By Bronwyn Ormsby and Alan Phenix
Since their introduction in 1956, waterborne acrylic emulsion paints have been widely adopted by artists. These paints offer a range of technical differences in relation to traditional oil paints, including rapid drying, versatility, durability, and an ability to be thinned with water—properties exemplified in David Hockney's A Bigger Splash, where the paint was applied directly to bare canvas and could be repeatedly applied wet-on-dry in multiple layers to produce a crisp painting in pure, clean color.
However, as with all new materials used in art, targeted research has become increasingly important in order to determine appropriate conservation strategies, a fact not lost on Hockney himself:
Oil paint has been used by artists for six hundred years, so modern conservators have six centuries of experience to draw on and develop. Acrylics, on the other hand, are little more than half a century old. It is extremely important and very welcome that . . . research into the future conservation of these relatively new materials is being done now to ensure these artworks will be kept in good condition for centuries to come.¹
In contrast to traditional oil paintings, acrylic emulsion paintings are rarely varnished; as a result, airborne dust and dirt deposit directly onto the paint surface, building up over time. Eventually, this process may compromise the painting's appearance to such a degree that cleaning is warranted.
Surface cleaning of acrylic emulsion paintings can be difficult for a variety of reasons. Often the surfaces are delicately nuanced, and even the very slightest alteration—such as burnishing, tidelines, or a roughening of the surface—can critically influence appearance and coherence. These paints are generally soft at room temperature, and dirt can become firmly ingrained—in the worst case, possibly permanently embedded in the paint surface—hence the margin between successful dirt removal and damage to the paint film can be slim. Dirt deposition can also be exacerbated by greasy deposits on the surface, such as skin oils resulting from improper handling; indeed, the presence of tenacious dark finger marks is not uncommon with acrylic paintings. Artists' acrylic emulsion paints are also sensitive to a wide range of liquid agents commonly used for surface cleaning, and can be vulnerable to swelling and pigment removal. One of the key challenges, therefore, is to find cleaning agents which avoid or minimize this risk, but which are also effective at dirt removal.
In addition, conservators faced with cleaning acrylic emulsion paintings must consider important practical and ethical questions, such as the impact of cleaning treatments on any surfactants (detergent-type substances) that may be present as original constituents of the paint. The consequences of the removal of surfactant during cleaning have been explored to some extent; however, secure and consistent perspectives have yet to be developed. It is known that surfactant originally present in the paint can migrate and collect at the surface, where it may contribute to the retention of surface dirt, and that the removal of surface dirt can also result in the removal of this original surfactant material. Practitioners have not universally agreed whether this removal is desirable or acceptable. The long-term effects of such cleaning treatments remain uncertain.
In light of the complexities and difficulties confronting conservators working in this area, the Getty Conservation Institute (GCI) has embarked on several collaborative initiatives aimed at improving understanding of, and practical approaches to, the cleaning of works of art made from acrylic emulsion paint media. A partner in these efforts has been Tate in London.
RESEARCH AND COLLABORATION
Since 2003 scientists at Tate have been characterizing the surfaces of acrylic emulsion paints and exploring the consequences of surface cleaning treatments. A paper delivered by Tate and GCI scientists at the "Modern Paints Uncovered"² conference at Tate Modern in 2006 (coorganized with the GCI and the National Gallery of Art in Washington, DC) presented observations on the gradual buildup of surfactant on paint surfaces over time and on its subsequent loss through light exposure and water-based cleaning treatment. Assessment of bulk paint film properties such as stiffness, softness, and flexibility demonstrated that these physical properties were not significantly altered by water-based cleaning treatments, and that non-water-based systems (such as simple hydrocarbon solvents) did not remove surface surfactant. More recent research forming part of the Tate AXA Art Modern Paints Project has involved evaluating the surface cleaning treatment of five paintings from Tate's collection dating from 1962 to 1973. Examination of these works of art has demonstrated that surfactant is not always present on painting surfaces, and that currently used cleaning systems will at least partially remove any surface surfactant present, often resulting in a slight increase in surface gloss.³
An opportunity to advance research into the cleaning of acrylic paintings arose in early 2008 when scientists at the Dow Chemical Company, based in Midland, Michigan, approached the GCI about establishing a collaborative research project on modern artists' paints. With the acquisition of Rohm and Haas Paint and Coating Materials in April 2009, Dow became one of the world's largest manufacturers of base latexes for acrylic house paints, as well as many other raw materials used in architectural and industrial paints, fine-art acrylic paints, cleaning products, and conservation materials. In spring 2008, GCI scientists Tom Learner and Alan Phenix began working with Dow research chemist Melinda Keefe and Tate conservation scientist Bronwyn Ormsby on a project to explore the potential of Dow's high throughput (HTP) testing and analysis facilities for developing cleaning formulations for the removal of dirt from artists' acrylic emulsion paint films.
