Documents, manuscripts, prints, drawings, pamphlets, periodicals, newspapers, postcards and ephemera are typically made of paper—an organic substance that is vulnerable to deterioration over time.
All paper will deteriorate if mistreated or stored improperly. Some types of paper are particularly vulnerable—for example, the acidic wood-pulp paper that was produced throughout much of the 19th and 20th centuries. Unlike earlier papers, which were made of higher-quality fibers (commonly called rag papers), wood-pulp papers contain natural impurities and byproducts of the manufacturing process that break down to form acids in the presence of heat, light, and moisture in the air. Pollutants in the air and/or direct contact with poor-quality storage enclosures also cause discoloration and embrittlement of paper.
There are a number of steps that can be taken to preserve vulnerable paper collections. These include providing a cool, dry, clean, dark, and stable environment; protecting collections from disaster; handling collections carefully; choosing appropriate storage furniture; and using protective storage enclosures. Storage enclosures lessen the effects of fluctuations in temperature and humidity and provide protection against abrasion and handling, but they must be strong, durable, and chemically stable so that they do not damage the materials they enclose.
The goal of this section is to provide the background information necessary to select the most appropriate storage systems for flat paper (storage of photographs is addressed in a later section of this publication). It is oriented toward collectors, artists, archivists, and librarians who are new to the field of preservation. No introduction, however, can provide all the answers. If your collections are extensive, in poor condition, or include works of art, it would be advisable to consult a professional conservator. The American Institute for Conservation of Historic and Artistic Works (AIC) provides an online "Find a Conservator" tool that provides the names of conservators in your region.
The information in this section reflects our current understanding of the storage requirements for paper. It will be revised as new information and products become available.
To provide long-term protection, storage containers and enclosures should be made of materials that are strong, durable, and chemically stable. Enclosures and boxes should be tailored to the size, condition, and anticipated use of the objects being enclosed.
The terms "archival" and "archival quality" are often used to describe storage products, but these are non-technical terms that do not, of themselves, convey any specifics about the suitability of these products for use in preservation. It is important to evaluate the specific characteristics of each product and to choose the appropriate type of product for the item to be stored. For storage materials made from paper and/or board, these characteristics include (but are not limited to) acidity, alkalinity, the presence of lignin, fiber type, and adhesives used. Note that different characteristics apply to plastic storage materials, which will be considered separately below.
Acidity and alkalinity are measured by pH using a logarithmic scale of 0–14. The pH of storage materials made from paper and board should ideally be in the 7–8.5 range.
Paper to be used for storage enclosures should be acid-free. Acid-free storage materials have a pH of 7.0 or higher. It is important to realize that although acid-free materials are not acidic when they are produced, they can become acidic over time. This can be due to internal impurities introduced in manufacturing or to external impurities such as pollutants, which degrade to produce acids.
For this reason, an alkaline reserve or buffer is often added to paper or board during manufacture to neutralize acids that may be produced over time. This alkaline reserve is usually 2-3% calcium or magnesium carbonate. Most paper collections will require buffered enclosures. While an alkaline buffer in storage enclosures is generally desirable, there are a few types of collections that are sensitive to alkaline materials and should therefore be stored in pH-neutral enclosures, not alkaline. These include blueprints and diazo reproductions, works of art with pigments that react to high pH, albums and collages with wool or silk components, and other items that contain animal proteins. Some photographs and textiles may also be alkaline-sensitive; see later sections of this publication for more information on these materials.
Storage materials for paper objects should also be lignin-free. Lignin is a natural component of the cell walls of plants and trees. If it is not removed during manufacture, it can react with light and heat to produce acids and darken paper. Lignin-free actually means low-lignin; lignin-free materials usually have a maximum of 1% lignin.
Other components of paper or board enclosures that should be considered when determining their suitability for long-term preservation include fiber type and adhesives used in the enclosures. While cotton fiber makes the most chemically stable paper and board, it is possible to make high-quality paper and board from wood pulp by using a chemical process that removes impurities (the resulting pulp is usually termed chemical wood pulp or purified wood pulp). Groundwood pulp (also known as mechanical wood pulp), on the other hand, is always of poor quality and cannot be used to make suitable enclosures. In addition, adhesives used in enclosures must not discolor, deteriorate, or fail, and they should not discolor or damage adjacent materials.
