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Wet-cleaning acrylic emulsion paint films: An evaluation of physical, chemical and optical changes
Abstract
An extensive study on the effects of cleaning acrylic emulsion paint films with aqueous systems and organic solvents has been made. In particular, the relationship between changes in the paint’s properties and the removal/extraction of surfactant from the surface or bulk of the films has been examined. The methodology involved several analytical and visual techniques to monitor a number of chemical, physical, and optical properties prior to and aft er surface cleaning treatments, as well as natural and accelerated aging. These included various forms of thermal analysis, Fourier-transform infrared spectrometry and microscopy, as well as color and gloss measurements. Results
indicate that there is a clear link between changes in physical properties, such as glass transition temperature, with the extraction of surfactant from the bulk film resulting from immersion in aqueous-based systems. However, more realistic simulated treatments, such as swab rolling with aqueous systems for short periods of time, removed only the surfactant that had collected on the paint’s surface and had a negligible effect on the physical properties of the bulk film. Optical changes include a slight increase in gloss with swabbing treatments, occasional pigment removal, and an increase in the surface area of some cleaned films. Interestingly, the use of aliphatic hydrocarbon solvents, such as Stoddard solvent, consistently left the surface surfactant and physical properties unaffected. In general, the changes in properties caused by wet treatments were minimal when compared to those caused by changes in ambient temperature and relative humidity.
... A previous publication summarized some of the most relevant outcomes regarding the behavior of acrylic emulsion paints [4] . Among others, some studies revealed that p(EA/MMA) based films had major amounts of surface surfactant regardless of pigment in comparison to p(nBA/MMA) paints [8] , pointing out that the quantities of PEO surfactants in these paints may partially depend on the binder emulsion type. The water sensitivity of PEO-based surfactants which can be easily removed from paint surfaces has also been widely demonstrated both using water immersion and by mechanical action. ...
... All these aspects should necessarily be considered when raising the cleaning of these type of paint surfaces, aspects that have been widely discussed on previous studies [3-5 , 13] . Thus, the high swelling capacity [8] of these films and the potential solubilization of additives in the bulk of the film, and their migration to the surface [4 , 14] , makes it difficult for conservators and restores, to treat them without provoking changes in the physic-chemical and mechanical properties of the film [15] . ...
Acrylic paints became popular among artists in the late 50 s. Some of the main conservation issues of these paints are inherent to their composition characteristics, for instance, their high sensitivity to water and a wide range of polar solvents. This makes difficult to stablish an accurate and respectful cleaning treatment for this kind of artworks. As reported on previous studies, the application of pH and conductivity adjusted solutions using accurate methods, such as confined on chemical gels, improved this kind of procedures. The aim of this work is to extend a previous study where the effect of water based cleaning treatments was tested on Liquitex acrylic paint mock-ups, and deepen on evaluating the alterations both on the surface and in the bulk of the paint film. In this paper, six acrylic commercial paints of two widely used paint brands, Titan Arts-Acrílico extrafino (Spain) and Hyplar Acrylic Colors® (USA), were selected to compare the effect of the cleaning treatment on their surface and binder matrix. Samples were prepared using Mylar sheets and left to dry in a dark and dust-free environment for three years. Adjusted water solutions were applied both using cotton swab and cryogels for comparison. Paints were characterized using Fourier Transform Infrared spectroscopy (FT-IR), pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), Thermogravimetric Analysis (TGA) and Atomic Force Microscope (AFM). All the samples showed different reaction to cleaning according to their different composition. This study revealed that those paint films where most surface alterations are observed after cleaning, are not those that suffer greater changes in the binder matrix. Moreover, a set of samples was aged under accelerated conditions (solar radiation under controlled temperature and humidity). The accelerated ageing was carried out under isochronous sampling up to a maximum of 1426 h. This tests revealed certain degradation processes such as chain scission of the binder that coincide with those alterations observed in several mock-ups after application of the cleaning treatment.
... Ormsby et al. focused on acrylic paints, specifically investigating the effects of solvent exposure on the chemical, optical, and physical properties of the samples [73]. Comparisons between acrylic brands and exposure methods of swabbing or immersion were considered, showing a strong effect on the dimensional extension of samples after being immersed in the solvents, especially more polar solvents. ...
