Lamination could be the cardinal sin of preservation. In a field where the golden rule is to do nothing you can’t undo, using heat to bond plastic to priceless documents is a major faux pas.
But in the early 20th century, lamination was a celebrated new tool in the conservator’s arsenal. Among its proponents: the National Archives and Records Administration (NARA)
and the Library of Congress
. From the late 1930s until the 1980s, NARA laminated what may total thousands of documents—including the Emancipation Proclamation and Louisiana Purchase paperwork. Now modern conservationists are trying to make the best of it.
In the 1930s, archives that could afford the expensive equipment laminated their collections with zeal. The new technology was a timesaver, and silking—the previously preferred method for protecting fragile papers—was falling out of favor “partly because of the time and skill needed to achieve a good end product, and partly because in some cases the silk or the adhesive used had poor mechanical and chemical properties upon aging,” says Mary Lynn Ritzenthaler, chief of NARA’s Document Conservation Division.
Before lamination, documents would be deacidified in a bath. Technicians then placed each paper (sometimes with a tissue or muslin backing for support) between sheets of cellulose acetate film and pressed it with heated hydraulic plates to melt the plastic.
Though the National Bureau of Standards (now the National Institute of Standards and Technology) initially supported lamination, the technique did have drawbacks: Wax seals on documents melted, some papers became translucent and pigments occasionally would bleed. (See http://anthropology.si.edu/conservation/lamination
for examples.) Some effects weren’t apparent for years. Most crucially, lamination can trap acids in a plastic chamber, potentially creating a microenvironment that damages the document inside.
“As it became clear that cellulose acetate film was not as stable as originally thought, institutions abandoned it in favor of encapsulation in polyester film,” Ritzenthaler says.
Archives with laminated documents may keep them as-is if the items appear stable—that is, with no distortion, cracking, warping or odor. “When [the item is] stored in good environmental conditions, and when the lamination was done properly in the first place using specified materials, it continues as a suitable support system for records,” adds Ritzenthaler.
If an item appears to be in danger, delamination—removing the plastic layers with acetone solvent—might be called for. “[NARA] has not initiated a program to delaminate previously laminated documents,” Ritzenthaler says. “Delamination is carried out on a case-by-case basis when it is necessary” and so long as the document and any writing or other media on it won’t be affected by the solvent.
NARA stopped laminating documents in cellulose acetate film in the early 1980s. Still, it’s not racing to undo all lamination—or silking, for that matter. “Many thousands of documents were treated using these support mechanisms that rendered them safe to handle without damage,” Ritzenthaler says. “There are extensive examples of both support techniques in repositories across the country that have aged well and protected documents and manuscripts.”