Q. When painting with oils I always seem to get dull areas (flat, rather than somewhat glossy) in the finished work. Why is this happening? Can I fix the problem after the painting’s complete?
A. The condition you describe is known as sinking in. One thing that causes it is a too-absorbent ground layer. Another—and what I suspect is the culprit in this case, since the dullness only shows up in spots—is the use of too much solvent to thin the paints. This can result in an underbound paint layer, meaning that there’s not enough oil content to keep the pigment adhered to the ground.
To avoid sinking in, you need to use less thinner with your paints and mediums. It’s perfectly fine to thin paints with solvent for the first layer of the painting, but not so much that the paint resembles transparent watercolor. Subsequent applications should contain only enough thinner to make the paint plastic. A good way to tell if it’s the right consistency is to see whether it’s hiding the weave of the canvas somewhat and you can still see some of the brushmarks.
In general, I’m not an advocate of using painting mediums with oils, mainly because artists tend to overuse them. But in the case of your multilayer paintings, it will be necessary to add an oil-containing medium in the upper layers in order to adhere to the fat-over-lean rule (oilier paint must be painted over less oily paint). If you use a homemade medium—such as three parts stand linseed oil, one part damar varnish, and six parts gum turpentine or mineral spirits—use it sparingly and don’t thin the paint further with more solvent as you work.
You may want to try one of the alkyd painting mediums now widely available in a variety of viscosities (Winsor & Newton’s Liquin and Gamblin Artist Colors’ Galkyd are two reliable brands). These have the added advantages of drying more quickly, being more stable and being less likely to crack than linseed oil-containing mediums.
To get rid of the dull areas in a completed painting, you can varnish it—but use a diluted retouch varnish before you put on a final coating. You can make a retouch varnish by diluting one part regular-strength damar varnish with four parts gum turpentine (mineral spirits doesn’t work as well when diluting straight damar varnishes).
Your retouch varnish should be thinly brushed onto dull areas with a soft brush, one layer at a time. Allow each layer to dry to see if the retouch has saturated the paint film and returned it to its glossy state. You could also use a spray-on retouch varnish, or one already prepared to the correct dilution—check with your art supply shop. If you choose a spray varnish, be aware of safety and health considerations: Your studio must be equipped with an exhaust fan to remove harmful spray vapors, and you must carefully read all label precautions.
Once the dull areas have disappeared, you can varnish the entire painting with a thin coat of your favorite final varnish mixture. For this, I don’t recommend damar varnish; it’s too likely to yellow and crack with age. I suggest you try one of the acrylic solution varnishes that are thinned with mineral spirits (both Winsor & Newton and Golden Artists Colors make them) or Gamblin’s Gamvar, a low-molecular weight styrene resin varnish developed with the participation of the National Gallery of Art’s conservation department. It, too, is thinned with mineral spirits.
“Every time people tell me I cant do that, I know Im on the right track,” says Betsy Dillard Stroud, who, in addition to creating luminous paintings, writes articles about art, as well as works of non-fiction. “You have to go full steam ahead against all the caveats,” she says. A signature member of the American Watercolor Society (she won a High Winds Medal in 1992), the National Watercolor Society, the Rocky Mountain National Watermedia Society, and the Southwestern Watercolor Society, Stroud is a born Virginian, educated at Radford College with a B.A. in fine arts and the University of Virginia with an M.A. in the history of art. Her paintings are represented by Cynthia Woody Gallery in Scottsdale, Arizona; the Roberts Gallery at El Pedregal in the Boulders in Carefree, Arizona; the Milagro Art Gallery in Tucson, Arizona; and the Madison Avenue Art Gallery in Memphis-Germantown, Tennessee.