## 3 Results and Discussion
### Peeling off Cleaning  
In the second case, chemical attack on the layer of dirt was combined with mechanical action. For this purpose, we studied the cleaning of steel plates on which 0.28 g of peanut butter had been previously spread. The steel plate was submitted to the action of a flat vibrator at 11,000 rpm during the cleaning process. To study the effect of the cleaning product on the peanut butter residue, this cleaning process was followed by the acquisition of sequential images during the necessary time until the entire surface was cleaned. The original mean color of the peanut butter in our lighting conditions was ocher (230,222,193) (image 1 in Figure 7), changing after a short time and after the chemical attack to a quite intense white color (250,250,240) (image 2 in Figure 7). Therefore, color increments of (20,28,47) units for each color coordinate were observed. This made the changes more evident in the blue coordinate than in red or green, although they were also noteworthy for these coordinates. After the test was completed, when the steel plate was removed from the cleaning solution, it was observed that the peanut butter layer had a gelatinous appearance, its volume had increased considerably, the color was much whiter and it easily peeled off the surface in the form of a film (image 3 in  
Figure 6: 3D plots of mean color intensity (**A**) and variance of color intensity of red color (**B**) against the elapsed time and the distance in pixels from the left side of the analyzed sample in a methanesulfonic acid-based product, BMSNP (5%). Figure 7). An accelerated video of this process can be seen in the Supplementary Materials (Video S2). Figure 7 shows how the chemical attack of the cleaning product MF174 UW took place during the first 4-6 h until the mean color intensity (Figure 7A) and its variance (Figure 7B) reached almost constant values for the three colors. Unexpectedly, the variance did not show a peak as in theory (Figure 3) for the change from the ochre color (image 1 in Figure 7A) to white (image 2 in Figure 7A). We can explain this fact considering that the initial color dispersion for the steel surface coated with peanut butter was high enough due to the spreading procedure of peanut butter, which caused a non-homogeneous layer, and because some shadows were formed in our lighting conditions. Therefore, we observed only a decrease from the inhomogeneous color of the peanut butter to the more homogeneous color of the chemically attacked layer. On the other hand, the 3D plots of mean red color intensity and its variance against the elapsed time and the distance in pixels from the top of the metal sample (Figure 8) showed that the color changes occurred earlier and more extensively on the bottom of the metal plate. However, the swelling of the peanut butter might have affected the quality and accuracy of these observations (image 3 in Figure 7). In the following experiment, we added the effect of mechanical action generated by a flat vibrating motor at 11,000 rpm during the chemical peanut butter cleaning. In Supplementary Materials there is an accelerated video corresponding to this experiment. For the same composition (1% MF174 UW), the chemical attack of the cleaning product was also observed since there was a color change from ocher to white (Figure 9). After the chemical attack, some fragments peeled off from the peanut butter. In terms of color change, the blue color hardly changed in this last step, but the intensity of red and green decreased as the surface of the steel became darker (Figure 9A). The variance evolution of the three colors over time (Figure 9B) showed the effect of chemical attack during the first 30 min, as before, due to the bleaching of peanut butter. Then, a peak appeared in the three coordinates, but not synchronously. The maximum for blue appeared earlier than for the other two colors, caused by the change from ocher to white, which involved the greatest increase in the blue coordinate (Figure 9A).