Book excerpt: The cleaning of a work of art often involves removing not only dirt and grime but also unwanted layers of varnish, gilding, and paint from the work's surface. The challenge for conservators lies in finding a cleaning agent that will act on one layer without affecting the layer being preserved and without leaving any harmful residues on the cleaned work. This book, which examines gel cleaning in the treatment of paintings and painted works of art, presents the methodologies, data, and results of a collaborative project of the Getty Conservation Institute and Winterthur Museum. Among the issues covered are the theory and application of gel cleaning systems, the detection of residues left on the surfaces of objects cleaned with these systems, research into solvent-gel and solvent residues, stability of surfactants during natural and artificial aging, and recommendations for formulating gels for specific cleaning tasks.