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 suffered in the last decades of serious decay phenomena. The sharp increase of deterioration processes observed in different areas caused missing of large pieces of marble details from the statue surfaces. Macroscopic observation of the marble surface showed different forms of alteration as well as the massive presence of salt efflorescences. The main aim of this paper is to assess if there is a relationship between the decay observed and the presence of salt efflorescences and secondarily to 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 exfoliation and lamination of surface scales has been taking place. The survey on the moisture content of the masonry brick structures under the steps of the monument has established that moisture from the foundations is transmitted by capillary rise to brick structure and to marble. Water capillary migration transports ions from the lagoon water through the brick structure and deposits salt crystals into marble at a sub-surface level. 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 it has been recommended the immersion of statues inside deionised water baths.