Historically, a final varnish was applied to a finished painting which had dried for at least 6 months to protect it. Varnishes such as Damar* must be applied to a very dry canvas. Final varnishes protect paintings from smoke, dust, etc. They are removable. When restorers clean paintings the varnish is removed, taking the pollutants with it. After the needed restoration is done a fresh final varnish is applied.
In the modern world I do not believe that most art collectors subject paintings to the same kind of environmental assaults that the great masters faced, but some protection is not a bad idea. Dust and pollen have a way of settling even in the best of abodes.
That said, the above is not my main concern. I have serious doubts that my work will survive the ages (just saying), but I want my paintings to look the very best they can. Varnishes enhance oil paintings by making them more luminous and evening out the dull areas. Each color dries in its own specific way. Earth tones and darks usually become dull as they dry. Varnishes return paintings to that luscious wet paint appearance. Transparent darks come alive, dull colors become glossy, and the canvas has a uniform finish rather than patches of dull and gloss.
Most of the time I use a retouch varnish, either Weber or Windsor Newton. I can't tell any difference between the two. They can be applied as soon as the painting is dry to the touch and they dry within a few hours if not sooner. Retouch varnishes are made to paint into, thus the name. A painting finished this way can be reworked later without removing the varnish. Though not a final varnish, the aesthetic effect is about the same.
There is now at least one final varnish that can be applied as soon as the painting is dry to the touch. Gamvar, a Gamblin product, is easy to use. If I decide to go this route I make sure that I do not have plans to rework the painting later. I also note on the back of the painting that I have applied a final varnish since I can't be sure it isn't retouch varnish just by looking.
Whether I am using retouch or Gamvar, here is how I do it-
I apply the varnish as evenly and thinly as possible using a disposable foam brush over the entire painting. That's it. I let it dry 24 hours before framing because sometimes they are a little tacky after initially drying. This is the only time I use disposable brushes. I do it because washing the varnish out of the brush is very difficult. I have never tried a spray varnish so I cannot address that but I know there are those who prefer doing it that way. Here is a link to Gamblin's varnish Q&A article. https://gamblincolors.com/varnishing-help/ The product comes in a glossy or matte finish. I prefer glossy. At the time of this writing it is not available as a spray.
Recently I was asked if there was a varnish with UV protection for paintings that are in direct sunlight. I found this on the internet which looks like a good product but I have not tried it. https://www.dickblick.com/products/lascaux-uv-protect-spray-varnish/ It is best to avoid direct sunlight on fine art of any medium, but if unavoidable this is certainly a consideration.
Here is a painting with one swath of retouch varnish applied. I think you can appreciate from the photo how much better that area looks. The background is luminous and the bright colors more brilliant.
Thanks for reading!
* Damar is a hard natural resin that comes from a family of deciduous trees that grow in the East Indies. It tends to darken with age. It can be purchased as crystals for custom mixes or as a liquid or spray.
