Unveiled materials and techniques in wall paintings hidden for centuries in the church of San Francesco del Prato (Parma, Italy)

The church of San Francesco del Prato in Parma (Italy) is a masterpiece of the Gothic style, dated back to the 13th century. However, its historical and monumental value could not be appreciated for a long time, especially due to the transformation of the building into a city jail. The recent restoration works brought back to light valuable frescos and wall paintings belonging to different periods. An in situ campaign was performed on the 15th-century wall paintings adorning the vault and the walls in the church apse, by using mobile Raman and X-ray fluorescence equipment. The characterization of the art pieces was further carried out with micro-Raman spectroscopy and gas chromatography–mass spectrometry analyses. Overall, a quick and thorough identification of the colours palette of the wall paintings was successfully obtained through the in situ measurements. Laboratory analyses corroborated the understanding of the techniques through the identification of pigments and binders. In addition, micro-Raman analyses highlighted the presence of degradation products. Interestingly, a pigment hierarchy has been noted in relation to the painted contents, enhancing the preciousness of holy figures and their distinctive details.