In order to be successful at making good storage enclosure decisions, it will be important to be able to identify and segregate different print types so that the correct enclosure material and design can be used. It is highly recommended that users of these recommendations begin by studying the Print Comparison Tool in the Identification section of this site.
The primary purpose of storage enclosures is to provide physical protection for the object while not also posing a physical or chemical threat itself. Enclosure surfaces are also often used for labeling either directly by using pen, pencil, or ink stamp, or by the application of printed pressure sensitive labels. In these recommendations, we will only consider enclosures for storage and not for display which would include mounting adhesives, frames, and glazing. Mat board will be considered as many objects are stored matted. For recommendations on framing materials see Precautions for Display.
Note that the following approach is based on two existing ISO standards, 16245 Information and documentation - Boxes, file covers and other enclosures, made from cellulosic materials, for storage of paper and parchment documents, and18902 Imaging materials - Processed imaging materials - Albums, framing and storage materials, as well as research on this subject performed by IPI as part of their DP3 Project. A majority of potential problems will be averted if, at the very least, these standards are utilized when procuring storage materials. However, they are not completely satisfactory due to some unique issues associated with certain inkjet print types and products (see below). Institutions should purchase these standards and collection care personnel should become familiar with their requirements.
Note that objects safe to house in enclosures that meet ISO 18902 will also be safe in enclosures that meet ISO16245, as the former is more restrictive. However, collection objects requiring the use of ISO 18902 should not be assumed safe in those deemed acceptable by ISO 16245. Because of this, procurement can be simplified by using ISO 18902 for all enclosure materials.
Dye sublimation and traditional color photographic prints are similar enough in composition and performance over the long-term that they can be housed using the same storage enclosure guidelines detailed in ISO 18902 Imaging materials — Processed imaging materials — Albums, framing and storage materials.
Desktop and office laser printers are typically used to create documents, though they are occasionally used for ephemera, imaging, fine art, and other purposes. Electrophotographic digital presses are used to print additional objects type such as mass advertisements, books and periodicals. Because laser printers are essentially digital versions of photocopiers, printouts from these modern devices can be cared for like those from the earlier analog equipment. There are two important differences. First, the modern color laser printers do a better job fusing the colorants to the paper surface, so they are more resistant to abrasion. Also, as color laser printers did not appear until 1993, the paper they are printed on is highly likely to be alkaline as opposed to acidic, since the switch from acid to alkaline paper by the papermaking industry occurred during that period. This means that color laser prints are likely to be inherently more stable than older B&W laser and both color and B&W photocopies. For these reasons, IPI recommends the use of the ISO 16245 Information and documentation - Boxes, file covers and other enclosures, made from cellulosic materials, for storage of paper and parchment documents standard to select paper enclosures for these objects. If plastic enclosures are desired then ISO 18902 Imaging materials - Processed imaging materials - Albums, framing and storage materials may be used. It is important to emphasize that polyvinyl chloride (PVC) plastics should never be used, as their chemistry can soften printed toner causing permanent transfer from the document to the plastic.
It is more difficult to select safe enclosures for inkjet because of the diversity of the ink and paper formulations used, as well as the variety of print formats (e.g. photos, documents, fine art, ephemera, etc.). It will also be helpful to differentiate dye and pigment inkjet, as the latter is more sensitive to abrasion.
Inkjet Documents, Books, Periodicals and Ephemera
When printed on plain papers, and whether dye or pigment, inkjet can be stored using enclosures that meet ISO 16245 Information and documentation - Boxes, file covers and other enclosures, made from cellulosic materials, for storage of paper and parchment documents. If a specialty office paper (e.g. presentation paper, inkjet-specific paper), as opposed to a plain office paper, was used to create the object, then the requirements of ISO 18902 Imaging materials - Processed imaging materials - Albums, framing and storage materials should be followed. If plastic enclosures are used for inkjet on any paper, then ISO 18902 should be used.
