ENCAPSULATION IN POLYESTER FILM
USING DOUBLE-SIDED TAPE
by
Sherelyn Ogden, Head of Conservation, Minnesota
Historical Society
Northeast
Document Conservation Center 100 Brickstone Square Andover, MA 01810-1494
www.nedcc.org
TECHNICAL
LEAFLET - STORAGE AND HANDLING,
Section 6, Leaflet 5
Encapsulation is a simple technique designed to protect documents
from physical wear and tear and from grime. The document is enclosed between
two sheets of clear polyester film, the edges of which are sealed with
double-sided pressure-sensitive tape. After encapsulation, even a brittle
document can usually be safely handled. The process is easily reversed by
carefully cutting the film envelope along the edges in the space between the
tape and the document.
Polyester film can also be sealed using equipment that forms either an
ultrasonic or heat-activated weld. Double-sided tape, however, is the most
practical method when a limited amount of encapsulation is done because of the
cost of the equipment needed for ultrasonic or heat welding.
Encapsulated documents are held in place in the film envelope by static
electricity. The static also helps to hold torn paper together, reducing the
need to repair small tears before encapsulation. However, the static can also
lift loosely bound media from the paper. For this reason the technique is
inappropriate for documents with media that are not firmly bound to paper, such
as pastel, charcoal, and some pencil. If in doubt, test: if the media lift off
on a tiny swab rubbed gently in an inconspicuous spot, the document should not
be encapsulated.
Research by the Library of Congress demonstrates that acidic papers may age
much faster after encapsulation. It further shows that leaving an air space at
the corners of the film package does not slow this aging as was once speculated.
Documents should be alkalized (deacidified) by a qualified person before
encapsulation. If this is not feasible, encapsulation may still be desirable to
protect very fragile or heavily handled material. The Library of Congress finds
that, in such a case, including a sheet of buffered paper the same size and
shape as the document to back it in the enclosure can slow the rate of
deterioration.
Documents that are not alkalized before encapsulation should be labelled for
future custodians. A label typed onto buffered paper and inserted in the
envelope is more secure than one attached to the outside of the envelope. If a
buffered backing sheet is used, it can be labelled.
It is important to remember that encapsulation, like any conservation technique,
should not be used for every document. The decision to use this strategy to
preserve documents should be a matter of informed judgment, weighing the need
to support or protect the document against the possibility that chemical
deterioration may occur at an increased rate.
MATERIALS
Polyester is strong, flexible,
and relatively inert. If free from plasticizers, UV-inhibitors, dyes, and
surface coatings, it will not interact with documents. Mylar Type D and Melinex
516 are polyesters safe for use on valuable materials. These are widely
available in 3-, 4-, and 5-mil thicknesses. The thickness of the film should be
chosen for its ability to support the surface area of the object being encapsulated;
large objects require thicker film.
Testing at the Library of Congress found 3M Scotch Brand double-sided tape no.
415 the only acceptable tape for encapsulation. It is sufficiently stable to
minimize problems from creeping or deteriorating adhesive, although creeping
does sometimes occur.
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Figure 1a. ............... Figure 1b. |
Materials Needed:
Scalpel, knife, or good scissors
Lint-free cloth (cheesecloth)
1 weight
1 window-cleaning squeegee (Figure 1a)
1 hard rubber brayer (optional) (Figure 1b)
Polyester film (Mylar Type D, Melinex 516) pre-cut or in rolls;
3-4 mil for small and medium-sized documents,
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Figure 2. |
5 mil for large documents.
3M Scotch Brand double-sided tape no. 415, 1/4" or 1/2" wide,
depending on size of document.
A work surface can be prepared by taping 1/4"graph paper to the underside of
a sheet of glass or Plexiglas (optional). The lines on the graph paper assist
in laying the tape straight (Figure 2).
INSTRUCTIONS
1.
If you are using a backing sheet
of buffered paper, cut the sheet to the dimensions of your document.
2.
Cut two sheets of polyester film
at least two inches larger than the document in each dimension.
3.
Place one sheet of film on a
clean, flat, work surface. Wipe the surface of the film with a lint-free cloth
to remove dust and improve the static charge, which will adhere the film to the
work surface.
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Figure 3. |
4.
Center the backing sheet, if one
is used, on the film and place the document on top of it. If a backing sheet is
not used, center the document on the film.
5.
Place a weight on the center of
the document to hold it in position (Figure 3).
6.
Apply the tape to the film along
the edge of the document, leaving a space of 1/8" to 1/4" between the
edge of the document and the edge of the tape (Figure 4). The ends of the tape
should be cut square and butted on three corners with no overlap (Figure 5a).
Alternatively the tape edges can be cut on the diagonal to make a more elegant
joint (Figure 5b). Leave a gap of at least 1/16" at the fourth corner to
allow air to escape. Leave the brown protective paper on the tape.
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7.
Wipe the second sheet of film
with a lint-free cloth.
8.
Remove the weight from the
document and center the second sheet of film over the assembly, cleaned side
down.
9.
Replace the weight on the center
of the top sheet of film.
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10. Lift one corner of the top sheet of film. Carefully peel the
protective paper from the tape along one edge of the document. Lower the corner
of the film and rub the film over the tape to adhere it (Figure 6). Repeat for
the other three edges.
11. To remove air from between the sheets of film, slide the squeegee
across the envelope towards the air gap left in one corner of the envelope
(Figure 7).
12. Roll the brayer or squeegee over the tape to bond it firmly to the
polyester, or run your finger over the tape to secure the bond.
13. Trim the envelope, leaving a 1/8" to 1/4" margin of
polyester outside the tape on all four edges. Rounding the corners of the
envelope will help prevent scratching or cutting other materials during
handling.
Good encapsulation takes
practice. Expect to try this several times before you are satisfied with the
result. Do not give up; you will quickly gain proficiency.