Characterization of Barium Hydroxide Used as Consolidating Agent for Monumental Surfaces in Venice

Abstract

Barium hydroxide was one of the most widely used inorganic materials to consolidate calcareous stones during the 19th and 20th. The consolidation process occurs through a carbonation reaction. Several researchers studied the consolidation mechanism; however, the results are sometimes in conflict. More experimental work using modern analytical techniques and a multi-analytical approach is necessary to shed light on the mechanisms involved. This research aims to validate the chemical composition of the developed secondary products and to evaluate the treatment’s effectiveness over time. Carrara marble and Vicenza white limestone were treated and subjected to natural, artificial, and biological weathering. Furthermore, only a few microsamples were collected from Venetian historical artifacts treated in the 1960s and 1970s. Microscopic observations, sponge tests, FTIR, SEM-EDX, and microbiological analyses investigated the stability of the treatment over time and ascertained the chemical composition of the acicular crystals developed from the carbonation reaction of barium hydroxide. The results prompted a number of considerations useful for future restorations and for developing innovative compounds for consolidation interventions.

The (Building) Stones of Venice under Threat: A Study about Their Deterioration between Climate Change and Land Subsidence

“…The elemental surface analysis also revealed significant levels of sulphur (Table 4) strongly linked to the presence of this pollutant in the Venetian atmosphere. As it is well known, the presence of sulphur on carbonate matrices can induce the development of gypsum, through the chemical reaction of sulphation [23,24]. Quantitative chemical analysis revealed a variable distribution of this element depending on the lithotype and the exposure.…”

“…In the case of San Giobbe campus, the direct contact with rain or acid mist and the direct exposure to industrial emissions from Porto Marghera, rich in nitrogen oxides and sulphur (NOx and SO2), carry out a potentially more aggressive effect on exposed stone surfaces. The sulphur quantity recorded drastically decreased during lockdown period due to COVID-19 pandemic emergency [24].…”