By Armand Cabrera
The last piece of painting anatomy is varnishing your painting if it is painted in oils. No painting step creates more uncertainty and problems for oil painters then varnishing. A varnish layer was added to paintings for protection from chemical reactions from air and sunlight and also dust and soot from household smoke from candles, oil and gas lamps, wood and coal burning stoves and fireplaces. Another benefit to varnishing a painting was the varnish evened the painting out visually. Oil paintings have different pigments drying to different finishes of glossiness. Some were very flat and some shiny. Applying a varnish unified the painting surface and gave the colors a fresh wet look.
When varnishing, a thin uniform coat of varnish is preferable to a heavy coat. A heavy coat is actually less durable and more susceptible to decay and problems. The best application is spraying on varnish while the painting is laying flat and then once the varnish has set turning the painting towards a wall face down to prevent dust and other objects reaching the surface.
There are a number of picture varnishes on the market, but basically they break down into two camps matte and glossy varnish. The three most accepted materials for varnishes are Damar, Mastic and Acrylic; two of them, Damar and mastic are made from trees the third is an acrylic solution, methacrylate, a polymer that has been used by museum conservators since the 1930's as a final varnish. Damar and its acrylic substitute have the best properties for picture varnish. Varnishes have other compounds added to them to make them have a matte finish and there is no matte varnish recommended as a final varnish by conservators.
The question of when to varnish is a nightmare for painters. According to the material handbook a painting should be varnished sooner than too late. That is, after the oil in the pigment has dried. When using linseed oil, that is about two months’ time in a normal climate. The reason for this is oil paints begin adverse chemical reactions when exposed to air and sunlight. The sooner you seal them from these the better it is for the painting. Another train of thought is to varnish as soon as the painting is dry to the touch and let the varnish age with the painting. This works better if you are using an acrylic varnish which will retain a more flexible structure over time.
My best advice is to try some tests and see what kind of results you get. I usually varnish my oil paintings within the first couple of months and I use an acrylic varnish.