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Millennium Special Report
C&EN 75th Anniversary Issue
Tools of the trade
Standard analytical methods used to analyze works of art

A Special And Enduring Relationship

Gamblin Bets On Conservation

Related Stories
[C&EN, Apr. 16, 2001]

Taking A Closer Look At Art
[C&EN, June 5, 2000]

Science Inspiring Art Inspiring Science
[C&EN, May 22, 2000]

The Right Chemistry For Fragile Frescoes
[C&EN, Jan. 24, 2000]

Chemistry In The Service Of Art
[C&EN, Sept. 7, 1998]

Related Sites
National Gallery of Art (NGA)

J. Paul Getty Museum

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July 30, 2001
Volume 79, Number 31
CENEAR 79 31 pp. 51-59
ISSN 0009-2347
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Conservation scientists at the National Gallery of Art work closely with conservators, curators to preserve nation's treasures


TEST SUBJECT Govaert Flinck's "Portrait of a Man" shows the comparability of natural resin and synthetic resin.

Sometimes chemistry can improve on nature. Case in point: the 1641 oil painting "Portrait of a Man" by Dutch artist Govaert Flinck introducing this article. The image on the left shows the partially conserved painting. Only the right half is coated with a natural resin varnish. Next to it is the painting after conservation. It is now completely coated--the right side with the natural resin varnish, the left with a synthetic resin, a product of the chemical industry.

Why and how the painting came to be treated in this manner is a fascinating tale involving art and chemistry, and especially conservation scientists at the National Gallery of Art (NGA) in Washington, D.C., and conservators at the J. Paul Getty Museum in Los Angeles, which owns the painting.

Like most Old Masters, the Flinck portrait was probably originally coated with a natural resin varnish. The varnish was applied not so much for protection, but to make the painting look darker, more glossy, and the colors more saturated. Unfortunately, over time, the thin varnish layer deteriorated--it became more yellowed, cracked, and hazy. And, because of oxidation and other chemical reactions, the varnish became more insoluble and more difficult for the conservator to remove. Instead of enhancing and protecting the painting, the natural resin obscured it.

Reapplying a natural varnish will only repeat the degradation cycle because the coating will again deteriorate as it ages. So what is an art conservator to do? Turn to a breed of chemists called conservation scientists, of course.

Conservation scientists help conservators understand materials and methods artists used to make works of art and, in some instances, they help determine what is original to the work and what was added in previous restorations. They also develop and test new materials--often from the chemical industry--to help conservators preserve artworks.

For example, several decades ago, a booming chemical industry created a plethora of synthetic thermoplastic products, and many clear synthetic polymer coatings became widely available. Polyvinyl acetate, poly(n-butyl methacrylate), and other thermoplastics were believed to be more stable than natural resins, and some conservators enthusiastically appropriated them each for their own purposes.

But they adapted the industrial products with little scientific understanding of how the synthetic resins would function as art materials. Then along came pioneering conservation scientists like Robert L. Feller, who served as science adviser to NGA and who retired as director of the Mellon Institute in Pittsburgh. Feller and others showed that these synthetic resins underwent autooxidative cross-linking reactions and also became more difficult for conservators to remove as they aged.

After much research, Feller, in the mid-1980s, introduced the stable resin Acryloid B-72, an ethyl acrylate/methyl methacrylate copolymer made by Rohm and Haas. This synthetic resin became a conservation staple, even though it, too, had some severe drawbacks. Its chief disadvantage was that it didn't produce the same optical appearance as the natural resin varnishes. Conservators went back to using their old standby--traditional natural resins.

Conservation scientist E. René de la Rie, then at the Metropolitan Museum of Art in New York City and now the head of scientific research at NGA, began work on what he calls his "claim to fame" research. He believed that low viscosity and low molecular weight were the keys to finding stable synthetic resins with optical properties similar to natural resins. His search led him to hydrogenated cyclic hydrocarbon oligomers--called hydrogenated hydrocarbon resins--and urea-aldehyde oligomers--called aldehyde resins.

