1 INTRODUCTION

Tracing papers have been used as the primary supports for a wide variety of materials found in museums, libraries, and archives, such as architectural drawings and fine arts paintings. As supports for architectural drawings and other technical designs, original tracings are frequently handled directly by workers and researchers, since they cannot always be effectively reproduced in photographs, facsimiles, or microfilm. Reproductions may not, for instance, capture faded or smudged media. In addition, reproductions may not clearly replicate subtle but important differences in media that may represent various elements or stages in design, or changes in media such as erasures, that may indicate the evolution of design concepts. Finally, notations in the margins or on the reverse of the drawings are often cropped in reproductions. Tracing papers are also used as supports for paintings by artists attracted by their translucency and relatively low cost. If exhibited, these papers may be damaged not only by handling but also by exhibition conditions. Unfortunately, the composition, size, age, past use, and fragility of tracing papers, compounded by handling and exhibition, makes them particularly susceptible to degradation and thus they frequently require conservation treatment.

Conservation treatment of tracing papers is complicated not only by diverse and sensitive media but also by the very nature of the paper supports. Contemporary tracing papers are produced by specially formulated compositions and manufacturing processes intended to achieve specific chemical and physical properties, such as translucency, whiteness, and smoothness. Special formulations and procedures may, however, render these papers exceptionally susceptible to surface marring, discoloration, and embrittlement. Tracing papers may absorb extraneous material such as adhesives, resulting in embedded stains that are difficult to remove. Often the papers are extremely hygroscopic, which makes them particularly susceptible to planar distortions and dimensional changes. Different manufacturing processes may also render the papers exceptionally sensitive to solvents used in conservation treatments (Baker et al. 1989). A review of the conservation literature indicates that the translucency of tracing papers may be affected by some solvents used for washing or deacidification (Flieder et al. 1988; Glaser 1988; Yates 1984); by consolidation or lining with aqueous, solvent-activated, or thermoplastic adhesives (Bachmann 1983, 1986; Bush 1986; Jirat-Wasiutynski 1980; Hoffenk de Graaff and Wolff 1982; Saucois 1981; Steinkellner 1979; Stone 1987); by stain-removal (Flieder et al. 1991); or by humidification and flattening (Flamm et al. 1990; Hofmann et al. 1992; McClintok 1986; van der Reyden et al. 1992a, 1992b).

To evaluate the effects on tracing papers caused by aging and by various types of solvents and solvent application techniques, several research projects were undertaken. This paper describes first the research design, followed by a separate description of each project with its experimental research procedures (methods and measurements), findings and discussion, and conclusions.1

1 The lack of previous work on this topic made sample choice difficult and made the number of necessary measurement replications for statistical validity unknown. The primary goal, then, was to identify promising areas for future, more in-depth, work, while maintaining a degree of usefulness in the data collected. Therefore, the number of replicates for each measurement varied. In some instances, one measurement of each sample was taken to provide a general overview; in others, multiple measurements were made to determine the significance of the differences seen. The tables of data included provide the number of replications and standard deviation, when calculable, to aid the reader in this determination.