Courtesy of Northeast Document Conservation Center
Transparent book jackets made of polyester film offer a number of benefits:
1. they protect the cover from dirt and from scuffing as the book is handled and shelved;
2. if a cover has powdery red-rotted leather, the jacket contains it, so that it doesn’t rub off on the book’s neighbors;
3. transparent polyester allows the book’s cover to be seen and its title to be read through the jacket;
4. shelf labels can be attached to the jacket’s spine rather than directly to the book avoiding possible harm to the book from unstable label adhesives.
It is important to note that not all polyesters are acceptable for use. Only ones that have been tested and proven to be chemically stable for long periods of time should be used. The polyester film chosen should be free of plasticizes, ultraviolet inhibitors, dyes, and surface coatings so that the film does not interact with the material it is intended to protect and hasten its deterioration. Mylar type D, manufactured by Dupont, and Melinex 516, manufactured by ICI, are two types of polyester film that are acceptable for use on books. Four mil polyester is suitable for most books.
The best known and easiest-to-make polyester jacket is a simple wrap-around (Figure 1). A disadvantage of this design is that it is not fixed in place on the book; as a result it tends to shift out of alignment, especially on large heavy books. The jacket can be held in place with tape or straps but this leads to other problems. Another disadvantage is that the edges of the book are exposed and are subject to abrasion.
The following book jacket was designed to avoid these disadvantages. It incorporates flaps, which help hold the jacket on the book, and which cover and thus protect the edges of the book.
When constructing polyester jackets, you will need a straight edge, a bone folder, and either scissors or a mat knife. Cutting and creasing can be done on a self-healing mat or on a large piece of book board.
1. Cut a piece of polyester with a vertical dimension equal to 1 2/3 times the height (H) of the book and a horizontal dimension 4 times the width (W) of the book plus the thickness (T) of the book (Figure 2).
2. Wrap the polyester around the book such that the edges of the polyester are even with each other and the book is centered between the top and bottom of the polyester (Figure 3). It is important to note that polyester has a smooth surface and extra care must be taken to make sure that the book does not shift, especially while being measured.
3. Place the book on a clean work surface and open the polyester flat, being careful not to change the position of the book on the polyester film (Figure 4).
4. Mark the position of the book on the polyester film by making dents with the point of a bone folder at the corners of the book and at both ends of the joint (Figure 4).
5. Wrap the polyester over the book again and turn the polyester and book over being very careful that the book does not shift on the polyester. (Figure 5).
Repeat step four.
6. Using a straightedge and bone folder, crease the polyester straight across connection the dents as illustrated (Figure 6). Broken lines represent creases.
When creasing the polyester, place the straightedge on the film with its edge next to, but not covering, the two dents to be used as guides. Press the point of the bone folder into the polyester and pull it along the edge of the straightedge, creating a linear indentation. the straightedge should be held down firmly to prevent slippage. Without releasing the straightedge, reinforce the crease by inserting the bone folder beneath the polyester and rubbing it firmly against the straightedge (Figure 7).
7. At all “a” locations (Figure 8 ) make a second crease parallel to the first, outside the first. and at a distance from the first equal to the thickness of the book’s cover.
8. Cut as shown in figure 9. Unbroken lines represent cuts.
9. Fold the polyester film at all creases. Make folds sharp by burnishing them with a bone folder. Remember that closely spaced parallel folds need to be made a all “a” locations. After these have been made, shape them with fingers until both folds take on a 90 degree angle (Figure 10). Dampening finger tips slightly with a moist sponge will make this shaping of the fold easier.
10. Wrap the polyester film jacket around the book, tucking the end flaps inside the front and back covers. Tuck the top and bottom flaps between the outer surface of the book cover and the polyester film (Figure 11). The top and bottom flaps will be visible through the polyester film jacket.
Polyester film is difficult to work with and you may need a few tries to construct the jacket correctly. Once you have mastered the technique, construction time is about 10 minutes per jacket, excluding set-up time.