The goal of the project with Dow is to contribute to the development of frameworks for the selection of liquid cleaning agents for the removal of surface dirt from artists' acrylic paints—specifically, to identify effective cleaning formulations with low damage potential (i.e., risk) to paints of this type. High throughput research at Dow involves automated material handling, data handling and management, statistical design, analysis methods, and visualization tools that are used in parallel to increase dramatically the speed and success of their research and development programs. This methodology has been applied in many areas of Dow's research and development activity, including identification of catalysts for the production of plastics, formulation design for paints, and cleaners for hard surfaces and fabrics.
The initial outcome of this collaboration has been the development of methodologies for the rapid discrimination and screening of the cleaning efficacy of possible cleaning liquids, and for the evaluation of the effects of these liquids on representative test samples of artists' acrylic emulsion paints. Broadly speaking, the test method involves a series of automated test functions, including:
- an automated HTP cleaning test device capable of simultaneously cleaning up to twenty-four separate areas of a reference paint film;
- automated image analysis, coupled with data mining, for determination of cleaning efficacy of test liquids;
- analysis of the effects of cleaning liquids on paints using atomic force microscopy (AFM) for visualization of surface morphology; parallel dynamic mechanical thermal analysis (p-DMTA) for monitoring changes in mechanical properties; and desorption electrospray ionization mass spectrometry (DESI-MS) for chemical analysis of extracted original surfactants and/or residues from cleaning liquids.
The first results and insights from the GCI-Dow-Tate project were presented at the general session of the American Institute for Conservation annual meeting, held in Los Angeles in May 2009.
To promote and develop specific technical skills for the cleaning of acrylic emulsion paints within the conservation profession, it was seen that some form of knowledge transfer vehicle was needed, in order to disseminate the findings of recent scientific research and integrate them with the latest perspectives on cleaning technology. As a first step toward developing an advanced training package on the cleaning of acrylic painted surfaces, in July 2009 GCI held a colloquium on this topic, conducted as a trial workshop for practicing conservators.
Participants at the colloquium—entitled "Cleaning of Acrylic Painted Surfaces: Research into Practice"—were invited specialists (conservators, conservation scientists, and conservation educators) with expertise relevant to the conservation of acrylic painted surfaces. The event was led by Bronwyn Ormsby, Richard Wolbers (Winterthur Museum/University of Delaware Program in Art Conservation), Chris Stavroudis (independent conservator, Los Angeles), and Tiarna Doherty (J. Paul Getty Museum), with Tom Learner and Alan Phenix. The colloquium provided the opportunity for specialists in the field of artists' acrylic paints to explore strategies for problem solving relating to the difficult technical and ethical challenges presented by paintings in this medium. Additionally, the colloquium enabled experienced practitioners to evaluate new cleaning substances and formulations, including novel cleaning agents that have emerged from the GCI-Tate-Dow project.
The colloquium and the other initiatives described above—along with work being conducted by other researchers and conservation practitioners around the world—will, it is hoped, provide useful frameworks for the conservation treatment and preservation of these relatively new materials. While a considerable amount of modern and contemporary art is neither built nor intended to last for centuries—a reality which presents conservators with huge technical and philosophical problems—acrylic emulsion paintings, on the whole, represent an important medium of artistic expression that, given appropriate care, have the potential to convey their message, as Hockney put it, "for centuries to come."
Bronwyn Ormsby is a senior conservation scientist at Tate. Alan Phenix is a scientist with GCI Science.
2 B. Ormsby, T. Learner, G. Foster, J. Druzik, and M. Schilling, "Wet-Cleaning Acrylic Emulsion Paint Films: An Evaluation of Physical, Chemical and Optical Changes," in Modern Paints Uncovered: Proceedings from the Modern Paints Uncovered Symposium, May 16–19, 2006, Tate Modern, London, 187–98 (Los Angeles: Getty Conservation Institute, 2008).
3 B. Ormsby, P. Smithen, F. Hoogland, T. Learner, and C. Miliani, "A Scientific Investigation into the Surface Cleaning of Acrylic Emulsion Paintings," in ICOM [International Council of Museums] Committee for Conservation, 15th Triennial Conference, New Delhi, 22–26 September 2008: Preprints, 2:857–65 (New Delhi: Allied Publishers, 2008).