By Michael Schilling, Susan Lake, Elizabeth Steele, and Suzanne Quillen Lomax
Throughout the 20th century, artists continually redefined our conception of what constitutes art, a process that included a proliferation in the employment of materials not previously known or used. As never before in history, artists have had at their disposal a tremendous assortment of natural and synthetic materials—and the license to use them. Modern artists have wholeheartedly embraced this profusion of products. New materials now incorporated into art include pigments with never-before-seen shades and hues, a variety of synthetic paint media, exquisitely transparent plastics, supple fabrics, exotic metal alloys, quick-setting adhesives, and electronic devices, to name merely a few.
Even the long-established field of painting has seen a change. Paintings created in earlier eras reflected a relatively limited supply of artists' materials. The only available paint media were waxes, plant gums, egg, milk, animal hides, vegetable oils, and plant resins. Pigments came from mineral deposits or were extracted from plants, insects, and animals. Today, however, artists are not limited to these traditional materials but may also choose from a variety of commercial paint mediasuch as acrylics, nitrocellulose, and alkydsas well as a profusion of synthetic pigments.
Given that research into artists' materials and their use plays an important role in conservation, the tremendous increase in the number of available materials has created new challenges for conservation professionals.
Examination and analysis of artists' paints yields information about artistic techniques and materials that helps guide decisions about care and conservation treatment. Conservators of modern art also take a keen interest in art as a process, carefully researching the ideas behind the specific techniques that the artist used to create the work. The challenge is finding conservation solutions that preserve a painting without disregarding the artist's intent.
How can we learn more about the complex formulations of contemporary artists' materialsformulations that are routinely changing? For example, an artist may have used the same brand of acrylic paint over a 10-year period, but the manufacturer may have modified the formulation several times during that period. Because product formulations are complex and may change rapidly, a single formulation may not be representative of an entire class of paint medium; this fact creates difficulties for conservators and conservation scientists. (Formulation changes can also make it difficult for an artist to develop a consistent set of refined working techniques.)
Conservators of modern and contemporary art have access to many sources of information not available to colleagues who preserve works of art from earlier times. Product labels or library holdings (for example, those of the Getty Research Institute) are such sources; sometimes records of product formulations can be obtained from manufacturers. Archival collections of artists' materials are also important sources of information. For example, Yale University, Tate, the Netherlands Institute for Cultural Heritage (ICN), and the National Gallery of Art, Washington, house invaluable collections of pigments, paints, varnishes, and media that scientists can study.
In addition, interviews with artists provide a unique source of information that may permit conservators to learn what products were employed in making a particular work of art, how the materials were used, the original intent of the artist, and the artist's attitude toward future conservation treatments. In 2000, 11 European museums, coordinated by the ICN and Tate Modern, established the International Network for the Conservation of Contemporary Art (INCCA). Although still in its infancy, the INCCA Web site (www.incca.org/) already contains a wealth of information. Another example is the Artists Documentation Program, in which artists are interviewed on film in front of their works. The program was initiated in 1991 with support from the Andrew W. Mellon Foundation and the Menil Foundation by Carol Mancusi-Ungaro, now director of conservation at the Whitney Museum of American Art in New York and director of the Center for the Technical Study of Modern Art at Harvard.
Still, even with these resources, much work remains to be done in identifying the vast number of materials used by contemporary and modern artists and in developing a better understanding of the properties of these materials. Conservation science can play a significant role in this effort. There are now a number of scientific analytical techniques to aid in identifying artists' materials and techniquesand although most were refined and developed to study works of art made with more traditional materials, they can also be applied to 20th-century artworks and their materials. From minute samples of paint, pigments are identified with polarized-light microscopy (PLM), X-ray fluorescence (XRF), and X-ray diffraction (XRD). Organic binding media may be identified with gas chromatography (GC), liquid chromatography (LC), and mass spectrometry (MS). Another tool Fourier-transform infrared microspectrometry (FTIR), is useful for identifying pigments and media.
Identification of the materialsand their propertiesin contemporary objects is being pursued at several major institutions. At Tate, for instance, Thomas Learner developed a technique for identifying modern paint media using pyrolysis gas chromatography-mass spectrometry. Scientists at the Canadian Conservation Institute constructed a transportable FTIR spectrometer that has been used to differentiate traditional materials such as Japanese lacquer from imitations made from cashew oil or alkyds. And at the Carnegie Mellon Research Institute, Paul Whitmore developed a device for assessing, in a microscopic-sized spot, the lightfastness of contemporary colorants early in an object's life.
Many modern and contemporary paintings have not yet undergone major conservation treatments, a process that can sometimes remove components from the original paint media. As a result, natural aging processes are the predominant factors in the alteration of the composition of materials in modern and contemporary paintings. They are, therefore, ideal candidates for scientific study of the material aging processes.
