CONSOLIDATION OF POROUS PAINT IN A VAPOR-SATURATED ATMOSPHERE
ERIC F. HANSEN, ROSA LOWINGER, & EILEEN SADOFF
This article presents what we hope will be a useful technique—the application of a consolidant solution in an atmosphere having a high concentration of the same solvent used in formulating the solution—along with some simple visual evidence that such a procedure is more effective than certain procedures used in the past. The information is designed to be of direct benefit to the practicing conservator; some practical considerations are noted based on the authors' experience. The factors affecting the appearance of matte paint are briefly discussed, and a physical explanation of the processes by which this technique minimizes changes in appearance is presented.
Paints that have a high pigment volume concentration (PVC) may be light and matte in appearance. In addition, the paint may be friable or powdering due to the lack of resin or binder. Consolidation may be required to prevent loss of paint from the surface. However, high PVC paints are also porous, and they easily absorb consolidant solutions, with the result that darkening or discoloration can occur. Other undesirable results of a consolidation treatment may include increased gloss and the formation of “tide lines” (see sec. 3).
Coatings with a high PVC are often encountered in at least three widely different classes of objects. Ethnographic objects may have been painted using such pigments as kaolin and ochres applied from a water slurry, containing no binder at all. Small amounts of binders may have been added, or organic material of limited durability may have been used. Modern works of art may have a high PVC paint if an artist specifically tried to achieve a matte appearance or experimented in novel paint formulations. Medieval panel paintings executed with water-soluble binders, glue, or resins may be powdering and may have a high PVC (Schiessl 1989).
The results of consolidating powdering, matte paint under different conditions are compared on the basis of a qualitative visual rating scale (sec. 6.2). Wooden blocks painted with yellow ochre, red ochre, and kaolin, prepared with no binder, were consolidated with the acrylic resin Acryloid B-72 or the poly(vinyl acetate) resin AYAF in solutions made with solvents of differing volatilities (Table 1). The consolidant solutions were applied in two ways: in air and in an atmosphere saturated with the solvent used to dissolve the resin. The results of these tests and the implications of this method for the consolidation of a wide variety of objects with powdering surfaces are discussed, along with suggestions for optimizing the procedure.
Table 1. RELATIVE SOLVENT VOLATILITY