AIC's 44th Annual Meeting

Part I: Conductivity, or more specifically, ionic strength, constitutes a substantial factor in the design of aqueous treatments for those works of art on paper that require improved control of local or overall washing. A conductivity-sensitive approach to treatment enables conservators to create chemically specific aqueous environments, minimizing swelling and disruption of paper fibers during aqueous exposure, while maximizing removal of soluble discoloration products. This presentation aims to clarify both the theory and chemistry of conductivity in the context of paper conservation practice. Since the effects of conductivity are a relatively new line of inquiry in this specialty, this study relies on scholarship produced not only by conservators and conservation scientists specializing in paintings and objects conservation, but also by researchers from the paper-making and agricultural industries. Based on extensive literature review, a theoretical model for the chemical and physical interactions between low-to-moderate conductivity water and discolored paper will be described. By combined chemical and physical effects on the microscopic and molecular level (for example: diffusion and osmotic effects), a salt in aqueous solution may be exploited to mitigate or to encourage the movement of soluble ions not only through the fiber web, but through the walls of individual paper fibers and fibrils. This research addresses the effects of one such electrolyte: aqueous ammonium acetate (a volatile, neutral salt) on discolored paper substrates. A selection of case studies and practical mock-ups demonstrating the efficacy of ammonium acetate solutions will be presented, followed by recommendations and provisional guidelines for incorporating the solutions into laboratory practice. The effects of conductivity-adjusted solutions are distinctly advantageous for moisture-sensitive papers and can improve the performance of local wet treatments when using swabs, poultices, and rigid polysaccharide gels. Considering that ammonium acetate has been untested in the field of paper conservation, this presentation will conclude with the results of pH testing, accelerated aging experiments, and chemical analysis conducted to assess the potential for salt residues remaining in treated paper.

 

Part II: While gel treatments are not novel to the field of art conservation, until recently, their use has been relatively limited within paper conservation in comparison to other specializations. Articles and presentations describing treatment of paper objects with gels have increased markedly over the past decade, reflecting a fundamental shift in the paper conservator’s approach to treatment, an approach that calls for less manipulation of the object, greater control, and targeted cleaning. This paper offers an overview of the use of rigid gel systems in local and overall cleaning of works on paper. Agarose and Gellan gum—two naturally occurring polysaccharides—are cited most frequently in the literature and are the focus of this paper. Both form colorless, rigid gels that make them ideal for many paper conservation treatments such as aqueous and solvent-based poulticing; stain and tideline reduction; and overall washing. Dependent upon the specific polymer, these gels may be prepared with deionized water or aqueous solutions that utilize chelators and other buffers to adjust pH and conductivity. Following a discussion of the advantages of gel treatment and rationale for selecting a gel, the properties of Agarose and Gellan gum as well as factors that impact the performance of each will be addressed. These factors—casting thickness, concentration, additives, and use of a barrier layer among others—may be modified to optimize or tailor treatment and examples drawn from practical experience will be presented. A case study will describe controlled washing of a chine-collé print on large sheets of Gellan gum. This example illustrates some of the distinct benefits of rigid polysaccharide gel—notably highly efficient and even cleaning—in treating an object that could not be bathed by immersion given its lamellar structure. The paper will conclude by summarizing the results of a scientific study that utilized fluorescein dye to assess relative amounts of residue left by the gels when used to treat three different types of paper for varying lengths of time. While residue from the rigid gels was generally minimal, the factors that contribute to gel residue as well as methods for prevention will be discussed.