Dangers of Excessively Thinning of Paint

Many ask if there is any danger of thinning oil paint with solvents when painting. It is impossible to preserve paint films that have been extremely thinned out through solvents, such as turpentine or mineral spirits, without a severe change in their appearance. These excessively thinned paint films are very much like pastel drawings on paper. There is hardly anything more than the canvas’s rough tooth acting as a pigment binder. Very frequently, the mere passing of a dry cotton swab (as is the practice in cleaning paintings) over the surface of this type of paint film will result in the removal of some pigment. This condition exists because there is hardly any oil binder present. Once such a paint film becomes soiled with grime, removing the grime is almost impossible without some pigment.

Does Varnish Protect the Painting?

If such a paint film is protected with varnish, the varnish will become part of the paint film. When it comes time to remove the varnish, it will be impossible to avoid removing quantities of the paint and the varnish.
While diluting oil paint, if the artist used a solution of highly diluted bodied (stand) oil in turpentine or mineral spirits instead of turpentine or mineral spirits alone, the chance of permanence in such thinned-out paint films would be good.

How Do Solvents Affect Paint Films?

A study by Charles Tumosa and Marion Mecklenburg at the Museum Conservation Institute shows further problems with the solvents in oil paint.

Solvents’ removal of compounds can result in the loss of color saturation and embrittling the paint film by promoting cracking, thus affecting its overall strength and leading to an eventual collapse of the paint structure. Read how the use of solvents can affect dried oil paint films in The Potential for Solvent Disruption of Oil Paints.

Read more abut the use of solvents when oiling out in the online course Matte, Glossy Paint and Everything In-between.

Based on an excerpt from “Is Your Contemporary Painting More Temporary Than You Think?” by Louis Pomerantz.