Polyester Encapsulation
This article originally appeared in Exchange,
a newsletter published by the Wisconsin Historical
Society. (Volume 26, Number
2, March/April 1984) It is the 15th in a series
of articles titled Conservation Corner.
The series features information about maintaining
an adequate environment for the storage and exhibition
of historical collections, employing proper collection
care techniques, and recording and cataloging historical
collections. This article was written by Tom McKay,
retired local history coordinator for the Wisconsin
Historical Society.
For more than a quarter of a century, lamination was the chosen treatment
for the protection of brittle, fragile, deteriorating
paper documents. However, the process has become increasingly
suspect for a number of reasons, among them its irreversibility
as the laminates become one with the document through
the application of heat and pressure. Therefore, the
Library of Congress has developed a procedure as a
substitute for lamination: encapsulation of paper documents
in a polyester film such as Mylar, Melinex or Scotchpar.
These synthetic films are clear and inert. They contain
nothing harmful to paper. Aging tests have proven them
to be archivally sound, safe, and durable. Because the document is
not fastened to the polyester, the document can be removed quickly
and safely from the polyester enclosure should it be desired. And,
perhaps the most attractive feature of the procedure, it can be done
by anyone, without any sophisticated equipment.
There is nothing mystical about encapsulation, and there is more
than one right way to do it. Encapsulation requires
no awesome talent, just a little practice and patience.
Several pamphlets and instruction sheets are available,
including the Library of Congress publication, Polyester
Film Encapsulation, illustrated by Margaret R. Brown
(stock #030-000-0014-1).
Encapsulation encloses the sheet of paper one wants to protect within two sheets of polyester. Ready-made polyester envelopes in a wide variety of sizes, shapes, and weights can be purchased from a growing number of suppliers, but it is often more expedient and less expensive for the owner or custodian of paper records to make the polyester enclosure himself or herself. For this he or she will need only a few basic skills, tools, and materials. Anyone who can use a scissors and ruler with confidence has the necessary skill.
The tools used in preparing an encapsulation are a hard, flat surface on which to work, a scissors, a ruler, a lint-free cloth, a squeegee or rubber roller, a sharp utility knife, and one or more small objects to be used as weights. A grid-patterned paper covered with plate glass can also be useful as a guide in positioning the tape which seals the envelope.
The materials used in encapsulation are polyester film such as Type
D Mylar manufactured by DuPont; Melinex Type "O" manufactured
by ICI; or Scotchpar manufactured by the 3M Company;
a roll of quarter-inch Scotch-brand double-coated adhesive
tape # 415 — also a 3M Company product. Because of its widespread
use and, therefore, ready availability, the Wisconsin Conservation
Service Center uses Mylar polyester film to encapsulate. For ease
in this discussion I will use the trade name, Mylar, as a generic
term interchangeably with polyester film.
All polyester films are accompanied by a certain degree of static charge. Never encapsulate papers with fugitive or flaking design layers such as charcoals, pastels, or any loosely bonded particles from their support paper. For this reason, photographs with emulsions that are cracked or flaking should not be encapsulated.
Once an item is encapsulated, it requires slightly more storage space.
It will be at least one inch wider and one inch longer
than it was before being encased in the polyester.
It will also be somewhat thicker and heavier. The Mylar
has a shiny and reflective surface, a possible distraction
if the item is exhibited. [Editor's note: encapsulation
has proven an attractive and safe technique for exhibiting
paper items. Its use in exhibits for protecting documents is recommended.]
With ordinary attention to the light source, a Mylar encapsulation
item can be photographed, and Mylar poses no problem in photocopying.
Many innovative techniques have been devised to allow for binding encapsulated pages into book form, encapsulating folded documents, and making pamphlet covers. Machines have been perfected that seal the polyester envelopes with ultrasound or radio waves, but for our purposes, it is quite enough to concentrate our efforts on the conventional encapsulation of flat, single sheets of paper.
