The frieze of the Art of War in the Ducal Palace of Urbino: conservation issues, materials, and executive techniques

The frieze of the Art of War was originally positioned along the sides of the facade of the Ducal Palace in Urbino (Marche, Italy), and it is currently located in the palace’s Chancellery Room. The frieze, probably elaborated by Federico da Montefeltro around 1474, consists s of stone bas-reliefs illustrating a rich iconographic repertoire depicting numerous engineering machines and symbols related to the military and political spheres. The present work aims to deepen the knowledge of the Art War frieze and to clarify some doubts regarding the original shape of the bas-reliefs, the constituent material, and the executive technique; conservation issues were also considered. Polarized light microscopy observations were carried out on the stone materials, identifying the use of a packstone referable to the Calcare Massiccio A Formation (Hettangian-Lower Pliensbachian p.p.). This stone, locally known as Piobbico Travertine, was excavated in the Val d’Abisso quarries, part of the Umbria-Marche ridge. Ca-oxalates were detected by Fourier transform infrared analysis in the brownish patinas that mainly cover the surfaces of the bas-reliefs; they could be related to ancient conservation treatments and/or to biological agents. Regarding the execution technique, a thorough autoptic examination allowed for a better understanding of the original conformation of the bas-reliefs and the carving process. Stylistic and executive differences in the execution of the same detail were observed in different bas-reliefs, confirming the activity of various sculptors. Different decay typologies were used to consider the debate regarding the original arrangement of the frieze on the facade, validating the most accredited hypothesis.