On the Mechanisms of Marble Deterioration of Antonio Canova Cenotaph in Santa Maria Gloriosa dei Frari Basilica in Venice

The funerary cenotaph dedicated to Antonio Canova in the Frari basilica was erected in 1827. Since the beginning, some alteration features were recorded. In the last decades, some areas showed a sharp increase in deterioration processes due to large pieces of marble details missing from the statue surfaces. Macroscopic observation of the marble surface showed different forms of alteration as well as the massive presence of salt efflorescence. The main aim of this paper is to assess if there is a relationship between the decay observed and the presence of salt efflorescence, to subsequently ascertain the source of salts, and consequently to propose how to intervene to stop any further cause of alteration. In order to assess the relationship between the different types of alteration macroscopically observed, some samples were taken from the specific areas showing significant alteration features. Optical (OM) and scanning electron microscopic (SEM) observations associated with energy dispersive analysis (EDS) allowed us to explain the stages, each one corresponding to different features, through which the exfoliation and lamination of surface scales have been taking place. Moisture content in the brick structure was in the range of 17–26% until 140 cm of height. Above this height, moisture content is decreasing, and the maximum height of the capillary rise front is between 200 and 250 cm. In these areas, ions coming from the foundations of the monument deposit salt crystals within marble at a sub-surface level, causing the detachment of marble surface layers. In order to stop the rapidly increasing rate of decay observed over the last decades, it has been recommended to remove the statues from the basement and to insert a damp-proof course to prevent any further capillary rising damp. For the removal of embedded salts in the statues, the immersion of the removed statues inside deionized water baths has been recommended.