8 PRACTICAL CONSIDERATIONS

One reason for exploring the method of working in a saturated atmosphere is that there are some drawbacks to working with DEB. DEB can be retained in treated objects for a long time, resulting in a noxious odor that may persist for years. In addition, the degree of consolidation or reduction of discoloration is not always acceptable (Walston et al. 1987). The possible reasons for this result include the plasticization of resins when a large amount of solvent is retained and the fact that DEB is not a good-quality solvent for acrylic polymers. Some physical properties of thermoplastic polymers used in conservation have been shown to be affected by the quality of the solvent used for their application (Hansen et al. 1991).

There are obvious limitations to the use of a saturated vapor atmosphere, especially in regard to undesirable softening of resinous areas of an object. This problem was apparent quite early in this study when the paint on brush handles softened because it was solvent sensitive. Another consideration is the difficulty in removing a consolidant that is well distributed throughout a fragile paint layer (Hansen, Sadoff, and Lowinger 1990). Only highly light stable, nonyellowing, thermoplastic polymers should be used.

Consolidation in a saturated atmosphere is particularly suitable in some situations and not suitable in others. Suitable surfaces are porous ones where penetration can be achieved, either in the painted layer alone or in the paint and substrate. Surfaces that are matte due to surface roughness and not porous, or paint and substrates where improved penetration is not required, should not benefit by this method. Matte surfaces due to surface roughness might be successfully consolidated with viscous solutions that do not penetrate but also do not level well, conforming to the surface geometry. Factors affecting this effect have been discussed by Feller, Stolow, and Jones (1985).

In contrast, paint might also be porous and lifting or flaking but not be in need of consolidation. If all that is required is adhesion of the porous paint to the substrate, discouraging penetration into the paint by the adhesive solution would minimize darkening or discoloration. Futernick (1989) found that if a porous paint was saturated with a nonpolar organic solvent, such as toluene, it could be adhered with an aqueous emulsion that did not penetrate into the pores of the saturated paint.