Encapsulation: A Useful and Versatile Tool for Book and Paper Conservation

Encapsulation, or polyester encapsulation, is commonly used by museums and libraries to stabilize, store, and protect paper-based artifacts, especially fragile ones. The paper-based artifact is sandwiched between two sheets of archival polyester film, which are sealed, partially or fully, along the edges. It is an efficient and low-cost conservation method that allows the encapsulated artifact to be viewed and handled safely. It also decelerates the degradation of paper (Figure 1). Finally, encapsulations are very easy to remove should such need become necessary in the future.

At NYPL Conservation, we endeavor to improve and maintain the condition of our vast collections for the public. There is often more than one way to treat an object, so it is important to achieve a balance between the treatment goals and the available resources, including time. As conservators, we ask ourselves these questions before treatment: What is the value (not just monetary value) of the object? How is it going to be used? How urgent is the need for it? What risks are involved? How much time and resources can be reasonably allocated to its treatment? As a student in book conservation, I have been training myself to think about these questions during my final year internship for graduate school, which I am completing at NYPL. 

After considering these questions carefully with my internship supervisor, Ursula, Mitra, I chose encapsulation for three different items that I treated. Ursula is an expert in using encapsulation creatively and showed me its huge potential as a conservation method. Encapsulation, though by no means a universal solution, has proved to be a versatile tool for book and paper conservation.

Scrapbook 1940 from the General Research Division documents the activities of the American Russian Institute during the Cold War period. It is a commercially-produced scrapbook. Two hollow plastic posts go through the covers and the pages, pinning them together. A cord is then laced through those two posts. The scrapbook came to Conservation because it was requested by a researcher, but could not be served given its condition. The binding of the scrapbook has broken. The paper is so brittle that it shatters with slight handling, manifested by the numerous breaks and losses throughout the book (Figure 2).

I thought that this scrapbook was a good candidate for encapsulation for several reasons. First, the low-quality mounting pages are so irreversibly brittle (Figure 3) that mending is not an option. Second, the mounting pages contain annotations, so separating them from the memorabilia would undermine the informational value of this book. Third, encapsulation would allow the pages to be re-bound in its original post binding, allowing researchers to handle this item as was intended. Finally, all the memorabilia attached to the scrapbook pages were also suitable for encapsulation.

I used an ultrasonic welding machine (Figure 4) to complete all the encapsulations for this scrapbook. Our ultrasonic welder was devised by Bill Minter, who designed and fabricated most of the welding machines used in U.S. libraries. Instead of using heat to fuse the polyester films together, ultrasonic welders use low-frequency energy pulses.

For all three encapsulation projects, I used 3 mil thick Melinex® 516 polyester film. It is transparent, chemically stable, and available in different thicknesses. The ultrasonic welding machine comes with a set of shims (Figure 4), which adjust the distance between the welding head and the table to accommodate polyester films of different thicknesses. Choosing the appropriate thickness of polyester film is key for encapsulations to work well.

This scrapbook contains different formats of memorabilia, including single sheets, multiple sheets adhered or stapled together, pamphlets, and fold-outs. Customized encapsulation can preserve the integrity of the information and the original reading experience, such as paging through the pamphlets, folding and unfolding the fold-outs, etc.

TYPE 1: Single sheets

For pages with only single-sheet attachments, I sandwiched each page between two sheets of polyester film slightly larger than the page. I sized the top film wider than the bottom film at the spine edge, which I used as a stub for rebinding later. (Figure 5)

TYPE 2: Multiple sheets

Some memorabilia are multiple sheets adhered or stapled together and then mounted to the scrapbook page.

For only two attached sheets that are mounted to the page, if the two sheets were already separated, as on the right mounting page, I encapsulated each sheet individually. If the two sheets were still attached to each other, as on the left mounting page, I designed the encapsulation to accommodate the restricted opening. (Figure 6)

Sometimes, three or more attached sheets are mounted to the page. I separated these sheets and encapsulated each individually as if it were a mounting page (with the wider spine edge on the top film for post binding). These individually encapsulated sheets were placed in the proper position with the original associated mounting page, which I encapsulated with the bottommost sheet in the group. I used spot welds to prevent each sheet from shifting around in the encapsulation. (see video below)

TYPE 3: Pamphlet

Only the covers of the pamphlets are encapsulated since the texts are protected by the covers. (see video below)

TYPE 4: Fold-outs

There are three types of fold-outs in this scrapbook: half-fold, tri-fold and roll-fold. Every panel in the fold-out is protected between polyester films. (see video below)

Opening and closing an encapsulated fold-out puts a lot of stress on the joints of the fold-out. If the paper is too weak to withstand that stress, the fold-out was cut along the joints and each panel encapsulated separately. (Figure 7)

