and the occurrence of the migration phenomenon from bulk to surface due to selective corrosion processes. These pieces of information compared with those achieved via scanning electron microscopy combined with energy dispersive X‐ray spectroscopy, optical microscopy and X‐ray diffraction reveal the complex chemistry and morphology of the patina, highlighting also the correlation between patina and burial context. Copyright © 2012 John Wiley & Sons, Ltd.

Novel approach to the microscopic inspection during laser cleaning treatments of artworks

The present work focuses on the potential of 3D digital microscopy for assessing micro-morphological features during laser cleaning treatments of artworks. This application requires preliminary optimization studies aimed at defining operative irradiation parameters and practicable degree of cleaning, as well as in situ diagnostic assessments during the restoration work. To this goal, we developed and tested a dedicated 3D digital microscope by implementing the "shape-from-focus" technique. The significant potential of this instrument, which provides textural and chromatic information, was proven for the phenomenological characterization of black crust removal from stones, earthy concretion from bronzes and dark varnish from easel paintings. Comparative measurements using 3D digital microscopy and contact microprofilometry were performed after laser cleaning tests of prepared samples, genuine archaeological bronze artefacts and a stone sculptural element from Florence's Dome. The results achieved demonstrate the effectiveness and reliability of the novel approach and the advantages it provides with respect to alternative techniques, which will allow the methods to be used in the wider restoration community.

Some Long Term Corrosion Patterns in Archaeological Metal Artefacts

Long term corrosion phenomena are generally not obtained in laboratorial corrosion experiments. Particular features, such as strong intergranular corrosion, can be an indication of the antiquity of a metallic artefact. In the present study, various corrosion features from several archaeological bronze artefacts, with ages ranging from 2 to 5 millenniums, are examined using optical and scanning electron microscopies. Elemental composition was obtained through micro-EDXRF analyses. Corrosion patterns could, in some occasions, be related to specific thermomechanical treatments performed before burial and, in others, with particular phases present in the artefact.

Uncommon corrosion phenomena of archaeological bronze alloys

In the framework of the EFESTUS project (funded by the European Commission, contract No. ICA3-CT-2002-10030) the corrosion products of a large number of archaeological bronze artefacts are investigated by means of the combined use of scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and optical microscopy (OM) and tentative correlation of their nature with the chemical composition of the artefacts and the burial context is proposed.

Unalloyed copper inclusions in ancient bronze artefacts

Ancient bronze artifacts, that represent a considerable part of the archeological finds, have been largely studied because of their complex degradation phenomena taking place in the long time span that have not been fully understood. One of the peculiar features of ancient bronzes is the presence of inclusions of copper unalloyed with tin. Unalloyed Copper Inclusions (UCI) have been observed in buried archaeological bronze artefacts by several authors, but each paper reports only on a limited number of cases. In our extensive studies on bronze artefacts, UCI have been observed in many bronze artefacts with very different features and purposes. Both as-cast and wrought artefacts were studied, so that the influence of the manufacturing process and the composition of the artefacts on the formation of UCI might be evaluated. The microstructure and composition of these artefacts were studied and the features of UCI have been related with those of the surrounding phases. The results have been discussed and compared with those obtained by other authors. The presence of UCI in buried archaeological bronze artefacts could indicate some unusual corrosion processes that might need to be accounted for when designing conservation treatments.

Corrosion of archaeological bronze artefacts in acidic soil

Corrosion of bronze in soil is a well-known phenomenon. In particular, archaeological artefacts which may remain in the soil for thousands of years are subject to severe corrosion. However, bronze objects excavated 50–100 years ago seem to be less corroded than those found today. Therefore, recent pollution of the soil is suspected to accelerate the corrosion. An interdisciplinary project has been started in Sweden to search for correlations between the degree of bronze corrosion, corrosion products, general archaeological and environmental conditions, and parameters characterizing the soil chemically.