The first Biennial Conservation Colloquium was held at the University of Illinois at Urbana-Champaign in early November 2014. 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.  This review 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!

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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!

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The first topic of the afternoon was pressure sensitive tapes and adhesives, presented by Elissa O’Loughlin, Senior Conservator in the Division of Conservation and Technical Research at the Walters Art Museum. Over her 30 year career, O’Loughlin has conducted extensive research on the history of tapes, their usage in libraries and archives, and their effects on cultural heritage materials. She was awarded a Samuel H. Kress Conservation Publication Fellowship by FAIC in 2013 for her forthcoming publication, A Conservation Guide to Pressure Sensitive Tapes; History, Identification, Treatment, and continues to teach a popular tape removal course for mid-level conservators (read a review here). In her spare time, O’Loughlin also makes some amazingly useful brass tools.

“To conquer a large topic, you have to divide it and go bit by bit.”

The sheer variety of pressure sensitive tapes available on the market historically and today is overwhelming. O’Loughlin began with a discussion of nomenclature and materials, insisting “sussing out materials categories is really important”. She presented a list of three major types of tape: Rubber, Synthetic, and Other. Rubber tapes are typically packing, sealing, masking, and joining tapes, and are the workhorses of the commercial tape world. Synthetic tapes are often the tapes used for home or office, such as Scotch Magic Tape. O’Loughlin’s “Other” category included silicone, Very High Bond (VHB), or security tapes, and are not found as often on library and archives materials.

O’Loughlin displayed a large tree diagram of different carriers and adhesives of commonly available tapes and their composition. Tape carriers can be made of plastics, textiles, metal, paper, or other materials. Common plastics for carriers are cellophane, cellulose acetate, and polyester. Tape adhesives have several components, such as elastomers, plasticizers, tackifiers, dyes, fillers, and other chemicals (like surfactants and optical brighteners). Elastomers, or the “backbone” of the adhesive, can be natural rubber or synthetic. Plasticizers, or the lubrication required to get long molecules moving together (think olive oil in pasta), can be vegetable oil, mineral oil, petroleum. Tackifiers are often natural or synthetic resins. When broken down into this extensive list of components, it became clear that tapes are not as simple as they initially appear and accurate identification is important for making appropriate treatment decisions and identifying optimum storage environments. For example, weak acids are the degradation products of rubber-based adhesives, so removing the carrier and excess adhesive from a paper object’s surface isn’t really enough. Adhesive that remains embedded in the paper fibers will continue to react and can cause the paper to fall out. The quick fix for these materials is cold-storage, but not everyone has access to that kind of storage environment.

So how do you quickly identify the tape on the object in front of you? O’Loughlin provided several tables of aging characteristics and quick identifiers, which I have reproduced below:

Aging Characteristics
Rubber	Acrylics
– 3 Stages clearly observable – Solubility shifting – Procedes at variable rate – Strong chemically driven forces – Loss of volatiles – Color change (yellow a clear indicator) – Brief stability – Become embrittled – Usually paired with poor carrier (cellophane)	– Aging not easily observable – Not soluble in paper-friendly solvents (boiling toluene!) – No strong chemical forces driving aging – Loss of volatiles – No significant discoloration – Have long term stability (compared to rubber) – Some carriers may deteriorate

Quick Indicators
Rubber	Acrylics
– Discoloration- Brittle, yellowed carrier – Adhesive failure – Penetration of adherend by adhesive components – Significant florescence at 365 nm	– Frosted carrier – Minimal discoloration of carrier or adhesive – Shrinkage of cellulose acetate carrier – Ooze of adhesive (soft solid at RT)

A few other handy tips that came up during the presentation: a simple test of a plastic carrier with acetone can tell you a great deal. If the carrier dissolves, it’s likely cellulose acetate and you can quickly determine that the adhesive is synthetic. If you heat the adhesive and smell pine or tree sap, there is a resin component. If using a cotton swab and solvent to remove a rubber-based adhesive, a quick check of the swab under UV will tell you if the solvent is effective. If the swab fluoresces, you know that it is working.

A large portion of O’Loughlin’s talk was a history lesson on the development, use, and analysis of tapes from her upcoming book. She joked that if we mark eras of human culture by the materials that we use (Bronze Age, Iron Age, etc.), then the period since 1928 would be known as the “Sticky Plastic Tape Age”. O’Loughlin reports that although problems with tape aging were being described as early as 1935, expediency of function probably overshadowed any long-term faults. Compared to other available adhesives at that time, tapes did not require complicated or time-consuming methods to apply or dry: they just worked. Over the course of the talk, I learned a great deal about WPA programs for repairing library materials with tape and early testing conducted by NARA and the Library of Congress. O’Loughlin’s history was both educational and entertaining; I am really looking forward to reading the rest of her book.

Following the talk, there were a few minutes for audience questions and general discussion. Conservators hate tape. We get angry just thinking about the armies of past library volunteers, carefully covering entire objects in it. Tape that took only a few seconds to apply can take hours to reverse- or may not come off at all. Even so-called “archival tapes”, like Filmoplast, have aging and reversibility problems that have been discussed in the literature for several decades now. We have to understand that the library and archives custodians of the past were well-meaning; however, I’m reminded of that old proverb about the road to hell being paved with good intentions. The discussion was a good reminder that conservators now have so much information at our disposal. Commercially produced “archival” products can be seductive in how easy they are to purchase and apply, especially in the face of limited staffing and massive collections; however, those same products often have negative long-term implications for the object. A little research can often yield a simple repair technique, using predictable adhesives that are already available in your lab.

