By Giacomo Chiari and Marco Leona

Conservation science is the commonly used term for a number of related disciplines relevant to scientific research in the study and conservation of cultural heritage. Generally speaking, work in this field falls into three major areas, which interact with one another so extensively that it is often difficult to distinguish them from one another.

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The first area includes archaeometry and technical art history (debatable terms, perhaps, but well-established ones), which involve the study of cultural heritage with the goal of knowing what the heritage is made of, when it was made, where it was made, and how it was made. In archaeometry, archaeologists and archaeological scientists generally study sets of excavated objects and their context, while in technical art history, art historians and museum scientists tend to focus on individual objects removed from their context.

The second area of research encompasses study of the changes occurring in objects and the causes of degradation, with the goal of reducing deterioration, if not stopping it forever (a difficult thing to do, as this runs counter to the second principle of thermodynamics). This area involves the study and development of methods for mitigating deterioration.

Finally, there is a third area, sometimes called technology transfer. Whether they are engaged in archaeometry or in conservation, conservation scientists often create or modify instrumentation to facilitate their work, since the conservation field represents too small a market to provide sufficient incentive for manufacturers to produce instruments specific to conservation science. The creation of new tools, or the upgrading of old ones, is necessary for increasingly better analyses of a greater number of materials, using smaller samples or no samples at all. These goals are achieved either by adapting instrumentation from other branches of science or by the ad hoc design and optimization of new instruments. As Irwin Scollar, formerly of the Rheinisches Landesmuseum in Bonn, is reported to have said, "We're fighting a guerilla war with available weapons, or probably those captured from the enemy."

Conservation scientists often act as interpreters for professionals with different backgrounds. The conservation scientist becomes the link between scientific theory and cultural heritage application, or between cultural theory and scientific application (for example, exploring the geochemical literature to identify techniques for determining the provenance of rocks used to produce Neolithic tools, and finding a laboratory with experience in those techniques and a willingness to do the research).

With regard to the ways in which conservation science work is carried out, an important distinction should be drawn between research conducted in academia and research institutions, on the one hand, and research conducted in museums and field projects (i.e., archaeological sites, monuments, etc.), on the other. Non­conservation academic research allows scientists to explore in detail a specific problem or an area of interest. In general, one can focus on a single topic and establish the goal of the research, the research strategy, and possibly the final outcome.

For conservation scientists working in a museum full of objects (often lacking a well-documented provenance) or working at an archaeological site or historic building, the challenge is very different. Rather than a specific research topic, a material object or structure is typically at the center of the conservation scientist's focus. The problems faced are not chosen by the scientist nor are the means of solving them necessarily available.

No single practitioner can be expected to possess all the expertise needed to deal with the various aspects of cultural heritage. Nevertheless, the economics of cultural institutions are such that even the few museums and sites that are fortunate to have scientific laboratories can hardly support more than one to three scientists on their regular staffs. Therefore, cultural institutions must cooperate among themselves, as well as with academic laboratories, in order to effectively conduct advanced research.

An Evolving Field

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Conservation science is coming of age in its development. Any new scientific field has an experimental, or embryonic, stage in which scientists from other fields sporadically venture into its new activities, bringing with them expertise but only a modest understanding of the needs of the discipline—sometimes with questionable results. Then a small number of scientists begin to join forces, committing their careers to the new field, gaining over time a fuller understanding of it and a systematic approach to it.

This is how conservation science was born. In its earliest days, it was not considered by the scientific community to be hard science. In recent years, funding from governments and private institutions has attracted more scientists, and the number of researchers in the field is now large enough that international meetings are regularly convened for participants to share ideas and results. Peer-reviewed journals allow for the circulation of related work and (no less important) create a sense of identity for conservation scientists. Greater visibility and a greater commitment to research in conservation can attract talented young people who a few years ago would have selected one of the more traditional branches of science.

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As in other branches of science, the tremendous progress in technology—including the advent and use of personal computers—has significantly altered the field. In conservation science, new analytical techniques have made possible microinvasive or noninvasive approaches. For example, binding media analysis has always been difficult. Today, however, one can detect, after centuries of aging, minimal amounts of organic materials using refined versions of gas chromatography–mass spectrometry. Drawing from techniques developed in biology and biotechnology, it is now possible for conservation scientists to use antibodies to identify parts per million of proteins, allowing them to distinguish rabbit glue from fish glue or cowhide glue, or parchment made of sheepskin rather than goatskin. This information is fundamental to the art historian for identification and attribution and fundamental to the conservator for treatments.

Now available are new techniques such as environmental scanning electron microscopy, portable X-ray fluorescence, and Raman spectrometry, which are totally noninvasive—i.e., they do not require samples from an object or involve the risk of damaging it with dangerous radiation analysis. Both the purchase cost and the difficulty of operation of this equipment have dramatically decreased. For most techniques, there is now a portable version of the instrumentation, making it possible to take the analysis to the object rather than bringing the object to the laboratory. These portable instruments have made advanced instrumentation increasingly available to conservation research laboratories and increasingly useful for fast, noninvasive or microinvasive materials analysis.

