Typical plastic degradation” was Jia-sun Tsang’s shorthand for the problem before her. The object of her concern, from the collections of the Smithsonian’s National Museum of American History, Behring Center, was a salesman’s sample kit for a brand of plastic sold under the name Lumarith in the 1920s.

Easily melted and molded into virtually any shape, the product was popular with makers of everything from fountain pens and toys to electrical appliances. But with the passage of years, the kind of plastic used for Lumarith, cellulose acetate, broke down, giving off a telltale vinegar smell. Several of the brightly colored samples in the kit were warped, cracked, and unpresentable. Tsang, a conservator with the Smithsonian’s Museum Conservation Institute, and a team of Smithsonian scientists used a variety of noninvasive analytical techniques, including several forms of spectroscopy to pinpoint the molecular structure of the plastic and figure out precisely the cause of the samples’ degradation. Tsang determined that much of the problem was due to leaching of triphenyl phosphate, a fire-retardant compound often added to cellulose acetate to facilitate its softening and flow during the molding process.

Tsang’s study concluded that triphenyl phosphate in cellulose acetate was a particular risk factor for plastic degradation, and that artifacts containing the chemical should not be stored in close contact or in an enclosed space with other cellulose acetate plastics and metals. Case closed, but the larger problem was far from settled.

Malignant

While society at large frets about plastics that pile up and seem to last forever— grocery bags clogging landfills and soda bottles washing up on beaches—Tsang worries about the thousands upon thousands of artifacts in museum collections made of plastic, objects that in many cases are crumbling and cracking and sometimes damaging other artifacts as they break down.

“Plastic is a 20th-century material—it is everywhere,” she says. But most plastics—cheap to produce and adaptable to almost infinite uses—were not created for the ages. “When they get to a museum, it’s our problem,” Tsang says. “We have to take care of them.”

A year-long survey at the American History Museum revealed that many plastics in its collections are from among the five types that museum conservators have identified as “malignant.” Not only are these problem plastics—cellulose nitrate, cellulose acetate, polyurethane, polyvinyl chloride and rubber—more prone to deterioration than other plastics but also their breakdown often produces gases that damage metal, paper or other plastics stored in their vicinity. In most cases, this harmful offgassing can’t be prevented, only slowed, which means degrading plastic artifacts must be isolated from other objects in museum collections.

Probably no Smithsonian museum has more plastic artifacts than the American History Museum. Scratch the surface of its collections and you will find plastic jewelry, plastic eyeglasses, plastic artificial hearts, even the first plastic shoes (sold under the trade name “Corfam”).

“We have a set of Bakelite salt-and-pepper shakers that were owned by Leo Baekeland, the inventor of Bakelite,” says Ann Seeger, deputy chair and curator in the American History Museum’s Division of Medicine and Science. Bakelite is a plastic once widely used for manufacturing radios, telephones and other products.

Nondestructive analysis

The earliest plastic, cellulose nitrate, was invented in the mid-19th century. “Celluloid or cellulose nitrate was an extremely flammable substance, but we have cigarette holders, candlestick holders and matchbook holders made of celluloid,” Seeger says. If those uses for the plastic strike the curator as “very surprising,” imagine the reaction of long-ago pool players to celluloid billiard balls, which had a habit of exploding on impact.

“That’s why I love working with the American History Museum folks,” Tsang says. “I get all of this nice material to study.” Tsang’s specialty is conservation of modern paintings and other contemporary art, so a history museum might not seem like her usual haunt. However, before entering the field of fine-art conservation, she was a clinical chemist at the Medical College of Ohio. “Because of my background, I always like to get into the science,” she says.

Her interest in nondestructive analysis and testing of museum objects has taken her down some unusual research paths at the Smithsonian, such as consultation a few years ago with staff at the Smithsonian’s National Air and Space Museum about restoring the acrylic nose cone of one of the first U.S. guided missiles. “So the crossover between an acrylic painting,” Tsang says (gesturing toward an easel in her work area that holds a large painting she is restoring), “to plastic is natural for me.”

Rehousing

Lately, Tsang has been working closely with Seeger, as the two of them try to systematically identify the probable causes of deterioration in the museum’s plastic artifacts.

According to Seeger, not only have they separated the degraded Lumarith samples from the rest of the salesman’s kit (part of a collection Seeger curates) but the museum also is embarking on a “rehousing project” for its problem celluloids, first by relining storage trays with absorbent paper that will soak up off-gassing by-products. “We’re going to start monitoring the collection more closely,” Seeger says. “I’d like to get new storage units that are open so there will be more air circulation for the celluloid. It is important not to keep them contained in a drawer.”

Meanwhile, Tsang continues adding to her knowledge through workshops and consultations with plastic preservation researchers at museums in Europe, where plastics conservation has been studied longer than in the United States.

“I want to draw people’s attention to the problem of plastics degradation in museums,” Tsang says. “There is an issue here—let’s work together.”