- Cut two pieces of Mylar two inches longer and two inches wider than the document to be encapsulated.
- Place the document on the table.
- Place one sheet of the cut Mylar on top of the
document.
- Wipe the side of the Mylar facing up with a lint-free cloth.
- Position the document and the sheet of Mylar carefully so that at least one inch of the Mylar extends beyond the document on all sides.
- Place a weight at the center of the Mylar to hold it and the document beneath it in position.
- Place a strip of double-coated tape (exposed-adhesive
side down) on the Mylar in line with one edge of
the document leaving a 1/8- to 1/16-inch space between
the edge of the tape and the edge of the document.
Extend the tape on all four sides about one inch
longer at each end than the length of the side of
the document. The tapes will then intersect (one
cross over the other) at each of the four corners.
- Miter the tape at each corner. This is done by placing a straight edge across the tape at the corner and bisecting the angle of junction with a utility knife. Cut only the tape. Do not cut through the Mylar under the tape. When the tape, its adhesive layers, and backing paper have been cut through completely, remove the two pieces of tape that have been cut loose.
- Remove the document from below and postion it on top of the Mylar between the tapes you have just put down.
- Wipe the surface of the second sheet of Mylar that
will be facing the document. Note:
polyester film cut from a roll will tend to curl
in the direction it was rolled. Therefore, it is
necessary to plan the enclosure so the sheets of
Mylar are joined with like-curved surfaces facing
the document and each other, i.e.: convex surface
facing convex surface or concave facing concave.
The two sheets will then oppose each other's tendency
to curl and the protective envelope will lie flat.
- Place the second sheet of Mylar, cleaned side down, on top of the document. Line up its edges with those of the taped sheet of Mylar underneath the document.
- Put a weight at the center of the upper or covering sheet of Mylar.
- Lift one corner of the upper sheet of Mylar, reach under and carefully peel the backing paper from one strip of tape.
- Peel back paper from one of the adjacent strips of tape.
- Allow the edge of the lifted Mylar sheet to fall back onto the now exposed adhesive layer of these two strips of tape.
- Squeegee the Mylar along the two tape edges from which the backing paper has been removed.
- Peel backing paper from the third strip of tape and squeegee along the edge of the tape.
- Thoroughly squeegee the envelope toward the open edge of the package to remove as much air as possible.
- Position a long straight pin at one end of the tape from which the backing paper has not been removed. The point of the pin is placed on top of the document; the rest of the pin projects outside the
taped area.
- Peel backing from the remaining strip of tape. Allow the Mylar to settle over the exposed adhesive on this last edge.
- Force remaining air out by running the squeegee
across the Mylar toward, but
never over, the pin.
- Remove the pin carefully.
- With a rubber roller or soft lint-free cloth rub over the taped edges of the encapsulation, to assure good adhesion of the Mylar to the tape and also to force out any air remaining in the envelope.
- Trim all four edges of the encapsulation to within 1/8 to 1/16 of an inch of the outer edge of the tape. The Mylar thus left to extend beyond the edges of the tape prevents them from picking up lint and dust particles.
- Round all corners of the encapsulation with a fingernail clipper or small scissors. Be careful not to cut down too far and expose the tape. Before rounding, corners will be sharp and could damage other documents.
- Wipe both sides of the encapsulation with some enthusiasm to remove any fingerprints. This also tends to build up more static charge.
The document, now strengthened and protected in its polyester envelope, may be handled quite normally, without fear for its safety. Its brittleness has been compensated for. Within the encapsulation it cannot be soiled or further damaged by handling.
The steps outlined above may not demystify the encapsulation process at first reading, but using them as a step-by-step guide while you work through the procedure should convince you of its glorious simplicity as a preservation tool. With a little practice I am confident you will agree with those who believe encapsulation, second only to proper storage, is the easiest and safest thing one can do toward the preservation of paper records.
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