Department of Anthropology, National Museum of Natural History
by Marit Munson, with contributions by Jayne Girod Holt,
Susan Peckham, Tara Kennedy and Claire Grundy.
L. Rose and Candace Greene
papers, present in archives across the country, may pose serious
problems for archival collections. Lamination was a popular
preservation method, adopted by many institutions handling large
collections of archival materials. First introduced in the 1930s,
lamination quickly became the primary choice for repairing and
strengthening papers on a large scale. Now, however, conservators
recognize that the materials used in lamination may degrade,
damaging the very objects the process was intended to preserve.
This paper —
Explains the major problems associated with lamination
Provides a key to determining if a collection includes laminated
Describes how to assess the condition of laminated objects
Outlines steps that archivists and collection managers can
take to reduce risks to their collections
a list of resources
for further study
a glossary of lamination
is a method of strengthening fragile papers. Less time-consuming
than traditional methods, lamination was widely used by archives
from the 1930s through the 1970s. The lamination process involved
deacidifying a document, layering it between tissue and thin
sheets of plastic, and fusing them together in a heated press.
In archival contexts, lamination refers to the process of fusing
a sheet of paper between two thin sheets of plastic —
usually cellulose acetate. The archival community embraced lamination
in the early 1930s as a means of strengthening fragile papers.
It provided stability for weak or damaged documents in less
time than traditional methods, making it cost-effective for
large collections. Collections were often laminated before microfilming,
to facilitate rapid handling. Lamination was also seen as a
means of preventing damage from environmental contaminants and
grime from handling.
The National Archives, the Library of Congress, and other organizations
with large collections-- and budgets large enough to afford
the equipment — began lamination projects in earnest by
the late 1930s and 1940s. Institutions or organizations lacking
the resources to acquire their own equipment often contracted
the work to these other agencies. Lamination was recommended
initially for records of little intrinsic historical importance,
but it was soon applied indiscriminately. Publications of the
era described lamination as a panacea, and even such priceless
documents as the Emancipation Proclamation were laminated.
As the lamination process was developed, numerous inventors
and scientists — most notably William Barrow — experimented
with ways to refine the technique. The National Bureau of Standards
eventually made an attempt to standardize lamination, recommending
a process with several stages. First, the document was to be
deacidified, neutralizing the potentially damaging acids inherent
in some paper. Next, the document was layered between thin sheets
of a plastic — usually cellulose acetate — and tissue.
The use of a plasticizer in the cellulose acetate increased
the flexibility of the otherwise brittle plastic, as well as
decreasing the temperature required to soften it. The addition
of a thin layer of Japanese tissue on top of the cellulose acetate
film greatly improved the tensile strength, internal tear resistance,
and folding endurance of laminated documents. It also reduced
the shiny appearance of the plastic laminate. Finally, the five-layer
"sandwich" of materials was placed into a heated laminating
press. The heat melted the plastic layer, while the high pressure
forced the cellulose acetate into the interstices of the paper
itself, sealing the document within a semi-flexible plastic
Despite the National Bureau of Standards' attempt to standardize
this lamination process, there was considerable variation in
technique and in materials. Each laboratory generally retained
its own protocols, and the process often boiled down to an individual
operator's or technician's choice of what functioned well.
is lamination a problem?
push for lamination was a well-intentioned attempt to address
the condition of many fragile historic documents, but we now
know that lamination was not the cure-all that librarians and
archivists had envisioned. In fact, lamination may cause numerous
problems for collections.
from the lamination process.
The first problem associated with lamination is damage
caused by the lamination process itself. The application of
heat and pressure during lamination was sometimes poorly controlled,
resulting in burned or scorched papers. High temperatures caused
some media to melt or bleed, damaging wax seals, discoloring
pigments, or blurring lines (Figure 1). Other media may have
been partially solubilized — that is, some pigments or
inks may have run or smeared (Figure 2) due to a chemical reaction
during the lamination process.
problems. In addition, laminated documents often
have aesthetic problems. The cellulose acetate laminate greatly
alters the appearance and texture of documents, giving the paper
a shiny surface with an uncharacteristic hard, plastic feel.
