Conserve

O Gram
July 1993 Number 13/3

Polyester Encapsulation
Polyester encapsulation is a way of sandwiching unhardened gelatin emulsion may stick to plastic,
a paper object between two pieces of stiff, or may develop shiny spots, calledferrotyping.
chemically inert, clear plastic. All four edges of When in doubt about the safety of polyester
the plastic are sealed to hold the paper firmly in encapsulation for a paper object, consult a paper
place. This technique provides support and conservator.
protection to fragile or damaged papers which
otherwise could not be handled, or which would The Problem of AcceleraJedAging
not receive sufficient protection in a print
storage folder. Removing the object requires Buffering an acidic paper object before
that the encapsulation be cut open. Other permanent storage in an encapsulation is
configurations of polyester enclosures are the recommended to slow down the future rate of
U-seal (three-sided seal) or the L-seal deterioration. Buffering places a form of
(two-sided, one corner joined). These magnesium or calcium carbonate into the paper
enclosures provide somewhat less protection but fibers where it neutralizes acids already present.
do allow the object to be extracted without A reserve of buffering agent remains in place to
destroying the encapsulation. neutralize future acid formation. Buffering
should only be performed by, or under the direct
Appropriate Uses supervision of, a paper conservator because it is
a complicated interventive treatment.
Encapsulation is useful for large paper objects
such as maps, newspapers, and blueprint If buffering is not immediately possible, museum
drawings that are awkward to handle and records should note that the ohject is
susceptible to tearing. This procedure can be encapsulated but unbuffered. This information
used to store brittle or damaged papers before also should be included inside the encapsulation
corrective treatment by a conservator. in a note written on archival paper. If the
Encapsulation is an excellent way to protect document is one-sided, a piece of buffered paper
letters or other documents that are handled (e.g., Permalife interleave) slightly larger than
during research, and which often need both sides the object, can be encapsulated with it. This
visible. paper will also provide some buffering benefit.
Write the catalog number on the buffered paper
An electrostatic charge, generated by rubbing the in soft pencil and note that there is no
plastic sheets, holds fragments of paper in information on the reverse side of the object so
alignment within the encapsulation; however, the encapsulation will not be unnecessarily
this will damage friable media such as charcoal, disturbed in an effort to view the hack.
pastel, or flaking watercolor (gouache).
Therefore, encapsulation should not be used with Choosing the Proper Materials
these objects.
Polyester film used for archival storage must be
Do not store early gelatin photographs in any clear, thick enough to provide support, and
kind of polyester folder or envelope. The contain no plasticizers which will evaporate. It
National Park Service Conserve O Gram 13/3

must not deteriorate with age or release Procedure

chemicals harmful to papers or media. Two
brands considered safe for archival storage are Prepare a clean work space. Assemble the
Mylar«l Type D and Melinex 516. They are polyester film, double-sided tape, scissors, and a
available from conservation materials suppliers. piece of lint-free cotton cloth. A two or three
pound, cloth-covered weight will be needed to
Polyester film is sold in both sheets and rolls. keep paper and polyester from slipping out of
Sheets are convenient as a way of standardizing alignment. A ruler or straight edge and a mat
a storage system. The sheets should fit knife will be needed if the polyester is to be
uniformly within storage folders, boxes, trimmed. A large sheet of gridded graph paper
drawers, or file cabinets. This prevents small may be taped to the work surface to aid in
paper objects from being lost in a box or drawer laying the tape in straight lines. (Special gridded
with larger objects. However, sheets used for encapsulation work surfaces are also available
encapsulation can be trimmed to fit the size of from archival materials suppliers.)
the individual object if this is more convenient.
Check the object's dimensions to determine if
If polyester film is purchased in rolls, each piece the object is square. The largest square
of film must be cut from the roll, which is dimension is the measurement that is needed.
usually difficult to do with precision. However, The gridded paper simplifies this step. Place the
because many prints and maps are larger than object on the grids and measure. The square
the available pre-cut polyester sheets, a roll of corner of a table or a right angle made from two
polyester, available in 40" or 60" widths, would yardsticks can also be used to assist in
be necessary for these objects. determining the square dimensions of an object.