De la Rie was able to show that these synthetic resins stayed transparent and glossy and didn't yellow or crack as they aged. They remained soluble in less toxic, low aromatic hydrocarbon solvents and, therefore, would be easier for conservators to remove than natural resin and earlier polymeric synthetic resin varnishes, which harden as they age. And they obtained the level of color saturation and gloss sought by conservators.

The synthetic hydrogenated hydrocarbon and aldehyde resins share a feature with natural resins: low viscosity. And they, along with natural resins, are low molecular weight. De la Rie's eureka moment proved correct.

With de la Rie's data and encouragement, Mark Leonard, Getty's chief painting conservator, conducted a daring experiment with the Flinck portrait to test the optical properties of a synthetic resin varnish against those of a natural resin.

To regain the image hidden under the aged natural resin varnish, Leonard removed the painting's cloudy coating with a relatively mild organic solvent mixture. He kept the left half uncoated but varnished the right half with gum mastic, a triterpenoid tree exudate.

In appearance, the varnished side is more vibrant and wetter looking than the "naked" left-hand side, which by comparison has a dull, dry look. Moreover, the contours of the man's robe are clearly discernible on the varnished side and nearly indecipherable on the other side.

Leonard then varnished the left side of the portrait with a synthetic coating fully tested by de la Rie--the hydrogenated hydrocarbon resin Arkon P90 made by Chicago-based Arakawa Chemical. If one were to look very, very closely, one might be able to discern a faint demarcation between the natural and synthetic varnishes. But visually the two halves appear so nearly identical that in blind testing, several conservators could not confidently distinguish the natural varnish from its synthetic cousin.

So, here you have a case of chemistry besting nature. The synthetic resin varnish has all the positive attributes of a natural resin varnish but none of its drawbacks.

ARTISTS' FINGERPRINTS Elemental dot map (below) shows that Gentileschi, who originally painted "St. Cecilia & an Angel," used lead-tin yellow pigment in hair and blouse decoration, but Lanfranco used lead-tin-antimony yellow when he painted the red drapery over the original composition.
"Conservation science, as it applies to organic components of works of art, is chemistry in the fourth dimension."
Several years later and now at NGA, de la Rie applied the same principle of low viscosity, low molecular weight to develop and fabricate stable yet reversible paints that can be used by conservators to retouch damaged paintings. He partnered with the Getty's Leonard, another conservator in private practice, a manufacturer of artists' materials, and nearly his entire scientific research staff at NGA to undertake this research endeavor. These paints are now commercially available through Gamblin Artists Color Co. of Portland, Ore., and are used by conservators around the globe.

De la Rie--a Ph.D. physical chemist with a keen "interest in making new materials and techniques available to conservators"--came to NGA in 1989. He inherited a department--then known as the science department--that was fully integrated into the museum's conservation division.

It hadn't always been so. In 1983, when Ross Merrill became chief of the conservation division, all departments within the division acted as independent fiefdoms. Under his direction, Merrill insisted that all departments, including the science department, function as equals in a cohesive whole. He was convinced that "scientists were handmaidens to conservators" in the sense that scientists helped "conservators understand the art object as a material object." They helped conservators restore an object as close to the artist's intent as possible.

When de la Rie came onboard, the science department was small and focused on inorganic analyses. It conducted no basic research, which Merrill was intent on changing. "I knew that if I wanted to get top-quality chemists, I couldn't hire people just to do analytical studies but I needed a research component to attract them," Merrill explains. De la Rie was hired to make Merrill's intent a reality.

IN TURN, as de la Rie explains, it was his challenge "to make the department work, to find the balance between ad hoc problem solving and long-term research." There are "not many places where that balance happens," he adds.

Since his arrival, de la Rie says the department "has grown in size and scope." He has added "analyses of organic components and has built in a research component," hired more staff, and purchased needed equipment with grant support from the Andrew W. Mellon Foundation, which also endowed his position.

To reflect its evolution from an analytical lab to one also doing basic research, the department's name was changed to scientific research.

