Rodorico Giorgi

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.

Hydroxide nanoparticles for cultural heritage: Consolidation and protection of wall paintings and carbonate materials

Colloids and Material Science are nowadays providing innovative and effective technological solutions in a wide range of applicative fields. In the last decade, nanomaterials have been specifically designed to ensure the long-term restoration and preservation of movable and immovable artworks. The main tasks to address by conservation scientists concern the cleaning, the deacidification and the consolidation of different kinds of artistic substrates. The aim of the present contribution is to provide an up-to-date overview on the synthesis and preparation of colloidal systems tailored to the consolidation and protection of wall paintings, plasters and stones, highlighting the most recent improvements. Two case studies, widely representative of typical consolidation problems, are presented, i.e. the preservation of wall paintings belonging to a Mesoamerican archeological site and the consolidation of two Italian Renaissance buildings.

Colloid and materials science for the conservation of cultural heritage: cleaning, consolidation, and deacidification.

Serendipity and experiment have been a frequent approach for the development of materials and methodologies used for a long time for either cleaning or consolidation of works of art. Recently, new perspectives have been opened by the application of materials science, colloid science, and interface science frameworks to conservation, generating a breakthrough in the development of innovative tools for the conservation and preservation of cultural heritage. This Article is an overview of the most recent contributions of colloid and materials science to the art conservation field, mainly focusing on the use of amphiphile-based fluids, gels, and alkaline earth metal hydroxide nanoparticles dispersions for the cleaning of pictorial surfaces, the consolidation of artistic substrates, and the deacidification of paper, canvas, and wood. Future possible directions for solving several conservation issues that still need to be faced are also highlighted.

Nanoparticles for Cultural Heritage Conservation: Calcium and Barium Hydroxide Nanoparticles for Wall Painting Consolidation

Nanotechnology provides new concepts and materials for the consolidation and protection of wall paintings. In particular, humble calcium and barium hydroxide nanoparticles offer a versatile and highly efficient tool to combat the main degradation processes altering wall paintings. Clear example of the efficacy and potentiality of nanotechnology is represented by the conservation in situ of Maya wall paintings in the archaeological area in Calakmul (Mexico).

Innovative Hydrogels Based on Semi-Interpenetrating p(HEMA)/PVP Networks for the Cleaning of Water-Sensitive Cultural Heritage Artifacts

Water-based detergent systems offer several advantages, over organic solvents, for the cleaning of cultural heritage artifacts in terms of selectivity and gentle removal of grime materials or aged varnish, which are known to alter the readability of the painting. Unfortunately, easel paintings present specific characteristics that make the usage of water-based systems invasive. The interaction of water with wood or canvas support favors mechanical stresses between the substrate and the paint layers leading to the detachment of the pictorial layer. In order to avoid painting loss and to ensure a fine control (layer by layer) of grime removal, water-based cleaning systems have been confined into innovative chemical hydrogels, specifically designed for cleaning water-sensitive cultural heritage artifacts. The synthesized hydrogels are based on semi-interpenetrating chemical poly(2-hydroxyethyl methacrylate)/poly(vinylpyrrolidone) networks with suitable hydrophilicity, water retention properties, and required mechanical strength to avoid residues after the cleaning treatment. Three different compositions were selected. Water retention and release properties have been studied by quantifying the amount of free and bound water (from differential scanning calorimetry); mesoporosity was obtained from scanning electron microscopy; microstructure from small angle X-ray scattering. To demonstrate both the efficiency and versatility of the selected hydrogels in confining and modulating the properties of cleaning systems, a representative case study is presented.

Hydroxide Nanoparticles for Deacidification and Concomitant Inhibition of Iron-Gall Ink Corrosion of Paper

This Article reports an investigation on the use of magnesium hydroxide nanoparticles dispersed in alcohols to inhibit two different and synergistic degradation processes usually affecting historically valuable manuscripts and, more generally, paper documents. We show that the preservation of paper from acid hydrolysis and oxidative ink corrosion can be achieved by stabilizing the final pH of deacidified paper around 6.5 to 7.5. Reactive magnesium hydroxide nanoparticles with a narrow size distribution, obtained by using a novel synthetic procedure, are very efficient in controlling papers pH to avoid further degradation of cellulose from acid hydrolysis, oxidative ink corrosion, or both. The deacidification and antioxidant actions of magnesium hydroxide nanoparticles are compared with magnesium oxide particles present in one of the best mass deacidification methods (Bookkeeper).

Micelle, microemulsions, and gels for the conservation of cultural heritage.

Past restorations performed with acrylic and vinyl polymers showed detrimental effects to wall paintings that lead to the complete disfiguration of the painted surfaces. The removal of these materials performed with the traditional solvent-based methodology represents a real challenge to conservators and usually achieves very poor results. This review reports on the new palette, nowadays available to restorers, based on microemulsions, micellar systems, physical and chemical gels specifically formulated for the cleaning of cultural heritage artefacts. These systems have been developed in the last twenty years within the cultural framework of colloids and surface science.

Gels for the conservation of cultural heritage.

Gels are becoming one of the most important tools for the conservation of cultural heritage. They are very versatile systems and can be easily adapted to the cleaning and consolidation of works of art. This perspective reviews the major achievements in the field and suggests possible future developments.

Calcium hydroxide nanoparticles from solvothermal reaction for the deacidification of degraded waterlogged wood

HYPOTHESIS A combination of acid and iron ions inside the wood has been corroding the cellulose matrix of the Swedish warship Vasa, imposing its deacidification. Past deacidification treatments displayed poor penetration inside the wood matrix with limited efficacy. A vacuum assisted treatment of wood using newly developed calcium hydroxide nanoparticle dispersions represents a possible candidate for the treatment of acidic waterlogged wood objects such as sculptures and decorative artifacts. EXPERIMENTS A solvothermal process was used for the synthesis of calcium hydroxide nanoparticle dispersions. Before the application on waterlogged wood, the physico-chemical characterization of these systems was carried out using several techniques. The efficacy of the deacidification treatment of wood samples from the Vasa was assessed by determination of pH and Differential Thermal Gravimetric (DTG) measurements. FINDINGS The proposed solvothermal reactions can be used to produce stable and highly concentrated calcium hydroxide nanoparticle dispersions in alcohols, needing no further purification before the application. This process has also the advantage to be upscalable to industrial level. Both pH and DTG measurements showed that the newly developed dispersions can homogenously penetrate inside the wood up to 20cm, neutralizing acidity and creating an alkaline buffer inside the wooden matrix, to hinder the degradation of residual cellulose.

Stable dispersions of Ca(0H)2 in aliphatic alcohols: properties and application in cultural heritage conservation

The kinetic stability of dispersions of Ca(OH)2 particles (1-2 µm) in short-chain aliphatic alcohols was investigated. The alcohols were shown to strongly enhance the kinetic stability with respect to water. Ca(OH)2 crystalline nanoparticles were also synthesised at 60 °C from aqueous supersaturated solutions. The nanoparticles were characterised by scanning electron microscopy and atomic force microscopy techniques. The kinetic stability of the Ca(OH)2 nanoparticle dispersions was higher than that of the micron-sized particles. Dispersions of the nanoparticles in 1-propanol were successfully tested as consolidating on aerial mortar and carbonatic stone specimens. Applications of these dispersions on carbonatic stones presenting flaking and powdering from architectonic sites in Rome and near Padua gave positive results.