LibraryWorks - Archival Storage of Paper

Best Practices

Archival Storage of Paper

Courtesy of Gaylord

Introduction

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 article 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 "Guide to Conservation Services" (at http://aic.stanford.edu) that provides the names of conservators in your region. If you are unable to use the online guide, contact AIC at 202-452-9545 or email info@aic-faic.org.

Selecting Storage Materials

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.

TERMINOLOGY

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.

Highly Acidic    pH of Storage Materials

<------------------ ----------->

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

MOST ACIDIC NEUTRAL MOST ALKALINE

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, alkaline. These include blueprints and diazo reproductions, works of art with pigments that react to high pH, and albums and collages with wool or silk components. Some photographs and textiles may also be alkaline-sensitive.

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

Please Note: Product type and adhesives used in the enclosures. While cotton fiber makes the number references in most chemically stable paper and board, it is possible to make high quality text and photos along 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). Ground wood 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.

The American National Standard for Permanence of Paper for Publications and Documents in Libraries and Archives provides specifications for paper that will last several hundred years under normal use. This standard is intended for publishers and paper manufacturers, but can also be useful in evaluating paper enclosures.

TYPES OF ENCLOSURES

Boxes: The boxboard used for most document boxes is 60mils or points (pts.) thick (there are 1 000 points in an inch, so 60 pts. is .060 inches thick). Lighter weight stock (40 pt.) is sometimes used for small boxes. Boxes are also available with a polyester film laminate coating 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 non-buffered 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 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 in this article. For these materials, an unbuffered 100% cotton rag board is available. Mat board is available in two- and four-ply thickness. The heavier weight is 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 polyester sold under the brand Melinex, is recommended because it is very stable. It is used for various types of envelopes, sleeves, and folders. Polyester also comes in rolls or pre-cut sheets and is available in thicknesses of 1 to 5mil; 2 to 3mil is used for average-sized documents, while oversized prints and maps need the extra support of 4 to 5mil. 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.

Standards for Materials

While there is no one standard that specifically governs storage materials for paper objects, there are several standards that provide helpful information for evaluating individual products. These include the American National Standard for Permanence of Paper far Publications and Documents in Libraries and Archives, ANSI/NISO Z39.48-l 992 (R2002); Guidelines for In formation About Preservation Products, ANSI/NISO Z39.77-2001; and Photography— Processed Photographic Materials—Photographic Activity Test for Enclosure Materials, ISO 14523:1 999. 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. Responsibility for adherence to standards rests with the suppliers.

Preparing Collections

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 (71200) will protect items from dirt and oils on your hands. Do not eat or drink around collections. When moving paper documents or art- works, particularly brittle items, support the item carefully from below.

  • Remove extraneous materials—paper clips, rubber bands, wrapping material, old folders, and any other material that is not pertinent. If foreign matter (such as pressed flowers) must be saved as artifactual evidence, place it in a separate enclosure.

  • Unfold and flatten papers wherever possible without causing damage to the folds. Remove letters from envelopes. If the paper is brittle or inflexible, it may need to be humidified before unfolding. Consult a conservator for proper procedures. Prints, drawings, and extremely fragile or valuable items should be treated by a conservator. Once materials have been unfolded, remove surface soil with a soft brush. Isolate newsprint because it is highly acidic and will stain adjacent paper. Newspaper clippings can be replaced with photocopies on alkaline paper or placed into a separate envelope. Fax copies are similarly unstable and should be reproduced or isolated.

  • Note any badly damaged items—place them in individual folders, and set them aside for professional conservation treatment. Do not undertake any "first aid" unless you have received training and are qualified to do so.

  • If it is necessary to place identifying information on the object itself, use a No. 2 pencil and write on the verso or in the lower right margin. Repeat the identification on storage folders and envelopes in pencil or by applying typewritten labels. Never use ballpoint or felt-tip pens that might stain or bleed. Never apply labels directly to a document or work of art; labels are intended for boxes, folders, and other enclosures.

  • To the extent possible, store objects of similar size and weight together. If heavy or bulky items are stored with lighter ones, damage can occur from uneven pressure.

  • Label boxes with adequate information about their contents. This curtails unnecessary browsing and rifling through the documents.

Selecting Storage Furniture

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.)

The Storage Environment

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 70.2F 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.

Case Studies

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 Bros. can be used to solve the storage needs of paper collections.

CASE STUDY: DOCUMENTS

Scope: Documents, Manuscripts and Papers (letter or legal size).

  1. 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.

  2. Papers that are strong, flexible, and of similar size can be placed directly into acid-free folders. The number of items per folder depends upon the thickness of the paper, the condition of the paper, and the nature of the document. For example, a single folder can be used to house one valuable print, 10—15 older manuscripts, or 50 modern office records. Providing adequate protection is the primary concern. Folders come with and without reinforced tabs, in letter or legal sizes with full, half, third or fifth cut tabs.

