To be developed…
MITRA on Varnishes: This excellent article covers a number of related topics: the ideal properties of a final surface coating, the pros and cons of varnishing, and practical advice on applying varnishes.
Sound advice from MITRA: “It is important to remember that even if the source of a varnish is “natural” (e.g. is harvested from the sap of a tree) this does not necessarily mean that it is a superior product that will withstand the test of time.”
Why Varnish a Painting?
Here’s an explanation from George O’Hanlon on Natural Pigments: “Although the Impressionists and many 20th century artists eschewed the application of varnishes on their paintings, varnishes are very important for protecting paintings from dirt, air pollution, handling, etc. from the environment. An unvarnished painting is vulnerable to dirt and dust that will eventually become embedded in the paint. It is also subject to deterioration caused by ultraviolet light and oxidation, and abrasion from handling and transport. A varnish can protect the painting from dirt, ultraviolet light and abrasion. Over the years dirt and dust adhere to the varnish rather than the painting and when the varnish has served its protective function, it can be removed and the painting re-varnished to look as good as new. Applying a varnish to your painting than is an important part of maintaining its appearance and value.”
When Should You Varnish a Painting?
The best practice is to allow the paint to cure for 6 to 12 months after the last brushstroke is dry to the touch before applying varnish.
If you applied the varnish before the paint was well cured, there’s the possibility that some paint will come off with the varnish, in which case you might have some retouching to do. After the retouching, wait six months before re-varnishing, and all should be well.
Varnishing too late is better than not varnishing at all, but the longer the dried, cured paint remains unprotected, the faster it will oxidize on the surface, and the more dirt can become embedded in it. If there are flies landing on it, they leave little dots of brown fly excrement that will eat into the paint, among the other undesirable possibilities that varnish protects against. If there’s tobacco or marijuana smoke in the air or smoke from cooking, the surface of the painting will likely receive some of it, probably not to good effect. This is why I recommend varnishing sometime between 6 and 12 months after the last brush stroke is dry.
Varnish is best applied on the hottest, driest day of the year at the hottest and dryest time of the day, and not until the last brushstroke has had at least six months to cure. If the varnish is applied when the humidity is high, there could be moisture absorbed from the air by the more hygroscopic pigments in the painting, the worst of which in that respect would be umbers and yellow ochre because of their clay content. Clay is highly hygroscopic, meaning that it absorbs water from the air.
Damar is no longer the best varnish available, though it remains popular with painters who aren’t up to date on new materials.
The drawbacks of damar varnish are that it grows more yellow with age, eventually turning brown. Over time, it becomes increasingly insoluble and brittle, thus crack-prone. It changes the appearance of the painting after 30-40 years, and has to be removed and replaced with new varnish.
Product Names: Gamvar, Conservar, UVS Finishing Varnish
There are now varnishes on the market that have the same desirable optical qualities as damar but do not yellow or embrittle, and these remain easily removable with milder solvents than are required to remove aged damar. These varnishes, developed by Rene De La Rie, conservation scientist at the National Gallery in Washington, are based on a synthetic resin called regalrez.
There are at least three companies who offer regalrez varnishes: Natural Pigments (Conservar,) Gamblin (Gamvar,) and Conservators Products Company (UVS Finishing Varnish.)
Varnishing Product Suggestions:
1. I’ve used UVS Finishing Varnish on many of my paintings, with good results every time.
2. Soluvar is an acrylic resin varnish that some museum conservators like, but it’s not my favorite because it will need to be removed and replaced in 40 years or so when the defects of acrylic resins begin to show up.
3. My experiences with Gamvar have all been positive.
I’m equally happy with Rublev Conservar, Gamblin Gamvar, and Conservators Products Company’s UVS Finishing Varnish. I have had no trouble with any of them.
MSA Acrylic Varnishes
There are also MSA acrylic varnishes available from Golden that some painters and conservators like. Those, too, are better than damar in most ways.
The WN gloss varnish is an acrylic MSA varnish that might be all right.
This is from a post in the archives from Sarah Sands, Production Research at Golden: “All synthetic resin varnishes, including our MSA and Archival Varnishes, are more porous then past natural resin ones and as such should allow oxygen to continue to penetrate. However, additional coatings of any type will slow this process down, and retouch varnishes, in general, are not well-liked by conservators. The issues are less about oxygen and curing than the fact that in young paint films the varnish will become more tightly integrated into the structure of the paint, making removal more difficult in the future without risking color lift. Also, exposure to solvents – even OMS – will invariably extract low molecular weight fractions from the paint film, including free fatty acids, and this can lessen the flexibility of the paint. While we know that people use our products in this way we do not recommend retouch varnishes in general unless the paint is at least hard-dry, are applied minimally, and are NOT painted on top of.”
Some artists apply retouch varnish spray as a last layer when their painting is finished, so that it will look good when sold before it receives the actual final varnish later.
Virgil advises against this approach to varnishing, especially for an insufficiently cured oil painting. Here’s why: