David Chelazzi

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.

Nanomaterials in art conservation

Tackling the degradation of cultural heritage requires a global effort. We call on all material scientists to develop new nanomaterials and methods for the preservation of artwork.

Interactions between nanostructured calcium hydroxide and acrylate copolymers: Implications in cultural heritage conservation

The interactions between an acrylic copolymer, poly ethylmethacrylate/methylacrylate (70:30) (Poly(EMA/MA), and Ca(OH)2 nanoparticles were investigated in order to establish the reciprocal influence of these two compounds on their peculiar properties. The carbonation kinetics of Ca(OH)2 nanoparticles by atmospheric CO2 was investigated by FTIR and SEM measurements and compared to that of a nanocomposite film. CaCO3 formation occurred even in the presence of the copolymer, but only after an induction period of ca. 200 h and with a lower reaction rate. Some implications in cultural heritage conservation dealing with application of nanolime on artifacts previously treated with acrylic copolymers were discussed. Contact angle measurements, mechanical cohesion properties, and water vapor permeability allowed us to conclude that the optimum behavior of nanolime with respect to transpiration was not compromised by the presence of the copolymer, and the behavior in terms of mechanical properties recovery by the application of Ca(OH)2 nanoparticles remained excellent even in the presence of poly(EMA/MA).

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.

Nanotechnologies in the Conservation of Cultural Heritage

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Nano-Materials for the Conservation and Preservation of Movable and Immovable Artworks

In the context of the FP7 NANOFORART project (Nano-materials for the conservation and preservation of movable and immovable artworks) new nano-materials and responsive systems have been developed and experimented for the preservation of works of art. Conservation of cultural heritage is still mainly based on traditional methods and conventional materials that often lack the necessary compatibility with the original artworks and a durable performance in responding to the changes of natural environment and man-made activities. The main challenge of NANOFORART is the combination of functional materials arising from the recent developments in nano-science with innovative techniques in the restoration of works of art. The research activity has been focused on the development of manageable methodologies, based on nanosized structures and with a low environmental impact. The main tasks include the production of dispersions of nanoparticles, micellar solutions, microemulsions and gels, in order to offer new relia...

Organogels for the cleaning of artifacts

Abstract The cleaning of artifacts must not alter the original properties of the objects. While the use of free solvents is risky, their confinement into polymeric networks can allow the safe removal of unwanted layers from artifacts. Recently, a methyl 2-methylprop-2-enoate (MMA)-based organogel was formulated as loaded with butan-2-one (MEK), and used to remove aged varnishes from canvas paintings. However, this formulation is not enough retentive to allow its use on paper, where higher retentiveness is needed to avoid the uncontrolled spreading of MEK and dissolved materials. Here, a new PMMA-MEK gel was designed to overcome this limitation. The amount of cross-linker and monomer used in the synthesis of the gel were tuned to achieve optimal retentiveness. Differential scanning calorimetry (DSC), differential thermogravimetry (DTG), small-angle X-ray scattering (SAXS) and attenuated total reflection fourier transform infrared spectroscopy (ATR-FTIR) provided information on the solvent content, release rate, and mesoporosity of the gel as compared to the previous system. The lower solvent release rate of the new formulation allowed the safe removal of wax that jeopardized a 19th century paper document. The removal was confirmed through optical microscopy and ATR-FTIR, which also highlighted the absence of gel residues on the treated surface.

Polymer Film Dewetting by Water/Surfactant/Good‐Solvent Mixtures: A Mechanistic Insight and Its Implications for the Conservation of Cultural Heritage

Aqueous nanostructured fluids (NSFs) have been proposed to remove polymer coatings from the surface of works of art; this process usually involves film dewetting. The NSF cleaning mechanism was studied using several techniques that were employed to obtain mechanistic insight on the interaction of a methacrylic/acrylic copolymer (Paraloid B72) film laid on glass surfaces and several NSFs, based on two solvents and two surfactants. The experimental results provide a detailed picture of the dewetting process. The gyration radius and the reduction of the Tg of Paraloid B72 fully swollen in the two solvents is larger for propylene carbonate than for methyl ethyl ketone, suggesting higher mobility of polymer chains for the former, while a nonionic alcohol ethoxylate surfactant was more effective than sodium dodecylsulfate in favoring the dewetting process. FTIR 2D imaging showed that the dewetting patterns observed on model samples are also present on polymer-coated mortar tiles when exposed to NSFs.

Consolidation of Wall Paintings and Stone

Several degradation processes affect immovable works of art such as wall paintings and stone. For example, the loss of binder and the crystallization of salts within the pores of the substrate lead to the detachment of surface layers and the flaking of pigments. Synthetic polymers have been used for consolidation purposes since the 1960s due to their short term appealing performances and a misconception about their stability. However, these materials can undergo degradation, besides they alter the physico–chemical properties of inorganic porous matrices, possibly damaging the works of art. Alternatively, inorganic compounds such as alkaline earth hydroxides can be used for the durable consolidation of artistic and historical objects. The effectiveness of the treatment is highly increased when the size of the consolidants is reduced to the nanoscale, and dispersions of nanoparticles in solvents (e.g. alcohols) exhibit good penetration and consolidating power. This chapter illustrates the main formulations of nanomaterials that have been developed in the last decades for the consolidation of wall paintings and stone, providing references to real case studies and application fields. Finally, a whole section is dedicated to applicative procedures and protocols for the use of nanoparticles dispersions.