Around the world, museums and private collectors are discovering an unstoppable, irreparable problem with their exhibited and stored plastic items. They are cracking, crazing, hardening, discoloring and even melting.
In short, plastic artifacts are deteriorating.
Although this problem is gaining attention, conservators, collectors and curators still are learning about the breakdown of plastics, how to slow the process and what the future holds for newer plastics.
Plastics are an integral part of our lives but they, like us, cannot escape old age.
``This is a huge problem [worldwide] and so few people are looking into it,'' said Julie Reilly, chief conservator and head of the Nebraska State Historical Society's Gerald R. Ford Conservation Center in Omaha, Neb. ``They don't have a feel for the monetary value of the things being destroyed.''
``All materials have a lifetime; they age and weather,'' said Paola Antonelli, associate curator for the department of architecture and design at the Museum of Modern Art in New York.
Objects made from cellulose nitrate are the biggest problem today. A semisynthetic material, cellulose nitrate is highly flammable. For more than 100 years, from its experimental stages in the 1840s to the end of production in the 1950s, items such as combs, brushes, toiletry articles, toys, dolls, jewelry, false teeth, imitation patent leather, buttonhooks, golf balls and piano keys were made using cellulose nitrate.
At the Museum of Science and Industry in Chicago, Colleen Moore's Fairy Castle required more than $75,000 in repairs and restoration involving celluloid plastic, metal and other materials. The 9 square-foot castle was the silent film actress's ultimate doll house. More than 700 artists and craftsmen, some of them Hollywood set designers, painted, carved and sculpted the castle. It was completed in 1929 and stands 12 feet tall at the tip of the highest tower.
When renovations began, the flooring and windows, made of cellulose nitrate, were warped and cracked. Tiny pieces of furniture, long thought to be carved ivory, had warped and discolored. The library floor, instead of being wood-grain brown, had turned to mustard yellow. And other sections of the castle contained more plastic than conservators had earlier imagined.
``There had been extensive light damage,'' said curator Mike Sarna. ``[The plastics] are breaking down. We had to stabilize the entire environment — plastic, metal, running water, bone and fabric.''
``There are parts that look like bone in the castle,'' Sarna said. ``It's really amazing; you'd never think it was plastic.''
``We got rid of all ultraviolet light and replaced it with fiber optics and isolated the plastics from touching other materials,'' he added.
Sheets of PET, a more stable material, were placed between any celluloid object and whatever it had touched. The celluloid had left residue on metals. Warped floors now are held in place by small screws. Windowpanes, curled and brittle from back lighting, were replaced with colored PET.
Keith Lauer, curator of artifacts and collections at the National Plastics Center and Museum in Leominster, Mass., collects combs, many of which are made from cellulose nitrate.
``They change color, crack, crumble and fall apart,'' he said.
Lauer theorizes that the thicker the piece, the more apt it is to deteriorate. In thick combs and mirror handles, plasticizer used in processing can become trapped. Over time, it comes to the surface and emits a gaseous acid.
``We call this `the disease,''' he said. ``If one affected item is placed next to another, which is unaffected, the disease can spread. It's a serious concern.''
Reilly has seen firsthand how cellulose nitrate attacks other objects. In an Asian collection at the historical society, celluloid beads in necklaces caused metals to corrode and the string holding the beads in place to break down. As a result, beads were rolling all over the storage drawer.
Lauer also has a collection of animals blow molded from cellulose nitrate that seem to be in fine condition. He attributes this to the thin plastic.
``[Blow molded items] are so thin that any trapped plasticizer has long since evaporated if it came to the surface,'' he said.
``A lot of my things were made in the 1920s and they're not deteriorating. The material and the material quality makes a difference.''
However, Lauer said he heard about dolls housed in a London museum that looked like they were crying; in actuality, they were leaking acid.
One of the first objects to use the blow molding process was the Kewpie doll, made of cellulose nitrate, Reilly said. Because of the material's inherent tendency to degrade, she said collectors need to take steps to preserve the early dolls. In addition, it is important to have these items to show the early technology developed to make them, she added.
Several other plastics have caused some problems for those interested in preserving a part of history. These include Bakelite, cellulose acetate, polyurethanes and even some early polyethylenes.
Although Bakelite is fairly stable, it does fade and change color. Developed in 1907, Bakelite was the first totally synthetic plastic. Sarna has seen examples of it changing color from blue to green.
Cellulose acetate, not as combustible as its cousin cellulose nitrate, was used as a clear packaging film. It discolors and warps as it ages. Early films printed on cellulose nitrate have been transferred to cellulose acetate and are refrigerated to help preserve them.
Early PVC can deteriorate, said Reilly. She also has seen early Tupperware—made from PE—and animation films and other objects made from plastic sheet shrink, become brittle and deform.