Barbara H. Berrie, a Ph.D. inorganic chemist, came to NGA in 1984, taking "a job I always wanted." Over the years, she observes, the department has "added organic chemists, biochemists, people with experience in working with archaeological materials, and scientists from disciplines other than chemistry."

Today, the department consists of 10 people: five chemists; a botanist who functions more and more like a chemist; an art historian who uses the tools of science; a technician with a B.S. in chemistry "who does a little bit of everything," Berrie says; and two fellows. One fellow just received his Ph.D. in conservation science from the University of Amsterdam, de la Rie's alma mater, and the other, an M.S. biochemist, recently left to take a position in Paris.

NGA's scientific research department is one of the largest and best equipped scientific laboratories within a fine arts museum. It is also one of the few to be fully integrated into a conservation department under a single administrative director.

"It is important that scientists be exposed to works of art and to the problems conservators have," de la Rie says. The Mellon Foundation's museum and conservation program, under the direction of Angelica Z. Rudenstine, recognizes that, too, and is committed to repeating the success at NGA by supporting science within conservation at other museums.

One of the things conservation scientists do is analyze the materials of an artwork to determine if they are consistent with the object's presumed date or attribution. Berrie, for example, analyzed the paints in the circa 1617 oil painting "St. Cecilia & an Angel" to determine if the painting owned by NGA was completely the work of Orazio Gentileschi or if parts were later overpainted by a contemporary, Giovanni Lanfranco.

By examining cross-section samples of different areas of the painting with a scanning electron microscope/energy dispersive spectrometer (SEM/EDS), Berrie was able to produce an elemental dot map showing the distribution of various elements within the cross sections. Cross sections of the saint's hair and the decoration on her white blouse--areas known to be painted by Gentileschi--contained the pigment lead-tin yellow. However, cross sections of the red drapery contained a different pigment, lead-tin-antimony yellow, used here by Lanfranco.

From this detective work, Berrie concurred with curators that two artists worked on the canvas and that "Lanfranco overpainted Gentileschi's work." The painting is now attributed to both Italian artists.

Berrie's chief interest is pigments, and she was one of the first scientists to characterize a new form of one of the pigments--lead-tin-antimony yellow--found in "St. Cecilia" and in other 17th-century Roman paintings.

7931sci45xxxx 7931sci46x
VISIONARIES Merrill (left), De la Rie
"Analytically, [the samples] look like something taken off your shoe."
While de la Rie devotes most of his time to research, Berrie "spends more time working on issues relating to individual works of art," helping conservators and curators solve questions about objects. "I see solving problems as a kind of research. Certainly, some of the issues raised are as difficult to pin down as research," Berrie says. They may even be more challenging.

Complicating Berrie's analyses are several factors beyond her control. Her samples are not pure. "Analytically, they look like something taken off your shoe," she laughingly explains. And, when analyzing an inhomogeneous art object, she can't change one variable at a time, as scientists can do in controlled research.

Still, she regularly uses equipment and analytical methods found in any well-equipped research lab: X-ray fluorescence spectroscopy (XRF), Fourier transform infrared spectroscopy (FTIR), SEM/EDS, gas chromatography/mass spectrometry (GC/MS), X-ray powder diffraction, and compound microscopes. But then, Berrie also uses "equipment" not widely found in labs--like pigs' eyelashes to pick up very light samples. Berrie discovered this tool while visiting the microanalysis section at the National Institute of Standards & Technology.

"The chemistry I do is not hot-dog chemistry, just good old-fashioned general chemistry," Berrie says. She cites the example of understanding the pattern of corrosion on a 14th-century Spanish ciborium, the container for the holy wafer during communion services. The ciborium is made of gilded copper and champlevé enamel. Two glass enamel colors--a bright turquoise alternating with a duller gray-green--are found on the lid and foot. There is evidence of devitrification in the gray-green enamel and corrosion of the surrounding metal.

Using XRF, Berrie characterized the gray-green glass as being high in potassium and low in lead. The turquoise-colored glass had a high lead content, which appeared to inhibit corrosion.

