The Role of Drying Oils

(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987 revised 1998)

The most important and unique characteristic of oil paint is the thin coating of oil on each particle of pigment.  As said above, this coating consists of a “drying” oil such as linseed or poppy oil.  The oil dries through oxidation, a chemical reac­tion between the oxygen in the air and the oil, and not through evaporation.  This oxidation process creates a remarkably durable and flexible paint film.  Since each particle is separated by a clear film, light can pass between some of the particles of pigment, as well reflect off others.  It is these characteristics that give this painting medium its great depth and luminosity, when used correctly.

The three most common errors in oil painting are caused by varnishing a paint­ing before complete oxidation has occurred, stripping the protective coating off the pigment particles by using too much thinner, and painting a faster drying paint film over a slower drying paint film.  It is easy to see how the first error can occur.  A painting may appear dry to the touch in several days or weeks and fool a painter into thinking that it is dry.  But the typical oil painting will take a year or more complete the process enough for a final varnishing.  This timeline is often in conflict with an artist’s desire to hang a show and sell the works soon after they are completed.  What most often happens is that the works that left unprotected or are varnished to soon.  Applying a varnish seals the surface of the painting and cuts of the oxygen supply, which is only a problem it the painting is not fully dry.

The second error, using too much thinner, occurs when there is insufficient knowledge of the role media plays in painting.  Painters will often buy the finest oil paints and then saturate them, using no medium, with the cheapest paint thinner, only to complain about how bad the paint looks and handles.  It is estimated that half the price you pay for a tube of paint is for the labor that it required to properly coat each particle of pigment.  When you use only thinner, or when there is too much thinner in your medium, you remove or damage that precious protective coating and dramatically reduce the quality of your paints.

Third, applying a faster drying paint over a slower drying paint results in cracking and shriveling of the upper most paint layers.  One of the side effects of the industrial age and the increased availability of manufactured paints was the lack of interest in and the subsequent dissolution of many of the artist’s academies where a painter learned their craft.  One has only to walk the galleries of Musee d’ Orsy in Paris, or for that matter any substantial collection of paintings from the mid-1800’s to find numerous tragic examples of this error.

Without a thorough understanding of the role of drying oils, solvents, var­nishes, and pigments, no painter is equipped to take advantage of what oil paints can truly do.

(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987 revised 1998)