title: A follow-up on the analytical study of discolouration of the marble statues of Orsanmichele in Florence.
abstract: The research complements the complex study carried out to understand the source of brown discolourations of ten marble statues in the Church of Orsanmichele in Florence, Italy. Originally located in exterior niches, the statues were restored to reverse the extensive alterations they had undergone throughout the centuries. One of the major alterations was the application of a dark brown patina that dated just after 1789. After the statues were placed indoors, brownish discolourations started to appear on their surfaces. Cross sections were examined using FTIR mapping and immunological methods. In parallel, the pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) data already obtained from the statues' scrapings were compared with data from aged casein films applied to microscope glass slides and aged milk-treated marble. All the statues had been treated with milk-based substances before the time the bronze patina was applied. The values of temperature and illumination of the room were important factors in the ageing of organic substances and in the formation of calcium oxalates. It is likely that products of thermo-oxidation and photo-oxidation of the oils together with the oxalates caused the darkening. The marble samples corresponded to a Lunense provenance.
authors.affiliation: Ministry of Cultural Heritage, via Belle Arti 56, 40126, Bologna, Italy. daniela.pinna@outlook.com.
authors.forename: Daniela
authors.initials: D
authors.lastname: Pinna
authors.affiliation: Opificio delle Pietre Dure, viale Filippo Strozzi 1, 50129, Florence, Italy.
authors.forename: Monica
authors.initials: M
authors.lastname: Galeotti
authors.affiliation: Metropolitan Museum of Art, 1000 5th Ave, New York, NY, 10028, USA.
authors.forename: Adriana
authors.initials: A
authors.lastname: Rizzo
authors.affiliation: CNR Istituto per la Conservazione e Valorizzazione dei Beni Culturali, via Madonna del Piano, 10, 50019 Sesto Fiorentino, Florence, Italy.
authors.forename: Emma
authors.initials: E
authors.lastname: Cantisani
authors.affiliation: Department of Chemistry "G. Ciamician", University of Bologna, Ravenna Campus, Via Guaccimanni 42, 48121, Ravenna, Italy.
authors.forename: Giorgia
authors.initials: G
authors.lastname: Sciutto
authors.affiliation: Department of Chemistry "G. Ciamician", University of Bologna, Via Selmi 2, 40126, Bologna, Italy.
authors.forename: Martina
authors.initials: M
authors.lastname: Zangheri
authors.affiliation: Department of Chemistry "G. Ciamician", University of Bologna, Ravenna Campus, Via Guaccimanni 42, 48121, Ravenna, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Prati
authors.affiliation: Department of Chemistry "G. Ciamician", University of Bologna, Ravenna Campus, Via Guaccimanni 42, 48121, Ravenna, Italy.
authors.forename: Rocco
authors.initials: R
authors.lastname: Mazzeo
authors.affiliation: Department of Chemistry "G. Ciamician", University of Bologna, Via Selmi 2, 40126, Bologna, Italy.
authors.forename: Aldo
authors.initials: A
authors.lastname: Roda
mesh_terms: D002119:Calcium Carbonate; D008401:Gas Chromatography-Mass Spectrometry; D007558:Italy; D010084:Oxidation-Reduction; D013696:Temperature
chemical_list: D002119:Calcium Carbonate
keywords: Colour measurements; Fluorescence; Immunoassay technique; Marble statue discolouration; Microclimatic survey; Oxalates; TMAH; py-GC/MS; μ-FTIR-ATR mapping