Electrochemistry for Cultural Heritage

Written by Francesca Di Turo

Translated by Sarah Fortunee Tabbakh

Italian Version Here

 

When talking about the diagnostic analyses to be carried out on cultural heritage, we hardly find electrochemistry amongst them. This is due to the seeming difficulty in analyzing the data, the unavailable tools, and the little understanding of the techniques and the answers they can provide – the main reason as to why this technique is rarely used, if you ask me. 

Actually, studying a voltammogram isn’t any more difficult than interpreting a FTIR or a Raman spectrum. The most widely used electrochemical techniques in the field of cultural heritage are Electrochemical Impedance Spectroscopy (EIS) and Voltammetry (linear, cyclic, wave, square, etc.). 

As any "traditional" analysis, these techniques have advantages and disadvantages and the material to analyze should always be taken into consideration before carrying out any examination. EIS is traditionally used to evaluate the effectiveness of metal protective agents, as it allows to obtain information about the charge transfer resistance of the analyzed sample. 

Research has been going a little further, trying to understand how useful it can be in the study of natural patinas (for example, noble patinas). EIS allows us to understand if they are, in fact, protective or not of the underlying metal. 

The main advantage, and it is not to be taken for granted, is that the EIS is available as a portable tool for in situ analysis. Various studies have been carried out in Italy by Paola Letardi (Ismar - CNR) ^[1] and Emma Angelini ^[2], whose contribution at an international level was decisive in launching the research. In fact, Emilio Cano’s Spanish group has collected their results, collaborating in the development of portable cells and the evaluation of corrosion of metal materials of historical and artistic interest. ^[3,4] 

Going back to Voltammetry, its applications range from pigments to metals, expanding the analytical possibilities of this technique. Since we need to use non-destructive or, at the utmost, micro-destructive techniques, the Voltammetry of Microparticles (VMP) stands as one of the best options for the analysis of artifacts. The founder of the VMP, Franz Scholz, had modified a pre-existing technique (the square wave voltammetry, at the basis of the VMP) in order to characterize minerals ^[5]. 

Let’s move on to the Solid State Electrochemistry: in fact, traditional voltammetry is performed with the sample in solution, which is not the case in VMP. 

In Solid State Electrochemistry, as the name suggests, the solid sample, as well as the related redox reactions, are analyzed at the interface between electrode and electrolyte. The potential of this technique for cultural heritage was identified by Antonio Doménech-Carbò, who initiated this line of research. The VMP can easily integrate the techniques we consider traditional, since it allows to obtain a qualitative analysis of the compounds found on the surface of a material. It is micro-invasive since the sample particles are transferred to the graphite electrode to perform the analysis - which is also possible to carry out in situ. The potential of the materials we want to analyze should always be taken into consideration in order to obtain the wanted results. 

Furthermore, the electrochemical signal changes according to the crystallinity of the sample: powders have a different signal than archaeological patinas. It may seem an obstacle but it actually allows us to have a clear distinction of the materials we are analyzing. Electrochemistry can effectively contribute to archaeometric analyses, both for the mere characterization of the materials and the study of authenticity and dating ^[7]. 

Although electrochemistry is not yet part of the routine analyses for cultural heritage, the production rate of scientific works is very high, both in the case of the EIS and of the VMP. 

Here was a superficial summary of the aforementioned techniques and, above all, of their applications for diagnostics; in the future, I hope to be able to deal with them personally. In the meantime, here is a non-exhaustive bibliography that can help you discover the world of electrochemistry for cultural heritage! 

Bibliography: 

[1] P. Letardi, Laboratory and field tests on patinas and protective coating systems for outdoor bronze monuments, in: J. Ashton, D. Hallam (Eds.), Proceedings of the Metal04, National Museum of Australia, 2004, pp. 379–38. 

[2] E. Angelini, S. Grassini, M. Parvis, F. Zucchi, An in situ investigation of the corrosion behaviour of a weathering steel work of art, Surface and Interface Analysis 44 (2012) 942–946. 

[3] E. Cano, D. Lafuente, D.M. Bastidas, Use of EIS for the evaluation of the protective properties of coatings for metallic cultural heritage: A review, Journal of Solid State Electrochemistry 14 (2010) 381–391. 

[4] E. Cano, D.M. Bastidas, V. Argyropoulos, S. Fajardo, A. Siatou, J.M. Bastidas, C. Degrigny, Electrochemical characterization of organic coatings for protection of historic steel artefacts, Journal of Solid State Electrochemistry 14 (2010) 453–463. 

[5] F. Scholz, B. Meyer, Voltammetry of solid microparticles immobilized on electrode surfaces, in: A.J. Bard, I. Rubinstein (Eds.), Electroanalytical Chem- istry, a Series of Advances, vol. 20, Marcel Dekker, New York, 1998, pp. 1e86. 

[6] A. Domènech-Carbò, M.T. Domènech-Carbò, V. Costa, Electrochemical methods in archaeometry, in: F. Scholz (Ed.), Conservation and Restoration, Monographs in Electrochemistry Series, Springer, Berlin-Heidelberg, 2009. 

[7] A Doménech-Carbò, Electrochemical dating: a review, Journal of Solid State Electrochemistry, 2017