Time-Resolved ATR–FTIR Spectroscopy and Macro ATR–FTIR Spectroscopic Imaging of Inorganic Treatments for Stone Conservation

Abstract

In this study, the novel application of ATR−FTIR spectroscopy and macro ATR−FTIR spectroscopic imaging overcame an analytical challenge in conservation science: the time-resolved, chemical, and spatial investigation of the reaction of inorganic treatments for stone conservation (ammonium oxalate, AmOx; ammonium phosphate, DAP) occurring in water-based solutions. The aim was to (1) assess the composition and localization of reaction products and their phase variation during the reaction in real time and directly in an aqueous environment and (2) investigate the reaction of AmOx and DAP with calcite and the transformations induced to the substrate with a time-resolved approach. The new analytical results showed that for both treatments, the formation of new crystalline phases initiated at the early stages of the reaction. Their composition changed during the treatment and led to more stable phases. The reactivity of the stone substrate to the treatments varied as a function of the stone material features, such as the specific surface area. A clear influence of post-treatment rinsing on the final composition of reaction phases was observed. Above all, our research demonstrates the actual feasibility, practicality, and high potential of an advanced ATR−FTIR spectroscopic approach to investigate the behavior of conservation treatments and provided new analytical tools to address the choices of conservation in pilot worksites. Lastly, this study opens novel analytical perspectives based on the new possible applications of ATR−FTIR spectroscopic imaging in the field of conservation science, materials science, and analytical chemistry.

Recent advances and applications to cultural heritage using ATR-FTIR spectroscopy and ATR-FTIR spectroscopic imaging

“…The degradation products can be detected using ATR-FTIR spectroscopy 161,162 161 In a very recent study of the Carrara marble and its treatment was studied in situ via ATR-FTIR spectroscopy and with macro ATR-FTIR spectroscopic imaging. 181 In the case of ceramics, FTIR spectroscopy is able to identify mineralogical compositions, 168 firing temperature and atmosphere. 169 ATR-FTIR spectroscopy combined with principal component analysis (PCA) has been utilised to classify Hellenistic and Roman ceramic shards and determine their firing temperature.…”

“…161 In a very recent study of the Carrara marble and its treatment was studied in situ via ATR-FTIR spectroscopy and with macro ATR-FTIR spectroscopic imaging. 181…”

The “Historical Materials BAG”: A New Facilitated Access to Synchrotron X-ray Diffraction Analyses for Cultural Heritage Materials at the European Synchrotron Radiation Facility

“…Several inorganic-mineral treatments are available and ammonium oxalate (AmOx, (NH 4 ) 2 C 2 O 4 ·H 2 O) is one of the most widely used for the conservation of calcium carbonate stone materials (both natural and artificial) [ 51 , 52 , 53 ].…”

Synchrotron X-ray diffraction computed tomography to non-destructively study inorganic treatments for stone conservation

“…The DAP treatments dissolve calcium ions from calcite grains, but the possible effects induced by the reagent on calcite crystals (e.g. structural variation) are still unknown ( Possenti et al., 2021 ). Octacalcium phosphate (OCP) and hydroxyapatite (HAP) have been identified as reaction products in previous studies using a complex SR-XRD investigation ( Possenti et al., 2019a ).…”

“…Octacalcium phosphate (OCP) and hydroxyapatite (HAP) have been identified as reaction products in previous studies using a complex SR-XRD investigation ( Possenti et al., 2019a ). However, HAP and OCP have different stability and solubility ( Dorozhkin, 2007 ), and their crystallization depends on the reaction conditions and the calcium ion availability ( Possenti et al., 2019c , 2020 , 2021 ; Sassoni, 2017 , 2018 ; Wang and Nancollas, 2008 ). Moreover, different CaPs may be formed by DAP in different treatment modalities and/or on different stone substrates, influencing the final composition of the treated lithotypes.…”