Completion of IMLS Funded Project: Pollution Damage Mitigation for Inkjet Printed Materials in Museum Collections
IPI received funding from the Institute of Museum and Library Services for a three-year, major research and development project aimed at creating effective strategies to mitigate the damage to modern, inkjet-printed materials caused by airborne pollutants. This was in response to a 2008, IPI survey of the field, which had found that approximately 80% of cultural heritage institutions already have inkjet prints in their collections and that objectionable deterioration to many of these materials has already occurred including (but not limited to) fading, yellowing, color bleed, surface cracking and delamination. Earlier IPI experimental work established a clear connection between ozone and nitrogen dioxide and each of these forms of decay.
Figure 1 below illustrates what can happen when prints are exposed to high concentrations of ozone. The first print shows dramatic fade where almost the entire image is destroyed. The second image shows significant fade, but the black areas of the image have also shifted to a bronze color. The last image shows moderate fade but also heavy yellowing causing additional color shift in the image.
The next two images (figure 2) illustrate an original print and one that has not only faded but the image layer has cracked causing portions of the ink receiver layer to delaminate leaving large losses.
The final example below illustrates a unique effect of nitrogen dioxide on some inkjet prints, image bleed (figure 3). Image bleed has typically been associated with high humidity, but tests at IPI have shown that nitrogen dioxide can induce significant bleed even under moderate humidity conditions such as 50% RH. Like ozone, nitrogen dioxide can also cause fade and yellowing.
Fortunately, deterioration due to pollutants occurs by chemical reaction and may potentially be slowed by reducing temperature or by minimizing contact between the pollutants and the collection objects through the use of enclosures. The particular experiments in this project attempted to quantify the overall effectiveness of low temperature in slowing attack by atmospheric ozone and nitrogen dioxide, as well as the degree of protection afforded by common enclosures (sleeves, envelopes, and boxes) made of paper or plastic.
Reduction of Pollutant-Induced Deterioration through the Use of Lower Temperatures
The first step was to quantify how temperature affects the rate of pollutant-induced decay in inkjet-printed materials. IPI used the Arrhenius Method as the basis for this work.Special detectors were created on several inkjet printers (figure 4). These detectors were typical inkjet print materials previously determined to be highly sensitive to pollutant-induced fade and bleed. These highly sensitive examples would act as a sort of miner’s canary and provide the most conservative results.
The detectors were exposed inside IPI’s existing pollutant testing apparatus (figure 5) to each pollutant at a series of increasing temperatures with the relative humidity held at 50%. Test samples were removed at predetermined intervals to track the changes to the targets over time. At each interval, the detectors were measured for fade and yellowing. In addition, the materials exposed to nitrogen dioxide were measured for colorant bleed.
From the test exposures for each temperature, the incubation time required to reach noticeable fade or yellowing was determined. Using the Arrhenius prediction methodology, the exposure times to reach those changes were plotted against the reciprocal of the temperatures and the time to reach the same level of change at lower temperatures (room, cool, and cold) extrapolated. The potential benefits of reduced-temperature storage could then be established.
Measurements documenting the effect of nitrogen dioxide on line width and blur were intended to establish the potential for low storage temperatures to minimize pollutant-induced colorant bleed. Unfortunately, it was found that the numerical results did not match the visual appearance of the changes, so the measurement was dropped. The visual assessments were then used to examine the relationship between bleed and temperature; however, none was found. Further research is this area will be important.
An additional qualitative analysis, not included in the original project proposal, was added during this phase. The surface layers of some inkjet prints cracked during the ozone exposures. Again, visual assessment was used to evaluate the samples for this property. In this case, there was a clear relationship between temperature and cracking.