... The T g of the samples would increase with extended immersed solvent exposure, showing an opposite trend than previous data on oil paints, most likely due to embrittlement of the acrylic paints as a result of the solvent exposure. The samples that were swabbed experienced significantly smaller changes in the DMA data, leading to the conclusion that using swabs for solvent exposure will reduce the overall changes to the bulk properties of the paint compared to full immersion of the paint film, even if some surfactants are lost at the surface of the film [73]. Titanium white acrylic paints exposed to temperature and RH sweeps showed typical responses corresponding to an embrittlement/decrease in T g with a decrease in RH, indicating a strong relationship between the water content of the paint and the mechanical properties [74]. ...
While the chemistry of artists’ paints has previously been studied and reviewed, these studies only capture a portion of the properties affecting the response of paint materials. The mechanical properties of artists’ paints relate to the deformation response of these materials when a stress is applied. This response is dependent on many factors, such as paint composition, pigment to binder ratio, temperature, relative humidity, and solvent exposure. Here, thirty years of tensile testing data have been compiled into a single dataset, along with the testing conditions, to provide future researchers with easy access to these data as well some general discussion of their trends. Alongside the more commonly used techniques of tensile testing and dynamic mechanical analysis, new techniques have been developed to more fully investigate the mechanical properties, and are discussed along with salient results. The techniques have been divided into two categories: those that are restricted to use on model systems and those that are applicable to historic samples. Techniques applied to model systems (tensile testing, dynamic mechanic analysis, quartz crystal microbalance, vibration studies) require too large of a sample to be taken from art objects or focus on the mechanical properties of the liquid state (shear rheometry). Techniques applied to historic samples incorporate the use of small sample sizes (nanoindentation), optical techniques (laser shearography), computational simulations (finite element analysis), and non-invasive comparative mechanical properties (single-sided nuclear magnetic resonance) to investigate and predict the mechanical properties of paints.
... However, these systems were not further investigated due to time constraints and concerns around the possible swelling of the paint and coating layers. The removal of soiling and grime from synthetic polymer painted and coated surfaces can pose particular challenges around the use of water and organic solvents during cleaning, including the risk of swelling, extraction of lower molecular weight components, and the layers becoming more vulnerable to removal [8][9][10][11]. Any conservation treatment would therefore need to consider the extent of soiling removal possible, explore the risks to the underlying coating, paint, papier mâché or cotton rope layers, as well as consider how the soiling removal process may affect the appearance and viewer's reading of this early and significant Hesse work. ...
... Partially hydrolysed poly(vinyl acetate)-borax (PVAc-borax) mouldable gels [28][29][30][31] were included due to their ability to conform and maintain a specific shape; and the rigid polysaccharide gel Agarose [32][33][34][35][36] was included due to the possibility of applying this material warm and left to gel in situ. More recently, a series of novel hydrogels known as the Nanorestore Gel ® series, 9 showing unique cleaning fluid retention capabilities and physical flexibility, form part of a range of materials developed to avoid the limitations of traditional solvent thickeners [37,38]. The Nanorestore Gel ® Peggy series 10 was specifically developed within the NANORESTART project for the cleaning of contemporary works of art with textured or irregular surfaces. ...
This paper describes the methodology and practice-based research underpinning the development of a successful cleaning strategy for Eva Hesse’s sculpture Addendum (1967, Tate Collection T02394). Research strands included: technical and art historical investigations to determine the materials and construction of the work of art and to define the aims of the conservation treatment; the production, soiling and accelerated ageing of mock-up samples using contemporary equivalent materials; and the systematic, iterative evaluation of soiling removal systems, which were further refined for appropriate use on the work of art. The comparative cleaning system evaluation was employed to determine options which offered optimal soiling removal efficacy and posed minimal risk to the work of art. Newly developed Nanorestore Gel® Peggy series (i.e. polyvinyl alcohol (PVA) and polyvinyl alcohol/polyvinylpyrrolidone (PVA/PVP)-based hydrogels), designed for the cleaning of modern and contemporary art, were evaluated with a range of other gels, emulsifiers and cosmetic sponges and assessed through a combination of empirical observation, microscopy and spectroscopic techniques. Promising options, combined with tailored aqueous phases derived from trials on mock-up samples, were then evaluated on discreet areas of the sculpture. After extensive testing, the top papier mâché section of Addendum was surface cleaned using an aqueous solution applied with cosmetic sponges, and the ropes were surface cleaned using a modified version of Nanorestore Gel® Peggy 5 (PVA/PVP) loaded with a tailored aqueous solution. The optimisation of this hydrogel, combined with the extensive supporting research, enabled the successful, low-risk, conservation treatment of Addendum for the first time since acquisition.
