AIC's 47th Annual Meeting

This talk will be presented in conjunction with “Use of Heat and Solvent Set Repair Tissues” presented in the Book and Paper Specialty Session.
In this work, the National Archives and Records Administration (NARA) and the Library of Congress (LC) will report on their recent joint testing of a variety of heat and solvent set repair tissues. The goal of this research project was to provide analysis of physical and chemical changes for an assortment of well-tested and commonly employed pre-coated heat and solvent set adhesive tissues for use across a variety of paper based materials. Heat and solvent application methods were compared.

In 2013, the Library's Conservation Division was informed that adhesives used for many years to make “Library of Congress Heat Set Tissue” were no longer available. LC and NARA collaborated on a joint research project to identify replacements. At the end of the study a suitable mending tissue was identified and both institutions proceeded to use the material on their collections. Concerns were raised when it was later discovered that some of the materials used in the research project had turned brown after being stored at ambient conditions.

As noted in the 2015 AIC presentation, “Heat-Set Tissue: Finding a Practical Solution of Adhesives,” commercially available conservation adhesives have been discontinued or reformulated with disconcerting frequency. For this reason, another goal of this work was to continue evaluating the properties and behaviors of “known” adhesive compositions to assess their consistency. In addition, the authors will present suggestions for analytical testing methods of these adhesives for future quality control.

The adhesives and tissues tested here were chosen based on common usage at NARA, LC, and across the broader conservation field. Adhesives were applied to test substrates using both solvent and heat set methods, with the goal of evaluating how the application method affected adhesive properties and aging. Tests were conducted to assess reversibility after aging, blocking of mends and fills under pressure, effect on silver-based photographic materials, and color change following artificial aging. Color change was evaluated using both qualitative and quantitative methods to compare visual perception of color change with calculated ΔE CIE-L*a*b* values. Given concerns about changing formulations over time, these tests were also designed to set a baseline series of properties to monitor in the future.

Discoloration due to aging was found to be primarily a factor of the adhesive composition itself, with some additional contribution from the tissue and substrate. These discolorations were mostly found in a decrease of brightness and increase in yellowness. The application method did not significantly affect the color change. Adhesive tissues also behaved similarly in the PAT results irrespective of heat or solvent application. PAT success or failure depended only on adhesive composition and concentration.