The primary conclusions from this part of the project were the following:
- Reducing storage temperature from room to 5°C should extend life in ozone 1.9x-2.3x
- Reducing storage temperature from room to 5°C should extend life in nitrogen dioxide 3.6x-9.7x
- Reduction of storage temperature should lower the rate of embrittlement for many inkjet surfaces
- Further work is needed to develop accurate measures for line bleed
Reduction of Pollutant-Induced Deterioration through the Use of Enclosures
Reducing airflow over the surfaces of inkjet prints was already known to decrease the rate of pollutant-induced fade. As such, it is possible that protective storage enclosures and framing materials can also mitigate damage.
The experimental method in this phase involved exposing, in separate experiments with either ozone or nitrogen dioxide, inkjet prints in a variety of common enclosure types, materials, and configurations (figure 6).
List of tested enclosure configurations:
- No enclosure (free hanging)
- Paper envelope (non-buffered paper)
- Paper envelope (buffered paper)
- Polyester sleeve
- Cardboard box
- Paper envelope (buffered) and cardboard box
- Polyester sleeve and cardboard box
- Cardboard box with matted prints
The various enclosure types and configurations were then ranked in terms of their ability to block ozone and nitrogen dioxide-induced deterioration. The paper envelopes (both buffered and non-buffered) provided almost no protection compared to no enclosure at all. The polyester sleeves showed a significant improvement in both ozone and nitrogen dioxide blocking over both buffered and non-buffered paper envelopes (figure 7) and even paper envelopes within cardboard boxes. Polyester sleeves inside boxes provided no additional protection over polyester sleeves alone.
Matted prints in boxes were also fairly well protected. It may be that the large mass of paperboard (the mats) may absorb and reduce gas concentrations as air infiltrates the mat stack. However, only the center of the stack was tested, and since we know that prints in paper envelopes in cardboard boxes are vulnerable, the prints at the top of the mat stack or the bottom may be more vulnerable than the current results indicated.
In addition to showing the relative effectiveness of various enclosure types (materials, designs, and configurations), the experiments also showed that polyester maintains its effectiveness over time. Paper enclosures, both envelopes, and boxes were variable in their protection over time.
The primary conclusions from this part of the project were the following:
- Paper enclosures provided little to no protection against ozone or nitrogen dioxide-induced damage
- The addition of alkaline buffering to the paper envelopes provided no protection against ozone or nitrogen dioxide-induced damage
- Matted prints in boxes are better protected than prints alone in boxes, but prints at the top or bottom of the stack may be more at risk than those in the center.
- Polyester sleeves provide a high degree of protection even over extended periods
Synthesis of Phase One and Two Results
The project’s research question: “Which would be the better approach to preventing the damage to inkjet prints by pollutants, lowered-temperature storage or enclosure selection?” can now be answered. It appears that polyester enclosures provide sufficient shielding against pollutants and do so over time. This is clearly the easiest and most cost effective method to achieve protection from ozone and nitrogen dioxide.
Two other important considerations must be made as some inkjet print materials are also sensitive to thermal-induced yellowing and humidity-induced color bleed. While we believe that pollution is the greatest threat and the first step to the preservation of these objects will be pollution mitigation, it will also be necessary to create policies for optimal storage temperature and relative humidity. The choices any institution makes will be based on their particular inkjet print types, sizes, and quantities as well as their existing resources including cold-temperature storage space and funds for housing materials. IPI is currently working on integrating its completed temperature, humidity, and pollution research into a single cohesive strategy for long-term storage of the materials
In addition to the above, during this project we developed a greater appreciation for the damage that pollution can do to the physical integrity of inkjet printing papers. Most of the concern regarding inkjet has been colorant fade, but this has been more of a problem for dye-based inkjet than pigment which, over time, has become the dominant colorant choice for artists and photographers. In fact many pigment inkjets are labeled as “archival prints”, as if to signify an inherent resistance to change for extended periods. But the use of pigment inks creates a false security as these experiments have shown. Papers can yellow, crack, and/or delaminate causing even greater objectionable damage than fade alone, and this occurs equally to dye and pigment inkjet.