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

[EN] A set of ancient Antoninianus silver coins, dating back between 249 and 274¿A.D. and minted in Rome, Galliae, Orient and Ticinum, have been characterized. We use, for the first time, a combination of nano-invasive (focused ion beam-field emission scanning electron microscopy-X-ray microanalysis (FIB-FESEM-EDX), voltammetry of microparticles (VIMP)) and destructive techniques (scanning electron microscopy (SEM-EDX) and electron microprobe analysis (EMPA)) along with non-invasive, i.e., micro-Raman spectroscopy. The results revealed that, contrary to the extended belief, a complex Ag-Cu-Pb-Sn alloy was used. The use of alloys was common in the flourishing years of the Roman Empire. In the prosperous periods, Romans produced Ag-Cu alloys with relatively high silver content for the manufacture of both the external layers and inner nucleus of coins. This study also revealed that, although surface silvering processes were applied in different periods of crisis under the reign of Antoninii, even during crisis, Romans produced Antoninianus of high quality. Moreover, a first attempt to improve the silvering procedure using Hg-Ag amalgam has been identified.Financial support was provided by Sapienza University of Rome (Ateneo funding, 2014 15) and Spanish projects CTQ2014-53736-C3-1-P and CTQ2014-53736-C3-2-P, which are supported with Ministerio de Economía, Industria y Competitividad (MINECO) and Fondo Europeo de Desarrollo Regional (ERDF) funds, as well as project CTQ2017-85317-C2-1-P supported with funds from, MINECO, ERDF and Agencia Estatal de Investigación (AEI). PhD grants of the Department of Earth Sciences, Sapienza University of Rome, are gratefully acknowledgedDomenech Carbo, MT.; Di Turo, F.; Montoya, N.; Catalli, F.; Doménech Carbó, A.; De Vito, C. (2018). 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New Insights into the Geochemical Processes Occurring on the Surface of Stuccoes Made of Slaked Lime Putty

The fresco technique performed with slaked lime putty as binding material has been well known since Antiquity. However, the geochemical processes that occur on the surface have been generally described as part of the carbonation process of the intonaco itself. When approaching this technique from experimental archaeology, it has been observed for the first time that during the execution period (from 0 to 20 h, approximately) the processes occurring on the surface of the stucco are different from those occurring inside. Furthermore, these processes lead to the formation of an epigenetic film of specific texture, stiffness and compactness. This study investigates the formation and evolution of this surface film using a series of slaked lime putty stucco test tubes. Samples were extracted at different intervals and subsequently analyzed by polarized optical microscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy. Results indicate that the development of the film, composed of an amorphous gel-like stratum and a micro-crystalline stratum, occurs in parallel to the carbonation occurring inside the stucco. Moreover, this process does not respond to the classical geological processes of calcium carbonate formation. It was also observed that its presence slows down the carbonation in the underlying strata (intonaco, intonachino, arriccio, etc.) and that the surface becomes more crystalline over time. The identification of this film has implications for the field of the conservation-restoration of fresco paintings and lime-based wall paintings

Isomerization and Redox Tuning: Reorganizing the Maya Blue Puzzle from Synthetic, Spectral, and Electrochemical Issues

[EN] A new approach to describe the composition of Maya blue (MB), an ancient organic- inorganic hybrid material, is presented. It is based on the analysis of attenuated total reflection-Fourier transform infrared (ATR-FTIR), Raman spectroscopy, UV-visible (vis) spectroscopic, and electrochemical data for indigo and dehydroindigo plus palygorskite hybrids, including a novel methodology using electrocatalytic effects on the oxygen reduction reaction. As a result, it is concluded that MB results from the tautomerization of indigo-to-indigo hemienol and the subsequent oxidation of these isomeric forms to dehydroindigo, all associated with the palygorskite clay framework, at temperatures above 100 degrees C. This model is also consistent with C-13 NMR data on indigo plus sepiolite hybrids. A consistent set of thermochemical parameters is obtained from ATR-FTIR, solid-state electrochemistry, and UV-vis diffuse reflectance spectra for the successive isomerization and redox tuning processes experienced by palygorskite-associated indigo.Projects PID2020-113022GB-I00 and RTI2018-100910-BC42, supported by MCIN/AEI/10.13039/501100011033 are gratefully acknowledged for all of the equipment employed. NMR was registered at the U26 facility of ICTS "NANBIOSIS" at the SCSIE of the Universitat of Valencia.Doménech-Carbó, A.; Costero, AM.; Gil Grau, S.; Montoya, N.; López-Carrasco, A.; Sáez, JA.; Arroyo, P.... (2021). Isomerization and Redox Tuning: Reorganizing the Maya Blue Puzzle from Synthetic, Spectral, and Electrochemical Issues. The Journal of Physical Chemistry. 125(47):26188-26200. https://doi.org/10.1021/acs.jpcc.1c0793226188262001254

Screening of Iberian Coinage in the 2(th)-1(th) BCE Period Using the Voltammetry of Immobilized Particles

