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Graphical abstract Abstract The cleaning of modern and contemporary paintings is a delicate and challenging operation. Many contemporary paintings exhibit rough, clotted and pitted surfaces, where the removal of soil is difficult. Gels are among the most efficient tools to achieve controlled and efficient cleaning of works of art. However, most gels used in the conservation practice are too rigid to adapt rough surfaces, or too mechanically weak to be removed without leaving polymer residues. Several formulations of physically cross-linked poly(vinyl alcohol) (PVA)-based hydrogels, obtained by cast-drying or freeze-thawing of aqueous polymeric solutions, were formulated and characterized. The viscoelastic properties, porosity, and crystallinity of the gels were studied, along with the behavior of water inside the polymeric network. It was shown that the properties of the gels were improved through blending with poly(vinyl pyrrolidone) (PVP). The most promising gel formulation, in terms of mechanical properties and water retentiveness, was assessed for the removal of soil from an alkyd painting mock-up. A traditional gel, gellan gum, was also tested as a reference system. The effectiveness of soil removal was investigated by 2D Fourier transform infrared (FTIR) microscopy, using a Focal Plane Array (FPA) detector. In conclusion, it was shown that the newly developed formulation grants the residue-free removal of soil from rough and irregular artistic surfaces, overcoming the limits of traditional cleaning methods. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Cleaning is one of the most important processes for the conservation of cultural heritage artifacts, but also one of the most delicate and potentially damaging to the original materials. Nowadays, aqueous cleaning is usually preferred to cleaning with organic solvents, because it is environmental friendly and less aggressive to artifact's materials. However, in some circumstances, such as cleaning paper documents, easel paintings and textiles, water-based systems can be invasive. The interaction of water with the hydrophilic support favors mechanical stresses between substrate and paint layers, which can eventually lead to paint detachment or paint leaching. Water-based detergent systems (such as micellar solutions and oil-in-water microemulsions) offer several advantages in terms of selectivity and gentle removal of hydrosoluble (e.g. grime) and hydrophobic (e.g. aged adhesive) materials. The confinement and controlled release of these water-based systems is achieved through the synthesis and application of chemical hydrogels specifically designed for cleaning water-sensitive cultural heritage artifacts. These gels are based on semi-interpenetrating p(HEMA)/PVP networks. Semi-IPN hydrogels are prepared by embedding linear polyvinylpyrrolidone physically into a network of poly(2-hydroxyethyl methacrylate). Water retention and release properties were investigated. The micro-porosity was studied by Scanning Electron Microscopy. To demonstrate both efficiency and versatility of the selected hydrogels in confining the most appropriate water-based cleaning system a representative case study is presented. [ABSTRACT FROM AUTHOR]

Water-based detergent systems offer several advantages,over organicsolvents, for the cleaning of cultural heritage artifacts in termsof 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 usageof water-based systems invasive. The interaction of water with woodor canvas support favors mechanical stresses between the substrateand the paint layers leading to the detachment of the pictorial layer.In order to avoid painting loss and to ensure a fine control (layerby layer) of grime removal, water-based cleaning systems have beenconfined into innovative chemical hydrogels, specifically designedfor cleaning water-sensitive cultural heritage artifacts. The synthesizedhydrogels are based on semi-interpenetrating chemical poly(2-hydroxyethylmethacrylate)/poly(vinylpyrrolidone) networks with suitable hydrophilicity,water retention properties, and required mechanical strength to avoidresidues after the cleaning treatment. Three different compositionswere selected. Water retention and release properties have been studiedby quantifying the amount of free and bound water (from differentialscanning calorimetry); mesoporosity was obtained from scanning electronmicroscopy; microstructure from small angle X-ray scattering. To demonstrateboth the efficiency and versatility of the selected hydrogels in confiningand modulating the properties of cleaning systems, a representativecase study is presented. [ABSTRACT FROM AUTHOR]

Abstract The removal of aged pressure sensitive tapes (PSTs) from contemporary drawings is a frequent and challenging task for paper conservators: in this work, an innovative method to overcome this issue is presented. Aged PSTs are largely found on paper artworks due to their use for mending, mounting and framing operations. Nevertheless, they may provoke several drawbacks on artworks (e.g. media bleeding and adhesive mass migration): the necessity of their removal promoted the development of several methodologies, but they all pose risks to both artefacts and conservation professionals. We propose a method involving polymeric gels able to load a "green" solvent, pertaining to the class of alkyl carbonates, which efficiently interacts with PSTs components; the embedment of the solvent into the gel network allows a feasible and effective intervention where the gel is directly applied on the top surface of the PST: the solvent gradually penetrates through the plastic layer of the PST (as proved by laser scanning confocal microscopy measures), swelling the underlying adhesive. In this way, the solvent-artwork contact is controlled. In order to optimize the processing costs and final properties of the gels, three formulations of poly (ethyl methacrylate)-diethyl carbonate (PEMA-DEC) organogels were synthesized, using different diluents and additives. A thorough physicochemical investigation of the systems was performed by means of rheology, gravimetric analysis, thermogravimetry, and IR Spectroscopy. After assessment on representative mock-up samples, the developed systems were successfully used for the removal of six aged PSTs from a drawing on paper by Keith Haring. [ABSTRACT FROM AUTHOR]

Hypothesis Due to their highly retentive properties, innovative recently developed, semi-interpenetrated hydrogels made up of poly(vinyl pyrrolidone) (PVP) chains embedded in a poly(2-hydroxyethyl methacrylate) (p(HEMA)) network should be efficiently used as cleaning material for fragile and degraded paper artworks. In restoration practice, indeed the wet cleaning of these artworks is usually performed by immersion of paper in water, a procedure which may lead to several drawbacks, including paper fibers swelling and dissolution of water-soluble original components. Experiments This class of gels were yet presented in literature, but their interactions with paper materials and ability to be spiked with active enzymes (as cleaning agents), have not been analyzed. To establish the suitability of these hydrogels as paper cleaning materials, first, a rheological and microstructural characterization of the gels was performed. Moreover, diffusion of macromolecules inside gels was studied using fluorescence microscopy, to check if these innovative hydrogels can be used as carriers for hydrolytic enzymes. Indeed, pastes and glues are usually found in old paper artworks, and their removal is a very delicate operation that requires a selective action, which is granted by specific hydrolytic enzymes. At the same time, spectroscopic analyses on paper samples under investigation before and after cleaning treatment has been performed, thus assessing the capabilty of these gels as cleaning materials. Findings With the aim of demonstrating the versatility of these hydrogels, several case studies, i.e., the removal of grime and water-soluble cellulose degradation byproducts, the removal of animal glue and the removal of starch paste from real samples, are presented. Results obtained with these gels have been compared to those obtained by using another gel used for paper artworks cleaning, i.e., Gellan gel. [ABSTRACT FROM AUTHOR]