Various electrochemical techniques can be used to obtain information about the condition of a metallic material in situ. In particular electrochemical impedance spectroscopy (EIS) has been shown to be a suitable method for in situ measurements on cultural heritage. This study investigates the applicability of the paste electrolyte cell for EIS testing of non-patinated copper and bronze and patinated bronze without and with the protective coating. Comparative measurements were made with three-electrode and two-electrode electrochemical cells and in three different types of electrolytes, an aqueous solution of sodium chloride, tap water and electrolyte paste in the solid state. The aim of this work was to compare the measurements in the two previously mentioned types of electrochemical cells, to evaluate the repeatability of the measurements and to determine the influence of the different electrolytes. The EIS spectra were measured and the numerical values of impedance at 0.1 Hz were taken as an indicator of the level of surface protection by patina or coating. The calculated values of relative standard deviation of repeatability showed satisfactory results in the case of electrolytic paste and tap water. By comparing the impedance for different electrolytes, it was found that the aqueous solution of sodium chloride did not give a commonly observed rating of the degree of surface protection. Electrolyte paste in the solid state proved to be a promising candidate for in situ measurements by detecting the impedance ranking in the following order: copper> bronze> patinated bronze> patinated bronze with a protective coating.