## 3 Results
### Microscopy  
After cold exposure of the original coatings on the substrate, the surface was examined with polarised light, ultraviolet light, and infrared microscopy in order to obtain information on lower strata such as preparations and intermediate layers. Fewer contaminant particles are visible deposited on the surface. The finishes retain their original appearance, regarding homogeneity and defects due to use. The microscopic documentation does not show any degradation or changes that would negatively affect the conservation of the support. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Code**} & **Nozzle** & \multirow{2}{*}{\(T\) **Surface**} & **Pressure** & **Time** & **Distance** \\  & **Temperature** (°C) & (°C) & **(bar)** & **Time** & **(cm)** \\ \hline COA1 & \(-85\) & \(-80\) & \(2.95\) & \(30\arcsec\) & \(0.5\) \\ COA1 & \(-85\) & \(-80\) & \(2.95\) & \(1\arcmin\) & \(0.5\) \\ COA1 & \(-85\) & \(-80\) & \(2.95\) & \(2\arcmin\) & \(0.5\) \\ COA1 & \(-80\) & \(-75\) & \(2.95\) & \(4\arcmin\) & \(0.5\) \\ COA1 & \(-80\) & \(-75\) & \(2.95\) & \(6\arcmin\) & \(0.5\) \\ COA1 & \(-80\) & \(-75\) & \(2.95\) & \(8\arcmin\) & \(0.5\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Test of thermal resistance of the substrate. Cycle conditions: exposure times, temperature, pressure and throw distance. Source: own elaboration, 2023. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Code**} & **Nozzle** & \multirow{2}{*}{\(T\) **Surface**} & **Pressure** & **Time** & **Distance** \\  & **Temperature** (°C) & & (°C) & **(bar)** & **(min)** & **(cm)** \\ \hline  
\hline \hline \end{tabular}
\end{table} 
Table 5: Aerosol thermal resistance tests. Cycle conditions: temperature, pressure, exposure times and projection distance. Source: own elaboration, 2023. Relevant chromatic and topographic changes have been identified in the aerosols. In some cases, the surface has become rougher and stiffer, showing a slight stoning of the surface. This could be a physicochemical alteration that some polymers undergo in removal processes, causing a whitish appearance that alters the original perception of colour. The aerosols with which this alteration is most noticeable are MTN_WB_R, MTN_94_R, MTN_WB_M and M_T. In the MTN_94_R, MTN_WB_R and MTN_WB_M aerosol samples, alterations can be seen in the topography, which is irregular, and there are particles that cause visible chromatic alterations. The texture is accentuated and white mottling is visible in the interstices of the material (Figures 5-7). The bitumen-based polymer M_T has a vitrified appearance with surface morphology showing more abrupt edges and conglomerates as a result of material shrinkage (Figure 8). The mottling caused by material contamination is reduced after cryogenic exposure. In the image taken with UV and IR light, more accentuation of the cavities caused by the aerosol application methodology was identified, as well as a more satin finish. Keeping the conditions of pressure (3 bar), distance (0.5 cm) and temperature (\(-80\)\({}^{\circ}\)C) constant, the M_T aerosol was sprayed in areas with the highest roughness. During the spraying, the stratum peeled off. The incidence of air caused a thermal shock that induced the loss of adhesive forces binding the aerosol to the substrate. The consequences of the thermal effect are visible macroscopically (Figure 9) and the glassy nature of the fractured edges of the polymer can be observed (Figure 10). Figure 5: Microscopic examination of MTN_94_R x50 with Dino Lite® and Dino Lite® AD413T-I2V: (**a–c**) pre-treatment spray; (**a1–c1**) appearance after cold application. Source: own authorship, 2023. Figure 6: Microscopic examination of MTN_WB_R x50 with Dino Lite(r) AD4113 ZT and Dino Lite(r) AD413T-I2V: (**a–c**) pre-treatment spray; (**a1–c1**) appearance after cold application. Source: own authorship, 2023.