The application of scientific analytical techniques to more recent works of art has increased our understanding of artists' materials and working methods, thereby enhancing our ability to preserve these paintings. These techniques were recently applied in research on paintings by two 20th-century U.S. artistsWillem de Kooning and Jacob Lawrencewhich was conducted in the laboratories of the GCI and the National Gallery of Art. This research illustrates how modern science can reveal new insights about contemporary works of art, which ultimately can aid in the conservation of these works.
Willem de Kooning
Throughout his long career, Willem de Kooning routinely exploited unconventional materials for his paintings. A wealth of historical and anecdotal records report that the artist regularly mixed house paint, safflower cooking oil, water, egg, and even mayonnaise with his artists' paints to achieve desired visual and textural effects. Despite the extent to which his methods and materials have been described by his contemporaries, there has been considerable confusion as to de Kooning's actual practices at specific times in his career. Additionally, there is concern that the idiosyncratic paint formulations that he reportedly used will have a negative effect on the long-term stability of his paintings. The paintings executed during the 1960s and 1970s, in particular, are problematic for conservators, with passages that remain soft and sticky. Such paint surfaces are easily deformed when touched, and they readily pick up surface dust.
To address these issues, a study was undertaken to analyze the binding media and pigments of a selection of de Kooning's paintings from the period of 1960-1977. Due to similarities in composition between traditional oil paint media and the media de Kooning reportedly used, it was possible to use GC-MS procedures developed for traditional paints to test samples from his paintings.
The results of the study provided valuable insights into de Kooning's choice of medium. First, no evidence was found in any of the samples analyzed to support the claims that de Kooning painted in egg tempera medium or with mayonnaise. Early in his career, de Kooning did use house paints extensively, often in combination with artists' oils. In paintings from the early 1960s, he abandoned his use of house paints and turned to artists' tube paints made from linseed, castor, and poppy oils. The earliest evidence of his use of safflower oil comes in paintings from 1964 or 1965, and it appears that safflower oil, mixed with water, artists' tube paints, and a solvent, became his medium of choice until the middle 1970s.
These analytical findings support anecdotal reports that de Kooning, increasingly frustrated with the fast-drying properties of the newer house paints, searched in the 1960s for a paint formulation that would meet his requirements for a medium that could be reworked over extended periods of time. This more fluid paint facilitated the complex and varied brushwork that is the hallmark of his paintings from this period. In two untitled paintings from 1977, de Kooning appears to have abandoned his safflower-and-water paint mixture entirely, turning to artists' tube colors exclusively after he learned of the dangers posed by nondrying oils.
From a careful review of the findings, it is clear that de Kooning's addition of water to his paintingsevidenced by air bubbles found in the painthas had little effect on the extent of breakdown of the oil media. Linseed oil paints were degraded to a greater degree than were paints made with slower-drying media, which runs counter to normal experience. Another important finding of this research is a greater appreciation for the influence of pigments on the stability and long-term tackiness of oil paints. The paints that remain soft generally are the full-strength cadmium colors or those containing synthetic organic dyes. By contrast, paints with significant amounts of white pigment have formed hard films.
These analytical results provide valuable information that will assist conservators in improving care for de Kooning's paintings from the 1960s and 1970s. Ultimately, the wisest course is preventive. It is recommended that these paintings be framed under glass, if possible; when this course is not practical, it is recommended that they be displayed and stored in as dust-free an environment as possible. When these paintings travel, they must be housed in frames to ensure that nothing will come in contact with their surfaces. Ultimately, if a painting must be cleaned, the analytical findings make it possible for informed choices to be made on how aggressively selected passages of the painting may be treated. Because the pigmentnot the binding mediumwas found to have the greatest influence on the stickiness of the paint, it is possible to use the pigment as a parameter for predicting vulnerability.
Jacob Lawrence's early training in the 1930s at the Utopia House and at the Works Progress Administration Arts Workshop in Harlem, New York, introduced him to the materials that he would use throughout his careertempera paints, various papers, illustration board, and hardboard. The use of matte, opaque, water-based paints would predominate in his work. Unfortunately, the precise kinds of aqueous media that Lawrence used have often been misidentified. Tempera, casein, gouache, and watercolor can be easily mistaken for one another, particularly when thinned to a wash consistency, and many of Lawrence's works have incorrect media attributions as a consequence.
To better identify the aqueous media used by Lawrence, a selected group of his paintings from 1938 to 1975 was studied. In testing the paint samples, pigments were identified using PLM, and FTIR was used in conjunction with GC-MS procedures developed for traditional paint media. The knowledge produced by this research of the medium in each Lawrence paintingknowledge grounded in fact, not speculationdoesn't just provide accurate information for scholars and historians and for museum records. It also sheds light on common deterioration problems associated with some of Lawrence's paintings, such as flaking paint or efflorescence formation, and it can guide their conservation.
