## 3 Results
### Room A  
In this room, measurements have been carried out on different walls and areas of ceiling and masonry. Although the 8 fluorescence images collected by the LIF sensor from the walls and ceiling are not easy to read individually (Figure 4), their reprocessing allows us to highlight only the areas characterised by the presence of specific materials. In the first stage, an already developed and tested processing method based on K-means has been used to individuate different polymers and distinguish between them. With reference to [30], the ratios I376/I445, I340/I445, and I315/I445 have been used as variables in the K-means algorithm to gather the data in 7 clusters. In the present case, the normalisation has been set at I445 instead of I500, since the filter at 500 nm was not available. The results evidence the ability of the method to individuate different classes of materials on the studied surface (Figure 5). At first, it is possible to notice the ability to correctly individuate the areas without any analytical value (brown areas) and the ones related to non-treated plaster (in dark blue). The yellow, blue, and cyan areas refer to the presence of consolidant and protective agents, constituted mainly by synthetic polymers. Red pixels probably refer to the honeycomb panels, although the proximity of these areas to the upper physical border of the optical filters makes their evaluation not completely reliable. Figure 4: (**a**) a picture of the west wall compared to (**b**) the raw fluorescence images collected at the eight wavelengths selected. Subsequently, an attempt was made to highlight only acrylic consolidant materials. Based on the data previously collected from reference samples, the ratio 340/290 was selected for this purpose. Furthermore, the complementarity with the RGB-ITR technique allows these areas to be integrated into a 3D model as an additional layer. Figures 6 and 7 present examples of the west wall and the ceiling. A short movie with LIF results as an additional texture of the 3D model produced by the RGB-ITR system is presented as Supplementary Materials attached to the present paper. Figure 5: K-means clustering in 7 groups performed on the LIF data collected on the west wall of Room A.  
Figure 6: Spatial distribution of polymeric acrylic protective on the west wall of Room A detected by LIF and overlapped with the 3D model produced by the RGB-ITR. A short movie can be found in the Supplementary Materials attached to the paper. The PAOA archaeologists hypothesise, based on considerations of the graphic composition of other mural paintings present in the same house of [PERSON] and in other buildings in Ostia, that, on the west wall, the most significant presence of the protective layer is in correspondence with the areas that must have contained the central figurative animal and vegetal elements of the fresco. Probably during the restoration works, some areas considered more interesting, and in any case with colours no longer bright, were treated with protective agents which also had the function of polishing. Then, over time, however, these polymeric materials worsened the readability of the fresco, probably due to the waterproofing of the film, which favours salt sub-efflorescence phenomena and a more rapid accumulation of dust [35]. In addition, the processing of RGB-ITR data allowed for the recovery of these details of the decoration (Figure 8). Three curves for the calibration of the colours were built up during the in-field campaign as a function of distance, using repeated measurements of a white target, Spectralon STR-99-020, placed at different distances and illuminated by the three lasers of the RGB-ITR system. After the application of such correction, the colours of the entire 3D models were enhanced with recursive processing in order to show what the original appearance of the decorations might have been. Figure 8: Result of the RGB-ITR data processing. (**a**) raw data acquired by the RGB-ITR scanner; (**b**) and image enhancement after the calibration procedure.