## 3 Results and Discussion
### FTIR Spectroscopy
In Figure 5c, which shows the scores plot of PCA (PC1 explaining 86.44% and PC2 explaining 7.92% of the total variance) for the water in agarose test, both varnished and cleaned samples were characterized by a positive value of PC2, whereas soiled surfaces assumed negative values. Along the PC1, it was expected to distinguish spectra by the effect of the cleaning. However, due to the high but unavoidable variability of the surfaces, remarked by the position of the varnish cleaned surface (grey stars), circumspect considerations must be applied. Nonetheless, it is quite clear that cleaning effectiveness did not seems to depend on the application time. In particular, for the SSw area, the longest application times were close to the soiled reference (the blue square at time zero). A first mild effect could be recognized in 30 min exposure, whereas longer time seemed to spread the soiling without removing it. This is shown by the PC2 loadings (Figure 5d), characterized by a high contribution of soiling diagnostic bands around 500 cm\({}^{-1}\). It means that for those spectra identified with a negative PC2, it was likely to strengthen the hypothesis that the soiling was not removed. In the case of the water in agarose, it was true for all the application times, suggesting the inadequacy of this method for both the chromatic and compositional features. and in the Ca spatial distribution inferred that deionized water in agarose has a weak action in the soiling removal, whereas Tween 20 (3%) in agarose and Velvesil(tm) Plus produced more remarkable effects. For what concerns the use of deionized water in agarose, it is worth noting that its removal action was mild. Further, we did not observe an improvement of the chromatic features, probably due to the weak capability of the gel to remove dark matter particles. This issue let us infer that such a method is not suggested in the presence of a dark soiled surface. Better results could be expected with longer application times and this will be the object of further experimentation. Regarding the Tween 20 (3%) in agarose, we demonstrated that it was the most effective in removing the dark matter in the shortest time employed in this research (45 min). Nonetheless, we also observed that not all the soiling matter was removed even at the longest time (180 min). In this case, the polar affinity coupled with the surfactant property of the solvent could be responsible for the removal action, revealing also the nature of the mixture soiling-sweat. As regards the Velvesil(tm) Plus, its effectiveness was proved within the first 5 min. A longer application time, 25 and 45 min, could compromise the varnish and its properties. Nonetheless, PCA results warn about the reading of these data since the presence of the product residues could cover the information about the cleaning effect. Moreover, it was shown that its non-polar and surfactant nature could also probably play a role in sweat removal. Despite this first observation, the study of the interaction between the Tween 20 or the Velvesil(tm) Plus and the sweaty surface is still an open challenge that requires further investigation. An outstanding result was represented by the PC1 loading being always positive for the spectral data. It is highly informative of the fact that is essential to go on with further data processing and manipulation, including, for instance, the reduction of the spectral range in specific areas of interest and a different pre-processing strategy, in order to enhance the tiny features that at the moment are hidden by the high similarity between the collected spectra. Above all, it is necessary to disclose the dynamics of the sweaty surface that was not possible to be deeply explained until now. In this perspective, further data processing is ongoing.