"It turns out," Berrie says, "that potassium glass is very unstable, and when the relative humidity goes up beyond--or down below--a certain level, it will hydrate or dehydrate." In the case of the NGA ciborium, the potassium glass was drying out.

"As it dries out, it gives off water to the environment, leaving behind potassium, which becomes potassium hydroxide, which in turn becomes potassium carbonate when the hydroxide interacts with carbon dioxide in the atmosphere," Berrie explains. The environment around the metal becomes very alkaline, and copper carbonate corrosion occurs.

After the conservator removed the corrosion, Berrie recommended that the ciborium be placed "in a case with extremely constant relative humidity, which can never fall below 40%." Simple chemistry. Simple solution. "And almost like forensic science," Berrie says.

OLD AND FUZZY X-ray fluorescence spectroscopy (below) reveals Kühn's 1907 portrait of Alfred Stieglitz to be a platinum print developed in mercury; the yellow-orange highlights are attributed to shellac coating.
IN COLLABORATION with paper conservator Yoonjoo L. Strumfels, Berrie is currently working "on discovering the palette used by Winslow Homer in his watercolors, and on how the palette changed over the artist's lifetime" as his painting style changed. NGA has 30 Homer watercolors in its collection, which the artist painted between 1870 and 1904. She and Strumfels will be presenting their results on Nov. 7 at a symposium held at American Chemical Society headquarters in celebration of the society's 125th anniversary.

In the future, Berrie intends to revisit her studies on "the chemistry of the discoloration of an organocopper compound, generically described as copper resinate." This compound, used as a deep green transparent pigment by Italian Renaissance artists, was long thought to deteriorate solely through a photochemical process. But, Berrie says, "there is substantial experimental evidence that the pH of the medium has a large effect on the stability of the pigment." If she can better characterize the deterioration process, she can help ensure "that undeteriorated green pigments in pictures remain that way."

Also in the future, de la Rie would like to involve Berrie and others in his department in research to understand how the pigment ultramarine blue discolors. Over time, the pigment fades or blanches, but no one knows whether it's a chemical or physical change.

Until conservation scientist Lisha D. Glinsman examined them, no NGA curator knew whether a "bronze" bust of Pope Paul III Farnese (1468–1549) in its collection and six others at other museums--all attributed to the Renaissance artist Guglielmo della Porta--were real or fakes. Glinsman, now working on her Ph.D. in chemistry, examined all seven using XRF to determine their elemental surface composition.

Her XRF analyses revealed all seven to be made of brass--not bronze--containing copper, zinc, lead, and tin. The high zinc content in most of the busts was not characteristic of Renaissance European brass. Furthermore, she was unable to detect impurities in any of the busts, impurities that usually are found in 16th-century copper alloy sculptures.

UNLEADED GLASS Corrosion (detail, right) evident in alternating gray-green enamel panels on foot of ciborium (left), a container for the holy wafer, is shown by X-ray fluorescence spectroscopy to be due to unstable high-potassium, low-lead glass; alternating darker blue panels have high lead content that inhibits corrosion.

They were certainly made "after the advent of electrolytic refining, because once you have electrolytic refining of the copper ore, you are not going to see impurities," Glinsman explains. And she concludes that the high-zinc, impurity-free brasses "were more modern than Renaissance, probably late-19th-century, early-20th-century creations."

Glinsman says, "The best part of my job is that I get to handle the art." And XRF "is so versatile" that she gets to examine a variety of objects from bronzes to paintings to photographs to colors and glazes. "If you want a quick survey of an object's elemental composition without taking a sample, this is the place to come," she says.

And come the curators and conservators did, when they wanted to understand the photographic process used by Heinrich Kühn to create his portrait "Alfred Stieglitz, 1907." While it is possible to recognize visually the difference between an albumen and gelatin print, it is difficult--if not impossible--to visually peg a platinum or palladium print. Kühn's print was either a platinum or palladium print.