Polyester film is available in several thicknesses; Assembling the Package

the most common for encapsulation are 3 mil
(0.003 inch) and 5 mil (0.005 inch). Film 1. Select or cut a piece of polyester film at least
thickness is selected to provide sufficient support 1½" larger in both directions than the paper
to the encapsulated object; this depends on the object to be encapsulated. Lay the polyester
weight and size of the paper to be encapsulated. film on the work surface and wipe it free of
Generally, larger papers require heavier films; lint with the cloth. Place the weight in the
thinner, lighter papers require thinner gauge center of the film.
films. A box full of documents encapsulated in
polyester film can be very heavy, so simply 2. Apply the double-sided tape along all four
purchasing the heaviest gauge of polyester for all edges of the polyester film. Another
objects may not be the wisest course. technique is to apply the tape on the film so
that it is half an inch or so from the edge of
The encapsulation is sealed in one of two ways: the object. The gridded work surface will
with a welding or sealing machine (a very make this step easier to accomplish with
specialized piece of equipment), or with precision. Leave the paper backing on the
double-sided tape. The recommended tape for tape. Remove the weight.
archival purposes is 3M #415 double-sided,
polyester transparent tape coated with an acrylic 3. Place the paper object within the tape
adhesive. The tape has a paper backing which is boundaries. Make sure that the object does
removed after the two pieces of polyester film not touch the tape. If the tape is too close to
are aligned. This ConserveO Gram will only the object, first remove the object, then
describe the use of double-sided tape. remove the tape and reapply it. Replace the

2 Polyester Encapsulation
Conserve O Gram 1313 NationalPark Service

object within the tape boundaries. (It is top piece of film back down over the paper
important not to lay the tape with the paper object in a rolling motion.
object in close proximity. If the tape should
adhere to the paper object , it will need to be
removed by a paper conservator.)

Polyester Film (Bottom Sheet)

Double-sided Tape

7. Using the cotton cloth and gently pressing in

th e directi on the film is closing, push the air
out of the package, starting in the middle of
the taped end. Rub the tape until it has
completely adhered.
4. Wipe the second piece of polyester film with
the clean , lint-free cloth. Lay the film over
the object and align all the edges. Plac e the
weight in the center of the package to keep
the object and the film from stipping.

5. Lift one end of the top sheet of polyester film

and remove the paper backing from the
double-sided tape . Gently lay the polyester
film back down over the tape. This will
anchor one end of the encapsulation package
and keep the two piece s of film from slipping 8. If excess polyester needs to be trimmed from
out of alignment. around the edges of the encapsulation, lay the
rul er or cutting edge on the tape and cut into
the marg in away from the object. This way ,
should the knife slip, only the polyester will
be cut.

6. Mov e the weight to the end that is taped

together . Lift up the top sheet of polyester
film and remov e the remaining paper backing
from the double-sided tape. Gently lay the

Polyester Encapsulation 3
 National Park Service Conserve O Gram 13/3

Sources

Materials and tools needed for polyester

encapsulation are available from archival-quality
materials suppliers, such as University Products,
P.O. Box 101, Holyoke, MA 01041-0101, (800)
628-1912; Light Impressions, P.O. Box 940,
Rochester, NY 14603, (800) 828-6216;
Conservation Resources, 8000-H Forbes Place,
Springfield, VA 22151, (800) 634-6932; and
Conservation Materials Ltd, P.O. Box 2884,
Sparks, NV 89431, (702) 331-0582.

Susan Nash Munro

Paper Conservator
P.O. Box 1011
Shepherdstown, West Virginia 25443

Formerly issued as Conserve O Gram 13/6. Revised 1993.

The Conserve O Gram series is published as a reference on The series is distributed to all NPS units and is available to non-NPS
collections management and curatorial issues. Mention of a product, institutions and interested individuals by subscription through the
a manufacturer, or a supplier by name in this publication does not Superintendent of Doc uments, U.S. Government Printing Office,
constitute an endorsement of that product or supplier by the National Washington, D.C. 20402, FAX (202) 512-2233. For further
Park Service. Sources named are not all inclusive. It is suggested information and guidance concerning any of the topics or procedures
that readers also seek alternative product and vendor information in addressed in the series, conta ct the National Park Service, Curatorial
order to assess the full range of available supplies and equipment. Services Division, Harpers Ferry, WV 25425, (304) 535-6410.

4 Polyester Encapsulation