Conservation Conversations // Adhesives in Library and Archives: A Colloquium Review (Part 1)

Last Friday, the first Biennial Conservation Colloquium was held at the University of Illinois at Urbana-Champaign. Four conservators traveled to Urbana from the UK and across the country to speak about their research or practical experiences with various adhesives in library and archives conservation. Thanks to generous funding from the UIUC Library and the Andrew W. Mellon Foundation, the day-long event was free to 50 attendees.  In this two-part series, I will attempt to summarize the major points of each talk and hopefully encourage others working in the field to visit us for the next event.

The morning began with a presentation by the eminent chemist, conservator, and consultant Velson Horie on the use of “PVA” in conservation. Much of Horie’s presentation (drawn from his course on Materials for Conservation) was dedicated to the physical and chemical properties of polymers and how they can inform treatment decisions. For instance, concentration, viscosity, and wetting or surface tension can be taken into consideration with the molecular weight to produce stronger or weaker bonds that will complement the object, repair materials, and application technique. Horie suggested thinking critically about an adhesive, consolidant, or coating’s Glass Transition Temperature (Tg) in relation to treatment goals and storage conditions. Materials with a glass transition below room temperature (RT) have a molten or rubber-like consistency. They can flow or creep into unwanted areas, and can easily pick up dirt or other foreign matter that can catalyze degradation. Ideally collection material will be stored in cooler temperatures, free from dust; however, library and archives conservators are often confronted with storage environments that are less than ideal and can choose their adhesives accordingly.

In discussing the properties of different dispersions, Horie often raised questions about how they fit into our general treatment philosophy. We generally follow the principle that the strength of an adhesive should match that of the object: it must be strong enough, but not too strong. Most of the cultural artifacts that we treat are incredibly weak, yet synthetic adhesives are designed to be incredibly strong. This makes them great for industrial purposes (like holding airplanes together), but not so great for book or paper conservation. Certainly, any material used in treatment must not harm the object (or the person applying it) and must be removable without harm. It must not alter to become irremovable, either. In this respect, the needs of conservators are also at odds with the common material specifications of the adhesives industry. Many manufacturers are engineering adhesives to resist dissolving, so that they do not fail when exposed to the elements. Jade 403 is essentially irremovable when applied to paper fibers, because the object would not survive the solvents or processes necessary to break the bond. Jade (R) is a removable, but not entirely reversible. While it is possible to part the adhered pieces, a film can remain on the object. Some conservators have been attempting to get around this by adding starch to their “PVA”. Starch molecules can reduce cross-linking by surrounding the “PVA” molecules, but then why not just use starch in the first place? Horie urged the audience to ask the following questions for every treatment: What are the needs of the object? Does it need material added, removed, or replaced? and What are the alternatives? Even though every object is different, we are creatures of habit. This served as a good reminder to always think critically about every stage of every treatment- especially when you think that you know what you are doing!

Frequently throughout his talk, Horie stressed the importance of strictly adhering to proper nomenclature as part of our professional dialog. All too often, statements are made about the properties of “PVA” without distinguishing the exact material in question. Some of the vinyl acetate derived polymers that we commonly call “PVA” include the homopolymers Polyvinyl Acetate (PVAC) and Polyvinyl Alcohol (PVAL); however, most commercial adhesives are copolymers made to achieve specific working properties. Jade 403, the adhesive used by many libraries and binderies here in the US, is a Poly(vinyl acetate/ethene) copolymer P(VAC/E). Horie also pointed out that conservators often use the term “adhesive” when we should be using “liquid adhesive”. His logic being that the liquid adhesive applied to the object is not necessarily the same material once dry, as solvents or dispersing agents have left the material.

Readers who have been following the Conservation DistList, Book Arts List, or Preservation Administration Discussion Group will be familiar with the recent discussions about vinyl acetate derived adhesives. Horie spoke at length about several methods of polymerization used by manufacturers, which helped to put some of the recent online discussion into perspective. In some of the methods, solvents, stabilizers, or emulsifiers are used and can end up in the final product. While organizations such as the Canadian Conservation Institute have conducted extensive testing on commercial vinyl acetate derived adhesives, manufacturers have been known to change the undeclared ingredients or manufacturing process without warning. This presents a significant concern for conservators, as new analysis and aging studies must be conducted. Horie has maintained a personal practice of creating a labeled sample of every batch of every adhesive that he acquires. As a result, he has built an extensive collection of naturally aged adhesive samples. This simple habit makes so much sense and I will begin following the practice myself.

Discussion about the shelf life of various “PVAs” and “EVAs” have also been trending lately on the email discussion groups. Following the presentation, several audience members asked Horie to elaborate about this topic. Polymer dispersions contain >50% water and many components that react with water and the microbes that contaminate the liquid. So like milk, the adhesive will go bad. Horie recommends agitating the adhesive prior to decanting and using the entire container within 6 months. One audience member pointed out that the container may have already been sitting in a warehouse for that period of time before it was even sold. Many resellers of material for conservation do not supply a lot number or date of original manufacture, so the end user is completely unaware of the real age of the liquid adhesive. As a professional community, we should be demanding more information from suppliers regarding the materials that we use.

In all, Horie’s remarks were timely and quite useful. They reminded me of the need to constantly re-evaluate what materials I am using for treatment and how I am applying them. I also need to re-read his book, Materials for Conservation!

Sarah Reidell, Associate Conservator for Rare Books and Paper at The New York Public Library, gave the second presentation of the day, entitled “What is that, Leathuh? : Adhesives and Conservation Techniques for Leather in Archival and Library Conservation”. The majority of Reidell’s presentation dealt with two topics that she has been teaching through workshops around the country in recent years: pre-coated repair materials and cast composite techniques. I was fortunate to be able to take the pre-coated repair materials workshop with a group of library and archives conservators recently at the Campbell Center for Historic Preservation Studies (pictured below). Not only was the workshop incredibly fun, but I learned so much from both Reidell and my fellow workshop participants. I have found pre-coated papers to be incredibly useful for the book and paper treatments that come through my lab. Many online resources are available for individuals that would like to learn more, so I will not elaborate on the topic here. I encourage you to read Mindell Dubansky’s excellent review of Reidell’s pre-coated repair materials workshop, which includes thorough description and images. A brief description of Grace Owen-Weiss and Sarah Reidell’s cast composite technique can be found in the 2010 Book and Paper Group Annual and extensive bibliographies are available on Sarah’s website.

One of the main take-away’s from Reidell’s presentation is that equivalents of many commercially-made repair tissues (like heat-set) can be made fairly quickly and easily in one’s own lab or studio. Making your own repair materials puts you in control of the ingredients and can make for more predictable performance and/or reversibility as the object ages. With so many adhesives and consolidants available, however, one can become paralyzed with all the possibilities. Like anything that involves a degree of manual dexterity, it is important to allow yourself to experiment and fail with a new material or technique. Finally, take advantage of professional development opportunities and don’t be afraid to ask for help from other conservators!

The next installment includes a summary of Elissa O’Loughlin’s talk on Tapes and Gawain Weaver’s talk on Photographic Adhesives. You can read that post here.