TYPE 5: Loose items/other

Detached items are commonly found in scrapbooks. It is not always possible to find where they were originally mounted and re-secure them in place. In those cases, I encapsulated these items and placed them back where I found them. For example, I found these fragments of a document were sitting loose between two pages (Figure 8). I pieced them together, encapsulate it, and incorporated it in-situ. (see video below)

The same design can be applied to the example below where a card was stapled to a two-sheet document. The card is made of much stiffer paper, making it difficult to flip through these two documents (Figure 9). The encapsulation makes the verso of the card and the texts blocked by the card now easily accessible. (see video below)

Besides bound items, encapsulation was also used for housing two 19th-century maps, Karte der Oetzhal & Stubaigruppe (1898) and Phelps & Watson’s Historical and Military Map of the Border and Southern States (1864) from the Lionel Pincus and Princess Firyal Map Division.

Karte der Oetzhal & Stubaigruppe, at some earlier time, was cut horizontally in two, and the top and bottom halves were then cut into small rectangular pieces and adhered to a fabric secondary support (Figure 10). The pieces from the top half were adhered to one side of the fabric and the pieces from the bottom half were adhered to the other side of the fabric. The map was then folded up completely to the size of one small rectangular piece. The map came to Conservation because repeated folding and unfolding had weakened and torn the fabric along some of the folds.

Whenever possible, conservators seek to remove old secondary supports such as the one on this map. Fabric secondary supports do not behave like paper and therefore can impart stress to the paper during handling or relative humidity changes. This can lead to deformation and/or breaks. 

I decided that Karte der Oetzhal & Stubaigruppe, unfortunately, was not eligible for a secondary support removal. Its double-sidedness and embrittled paper rendered a wet treatment risky. Mechanically separating the map with tools like a micro-spatula is equally tricky. Therefore, I separated the map into the earlier rectangular pieces along the folds and encapsulated between two polyester films with spot welding around each to prevent shifting (Figure 11). 

Phelps & Watson’s Historical and Military Map of the Border and Southern States was a fold-out map from the back cover of a pamphlet (Figure 12). It had separated into many pieces along the folds. One piece of the map is still attached to the pamphlet. One option was to lift it, reintegrate it with the rest of the map, and house the map and the pamphlet separately. The other option was to keep that piece in the pamphlet, and house the pamphlet and map together. I chose the second option.

The paper of the map was yellowed and brittle. Washing the map in alkaline deionized water brought out the discoloration and made the paper stronger. Lining it with Japanese paper on the verso and filling the losses with toned Japanese paper made the map whole again (Figure 13). It is not recommended to fold the map and put it back in the pamphlet. The standard housing for flat maps in the Map Division is polyester L-sleeves (similar to an encapsulation, but with only two sealed sides). The question was how to store the pamphlet with the map.

We devised an encapsulation with an integrated polyester jacket to hold the pamphlet, so that the map could be viewed in its entirety with minimal handling (see Figure 14 for the making process). The polyester jacket is situated where the piece of map in the pamphlet fits into the rest, so all that is needed is to open the pamphlet to the last page. It is impossible to lose the pamphlet this way. The map is not fixed in place but it barely shifts around due to the electrostatic force and the tight size of the L-sleeve. (see video below)

Special thanks to Denise Stockman (Senior Paper Collections Conservator) for supervising my treatments of the maps, Grace Owen-Weiss (Associate Conservator for Rare Books and Paper) for teaching me how to do a Dacron® lining for the treatment of the Phelps & Watson’s map, and other members of the conservation team at NYPL for assisting the lining process of the Phelps & Watson’s map (lining a large map is not a one-person job!) and sharing their valuable insights into the treatment of Karte der Oetzhal & Stubaigruppe.

All photos and videos are by the author. 

Shaoyi Qian is a recent graduate with a dual master’s degree (MS/MA) from the Conservation Center, Institute of Fine Arts, New York University, specializing in Library and Archive Conservation. She is interested in pop-up and movable books, paper-based children's toys, and paper ephemera from all time periods. She also enjoys the challenges posed by the structural condition issues in books. She will be the 2022-2023 Sherman Fairchild Foundation Post-Graduate Fellow at the Morgan Library & Museum.

Ursula Mitra is senior book conservator at the NYPL Conservation Lab. She graduated from the School of Library Service at Columbia University in 1992 with a Master of Science in Library Service and an Advanced Certificate in Library & Archives Conservation. During the degree program she interned at the Herzog August Bibliothek in Wolfenbüttel, Germany, and at the Trinity College Library in Dublin, Ireland. Subsequently she worked as a conservator at the Frick Art Reference Library from 1992-97, followed by two years as Conservator at NYU’s Bobst Library in New York City. In 1999 she began serving the greater New York City area in her private practice in Library Conservation and joined NYPL in September 2020.