Using her versatile instrument, Glinsman showed that the Kühn portrait was a platinum print developed in mercury. The print's yellowish-orange highlights come from a coating of shellac.

Christopher A. Maines, a Ph.D. physical chemist, works with curators and conservators to understand 20th-century polymeric materials--the coatings, adhesives, and pigment binders--in objects in NGA's collection. And to do this, he routinely uses pyrolysis gas chromatography/mass spectrometry (PyGC/MS) and FTIR.

With conservators, Maines also collaborates on devising "exhibition and storage strategies for light-sensitive objects such as albumen photographs, textiles, and latex-coated objects," he says. He monitors color fading in these objects using visible light reflectance spectrophotometry.

Maines was involved in research that led to the development of the retouching paints now being marketed by Gamblin, and he continues to monitor the photochemical stability of the synthetic oligomeric resin used in those paints. To do so, he uses PyGC/MS to identify degradation products and gel-permeation chromatography to chart changes in molecular weight distribution.

He plans on continuing his research into the rheology--"flowability"--of materials used in works of art. As Maines explains, he is "characterizing the rheology of traditional natural resins used as picture varnishes and is attempting to mimic their excellent handling properties with the use of photochemically stable synthetic polymers and oligomeric resins."

Maines came to NGA in 1990 as a Mellon fellow in conservation science, directly after receiving a doctorate from the University of California, Berkeley. In 1993, he left to become a conservation scientist at the Smithsonian's Freer Gallery of Art and the Arthur M. Sackler Gallery. He returned to NGA in 1997, when a conservation scientist position opened up.

The greatest change he's witnessed in his department is "the improvement in instrumentation--most notably in sensitivity, reliability, and user serviceability."

Suzanne Q. Lomax, a Ph.D. organic chemist, agrees. As a result, the scientists can "take smaller samples and see a wider range of materials than we could before," she adds. Plus, she says, "computerization has enabled us to reprocess, examine, and compare data in ways that were not available to us before."

After Berrie, Lomax has been at NGA the longest. She got her job in 1986 after answering an ad in C&EN. Not surprising given her background, Lomax concentrates on the organic components of art objects, analyzing their binders, waxes, or resins. "Conservation science, as it applies to organic components of works of art, is chemistry in the fourth dimension," she says. "Many of the organic components undergo substantial oxidation and change, presenting challenges for identification."

7931sci41x 7931sci44x 7931sci43xxxx 7931sci42x
DETECTIVES Berrie (left), Glinsman, Maines, Lomax
"The chemistry I do is not hot-dog chemistry, just good old-fashioned general chemistry."

SHE AND MAINES have looked at modern alkyd or acrylic binders using PyGC/MS. She has identified waxes using GC, natural diterpene or triterpene resins using GC/MS, and natural dyes using high-performance liquid chromatography. Before using these analytical methods, she often performs preliminary analysis by FTIR to determine the class of materials--protein, wax, or natural resin--present.

Lomax says her most challenging requests are for analysis of modern materials. Twentieth-century art, she explains, often uses nontraditional materials or traditional materials in nontraditional ways.

Most of her research--as opposed to analytical studies for conservators--has involved working with de la Rie on developing new materials for use by conservators as surface coatings and retouching paints. But Lomax has her own project in mind for future research.

When conservators ask her to examine paintings for their synthetic organic pigments, Lomax turns to the best tools currently available: X-ray diffraction and IR microspectroscopy. But for a variety of reasons, these small synthetic organic pigment particles are very difficult to analyze by these methods. Some researchers, Lomax explains, "have been examining these pigments using PyGC/MS. I would like to try to examine them by liquid chromatography/MS."

In the more immediate future, Lomax and other department scientists are likely to be asked to contribute their analytical skills to solving the problem of how to allow a fountain to be a fountain.

The bronze sculpture "Venus & Cupid" stands majestically in NGA's Garden Cafe. It was designed by a 16th-century Italian artist to be a fountain. But over the years it has developed bronze disease, an autocatalytic corrosion, and NGA turned the water off.

