Making Stuff Last.

Chemistry and materials science step up to preserve history, old and new

Around the world, archives, museums, and their storage facilities brim with society's most prized objects. Some have been stashed on dusty back shelves for decades, while others bask under spotlights and curious gazes.

If you're a patron of museums and archives, how can you be sure that on those shelves or under that glass, the treasures you value aren't slowly withering away? Are they really being preserved for future generations?

Truth is, behind the scenes, chemists and materials scientists are still struggling to understand how objects deteriorate. That's the first step to learning how to increase the life spans of the full menagerie of ancient and modern materials treasures, be they Rembrandts, retro medical devices, Barbie dolls, or beetles long extinct.

Sometimes, deterioration sneaks up so subtly that, for awhile, it's noticeable only on the molecular level. Once deterioration becomes visible, however, age may have altered the basic chemical foundation of a museum specimen. Then, it's difficult--sometimes impossible---for conservators to successfully clean or repair it.

That's why fundamental chemistry and materials science have become so central to museums' and archives' preservation efforts. With new understanding about how long-term storage environments can affect the condition of paper, wood, rubber, and cloth, for example, researchers hope that the need for difficult, risky conservation interventions will become less frequent.

Meanwhile, ongoing research is revealing which materials in historic objects have stood the test of time, and those insights offer guidance about what materials to use for making new objects that will last.

"What we're trying to do is put our conservator friends out of business," jokes Charles S. Tumosa of the Smithsonian Center for Materials Research and Education in Suitland, Md.

Some of the best-known museum preservation efforts are those that focus on art. This is a tricky business, Tumosa says. Scientists can't go around experimenting on centuries-old masterpieces.

Instead, researchers try to study the effects of different environments and cleaning procedures by testing new materials that are similar to the old ones. For this to be relevant, however, the researchers have to find ways to quickly age the young materials so that they better reflect the mechanical and chemical changes that the old materials have suffered. Then, the younger samples can be used to test conservation techniques including cleaning methods.

The more researchers discover about materials, the more often they learn that even their testing methods can be misleading. For example, Tumosa recently reported that a heating protocol commonly used for artificially aging materials doesn't work well for oil paints. He and his colleagues found that thermal treatments above 50 [degrees] C didn't render young oil paintings similar to genuine 200-year-old paintings. Their chemical composition didn't match that of the older art works, the team reported in Washington D.C. at the national meeting of the American Chemical Society in late August.

That mismatch suggests that testing new cleaning treatments on such heat-aged samples can be dangerously misleading.

More recently, Tumosa studied white zinc-oxide pigments in modern artists' oil paints. He and his colleagues found that these pigments produce a surprisingly brittle film. Following common preservation treatments, such as the application of a varnish overcoat, the zinc oxide-containing underlayer gets even more brittle, says Tumosa.

He's reported his results to three major producers of the zinc-oxide paints, and they're now considering replacing the pigment to make modern oil paintings more stable, he says.

"The people who are going to be doing conservation in the 21st century and 22nd century are going to be facing these problems," Tumosa says.

Artwork gets a lot of attention when it comes to preservation, but there's more to museums than art. Consider the category David W. Von Endt calls "pickled frogs and things that go bump in the night."

In the world's natural history museums, some 2 billion biological specimens are stored in fluids such as formaldehyde, says Von Endt, also of the Smithsonian Center for Materials Research and Education. The specimens represent a planetwide library of biological samples, he says. Some animals on shelves today were prepared as far back as the mid-19th century and have since become extinct, he says. And some have proven valuable for biomedical research, including monkey specimens that yielded clues to the history of the AIDS virus.

Von Endt investigates causes of deterioration in preserved biological artifacts and then looks for better ways of treating specimens for future scientists' use. Although many bottled animals appear well preserved, important biological molecules such as lipids, proteins, and amino acids have leaked into the fluid, he says. So, the tissues may no longer contain all the biochemicals that might matter to molecular biologists wanting to study them.

Currently, Von Endt is examining the preservation of proteins such as those in skin, hair, bone, and feathers. Rather than focusing on an individual animal, he searches for molecular constituents common to many species. For example, by studying a molecule in a preserved field mouse, he's also likely to learn about a chemical process in, perhaps, a preserved squid, he says.

By heating samples, Von Endt has found that keratins--proteins in feathers and hair--and collagen--a protein in bones and skin--have different relative stabilities in the different fluids. Feather keratin, for example, is only half as stable in alcohol-based storage fluids as hair keratin is. Adding formaldehyde to an alcohol-based storage fluid made collagen--but not keratin--more stable.

As Von Endt learns which fluids better protect particular materials, the long-term stability of the biological molecules in new specimens is likely to improve. Old samples could also be placed in new fluids to make them last longer, he says.

Most current genetic and molecular biology analyses didn't exist when the typical natural history museum biological sample was collected, notes Von Endt. "These specimens never were preserved with [modern research tests] in mind," he says. What's more, he adds, "we have no idea of the kinds of questions that are going to be asked of these specimens in the future."