In addition, the number of techniques that allow conservation scientists to examine the surface of an object, to even see under the surface (e.g., infrared reflectography) or through an object (e.g., radiography), or to reconstruct the object three-dimensionally (e.g., CT scan) has increased exponentially. Further progress in diverse techniques, such as hyperspectral imaging, confocal microscopy, and the scanning probe microscopies, is also expected.

In short, conservation scientists today can do things more rapidly, more precisely, and in a less damaging way then previously. They also can do things that just a few decades ago would have been impossible. The impact of this science applied to culture is tremendous and allows many historians—art and otherwise—to make great progress in their disciplines as well.

An Applied Science

When dealing with valuable cultural heritage, researchers have constraints in the size and amounts of samples that can be taken. For instance, the modus operandi of a geologist studying marble from a quarry and of a conservation scientist studying the same marble as used in a statue by Michelangelo are obviously different. The science is similar, but the goals and techniques are different. Moreover, most of the time, conservation scientists are dealing with unique assemblages of objects and their evolution over time, often under unknown conditions. In paleontology, the possibility of verifing a hypothesis by devising an experiment and reproducing the event in the laboratory is often precluded.

Conservation science is sometimes compared to forensic activities, since the goal is to reconstruct the action behind the production of the object by studying a few material traces. Greater interest in the material aspects of a work of art broadens the focus from the aesthetic or documentary value of the object to include a larger view of a human society, both in terms of the skills it perfected and of its relations with the environment and with other societies. The interdisciplinary aspect of such a search is obvious.

The scope of conservation science, though, is to determine not only how the object was made but also how it was modified by the passage of time, and what the mechanisms were that altered its original condition. If these deterioration mechanisms are still active (and therefore dangerous to the conservation of the object), it is the responsibility of the conservation scientist to help the conservator find methods to slow these mechanisms to the degree possible. This goal can be accomplished in various ways—one being to modify the surface of the object to make it more resistant to external attack. Much has been done in this direction, but efforts have not always been successful. Typically, the cause of these failures is a lack of understanding of the nature of the object or of the consolidant used, or of the combination of the two. The composite material that is created may be disastrous for the object when the two interacting substances are not compatible. It is the responsibility of the conservation scientist to ensure that these errors are not repeated.

Another way of ensuring a longer life for cultural heritage is preventive conservation. Once the basic mechanisms of deterioration are understood for individual objects and the impact of the environment on the objects is evaluated, one can try to mitigate these effects—not by changing the object's surface composition but by modifying the environmental impact using various kinds of protection (e.g., shelters, anoxia boxes, climate control devices, etc.). This approach to conservation relies heavily on a detailed knowledge of the nature of the objects, the environmental conditions and their interaction, and the ability to communicate with building engineers and facilities maintenance specialists.

Enhancing Understanding of Heritage

Art historians, archaeologists, museum curators, conservators, and architects generally recognize that understanding the material aspect of an object is necessary to comprehend it and its original context fully. Art is often solely understood as an inspired act of creation by an individual artist. While the artist's concept is certainly a component of the art object, the technique and the materials used are equally important. On the purely aesthetic side, they ultimately determine the final visual effect, and they have been chosen and manipulated by the artist with this in mind. On a broader scale, materials and techniques are an expression of the society in which the artist lived, and they reflect the role of the artist as a technologist. When the hidden technological information (the availability and choices of materials, studio practices, etc.) is revealed, a window is opened onto the economics of the period in which the object was created. The conservation scientist—by focusing on the material aspects of the work and by illuminating the link between the hand and the society that created it—plays a major role in this effort to contextualize the artwork.

Materials and techniques are also fundamental to under-standing how an art object interacts with its environment. The chances of survival of the work of art over time are, in fact, a function of the object's constitution and of its environment. If Leonardo da Vinci had been able to consult a conservation scientist before painting The Battle of Anghiari, that now-vanished masterpiece might still be with us.

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Since archaeology discovered modern instrumental analysis methods, the field has changed radically. The ratio of trace elements in obsidian flints can now precisely identify their quarry of origin, a fact that enables reconstruction in detail of the trade system in the prehistoric Mediterranean basin. The lead isotope ratio allows the same for coins and glass. Now there are ways of determining the temperature at which a ceramic was fired, of ascertaining the age of a wooden log within one year by examining the thickness of the rings, and of dating a soil layer more than 10,000 years old by looking at the shape of the pollen contained within it.

But to be able to obtain results in principle is not enough. Reference databases are essential. To see that two grains of pollen are different in two soil layers, or that an instrumental pattern is characteristically found in a particular sample and not in another, is only the first level of investigation and discovery. A more complete characterization of samples and objects requires that analytical patterns (pollen shapes and sizes, peak positions and intensities in a Raman spectrum) be unequivocally matched to those of known reference materials studied under reproducible conditions and catalogued in a reference library. The development of databases, including databases of aged substances, requires substantial commitment of both staff time and instrument use and is only possible when a large number of researchers are dedicated to the task. It is a sign of conservation science's maturity that it has reached this stage, as evidenced by the significant databases compiled by the Infrared and Raman Users Group (IRUG) and by mass spectrometry users.

