Soluble salt sources in medieval porous limestone sculptures: A multi-isotope (N, O, S) approach

• Published in: The Science of the total environment Vol. 470-471; pp. 559 - 566
• Main Authors: Kloppmann, W., Rolland, O., Proust, E., Montech, A.T.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-02-2014; Elsevier
• Subjects: Art and art history; Calcium Carbonate - analysis; Calcium Carbonate - chemistry; Capillary rise; Cultural heritage; Earth Sciences; Environmental Monitoring; Environmental Sciences; France; Geochemistry; Global Changes; Humanities and Social Sciences; Isotope fingerprinting; Nitrate; Nitrogen Isotopes - analysis; Oxygen Isotopes - analysis; Salts - analysis; Sciences of the Universe; Sculpture; Stone degradation; Sulfur Isotopes - analysis; Sulphate; France; Sulphate; Isotope fingerprinting; Cultural heritage; Nitrate; Capillary rise; Stone degradation; stone degradation; sulphur; sulphate; isotope fingerprinting; nitrogen; nitrate; capillary rise; cultural heritage; oxygen
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2013.09.087

The sources and mechanisms of soluble salt uptake by porous limestone and the associated degradation patterns were investigated for the life-sized 15th century “entombment of Christ” sculpture group located in Pont-à-Mousson, France, using a multi-isotope approach on sulphates (δ34S and δ18O) and nitrates (δ15N and δ18O). The sculpture group, near the border of the Moselle River, is within the potential reach of capillary rise from the alluvial aquifer. Chemical analyses show a vertical zonation of soluble salts with a predominance of sulphates in the lower parts of the statues where crumbling and blistering prevail, and higher concentrations of nitrates and chloride in the high parts affected by powdering and efflorescence. Isotope fingerprints of sulphates suggest a triple origin: (1) the lower parts are dominated by capillary rise of dissolved sulphate from the Moselle water with characteristic Keuper evaporite signatures that progressively decreases with height; (2) in the higher parts affected by powdering the impact of atmospheric sulphur becomes detectable; and (3) locally, plaster reparations impact the neighbouring limestone through dissolution and re-precipitation of gypsum. Nitrogen and oxygen isotopes suggest an organic origin of nitrates in all samples. N isotope signatures are compatible with those measured in the alluvial aquifer of the Moselle River further downstream. This indicates contamination by sewage or organic fertilisers. Significant isotopic contrasts are observed between the different degradation features depending on the height and suggest historical changes of nitrate sources.
•We use S, N and O isotopes to distinguish salt sources in limestone sculptures.•Vertical zonation of degradation is linked to capillary rise and air pollution.•Sulphate salts in lower parts are derived from river/groundwater.•Sulphate salts in higher parts show signature of air pollution.•Nitrates are derived from organic sources and rising groundwater.