Interference Info

Q. At an art supply convention a while back, I bought some acrylic interference paint. It seemed so easy to use and the results looked great, but now I realize that I don’t know how to use it. Can you help?
Juanita Knox
Lakewood, CA

A. Interference pigments are also sometimes called “pearlescent” or “iridescent” pigments, although since they work by interfering with light waves, thus causing the color, “interference” is the most accurate name. These pigments are not particles but flakes of mica, usually coated with a microscopically thin layer of titanium dioxide pigment. When ground into a paint vehicle, these flakes will simultaneously reflect and transmit light, causing a colored appearance that’s dependent on how the flakes are positioned toward the light source, the thickness of the paint film, and the refraction in the flakes themselves. The various colors (which can be red, yellow, green, blue, and some hues in between, like purple) come from the strengthening or weakening of light waves, and not any inherent color as in a normal pigment. These pigments were originally found mostly in the acrylic emulsion paints, but are now appearing in such media as oil crayons.

Interference colors aren’t strong. They’re intended to have an effect on other colors—to add a pearly sheen or luminosity—instead of being used by themselves. In fact, you’ll notice that if you look at a pile of this paint, it appears to be a gray, featureless blob with only a hint of color (unless the manufacturer has mixed in another pigment). To give interference colors their best effect, mix them into another color, perhaps of the same hue but also of other hues, to enhance the second color’s appearance. If you want to use an interference color alone—even though it’s very transparent—try it first against a dark background to see how it works. Typically, interference paints show up best when set against dark colors.

The same basic rules of thumb apply to these colors as for any color mixing:

  1. Decide whether you want the mix to be warm or cool;
  2. If you have to mix more than two colors (plus white), you’re likely to end up with a muddy mixture; and, most important
  3. No verbal explanation, color reproduction or demonstration is ever going to provide you with the answers that trying it out for yourself will.

With these specialty pigments, I’ll add a fourth caveat: Don’t overdo it. You’ll risk disabling a good painting idea for nothing more than a special effect.

There are other colors made using the same principles as interference colors, including pigments that look like bronze, copper or brass, but that are made of the same mica flakes coated with thin films of various mineral or iron oxide pigments. Paints made with these pigments can look remarkably like the actual metal, but they won’t discolor due to oxidation and age as the metallic pigments do. I’ve used these pigments in a painting, but the effect is so subtle (deliberately) that they can only be seen in a certain light.

Mark Gottsegen is an associate professor of art at the University of North Carolina at Greensboro.

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