Throughout the history of inkjet printing, a wide variety of colorants, coatings, and supports have been used to make the fine art and professional photographs collected by museums, libraries and archives. These materials have shown, based on anecdotal experience and scientific study, a high degree of variability in terms of permanence at room condition storage. Experiments at IPI have demonstrated that progressively lower storage temperatures result in progressively longer lifespans. However, there has been concern within the imaging industry and cultural heritage institutions that crossing the threshold into below-freezing conditions could have damaging effects on the image quality or the physical integrity of the prints. In fact, this concern was explicitly expressed in the International Organization for Standardization’s ISO 18920:2011 Imaging materials - Reflection prints - Storage practices, “The rates of degradation and the potential for physical problems with extremely low temperature and/or low relative humidity storage is not well known for rapidly changing technologies such as… the many different ink jet image media (dye, pigment, wax) and base media (porous, swellable, plain paper).” The standard recommends caution when considering freezing prints because ISO does not know whether such extreme conditions might cause irreparable harm. Therefore, establishing the safety of below freezing storage would be extremely beneficial to collecting institutions wishing to maximize the useable life of their inkjet collections.
To address the problem, IPI stored fourteen different inkjet photo and fine art prints in sealed bags at -12°F for one week. The print samples included aqueous dye and pigment ink sets as well as five different paper types: polymer-coated RC, porous-coated RC, porous-coated fine art, uncoated fine art, and porous-coated baryta. After thawing in the bags for 24 hours and then re-equilibrating to room conditions (70°F and 50%RH), the prints were evaluated for colorant bleed, paper yellowing, changes in gloss, embrittlement of the surface coatings, and increased sensitivity to abrasion. Image analysis software was used to measure the changes in line width to quantify ink bleed, colorimetry was used to measure changes in paper white, a glossmeter was used to monitor changes in surface reflectivity, a Sutherland rub tester was used for the abrasion tests, and a brittleness wedge tester was used to determine embrittlement of the paper coating. The measurements and the visual assessments for all fourteen prints for all tests clearly showed that freezing these inkjet prints would not be harmful. In fact, there were a few instances where the prints performed better after freezing, though the reason for this is not known. The changes were slight, however, so it is not expected that freezing can reduce any deterioration a print has already undergone.
Therefore, in terms of ink bleed, paper yellowing, gloss change, embrittlement, and abrasion, it is safe to freeze inkjet prints to increase material life. This provides an important option for those wishing to extend collection usability over long periods of time. However, it should be noted that while freezing is safe, it may not always be desirable since low temperature storage capacity in institutions may be limited, and other collection objects may have a greater need for storage at the lowest temperatures available. Since not every inkjet print type is as sensitive to decay, the items most likely to show rapid changes should be prioritized for cold or frozen storage. Also, very low temperature storage is costly to maintain, so cold, but not sub-freezing conditions may be more sustainable. Each institution will need to weigh their capacity for creating and maintaining frozen storage areas with their specific preservation goals.
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