``Degradation is the biggest problem we face in the future,'' Antonelli said.
MOMA displays objects from the last quarter of the 1800s through the present. According to curators, items made even more recently are falling apart. For example, clear plastic hatboxes have melted. And a PU self-skinning foam armchair is hardening and cracking.
``PU is used as stuffing in furniture in the domestic environment and we don't expect it to last,'' said Lynda Zycherman, conservator at the museum. ``In a museum, it becomes crisp and crumbly. It hardens in place and if you touch it, you make a dent.
``We have to be very careful how much we show [the PU chair],'' she added.
When plastics break down or fail in a museum environment, curators and conservators have an ethical dilemma.
Should the parts be replaced, thus changing the overall makeup of the piece and the artist's original intention? Or do museums display something that is falling apart or melting?
MOMA was forced to decide when the hanging fixture for a fiberglass sculpture failed and tore. It was repaired and reinforced with the same material, which was on the back and hidden from view.
``It was part of the supporting portion and had to be done,'' Zycherman said. ``It matches very well now, but we can't guarantee that in 10 years or 25 [years] it will still be invisible.''
Industry and museums have different standards,'' she noted. ``We're interested in the aesthetic point of view. You can't fix warps, scratches or yellowing without changing what the artist intended. By repeated polishing or subjecting pieces to ultraviolet light, you're dramatically speeding up degradation.''
What causes plastics to break down?
Conservators agree that the four most-detrimental elements to plastic are high temperature and humidity, ultraviolet light and inadequate ventilation. These, as well as pollutant and particulate levels, can be controlled in museums. What the items are stored in and the way they are stored also make a difference.
Low relative humidity and temperature slow the chemical reactions causing degradation. Some plastics will absorb moisture, which can cause stress that produces physical damage.
Air exchange and ventilation without dust is important for those items emitting vapors.
For example, Antoine Pevsner sculpted several dozen busts from cellulose nitrate in the 1920s, MOMA's Zycherman said. One was kept in an airtight case. When the case was opened, the bust immediately crumbled. The nitric acid did not have an escape and had remained stable in the airtight environment.
``Plastic is definitely not indestructible, but it is sturdy,'' said Sarna. ``Any material will deteriorate over time.''
Deterioration has three general phases, which Reilly compared to the life of Scotch tape. The first is a long, slow deterioration akin to the useful life of the tape.
``Some changes are so slow that in a generation visitors may not notice any change,'' Zycherman said.
The second phase is a quick, rapid deterioration. This corresponds to the gooey, sticky mess of older tape. It is in this stage that a plastic product can become very distorted if not handled properly. The loss in structural integrity is evident in phase three, which is another long, slow development—as when tape becomes dry, brittle and powdery.
Several measures can be taken to slow degradation, though it is impossible to stop or even prevent plastic from decaying as it gets older.
``Often there's not much we can do that is visually acceptable in a museum environment,'' Zycherman said.
``The problems [experienced with cellulose nitrate] may not be unique,'' Reilly added. ``This may happen to all polymers in a different way at different times. We're just seeing the tip of the iceberg.''
Prior to her work at the Nebraska State Historical Society, Reilly worked with the Smithsonian Institution on a research project to look into the deterioration of cellulose nitrate. Now, she deals with all kinds of plastics.
The first step in slowing degradation, she said, is to identify the plastic. Then it is isolated from the rest of the collection, or separated by polymer type.
For example, Reilly said it is important to separate out cellulose nitrate because it emits sulfuric and nitric acids that can mix with moisture and form acetic deposits on unaffected surfaces.
Preventative conservation involves proper exhibition techniques, handling, shipping, environmental control and storage. The Pevsner busts, for example, are now kept in a case that allows air to circulate. Museums also use refrigeration to slow reactions with oxygen, and sleeves to block UV light.
``Most of the money invested by museums is in the storage,'' Reilly said.
Shelves and containers can break down from acid-producing rust flakes. Stainless, enameled and powder-coated steels are not immune, but glass is a good storage container.
Sticky surfaces often can be swabbed with a small amount of water to get the acid out of the way and slow the breakdown. Before a plastic breaks down, a substance like Armor-All can be applied to inhibit oxygen reactions.
``In the scope of human history, the development of plastic has had a chemical, technical, industrial importance,'' Reilly said. ``In the future, we're going to be sorry we don't have these objects when we look back.''
According to Zycherman, only a few types of plastic are very fragile and they represent a slice of time.
``The general public's view that plastic is indestructible is a myth that comes from industry,'' Reilly added. ``It is not in their interest to make material that lasts forever, so plastic is stable for its lifetime of use. Industry does not look at time as we do; they look at 20-to 30-year segments and we look at 100-year chunks.''