Varnishing an Oil Painting

Some Background Knowledge and Buyer’s Advice

I was a little confused about the types of varnishes out there and didn’t know which ones were bad to use. So I asked a friend of mine. I learned a lot more than I needed to know, but still here is what I was told:

Varnishes, made from resins, have been around for thousands of years. Until modern chemistry, resins came from plant and animal extracts. They often have pleasant smells and were used in religious ceremonies in days of yore. However many craftsmen started using resins because when they are dissolved in solvents and when applied to certain surfaces they can have a protective quality about them once the solvent has evaporated away. After the solvent has evaporated, there remains a layer of protective resin-like layer. However when used on oil paintings, this varnish will last only a limited amount of years before it yellows, cracks or even becomes foggy.

Experts say that varnishes need to be changed (that is removed and re-applied without disturbing the paint beneath) every 40-60 years. If left on the painting these varnishes can damage valuable art work. In fact, I usually do not varnish my paintings unless I want to achieve a specific sheen or antique look.
Damar and mastic resins are still used popularly today. They are derived from plants but even though they are popular they behave quite badly over time. Stay away from water-based “varnishes” if you are painting in oils of course. Although they are fine for some arts and crafts painted with water-based paints and acrylics, you cannot use them on oil paintings. Traditionally these water-based varnishes are used not only to protect acrylic paintings, but also used to give them a shine that is similar to oils.

With oil paintings, it is best to use an acrylic-resin varnish (a solvent based varnish). So you’ll have to read carefully when buying varnish. Instead of dissolving the acrylic-based resins in water, these varnishes use solvents to dissolve the resin. Many of these varnishes have been examined by
accelerated age tests and also with tests for light and energy exposure. Knowledge is power, so buyers beware. If you’re really investing money and time in an important piece of artwork, you might want to re-think varnishing completely. If you decide to go ahead and varnish make sure you stick to solvent based (acrylic-resin) varnishes. Buyers of some more high-end art with varnishes will need to know that their art will need maintenance in years to come.