This book, to be published in 2006, will explain the fundamental principles that govern the interaction between paper and water. The book will reinterpret and reformulate knowledge from the scientific and conservation disciplines to present a coherent approach to learning that is reflective of the interdisciplinary nature of conservation. The work will be richly supported by visual aids, and it will be designed for use by diverse audiences either in academic teaching or extramural seminars or as independent reading. The project, which began in 2001, is supported by a Samuel H. Kress Foundation Publication Grant through the American Institute for Conservation and by a Leonardo da Vinci grant from the European Union (EU). Several European conservation organizations—International Centre for the Study of the Preservation and the Restoration of Cultural Property (ICCROM), Institute of Paper Conservation (IPC), and International Association of Conservators of Archival Material, Books and Graphic Art (IADA)—cooperated in the EU grant to test the didactic concepts of the forthcoming book in seminars. Eight such seminars, each presented by a scientist and a conservator, will be completed in Europe by the end of 2004. Also financed by the EU grant are videos and animations that are prepared at the Department of Conservation Sciences and Restoration Technology at the University of Applied Arts in Vienna. The book begins with an introduction and user guide. The seventeen chapters of the manuscript are grouped into the following seven sections. Paper and Water: A Guide for Conservators Gerhard Banik and Irene Brückle Still image from a video animation of Fig. 1 visualizing the dynamic process of water adsorption between two cellulose molecules. 20 HAND PAPERMAKING Fundamentals: The first section comprises three chapters that explain the basic structure of paper, the properties of water, and the effect of pure water on pure cellulose paper. Papermaking: The second section deals with paper production steps that influence the relationship between paper and water. One chapter deals with fiber processing (pulping and bleaching) and the other discusses the effect of the principal sizing agents on the paper-water interaction. Paper in the Environment: This section deals with the behavior of paper in the environment. It explains how paper interacts with water vapor in a humid climate, and it explains the role of water in paper deterioration. The chapter is by Paul Whitmore, director of the Research Center on the Materials of the Artist and Conservator at the Carnegie Mellon University in Pittsburgh. Aqueous Solutions: This next section concerns the aqueous solutions used in paper conservation. It discusses methods of water purification; the self-ionization of water and hydrogen ion concentration (pH); the preparation and function of aqueous deacidification solutions; and, lastly, considerations concerning the use of aqueous solutions in conservation treatments. The chapter on deacidification will be written by Anthony Smith, conservation scientist and former professor at Camberwell School in London. Aqueous Treatment: This section deals with the basic principles by which paper and water interact during aqueous conservation treatment. In the first chapter, we discuss the principal mechanisms that occur when paper is wetted. Practical considerations that relate to how efficiently paper can be treated during washing treatments are discussed, followed by a section that reviews washing methods. Paper Drying: The final section concerns the drying of paper. The first chapter explains the mechanisms of water removal during paper production. The chapter will be contributed by Steven Keller, associate professor at the College of Environmental Science and Forestry at the State University of New York at Syracuse. The second chapter in this section explains methods of paper drying used in conservation. Final Comments: The book concludes with general remarks about the significance of aqueous treatment in paper conservation. The reader may begin by looking at the drawings that were custom-designed for the book. These drawings constitute the book's visual backbone and can be adapted to various contexts throughout. The drawings can be read independently because they are supported by extensive captions. Then, the reader may refer to the running explanatory text that will appear alongside the drawings. This text contains additional illustrations that enhance the understanding of the drawings. These illustrations, too, can be looked at independently from the text and in relation to the drawings. To lend more life to the dynamic paperwater interactions, Alfred Vendl, professor for conservation science and film producer at the University of Applied Arts in Vienna, has produced animations that relate to the drawings. These will illustrate dynamic concepts relating to the interaction of paper and water and will be downloadable from a DVD that will accompany the book. Each chapter will point to references, and key sources will be available to the reader on a CD-ROM from which they can be downloaded in hard copy. Suggestions for exercises relating to the content of each chapter and a glossary will be appended. To explain paper-water interactions, a structural model of paper is developed that divides it into six levels: - molecular level - microfibril - macrofibril - fiber - paper microstructure - paper macrostructure The following is an example of the content of the book and it focuses on the different states of water adsorption on cellulose. On completely desiccated cel-lulose—it could be located on a fiber surface or in a fiber interior—the first water is adsorbed in a monomolecular layer (Fig. 1, right). Much of the monomolecular water is so strongly bound to the cellulose that it is almost permanently fixed. Additional water