Barbara Salvadori

Spectroscopic techniques in cultural heritage conservation: A survey

Abstract This review describes the application of selected spectroscopic techniques to the world of cultural heritage conservation. In recent times, science and technology have been applied to the world of cultural heritage, conservation and preservation. In this field, spectroscopic techniques represent one of the most powerful tools to investigate the structure of all the materials constituting the “cultural object.” In particular, this survey will consider the “status of art” in the field of some important spectroscopic techniques for the characterization of the following works of art: easel paintings, paper and ink artifacts, stone monuments and wall paintings, and archaeological ceramics. The spectroscopic techniques that have been used and will be reviewed are Fourier transform infrared spectroscopy and also coupled with the microscope, X‐ray fluorescence spectroscopy, proton‐induced X‐ray emission spectroscopy, ultraviolet, visible and fluorescence spectroscopy, Raman spectroscopy, and Mossbauer spectroscopy.

Evaluation of Gypsum and Calcium Oxalates in Deteriorated Mural Paintings by Quantitative FTIR Spectroscopy

This study dealt with the development of a procedure based on quantitative FTIR spectroscopy to determine the amount of some contaminants in wall paintings, mortars, and stone micro‐samples. As contaminants we selected gypsum, CaSO4 · 2H2O, and calcium oxalate monohydrate, CaC2O4 · H2O, among the most common polluting substances present in architectural porous materials. Calibration curves of absorbance versus analyte concentration were determined by adopting both the internal and external standard methods. As internal standard we used Prussian blue, Fe3[Fe(CN)6]4, that presents an unique infrared peak at 2094 cm− 1. The correlation coefficient for a linear fit was very good for every calibration, being in each case greater than 0.9900. Furthermore, the precision of the evaluation of gypsum and calcium oxalates varied in the range 8–15% and ca. 4% respectively. In order to verify the findings, some specimens, which came from real frescoes, were analysed both by DSC calorimetry and FTIR spectroscopy: we found a satisfactory match between the quantitative analyses performed by the two techniques. For the first time, the application of this method allowed the quantitative determination of the desulphatization power of the Ferroni‐Dini method—based on the ammonium carbonate and barium hydroxide technique—in the conservation of mural paintings. #Paper presented at the 5th IRUG Infrared and Raman User Group Meeting, The Getty Conservation Institute, Los Angeles, March 4–8, 2002.

Microemulsions and Micellar Solutions for Cleaning Wall Painting Surfaces

Abstract This paper presents a new approach for the elimination of hydrophobic materials from the surface of wall paintings. Nanostructured systems with well-characterized physicochemical properties are proposed as an alternative to unsupported organic solvents for solubilizing substances on porous painted surfaces. Due to the wide range of components that can be used in their preparation, these systems can potentially be used to remove a wide range of different types of organic materials. The results of experiments using oil-in-water microemulsions and micellar solutions as cleaning agents for wall paintings are given. The efficacy of these systems has been tested in several Italian conservation workshops for the removal of various hydrophobic materials. In particular, they have been successfully used during the conservation of the frescoes in the Loggia del Bigallo in Florence (affected by degraded natural organic materials), and for the removal of various synthetic organic resins from the surface of the Filippo Lippi frescoes in the apse of the Cappella Maggiore in Prato Cathedral. Furthermore, oil-in-water microemulsions have also been shown to be effective cleaning agents for the removal of oil- and acrylic-based paint used by vandals to deface an eighteenth-century a secco painting in the Villa del Barone in Prato. The results are supported by detailed photographic documentation and Fourier transform infrared (FTIR) spectra.

Optical and spectroscopic tools for evaluating Er:YAG laser removal of shellac varnish

Abstract We report on tests to remove naturally and artificially aged shellac varnish by laser and traditional chemical cleaning from the substrates of mural paintings. Optical tools were used for the evaluation of cleaning processes, in particular laser microprofilometry to assess the changes in the surface morphology and time-domain confocal optical coherence tomography (OCT) to evaluate varnish thickness. The cleaning assessment was integrated with molecular characterization provided by portable Fourier transform infrared spectroscopy operating in reflectance mode, and colorimetric measurements. This complete analytical approach led to optimized laser-based cleaning tests at 1.9 and 2.6 J/cm2 in the presence of isopropanol, which ensured controllable and safe partial removal of shellac varnish without alteration to the substrate morphology.

