Instrumental Analysis in Art and History
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ike a patient undergoing a fullbody medical scan, Albert Pinkham Ryder's late nineteenth-century painting titled "Lord Ullin's Daughter" stands still before a beam of probing particles. For 20 min, neutrons from a research nuclear reactor at the National Institute of Standards and Technology (NIST) in Gaithersburg, MD (formerly the National Bureau of Standards), penetrate the resinous and oily films of the museum piece. During the month or so following the neutron treatment, each of about 20 atomic elements in the layers of Ryder's painting respond with characteristic gamma ray and electron signatures. These write shadowy images of themselves onto sheets of film that nuclear physicist Yu-Tarng Cheng periodically places on the surface of the painting. Cheng is part of an effort in-
volving several Smithsonian Institution investigators who collaborate with scientists from NIST in the use of the NIST reactor for archaeological and art historical projects. In addition to using film for recording the spatial distribution of signals coming from the "activated" painting, a solid-state detector situated a few feet in front of the
FOCUS artwork records the gamma ray signals. This helps the researchers to calculate how much of a particular element (e.g., manganese in the raw umbers used by Ryder) is present in the painting. The technique is called neutron-activated autoradiography. The result: im-
ages and numerical data that tell of the spatial and quantitative distribution of elements, boundaries between different materials, images that a painter had made but then painted over, and patterns of brushstrokes even on underlying coats of the painting that are invisible to the museum visitor. Using nuclear reactors is a high-tech tactic that is allowing an interdisciplinary team of investigators from the Smithsonian Institution to learn about Ryder's painting technique. The research is part of ongoing preparation for a major retrospective of his work, which is slated to be hung in 1990 at the National Museum of American Art. Ingrid Alexander, a research art historian who recently joined the team, says that discoveries emerging from the autoradiography studies will become part of the curator's offerings to those who
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Sikyatki polychrome bowl from the site of Sikyatki. come to view the retrospective. Elizabeth Broun, acting director of the National Museum of American Art, is coordinating the preparations. She initiated the scientific investigation of Ryder's work in 1986. Alexander is part of a staff of 41 modern-day renaissance people at the Smithsonian Institution's Conservation Analytical Laboratory (CAL), one of a handful of labs at the Smithsonian's Museum Support Center. Some come to CAL from the analytical measurement/hard numbers side of scholarly inquiry; others come from the humanistic side—from disciplines like art history, archaeology, and social anthropology. But before long, the two sides merge within most individual CAL researchers. Investigators at CAL and in other conservation laboratories such as the University of Pennsylvania's Museum Applied Science Center for Archaeology (MASCA) and the Canadian Conservation Institute (CCI) in Ottawa are using the most modern techniques and instruments that analytical science can muster to pursue what are strictly humanistic questions. What happened to the pottery of the Hopi people when the Spanish entered their southwestern mesas in the sixteenth century? Did Rembrandt overpaint work he had completed earlier? What techniques
did Ryder use to create his seascapes? At research centers like CAL, MASCA, and CCI, art and science are one culture. Preserving and uncovering the human legacy is this culture's raison d'être. Patrick McGovern initiated a program at MASCA, for instance, that focuses on reconstructing how craftspeople in ancient times made their ceramic wares. To do this, he and colleagues analyze jewelry, pottery, and other ancient objects using xeroradiography (an X-ray technique resulting in xeroxlike images indicating regions of differing densities), petrography (a technique involving polarized light that is good for determining mineral inclusions in the same object), scanning electron microscopy, proton-induced X-ray emission (PIXE) spectroscopy, and neutron activation analysis (NAA). Using NAA, McGovern was able to determine that the Late Bronze and Early Iron Age (ca. 1550-1050 B.C.) pottery makers in central Transjordan—the fertile, 30-km-wide strip of highlands between the Jordan River and the desert—used the same clay source for this entire 500-year period, an era of great social change and cultural mixing. McGovern can use this information to make further inferences about the
