*3.3. Electrochemical Cleaning Using Chemical Cleaning Solutions*

We have also explored the effect of using chemical cleaning solutions, such as NH4OH and Na2S2O3, as the electrolytes for the electrochemical cleaning procedures with both the Wei and Barger methods. In Figure 5, the optical images of the daguerreotype before and after the application of the combined electrochemical and chemical cleaning are

shown. The improvement of the overall image quality when cleaning was performed with a solution of 0.15% NH4OH can clearly be seen. This procedure was applied with a 0.19% Na2S2O<sup>3</sup> solution with similar results. Figure 5B,D, right panel, correspond to the Barger method with an applied potential range of −0.9 V to 0.9 V, and −1.2 V to 1.2 V versus Ag/AgCl, respectively. Again, all of the images after cleaning showed more detail than before. NH4OH and Na2S2O3, as the electrolytes for the electrochemical cleaning procedures with both the Wei and Barger methods. In Figure 5, the optical images of the daguerreotype before and after the application of the combined electrochemical and chemical cleaning are shown. The improvement of the overall image quality when cleaning was performed with a solution of 0.15% NH4OH can clearly be seen. This procedure was applied with a 0.19% Na2S2O3 solution with similar results. Figure 5B,D, right panel, correspond to the Barger method with an applied potential range of −0.9 V to 0.9 V, and −1.2 V to 1.2 V versus Ag/AgCl, respectively. Again, all of the images after cleaning showed more detail than before.

like those obtained from the chemical cleaning experiment noted above.

*3.3. Electrochemical Cleaning Using Chemical Cleaning Solutions* 

It should be noted, however, that cleaning with a KCl solution (0.1 M), introduced

We have also explored the effect of using chemical cleaning solutions, such as

 ions into the solution. This site showed a greater amount of residual white haze (formation of AgCl) following cleaning than the site using the lower concentration KCl solution (0.01 M, Figure 4D, left panel). This was the result of the common ion effect reducing the solubility of AgCl. An improved image is observed for Figure 4B, left panel, where 0.01 M K2SO4 solution was used. All three sites showed great improvement optically after only 90 s of cleaning. EDX maps were also obtained before and after cleaning, showing results

*Heritage* **2021**, *4* FOR PEER REVIEW 8

processes. The regions of interest are marked with squares. Right panel: Optical images before (**A**,**C**) and after (**B**,**D**) electrochemical cleaning with 0.01 M KCl as the electrolyte. Image B, Barger method (−0.9 V to 0.9 V), and image D, Barger

**Figure 5.** Left panel: Optical images (**A**,**C**) before and (**B**,**D**) after electrochemical cleaning using the Wei method with an electrolyte solution: B, 0.19 M Na2S2O3; D, 0.15 M NH4OH. Middle panel: Optical image after all of the cleaning processes. The regions of interest are marked with squares. Right panel: Optical images before (**A**,**C**) and after (**B**,**D**) electrochemical cleaning with 0.5 M NH4OH. Image B, Barger method (−0.9 V to 0.9 V), and image D, Barger method (−1.2 V to 1.2 V). For example, in Figure 5C, right panel, it is difficult to see what is present, but after cleaning it becomes apparent that there is a very intricate table cloth (Figure 5D, right), where many details within it are now evident. According to the EDX maps, both the **Figure 5.** Left panel: Optical images (**A**,**C**) before and (**B**,**D**) after electrochemical cleaning using the Wei method with an electrolyte solution: B, 0.19 M Na2S2O<sup>3</sup> ; D, 0.15 M NH4OH. Middle panel: Optical image after all of the cleaning processes. The regions of interest are marked with squares. Right panel: Optical images before (**A**,**C**) and after (**B**,**D**) electrochemical cleaning with 0.5 M NH4OH. Image B, Barger method (−0.9 V to 0.9 V), and image D, Barger method (−1.2 V to 1.2 V).

*3.4. XRF Imaging*  A closer look at Figure 2 shows the optical images before and after cleaning, as well as the Hg Lα image. It is apparent from Figure 2C that the XRF image has revealed a finely detailed portrait of the little girl and the pretty purse with a very clean background, as if For example, in Figure 5C, right panel, it is difficult to see what is present, but after cleaning it becomes apparent that there is a very intricate table cloth (Figure 5D, right), where many details within it are now evident. According to the EDX maps, both the Barger and Wei method can remove both the halides and sulfides present on the surface.

Barger and Wei method can remove both the halides and sulfides present on the surface.

all the tarnish were removed. The most noticeable difference is that, while the various cleaning methods applied to the plate show nonuniform cleaning in the optical image
