In view of the multiplicity and breadth of the historical questions related to the deterioration and decay of the paintings, this research sector was one of the pilasters of the entire program of preliminary studies, and functioned as a constant point of reference for the other areas of research.

For the Basilica of San Francesco the research was conducted over a wide range of thematic topics ranging from those more akin to urban studies of the church and its surrounding environment to those regarding the history of previous restorations and the damage and deterioration specifically related to the painted walls of the choir.

More than 600 documents were assembled, most of them newly discovered, and the principal phases of the three previous restorations effected since the middle of the 19th century were accurately reconstructed : Gaetano Bianchi (1858), Domenico Fiscali (1915-16) and Leonetto Tintori (1962-64).

The results of the research were published in 1990: G. Centauro, "Dipinti murali di Piero della Francesca. La basilica di S. Francesco ad Arezzo: indagini su sette secoli", Milan, electa.

(See bibliography)

Traces of wall tombs identified by the termographic studies

A critical examination of the structural conditions of the physical plant of the Basilica of San Francesco, and specifically of the walls of the choir which are the natural support for the precious painted frescoes, constituted a contribution of fundamental importance to the entire Piero della Francesca project. The extensive and varied historical evolution of the damage and deterioration brought to light, often quite dramatically, the centrality of the question of the stability of the walls where congenital malformations of the original architectural structure itself and traumatic events of various kind and degree joined with inopportune attempts at restoration or conservation to greatly heighten the risk factor. The research program, which was able to rely on modern sampling techniques and "non-destructive" analytical methods like thermographic studies, also led to new findings that were useful for the study of the painted surface of the walls.

It would be fair to say that his was the most delicate area of research in as much as it pertains to the most intimate aspects of the work of art itself. As a first step a precise and systematic survey of the painted surfaces was carried out with the aim of defining and identifying all factors contributing to the deterioration of the surface, each of the previous restorations and, more particularly, aspects relative to the painting techniques employed by the artist. The visual survey made it possible to map out each day of work by the artist, the preparatory design and etched lines, the saline eruptions, raised or chipping paint, and previous restorations. In addition, it was in this sphere of research that a synthesis of the historical information and critical analysis that had been produced by the scientific research and diagnostic studies conducted on all the different levels.

 An invaluable and inexhaustible contribution to the project was provided by the organically programmed and systematically conducted scientific studies of the painted surfaces. Specifically, the following types of analyses were carried out: infrared reflectographic studies, tests performed with light shaving, infrared, ultra-violet, and microscopic photography, thermographic studies of emission and reflection, tests for the presence of metal fragments and plaster separation, photogrammetric and morphological mapping of the walls, chemical and radiochemical analyses of samples taken from the painted surfaces, mineralogical and petrographic analyses of mortar etc. The substantial amount of data and information gathered in these studies led to a precise diagnosis of the causes of the deterioration and scientific descriptions of important painting techniques, as well as the identification of areas where the surface and walls had been touched up or painted over.

With regard to definition of the possible causes of the deterioration special importance was given to studies of the climatic surroundings and environmental factors. For this reason both the spaces surrounding the paintings and the painted surfaces themselves were subjected to checking and comparative reading of thermo-hydrometric parameters, monitoring of humidity in pavements and walls, and analyses of atmospheric pollutants. These studies formed the basis for a better and more precise understanding, in relation to the differing values recorded at various hours during the day or from season to season, of the mechanisms which encourage and activate processes of deterioration of both plaster and paint. As in the other research areas, here too the correlation of current test results with previous historical events made it possible to arrive at an exhaustive examination of the factors involved in producing the current state of degradation.