## 5 Discussion  
The integrated investigations carried out on the _Visitation_ altarpiece, the _Martyrdom of Saint Sebastian panel_ and _[PERSON] and the Archangel Raphael_ canvas allowed us to improve the knowledge of [PERSON]'s painting materials and executive technique. Starting from the wooden supports, [PERSON] used poplar (_Populus_ sp.) as attested in other [PERSON]'s panel paintings, such as the _Madonna with Child and Two Angels_ of the Puskin Museum [60], the _Sacred Conversation_ of Montefiorentino and Fano, the _Annunciation_, the [PERSON] altarpiece and _Christ communicates [PERSON]_[1]. This wood species was widely employed in Italy from the late thirteenth to the early fifteenth centuries [61]. Protective layers, composed of gypsum and red lead, were found on the back of both the _Visitation_ altarpiece of Fano and the _Martyrdom of St. Sebastian_ panel. [PERSON] described the use of the gypsum-based layer on the _back of_ the _Virgin and Child_ of the National Gallery [61] and it is also attested in the _Sacred Conversation of Montefiorentino_[6]. While poplar wood supports are common in [PERSON]'s wooden artworks, the use of canvas is rare. The painter used a plain weave fabric in _[PERSON]_ (1475-1478) at the Vatican Museums, a herringbone canvas in _Tobias and the Archangel Raphael_ and in _[PERSON]_ also held in Casa Raffaello, Urbino [2]. Herringbone canvas was very unusual support in Italy at that time and was probably chosen instead of other types of canvas to provide greater consistency to the painting, and perhaps with that experimental attitude that characterizes [PERSON] in certain aspects of his work [6]. The integrated investigations carried out on [PERSON]'s paintings indicated the use of one or two ground layers made of gypsum mixed with animal glue applied to receive the paint layers as in the aforementioned _Virgin and Child_ panel [62] and in _Tobias and the Archangel Raphael_ canvas [2]. In the large panels (_Martyrdom of Saint Sebastian_ and _Visitation_), [PERSON] used thick ground layers, whereas in canvas paintings (_Tobias and the Archangel Raphael_ and _Saint Roch_), the preparatory layers are thinner, probably to accentuate the texture of the herringbone weave [2]. The presence of anhydrite is often associated with _gesso grosso_[41], due to the partial hydration of burnt gypsum. In _Tobias and the Archungel Raphael_, a carbon-based ink was detected in the underdrawing, confirming the response obtained by IR reflectographic images [6]. Regarding pigments, micro-invasive analyses confirmed and improved the results obtained through non-invasive investigations carried out on these three paintings in the same areas [6]. The blue hues examined were obtained using finely grounded azurite with few impurities. Hematite particles are probably referable to natural impurities that occurred in azurite [44]. The presence of Ag impurities in azurite could indicate provenance from the silver mines of Saxony, a known source of copper-blue carbonate [63]. Calcium carbonate might be intentionally added as a filler [64], as well as dolomite. In the green hues, verdigris basic was sometimes used overlapped or mixed with lead-tin yellow (type I), lead white, hematite and rare or pigment particles. The use of verdigris, either pure or mixed with other pigments (lead white, lead-tin yellow), is associated with the oil binder, and powdered glass was found in _[PERSON] and the [PERSON]_ painting. The yellow hues were obtained using lead-tin yellow type I both as an underlayer, combined with green pigments, or in glazes based on Cu-containing pigments (verdigris basic), as usual in that period and later [50]. Yellow ochre was widely detected in yellow and brown colors. In the red hues, the underlayer is composed of vermilion, lead white and colorless glass particles while the glaze layer is based on red lake and vermilion. Particles of vermilion are always added to brown ochre to reach the deep brown and brown-reddish hues.