title: Non-invasive identification of metal-oxalate complexes on polychrome artwork surfaces by reflection mid-infrared spectroscopy.
abstract: In this work a reflection mid-infrared spectroscopy study of twelve metal-oxalate complexes, of interest in art conservation science as alteration compounds, was performed. Spectra of the reference materials highlighted the presence of derivative-like and/or inverted features for the fundamental vibrational modes as result of the main contribution from the surface component of the reflected light. In order to provide insights in the interpretation of theses spectral distortions, reflection spectra were compared with conventional transmission ones. The Kramers-Kronig (KK) algorithm, employed to correct for the surface reflection distortions, worked properly only for the derivative-like bands. Therefore, to pay attention to the use of this algorithm when interpreting the reflection spectra is recommended. The outcome of this investigation was exploited to discriminate among different oxalates on thirteen polychrome artworks analyzed in situ by reflection mid-infrared spectroscopy. The visualization of the νs(CO) modes (1400-1200 cm(-1)) and low wavenumber bands (below 900 cm(-1)) in the raw reflection profiles allowed Ca, Cu and Zn oxalates to be identified. Further information about the speciation of different hydration forms of calcium oxalates were obtained by using the KK transform. The work proves reflection mid-infrared spectroscopy to be a reliable and sensitive spectro-analytical method for identifying and mapping different metal-oxalate alteration compounds on the surface of artworks, thus providing conservation scientists with a non-invasive tool to obtain information on the state of conservation and causes of alteration of artworks.
authors: Istituto CNR-ISTM (Istituto di Scienze e Tecnologie Molecolari), c/o Dipartimento di Chimica, Università degli Studi di Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy; Centro di Eccellenza SMAArt (Scientific Methodologies Applied to Archaeology and Art), c/o Dipartimento di Chimica, Università degli Studi di Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy; University of Antwerp, Department of Chemistry, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
authors: Letizia
authors: L
authors: Monico
authors: Francesca
authors: F
authors: Rosi
authors: Costanza
authors: C
authors: Miliani
authors: Alessia
authors: A
authors: Daveri
authors: Brunetto G
authors: BG
authors: Brunetti
mesh_terms: D001154:Art / Q000266:history; D056831:Coordination Complexes / Q000737:chemistry*; D049668:History, 15th Century; D049669:History, 16th Century; D049670:History, 17th Century; D010070:Oxalates / Q000737:chemistry*; D010151:Paintings / Q000266:history; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*
chemical_list: D056831:Coordination Complexes; D010070:Oxalates
keywords: Artworks; FTIR; KK transform; Oxalates; Paintings; Reflection spectroscopy