The responses of digitally-printed materials to light are highly variable. Prints created using materials from the primary categories (e.g. inkjet, electrophotography, and dye sublimation) as well as sub-categories (e.g. dye or pigment inkjet) can behave very differently from each other when on display. Even more problematic is that individual products within each category can show even greater variations. For these reasons it is difficult to provide singular guidance that will prove accurate for all modern digital prints. This is not to say that guidance cannot be given, or will lack any value, it will just be critical for collection care personnel to keep a hawkish eye on these materials in their exhibitions. For this reason, accurate print condition assessments before and after exhibition will be crucial in order to track and record the effects of display on each particular object. Periodic assessments during the exhibition period will be even more important so as to catch potential deterioration before it is visibly noticeable or, unfortunately, objectionable.
The focus of these precautions is to highlight issues related to the display of digital prints that may differ from traditional print types. They do not address how to set up or monitor exhibit spaces in general, or issues surrounding transportation of materials to or from offsite exhibitions. Additional concerns beyond just light will also be of concern to objects on display, including temperature, humidity, and the presence of airborne pollutants. All of these will exacerbate any decay induced by light and further reduce the useable life of the object.
Identification or verification of the types of prints intended for inclusion in an exhibit will be the first step. If a print is confirmed as an inkjet print, then a determination of whether the colorant used was dye or pigment will be critical, as dyes can be considerably more sensitive to light than pigments. However, even pigment prints will eventually fade and should not be assumed totally resistant to decay on display. Additionally, many printing papers, especially those specially coated for inkjet inks, can dramatically deteriorate on display and become yellowed or embrittled. Visit the DP3 Print Comparision Tool for more information.
Dye sublimation prints behave very much like chromogenic photographs when on display. For this reason, the same exhibition policies and materials can be used for both. The primary concern will be fading of the dyes. The rate of fade can be significantly reduced through proper lighting and framing. One positive difference between the two processes is that, unlike chromogenic, dye sublimation prints are not prone to yellowing. Special care should be given to dye sublimation prints made before or about 1994 as these will not have the protective overcoat that minimizes pollutant and moisture-induced damage. Display of pre-1994 dye sublimation prints is discouraged unless the absolute best lighting and environmental conditions are available, high-quality framing materials and techniques are used, and ongoing monitoring of the print’s condition is performed. All dye sublimation prints should be exhibited framed and glazed to provide physical protection and reduce UV exposure. Framing materials should meet ISO 18902:13 Imaging materials -- Processed imaging materials -- Albums, framing and storage materials.
Since laser prints are created using a process very similar to photocopies, they can be treated according to the existing care practices for the latter. One difference is that many laser prints, especially those most recent, are likely printed on alkaline papers, making them even more resistant to decay than their analog predecessors. Also, many laser prints, even if just black and white, may have been printed on a color laser printer. Theses colors may not be as fade resistant as pure black, so the objects should be periodically monitored for change when on display. Prints created on electrophotographic digital presses, both liquid- and dry-toner types, can be exhibited following the same materials and practices currently used for offset lithographic prints. Again, framing materials should meet recognized guidelines such as ISO 18902:13 Imaging materials -- Processed imaging materials -- Albums, framing and storage materials.
Inkjet prints are the most difficult of the three primary digital print processes to address. This is because the sensitivities of the different colorants and papers are so highly varied. Even prints of the same general type but made using different brands of ink and paper can behave in ways that are remarkably distinctive from each other. In addition, damage can come in many forms including fade, yellowing, cracking, and delamination. In some cases damage may not appear until an attempt is made to remove the print from the frame. Such handling stress may suddenly induce significant cracking and flaking in a print that otherwise showed no fade or yellowing.
In general, inkjet pigments are more resistant to fade than dyes. This does not necessarily mean that pigment inkjet prints are robust when on display for extended periods. Pigments can fade, just at a slower rate. Also, many inkjet printing papers can be used for either dyes or pigments with some examples being highly sensitive to decay by yellowing, embrittlement, or even increased sensitivity to abrasion and scratch. For these reasons equal care should be given to both dye and pigment inkjet prints and all should be thoroughly assessed before and after exhibition with additional periodic inspection during exhibition to catch problems early and remove from display if needed. Exhibition lighting should follow established practices for chromogenic photographs or prints and drawings containing fugitive colorants and sensitive supports.
