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Storage and Handling
5.6 Storage Enclosures for Photographic Materials

Storage enclosures for photographic prints and negatives are available in a variety of materials and formats. One must decide between buffered or non-buffered paper, paper or plastic, polyester or other plastics, sleeves or envelopes. Choosing the proper enclosure requires a knowledge of the alternatives. This leaflet reviews the various options, discussing advantages, disadvantages, and special precautions for each. Whatever enclosure is chosen, photographic prints and negatives should not be handled with bare hands. Oils and perspiration can damage emulsions. Lint-free gloves are available from conservation or photographic suppliers.

All enclosures used to house photographs should meet the specifications provided by the International Organization for Standardization (ISO) ISO Standard 18902: 2001. 1 The standard provides specifications on enclosure formats, papers, plastics, adhesives, and printing inks, and requires a variety of enclosure tests.

Paper Materials

The quality of pulp used to make storage paper is important to the preservation ofphotographs. Groundwood, from which many modern papers are made, contains lignin, which produces acids rapidly. Papers described as lignin-free are produced from cotton or linen (containing little lignin) or from wood fibers that have had the lignin chemically removed. Lignin-free buffered and non-buffered (neutral) paper enclosures are available.

The term acid-free is widely used to refer to archival-quality paper materials constructed of either neutral or buffered paper. A more precise distinction should be made between the two. Neutral enclosures, constructed of paper in the neutral pH range (6.5–7.5), do not contain acids that will damage photos stored in them, but have a limited capacity to neutralize acids from the environment or from paper deterioration. Buffered paper enclosures (pH 7.5–9.5) contain an alkaline material (such as calcium carbonate) that neutralizes acids as they form. In the past, conservators have recommended the use of neutral paper enclosures for storage of color images, cyanotypes, and albumen prints. It was believed that these processes were sensitive to the alkalinity in buffered papers. Recent research has indicated that buffered storage enclosures are not detrimental to photographs. Therefore whether paper is neutral or buffered is not a major criterion for choosing an enclosure.

Labels such as acid-free do not guarantee that a material is safe when used with photographs. Even archival papers may be harmful to the photographic image. The only way to be certain of the inertness of the paper is to have materials undergo the Photographic Activity Test (PAT) as specified in ISO 14523: 1999. 2 The PAT has two components: a test to detect image fading resulting from harmful chemicals in enclosures; and a test to detect staining reactions between enclosures and gelatin. Consumers should contact suppliers of archival materials to see if their products comply with ISO 14523: 1999, and have passed the Photographic Activity Test. 3

When PAT test results are not available, purchase materials from suppliers familiar with the special needs of photographs, and choose enclosures that are lignin-free, 100% rag, and not highly colored. Glassine enclosures are not recommended. Glassine paper is made with short, brittle wood pulp fibers, which are prone to rapid decay. Often in the pulp are additives which increase the flexibility and translucency of the paper. Therefore, glassine has three sources of potential harm to photographs: possible impurities from wood pulp, possible harmful additions, and deteriorating paper fiber.

In recent years, MicroChamber and other pro-active storage papers have become available. These scavengers contain activated charcoal and zeolites, which react with polluting gases, trapping them and removing them from the environment. These papers can moderate the destructive effects of pollutant gases. They may be particularly beneficial in an uncontrolled environment, especially if the collection contains color photographs, nitrate film, or early safety film.

Advantages and Disadvantages of Paper

  1. Paper enclosures are opaque, protecting the object from light. However, this makes viewing difficult, requiring the removal of the object from the enclosure. This increases damage from handling, abrasion, and fingerprinting, especially in heavily used collections.
  2. Paper enclosures are porous, protecting the object from the accumulation of moisture and detrimental gases.
  3. Paper enclosures are generally less expensive than plastic enclosures.
  4. Paper enclosures are easy to write on.

Seamed Paper Envelopes. An envelope is an enclosure with one open end; it may have a protective top flap. The seams in paper envelopes should be located at the sides and, if unavoidable, across the bottom. Any adhesives used in construction should be non-acidic and unreactive with silver. Most envelopes come with a thumb cut, but those without are preferred. Thumb cuts allow air to touch the photograph, and encourage users to grasp the photograph and pull it from the sleeve. Rather, to remove a photograph, push in slightly on the sides of the envelope, and tap the photograph out, handling only the edges. With seamed envelopes, the photograph should be inserted with the emulsion side away from the seam.

Seamless Paper Envelopes. The seamless envelope does not have any adhesive. The envelope is formed with three or four flaps which fold over to produce a pocket. The fourth flap, if present, closes the envelope completely, protecting the object within from dust and dirt. The construction of this envelope encourages the user to place the object on a flat surface to open it, which can be an advantage for brittle or fragile items such as glass-plate negatives. Also, this type of enclosure is constructed so that it can compensate for the thickness of an object.

Paper Folders. A folder is a sheet of paper that is folded in half. It is closed on one side only and must therefore be kept in a properly fitted box to hold the image effectively. If a paper folder is used for vertical storage in files, the photograph stored inside must be well supported to prevent sagging or curling. Folders are simple to make and are most useful for large or mounted items.