It's no shock that museum professionals find deterioration in objects that have outlived many generations of people. Conservators have worked hard to restore the Star-Spangled Banner, for instance (SN: 6/26/99, p. 408).

Surprisingly, however, scientists are finding that many materials of the modern world are deteriorating even faster than ingredients of older objects.

Some of the most vulnerable new materials are plastics. Museums display them as toys, medical equipment, footwear, inflatable furniture, and more, says Yvonne Shashoua of the National Museum of Denmark. "They're found in every museum in the world," she says.

Yet many plastics exhibited in museums can change so much chemically that within a decade they start to feel tacky. Many such objects must be taken out of a collection after just 20 years, says Shashoua. These plastics--including those in Barbie dolls--are made of polyvinylchloride, or PVC. Dolls from the 1950s and 1960s usually contain potentially toxic chemicals called phthalates, which were added during manufacture to soften the material (SN: 9/2/00, p. 152).

In recent experiments using microscopy and spectroscopy, Shashoua identified phthalates as the cause of the plastics' tacky surface. This discovery was unexpected, she says, because previously published literature had indicated that phthalates remain combined with the PVC.

To preserve plastic objects in museum collections for longer periods, Shashoua is now trying to figure out how to keep the phthalates within the plastic. First, she's measuring how fast phthalates evaporate from newly manufactured PVC and why phthalates migrate out of the plastic.

Recently, Shashoua also finished analyzing the PVC deterioration in one of the high-tech marvels of the 20th century: Apollo era spacesuits, 12 of which made it to the moon. Just 30 years ago, these materials protected men from the deadly void of space, but now they need protection themselves. An 18-month project funded by the Save America's Treasures program is under way to determine the best way to handle and store the much-borrowed, deteriorating suits (SN: 8/26/00, p. 135).

Lisa Young of the National Air and Space Museum's Paul E. Garber Facility in Suitland, Md., works with the museum's Space History Department to coordinate the Apollo spacesuit project, which is scheduled to finish analyzing all 12 lunar suits by the end of December and produce guidelines by next August for preserving them.

Her team does a variety of tests, including visual inspection of each suit and CT (computerized tomography) scans to see inside the suits' 20 layers of synthetic polymers and natural rubber. The investigators are also interviewing the original designers.

Young is now tracing the origins of the natural rubber components and investigating the changes that producers made over the years in the composition of rubber used in the suits. In 1971, for example, rubber makers added an antioxidant, and the suits created since then have held up better than the earlier ones. Young also aims to identify a gas that the aging rubber emits.

In another analysis, Young is examining aluminum spacesuit pieces to determine the alloys used, as well as the type of corrosion occurring. That information could indicate whether the aluminum parts need to be stored under different conditions than the other material or if conservation treatments, such as corrosion removal, are necessary.

Like most other preservation scientists, Young emphasizes that preventive measures usually work best. Trying to clean or restore museum artifacts, whether art or spacesuits, can often do damage.

Take, for example, the case of lunar dust. In the 1970s, most of the Apollo spacesuits were cleaned of the moon dirt that appeared to spoil their white surfaces. Today, just one suit remains in pristine condition, says Young. It's the one Harrison Schmitt wore on Apollo 17, and it was never treated or cleaned.

RELATED ARTICLE: Locking away tomorrow's history

In this period of transition between two millennia, it's not just museum curators who want to know the best way to store materials for decades to come. After all, it's a heyday for time capsules, and many people are aiming to save all kinds of everyday scraps for posterity.

But how do you store objects so that plastic doesn't get tacky, paper doesn't yellow, and--worst of all--tacky plastic doesn't stick all over yellow paper?

In the past century, plastics and other polymers made objects in our lives "cheaper, more accessible, sometimes better, and more fun to use," says Mary T. Baker, a materials scientist who heads Conservation Associates in Cairo. Naturally, people want to include objects made of these materials in time capsules, she says.

In response to this interest, Baker and her colleagues at the Smithsonian Center for Materials Research and Education in Washington, D.C., recently completed a 4-year project studying a variety of potential time capsule contents, as well as materials for the capsules themselves. They recently posted the guidelines on the Smithsonian web site (www.si.edu/scmre/timecaps.html). They recommend against including objects made of rubber and polyvinyl acetate, for example, and suggest wood should be sealed away from metals.

The materials scientists have also made recommendations regarding the storage of unusual materials that have been included in the White House Millenium Council's National Millennium Time Capsule, says Baker's Smithsonian colleague Dianne van der Reyden. Among the capsule's contents will be a pair of Ray Charles' sunglasses, a plastic replica of DNA, compact discs of recorded music, and vials of vaccines developed in the 20th century.

Much of the capsule's contents, however, will be paper--primarily letters and books. National Archives scientists who specialize in paper preservation stored these documents in protective folders and custom-made boxes.

The steel, copper, and titanium capsule and some of its contents will be on display in the rotunda of the National Archives building in Washington, D.C., from mid December through January. Then, it will retire to uninterrupted storage-most likely within the National Archives--for 100 years, says National Archives curator Bruce Bustard.