How to varnish an oil painting

It’s autumn in New Eng­land, so I’ve been catch­ing up on var­nish­ing. Why now? Because I have some paint­ings that have been sit­ting around for awhile, and because the warm weather is over. That means the humid­ity is gone. It’s always much bet­ter to var­nish when the air is very dry. Mois­ture increases the chances of bloom, in which the var­nish becomes slightly milky.

Do you need to varnish?

Yes, you do. Oil paint­ings need var­nish to pro­tect them from being dam­aged by par­tic­u­late mat­ter in the air. Var­nish also serves to even out the gloss pro­duced by dif­fer­ent pig­ments and to slightly darken the darks, increas­ing con­trast and giv­ing the paint­ing a bit of extra “pop.”

How long to wait

One of the incon­ve­nient things about oil paint is that you need to wait before var­nish­ing. If the paint is applied thinly, you should wait at least a cou­ple of months before var­nish­ing. If you have painted with thicker impasto, it may be a year (or more if the paint is really thick) before the paint­ing should be var­nished. If you need to sell a paint­ing before it’s ready for var­nish, it’s cus­tom­ary to let the buyer know when you rec­om­mend var­nish­ing and to vol­un­teer to do the job your­self if the new owner is will­ing to ship both ways.

Mate­ri­als

While I don’t like dammar var­nish in medi­ums (it’s too soft and too easy to dis­solve if the paint­ing is later cleaned), it’s good for var­nish­ing. You can buy dammar crys­tals and dis­solve them in gum tur­pen­tine to make your own var­nish, or you can buy var­nish pre-made. Never add min­eral spir­its to dammar, as it is not a strong enough sol­vent for this pur­pose. Use only high-quality gum tur­pen­tine (if it smells really bad, don’t use it) for thin­ning dammar. Turps works bet­ter for cleanup as well.

Because of the turps, always var­nish where there is very good ven­ti­la­tion. Choose a spot that is not dusty. Opti­mally, you would vac­uum the room the day before, then let no one into that room until var­nish time, so that the dust can set­tle and thereby stay out of your painting.

Prac­tice first

Var­nish­ing smoothly takes a lit­tle prac­tice. I’m always scared to var­nish a paint­ing I really like, even though it tends to come out just fine. If I haven’t done any var­nish­ing for awhile, I always start by var­nish­ing one or more stud­ies or paint­ings that came out badly, so I can make any mis­takes with them. The first few times you apply var­nish, test the whole process out on paint­ings you don’t care about first. Let those paint­ings dry and inspect for bloom, missed spots, dust, runs, uneven gloss, or stick­i­ness. If you have such prob­lems, keep prac­tic­ing on test paint­ings until you have a process that works con­sis­tently for you.

Var­nish process

I use a two inch nat­ural hair “gesso” brush for var­nish­ing. A wide brush is a must; with a nar­rower brush it is too easy to miss a few spots (I’ve made this mis­take). If nec­es­sary, clean the sur­face of the paint­ing with a clean, lint-free cloth. You can dampen the cloth slightly with turps if nec­es­sary. Make sure that there is no way that water or mois­ture can get on the paint­ing, the brush, or the container.

When you’re ready, dip the brush in the var­nish and wipe off the excess on the lid of the con­tainer. Apply the var­nish thinly and evenly, stroking the brush from one end of the paint­ing to the next. A lit­tle var­nish cov­ers a sur­pris­ingly large area. Don’t add more var­nish to the brush until nec­es­sary. I tend to keep stroking back and forth across the paint­ing until the var­nish becomes tacky. This tends to reduce drips and also reduce the gloss slightly.

When done, clean the brush in turps, then with soap and water. Make sure the water is nowhere near the newly-varnished painting.

Lean the var­nished paint­ing against a wall to reduce the like­li­hood that dust will land on it. Stay out of the room to limit the amount of dust you kick up until the var­nish is dry. In cool dry weather, var­nish dries overnight. I’ve heard of it tak­ing much longer in warm, humid weather. That’s one rea­son why it’s a good idea to test your var­nish process on a paint­ing you don’t care about first.

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Update 9 Novem­ber 2008: It’s impor­tant to clean your var­nish­ing brush thor­oughly after­ward. You’ll need to clean it in a strong sol­vent such as turps. Min­eral spir­its and other odor­less thin­ners won’t dis­solve dammar.