San Francesco d'Assisi (Apulia, South Italy): Study of a manipulated 13th century panel painting by complementary diagnostic techniques

The panel painting “S. Francesco d'Assisi” (Museo diocesano “Mons. A. Marena”, Bitonto, Italy), executed around the half of the 13th century and manipulated at least two times in the following centuries, was studied by various complementary analytical techniques in order to characterise the original medieval painting technique and the subsequent editions. Optical microscopy (OM), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), micro-Raman spectroscopy and pyrolysis–gas chromatography–mass spectrometry (Py-GC/MS) were applied on various samples taken from significant parts of the painting. Several in situ micro-Raman analyses were also performed. The results obtained confirm that the painting belongs to the 13th century Italian painting tradition. Furthermore, combination of various analytical techniques revealed that the 13th century original background, which now appears dark grey, was realised by applying a tin foil covered by a mecca layer composed of siccative oil and heated Pinaceae resin. Thus, originally the background should have had a gold-like appearance. The most important manipulation of the painting of S. Francesco probably dates back to the 16th century but shows a quite traditional technique.