INVESTIGATION OF XV CENTURY FRESCOES BY MEANS OF ELECTRON MICROSCOPY AND MICROANALYSIS

• S. Bruni (ENEA, Applied Physics Division, via Fiammelli, 2, 40129 Bologna, Italy)
• M. Gagliardi (ENEA guest researcher)
• G. Maino (ENEA, Applied Physics Division, via Fiammelli, 2, 40129 Bologna, Italy and Facolta di Conservazione dei Beni Culturali, University of Bologna, via Mariani, 5, 48100 Ravenna, Italy)
• D. Biagi Maino (Facolta di Conservazione dei Beni Culturali, University of Bologna, via Mariani, 5, 48100 Ravenna, Italy)

On the occasion of recent restoration works carried out in the Basilica of St. Petronio in Bologna, Italy, a deep scientific investigation of the frescoes in the St. Abbondio and Bolognini chapels have been performed; the considered frescoes were painted by Giovanni da Modena and his 'bottega', one of the most important artist in Northern and Central Italy in the first half of XV century, and they can be dated around 1420 according to stylistic studies. These frescoes represent one of the most important masterpieces of the Bolognese painting school.

From these wall paintings, generally considered as executed with the well-known technique of 'buon fresco' in the relevant historical and artistic literature, a number of microscopic samples have been extracted probing significant areas of the artistic work and submitted to proper scientific investigation. Analyses have been carried out mainly by means of scanning electron microscopy (SEM) and associated EDXRS microanalysis. Therefore, by means of the X-ray spectra, the elemental composition of the samples has been univocally identified.

A stratigraphic study has been also carried out with usual optical microscopy techniques. We were able to identify the pigments used by the artist and, above all, to reconstruct the execution technique which resulted to be painted 'a secco' (on dry plaster). This fact is confirmed by the observation of legands such as animal glue below the pigment layer in all the considered samples. The large presence of glue and the frequently observed detachment of painted layers are clear signatures of the dry execution on the walls of the church, contrary to the traditional well-established recipes for the realization of frescoes. On the other hand, the compositions of pigments used in the large frescoes clearly correspond to the well-established recipes described in the contemporary and subsequent literature on the subject.

Finally, a comparison is proposed with similar analyses reported in the scientific literature, in order to point out possible characterization of the works of different 'botteghe' active in North and Central Italy during the XV century, based on statistical cluster procedure in a suitable multidimensional space of the relevant parameters as determined by EDXRS analyses.