THE USE OF IMMISCIBLE SOLVENT COMBINATIONS FOR THE CLEANING OF PAINTINGS
4 IN PRACTICE
WE HAVE ESTABLISHED that we are cleaning with tiny ethanol-rich droplets dispersed in a relatively inactive hydrocarbon phase. The method is not dissimilar in approach to the surface cleaning method of working through a Stoddard solvent or petroleum spirit layer with an ammonia-water solution. One reason for employing this technique is to utilize the properties of immiscible solvents to reduce the active solvent's action after the swab is removed. The requisite of the solvents to separate tends to interfere with the wetting and swelling of the varnish. My empirical conclusion is that solvent action is more directly related to swab action: a “feeling” of greater control over, and response from, the swab.
Another advantage of using an immiscible system is that as the varnish is reduced in thickness, we require less solvent action to remove the remainder (or to reduce it to whatever level one wishes to clean). This is accomplished by reducing the number of ethanol droplets available for contact. Remember that in this immiscible combination, the hydrocarbons behave as a diluent.
Using a so-called non-active component such as white spirit offers other advantages in cleaning. As a slower evaporating solvent, it remains on the area, helping optically to saturate the varnish and paint layer, thereby increasing visibility of the varnish removal. It also affords a method of “harnessing” the active solvent; that is, it allows for the application of a manageable amount of active solvent with a suitable solvent strength, evaporation rate and diffusion rate, while controlling the action of same.