The 'Madonna and Child Enthroned with Saints' of Ambrogio Lorenzetti in the St. Augustine Church (Siena, Italy): Raman microspectroscopy and SEM-EDS characterisation of the pigments

Raman microspectroscopy combined with scanning electron microscopy was applied to the investigation of the Madonna and Child Enthroned with Saints of Ambrogio Lorenzetti (early 14th century; St. Augustine church, Siena, Italy). A detailed investigation of both the materials used for the wall painting and the alteration products was provided in order to increase the level of accessibility of this masterpiece and to stimulate its restoration. The results showed that the pigments used for this wall painting were those widely used by medieval painters: chalk white, white lead, yellow ochre, red ochre, red lead, cinnabar, Siena earth, green earth, verdigris, azurite, and carbon black. Gilded tin foil has been further used for the decoration of the haloes. The alteration products mainly consist of Ca sulfates and Ca oxalates. Fungal spores were further observed in correspondence to the application of lead-based pigments.