A novel methodological approach for the assessment of surface cleaning of acrylic emulsion paints

Poly(Vinyl Acetate) Paints: A Literature Review of Material Properties, Ageing Characteristics, and Conservation Challenges

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.

Easy-to-Make Polymer Hydrogels by UV-Curing for the Cleaning of Acrylic Emulsion Paint Films

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.

The Effect of Pollutant Gases on Surfactant Migration in Acrylic Emulsion Films: A Comparative Study and Preliminary Evaluation of Surface Cleaning

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.

Identification of Synthetic Organic Pigments (SOPs) Used in Modern Artist's Paints with Secondary Ion Mass Spectrometry with MeV Ions

This work reports on the first systematic study using secondary ion mass spectrometry with MeV ions (MeV-SIMS) for analysis of synthetic organic pigments (SOPs) that can be usually found in modern and contemporary art paints. In order to prove the applicability of the method to different chemical classes of SOPs, 17 pigments were selected for the analyses. The focus was on blue and green phthalocyanines, yellow and red (naphthol AS) azo pigments, red quinacridone, anthraquinone, and diketopyrrolo-pyrrole pigments. Since there are no reference spectra available for this technique, pure pigment powders were measured first to create a database. Simple two-component paint systems were also prepared for testing purposes by mixing synthetic organic pigments with alkyd and acrylic binders. Commercial paints that contain the SOPs with identical C.I. numbers as in the prepared two-component samples were analyzed. All pigments were successfully identified in commercial products in the MeV-SIMS mass spectra through molecular and larger specific fragment ion peaks in the positive-ion mode. The main advantages of MeV-SIMS over other techniques used in SOPs identification, like pyrolysis gas chromatography mass spectrometry (Py-GC/MS), direct-temperature resolved mass spectrometry (DTMS), and laser desorption ionization mass spectrometry (LDIMS), can be summarized as follows: (i) pigments and binders can be detected simultaneously in the same mass spectrum acquired over a short measurement time (up to 500 s), (ii) only small sample flakes are required for the measurements, which are analyzed without any chemical treatment prior to the analyses, (iii) samples are not consumed during the analyses and can be reused for other measurements, e.g., multielemental analysis by other ion beam analysis (IBA) techniques, such as particle-induced X-ray emission (PIXE). Compared to, e.g., Raman spectroscopy, the significant benefit of MeV-SIMS is the exact identification of the SOPs in the paints even if pigments of similar structures are measured.