Analytical Testing of Heat and Solvent Set Repair Tissues by Jennifer K. Hermann, Katherine Kelly, Alisha Chipman, Kate Morrison Danzis, Andrew Davis, Yasmeen Khan, Steven Loew, Tamara Ohanyan, Lauren M. Varga, Anne Witty, and Michele YouketAbstract: https://aics47thannualmeeting2019.sched.com/event/IumJ/photographic-materials-analytical-testing-of-heat-and-solvent-set-repair-tissues
This, the first of a set of two talks on heat and solvent set repair tissues, was presented in the Photographic Materials specialty session and focused on analysis of the properties of adhesives that can be used to prepare repair tissues, and their suitability for conservation use.
Avanse/Plextol adhesive was a recipe used by the Library of Congress to make a standardized heat set tissue. Some component of the commercially-produced adhesives was changed by the manufacturer in 2013, and this caused the LC recipe to no longer have the same properties. Research continued in 2015 into the characteristics of the changed formula. The new adhesive did not adhere well to all papers and sometimes fell off shortly after application. The 2016 recipe of Avanse/Plextol turned more brown in 3 years than the original 1970s recipe.
Due to the discontinuation of the original product, there was a rush to find a suitable substitute adhesive. The National Archives and Records Administration (NARA) and the Library of Congress (LC) jointly carried out testing of repair tissues that were prepared using commonly used adhesives, and applied with heat and solvent methods in paper repair situations.
It was decided to test the following products: Avanse/Plextol (LC recipe), Lascaux 498 HV, Lascaux 303 HV, Aquazol 200, and Aquazol 500.
Products were tested for usability, reversibility, and blocking. If the adhesive could not be practically applied thinly to tissue and the product removed from release film, then it was discarded for testing.
The products were analysed by looking at FTIR, cross-sectional microscopy, glass transition temperature, PAT (photographic activity test), accelerated aging, and colour change (qualitative and quantitative).
Both sides of the tissue, as well as the release film and the probe, were tested to try to verify whether the adhesive was causing blocking (going through the tissue).
The PAT test was used to also test non-photographic paper, this allowed prediction of paper aging and ensuring that photographs in the collection are safe.
Quantitative colour change and PAT results did not depend on the application method (solvent or heat set).
The 2013-2017 version of Avanse/Plextol had a noticeable change in product smell/appearance and in FTIR analysis. Aged Plextol became brittle but the paper itself did not change much - the adhesive itself was changing colour.
The recipes that best met the requirements for use were:
5% Aquazol 500 in water
An audience member asked whether products such as Paraloid and Crompton tissue were considered for inclusion in the tests. The speakers replied that the choice of adhesives for testing was influenced by information collected from previous studies (eg. adhesives analyses by CCI).
The second of the two talks was later presented in the Book and Paper specialty session. It briefly reviewed the above background, then introduced the set of six tested adhesives and discussed their use in making heat and solvent set tissues, with practical tips and case studies.
Julie Niven, Archives Conservator