What about varnish?
What About Varnish?
Many artists are not sure when, why, or how a painting should be varnished. Let’s have a look at these questions. If you do a water color painting on paper it is normal to frame it behind glass to protect it. After all, watercolor paint is not much more than pure pigment with a very small amount of binder. It has to be protected and there is no way that you could clean the painting without damaging it. Because oil and acrylic paints have a heavy binder (linseed oil and acrylic polymer emulsion) that surrounds and protects the pigment, it is not as obvious why an additional layer is required to protect the painted surface. But it still needs protection. Think of the varnish layer on an oil or acrylic painting like the glass on a watercolor. You can wipe and clean the glass without harming the painting. Likewise, a layer of varnish can be cleaned, and the oil or acrylic paint will not be disturbed.
When a painting hangs it collects on its surface dirt, dust, smoke, grease, and various pollutants in the air. Over the years the accumulation of these elements can cause the painting to look darker or more brown or yellowish. Some of the dirt may be well imbedded into the surface and will required strong cleaning agents to remove them. A thin layer of varnish can easily be periodically cleaned or even removed by a professional restorer along with all the accumulated dirt leaving the painting looking as fresh as the day it was painted. If the dirt is stuck to the unprotected paint layer itself, then removing it may mean damaging the image. Especially if there are thin, delicate layers of paint or glazes. The Varnish is meant to be a temporary layer of protection that can be gently cleaned and eventually removed and replaced once it has accumulated too much dirt. The process of removing the varnish is called “Stripping” and is best done by a professional restorer.
It is common to think that somehow acrylic paintings don’t need a varnish as much as oil paintings do. This is false. In fact, the dried acrylic resin is more sensitive to solvents than a dried layer of oil paint. Moreover, acrylic resin is thermoplastic and electrostatic. In warm temperatures it becomes softer and more sticky so dirt sticks to it more easily. Because it is electrostatic it actually attracts dirt particles floating in the air! The bottom line is if an art work of any kind is exposed to the air it will get dirty and need cleaning and it is better to clean or replace the varnish than to risk damaging the image by cleaning. Another important point to mention is that some artists like to use oil and acrylic paintings in thin washes, like watercolors. When this is done the binder (linseed oil or acrylic resin) is diluted so much that the pigment is left virtually unprotected, like a watercolor painting. In this case it is best to frame these pieces behind glass as you would with a watercolor painting since the addition of a varnish layer would effectively become the binder and then you would not be able to clean or remove it without damaging the paint.
Two Kinds of Varnish
The original varnishes used for oil and tempera paintings were natural resin varnishes like Damar and Copal. Natural resin varnishes are still used by some artists on oil paintings but should not be used on acrylic paintings because these varnishes need to be dissolved in solvents like turpentine that are normally harmful to acrylic paint. The new synthetic acrylic solution varnishes are in more common use now and can be used on either acrylic or oil paintings. They are made with an acrylic resin that is dissolved in mineral spirits rather than water like the paints. These varnishes are supposed to be non-yellowing, unlike the natural resin varnishes that tend to take on an amber hue over time.
Spray on or Paint on Varnish?
There are certain advantages to spraying your varnish on rather than painting it on, and vice versa. The greatest advantage of spraying varnish is that it allows you to apply the varnish in a thin, even layer. Varnish layers should be quite thin so they can be easily removed. The habit of some painters old and new to pour a thick layer over their work is not recommended. The problem with spraying varnish is of course the potential health hazard. You should spray your paintings in a well ventilated space and use a respirator. The best quality acrylic solution varnishes do not come in spray cans as far as I know, though they can be diluted and used in a sprayer. When brushing the varnish on use a good quality wide brush that is use only for varnishing. Apply the varnish in a thin even coat and then without dipping the brush, gently wipe over the varnish to smooth it out and pick up any excess.
Gloss or Matte Varnish?
The choice here has to do mostly with the visual effect sought. A matte varnish is simply a gloss varnish with tiny transparent particles added to it that deflect the light. The addition of these particles does mean that the varnish coat will be somewhat less durable and more prone to scratches. The good quality acrylic solution varnishes come in both matte and gloss and can be mixed in any proportion to achieve the desired effect. For most images a mixture of between 4- 6 parts gloss to 1 part matte varnish is a good all around varnish.
