## 3 Results
### Room B  
In Room B LIF measurements have been carried out and the 3D model has been created for the north-west area. In Figure 10, LIF images at the 8 wavelengths corresponding to the filters used are presented. Once the raw data are processed, it is possible to obtain the maps reported in Figure 11, that highlight the presence of different substances on the surface. As for Room A, the LIF data processing highlights different characteristics regarding both the masonry and the fresco decorations. As regards the masonry, it makes the areas subjected to reconstruction, already in ancient times, clearly visible. The boundaries of the reconstructed area are identified, although probably made with reused original bricks (Figure 11 left). The reconstructed area on the north wall would seem to correspond to that of a bricked-up door at the time of the architectural and functional transformation of the building (4 th century). The rest of the wall (darker area) must be recognised as a \"mimetic\" restoration carried out between the 1930s and 1940s. This is part of the restoration works carried out on a large scale in Ostia in that period with additions done using the same building materials used in Roman times and found in large quantities in the collapses. In many cases, therefore, the portions of restored masonry are completely indistinguishable  
Figure 11: Results of the processing of LIF data of the north-west corner of Room B, compared with a picture (**on the left**). In false colours (**in the center**), deriving from the same procedure used for Figure 9 right, and in greyscale (**on the right**) to put in evidence consolidating treatment on the decorations. Figure 10: Fluorescence images at 8 different wavelengths collected by the LIF sensor. The lighter the areas are the more intense the fluorescence signal is (corresponding to a higher concentration of fluorescent material in that area). from the original ones, unless they turn into expensive and invasive operations such as the sampling and chemical-physical analysis of the mortars. For this reason, the LIF results, which demonstrate its ability to distinguish between the original masonry and the restored one, are all the more interesting. As regards the fresco decoration, the LIF measurements, in Room B too, document a modern restoration intervention, with the presence of synthetic polymeric material probably used as a protective agent only on some parts of the decorations (light orange/pink areas in Figure 11 centre and light grey areas in the Figure 11 right). In Figure 11 centre, since an RGB representation is used, different hues correspond to different surface compositions. In Figure 11 right, only the value of the intensity ratio I340/I290 is shown using greyscale, so that, comparing the results of the LIF investigation with the historical documentation relating to the restoration interventions, it is possible to hypothesise that the different values of this ratio are linked to a different concentration of the material detected, most likely identifiable with the Paraloid(r) (acrylic resin). This synthetic polymer has been widely used since the end of the 1960s to consolidate the paint film, to allow the detachment of the paints, and to revive the colours by saturating their tone [36]. Furthermore, two other areas are highlighted by LIF on the fresco of Room B (Figure 11 centre): the one on the far left, which shows a complete discontinuity with the rest, and areas of approximately circular shape (4) on the decoration on the north wall. The latter do not present any fluorescence band, thus suggesting the presence of materials that absorb radiation, but are not active in fluorescence, as happens for example in the case of historical earth pigments. Then, the LIF results allow, on one hand, the integration of knowledge related to previous conservation interventions, helping to reconstruct specific actions that were otherwise undocumented, and, on the other hand, they help guide possible new investigations.