Boxes: The boxboard used for most document boxes is 60 mils or points (pts.) thick (there are 1000 points in an inch, so 60 pts. is .060 inches thick). Lighter weight stock (40 pt.) is sometimes used for small boxes. Boxes suitable for long-term storage of paper items are available in several types of board, all of which are acid-free, lignin-free and buffered with a pH of 8.0-9.0. Boxes are also available with a polyester film laminate coating (Gaylord Archival® DocuDry™) to resist water damage. All boxes should be sturdy enough to support the contents and have reinforced corners and snug covers that prevent soil and pollutants from entering.
Folder Stock: Acid-free folders of various sizes are available in both buffered and unbuffered stock. The typical weight is 10-pt. with 7-pt. available for lightweight items and 20-pt. for oversized maps and prints.
Interleaving Material: Interleaving sheets are sometimes used to protect paper objects in storage. Tissue, glassine, various types of paper and clear polyester film can be used for this purpose. Acid-free tissue is available with or without an alkaline buffer, as is paper. Glassine is a smooth translucent paper that is not abrasive and can generally be used with friable (i.e., easily crumbled) media such as pastel or charcoal, but it is not very stable. Glassine is acid-free and unbuffered and should be replaced periodically if used. If polyester film is used for interleaving, it should meet the criteria for safety noted below, and it should not be used for items with friable media because of its electrostatic charge.
Mat Board: When matting and framing works of art on paper, conservation mounting/matting board (either a 100% cotton rag board or a purified wood pulp board) must be used both for the backboard and the window mat. For most materials, mat board should be acid-free, alkaline buffered, and lignin-free—with the exception of the alkaline-sensitive materials mentioned earlier. For these materials, an unbuffered 100% cotton rag board is available. Mat board is available in two-, four- and eight-ply thickness. The heavier weights are recommended for oversized documents that need additional support. For hinges used to attach works of art to the backboard, Japanese paper (which is lightweight, lignin-free, and long-fibered) and a starch-based paste are recommended.
Plastic: Clear plastic enclosures are particularly useful for objects that receive continual handling, are too brittle to be handled unprotected, or like postcards, must be browsed to view the images. As noted above, artwork with friable media such as charcoal or pastel should never be placed in plastic because static electricity can lift the image from its support. Remember that plastic enclosures provide no protection from light. All items in clear plastic enclosures should be placed in boxes for long-term storage.
Polyester, polypropylene and polyethylene are the three types of plastic that are suitable for storage of paper objects. They should be uncoated and free of additives. Uncoated archival polyester is recommended because it is very stable. It is used for various types of envelopes, sleeves and folders. Polyester also comes in rolls or precut sheets and is available in thicknesses of 1–5 mil; 2–3 mil is used for average-sized documents, while oversized prints and maps need the extra support of 4–5 mil. Polypropylene is commonly used for containers. Polyethylene is highly flexible but not as clear; it is used for sleeves and bags. Polyvinyl chloride (PVC) enclosures, sometimes referred to as vinyl, are not acceptable for use because they are very unstable.
Documents may also be encapsulated between sheets of polyester using double-sided tape with a 1/4" margin between the document and the tape. However, current research indicates that acidic paper deteriorates more rapidly if sealed in polyester. It is advisable to place sheets of buffered paper behind the documents before putting them in polyester or to consult a conservator about having them deacidified. An alternative to encapsulation, especially suitable for oversized documents, is a folder with a polyester cover sheet.
There is no one standard that specifically governs storage materials for paper objects. The Photographic Activity Test (PAT) is a standardized test that is used to determine whether enclosure materials are safe to use with silver image photographs. It is discussed further in the section on storage of photographs.
Responsibility for adherence to standards rests with the suppliers. Gaylord Archival products are manufactured to the most recent national preservation standards. The company purchases or manufactures materials to standards published by the American National Standards Institute (ANSI), the National Information Standards Institute (NISO), and the International Organization for Standardization (ISO) when available or to industry-wide standards established by national institutions such as the National Archives and Records Administration and the Library of Congress Preservation Directorate. Specification information is available from Gaylord Archival on request.
Once you have selected the appropriate storage materials, the documents and other paper items should be prepared for storage. Always follow proper handling procedures when working with collections. Using white cotton gloves will protect items from dirt and oils on your hands. Do not eat or drink around collections. When moving paper documents or artworks, particularly brittle items, support the item carefully from below.
Once paper objects have been placed in enclosures and boxes, they must be stored in non-damaging furniture. Wood storage furniture is not recommended because it can emit acids and other harmful substances. It is possible to use a sealant on wood furniture, but this will not provide complete protection, and the sealant itself may emit damaging vapors. Even if wood shelves and drawers have been sealed, they must be lined with a barrier material, such as Marvelseal®, for additional protection.