This is the peer reviewed version of the following article: A. Doménech-Carbó, M. T. Doménech-Carbó, C. Álvarez-Romero, T. Pasíes, M. Buendía, Electroanalysis 2019, 31, 1164, which has been published in final form at https://doi.org/10.1002/elan.201900090. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.[EN] The voltammetry of immobilized particles (VIMP) was applied for grouping a series of 86 Iberian coins nominally minted in the cities of Iltirta, Castulo and Obulco in the 2(th)-1(th) BCE period for which there are no chronological data. Using characteristic signatures for the reduction of cuprite, tenorite and lead corrosion products in the patina of the coins, voltammetric grouping of coins was proposed. Voltammetric data were found to be consistent with textural and compositional properties of the surface and subsurface of selected coins using FIB-FESEM-EDX. The obtained data confirmed a clear separation between the productions of Iltirta on one side, and those of Castulo and Obulco on the other side, indicating the possibility to establish a rough chronology for these productions.Project CTQ2017-85317-C2-1-P, supported with Ministerio de Economia, Industria y Competitividad (MINECO), Fondo Europeo de Desarrollo Regional (ERDF) and Agencia Estatal de Investigacion (AEI), is gratefully acknowledged. The authors wish also to thank Mr. Manuel Planes and Dr. Jose Luis Moya, technical supervisors of the Electron Microscopy Service of the Universitat Politecnica de Valencia. Thanks to Manuel Gozalbes for his technical assistance in the numismatic domain and Gonzalo Cores and the Museu de Prehistrica de Valencia for facilitating the access to its collections.Doménech-Carbó, A.; Domenech Carbo, MT.; Álvarez-Romero, C.; Pasíes, T.; Buendía, M. (2019). Screening of Iberian Coinage in the 2(th)-1(th) BCE Period Using the Voltammetry of Immobilized Particles. Electroanalysis. 31(6):1164-1173. https://doi.org/10.1002/elan.201900090S11641173316P. P. Ripollès V. Heuchert A. Burnett Coinage and identity in the Roman provinces Oxford University Press London 79 93M. Gozalbes Circulación y uso de los denarios ibéricos in M. Campo Ús i circulació de la moneda a la Hispania Citerior XIII Curs d'història monetària d'Hispania Museu de Prehistòria de València València 83 103Constantinides, I., Gritsch, M., Adriaens, A., Hutter, H., & Adams, F. (2001). Microstructural characterisation of five simulated archaeological copper alloys using light microscopy, scanning electron microscopy, energy dispersive X-ray microanalysis and secondary ion mass spectrometry. Analytica Chimica Acta, 440(2), 189-198. doi:10.1016/s0003-2670(01)01061-3Linke, R., & Schreiner, M. (2000). 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On the photoluminescence changes induced by ageing processes on zinc white paints

Recent research is focusing on the study of interaction mechanisms between pigments and binders, as they are crucial for understanding paint ageing and conservation issues. In this work, we investigate these mechanisms and follow the changes induced by ageing on zinc white paint by employing Fourier Transform Infrared (FTIR) and Time-Resolved Photoluminescence (TRPL) spectroscopies. The two techniques, applied on thermally aged mock-up samples and on a 19th oil painting, provide complementary information on the effect of the binder on the ZnO pigment particles. The characterization of the infrared absorption spectra confirms the well-known tendency of amorphous metal carboxylate formation in zinc white paint following ageing. At the same time, the ageing of paint film produces significant changes in the photoluminescence emission from defect centres of ZnO. The emission that is mostly affected by the changes of the micro-environment is the blue band (430 nm) – associated with surface defects – whereas the green emission (530 nm) is stable. The results demonstrate that the evolution of the pigment-binder system has detectable consequences on the crystalline structure of the pigment particles and we speculate that the main cause of these modifications is the functionalization of the pigment particle surfaces. The possibility to follow crystal structure changes with time-resolved photoluminescence can thus support chemical studies on metal carboxylate formation and paint deterioration by providing information about pigment-binder interactions

Nafion® as advanced immobilisation substrate for the voltammetric analysis of electroactive microparticles: the case of some artistic colouring agents

Voltammetry of microparticles is applied to characterise and to identify solid analytes of interest in the field of cultural heritage. Nafion® is used for the immobilisation of solid microparticles onto the surface of a glassy carbon electrode by exploiting the deposition onto the electrode surface of a micro-volume of a suspension of the microsample in polymeric solution. Cyclic voltammetry and square wave voltammetry are applied to characterise and to identify the microparticles immobilised in the Nafion® coating. The analyte studied in this work is Prussian Blue as a typical inorganic pigment, with a relatively simple electrochemical behaviour. The proposed method is applied to a sample of Venetian marmorino plaster. The performance of Nafion® for this analysis is compared with that of the polymer Paraloid B72

The analysis of European lacquer : optimization of thermochemolysis temperature of natural resins

In order to optimize chromatographic analysis of European lacquer, thermochemolysis temperature was evaluated for the analysis of natural resins. Five main ingredients of lacquer were studied: sandarac, mastic, colophony, Manila copal and Congo copal. For each, five temperature programs were tested: four fixed temperatures (350, 480, 550, 650 degrees C) and one ultrafast thermal desorption (UFD), in which the temperature rises from 350 to 660 degrees C in 1 min. In total, the integrated signals of 27 molecules, partially characterizing the five resins, were monitored to compare the different methods. A compromise between detection of compounds released at low temperatures and compounds formed at high temperatures was searched. 650 degrees C is too high for both groups, 350 degrees C is best for the first, and 550 degrees C for the second. Fixed temperatures of 480 degrees C or UFD proved to be a consensus in order to detect most marker molecules. UFD was slightly better for the molecules released at low temperatures, while 480 degrees C showed best compounds formed at high temperatures