Publication Type:Conference Paper
Source:Cleaning, retouching and coatings: Contributions to the 1990 IIC Congress, Brussels, p.85-92 (1990)
Keywords:aging, cleaning, color, leaching, linseed oil, models, oil paint, organic solvents, paint, pigment, removal, solvents, swelling, varnish
Cleaning science barely exists. This article reviews the scattered data, and assembles a partial model of the physical aspects of varnish removal from oil paint. Organic solvents diffuse into varnish or paint as a swelling front; penetration time varies as the square of thickness. Capillary penetration is a separate issue. A chart of solvent penetration vs. time is given, based on the data of Graham and Stolow. During swabbing, slow penetrating solvents can swell more paint than fast ones if the dissolution rate for the varnish is too slow. Data from five authors on swelling of linseed oil are compared. The data will not fit the Teas chart, but they do fit a three-dimensional solubility parameter space. Swelling and leaching of moderately aged paints are substantial; however, this may not be so for very old paint and this requires study. Water takes days to diffuse through pure oil medium but it can channel along flocculated pigment surfaces in minutes. Adsorption of solvents by pigments can cause debonding of the medium, which may explain some blanching or color lifting. Alcohols and water prefer inorganic pigments, while ketones and less polar solvents prefer organic pigments.