Varnish serves two purposes, protection and rejuvenation of the painting’s surface. Wet paint has a relatively even surface that reflects light consistently. As the painting dries, because of absorption and evaporation, that surface becomes microscopically rougher, scattering light, making the painting look hazy and dull. Varnish evens out that surface, making it look like it did when it was wet.
Historically, varnish was made from natural resins like damar and mastic. These resins turn brown and become brittle over time. Also, they become cross-linked with the oil, making it nearly impossible to remove. Newer synthetic resins have been developed that don’t have these drawbacks. One of those resins is Regalrez 1094. Here’s a recipe adapted from research done by the National Gallery of Art in Washington, DC.
- 50 grams Regalrez 1094 resin
- 250 milliliters Gamsol
- 1 gram (about 33 drops) Tinuvin 292
- 1 gram (about 50 blobs) Kraton G, pre-dissolved in ~30ml mineral spirits
- optional 3 grams Cosmoloid 80H microcrystalline wax, for a satin finish
The Regalrez resin will come in a bag of small chunks. It speeds up the process if you pulverize it to a powder first. You can just put it in a heavy ziploc bag and hit it with a rubber mallet. Use a funnel or a make a paper cone to get it into a bottle or jar with the Gamsol. Shake that every few hours and it the crystals will eventually dissolve. You can then add the pre-dissolved Kraton G and Tinuvin 292.
The varnish can be brushed on. If it beads up and refuses to ‘stick’ to the painting, you can try scrubbing the varnish brush into the painting. If this won’t work, wipe the problem area with strong mineral spirits or turpentine. This beading up happens when there’s a slick surface, maybe from many oil-rich glazes. Scrubbing or wiping with a strong solvent ever so slightly roughens the surface so it’ll accept the varnish.
The recipe above generally makes a varnish that isn’t terribly glossy, depends on absorbency of the painting. If you want a satin or matte appearance, you have a few options. The easiest is to wait for the varnish to set up a bit, maybe 30 minutes, and drag a dry brush through the varnish layer to slightly disturb the surface, making it more matte. You could also add some microcrystalline wax to the varnish (Cosmoloid 80H). I prefer to varnish first with a gloss varnish to make the colors rich, then spray apply a matte varnish on top of that to adjust the sheen.
This varnish is removable with Gamsol, mineral spirits, or turpentine.