The word tempera comes from the Latin temperare, meaning to "mix" or to "regulate." The classic recipe, as recorded by Cennino Cennini in Il libro dell'arte in the late 14th century, calls for emulsifying egg yolk with water, and is considered by purists to be true tempera. However, in the first half of the 20th century, many new water-based paints were developed to meet a demand from the growing advertising industry for fast-drying, opaque, matte paints. Recipes changed in response to availability and cost of raw materialsyet paint manufacturers classified most as tempera. While a shared characteristic of these paints was the ability to be thinned with water, the binding media may have included such combinations as gum and glue; starch and glue; glue and egg; egg and oil; egg, resin, and oil; and casein and glue.
Blind Beggars (1938) is among Lawrence's first recognized works executed with a commercially produced tempera. Analysis revealed that the red paint is composed of iron oxide red and transparent mineral filler, and the binding medium was identified as a mixture of gum and glue. Although Blind Beggars is in good condition, the presence of glue in the binder may be among the causes of instability in the paint layers in many of Lawrence's early tempera works. Awareness of this characteristic in some of his paintings should alert museums and collectors to the need for careful regulation of the relative humidity in which these paintings are exhibited. Knowledge of the components of the paint film will enable conservators to make better choices of adhesives, materials, and techniques for the treatment of these paintings.
In the late 1940s, Lawrence made his own egg tempera using a recipe—which he recalls obtaining from a friend—that called for equal parts egg yolk and water, plus a few drops of formaldehyde as a preservative. Analysis of the binding medium on Lawrence's Checker Players (1947) confirms it to be composed of pure egg. In contrast, analysis of the medium in Vaudeville (1951), another egg tempera painting, indicates that it is a commercially prepared medium incorporating oils and plasticizers into the paint. One problem with some egg temperas is the formation of efflorescence on the artwork's surface, an aging phenomenon. Generally associated with dark hues, a white crystalline substance was noted on the surface of many works examined for this study. A sample of this white crystalline exudate taken from Magic Man (1958) was identified as a free fatty acid deposit.
The best means for removing efflorescence from the surface of a painting is currently under consideration by conservators; approaches range from removing it with a soft brush or a small vacuum to using a cotton swab dipped in solvent. Could the commercial preparation of the egg tempera be the cause of the efflorescence? Works by Lawrence executed with a medium consisting solely of egg yolk do not seem to exhibit the white exudate. The analysis conducted on Lawrence's paints adds to the growing body of scientific knowledge of the causes and treatment of efflorescence in paint films.
In a later work on paper, Street to Mbari (1964), more than one medium may be present. Like so many Lawrence pictures dating from the 1960s onward, the medium had been assigned as gouache. However, analysis of one color sample identified glue as the principal binder, which indicates a tempera medium. From the 1950s through the 1970s, it appears that Lawrence bought different types of water-based paints. It seems probable that at many points in Lawrence's career, he simply had an aqueous media palette, and that he didn't distinguish among media but, rather, bought paints for their colors. Given the abundance of newly available, commercially prepared aqueous media in the 20th century, it should be no surprise to find many different types of paint in a single work of art.
This increased understanding of the extent of Lawrence's use of commercial paints is important for the ultimate conservation of his work. Commercial paint tubes often contain additives to preserve the contents, whereas paints mixed by artists from simple recipes generally do not; ultimately, these compositional variations could lead to different pathways of deterioration for commercial versus homemade paints, and hence they require different approaches to conservation and preservation.
A Multidisciplinary Challenge
Modern and contemporary paintings present a variety of new challenges to conservators. Today's artists can choose from an incalculable variety of commercially available products. Yet neither the long-term aging behavior of these materials nor safe methods for conserving the vast majority of them are known.
Given the magnitude of the task, multidisciplinary collaborations on national and international levels are essential for preserving modern and contemporary paintings. Fruitful partnerships have been established between manufacturers of artists' materials, conservation science laboratories, and organizations that set standards, such as the American Society for Testing and Materials (ASTM). Research priorities have been discussed at meetings of conservation professionals, and based on the enthusiasm expressed by the participants in these meetings, on the commitment of institutional resources, and on the extent of the partnerships, it can be said that the future of modern and contemporary paintings conservation looks bright. But it is clear that curators, conservators, and conservation scientists will need to work closely together in order to preserve the diverse, evolving legacy of today's artists.
Michael Schilling is a senior scientist and head of the analytical research section at the GCI. Susan Lake is the head of conservation at the Hirshhorn Museum and Sculpture Garden. Elizabeth Steele is the conservator at the Phillips Collection. Suzanne Quillen Lomax is an organic chemist at the National Gallery of Art, Washington, D.C.