Image of report front cover

2017-22

Tidelines, residual damage on paper at a former wet/dry boundary, are produced by environmental wetting and some cleaning treatments.  They interfere with the appreciation of historical artifacts and weaken paper, predisposing it to further damage. In this project, scientists at Dartmouth College, the Library of Congress, and The Metropolitan Museum of Art drew on a suite of complementary characterization techniques to further our understanding of tideline formation.

Pages from selected Library of Congress Barrow Collection books showing how new tidelines are created on these and model papers.

The study included historical materials  as well as sized and unsized modern papers similar to historical materials. We characterized changes across the wet-dry boundary of each, recorded the migration and deposition of inorganic materials associated with tidelines, and investigated the effects of artificial aging using scanning electron microscopy, scanning and mapping micro X-ray fluorescence (XRF), synchrotron XRF, and high resolution X-ray microcomputed tomography.

Modern model papers were held with their lower edge in water for 15 hours, then lifted and allowed to dry. In the model samples that had tidelines created on them in the laboratory, these tidelines ran across the entire width of the sample and had an approximate width of 0.5 mm. Modern gelatin-sized papers immersed for 15 hours did not form tidelines visible to the naked eye. However, UV light revealed a faint fluorescence at the water immersion line in these samples. This suggests that un-degraded sizing effectively prevents vertical transport of water and thus provides protection against tideline formation.  A sample immersed for over 53 hours began showing fluorescence at day 20 of aging, suggesting that longer immersion or aging permits tidelines to form. Aging of the tideline formed on the Whatman No.1 paper produced gradual diffusion of some elements and showed a distinctive multi-zone appearance in UV light after 21 days. Artificial aging of tidelines generally produced darkening from yellow to brown.

Dark blue image of paper with a thin light blue line running horizontally through it.

Laboratory produced tideline made with deionized water on Whatman Number 1 filter paper (pure α cellulose), after 21 days of artificial aging in white light (background) and UV light (inset). Illustrates primary (upper) and secondary (lower) tidelines.

Although the historical samples were all sized papers, they had tidelines and new tidelines could be produced on them. This suggests that sizing will naturally break down over time and allow tideline formation.

This project produced visually arresting images of the chemistry and microstructure of tideline regions and new information about the inorganic chemistry associated with tidelines (the distribution of various elements and compounds in the original paper which help explain the reactions taking place). The insights we gained will be useful to the scientific community and conservators, but raise further questions that we hope to answer with future work.

This project was funded through a grant from NPS National Center for Preservation Technology and Training (NCPTT)

National Center for Preservation Technology and Training
645 University Parkway
Natchitoches, LA 71457

Email: ncptt[at]nps.gov
Phone: (318) 356-7444
Fax: (318) 356-9119