AIC's 52nd Annual Meeting

The cloth covered box for rare books, commonly referred to as a clamshell or drop spine box, is often considered the gold standard for housing library materials. They are valued by curators for their aesthetic qualities and rigid protection. Learning how to build them is part of the training for many book conservators and technicians. At the Library of Congress (LC), clamshell boxes were introduced in the 1970s. They continue to be made but their production has curtailed recently due to variety of reasons including availability of materials, cost of labor, and cheaper, faster alternatives like custom fitting corrugated boxes. For many curators and specialists, however, clamshell boxes are still seen as the preferred enclosure. As a result, approximately 25 clamshell boxes are made every year for rare and unique items.

The most common adhesive used for clamshell box making at LC has been PVAc (poly-vinyl acetate) and this is generally true in book conservation as a whole. While the working properties of PVAc have made the formulations an obvious choice, concerns about stability and off-gassing have also played a significant role in the reduced number of clamshell boxes made at LC.

In 2011 those concerns led LC conservators and scientists to evaluate PVAc as an adhesive for covering housings in which the adhesive film and covering cloth would be even closer to the enclosed book covers than in a typical clamshell box. All the PVAc films tested performed poorly. In 2017, six years later, the naturally aged PVAc films were evaluated again. Surprisingly, the films still performed poorly, including films that had been diluted in 9:1 wheat starch paste to PVAc ratio. As a result of those tests, LC conservators began to move away from using PVAc as the primary adhesive or avoid it all together in box construction.

The purpose of the most recent research was to advance the evaluation process and collect data on possible replacement adhesives. This goal was accomplished by building multiple clamshell boxes solely for the purpose of testing a formulation of PVAc commonly used by conservators along with a wide variety of other adhesives for comparison. Some of the other adhesives were designed for library and archives conservation and some used in other specializations. Evaluation was broadly separated into two categories: usability as determined by conservators making the sample clamshell boxes and chemical risk to collections as determined by LC Preservation and Research and Testing (PRTD) staff. Usability criteria included evaluating the ease of preparation for each adhesive, flow when applied to the substrate, open time for working, tack, and other features. PRTD analysis included Oddy testing, direct thermal desorption gas chromatography mass spectrometry, and air sampling in order to understand the potential risk the adhesives pose to collections. Results of the usability and risk of components of the project will be discussed as well as future research initiatives.