Summary of IPI’s Research into the Tendency of Digitally Printed Materials to Block or Ferrotype at High Humidity
Blocking is the phenomenon of prints becoming adhered to each other front to back as in a stack, face-to-face as in a photo album or to smooth surfaces in contact with the prints such as glass in frames or plastic sleeves in enclosures. Ferrotyping is similar to blocking, but instead of bonding between prints or to adjacent materials, the softening of the print surface causes the gloss of the print to be degraded.
It has long been known that the gelatin layer used in traditional photographic prints can bond to glass in framing packages and many types of plastic sheeting used in storage enclosures. This happens when the glass transition temperature of the print’s gelatin layer is exceeded.
IPI performed the experiments described below to determine if digitally printed photographs were as likely to ferrotype or block as traditional silver-halide photographs. Preliminary testing at IPI indicated that 30oC (86oF) at 90%RH could replicate the blocking effects often seen with traditional photographic prints. These conditions are not designed for accelerated aging, but instead to simulate a worst-case scenario where a print may be stored, even briefly, in a hot, humid environment.
Sixteen different unprinted digital papers were tested from the following groups: inkjet specialty-photo (both porous and polymer), inkjet fine-art, dye sublimation (printed without image to include overcoat), chromogenic (processed without image), and coated digital press. Several examples from each type were tested when possible. Additionally, 10 different printed digital photographs were tested...
Image Permanence vs. Image Preservation
Last issue we discussed the differences between the terms image permanence and print permanence. Now we look at why the terms image permanence and image preservation are not synonymous. The first describes a material while the second describes an action.
Image permanence is a function of the chemical and physical make-up of the print material and its sensitivity to environmental stress factors such as light, pollution, and extremes of humidity. For example, the long-term stability of a specific print product under normal-use display conditions can be predicted by performing an accelerated lightfastness test. We often see these predictions converted to years of life expectancy for display on the manufacturer's product literature and advertising.
Image preservation, on the other hand, is the strategies we employ to maximize the life of prints. It describes the actions we can take to ensure the print will survive and not how well the print performs after those measures are taken. Image permanence data has its greatest use in the marketplace where consumers select products to create their digital output in hardcopy form. Once the objects are created however, image permanence data becomes only one component in the development of overall strategies for long-term collection preservation. These strategies will include storage environment recommendations, housing material selection, and display and use policies.