Inkjet Art, Photographs, and Graphics
Inkjet objects printed using specialty imaging or graphics papers (e.g. photo, fine art, etc.) need a more thoughtful approach to housing because of their unique physical and chemical properties. For these reasons, the more restrictive ISO 18902 Imaging materials - Processed imaging materials - Albums, framing and storage materials should always be used as the basis for selecting their enclosures; however, IPI recommends, based on the DP3 Project research, that for some objects, additional restrictions above and beyond the standard also be followed.
While ISO 18902 allows the use of pressure sensitive adhesives (PSA) directly on photos for mounting purposes, these adhesives should not be used directly on fine art inkjet prints or photographs. This applies to either dye or pigment inkjet. While most PSAs will be non-reactive, some can cause deep yellowing in a matter of months. The chemical mechanism of this problem is not yet known and no test method exists to predict the reaction. For these reasons, no PSAs should be applied directly to inkjet-printed art, photographs, or graphics even if they meet ISO 18902 or pass the Photographic Activity Test (see below).
Water-based adhesives (such as starch pastes used for hinging) should not be used on the versos of printed areas in dye inkjet prints as the moisture can migrate through the paper and induce bleed of the colorants. It may be carefully applied to areas that are not directly behind colorants such as white borders. Additionally, adhesives that remain hygroscopic after drying can pull additional moisture into a print over time, further damaging dye-based images.
The surface of pigment inkjet prints, or dye inkjet that used carbon pigment for the black ink, can be extremely sensitive to abrasion. For this reason only smooth plastic films, such as polyester sheeting, should be used in contact with print surfaces. It is important to point out that if high pressure is applied to the plastic, even without movement, the abrasion may still occur. The optimal approach is to not allow any material to contact the print’s surface. This can be achieved using window mats to keep the objects separated while stacked. This may not be possible for extremely large prints, in which case the plastic sheeting and extreme care should be used. If window mats are used, it should be noted that over matting of a printed edge can result in abrasion damage under the mat.
Prints should also not be stacked in boxes or other enclosures in direct contact with each other or with potentially abrasive interleaves. As stated above, many inkjet prints are significantly more sensitive to abrasion than traditional photographic materials, so even photograph-safe interleaving papers should not be used. IPI research showed that even high-quality interleaving papers could cause colorant smear or polishing/burnishing of the image (see below). Smooth plastics are preferred. In general, it may be best to treat the surfaces of inkjet fine art, especially pigment inkjet, more like pastel or charcoal drawings than photographs.
Enclosures can be fabricated from a single material such as a paper folder made from a sheet of cardstock, or it can be more complex such as boxes made of stiff binder’s boards covered with a decorative material on the outside and a white paper on the inside. Different adhesives are often used at various stages of the box’s fabrication. Each component can contribute to the utility and stability of the enclosure, but it can also contribute to deterioration of objects housed inside. The potential reactivity of all enclosure components should be considered.
Comments on the Photographic Activity Test
IPI believes that all enclosures intended for use with traditional photographs should pass the photographic activity test (PAT). The test has also been used to evaluate enclosures for some digitally-printed images: inkjet, electrophotography, and dye sublimation; however, the test has not been 100% effective at separating certain reactive mounting adhesives for inkjet prints (see above). Results of the PAT are important when selecting storage enclosures for digitally-printed objects as they will catch many potentially harmful interactions, but they may not be a guarantee of safety, especially with respect to adhesives.
Cautions on Environment
Selecting safe storage enclosures is not sufficient to prevent deterioration of digital print materials. Many other factors affect the potential longevity of digitally printed materials when in storage, including the temperature and humidity of the storage area as well as the presence of airborne pollutants. Ongoing monitoring and evaluation of storage environments can be help in spotting developing harmful trends before they fully emerge. Such data can also be used to determine if any damage to the digital prints in the collections can be attributed to inadvertent fluctuations from intended standards. See Recommended Storage and Sustainable Preservation.