Measurement of Gels and Gel Component Residues

This component of the research, carried out at the Conservation Institute and California State University, Northridge (CSUN), was the first area to be addressed. Experiments with painted canvas samples showed that the quantities of gel residues left on the cleaned surface were very small. This was put into perspective by comparing the residue quantities with the quantity of matter transferred to the paint surface by the touch of a finger. A similar test carried out on four different materials representative of topographically complex materials common to objects in museum collections showed that the normal gel-cleaning procedures used for low porosity materials are not efficient enough to remove gel residues from the surface pores of highly porous materials.

In the process of this work, complementary needs were identified and included in the project (see Solvent Retention and Residue section).

• To quantify the amount of residue, a very sensitive methodology was developed using 3H and 14C radiocarbon-labeled gel components.
• As cleaning a surface is a subjective procedure—based on the individual techniques and experiences of the conservator—a cleaning experiment took place in November 1998, in Los Angeles, using the above methodology to investigate the effect that personal techniques may have on residue quantities. Participants included experienced international conservators and leading international scientists, who have carried out independent related gel-cleaning system research.
• An artificial accelerated-aging test was carried out to measure the degradation process of both the Ethomeen and Carbopol components of a gel residue on the surface of the painting that had been superficially cleaned.
• Gel component decomposition products—as a result of UV radiation—were studied by residual gas analysis, and the surface distribution of residues were studied through two-dimensional autoradiography, in combination with laser profilometry.
• The data from a cleaning experiment conducted at CSUN in September 2000 on three-dimensional material samples—plaster, marble, terracotta, and gilded wood—were studied and compared with the results of the cleaning experiment on the canvas painting.