is adsorbed as multimolecular water (Fig. 2). These water molecules are attached to the cellulose via other water molecules. With increasing distance from the cellulose surface, the adsorbed water becomes increasingly mobile and able to dissolve and transport substances to and from the cellulose surface. Multimolecular water occurs in several layers. Beyond that point, capillary water condenses on the cellulose surface. Capillary water behaves more like liquid or free water and is more mobile than multimolecular water. Because of the strong hydrogen bonding in liquid water, the water molecules join together to form large aggregates or clusters. The clusters are formed and disappear continuously in rapid succession, each lasting only 10–12 seconds. The formation of clusters is suppressed in the vicinity of cellulose where water is attracted to the hydroxyl groups that enforce the layered structure. The characteristic shape of the water sorption curve seen in a typical sorption isotherm for pure cellulose can be set into relation with the stages of water adsorption discussed above, and it can also be interpreted in light of water transport mechanisms that occur in paper exposed to humid environments (Fig. 3). The vertical axis of this sorption isotherm shows the grams of water adsorbed by 100 grams of pure cellulose, and the horizontal axis shows RH levels from 0% to 100%. When paper is moved from a drier environment to a damper one (or vice versa), different water transport mechanisms take effect. Most of them occur in pores between the fibers of the paper sheet. Water adsorbed onto the cellulose surface at RH levels below 20% is strongly bound and does not participate in transport mechanisms. Water transported through paper at low RH levels occurs exclusively via gas diffusion (Fig. 4). Only the water that appears in the interior of the arrow participates in the diffusion process. The arrow also indicates the direction in which the water moves, and we assume that it migrates from a location of higher concentration to a location of lower concentration in the paper. Such situations occur in paper during storage climate changes or during aqueous conservation treatment, including humidification or drying. With the accumulation of multimolecular water, surface diffusion begins (Fig. 5). Simultaneously, gas diffusion continues as long as the pores remain open between the fibers. Multimolecular water accumulates across the medium RH range, between roughly 20% and 80% RH. The adsorption curve (Fig. 3) rises less steeply within this range as many of the most easily accessible hydroxyl groups within the cellulose fiber have already adsorbed water, so additional water is attracted more weakly to the cellulose. The water content of pure cellulose over this RH range increases only from about 3% to 8%. The ability of water to move around remains relatively restricted. When the RH rises above 80%, we see a steep increase in the water absorption of paper. Between 80% and 100% RH, the water content of pure cellulose Fig. 3. The sorption isotherm shows the weight increase of pure cellulose when exposed to 0–100% RH conditions. Different states of water adsorption prevail at different humidity ranges. Fig. 4. The transportation of water through paper pores at low RH is governed by gas diffusion. Fig. 5. The transportation of water through paper pores at medium RH conditions is governed by surface diffusion. 22 HAND PAPERMAKING increases from 10% to 24% (Fig. 3). This coincides with the onset of capillary water transport in paper (Fig. 6). This water is much more mobile than the multimolecularly adsorbed water. It is this range on which the conservator's critical attention focuses during humidification treatment. Bulk-solid diffusion occurs inside the cell wall of the papermaking fiber and over a wide RH range (Fig. 7). In pores that allow the accumulation of multimolecular water, transport can occur, as seen in the lower portion of this drawing illustrating a large intrafiber pore. The upper pore is too small to allow water transport. At the lowest and highest RH levels, gas diffusion or capillary transport dominate, respectively, but across the rest of the RH spectrum, different transport mechanisms are likely to occur simultaneously. We should also note that not all papers absorb the same amount of water. At 65% RH, for example, a cotton paper may absorb only 6.5% its weight in water, whereas a chemically purified wood pulp paper may absorb 7.5% and groundwood may absorb 9.5% its weight in water. Cotton is more highly crystalline than other kinds of fibers and therefore is less accessible to water, which accounts for its lower moisture content. Cellulose in chemically purified, wood pulp is less crystalline and therefore more accessible to water. Groundwood fibers, as well as bast fibers, characteristically show a higher water content than cotton or purified wood pulp because they contain hemicellulose, which is extremely hygroscopic. The pathways of water transport through paper can be related to different practical situations: to the dampening of paper in preparation for printing or conservation treatment; to the effect of water on paper stored in humid climates; and to conservation treatments that require the application of water. The planned book will not provide a step-by-step guide to conservation treatment but rather will highlight principal mechanisms that apply in many situations when paper interacts with water. The information presented will, it is hoped, be applicable to and interpretable in different contexts and will allow practitioners working with paper to understand this unique man-made material in greater detail. For updates on the progress of the project or to contact the authors, visit the "Forum" of the website of the Staatliche Akademie der Bildenden Künste Stuttgart: www.sabk.de.