Light and Pollution Synergies
Many inkjet colorants and papers can be extremely sensitive to pollutants, such as ozone, and light can exacerbate that sensitivity. It is even possible that dosing the print with pollution during exhibition may show no damage initially but changes, especially yellowing, can follow in subsequent storage. For these reasons, inkjet prints should be exhibited framed with glazing to minimize air flow across the print’s surface and protect from UV exposure.
Dye Inkjet and Humidity
As mentioned previously, environmental conditions of exhibition areas can have a major impact on the decay rates of the objects being displayed. One area of high concern involves dye inkjet prints in uncontrolled-humidity environments. These objects may show color bleed even after only short periods above 70% RH. Exposure to even higher humidities can cause severe and irreversible damage to some prints in much less than 24 hours.
Framing Materials for Inkjet Prints
The ISO 18902:13 Imaging materials -- Processed imaging materials -- Albums, framing and storage materials should be used for inkjet prints. While this document is specifically intended for photographs, the guidelines are a good starting point for selecting mounting and framing materials for other inkjet-printed object types such as fine art, graphics, documents, and ephemera. This standard provides specifications for framing materials to be inert in contact with prints over time. Various requirements from pH to lignin levels are given. The table to the right shows the keys elements of the document; however, institutions should purchase the standard and become familiar with all of its provisions.
First and foremost will be to make sure the print has dried fully before framing as some paper types can hold significant quantities of water from the printing inks for extended periods of time. If framed too early, this moisture can slowly exude into the frame package, elevating the humidity inside. The time for curing will vary from print to print based on a number of factors including the ink and paper chemistries as well as the printing and drying environments. Some prints may take as long as two weeks to cure.
Another particular area of concern is when using the standard to select adhesives for mounting. Pressure sensitive adhesives (PSA) should not be used directly on inkjet prints. This applies to either dye or pigment inkjet. While most PSA will be non-reactive, some may cause deep yellowing in a matter of months. The mechanism of cause is not yet known and no test method exists to predict the problem. For these reasons no PSA should be applied directly to inkjet-printed art, photographs, or graphics even if they otherwise meet ISO 18902 or pass the Photographic Activity Test.
Caution should be used when applying water-based adhesives to the reverse of image areas printed with dye inkjet as the moisture can wick through the paper and cause bleeding of the colorants. Water-based adhesives may be carefully applied to areas that are not directly behind colorants such as unprinted, white borders. It is also possible that hydroscopic adhesives, such as starch, may cause no harm when initially applied, but may later absorb enough moisture from the air to induce bleed to a dye printed on the other side.
ISO 18902:2013 also stipulates that glazing limit UV exposure to the object. Only glazing (acrylic or glass) that blocks 97% of UV energy from 300 nm to 380 nm should be employed. This approach has been shown to help reduce the rates of colorant fade, paper yellowing, and embrittlement of inkjet receiver layers. Note that plain glass or acrylic glazing without additional UV filtering does not provide adequate protection against these types of damage.
Over-matting image areas may result in abrasion or scratching of printed colorants under the mat. This can be prevented by matting only over unprinted borders. If this is not possible, then minimizing compressive force on the print by the mat will reduce the chance for damage.
Finally, in addition to framing, a variety of other materials (such as rigid supports, liquid or spray coatings, and laminates) and techniques (such as face mounting) have been used to mount and display inkjet prints. These were not included in the original DP3 Project simply because the extremely large number of possible combinations made it untenable at the time. Unfortunately, because the performance of these materials and techniques over many years will likely be highly variable, existing anecdotal experience with objects will not be a reliable guide for predicting future results even with very similar prints.
Monitoring Prints on Display
Because it will not be possible to predict the long-term display behavior of any print, it will be necessary for collection caretakers to understand each object as best as possible and develop an exhibit plan that matches its unique needs. From here, periodic monitoring will be very important, especially for the dye-based processes (dye sublimation and dye inkjet) as well as fine art and photo inkjet papers. Collecting and periodically reviewing ongoing records of display conditions (temperature, humidity, light, and air pollutants if possible) will be helpful in identifying potential problems before they cause damage or, if necessary, understand why some objects may have changed during exhibition. It should be emphasized that for the most sensitive materials, display of facsimiles may the best form of protection.