## 3 Results and Discussion
### [PERSON]'s Painting Materials and Technique  
The restoration treatment, which removed the large [PERSON] retouching mechanically with the use of scalpel and aided by stereomicroscopy [39], allowed a more complete characterisation of the painting materials and techniques of the original painting by [PERSON]. The elements detected by MA-XRF and the deduced hypothesis regarding the materials employed by the artist, as discussed here, are broadly consistent with those expected during the late XV century. Lead white, the use of which is most likely attested by the presence of Pb (Figure 4a), is employed in flesh tones (where it is most likely present as background as seen by optical microscopy [39]), in the red [PERSON]'s garment and in the white [PERSON]'s robe. Pb traces are also detected in the [PERSON]'s blue mantle, even though those might be related to residues of [PERSON]'s retouching. Instead, no Pb is found in the background as consistent with the absence of a preparation/imprimatura layer, as expected in the distemper painting technique. Fresh tones, in addition to Pb, are characterised by the presence of Hg (Figure 4b) used in cheeks, lips and highlights in general, both in the [PERSON] and in the [PERSON], attesting the use of vermilion/cinnabar. The [PERSON]'s hair also contains Hg. Volumes in the [PERSON]'s flesh tone are built with the use of Fe-based materials, such as earth and ochres, employed mostly in shadows (Figure 4c). On the contrary, the [PERSON]'s flesh tone does not contain a significant amount of Fe-based materials (with the exception of the shading of the eyes, nose and cheeks); visually, the two flesh tones are indeed different. The [PERSON]'s eyes also contain Fe-based materials. Figure 3: The _Madonna Poldi Pezzoli_ before restoration, MA-XRF maps: **(a)** Au L\(\alpha\); **(b)** Hg L\(\alpha\). White is associated with maximum counts and black with minimum ones. Figure 4: _Cont_. The red robe of the [PERSON] is characterised by the presence of Pb, which similarly to flesh tones is present as a white base [39]. Elements typical of red mineral pigments, such as Hg or Fe for vermilion and red earth, were not detected in this area, leading to the likely hypothesis of the use of a red organic dye. Original shell gold decorations are also present over the red robe (less extended than in [PERSON]'s retouching). The white puff of the [PERSON]'s proper left sleeve is painted with lead white with the addition of a Ca-based compound. Possibly, Ca is present as a component of Bianco di San Giovanni, maybe to give transparency effects [39]. The blue mantle is painted with a Cu-based compound (Figure 4e), most likely azurite. The green border contains Cu as well and an evident amount of Zn traces (Figure 4f), which is consistent with rossite impurities in malachite [49]. The dark background is characterised by the presence of Ca, possibly related to the use of bone black (P is hardly detected, as no He was employed during measurements), and Fe, indicating the presence of earth/ochres likely used to warm the black tone. In the Ca map, a long vertical lacuna, visible also in the Pb map, is evident on the [PERSON]'s proper left hand. In the upper-right corner of the painting, there is an area presenting higher counts of Fe and less Ca. This area corresponds to a region of the painting where the conservator found gold particles (so tiny that they could not be detected by XRF). These particles form the words \"Nigra sum sed formosa\", the first sentence of the _Carticle of Particles_, words that are no longer visible and were most likely concealed/covered at some point [39] with Fe-based materials. MA-XRF maps acquired before and after conservation are interesting to compare, as is visible in Figure 5. The most significant difference is visible in the Fe and Pb maps (Figure 5a,b and c,d respectively) in the blue mantle. Vermilion (Figure 5e,f) was present in the red robe of the [PERSON], but after conservation it is found only in flesh tones.