## 2 Materials and Methods
### Characterisation Techniques  
In order to obtain information on the morphology and aspect of natural or artificial corrosion layers samples and specimens were observed by means of a Leica M205C stereomicroscope equipped with a Leica DFC 290 camera (Leica Microsystems, Buccinasco, Italy). Laboratory Fourier Transform Infrared Spectroscopy (FTIR) were performed by means of a Thermo Nicolet 6700 spectrophotometer (Thermo Fisher Scientific, Waltham, MA, USA), to investigate the chemical composition of the patinas. Moreover, when a more punctual investigation was needed, micro-FTIR (\(\mu\)-FTIR) analysis were performed by means of a Thermo Nicolet Continuum FTIR microscope (Thermo Fisher Scientific, Waltham, MA, USA) coupled with a MCT detector operating in the spectral range between 4000 and 600 cm\({}^{-1}\). In this case, the samples were pressed in a diamond cell with a 100 \(\upmu\)m opening. All the other samples and specimens, then, were investigated in macro Attenuated Total Reflectance (ATR) mode by means of the Thermo \"Smart iTX Accessory\" (Thermo Fisher Scientific, Waltham, MA, USA), equipped with a diamond window. A DTGS detector with a detection range between 4000 and 400 cm\({}^{-1}\) was employed. XRD analyses were carried out by means of an X-ray diffractometer Philips PW1830 (Philips, Amsterdam, Netherlands), Bragg-Brentano, thin film geometry, and copper anti-cathode (K\(\alpha\)1 radiation with wavelength \(\lambda\) = 154,058 A). \begin{table}
\begin{tabular}{p{142.3 pt} p{142.3 pt} p{142.3 pt}} \hline
**Patina** & **Procedures** & **Obtained Corrosion Products** \\ \hline Cuprite patina by immersion in deionised water & Wet and dry cycles were performed by immersing specimens in deionised water for two days, and then leaving them to dry for two days. Then, 10 cycles were performed. & Cuprite \\ \hline Cuprite patina by immersion in NaCl & Wet and dry cycles were performed by immersing specimens in artificial seawater for two days, Seawater was prepared with a 3.5\% aqueous solution of NaCl & Cuprite Paratacamite \\ \hline Cuprite by “boiling” solution & Specimens and the sensors were immersed in a boiling solution of CuSO\({}_{4}\) 5H\({}_{2}\)O (6.25 g/L), Cu(CH\({}_{3}\)COCO)\({}_{2}\) -H\({}_{2}\)O (1.25 g/L), sodium chloride (NaCl), 2 g/L and KNO\({}_{3}\) (1.25 g/L), followed by rinsing in boiling demineralised water and drying in air [51]. & Cuprite \\ \hline “Applied paste” patina with chlorides and sulphates & A mixture CuCl, CuCl\({}_{2}\) -2H\({}_{2}\)O, CuSO\({}_{4}\) 5H\({}_{2}\)O in a ratio of 3:1:4 was ground in a mortar and mixed with water in a ratio of 1:2 obtaining a sort of paste. Then, the patina was applied by brush on the metal surface [51; 77]. & Cuprite \\ \hline “Applied paste” patina with chlorides & A mixture CuCl, CuCl\({}_{2}\) -2H\({}_{2}\)O in a ratio of 3:1 was ground in a mortar and mixed with water in a ratio of 1:2 obtaining a sort of paste. Then, the patina was applied by brush on the metal surface [51; 77]. & Cuprite \\ \hline Atacamite patina by immersion in CuCl\({}_{2}\) & Copper specimens underwent wet and dry cycles in a 0.25 M solution of CuCl\({}_{2}\). They were immersed for two days and then left to dry for two days. Then, 10 cycles were performed. & Atacamite \\ \hline Brochantite patina & Copper specimens and sensors were immersed in a 5.4 g/L boiling solution of CuSO\({}_{4}\) for 1 h. Then, they underwent wet and dry cycles in an 8 g/L solution of CuSO\({}_{4}\). They were immersed for two days and then left to dry for two days. Then, 10 cycles were performed. Procedure adapted from [100]. & Brachantite \\ \hline Nitrate-based patina & Copper specimens underwent wet and dry cycles in a 116 g/L solution of Cu(NO\({}_{3}\))\({}_{2}\) -2.5 H\({}_{2}\)O. They were immersed for two days and then left to dry for two days. Then, 10 cycles were performed. Procedure adapted from [105]. & Gehrandtite; Cu(NO\({}_{3}\))\({}_{2}\) -2.5 H\({}_{2}\)O \\ \hline \end{tabular}
\end{table} 
Table 2: Procedures for the realisation of laboratory artificial patinas.