Metal furniture with a baked enamel coating is acceptable for preservation purposes, but powder-coated steel or anodized aluminum furniture is preferred. As with enclosures, the choice of furniture will depend on the budget and the types of materials in the collection.
Regardless of the type of furniture, it should be appropriate for the types of collections to be stored in it. Open shelving is best for air circulation, although closed cabinets are sometimes needed for security purposes. Shelves should be adjustable, and collections should not protrude off the shelves or be crowded together. The lowest shelf should be 4–6 inches off the floor to reduce the chance of damage from flooding. Specialized furniture that will allow oversize items to be stored flat (e.g., map cases or shelving for oversize boxes) should be used.
A cool, dry and stable storage environment is crucial to the long-term preservation of paper collections. Heat and moisture accelerate the chemical reactions that cause paper to deteriorate, and high moisture levels can result in mold growth. Research has shown that lower temperatures and a lower relative humidity will greatly extend the usable life of paper collections.
Maintaining a stable environment is also very important. While boxes and storage enclosures can provide some protection against short-term environmental fluctuations, they will not protect collections against long-term changes in environmental conditions. Over time, climate fluctuations can cause paper to expand and contract, leading to distortion and weakening of the paper. Research has shown that large and frequent fluctuations, such as those that occur at night and on weekends if climate control systems are turned off or settings are altered, greatly accelerate paper deterioration.
There is no national standard for environmental conditions, but the National Information Standards Organization (NISO) has issued a technical report entitled Environmental Guidelines for the Storage of Paper Records, which gives suggested values for temperature and relative humidity for storage of paper records in libraries and archives. This report recommends a temperature no higher than 70°F and a relative humidity somewhere between 30% and 50% that can be maintained consistently.
Some practical suggestions for keeping the environment moderate and stable include: using portable dehumidifiers and air conditioning units in summer to lower humidity; lowering heat levels in winter to prevent humidity from becoming extremely low; and avoiding storage of collections in basements or attics where climate extremes tend to occur.
It is a good idea to monitor the climate in storage areas to ensure that it remains moderate and stable. Monitoring instruments ranging from humidity indicator cards to hygrothermographs and data loggers are available. See the NEDCC publication for more information on choosing an appropriate monitor and implementing an environmental monitoring program.
Selecting specific enclosures and boxes requires careful consideration. Physical condition, size of collection, anticipated use, and budget all play a part in the final choice. The second half of this section will present several case studies to show how products available from Gaylord Archival can be used to solve the storage needs of paper collections.
Scope: Documents, Manuscripts and Papers (letter or legal size)
A. Select appropriate primary enclosures that will protect the contents and allow them to be removed for use without damage. The size should be larger than the unfolded sheets so that edges don't protrude and become damaged.
(a) File folder inserts or slings - Insert the item into a paper folder (aka file folder insert) or envelope sling before placing it into a folder. Paper folders can also be used to group papers instead of using staples or paper clips, which can be damaging.
Individual polyester enclosures - These provide fragile or small items with protection from handling while retaining visibility.
Interleaving with 20 lb. buffered paper - This protects documents from adjacent material and provides support during handling, especially for oversized documents. Objects can be removed from folders by lifting the larger interleaving sheets beneath them. Use interleaving paper, envelopes or folders to separate valuable documents from highly acidic materials such as newsprint, or replace newspaper clippings with photocopies on alkaline paper.
Be aware that envelopes containing paper collections should not be interfiled with book collections, because envelopes do not provide sufficient support for the items stored inside. If pamphlets or groups of documents must be shelved with books rather than in boxes, the items should be placed in pamphlet binders (see Case Study IV).
B. Place folders and envelopes in sturdy boxes. Storage boxes should be strong, have reinforced corners, and match the size of the enclosures. To the extent possible, store items of similar size and weight together. Heavy or bulky items can damage lighter items stored in the same box.
If there are not enough folders to fill a box, use an adjustable spacer to hold the folders upright and prevent them from slipping or sagging.
C. Large collections of office records should be stored in record storage cartons. These are available in buffered and unbuffered board. The unbuffered cartons should be used only for short-term storage. Cartons must be strong and easy to transport.
Scope: Documents, Papers, Maps, Posters and Ephemera (larger than legal size)
A. Select primary enclosures that provide adequate support. Folders are available in large sizes and should be made of heavier 10 or 20-pt. folder stock (instead of 7 or 10-pt.). Likewise, 4 mil polyester film or a combination of 2–3 mil for the front sheet and 5 mil for the back sheet should be used if oversized documents must be encapsulated.
