Summary of Study on Minimum Force to Abrasion for Documents and Photographs
In January of this year, IPI published its results on abrasion sensitivity for digital press prints. These were summarized in the March issue of the DP3 Newsletter. The purpose of this new project was to determine the minimum levels of force and number of abrasion cycles necessary to produce a just noticeable difference (JND) in documents and photographs printed with digital technologies. The results of this work are intended to help cultural heritage institutions that collect these materials develop policies for use and care to prevent damage to their collections. In these experiments a variety of digital printers and papers commonly used for photographs and documents were studied. Specimens were abraded using either ¼-lb or 2-lb loads. The lighter weight was used to replicate physical handling such as sorting sheets in small stacks or sliding prints in and out of enclosures. The heavier weight was used to emulate documents and photographs being pulled from large stacks as well as the possible damage to materials in stacks during transport. The abrading surfaces included the unprinted reverse sides of prints to simulate prints in stacks, as well as buffered envelope paper and clear polyester sleeves to simulate individual prints in enclosures.
A series of abrasion cycles (1 to 1000) were applied to each of the test prints to determine the minimum number at which damage would be observed. Visual observations were also correlated with image analysis software data to determine if a quantifiable threshold limit for this property was possible. Measurements and observations included smear of colorant from printed areas to adjacent white areas as well as loss of density in the printed area. The changes in average gray levels were measured with image analysis software for both the black patches and adjacent unprinted areas before and after abrasion. Gloss measurements were made before and after testing to determine the extent of gloss change in the printed patches of photographs. The results showed that the number of cycles needed to initiate damage varied depending on printer paper combinations (see chart below – IJ stands for inkjet).
Transfer of colorant from printed areas to the adjacent white unprinted areas was quite noticeable in some cases even at fewer than ten cycles. In other cases, even 1000 cycles caused no smear damage. Photographs and other art printed using pigment inkjet printers were the most sensitive.