Abstract
In this paper, we analysed the efflorescences present in the frescos of a monumental complex named S. Pietro a Corte situated in the historic centre of Salerno (Campania, Italy). The groundwater of the historic centre is fed by two important streams (the Rafastia and the Fusandola) that can be the sources of water penetration. The aims of this work are to (i) identify the stream that reaches the ancient frigidarium of S. Pietro a Corte and (ii) characterize the efflorescences on damaged frescos in terms of chemical nature and sources. In order to accomplish the first aim, the water of the Rafastia river (7 samples) and the water of the Fusandola river (7 samples) were analysed and compared with the water of a well of the Church (7 samples). The ionic chromatography measurements on the water samples allowed us to identify the Rafastia as the river that feeds the ancient frigidarium of S. Pietro a Corte. To investigate the nature and the origin of the efflorescences (our second aim), anionic chromatography analyses, X-ray diffraction measurements, and the isotopic determination of nitrogen were performed on the efflorescences (9 samples) and the salts recovered from the well (6 samples). Results of these analyses show that efflorescences are mainly made of potassium nitrate with a δ15N value of + 9.3 ± 0.2‰. Consequently, a plausible explanation for their formation could be the permeation of sewage water on the walls of the monumental complex.
Highlights
IntroductionResponsible Editor: Michel SablierInvestigations on the deterioration of cultural heritage caused by efflorescences Over the past decades, the degradation of cultural heritage due to exposure to atmospheric and water pollution has become an increasing concern, highlighting the need to know the origin and the evolution of pollutants to preserve it (Alfano et al 2009; Di Turo et al 2016).Several air pollutants (NOx, SOx, and CO2) have negative effects on cultural heritage because of their chemical reaction with raw materials, so many efforts were devoted to finding simple methods able to monitor their concentration (Cucciniello et al 2012, 2017; Motta et al 2014, 2018).The formation of efflorescences is one of the most important issues concerning the preservation of cultural heritage
The first part of this work regards the chemical investigations of the water of the two important streams of the city of Salerno, which feed the underground aquifer of the historic centre, to discover which of them reaches the well found in the frigidarium of the Monumental Complex of S
X-ray diffraction and anionic chromatography allowed the determination of the chemical composition of the efflorescences: they are principally made of nitrate in the form of saltpetre
Summary
Responsible Editor: Michel SablierInvestigations on the deterioration of cultural heritage caused by efflorescences Over the past decades, the degradation of cultural heritage due to exposure to atmospheric and water pollution has become an increasing concern, highlighting the need to know the origin and the evolution of pollutants to preserve it (Alfano et al 2009; Di Turo et al 2016).Several air pollutants (NOx, SOx, and CO2) have negative effects on cultural heritage because of their chemical reaction with raw materials, so many efforts were devoted to finding simple methods able to monitor their concentration (Cucciniello et al 2012, 2017; Motta et al 2014, 2018).The formation of efflorescences is one of the most important issues concerning the preservation of cultural heritage. The process involves three main steps: (i) the dissolution of salts in water in the Environ Sci Pollut Res internal part, (ii) the migration of water and salts to the surface, and (iii) the evaporation of water leaves a coating of salts. They damage sculptures and frescos and are reformed a few months after their mechanical removal (Backbier et al 1993; Gázquez et al 2015; Siedel 2018; Alexandrowicz and Marszałek 2019). Different mechanisms are involved in the formation of these salt coatings (Scrivano and Gaggero 2020), and in the case of saltpetre efflorescences, possible sources are the nitrates present in the infiltration groundwater and the atmospheric nitrogen oxides (NOx)
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