Curators, conservators, and the scientific research department are "trying to figure out how water can safely circulate through the bronze sculpture once again," Berrie says. That means finding a suitable pretreatment for the water flowing through the fountain and water-impermeable coatings for the sculpture itself. Many traditional water treatment solutions "are not appropriate for use with works of art," Berrie says, "so finding a solution that is effective and safe for the artwork requires creativity." The project has taken "me out of my chemistry experience into water chemistry and plumbing," she adds.

After the sculpture is treated to remove the corrosion, it will be coated with water-impermeable substances--including beeswax--and reinstalled in the new sculpture gallery that NGA plans to open in 2002, Berrie says.

Also in the future, Merrill envisions "scientific research into the problems and solutions of conserving modern paintings." And he cites de la Rie's "personal interest in the validity of using accelerated aging" to study changes in materials. Accelerated aging is now widely used in museum conservation departments, but no one has studied how comparable it is to natural long-term aging of works of art.

BRONZE DISEASE Conservation scientists are trying to figure out how to have water circulate safely through this corroded bronze "Venus & Cupid" fountain, a fixture in the National Gallery of Art's Garden Cafe.
ANOTHER OF de la Rie's interests is the eventual digital imaging of NGA's works of art. He is collaborating with Rochester Institute of Technology color scientist Roy S. Berns on what he expects will be a three-year research project.

Berns spent nine months at NGA last year designing digital imaging technology for NGA. He and de la Rie have defined projects with the aim of getting "highly accurate color images of the works of art so as to be able to extract scientific data like pigment identification," de la Rie explains.

"Chemist now take small samples from works of art to determine molecular composition," de la Rie continues. "But the power of digital image analyses is that you get a direct measure of the image, and you can follow changes in the image as a result of time and intervention."

Although digital imaging is not yet being used to its potential in the U.S., it is in Europe. A joint effort--known as the Vasari Project--between the National Gallery, London, and the Doerner Institute in Munich, Germany, developed a technique to get "accurate color representation and measurements," de la Rie says. "It is now being used to track changes in works of art after they have been on exhibition."

Digital imaging "takes conservation science away from chemists," de la Rie admits, "but I've always felt there was a need for physicists and people who can interpret images in a scientific way."

De la Rie is probably correct in citing a need for physicists in conservation science. But their introduction to the field would cut into the already limited job opportunities for chemists who--like de la Rie, Berrie, Glinsman, Maines, and Lomax--seek a way to combine their love of chemistry with their love of art. The few slots for chemists in museums today are not likely to increase greatly in the future--even with Mellon Foundation funding.

Still, for those chemists fortunate enough to find a niche in a museum, the challenges, though different, can be as demanding and rewarding as those in academia or industry. Combine sometimes difficult chemistry, severe deterioration, and incompatible materials with objects that are priceless treasures, and you get some sense of the hurdles this different breed of chemist faces daily.

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Tools of the trade
Standard analytical methods used to analyze works of art
Gas chromatography (GC) Paint binders including oil, wax, low-molecular-weight resins
Pyrolysis GC High-molecular-weight polymers, oils
High-performance liquid chromatography (HPLC) Organic dyes
GC/mass spectrometry (MS) Amino acids in proteinaceous binders, structural information on organic materials
HPLC/MS Synthetic organic pigments, natural and synthetic low-molecular-weight resins
Ultraviolet-visual spectroscopy Yellowing of materials, organic pigments and dyes
Fourier transform infrared spectroscopy with microscopy Small organic binders (nondestructively)
X-ray fluorescence spectroscopy Elements (nondestructively)
X-ray powder diffraction with Gandolfi cameras Mineral pigments, corrosion products (small samples only)
Polarized-light microscopy Pigment identification, cross-section analyses
Scanning electron microscopy with energy dispersive spectrometry Pigment identification, cross-section analyses
Xenon arc weather-o-meter Accelerated aging
SOURCE: National Gallery of Art

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A Special And Enduring Relationship

The National Gallery of Art (NGA) was created in 1937, the gift of Andrew W. Mellon--former secretary of the Treasury, successful financier, and avid art collector--to the U.S. His son Paul made certain that the tie binding the nation's art museum and the Mellon family--now via the Andrew W. Mellon Foundation--was never severed.

