Varnishing Oil Paintings

Tuesday, October 12, 2010

Varnishing oil paintings
Picture courtesy of John Kannenberg
A go-to overview of why and which to help you figure out if your painting has been varnished to conservation standards...

This is a companion and follow on article from the last technical article on varnishing acrylic paintings.

Why do we varnish oil paintings?

Uncoated oil paints will absorb atmospheric moisture even in regulated environments and can eventually develop friable surfaces that will crack. A layer of varnish protects the paint from shallow scratches, atmospheric pollution (dust, hair, chemicals) and, ideally, UV radiation. This layer can be removed and replaced when it has become too dirty to wipe clean, and the painting will still remain in perfect condition.  

An artist may also choose to apply varnish to bring out and highlight the lustrous gloss of oil paints. Or they may want to unify the painting surface with a single finish. Oil paints dry to varying degrees of glossiness depending on the pigments, with dark colours tending to dry far more matte than lighter ones.

What's the difference between permanent and retouch varnishes?

Retouch can be painted over and is often used in the painting process to restore the undried appearance to a dried patch of painting for colour matching while an artist continues the work. It is also used as a temporary final varnish for touch dry works, though this is not necessary as a thin coat of final varnish can be used safely in this situation. Retouching varnish doesn’t have the quality that a final varnish has. A final/finishing/permanent varnish makes your painting look a lot better.

Permanent varnish is a confusing name as it is (or should be) removable. More accurately, it is a final varnish that goes onto a dried painting as the final, finishing removable protective layer.

How long do I have to wait to varnish an oil painting?

The Gamblin website answers this really well:
"How to tell if a painting is ready to varnish is easy - just touch it. If there are impasto areas, gently press your fingernail into that impasto. If it is firm underneath the top layer of the painting then it is ready for varnishing."

"In general we recommend painters using alkyd resin painting mediums wait three months before varnishing. Painters using an oil/dammar mix in their painting mediums should wait six months."

And what if the painting is touch dry, sold and needs to be shipped? Varnish is better than no protection. Just remember that this final coat is meant to be thin! A thick coat on a fully cured painting may not cause any problems apart from raising a learned eyebrow, but on a touch dry painting it will significantly retard or even prevent the drying and curing process, with unpredictable consequences. A painting can continue to dry under a thin coat of final protective varnish.

A varnish can be used mixed in with the paint to add gloss, right?

Yikes NO! I mean, yes, this can physically be done but it's really not a sound idea. Here's why:

A medium (something that is mixed in with the paint to alter it's properties) becomes integral to the paint. It can't be removed separately. If varnish is used mixed in with the paint and then that same varnish (or one that dissolves in the same solvent) is used as a final varnish, what do you think happens when that final layer of varnish gets removed for cleaning? Yep, the paint layers dissolve and get cleaned off as well. Hardly ideal!

This situation can be a problem when an artist has used Dammar as both a medium and varnish in the same painting. Watch out!

All varnishes are formulated to be removable (at least they should be). Solubility is one of the characteristics that distinguishes a varnish from a medium.

What's the best varnish to use? 

There's a bit of debate over this. The traditional versus the modern.

The traditional go-to varnish is Dammar. This is a natural tree resin. As such, it's source is variable. Gum can be contaminated with gum from other trees. The quality varies from year to year. The artist has to be quite careful to apply it thinly. It is known to crack and yellow. The lifespan is around 20 years for a coat of this varnish. It is very easy to remove with gum turps and Dammar has been used for around 400 years so it's properties are well known and familier.

Modern synthetic varnishes are can be an acrylic solution or a styrene varnish or a ketone resin.  They are more consistent in quality and easier for artists to apply well than natural resin varnishes. Although not predicted by computer aging simulations, in real life they do darken a little with age, but they are not as prone to cracking as the natural resins.  They tend to be a little harder to remove, and mineral turps is often used as the solvent. 

Although both varnishes do the job of protecting a painting from atmospheric pollution etc, conservationists now tend to prefer and recommend the synthetic varnishes. These have the added advantage of being mould resistant ( because they "close off" completely i.e. they do not leave any capillary holes for drying, they do not trap any water or "food" for mould on the surface) and can have UV protection built in.

To UV or not to UV?

Again from AMIEN:
"The best varnish for your oil painting will contain UV inhibitors. They will delay the deterioration of the most egregiously poor color (say, a fluorescent marker color) for ~5 - 10 years in an outdoor exposure. That might not seem much, but put that color, coated, indoors in a low-light exposure and try to extrapolate a service life: it will be longer, but how much longer is difficult to say... We have to say that the UV inhibitors offer an advantage, especially when incorporated into coatings that will be applied to colors that are good in the first place, and that such coatings are better than unmodified coatings, and that coating paintings of certain types is a good thing."

For artists - here is a list of modern synthetic varnishes with UV inhibitors

This is not an exhaustive list. If you know of others, please let me know in the comments. I am happy to add them. 
Lascaux UV Protect
Windsor & Newton Conserv-Art Gloss Varnish
Golden MSA Acrylic Varnish

After personally contacting all the Australian manufactures, the only Australian made varnishes that make this list are by Derivan as part of their Matisse range (stunning customer service too by the way):
Derivan Matisse MM14 High-Gloss Varnish (turps-based), MM15 Matt Varnish (turps-based), and MM29 Final Varnish Satin Finish

And some spray on varnishes that do the job. Artists, please note that spray on varnishes are very very baaaad for your health unless you have seriously excellent ventilation and wear protective gear.
Krylone Conservation Varnish and UV Archival Varnish

Some tiny tips on the how-to of varnishing

  • Your varnish brush should not be used for any other purpose so it is always clean-no color.
  • Soft brushes generally leave thicker layers of varnish
  • Stiff bristle brushes can leave very thin coats through a gentle scrubbing motion.
  • Mix matte & gloss to get satin
  • Use two coats for the final varnish
  • Allow each layer of varnish to dry overnight 


Technical linky goodness

An excellent thread on varnishing on a top forum.
Excellent article on varnishes, mediums and what conservators like at the moment based on an interview with a conservator:

More art technique articles

This article is one in an ongoing series of technical articles for artists, all archived together and accessible from here. The topics range from details on materials, to the business of art, to specific art techniques. Please make use of this resource.

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