Preliminary investigation of combined laser and microwave treatment for stone biodeterioration

Abstract In this work, the potential applications of surface laser removal of biological crusts from Carrara marble artefacts and in-depth microwave selective heating for treatment of possible endolithic growths have been evaluated. The investigations were carried out on seriously deteriorated marble fragments from the monumental tombs of the English Cemetery in Florence, Italy. The second harmonic (532 nm) of a Q-switched Nd:YAG laser was used for cleaning while a microwave system emitting at 2.45 GHz was tested for in-depth sterilization. As is well known, microwaves are strongly absorbed by water via dipolar energy dissipation, which permits selective heating of endolithic organisms. The effects of laser and microwave treatments were characterized using scanning electron microscopy (SEM) along with chlorophyll fluorescence with pulsed amplitude modulated imaging. The latter has allowed the quantification of the impairment effects to photosystem II of epilithic phototrophic organism residues by mapping the maximum quantum yield, while the damage to endolithic growths was evaluated by means of SEM following osmium tetroxide staining of cytoplasmic lipids. The results provide an early picture of the development and application perspectives of the combined laser and microwave treatments in the conservation of biodeteriorated stone artefacts.

Laser cleaning of a nineteenth-century bronze sculpture: In situ multi-analytical evaluation

Abstract Laser cleaning of bronze artefacts is a very promising conservation approach and its wider distribution would benefit from further studies of its advantages and drawbacks. Some important references are available, yet laser cleaning cannot be considered a traditional method for bronze surfaces. In this paper, we report on the evaluation of cleaning tests performed on an important statue of Napoleon, depicted as Mars the Peacemaker, cast by Righetti in 1811 after a model by Antonio Canova. The sculpture is exposed to the outdoor environment in the main courtyard of the Brera Gallery, Milan, Italy. An analytical survey of corrosion products was carried out using X-ray diffraction, micro-Fourier transform infrared spectroscopy (μFTIR), and μRaman spectroscopy; and scanning electron microscopy with energy-dispersive X-ray spectroscopy analysis was applied to cross-sections. The results showed the ubiquitous presence of brochantite Cu4(SO4)(OH)6. Antlerite Cu3SO4(OH)4 is also occasionally present. Residues of an past conservation treatment (Incralac®) and of proteins were detected by μFTIR. Laser cleaning tests were carried out with an El.En. Combo laser, both in long Q-switched and short free-running regimes. Evaluation of the effects of cleaning was carried out with a portable microscope and a reflectance colorimeter. Moreover, a portable FTIR spectrometer was used in order to evaluate the presence of coating residues and corrosion products after cleaning. Electrochemical impedance spectroscopy was used in situ on a selection of the tested areas in order to characterize the effect of laser cleaning on the rate of corrosion. A specially designed contact probe was used for measurements in the frequency range 100 kHz–10 mHz both before and after cleaning.

Painted Fiberglass-Reinforced Contemporary Sculpture: Investigating Composite Materials, Techniques and Conservation Using a Multi-Analytical Approach

A multi-analytical approach was used to study the constituent materials, manufacturing technique, and state of conservation of a contemporary sculpture. This sculpture, entitled Nuredduna, was created by Aligi Sassu in 1995 and is located in the “Bellariva garden” in Florence (Italy). Fourier transform infrared spectroscopy (FT-IR), optical and electronic microscopy (OM and SEM-EDS), X-ray diffraction (XRD), and portable X-ray fluorescence (XRF) highlighted the multi-layered structure of the statue: fiberglass and an overlay of different layers (gel coat) applied with an unsaturated polyester resin added with aggregate materials and bromine compounds. A top-coat in acrylic black varnish, used as a finish, was also found. The combination of these materials with their different compositions, environmental impact, and even vandalism have negatively affected the state of conservation of Nuredduna, causing the loss of strata in its lower parts (legs and feet).