The Stone Surface Cleaning According to Criteria of Effectiveness and Controllability: The Procuratie Nuove Case of Study (Venice)

The Procuratie Nuove (St. Mark Square, Venice) was built between 1587 and 1655 and was subjected to an exceptional restoration intervention, closed in 2018 under the direction of the Superintendence of Venice. The intervention was a significant opportunity to study the criteria for choosing cleaning methods applicable in a very articulated and emblematic context, with evidence of past treatments emerging alongside the deposits and decay layers. This contribution presents the most significant results in assessing the different cleaning methods' impacts. The objective verification through a semi-quantitative analysis of two species associated with the effectiveness of the method (removal of gypsum) and its controllability (preservation of calcium oxalate) was proposed. The tests showed that the effective removal of gypsum left the surface with a dark colour, often associated with the concept of “dirt”. That was an opportunity to propose and share a different approach to cleaning historical architectural surfaces with citizens and stakeholders.