An article written by conservator and master paint maker, George O’Hanlon
“Do I really need to wait six months?
The Big Sleep before Varnishing
The age-old advice to wait at least six months before varnishing oil paintings is a good practice, but one that is resisted by many artists. And it is understandable why because when a painting is completed it often needs to be delivered immediately for exhibit or into the customer’s hands.
So, artists often tout the recommendation to wait until the painting is “touch dry”. For some this may be a sufficient amount of time. This recommendation, however, assumes that all paintings are created under the same conditions. Of course, we know this is never the case, since one painter paints on absorbent substrates, another on non-absorbent surfaces, another will use lead white others will use slower-drying titanium white, many paint with impastos and others with thin applications of paint.
A few manufacturers claim that their varnish can be applied much earlier, such as when the painting is “touch dry”, so many artists grab this idea and run with it thinking the moment the paint surface feels dry they have a green light to varnish. However, even these manufacturers are a little more cautious by recommending to test the surface of the painting for sufficient dry time such as with a “fingernail test”.
Somehow many artists believe there is something special inherent in these varnishes. One blogger writes:
Gamvar allows the painting to continue to breathe so the paint underneath can still continue to dry. It doesn’t stop the drying process.
In reality, all varnishes are permeable so oxygen will diffuse into and through them, allowing the polymerization of oil paint underneath. All varnishes, of course, slow the ingress of oxygen into the paint film, thereby delaying the drying process.
Waiting at least six months is still the best practice that can apply to a wide range of painters. In lieu of that, an artist may use (with due caution) the test described below as a method to determine when the painting is ready to be varnished, if she cannot wait the prescribed six months.
The “fingernail test” may be what some manufacturers had in mind for the test method for “Dry Hard Time” described in ASTM D1640:
With the end of the thumb resting on the test film and the forefinger supporting the test panel, exert a maximum downward pressure (without twisting) of the thumb on the film. Lightly polish the contacted area with a soft cloth. The film is considered dry-hard when any mark left by the thumb is completely removed by the polishing operation. Remove any coating from the thumb immediately. The use of a glove, finger cots or the presence of freshly-applied cosmetic products/hand creams may interfere with the test results.
Variations of this test may be used but will also give different results. A problem with using a hard and sharp object such as a fingernail (in contrast to a flat thumb) is that it can give false results depending upon the amount of pressure exerted into the paint film.
Whereas the test described above may work in your case, always keep in mind that some interpretation of the results is involved, often leading to different conclusions. The safest and best practice is to wait the prescribed amount of time—at least six months. But if you cannot do so, then use the test method ASTM D1640, and good luck.”
For more information on varnishing, please consult this article: