The Legend of the True Cross:
restoration , first phase (1991-96)

The preliminary studies first revealed the grave state of deterioration of the fresco cycle, with raised or chipping paint brought about by sulfatation, or the the transformation of the calcium carbonate in the plaster into "gesso" caused by environmental factors and the presence of salts in the walls carried by polluting water that penetrated the walls by infiltration. This was exacerbated by the large amount of water contained in the cement that was used to fill in the lesions in the walls as part of the restoration performed by Domenico Fiscali in 1915-16 (see illustration). Leonetto Tintori had already attempted to check this process in 1963 by using acrylic resins but this attempt failed to resolve the problem.

All of the restoration issues were brought to resolution thanks to the application of the most modern scientific techniques in correlation with the data provided by the continuous monitoring of the interior environment. The methodologies of intervention were defined on the basis of the knowledge acquired through the long and complex program of research and preliminary studies that produced the broadest and most complete information that it is possible to obtain prior to a restoration of this degree of importance and complexity.

The preliminary studies also brought to light the various techniques employed by Piero in the execution of the murals. Besides the usual "buon fresco" technique the diagnostic ultra-violet photographic tests revealed the use of organic blending agents and difficult pigments and the use of oil tempera applied "mezzo fresco" or on dry surface to obtain a rich spectrum of chromatic and lightening effects.

The restoration of the frescoes, begun in 1993, was completed for the left wall of the choir in the autumn of 1996. The results were presented at the Convention, "Il Giardino ritrovato. Il restauro della Leggenda della Vera Croce di Piero della Francesca a conclusione della prima fase: dalle problematiche del degrado al risanamento" (Arezzo, main hall of the B.P.E.L., November 22-23, 1996).