Sometimes, the qualities you love about particular paints (the reworkability of oils, for instance, or the spontaneous excitement of watercolor) can be the very things driving you crazy as you work. But performance-altering mediums and additives are an excellent way to hold on to your sanity for a bit longer. Just a few drops in your paint can make it behave the way you want. There are mediums that thicken paints and those that thin them. You can buy gels that make oil, acrylic and watercolor paints more transparent, while enabling you to create bold impasto effects. In this article, I?d like to focus on four types of mediums: siccatives, retarders, extenders and surfactants.
Setting the Pace
You can speed up your paint?s drying time with a siccative (or drier) or slow it down with a retarder. Use siccatives carefully in oil paints, because of the risk for undesirable side effects such as darkening or weakening of the paint when it dries. Alternatively, I?ll sometimes add a bit of alkyd medium to my oils to speed things up. The more you add, the faster your paint will dry. I often paint with alkyd glazes, which will usually dry to the touch overnight.
Retarders, used primarily with watermedia, give you more time to work with the paint. You can slow the drying process of watercolors with an additive such as Winsor & Newton?s blending medium, and several companies market retardants for acrylics as well.
There?s also a little-known additive called Texanol (marketed by Kremer Pigments in New York) that allows acrylics to dry under much lower temperatures. If you like to paint landscapes en plein air on cold days, this might be worth looking into. The additive must be stirred in vigorously, because it repels the water a bit and can cause the pigment particles to flocculate (cluster together) in very watery washes. I avoid this problem by mixing the Texanol thoroughly into undiluted paint, and then diluting the mixture with water for washes.
Make It Last
Extenders allow your paint to go further without having to thin it or add more pigment. In many cases with acrylics and oils, an extender is simply the base medium from which a manufacturer?s paints are made—but without the pigment. You can extend your watercolors with liquid gum arabic or with Maimeri?s Medio per Acquerello (Italian for watercolor medium), which is gum arabic with a touch of glycerine.
Here?s an example of how useful extenders can be, from many years ago when I was still new at art. I had just painted a seascape in acrylics, in which I had blocked out the major forms with paint that had been slightly thinned, if at all. I then painted the fine details onto the major forms with paint that I?d diluted considerably with water. I was very happy with the results. But then I began to varnish the painting with a large brush. And to my dismay, the broad brushstrokes literally swept away most of the delicate details I?d so painstakingly rendered. My overly thinned paint hadn?t contained enough medium to bind it to the underlying surface. If I?d used an extender to dilute the paint, this wouldn?t have happened.
Lose the Outlines
A surfactant can be quite useful if you like to work with watercolor or acrylic washes. This additive reduces surface tension when you apply the paint to the support surface. The result is that you avoid the hard edges and rim lines that form when a wash dries.
Surfactants for acrylics usually have ?flow? in their names, such as Flow Release (Golden Artists Colors), Flow Releaser (Daniel Smith), Flow-Aid Flow Enhancer (Liquitex) and Flow Improver (Winsor & Newton). Ox gall is the traditional surfactant for watercolors, but I find acrylic surfactants to be more effective with watercolor washes.
Whichever you use, be aware that surfactants work well only on surfaces that are relatively smooth, such as cold-pressed watercolor board or Fabriano Uno Soft-Press and hot-pressed watercolor paper. They won?t work on rough or cold-pressed watercolor paper, because these surfaces are coarse enough to resist the surfactant.
There are a number of other mediums you can try. As you explore what they can do, keep two things in mind. First and foremost, always follow the manufacturers? instructions on the labels. And second, experiment with any new product and get to know how it works for you before you use it on an actual painting. Given these two precautions, there?s an adventure in store as you set out to expand your creative horizons.
Mediums in Action
Freckles (acrylic, 7×4?) is a demonstration painting I did of a sunburned face, and it involved some of the mediums I describe in this article. Here?s how it developed: I modeled the facial forms by overlaying several consecutive layers of diluted paint. To establish the general tonal areas, I initially used washes of burnt sienna that had been thinned considerably with plenty of pure water. Because this painting is on cold-pressed watercolor board, which is highly absorbent, these early washes soaked into the prone surface of the board and dried without building up a film.
I laid in the first wash without any additive, but I included a few drops of a surfactant to most of the subsequent washes. If I hadn?t, I would have ended up with an unsightly and distracting clutter of crisscrossing hard edges over the entire surface of the face.
Once a coating of acrylic had begun to build up on the surface, I could no longer use washes diluted only with water. That?s because there wouldn?t have been enough adhesive in the fluid to bind it firmly to the previous layers of paint. So I turned to Transparent Airbrush Extender (made by Golden Artists Colors). Although technically created for extending airbrush acrylics, I use it as a thinning medium for my fluid acrylics. It contains a ?leveling agent? that allows the paint to even itself out, thereby eliminating any trails left by brushstrokes. I mixed two parts medium to one part water and used that solution to dilute my acrylics.
The airbrush extender does have a drawback, in that it dries somewhat slowly (it contains a retardant to prevent the paint from drying too fast inside an airbrush and jamming it up). So to speed up the drying process, I apply heat. I consider this a minor inconvenience that?s well worth the results, which are smooth, well-blended skin tones.
Watercolor Effects: These two paint strokes (on cold-pressed watercolor board) demonstrate the textural effects you can get in watercolor with granulation medium (top) and texture medium (bottom), both by Winsor & Newton. With these additives, you can create a plethora of realistic textural effects, such as old timeworn leather, tree bark, stone and bricks. I sometimes use the granulation medium to produce the appearance of fur as well.
Changing the Look
Mediums can alter the appearance of your paint effects in addition to changing their performance. Many artists, for example, add wax mediums to their oil paints, or pumice to their acrylics, to achieve different textures. These additives are particularly vital to artists who like to do trompe l?oeil still lifes. You can also buy mediums that make watercolors iridescent or textured.
Granulation medium, made by Winsor & Newton, is a great watercolor tool for creating some fascinating textural effects. (A touch of white vinegar can induce an acrylic wash to granulate.) The granulation process requires a standing pool of water to do its job, since it only occurs when the pigment separates from the water and settles down on the surface of the paper or board. I also recommend using distilled or otherwise purified water, because ?hard water,? such as from the tap, may inhibit the medium?s performance. Granulation medium works best with heavy pigment particles, such as earth colors and iron oxides, which already have a tendency to sink in water.
Losing Your Edge
These two brushstrokes of an acrylic wash (on cold-pressed watercolor board) show you how surfactants work. I did the one on the left without a surfactant, and you can see the distinct boundary that the dried paint has left all the way around the stroke. In the second stroke, I added a surfactant, which has entirely eliminated the hard perimeter. This can make it much easier to do smooth and subtle modeling for portrait and figure paintings.