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influence, or lack thereof, of people entering the Transjordan region during this period. "That the same clay source was used throughout the transition period is partial evidence for saying that the same people and the same tradition of pottery making was in place," he said. More generally, he can learn something about how early technologies spread and evolved. About 100 miles south of MASCA is the Conservation Analytical Laboratory, just a few miles away from the numerous museums on the Mall in the capital. Research at CAL falls into three broad areas. Archaeometrical studies is one of them. It involves measuring the physical, chemical, and micromorphological features of things such as ancient pottery, pigments, plasters, and obsidians; old harpsichord strings; and ancient bones and teeth. Research biochemist Noreen Tuross is even doing biochemical investigations on ancient proteins that she is able to extract from such bones. Using techniques such as gel electrophoresis, she can separate and identify biological compounds—in this case, serum proteins like antibodies and albumin—as well as their amino acid building blocks. She can identify the latter using liquid chromatography. Because the protein in ancient bones is so scarce, Tuross must take special pains to extract it without damaging or losing it. In one of her projects, she hopes to use biochemical analysis of ancient proteins to discover what kinds of ills our ancestors faced tens of thousands of years ago. CAL's instrumental neutron activation analysis (INAA) facility at the NIST reactor, run by CAL research chemist James Blackman, provides an analytical resource for the research of CAL staff, postdoctoral fellows, and research collaborators. Some of the projects include assistant director for archaeometrical research Jacqueline Olin's examination of historic Spanish and colonial majolica ceramics, Blackman's investigation of Trans-Caucasian obsidian exchange research done in collaboration with Soviet archaeologists, and CAL archaeologist Ronald Bishop's Hopi ceramic project. Bishop, together with colleagues at the Smithsonian Institution and within the Hopi community in Arizona, is using INAA to learn about early Hopi ceramic technology and how it related to Hopi pottery production and exchange. He starts with drillings from sherds, or fragments, of Hopi pottery, which he brings to CAL's facility at the NIST reactor to get an elemental fingerprint of each sample. Then he ekes out infor-
mation from this data with various mathematical techniques. The number-crunching step helps him determine which fragments probably were made in the same pottery-making center. By combining this compositional analysis with design and fabrication studies of the sherds, Bishop and colleagues are beginning to paint a picture of how people in separate but nearby Hopi villages interacted between 1300 and roughly 1900 A.D. "We are attempting to learn how the Hopi organized themselves and interacted after they came together from various areas after the time of the great drought [of the late thirteenth century] in the Southwest," Bishop said. He is also interested in how the arrival of the Spanish in the sixteenth century, and others in later centuries, affected the design and fabrication of Hopi ceramic wares. For the three centuries between the great drought and the arrival of the Spanish invaders (ca. 1300-1600 A.D.), the Hopi people produced a beautiful and unique yellow pottery considered by Bishop and others to be one of the highest technological and artistic achievements of ancient native Americans. Soon after the arrival of the Spanish, the Hopi stopped making the yellow pottery. It was the present-day Hopi potter and engineer, Al Qoyawayma, who actually inspired the Hopi ceramic project, Bishop said. Qoyawayma has been trying for many years to rediscover the technique his ancestors used to make the yellow pottery. He approached Bishop several years ago at a scientific meeting they were both attending and suggested that the two should begin a collaboration. Bishop agreed wholeheartedly. Yet although sophisticated analyses can be made at CAL facilities, the chemical and physical formula for making the yellow pottery remains a lost art. The second prong of CAL's overall research program is conservation science, according to director Lambertus van Zelst. In this field, researchers try to understand the chemistry and physical mechanisms underlying the visible degradation of museum objects. For instance, in the soon-to-be-launched paint-leaching project, CAL researchers will try to figure out what happens to paint films when one layer of dirty or cloudy varnish is removed with a solvent to make way for a new coat. Such studies are crucial, according to van Zelst, because restorative practices like cleaning and revarnishing can injure paintings, especially if the procedure is periodically repeated. By uncovering the molecular processes involved, conservation scientists will be
