1 INTRODUCTION

It has long been known that solvents may remove portions of the oil media from dried paint films. This phenomenon was studied beginning around 1950 by both Graham and Stolow (Graham 1953; Feller et al. 1985). At the time, the choice of cleaning agents for paintings primarily consisted of either pure or mixed solvents. Conservators had to choose a solvent system that removed layers of dirt, varnish, and overpaint while affecting the original paint layer as little as possible. This decision often involved a choice between solvents with short cleaning times and fast penetration versus longer cleaning times and slow penetration. In the last few years, the range of choices has been expanded to include gelled solvents and aqueous cleaning systems (Wolbers et al. 1990). Gelled systems are used on the assumption that penetration into the original paint layer will be retarded while only minimally reducing the strength of the reagents, thus providing the conservator with more control of the cleaning process. Soaps are prepared from compounds that are chemically similar to the materials they are supposed to remove; this process is intended to produce a soap that removes these materials preferentially.