Plastic Materials

Plastic enclosures of archival quality may be made of polyester, polypropylene, or polyethylene. They should not be coated or contain plasticizers or other additives.

Polyester is the most inert, dimensionally stable, and rigid of the three. It can generate static electricity, which attracts dust, and it is expensive. Polyester enclosures should be ICI's Melinex #516.

Polypropylene is almost as rigid as polyester when it is the untreated "oriented" polypropylene used in sleeve formats, but is soft when it is the surface-treated polypropylene used for ring binder storage pages. Because specifications on the surface coatings of the soft polypropylene are proprietary information and not readily available, this material cannot be properly evaluated.

Polyethylene is the most easily marred and least rigid of these plastics. High-density polyethylene is a translucent, milky plastic which is naturally slippery. Low-density polyethylene, the clear polyethylene used in ring-binder storage pages, has incorporated antiblock and antislip agents which could be problematic.

Plastic enclosures made from polyvinylchloride (PVC) are unacceptable for archival photographic storage. This plastic, often referred to as "vinyl" by suppliers, is not chemically stable and will cause deterioration of a photograph over time.

Advantages and Disadvantages of Plastic

  1. Plastic enclosures have the great advantage of allowing an image to be viewed without being removed from the enclosure. This greatly reduces the chance of abrading, scratching, or fingerprinting the photograph, especially in heavily used collections.
  2. Plastic enclosures can abrade and scratch photographs during insertion and removal. Matte or frosted surfaces are not recommended as they are abrasive to emulsions. Low-density polyethylene also can have problems with abrasion. Abrasion can be avoided by minimizing the removal of photographs from enclosures, using properly designed enclosures (such as self-locking sleeves), or using plastics that are naturally slippery (high density polyethylene).
  3. Moisture and sulphides in the environment react with photographs to hasten their deterioration. Plastic enclosures protect the object from the  atmosphere.
  4. Plastic enclosures can trap moisture and cause ferrotyping (sticking with resulting shiny areas) of the image. This is a particular threat in storage environments with high relative humidity or in the event of a disaster involving water. Those plastics more prone to ferrotyping include surfacetreated polypropylene and low-density polyethylene.
  5. Plastic enclosures can be difficult to write on.
  6. Plastic enclosures can be flimsy and may require additional support, such as archival-quality Bristol board. Any information that should accompany the image can be recorded on this board.
  7. Plastic enclosures with low melting points (polyethylene) can melt during a fire, adhering themselves irreversibly to the materials stored inside them.

Plastic Envelopes. Plastic envelopes normally have heat-sealed seams, which eliminate any potential problem with adhesives. Both polyethylene and polyester envelopes are marketed by conservation product suppliers.

Plastic Folders. These may be successfully used in conjunction with paper envelopes, the polyester folder protecting the image from handling whenever it is removed from the paper envelope.

L-Velopes. These are a combination envelope-folder, being an envelope sealed on two adjacent sides. This allows for easy insertion and removal of objects, and provides more support than a folder. This design is particularly useful for smaller-format images.

Plastic Sleeves. Often these sleeves are enclosures open at two opposite sides made from polyester or polypropylene. Usually, these sleeves are a one-piece construction with a self-locking fold on one edge (also called top-flap sleeves). This fold provides for easy insertion and removal of the photograph with no abrasion to the image. However, when these sleeves are stored in groups, the folds can lock onto adjacent sleeves, making retrieval of the photographs difficult.

Polyester Encapsulation. Polyester encapsulation encloses a photograph between two sheets of polyester, sealed on all four sides with either double-sided tape or a special polyester welding machine. Encapsulation provides physical support and protection from the environment. It is useful for storing fragile prints, especially those that are torn. Encapsulation is not recommended for photographs adhered to poor quality mounts or for contemporary color photographs.

Ring-Binder Storage Pages. These pages are made to fit three-ring binders with slipcases. They are available in a wide variety of formats, sizes, and materials, including polyester, polypropylene, and polyethylene. They are an excellent alternative for small, concentrated collections of uniform size.

Polyester Sheet - Matboard Folder. These folders are made of a sheet of polyester and a sheet of matboard of the same size, attached together along one long edge with doublesided tape. The matboard gives needed support and the polyester allows the image to be easily viewed. These folders should be stored flat. They are particularly useful for storage of oversized photographs or photographs on rigid mounts. In time these folders will probably need to be replaced or the double-sided tape will break down, releasing the polyester from the folder and possibly sticking to the object.

Polyester Sheet Within a Paper Folder. This enclosure consists of a paper folder with a polyester sheet attached along an inner edge, opposite the center fold. The attachment is made with double-sided tape. The polyester holds the object in place and protects it from dirt and handling, but allows for easy viewing and removal. The paper folder provides support to the image and protects it from light. These folders are especially useful for small, fragile prints. However, over time the double-sided tape will release, necessitating folder replacement.

Summary

Many of the enclosures available for photographic storage have been described above. Each has been discussed individually, but often two enclosures can be combined to form another format with its own characteristics. An example is the use of polyester folders with seamed paper envelopes. Each of these systems has advantages and disadvantages. The final choice of enclosure will depend upon the particular needs of a collection and the available funds.


Written by Gary Albright

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