IPI Guide to Preservation

IPI Print Preservation Guide

Introduction

This guide provides basic information on the storage and preservation of digitally-printed photographs in scholarly and cultural collections. While there are many printing technologies for output from computers, this guide focuses on the three most popular forms of image (i.e. pictorial) hardcopy:

  • Inkjet
  • Digital electrophotography
  • Dye sublimation

Information on recommended storage conditions, selection of housing and framing materials, proper handling and display are included. Collection care personnel in cultural institutions are the intended audience for this guide, however, it will also be useful to photographers, artists, and the general public.

Digital Print Perservation Portal (DP3)

Since 2007, the Image Permanence Institute (IPI) has been evaluating the stability of digitally printed materials and developing techniques for mitigating damage and extending their useful lives. Years of laboratory research have characterized the strengths and particular vulnerabilities of the major digital printing materials and technologies. Results have led to some significant conclusions on the preservation of these objects including:

  • Digitally-printed photographs are highly variable in their sensitivities to decay forces
  • Cold storage significantly reduces deterioration rates caused by natural aging and pollution, especially for inkjet
  • Prints made using pigment inkjet can be very sensitive to abrasion
  • Inkjet dyes can bleed when exposed to high humidity even for short periods
  • Prolonged exposure to light can cause fade, yellowing, and embrittlement of both dye and pigment inkjet-printed photographs
Digital Print Preservation Portal logo

All of the work has been under the umbrella of the DP3 (Digital Print Preservation Portal) Project. Funding for the DP3 Project was provided by grants from The Andrew W. Mellon Foundation and the Institute of Museum and Library Services (IMLS). This guide presents a summary of research results with recommendations for preservation. The project website, www.DP3Project.org, contains all of IPI's scientific research in this area as well as supplementary information to aid in the care of digitally-printed photographs including descriptions of the materials and technologies for each type, an online print identification tool, examples of deterioration, best practices for care, and additional resources.


Storage Conditions

A variety of harmful forces can affect collection objects in storage resulting in multiple decay manifestations. For digital prints the primary drivers of deterioration are heat, moisture, and air pollutants, though each print type has its own unique sensitivities. Signs of decay include image fade, paper yellowing, ink bleed, and cracking or delamination of paper layers. Table 1 shows the types of damage that can result from each environmental factor. Control of temperature, humidity, and air quality can significantly extend the lives of these materials.

It should be noted that the sensitivities of digitally-printed photographs to damage are highly variable and product dependent. At times the behavioral differences between materials within a category are greater than those between categories. For example, photos printed on two different manufacturers' inkjet printers using equivalent ink and paper types can have radically different deterioration rates due to subtle variations in colorant and paper formulations. For this reason all objects should be treated as individually as possible with condition assessments made on a regular basis.

Temperature and Humidity Recommendations

As with most collection materials, temperature and relative humidity (RH) control the natural aging rates of digital prints. Extremes of either can cause significant additional damage that would not occur under proper storage conditions. IPI data has shown that, in the absence of pollutant gases, digital print inks, dyes, and toners are fairly robust at room temperature and moderate humidity. However, many of the inkjet printing papers can be prone to significant yellowing and even deterioration of the ink receiver coatings. Lower temperatures can reduce these rates of decay. For this reason IPI recommends cold storage for inkjet prints.

The recommended maximum storage temperatures and relative humidity ranges for each digital print process, based on IPI's data from the DP3 Project, are shown in Table 2. Recommendations from the IPI Media Storage Quick Reference (MSQR) for traditional blackand- white and color photographs are provided for comparison. Note that the recommendations for inkjet supersede those of the MSQR which was published before the extensive digital print preservation research at IPI.

Table 1. Risk Factors for Storage Envionments

risk factors for storage environments

Table 2. IPI's Recommendations for Digital Print Storage

Managing the storage environment

Humidity Extremes and Inkjet

High humidity should be avoided for all photograph types to prevent blocking, ferrotyping and mold growth. However, inkjet dyes can also bleed severely when exposed to high humidity causing noticeable image blurring and color fringing. Figure 1 shows the time to bleed for a susceptible inkjet print at 25°C (77°F). All conditions to the right of or in the dark gray area should be avoided. Prints should be safe below 65% RH. However, time to bleed rapidly diminishes as RH increases. Prints equilibrated to 80% RH or higher can show noticeable bleed in less than 24 hours. Very low humidity should also be avoided as it can exacerbate brittleness of some inkjet print layers making handling more risky. Like traditional photographs, digital prints should always be handled in RH conditions above 25%. This will be especially true for prints that have been on display because light and pollution exposure can increase the brittleness of surface layers over time.

