A multi-analytical approach for the validation of a jellified electrolyte: Application to the study of ancient bronze patina Francesca Di Turo a, ⁎, Caterina De Vito a , Fulvio Coletti b , Franco Mazzei c , Riccarda Antiochia c , Gabriele Favero c a Department of Earth Sciences, Sapienza University of Rome, P.le Aldo Moro 5, Rome, Italy b Soprintendenza Speciale per il Colosseo, il Museo Nazionale Romano e l'Area Archeologica di Roma, P.zza dei Cinquecento 67, Rome, Italy c Department of Chemistry and Drug Technologies, Sapienza University of Rome, P.le Aldo Moro 5, Rome, Italy abstract article info Article history: Received 18 March 2017 Received in revised form 25 May 2017 Accepted 26 May 2017 Available online 27 May 2017 This work reports the first employment of a gel polymer-based electrochemical cell to perform electrochemical impedance analysis of archaeological remains. The patinas of three Roman coins are studied through of electro- chemical techniques (especially Electrochemical Impedance Spectroscopy, EIS) along with Electron Scanning Mi- croscopy (SEM-EDS) and X-ray diffraction (XRD), in order to validate the results obtained with jellified electrolyte. SEM-EDS and XRD analyses reveal the composition of the patinas suggesting that the original alloys were made of Cu and Cu–Sn–Pb. Furthermore, EIS results make one able to assess some characteristics of coins, as for instance, the presence of a noble patina. This outcome is corroborated by the SEM-EDS and XRD analysis, sug- gesting that the method based on the jellified electrolyte on archaeological samples can be employed. Moreover, supporting studies are carried out using Voltammetry of Microparticles (VMP), which is able to detect the pres- ence of some specific corrosion products (cuprite). So far, EIS is not a common technique in the Cultural Heritage field despite it can provide useful information about the conditions of conservation, i.e., corrosion processes. Here we can show the advantages of developing a gel-based system for EIS measurement which allows carrying out a punctual and quick analysis on the ancient bronze roman coins. © 2017 Elsevier B.V. All rights reserved. Keywords: Bronze Roman coins Cultural heritage diagnostics Jellified agar 1. Introduction The use of metals and alloys had a key role in human history, charac- terizing the different ages and influencing the technological background and social life of ancient populations. Therefore, a deep comprehension of these materials and their corrosion can provide unique information about the technological background of the ancient civilization and the occurring post-manufacturing processes. Detailed analytical studies of alloys provide an accurate understanding of the ancient knowledge of the chemical and physical properties of metals [1]. Artefacts made of copper, iron or other metals and alloys are very common in the archaeological contexts [2–6]. In particular, bronze was extensively used in the past and the corrosion process uncovered in the burial condition have aroused a great interest among researchers in the last years [7]. As well documented by literature, the corrosion products give useful information for restoration and conservation of ancient metal artefacts [8–12] as they depend on either the usage or burial history as well as on the environmental conditions [13]. In fact, the presence of carbonates, chlorides, silicates, phosphates, and sul- phates enriched with elements such as Ca, K, and Al in the patina, suggests an intense interaction between the corroding metal and the soil [14]. Studying the corrosion products could be very difficult due to the layered structure and the multicomponent nature thereof. Indeed, it is often possible to distinguish a primary, secondary and tertiary patina [13]. The primary patina can be related to the usage of the object and it is mainly composed of metal oxides; the second and the tertiary pati- na are formed in the first burial condition and they are strictly depen- dent on mineralization, crystallization and complex chemical reactions occurring in the soil [11,15]. In the field of metals conservation, it is im- portant to distinguish between the so-called noble patina and vile pati- na: the first one is a passive layer constituted by a homogenous film of oxides which allows the conservation of the original metal below it [16]. The vile patina, conversely, can be very dangerous for the artefacts. It may consist in chloride-based compounds (nantokite, CuCl or paratamite and its polymorphs, Cu 2 (OH) 3 Cl, for example) which may lead to the pulverization of the metal due to the process known as “bronze disease” [17]. The vile patina is usually non-uniform and the pitting corrosion is a common phenomenon in this case [18]. However, Microchemical Journal 134 (2017) 154–163 ⁎ Corresponding author. E-mail addresses: francesca.dituro@uniroma1.it (F. Di Turo), caterina.devito@uniroma1.it (C. De Vito), fulvio.coletti@beniculturali.it (F. Coletti), franco.mazzei@uniroma1.it (F. Mazzei), riccarda.antiochia@uniroma1.it (R. Antiochia), gabriele.favero@uniroma1.it (G. Favero). http://dx.doi.org/10.1016/j.microc.2017.05.015 0026-265X/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Microchemical Journal journal homepage: www.elsevier.com/locate/microc