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The final talk of the colloquium came from Gawain Weaver, a photograph conservator in private practice based in San Anselmo, CA. Weaver has worked at many prestigious institutions over the course of his career, including the Getty Museum, the Amon Carter Museum, Library and Archives Canada, the Museum of Modern Art, and the Northeast Document Conservation Center. I took Weaver’s Care and Identification of Photographs workshop back in 2010 and I regularly make use of my notes from that workshop to properly identify and make decisions about objects in the collection here at UIUC. I’ve also heard some glowing reviews of a workshop that he taught recently with Jennifer Olsen. You can read about that workshop here. Weaver’s talk was titled “Photographic Adhesives: History, Preservation, and Treatment Issues”, and mainly focused on the adhesives and techniques traditionally used to mount photographs and their reversibility. For readers that are not familiar with early photographic processes, I would recommend the new Format ID Guide of the Preservation Self-Assessment Program (currently under development at the University of Illinois), as well as Graphics Atlas. Weaver presented a tremendous amount of information in this talk. The following summary is incomplete, but will serve as a general overview.

The earliest photographic adhesives are usually water-based liquids or pastes, and include starches, mucilage, dextrin, gelatin, and alcoholic mixtures of the aforementioned. Caoutchouc (natural rubber) and commercial mountants were also sometimes used, although long-term stability can be a problem with these products. Photos from the 19th century were typically adhered overall or just at the edges, with a brush or roller application. Weaver described the mounting techniques for salt print as the most rudimentary mounting techniques; however, there are so few remaining. Often higher quality mount paper is used than some other photographic processes, and starch or casein is the adhesive typically used. In Weaver’s experience, salt prints sometimes come off the mounts with water only, but they can be pressed very hard into the mat with a roller press.

Weaver reminded the audience that albumen prints curl a great deal on their own, so they are usually mounted. Albumen mounts are often a wood-fiber core with better paper laminated to the outsides. An all-over application of starch, casein, animal glue, or vegetable glue with a brush is characteristic. While a rolling press was typically used, Weaver provided some background on the development and evolution of burnishers and enamelers in the late 1800’s. These machines included rollers lubricated with wax or soap and sometimes heated, such as the one pictured above. He described the evolution of this equipment and its affect on the glossiness of photographs, stating albumen prints from the 1890’s can be almost unrecognizable. Obviously, all this pressing and burnishing can make albumen prints very difficult to remove from the mount.

Weaver described changes in mounting techniques at the turn of the century,  such as using dots or lines of adhesive instead of over-all application. Mounting along the top edge becomes more common for photographic prints that don’t tend to curl as much, like gelatin prints, platinum prints, or gravures. Rubber cement was more common as a mounting adhesive, starting in the 1920’s and 1930’s. Weaver stated that literature from the period includes discussion of the staining and non-permanence of rubber cement. Much like pressure sensitive tape, it seems convenience won out over issues of permanence.

In the 19th century, dry mounting really just meant water soluble adhesives, just with a drier application. Dry mounting tissues, or tissue dipped in shellac, were adopted from the hat-making industry and more widely used to mount photographs and prints after 1900. Weaver observed that Kodak continued to make a shellac-based tissue until the 1970’s, so it is quite common. He stated that use of these mounting tissues declined after the 1970, due to the rise in popularity of Resin Coated (RC) papers. Modern dry mounting adhesives are typically a vinyl acetate/ethene copolymer. For a better history of dry mounting processes, Weaver recommended Watkins’ article “Origins and Development of Dry Mounting” (1993).

Weaver spoke at length of different techniques for adhesive and mount removal. Photos from the 19th century are often removable with simple humidification. These prints can be soaked in cold water with some risk, while soaking in warm water carries a lot more risk. If the mount can be sacrificed, mechanical backing removal and application of a poultice may be effective. Animal glue stuck on gelatin emulsion is nearly impossible to remove, as gelatin swells more readily than the animal glue. Hot air pencils, heated spatulas, or heat guns can be useful tools for the removal of dry mount adhesives, but Weaver recommends models with digital temperature controls. Dry mounting tissues can also be reversed effectively with solvents such as acetone (for older tissues) or naptha (for newer tissues) in a polyester envelope with a blotter soaked in solvent or a solvent chamber; however, problems can easily occur.

As expected, Weaver issued frequent warnings of the risks of treatment throughout this part of the discussion. Each process has its own sensitivities and extensive testing is required to make appropriate decisions. Coatings (like pyroxylin) and finishes (like Ferrotyping) can be quickly and irreversibly changed during treatment. Similarly, albumen can easily crack. Some of these warnings were quite dramatic. After describing the removal of rubber cement staining using an acetone bath, Weaver showed a rather terrifying video of a matte collodion print in acetone. The image completely evaporated in around 12 minutes. In his experience, testing can be very misleading for individuals that are not intimately familiar with historic photographic processes and materials. For example, coatings on the image can make a solvent appear safe in testing when it will be detrimental in a solvent chamber or bath. According to Weaver, modern color processes, such as Dye coupler prints, are very complex and should be left to a professional with extensive experience. Because formulas from the manufacturers change so rapidly, and very little research has been done, it can be very difficult to determine which treatment techniques are safe.

Weaver’s talk was a good refresher on some of the materials and adhesives used to produce mounted photographs since the 19th century. Many of the adhesives and application techniques historically used, as well as the techniques for their treatment and removal, are familiar to book and paper conservators. Some of Weaver’s examples were also solid reminders that photographs are complex objects and treatment should not be approached casually.

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This review was originally written in two parts (Part I & Part II) for the “Conservation Conversations” series on Erin Fletcher’s blog, Flash of the Hand .