Sheets should be sorted and grouped by size, if possible. Place no more than 10–12 sheets into a folder. See page 4 for advice about interleaving, which is recommended to support fragile oversized items. Remember that certain types of oversize documents (e.g., blueprints and diazo reproductions) will need acid-free rather than buffered folders because of their sensitivity to alkalinity. If you buy both types of folders, be sure they are clearly labeled and staff knows when to use each type.
Storage/display folders with polyester cover sheets allow the contents to be viewed without damage and provide a backing of buffered material. These are more expensive, but worth the investment if the oversized items are fragile, valuable, or handled frequently. Remember, however, that these should not be used for artwork with friable media that may be lifted off the support by the plastic.
B. For small collections, folders may be stored flat in drop-front storage boxes. Because of their weight, boxes should be stored no more than two high. Another option is the Ackley Filing System which consists of corrugated boxes, file folders, L-sleeves and box labels, and is designed for horizontal or vertical storage of large documents.
C. Large collections of oversized maps, posters, and architectural drawings are best stored inside folders in metal flat files. Shallow drawers 11/2 inches deep are preferable so that the folders on the bottom are not crushed. See page 6 for general information about storage furniture. As with storage in boxes, folders should be sized to fit the drawer, and all folders should be the same size.
D. Use rolled storage when items are too large for flat files, as long as the items are flexible enough to withstand rolling and unrolling. Although flat storage is always preferable, it is not always possible. Rolled storage is a better alternative than sectioning maps or creasing drawings.
Use an acid-free tube that has a diameter of 3" or more and is several inches longer than the largest item being rolled. Depending upon their size and condition, 1–6 items can be wrapped around the outside of a tube with interleaving between individual items. The image should face the inside so that it is not exposed to light. The rolled document should be wrapped on the outside with acid-free paper or polyester wider than the document and secured with flat unbleached cotton tying tape (min. 5⁄16" wide). If the item is a blueprint, the wrapping paper or tissue should be unbuffered. A roll storage box will provide added protection.
The storage of prints and drawings is outside the scope of this pamphlet. If your collection includes such work, your storage needs should be reviewed by a conservator. In the interim, separate the items and follow these guidelines.
A. Store artwork flat. If possible, place each item in its own folder or place interleaving paper between each work of art to protect the surface. Remember that artwork with friable media such as charcoal or pastel should never be placed in plastic because static electricity can lift the image from its support. Place folders in clamshell or drop-front storage boxes.
B. For long-term storage of prints and drawings, conservators recommend window mats. These should be stored flat in reinforced boxes. For a description of procedures, see the AIC brochure and Matting and Framing for Art and Artifacts on Paper and How to Do Your Own Matting and Hinging in the NEDCC publication.
C. Matted artwork requires sturdy boxes that can support the extra weight of the mats. Their inner depth should be only 11⁄2 or 2 inches, again to keep the weight manageable.
Scope: Single Signature Pamphlets and Small Booklets
A. Pamphlet binders with four-flap inner enclosures provide maximum protection from abrasion when items are inserted and removed. Most pamphlet binders can be stored upright, provided there is adequate support from adjacent volumes.
B. Envelopes may also be used for pamphlets, but fragile pamphlets require the protection of a paper folder or envelope sling before being placed into the envelope. Choose envelopes that are large enough to allow the pamphlet to be inserted and removed without damage. If items in envelopes need to be shelved with books, use envelope storage binders or Pocket Binders to provide support.
C. If envelope storage binders are not used, envelopes should be stored in boxes. Use an adjustable spacer for partially filled boxes. Pamphlet boxes with flip tops (or crocodile boxes) provide upright storage. Average sized pamphlets can also be treated like documents and placed in file folders in pamphlet boxes. This treatment is typically used when the pamphlets are part of a larger archival collection.
D. Open pamphlet files are suitable for temporary storage only. They allow easy retrieval, but do not provide adequate mechanical support for long-term storage, nor do they protect items from light and fluctuations in the environment.
Scope: Unbound Periodicals & Newspapers
A. Collections of periodicals and newspapers should be stored flat in sturdy boxes because of their size and weight. The box depth should be shallower for contents that are heavy. When in good condition, issues can be placed directly into boxes. Polyester sleeves are available in large format sizes for newspapers and will provide long-term protection in flat storage. Adjustable spacers should be used to avoid slippage and sagging.
B. Single issues of average size may be treated as pamphlets.
C. Thin and fragile items require additional protection. They should be inserted into folders and envelopes before being put into boxes.