... The main spectral differences in aged samples (pure and diluted models) are in the presence of bands at 591 and 1452 cm À1 and the intensity increase of the 1171 and 1323-1332 cm À1 bands. The surfactant migration, studied by many research groups, [6,8,15,[30][31][32][33][34] might be difficult to be discerned by reflectance FTIR due to the limitations, such as analytical detection thresholds (being surfactant about 2-6 wt%), and possible interference from substrate and bulk paint film materials, as in this case where the overlap of the main PEO band at 1341 cm À1 with that of the pigment makes attribution ambiguous. ...
The characterization and conservation of materials constituting contemporary art pose a significant challenge for scientists and restorers due to the wide variability, heterogeneity in their compositions, and their chemical instability. This study aims to contribute to the understanding of the composition and ageing of materials in contemporary artworks, specifically, the analytical painting and the materials involved in a vandalic act. To this purpose, an acrylic painting on raw canvas is examined, Tela by Giorgio Griffa (1973), along with model samples purposely prepared together with the painter. Felt‐tip marker vandalic act, by which the painting was disfigured, is analyzed as well. The analytical approach entails a combination of noninvasive spectroscopic techniques to study the molecular composition and changes induced by artificial ageing in model samples. The results are correlated with those obtained on the painting to support the development of a suitable conservation treatment to remove the effects of vandalic act.
... Pereira [2] presents a review regarding the cleaning of synthetic paints and exposes the main problems regarding these paints: prone to surface damage and affinity for dirt and dust pick-up due to their low Tg and surface migration of additives. The concerns of cleaning acrylic emulsion paints via aqueous systems have been studied mainly by Learner and Ormsby [20], [49], [74], [75] who summarized them in swelling of the paint film, additive extraction, gloss changes, pigment removal and physical changes that could contribute to long-term deterioration, such as a decreased flexibility. ...
Poly(vinyl acetate) based emulsions were used amongst artists in the 20th century as a binding medium. Vinyl emulsions were cheaper but considered of lesser quality than their better-known counterpart – acrylics, and thus were less used and less studied. As such, there is still a lot to unravel in what concerns their long-term behaviour.
The central question addressed in this work, which is inserted within the goals of the research project Plastic Paints in Art: the impact of manufacturing processes on their long-term stability, is the impact of different formulations on the long-term stability of vinyl acetate-based emulsions. Immediate and complete information regarding the use of different additives and their impact is not available for synthetic paints. To complete this information gap, an ageing study with several emulsions based on different plasticizers was conducted. The emulsions in film form suffered accelerated ageing (Xenon-arc light source, =300nm) for 4000hours at and their optical, physical, and chemical changes were followed through a multi-analytical approach. A chronology for the introduction of plasticizers based on historical sources is also presented.
PVAc as a homopolymer remained stable after the accelerated ageing, which was something that did not happen for some of the emulsions. It was possible to conclude that different plasticizers, co-monomers, and the quantity in which they are present, influence the emulsions drastically.
Ângelo de Sousa, a Portuguese artist who used vinyl paints throughout the 20th century, is presented as a case study. Ângelos private collection was explored, and relationships between the information in the paintings inventory and paintings record were established. Microsamples from selected paintings were analyzed via ATR-FTIR to confirm the nature of the binder. Finally, two paintings with signs of microbial degradation were studied and, within the CleanART- Innovative methodology to clean fungal stains from paper documents and artworks research project, an innovative green technology of hydrogels based on an active principle derived from ionic liquids was tested showing promising results for the removal of fungal stains.
... Water and aqueous solutions have proved to be the most effective systems considering that the effect of pH and conductivity are variables that should not be underestimated for the overall evaluation of the cleaning action. However, this system has some disadvantages in terms of application; in fact, the water directly applied to the surface could cause swelling of the polymeric film with consequent structural and chemical fragility [18,19]. Therefore, the method of applying aqueous solutions is also a widely studied issue. ...