Since 1980, the Mellon Foundation's museum and conservation program, now directed by Angelica Z. Rudenstine, has awarded nearly $6 million to NGA to support conservation and conservation science.

Conservation science is fairly common in Europe. "But the U.S. is particularly weak in this area except for a few pockets," Rudenstine points out. NGA, however, is one of those few pockets of enlightenment.

NGA has had a robust conservation science department since 1989, the product of its forward-thinking chief of conservation, Ross Merrill, and support from the Mellon Foundation. In 1989, Merrill enticed physical chemist E. René de la Rie away from New York City's Metropolitan Museum of Art to head the conservation division's scientific research department.

Merrill initially hired de la Rie, a renowned expert in varnishes and coatings, under contract. But in 1991, the Mellon Foundation endowed de la Rie's position as director of scientific research. The Mellon Foundation had endowed Merrill's position of chief of conservation eight years earlier, in 1983. These are the only endowed positions in the conservation department.

Mellon Foundation endowment awards are usually challenge grants that require the receiving institution to match the endowment one-to-one or more. But NGA was not required to match Merrill's or de la Rie's endowments.

Of the few U.S. institutions other than NGA to have integrated science into their conservation departments, Rudenstine cites the J. Paul Getty Museum in Los Angeles, the Metropolitan Museum of Art, the Detroit Institute of Art, and the Boston Museum of Fine Arts. She also singles out the Smithsonian Center for Materials Research & Education, formerly known as the Conservation Analytical Laboratory, as having a particularly strong program.

Recently, however, the Smithsonian's Board of Regents voted to close the center. "People in the field view that decision as a very serious turn of events," Rudenstine says. She expressed hope that "Congress will step in to reverse that decision." On June 30, the Senate Interior Department Appropriations Committee voted to keep the Smithsonian center open until Smithsonian Secretary Lawrence M. Small sought guidance on the center's fate from a science advisory committee (C&EN, July 23, page 28).

Whatever happens to the Smithsonian center, Rudenstine's program is likely to change the landscape of conservation science in the U.S. "One of the things I'm very focused on now is science within conservation," Rudenstine says. "I've been thinking about this area for a couple of years. And I am now moving my program into a broader and deeper commitment to the scientific agenda," she explains.

Last December, Rudenstine's program awarded its first major grant under this new thrust to the Art Institute of Chicago, which until then had not had a senior scientist in its conservation department. The art institute received an endowment grant of $2 million, with no matching challenge grant required, to establish a senior conservation scientist position. It also received $750,000 to set up a scientific laboratory; it must match those funds at least one-to-one, Rudenstine tells C&EN.

This year, the Mellon Foundation endowed a science position in the Philadelphia Museum of Art's conservation department. It was that department's second science position, Rudenstine says, but the first endowed by the foundation.

Rudenstine is always on the lookout for first-rate institutions with strong leadership at the top and a real commitment to conservation. When she finds them, her program is likely to support their efforts to strengthen their scientific components. She deeply believes that a three-way dialogue among scientists, conservators, and art historians/curators is needed for the most productive conservation of art. When the three work together, she says, there is "a hugely better outcome from a scholarly and educational point of view."

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Gamblin Bets On Conservation

It was a tall order to fill and took fully seven years to accomplish. But in the end, a collaborative team of conservators, conservation scientists, and a maker of artists' materials produced new retouching paints--the first major formulation change in decades. These paints--also known as conservation, restoration, or inpainting paints--became commercially available to conservators last year.

Paints are composed of mineral or organic pigments and binders such as natural or synthetic resins. Retouching paints, however, must have specific attributes. They must be stable, reversible, suitable for use with a range of artistic styles and techniques, and materially different from the paints used by the artists of the works of art being restored.