  3. Papers that are acidic fragile, brittle, or torn need additional support and protection before placing them in folders. Options for protection include:

    (a) Paper folders or slings. Insert the item into a paper folder 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.

    (b) Individual polyester enclosures. These provide fragile or small items with protection from handling while retaining visibility.

    (c) 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 Object to separate valuable documents from highly acidic materials such as newsprint or replace newspaper clippings

  4. Paper envelopes can also be used to organize collections. Short or long side opening envelopes can house groups of papers or thin pamphlets on sturdy paper. Envelopes must be large enough for items to be easily inserted and removed without abrading the edges. If fragile papers or pamphlets are to be stored in an envelope, they must first be placed in a paper folder or envelope sling. Fragile papers or pamphlets need the added protection of a paper folder or sling before being inserted into an envelope or folder. 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.

  5. Groups of items can be placed into larger enclosures, depending on the size of the collection, where it will be stored, and how it will be used. Expanding folders are good for interim storage of collections that are growing rapidly, such as children's artwork, or active correspondence.

  6. 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.

  7. Upright storage in document cases is generally recommended for archival collections. All folders in a box should be the same size, and they should fit the size of the box. Folders must be adequately supported so that documents don't sag and become distorted. Folders should fill the box comfortably so that individual folders can be easily removed. 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. Adjustable document spacers can be purchased and fitted to your boxes. Dividers are also available to support and organize folders.

  8. Flat storage in drop-front storage boxes is sometimes appropriate, but also has some disadvantages. It gives overall support, prevents damage from slumping, and protects edges of brittle documents—but documents on the bottom of the box can be distorted by pressure from the items above, particularly if items in the box are different sizes and weights. If flat boxes are used, they should have drop-front construction to make safe removal of folders easier. They should be stacked no more than two high.

  9. Another acceptable storage alternative for paper documents is storage in a file cabinet with hanging folders. Acid- and lignin-free buffered hanging folders are available. Depending on how many items are in each folder, one or more folders may be placed in each hanging folder.

  10. 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.

CASE STUDY: OVERSIZED DOCUMENTS

Scope: Documents, Papers, Maps, Posters and Ephemera (larger than legal size).

  1. 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. 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.

  2. 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 (EAAB) which consists of corrugated boxes, file folders, L-sleeves and box labels, and is designed for horizontal or vertical storage of large documents.

  3. Large collections of oversized maps, posters, and architectural drawings are best stored inside folders in metal flat files. Shallow drawers 1-1/2 inches deep are preferable so that the folders on the bottom are not crushed. As with storage in boxes, folders should be sized to fit the drawer and all folders should be the same size.

  4. 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 (MJTS) 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.

CASE STUDY: WORKS OF ART

The storage of prints and drawings is outside the scope of this article. 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.

  1. 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.

  2. For long-term storage of prints and drawings, conservators recommend window mats. These should be stored flat in reinforced boxes. Although the size of the individual works of art may vary, they are often mounted in mats of consistent size and stored in flat storage boxes just large enough to accommodate the mats comfortably and eliminate any movement or shifting.

  3. Matted artwork requires sturdy boxes that can support the extra weight of the mats. Their inner depth should be only 1½ or 2 inches, again to keep the weight manageable.

CASE STUDY: PAMPHLETS

Scope: Single Signature Pamphlets and Small Booklets

  1. 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.

  2. 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.

  3. 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.

  4. 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.

CASE STUDY: PERIODICALS & NEWSPAPERS

Scope: Unbound Periodicals & Newspapers

  1. 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.

  2. Single issues of average size may be treated as pamphlets

  3. Thin and fragile items require additional protection. They should be inserted into folders and envelopes before being put into boxes.

  4. 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.

  5. 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.

CASE STUDY: EPHEMERA

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.

CASE STUDY: BOOKS AND OTHER BOUND MATERIALS

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.

  1. Custom-sized rare book boxes provide maximum protection. Gaylord carries a selection ranging from pre-scored 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 pre-made 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.

  2. 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. Pre-made jacket covers of 2mil polyester with acid-free paper backing would be suitable for modern books with dust jackets. Custom-sized polyester jackets can be made for hardcover books from Melinex®. 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.

  3. Cut a strip of DuPont Polyester film to height of textblock and 3 times textblock width plus book' thickness.

  4. Wrap the film around book so that ends are even.

  5. Using bone or Teflon folder, crease marks along fore-edge of book covers. Make crease marks at edge of spine, making sure DuPont film does not shift on book.

  6. On a cutting mat or other soft surface, line ruler up with dent marks and use folder to crease DuPont film, making sure creases are parallel. Fold along lines using folder to ensure fold is sharp.

* Red rot is a disintegration of the leather into a red powder.

For more information, please visit Gaylord at www.gaylord.com