Okay, so from "Glossing Over Things: Part I" we now understand why it is important to varnish an oil paintings after it has been finished. Next, let's discuss how to varnish that painting, and with what . . .
Today we have better varnishing options than our forebears had. If you can recall from Part I, the best properties a final picture varnish can have goes something like this:
The ideal picture varnish is a protective coating which levels out the sheen, intensifies the color, won't yellow, is easy to remove, and doesn't cross-link with the underlying oil film over time.This limits our choices to the modern synthetics, which is not a problem since they are terrific options to have. Synthetics come in two forms, as a liquid or an aerosol, and depending upon your preference, either will work. Both will return the color of your work to something close to how it looked when the paint was wet. Both will unify the surface by leveling out the "sinking in" caused by some pigments. Both kinds won't yellow much, or at all, and both easy to remove. And neither will cross-link (much) with the underlying paint film. All this is good. A win-win for all...
So really, it comes down to how you want to apply your varnish.
You spray on the aerosol kind (duh!) which, in most situations, makes the application easy. In addition, art material manufacturers such as Grumbacher and Winsor Newton, and even Kamar and others, all produce quality spray-on varnishes in wide a range of finishes. If you travel a lot, the aerosol cans will be available in almost every art store at your destination, so you don't have to worry about violating any FAA no-fly codes.
In terms of using a final aerosol varnish:
- If you prefer a gloss finish choose the gloss version of the aerosol.
- If you prefer a semi-gloss or matte finish, choose the version which produces that sheen.
- If you wants something in between any of those three options, then first lay down a gloss varnish, allow it to dry, and lightly coat it with one of the others. Re-applying it until you end up with the finish you want. (But lightly, in several coats.)
- It is better to spray on a varnish in several thin coats and not one thick one.
- It is ideal to spray outdoors in temperatures above 60 F, in normal humidity. If this isn't possible try to wait. If you can't wait make sure the painting and aerosol starts out at room temperature, take them outside, apply the varnish quickly, then bring both inside again to warm and dry conditions. If fumes are an issue, put the painting in a room you won't be in for a while.
- Never spray a varnish indoors unless you have a proper ventilation booth available. Your health is too important. The worst way you can get any art material into your body is through your lungs. Remember that.
There are also varnishes which you apply with a brush, much like the artist of old.
These varnishes may be more finicky to work with, but are more rewarding in many ways, and aren't that fussy to deal with after you do it once or twice. One liquid varnish I highly recommend is Gamar, manufactured by Gamblin Oil Colors. Gamar was formulated in conjunction with the conservation staff at the National Gallery of Art in Washington D.C. (USA) and it comes as a two-part formula you mix together: a jar of crystals and a solvent. You combine the two and shake the jar every hour or so, letting things dissolve over a period of 12 to 24 hours, the way artists used to dissolve damar crystals in the olden times. What you end up with is one of the best emulations of a natural varnish there is. With all the modern benefits and none of the traditional concerns.
Gamar has one of the highest refractive indexes I've seen in a synthetic varnish so it doesn't suffer from what I call 'the noxious plastic highlight'. What do I mean by that? Well, the medium of oil imbues a warm kind of clarity to a paint film that acrylic medium doesn't, and Gamar maintains the oil's warmth and clarity. That warmth and clarity is one of the reasons I choose to paint in oil, as opposed to acrylic, so I don't want to relinquish it at the varnishing point.
But at present, Gamar requires the artist to apply it with a brush, which can be inconvenient at times. If you are an artist who maintains a very smooth surface then you'll want to use a soft, natural-hair brush for the application, and work quickly. You will also want to use the "brush back into wet" technique of laying it down, which is to start at the outer edge of a painting, laying a band of varnish across the entire side, and then stepping into the dry area with more varnish, and brushing back into your previously varnished area. Always working from the dry into the wet every time. (And no, you don't re-coat the entire wet area with every pass. That would apply too much varnish in total. You feather your current pass into the last one.) This will minimize or prevent any brush strokes being left in the varnish. But you must work quickly because the solvent will be flashing off in the earlier passages and making those areas more tacky. So don't pause for a break once you begin. Cover the entire painting. And use the largest brush you have. And watch for errant hairs which may drop, from your head or the brush. (Which is a good argument for keeping a pair of tweezers close by as you work.)
Since the surface of my own paintings lean towards the textural – both in the marks I make, and in the actual thickness of the paint, I am less concerned about the 'velvet' and use a stiff boar bristle instead. It helps to get the varnish into the nooks and crannies. And any velvet isn't apparent in my textural areas. But I do pay close attention to how how the varnish goes down in large open areas, such as a sky, or in a flat passage of color.
Once the Gamar on it is a good idea to cover the painting to prevent dust or pet hair from being trapped in it. If the painting is small enough, a piece of elevated cardboard will do. If the varnish is thin enough, or has set and won't run, you can tip a larger painting against a wall (but off the floor!). I do this a lot myself.
Gamar, if unadulterated, will produces a high-gloss finish. If you wish to reduce the gloss the manufacturer recommend dissolving a little artist-grade wax in their version of an odorless mineral spirit (Gamsol) and then adding it to the Gamar before you apply it. (This will look a little milky, but retain most of the clarity.) How much wax you add is up to you but don't go overboard. I haven't had much success in consistently controlling the gloss, but others who work with it more regularly than me I do, have.