D. Polyethylene bags provide temporary protection, especially when the items are subjected to excessive handling. Collectors and dealers may find these particularly useful. However, given the evidence that acidic paper appears to deteriorate more rapidly when encapsulated, it is not advisable to use sealed bags for permanent storage of acidic materials. If comic books must be stored so that they can be viewed, polyethylene envelopes with buffered stiffener boards are available.
E. Open pamphlet files may be used for short-term storage of periodicals in good condition. The files allow easy retrieval, but they do not provide adequate support for long-term storage, nor do they protect periodicals without enclosures from light and dust.
Collections of paper ephemera provide the greatest challenge of all. Often size varies, the paper stock is poor, and people want to see the object itself. Common ephemera include postcards, greeting cards, brochures, and stereo views.
A. Collections of ephemera can be stored according to the recommendations for archival documents and pamphlets (see Case Studies I and IV). Before being placed in folders, fragile or small items should be placed in paper folders, envelope slings, or individual polyester enclosures for protection. Polyester enclosures are useful for any items that will be frequently handled. Where possible, ephemera should be sorted and stored by type and size, to prevent damage due to differing sizes and weights.
B. Collections of materials in a single format can be stored in polyester envelopes in appropriately sized boxes.
C. Albums and scrapbooks made of stable materials are another alternative for ephemera collections, especially for private collectors. A variety of 3-ring albums with plastic album pages and scrapbooks and scrapbook pages made from non-damaging materials are available.
Never attach ephemera with pressure-sensitive tapes, rubber cement, or damaging glues. Individual items can be attached to acid-free or buffered mounting paper using photo corners.
When objects have been mounted onto pages, they can be placed into polyester page protectors (sealed on one side), polyester sheet pockets (sealed on three sides), or polypropylene sheet protectors (sealed on three sides). Alternatively, polypropylene pages with various sizes of individual pockets are available; these are designed for popular sizes of photographs, but may also be appropriate for small ephemera. If an ephemera collection includes photographs, remember that any enclosures or pages that are to be used with photographs must pass the Photographic Activity Test.
Scope: Valuable and fragile books and other bound materials that require protection.
Book bindings are intended to protect the textblock, but sometimes the bindings themselves are so fragile or valuable that the books themselves require protective enclosures. Examples include: rare books that need additional protection against environmental pollution and light; fragile books that cannot stand upright on a bookshelf without sustaining damage; brittle books with loose pages; and damaged books that need temporary protection until a conservator can review and treat them. As more and more libraries rely on off-site storage, sturdy enclosures are also needed to protect items in transit.
Following are several options for protecting books and other bound materials. Ideally, enclosures should be custom-fit so that the items are not damaged by being jostled in the boxes. If a custom-made box is not possible, acid-free tissue paper can be used to fill the box around the volume.
A. Custom-sized rare book boxes provide maximum protection. Gaylord carries a selection ranging from prescored folder stock enclosures for lightweight books to sets of acid-free corrugated board that can be scored to create rare book boxes that are custom fit for larger or heavier books. A third alternative is a premade rare book clamshell storage box that comes with a supply of unbuffered tissue to wrap the book and gold title labels for the outside of the box.
B. Tying and wrapping are less expensive options. These are short-term solutions for items that need repair or treatment by a conservator. They also provide protection for less valuable items that are being sent to off-site storage. Wrap book in acid-free tissue or wrapping paper and tie with cloth pull fasteners or cloth tying tape.
C. Phase boxes are the traditional storage containers for library books. Gaylord Archival provides all the materials required to make phase boxes, including 60 pt. blue/grey board, washers and rivets.
D. Book jackets provide effective protection for book covers that are either valuable or vulnerable. Examples include books with modern dust jackets in private collections, bindings that would be damaged by fingerprints, and deteriorated leather bindings with "red rot*" that could spread to adjacent books. Custom-sized polyester jackets can be made for hardcover books from archival polyester. Do not use glue to attach the jacket cover to your book. If you use tape to attach the covers, apply from cover to cover. Do not apply tape to the bookbinding itself.
*Red rot is a disintegration of the leather into a red powder. Gaylord Archival carries the product Cellugel that consolidates the rotted leather so that the deteriorating book cover may safely be handled without danger of breathing the loose leather dust or soiling hands and clothes. However, it is recommended that you consult with a professional conservator on the proper use of Cellugel. In the interim, cover with a archival polyester book jacket cover, as described above, or isolate the book in a separate rare book storage box.