Mapping the Clock Tower of the St Mark's square in Venice (Italy): stones, deterioration morphologies and their distribution

In the frame of HYPERION EU project, aimed to develop a Decision Support System to improve resilience and sustainable reconstruction of historic areas against climate change and extreme events, Venice stands for its urban and architectonic complexity and richness. In this system, the mapping of the ornamental stones and their deterioration morphologies of the Venice Clock Tower (Torre dell’Orologio) façade acts as a milestone on which building the knowledge-acquisition process on stone artefacts and their decay products. The Clock Tower is an early Renaissance building (1499) in Lombardesque stile standing over the entrance to the Mercerie on the northern side of the St. Mark square. Detailed surveys and mapping of both building materials (mainly stones) and deterioration morphologies were carried out, the latter following the weathering forms glossary, coupled an evaluation of their intensity. The data output consists of several monothematic maps, which can be separately handled, each one focusing on exact lithology or specific deterioration aspects. Moreover, a simple approach to graphically summarize the total state of deterioration of the building is here proposed in the form of a Total Deterioration Index (TDI) and its representation. The stones used in the façade are regional ( Ammonitico Rosso and Scaglia Rossa ) and extra-regional limestones ( Istrian Stone ), as well as Mediterranean white and coloured marbles and stones already used in antiquity (i.e. Fior di Pesco or marmor chalcidicum, Porfido rosso antico or lapis porphyrites a volcanite from the Egyptian Eastern Desert, Proconnesian marble from the Microasiatic Marmara island, Pavonazzetto toscano and white Carrara marbles from Italian Apuan Alps). Their most frequent forms of deterioration detected are black crusts, patinas, discoloration and patterns linked to erosion processes. The interrelation of different mappings allowed some useful considerations about differences in the effectiveness of maintenance procedures between public and private management of the monument.