Simplified Mixed Photograph Storage

Since few institutions can provide special storage areas solely for digitally-printed photographs, these objects will need to be integrated with other collection materials. Fortunately, the basics of traditional photograph care can, with a few exceptions, be applied to digitally-printed photographs. IPI's MSQR provides information on thoughtfully merging multiple traditional media collection types into four or fewer common storage conditions. Table 3 provides qualitative ratings for each material at each storage condition and Table 4 defines the rating system. The temperatures in Table 3 correspond to general storage categories from the IPI MSQR.

Figure 1. Dye Inkjet bleed limits on an inkjet print at 25°C (77°F)

Dye inkjet bleed limits
Qualitive rating system

Table 3. Mixed Media Collections


Air Pollution

Pollution comes from a variety of sources including the air in the storage environment, housing and framing products, adjacent collection materials, and from within the object itself. Of these, the greatest threats to digital prints are air pollution and poor quality/reactive enclosures. Enclosures are addressed more fully on page 5. A variety of gases in the air can cause damage to digitally-printed photographs. Oxidizing agents such as ozone can cause fade or yellowing of many print types as well as embrittlement of inkjet paper coatings. Nitrogen dioxide can induce yellowing in all print types and bleed in some dye inkjet prints. For these reasons, exposure to air that has not been adequately filtered must be minimized. The reduced storage temperatures recommended on page 2 can help mitigate pollution-induced damage, but they are not equally effective for all gases. Nitrogen dioxide is strongly impeded, while ozone attack is only marginally slowed. Enclosures of low permeability, such as polyester sleeves, are helpful in reducing the rate of pollutant damage.

Air pollution comparison images

Housing and Framing Materials

Storage enclosures should provide physical protection for the object and should not pose a physical or chemical threat. Potential problems associated with enclosures include abrasion (resulting in scratches, scuffing, or smearing of colorants), yellowing of paper supports, and blocking or ferrotyping of print surfaces.

The approach suggested here is based on ISO Standard 18902 Imaging materials - Processed imaging materials - Albums, framing and storage materials, as well as research completed as part of the DP3 Project. A majority of potential problems will be averted if, at the very least, this standard is utilized when selecting storage materials. We recommend that institutions purchase Standard 18902 and become familiar with its requirements.

The ISO Standard can be applied directly to both dye sublimation and digital electrophotography. It is worth noting that vinyl plastic (PVC) enclosures should not be used with any imaging material - this is especially true for electrophotography because the plasticizers in the sheet can soften toner and pull it from the surface of the print.

It is more difficult to select safe enclosures for inkjet because of the diversity of ink and paper formulations used as well as their individual chemical and physical responses to enclosure materials. The ISO Standard is not completely satisfactory for inkjet prints due to some unique issues associated with certain damage types including adhesive-induced yellowing and bleed as well as abrasion.

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 inkjet 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 PSA should be applied directly to an inkjet photograph even if it meets ISO 18902 or passes the Photographic Activity Test (PAT).

Water-based adhesives (such as starch pastes used for hinging) should not be used on the verso of printed areas in dye inkjet prints because the moisture can migrate through the paper and induce bleed of the colorants. They 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 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. The optimal approach is not to allow any material to contact the print's surface. This can be achieved by using window mats to keep the objects separated while stacked. This may not be possible for extremely large prints, in which case smooth plastic interleaving and extreme care should be used.

Colorant smear example

Display Recommendations

The major concerns for digital prints on display are fade of the colorants, yellowing of the papers, and/or embrittlement of surface coatings. Exhibition procedures should follow established practices for chromogenic prints such as the American Institute for Conservation of Historic and Artistic Works Photographic Materials Conservation Catalog - Exhibition Guidelines for Photographic Materials. The primary cause of damage is ultraviolet (UV) radiation; however, energy in the visible spectrum can also contribute to decay. Digital prints should be framed with glazing to physically protect the surface and to protect against pollutant exposure. The glazing should block at least 97% of the UV energy. Framing materials should meet the requirements described above. As with storage spaces, environmental conditions have a major impact on the decay rate of material in exhibition areas. Exposure to extremes in humidity and high levels of pollutants must be avoided. Limiting display times and routine monitoring of prints on display can prevent noticeable and objectionable change.