Until 2000--when Gamblin Artists Color Co. of Portland, Ore., introduced its line of conservation colors--retouching paints available to conservators had several drawbacks. Most required relatively polar or toxic solvents. Lacking appropriate scientific studies, the stability of pigments and resins used to make the paints was often unknown. And many available retouching paints lacked desirable optical and handling properties.

Conservation scientist E. René de la Rie, head of scientific research at the National Gallery of Art (NGA), had earlier conceived the idea of using low-viscosity, low-molecular-weight synthetic resins as varnishes for paintings. Along with Mark Leonard, head of paintings conservation at the J. Paul Getty Museum in Los Angeles, and Jill Whitten, now a conservator in private practice, de la Rie eventually proved these synthetic resins were indeed suitable as picture varnishes.

The intellectual leap from varnishes to paint binders is not great. Employing "the notion that low viscosity is the key," the three collaborated again on finding "a low-molecular-weight synthetic resin" for retouching paints, de la Rie says.

Long and widely used natural resins have the nasty habit of yellowing and becoming insoluble in hydrocarbon solvents over time due to cross-linking and photooxidation. The work on synthetic varnishes showed that low-molecular-weight synthetic resins better mimic the optical and handling properties of natural resins than do polymeric resins, yet don't imitate natural resins by yellowing or becoming less soluble.

As a first go-around in the collaborative effort, Whitten hand ground pigments and used an experimental urea-aldehyde resin, Laropal A made by BASF, as the binder. Laropal A had previously been shown to be stable and readily soluble in low-aromatic hydrocarbon solvents. But initial retouching experiments at the Getty, under Leonard's supervision, using Whitten's hand-ground paints found the paints not to be suitable for a variety of reasons.

The three collaborators then turned to Robert Gamblin, president of the artists' materials company bearing his name, to make industrial milled paints using another BASF aldehyde resin in the Laropal series, Laropal A 81. The collaborators turned to this aldehyde resin because BASF stopped making Laropal A.

Unlike hand-ground paints, commercially milled paints have consistent pigment-particle shape and size from batch to batch. Moreover, industrially milled pigment particles are more thoroughly wetted by the resin than they ever can be by hand mixing. In short, the commercial paints are better dispersed, more finely ground, and less glossy than hand-mixed paints.

Gamblin made several trial batches of paints that were tested by Getty conservators for their ease of use and visual qualities. Concurrently, NGA conservation scientists tested their stability using accelerated aging. Using X-ray fluorescence spectroscopy, X-ray diffraction analysis, scanning electron microscopy/energy dispersive spectroscopy, gas chromatography/mass spectrometry, and pyrolysis-GC/MS, the scientists also determined paint composition and paint degradation during accelerated aging.

The scientists found that the urea-aldehyde resin paints exhibited good photochemical stability. And they determined that, in contrast to natural resins, the Gamblin paints could be removed using low-aromatic hydrocarbon solvents (less toxic solvents) after 3,000 hours of aging.

Eventually, sets of 20 colors and the aldehyde resin were distributed "to about 30 conservators in the U.S. and Europe who would use them in major treatments and report their impressions to us by a certain date," de la Rie says. In addition to those from NGA and the Getty, conservators from the Art Institute of Chicago, the National Gallery in London, and the Yale University Art Gallery, as well as several in private practice, collaborated in the research.

"We got a lot of positive feedback," de la Rie says. Participating conservators found that the low-viscosity, low-molecular-weight aldehyde resin paints handled like natural resin paints and had similar optical properties.

In addition to their comments on paint composition, the conservators also specified the palette of colors they wanted to see available commercially. In response, Gamblin now sells 33 conservation colors. Co-owner Martha Gamblin tells C&EN that "80 museums worldwide now use Gamblin Conservation Colors and, additionally, about 50 conservators in private practice in the U.S. are using the colors."

The company recognized that these conservation colors would serve a niche market. But as Gamblin explains: "The company was a consultant on the product's development because it is important that we be involved in all aspects of oil painting," including preservation. "It is not important that the product line fuel our growth as a company, but it is important to serve the community" of artists and conservators, she adds.

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