Project Objectives
This project addressed some of the outstanding and persistent concerns regarding the use of gels cleaning systems. In particular, the project studied the question of residue from these systems. If there was a residue, did it pose a future risk to the surface of the painting or object? These concerns were debated among conservators and conservation scientists, and other institutions had carried out research into various aspects of the concerns. Articles on their work are scattered throughout the conservation literature. The GCI and colleagues from the J. Paul Getty Museum, with the cooperation of Richard Wolbers (who developed these cleaning systems), carried out in-depth research in an attempt to settle the "residue question," with the collaboration of colleagues at the Winterthur Museum, Garden and Library; the Art Conservation Department, University of Delaware; and the Chemistry Department of California State University Northridge (CSUN).

The project's objectives included the following:

• investigation of various aspects of the gel cleaning materials, including—
  - understanding the actions and cleaning mechanisms of different system formulations
  - identifying and quantifying the residue components remaining on the surface
  - identifying the potential of this residue to contribute to further deterioration
  - defining the most appropriate cleaning system formulations
• providing conservators with parameters that can help them design a specific system for a particular cleaning problem;
• clarifying and determining the limitations of gel cleaning techniques;
• understanding gel-paint film interaction; and
• disseminating this information to the conservation community.

Project Summary
In treating painted surfaces, cleaning has been carried out mainly with organic solvents or alkaline-based aqueous cleaning solutions—or by using mechanical means, such as scalpels. The former offers minimal control over the cleaning process, which often involves selective removal of a layer or layers of grime, varnish, or paint; however, many of the solvents employed are quite toxic. Mechanical removal is extremely time-consuming and often presents considerable risk to the underlying layers. Conservators also have had the option of using wax-solvent paste mixtures. The high viscosity of these mixtures provides more control over the cleaning process, particularly for three-dimensional objects such as sculptures. The workability of these mixtures, however, limits their effectiveness in many cleaning situations.

Cleaning grime or other layers from unpainted surfaces in general also presents problems such as color change to the surface and absorption of the cleaning agent into porous surfaces.

In the mid-1980s, Richard Wolbers at the University of Delaware introduced solvent-based gels, resin soaps, and enzymes as alternative cleaning systems. For effective use of these systems, a basic understanding of the chemistry of all the layers is even more crucial than it is for solvent or alkaline-based cleaning solutions. These cleaning systems offer three important benefits: (1) they enable the cleaning of surfaces that could not be cleaned by traditional solvent or mechanical methods; (2) they enable a more controlled and selective cleaning than these methods; and (3) they have relatively low toxicity.

The GCI provided the first venue for introducing this new cleaning approach with a training course presented by Richard Wolbers in Los Angeles in August 1988. This was followed by other courses in 1989 and 1999 in Melbourne, Australia, as a collaboration with the National Gallery of Victoria. The "Wolbers Workshop," as it has come to be known, has been presented many times in many countries since then; these cleaning systems are now widely used by conservators worldwide. The popularity of the workshops indicates the importance of surface cleaning in conservation treatments.

Despite the widespread use of the gel cleaning systems, concerns continued among conservators and conservation scientists, particularly in regard to any residue that the gel mixtures may leave on the surface and any potential long-term effects the components of the residue may cause to the cleaned surface. Conservators and conservation scientists at a number of leading international institutions carried out research on various issues related to each of the cleaning materials—gels, resin soaps, and enzymes. No in-depth research had been carried out gel residue and its potential effect on a surface.

As part of its general research on the cleaning of surfaces, in 1998 the GCI initiated a collaborative project to attempt to resolve some of the significant questions regarding these systems, with particular emphasis on the "residue question." The research resulted in the clarifying of the quantity of any gel residue and its potential deterioration effect, the limitations of the cleaning techniques, and the development of parameters to assist conservators in choosing customized systems for specific cleaning problems.