By Thomas Learner, Michael Schilling, and René de la Rie
Ever since the successful modification of cellulose nitrate into a form that could be used as a paint binder in the late 1920s, modern and contemporary artists have benefited from the availability of the vast range of commercial paints introduced throughout the rest of the century. Acrylic solutions, acrylic emulsions, vinyl emulsions, alkyds, and nitrocellulose are a few of the many important types of synthetic resins to have been used in artists' paints, as well as in household and other industrial paint formulations. Interviews and other documentary sources confirm that all of these synthetic paint types have been utilized by many 20th-century artists, including those as influential as Francis Bacon, Richard Hamilton, David Hockney, Roy Lichtenstein, Pablo Picasso, Jackson Pollock, Bridget Riley, Mark Rothko, Frank Stella, and Andy Warhol.
Nevertheless, knowledge regarding how well any of these modern paint media will withstand the passing of time remains extremely limited. It is improbable that any artists' material will be completely resistant to deterioration. Research is therefore needed to determine the likely extent of this deterioration and whether it could be classed as "catastrophic" (such as the powdering of early cellulose plastics) or as "tolerable" (as in the oxidation and subsequent cracking of oil paints). By starting to research these questions now, the art community has an excellent opportunity to assess many of the potential problems before they appear on works of art and, consequently, to develop the necessary preventive measures to keep our modern collections in a near-pristine state.
Designing the optimum means for the preservation and restoration of works of art is an extremely complex task that requires a comprehensive understanding of all the materials with which they were made and of the way in which these materials react with one another, with environmental conditions, and with conservation treatments. This information can be obtained only by thorough monitoring of objects and extensive programs of analysis and examination of test materials subjected to artificial aging and/or trial treatments.
A new integrated collaborative project—initiated in 2002 by Tate in London, the National Gallery of Art (NGA) in Washington, D.C., and the Getty Conservation Institute (GCI)—will work to answer some of the many questions that we have about the character of modern paint materials. This project brings to bear extensive scientific expertise and equipment in the areas of materials identification and cleaning, with each organization concentrating on research for which it has appropriate experience and facilities. Throughout the course of the project, occasional exchanges of staff among the institutions will foster new ideas and make efficient use of available resources.
The project will focus on three main areas: cleaning of modern paintings, chemical analysis, and physical characterization.
Cleaning—usually meaning the removal of surface dirt and/or a picture varnish from the surface of a paint film—is arguably the most routine treatment carried out on painted surfaces. Although much is now known about the relative efficiency and safety of various cleaning techniques for traditional oil paints, an equivalent awareness of their effects on modern and contemporary works of art, especially those executed with synthetic paints, does not yet exist. Research into cleaning modern paints is therefore urgently required, in particular to find effective methods for removing surface dirt (the majority of modern paintings are not varnished) and to evaluate the possible consequential long-term damage to the paint film as a result of cleaning.
As part of the collaborative project, a comprehensive study on the cleaning of modern paints, including an assessment of the efficiency and safety of all methods and techniques currently used by conservators of 20th-century paintings, will be conducted at Tate, initially supported by funding for two three-year fellowships from the Leverhulme Trust and the Deborah Loeb Brice Foundation. One goal of this study is to establish rational criteria for the selection of specific cleaning processes. Aqueous and dry cleaning techniques will be highlighted, but some novel treatments currently under development will also be considered, including the use of lasers, enzymes, and liquid carbon dioxide. Potential changes to optical properties (gloss, color, and surface texture), physical properties (strength, hardness, and brittleness), and chemical properties (removal of components) of various modern paints by selected cleaning methods will be measured.
The NGA, with funding for a fellowship from Golden Artist Colors, will work closely with Tate on the cleaning study and will initially examine the likelihood and nature of materials that could be extracted from modern paints during these cleaning processes. For example, modern acrylic emulsion paints may contain 10 or more components (often called additives) that may be retained in the dried paint film. Removal of these components may affect the stability of the paint, its strength, or its tendency to crack and deform. In addition, changes in the composition and properties of the paints as a result of aging and cleaning will be investigated. At the GCI, supplemental studies of solvent extracts will be carried out with high-resolution mass spectrometry (MS), a research tool capable of detecting a broad range of materials.
Another component of the collaborative research project focuses on chemical analysis. The ability to establish the type of paint on a work of art is essential to an understanding of how it might alter in response to age, environmental conditions, or conservation treatments. The Conservation Department at Tate has been at the forefront of international research efforts to improve identification of the components of paint media used in modern and contemporary works of art. Major advances have been made in the development of analytical techniques for identifying synthetic paint media, such as pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS) and Fourier-transform infrared spectrometry (FTIR).
These analytical tools can tell researchers what materials are present in mixed paint media. But to determine the proportions of each substance, one must rely on quantitative analytical techniques. Because it is unlikely that any single quantitative test will be equally effective on all types of modern paint media, an alternative approach to quantitative analysis is to apply a suite of test methods, each of which is designed for a specific class of paint medium. Initial research at the GCI will focus on development of a quantitative analysis procedure for oil-based modern paints, such as alkyd formulations, natural oils, and water-miscible oil media. GC-MS protocols developed at the GCI for identification of traditional paint media will be evaluated for use on modern oil-based media, and modifications to PY-GC-MS procedures will also be considered. In subsequent phases of the research, tests for the other major classes of paint media will be developed.
A third element of this collaborative project is to develop a more comprehensive understanding of how paint films respond to fluctuations of temperature in their environment. Synthetic paint media may expand, soften, and even become slightly sticky upon heating and, conversely, turn extremely brittle at lower temperatures. Such changes in a paint's physical properties may strongly influence phenomena such as rates of soiling, extent of cracking, and cupping of its surface; changes are probably also affected by the presence and nature of pigments and diluting agents, exposure to light, and the age of the material. Research into these phenomena will be conducted at the GCI and Tate utilizing thermal analysis instrumentation, a set of tools that provides in-depth information about polymers, plastics, and other organic materials.
The combined results from each component of the project will assist conservators in selecting appropriate cleaning methods and techniques for modern paints, increase our understanding of the problems that may develop over time as a result of the additives in some commercial paints, and help guide treatments of paintings composed of modern oil-based media. In coming years, the project may adapt the techniques used in this research to develop a similar understanding of other kinds of paint media, such as nitrocellulose and vinyl emulsions.
Works from the 20th century represent the artistic legacy of our time. In order to pass along these works to future generations, it is essential to understand as comprehensively as possible the factors that could contribute to their deterioration. By beginning this kind of research now, we are in a better position to anticipate deterioration problems with the materials used in the art—and that knowledge, in turn, can help us promote measures to preserve and protect the work well into the years ahead.
Thomas Learner is a paintings conservator and conservation scientist at Tate Modern in London. Michael Schilling is a senior scientist and head of the analytical research section at the GCI. René de la Rie is the head of scientific research at the National Gallery of Art in Washington, D.C.