The addition of tissue in the laminating process helped reduce
the shine, but unfortunately also reduced the clarity of the
original documents, altering their colors and appearance. The
different kinds of presses used to apply pressure during the
lamination process produced a variety of new surface textures
on the documents. The overall result is a hazy look (Figure
3) that one curator has likened to the appearance
of plastic placemats. In other cases, the laminate renders documents
translucent; writing or images on the back of a page may show
through, making them difficult to see.
The washed out hazy look of this drawing is due to the laminate
and the tissue layer that were placed directly on the drawing.
Battle of the Little Bighorn, 1881. Drawing by Red Horse (Dakota).
vice. Lamination may also exacerbate problems
that were already present in the documents themselves (inherent
vice). If, for example, a document on poor quality paper was
not deacidified prior to lamination, the layers of plastic encasing
the item may trap acids within the laminate, causing the paper
to yellow and become brittle (Figure 4). In
other cases, torn documents were repaired using inappropriate
methods before they were laminated. Repairs with pressure-sensitive
tape, for example, are potentially damaging for any papers,
but lamination exacerbates the problem; the heat used in the
lamination process can kick off chemical reactions, while the
carefully sealed layers of laminate trap by-products, creating
a harmful microclimate for the paper. Encased in plastic, these
damaging repairs may be difficult for conservators to treat.
of the laminate. Deterioration of the materials
used in lamination may cause additional damage to laminated
documents. Remember that the lamination process drives the plastic
laminate into the paper itself. When the plastic begins to break
down, the document it encases will also suffer. The most widely
used laminate, cellulose acetate, is inherently unstable. Like
the cellulose acetate film base used in movies, the laminate
decomposes through a chemical reaction that causes the bonds
of the cellulose acetate molecule to break down. This decay
process releases acetic acid from the molecule, producing the
strong vinegar or ammonia odor that is called vinegar syndrome.
As the laminate deteriorates, it may warp, stretch, or peel,
placing great stress on the paper (Figure 5). In some cases,
the stresses from deteriorating laminate are literally splitting
the paper apart internally.
As cellulose acetate breaks down, it may exude plasticizers,
the chemicals added to increase the flexibility of the otherwise-brittle
film. Plasticizers exuded as a liquid may collect on the surface
of the laminate, giving it an oily appearance and often leaving
the surface quite sticky. When exuding leaves of laminated papers
come into contact with each other, they may stick together in
a block (Figure 6), making them unusable. The degradation of
plasticizers also reduces the flexibility of the laminate itself;
as this happens, documents are in danger of cracking, chipping,
or completely snapping apart. This is particularly troublesome
with laminated leaves that have been put in post bindings--
a common method of binding that places considerable stress on
the bound edge of vulnerable documents (Figure 7).
Secondary damage to neighboring objects. The most
alarming aspect of the problem is that unstable laminate and
plasticizers do not just affect single documents. As the materials
degrade, they are capable of triggering chemical reactions in
any nearby objects that are also made of cellulose acetate--
including previously stable laminated papers, photographic negatives,
and motion picture film. Once this degradation process begins,
damage will only become worse through time, unless properly
to Part Two:
Identifying and Assessing Laminated Papers »
Return to National Anthropological
Detail of a wax seal after lamination. Source: 18th century
land grants from the Pennsylvania State Archives.
2. Drawing with media that bled during the lamination
process. Note that only the purple pigment is affected. Drawing
by Charles Murphy (Bear Wings), Cheyenne. James Mooney Notebooks
This paper, already fragile before lamination, has become even
more yellowed and brittle after being sealed between sheets
Drawing by Carl Sweezy (Arapaho). James Mooney Notebooks 1903-04.
Figure 5. The
wrinkling of this laminate may place great stresses on the paper
enclosed within it. This image also shows the high surface gloss
and surface texture that may be present on laminated papers.
18th century land grant from the Pennsylvania State Archives
Figure 6. Example
of blocked papers, where sheets are stuck together; a conservator
uses a teflon spatula to gently separate the leaves. 18th century
land grants from the Pennsylvania State Archives
This page was chipped and torn when it was laminated. The white
tab, at the left, was added after lamination in order to place
the sheet in a post binder. Such binding places great stress
at the already torn left margin of the page. Drawings of Eskimo
By Guy Kakarook