better able to treat their museum object patients without killing them in the process. Researchers at the Canadian Conservation Institute, which serves Canada's national museums, are doing related studies. In one project, CCI researchers are looking into the ill effects that modern building materials may have on museum objects. "We are monitoring volatiles that are coming off of paint, wood, textiles, carpets, and other indoor materials," said John Taylor, who heads CCI's analytical research laboratory. CCI is collaborating with CAL and with the National Gallery of Art in Washington, DC, in a study of packing materials used for transporting priceless works of art. The aim is to evaluate thermal and mechanical properties of packing materials and how their vibration characteristics affect the artworks they are supposed to be protecting. Currently there is no international protocol, but Taylor suggests that such standardization could be one result of the collaboration. The work of research chemist David Erhardt at CAL is another example of conservation science. He is learning what it takes to keep historically important paper artifacts from crumbling—a considerable problem for libraries and facilities that hold huge amounts of all-too-mortal books, periodicals, newspapers, and photographs. First, Erhardt places standard paper samples in aging chambers where he can control the temperature and humidity levels. By studying the effect of environmental parameters, he hopes to determine the environmental conditions that most accurately compress several centuries' worth of aging into one year or less. Periodically he takes a piece of the sample paper and uses gas chromatography to evaluate the oxidative, hydrolytic, and photo-induced degradation products. These usually are simple sugars like glucose and xylose, which are the building blocks of the complex polysaccharides in wood fibers that make up the paper. The distribution and concentration of these simple sugars tell Erhardt how much and which type of degradation has occurred. This information, in turn, might serve as a guide for museum workers trying to choose environmental conditions that best preserve their paper-containing objects, according to Erhardt. The third part of CAL's research triad is conservation technology. "Once you figure out what is causing degradation, you need to do something to stop it," remarked van Zelst. For example, what CAL scientists learn in their
paint-leaching project may become part of the conservation and restoration protocols for paintings within the Smithsonian collection. "Museum conservation has improved so much in recent years because of the increased benefits observed from the use of analytical instrumentation," said van Zelst, who also is president of the American Institute of Conservation, which is to conservation professionals what the ACS is to chemists. Underlying the "scientification" of conservation efforts is a changing attitude within the museum conservation community. Restoring the appearance of damaged and deteriorating objects used to be the primary concern for most museum curators and historians, according to van Zelst. "Now we are more interested in getting at the causes of these processes and events, and the cures," he said. "Conservation is moving very rapidly from being a trade, which was known as restoration, to becoming a profession, which is conservation," CCI's Taylor added. Restoration efforts focus on making objects look the way the restorer thought they looked when the objects were new. Professional conservators try to preserve the object as it is without adding or subtracting from it, Taylor explained. The tools of the wellequipped laboratory, and the methods of the skilled and well-informed analyst, are fueling this shift. Art historical research also is taking on new complexions because of modern instrumentation. "Science and chemistry are opening a whole new avenue toward art historical information," Taylor said. Curators, art historians, museum directors, and museum visitors see paintings and museum pieces as they appear on the surface. "Today, with the advanced techniques that we have to examine a work of art, we can see more of the way the object has been made by the artist," Taylor added. "We can see underneath the surface." Alexander of CAL concurs. In the autoradiograph of Ryder's "Lord Ullin's Daughter," a figure seems to be leaning back with its legs braced on the seat of the boat. This is not very evident in the X-ray radiograph or in the painting. Furthermore, in looking at the painting you will notice that the water meets the sharp mountains in the background rather abruptly. But if you use neutron activation autoradiography to look at the area underneath the surface of the painting, as Alexander and her colleagues have done, you will see that Ryder painted in a gentle slope at the bottom of the mountains.
Ivan Amato
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