From their first employment in the 1950s, acrylic emulsions have remained widely used as art material today. Although under certain deteriorating conditions they are very stable, if exposed to high humidity and atmospheric pollutant gases, their structural and chemical conformation is strongly affected. Dealing with the resulting surfactant migration, various cleaning treatments were considered over the years. However, their choice remains difficult as they easily alter the acrylic component, especially if in contact with aqueous solutions. The present study focuses on investigating the stability of acrylic emulsion films exposed to accelerated aging by various pollutant gases. Firstly, a comparative analytical study was carried out in order to morphologically (by 3D optical and Atomic Force Microscopy) and chemically (by Raman and Infrared spectroscopy) characterize the reactions and degradation products. Subsequently, two water-based cleaning treatments were tested, and a preliminary evaluation of their cleaning effectiveness was performed. The results show that the reaction of atmospheric gas pollutants with water molecules in moisture leads to acidic reaction products that attack the acrylic matrix and favor the migration of the surfactant to the surface. The effectiveness of cleaning treatments depends on the aging conditions applied, which further lead to different surface morphological changes.
Since their development in the 1950s, poly(vinyl acetate) [PVAc] paints (also known as vinyl) have been used by many artists, most notably in countries such as Spain, Portugal, and the United Kingdom; they are also used globally as a common binder for house paints. However, only a relatively limited number of heritage scientific studies have focused on vinyl paints. Consequently, many critical aspects of this material, such as the degradation processes, variations in paint formulations, and responses to conservation treatments, remain largely understudied. This article aims to summarise the available relevant information on poly(vinyl acetate) paints from both the scientific and the conservation practice perspectives. The article provides a brief overview of the development of poly(vinyl acetate) paints as artist-grade and household products and the known differences in their formulations. It also focuses on poly(vinyl acetate) ageing behaviour, the physicochemical properties, the recent scientific research on poly(vinyl acetate) material characterisation and degradation, and the main conservation issues regarding these paints, such as those relating to cleaning treatments.
This paper details the conservation treatment of an acrylic painting on linen canvas which had suffered damage by termites. In response to the many challenges posed by such an unusual and extensive damage type, conservators at the Queensland Art Gallery | Gallery of Modern Art (QAGOMA) developed innovative solutions for structural treatment and loss compensation through problem solving and experimentation. The complexities of the treatment included finding appropriate conservation materials and techniques which were compatible with the specific sensitivities of an unvarnished contemporary acrylic emulsion painting. An innovative ‘back-filling’ technique using Evasol® was developed.
Las pinturas acrílicas en emulsión acuosa se han utilizado en el arte de forma masiva desde los años 60. Sus propiedades ópticas y versatilidad posibilitaron su rápida incorporación al ámbito artístico, convirtiéndola en una de las técnicas más reconocibles a nivel internacional. Desde entonces, muchos artistas se han servido de estos productos sintéticos y sus derivados para realizar sus obras, conformando un gran acervo en fondos y colecciones que hoy en día presenta problemas de conservación. Lo más grave de esta situación es que los problemas identificados están intrínsecamente relacionados con su composición y propiedades de envejecimiento. En general, las películas acrílicas son muy sensibles a los solventes orgánicos y el agua, por lo que los métodos de limpieza tradicional no son adecuados para su intervención. Esta publicación pone en contexto parte relevante de la literatura científica referente a los nuevos métodos de limpieza basados en sistemas acuosos y gelificados.
The cleaning of acrylic emulsion paint surfaces poses a great challenge in the conservation field, due to their high water sensitivity. In this article, we present easy-to-make polymer hydrogels, made by UV-photopolymerization, that show excellent cleaning properties. The formulation of hydrogels obtained by UV-curing and their performance as dry cleaners for acrylic paints was investigated. First, different hydrogel formulations based on functional acrylic monomers were used to formulate a series of UV cross-linked hydrogels by fast UV photopolymerization. Their effectiveness on surface dirt removal was investigated by SEM microscopy and colorimetry. The hydrogels showed excellent cleaning properties and controlled water release, and they still performed satisfactorily after several cleaning uses. The obtained UV-hydrogels were compared to the well-known agar gels, showing benefits in terms of reducing excess water. This article shows that easy-to-make UV-cured hydrogels are an efficient tool for the cleaning of surface dirt from water-sensitive paintings, overcoming the limits of traditional cleaning methods.
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