Impact on Conservation

Modern art theory notwithstanding, we do not like modification in the appearance of our masterpieces. Even in cases where the artist's intent seems to include deterioration, museums (and perhaps human nature, in general) are ill disposed to accept it. A notable work of art constitutes significant capital, and ultimately, a museum's collection is its main asset. Substantial resources are spent by museums to conserve works that the artists may have never intended to be permanent.

Slowing down deterioration, stabilizing objects, and assuring that display and storage conditions are of the best quality to preserve and maintain works of art for the longest possible time are among the main mandates of the conservation scientist. If archaeometry has often been compared with forensic sciences, so has conservation been compared with medicine—besides the diagnosis, one needs the cure.

Maintaining an object unchanged forever is generally acknowledged to be an impossible goal. Yet conservation scientists are often requested to suggest or devise techniques and materials that strive to do precisely this. It is accepted conservation practice that the visual aspect of the object should not be altered by a treatment. But the understanding of the complexities of objects and of the information that can be obtained from them has now grown to include their broad chemical-physical properties. These properties should not be modified, for such changes might hinder or prevent future studies or treatments. Since damage to objects can often be attributed to past improper treatments, reversibility—the ability to undo any intervention performed on an object—has become a desired component of conservation treatments. Of course, no human activity is fully reversible: if stopping deterioration runs counter the second principle of thermodynamics, then reversibility truly violates Heisenberg's uncertainty principle. However, modern conservation and conservation science can evaluate the risks of new treatment, and of any intervention in general, with the tools of risk management and the concept of retreatability rather than reversibility. Treatments or interventions (such as sampling) are never good or bad. They may be more or less invasive, more or less needed, more or less urgent, and more or less feasible.

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Conservation science has contributed enormously over the past thirty years to the ways in which cultural heritage is preserved, displayed, and utilized. New conservation materials, such as varnishing resins specially developed in collaboration between museum scientists and industrial researchers, are now commonplace in the paintings conservation laboratory. Today, cleaning of works of art can be done in very specific and controlled ways through laser cleaning, first developed for outdoor sculpture but now increasingly used for other substrates (from graffiti-defaced rock art to amalgam gilt bronze). These instances are examples of close collaboration between industrial and academic researchers and museum conservators and scientists.

Conservation science is also making contributions to the prevention or limitation of further damage to collections through greater understanding of display and storage environments. The ability to monitor color change in light-sensitive objects and the understanding of fading caused by light has increased greatly as a result of the concerted efforts of several laboratories around the world. The possibility of monitoring the light exposure of water-colors or photographs while they travel for exhibitions is now a reality, accomplished with a tool as simple as a highly light-sensitive dye-coated paper strip. Likewise, it is now possible to predict an object's propensity to fade by using a simple microfading test. From the adoption of a common accelerated corrosion test used in metallurgy to evaluate which materials can be used in display and storage cases, to the development of diffusion tube and ion chromatography techniques to quantify corrosion-inducing airborne pollutants, preventive conservation has become a science with dozens of practitioners in a number of museums.

Conserving single objects is only a small part of the more general duty of conserving cultural heritage for future generations. Major risks now include not only unavoidable natural catastrophes (the Bam earthquake in Iran is a recent example) but also large-scale damage due to war, looting, theft, and illegal excavations. Equally powerful destruction agents are the consequence of normal human activities, often praised as economic development—for example, the demolishment of old buildings. The detrimental effect that industrial society generally has on the environment certainly can disrupt the material stability of cultural heritage objects.

Although these are enormous problems for which complete and lasting solutions may never be found, science can significantly contribute to mitigating their negative effects. Seismic damage mitigation devices are already installed in many museums and historic buildings. Specially sealed cases can protect delicate objects from aggressive environments. Satellite images can show the presence of archaeological sites before potential excavation, thus forcing authorities to limit new construction.

Further development of the profession requires greater educational programs and opportunities, including university curricula at all levels and in the various branches of research, coupled with more internships in museums and in the field. Growth in the number of available jobs and the hiring of appropriately trained professionals should be supported simultaneously, in order to allow for balanced development. To some degree, this process is at work in several countries, but much more remains to be done.

The field of conservation science is in expansion, and more and more innovative approaches are likely to be developed in the years to come. This optimistic assessment is mitigated only by the fact that the challenges confronting the field will, inevitably, increase in complexity and size, with the passage of time and the growth of human society.

Giacomo Chiari is chief scientist at the Getty Conservation Institute. Marco Leona is David H. Koch scientist in charge of the Department for Scientific Research at the Metropolitan Museum of Art, New York.