Gold leaf has been used to beautify and evoke meaning in painting throughout history, functioning as a luminous counterpoint to the flesh, fabric and nature painted with pigmented media. Artists today still use gold leaf, but have also added other metal foils, glitters, iridescent and interference paints to their palettes to activate and enliven their work. For oil painters looking to expand their options into the realm of special effects colors, Williamsburg Handmade Oil Colors has six Iridescent colors that shimmer like metal: Pale Gold, Silver, Copper, Bronze, Pewter and Pearl White and four Interference colors: Violet, Red, Blue and Green, that flash like pearlescent shells, insect wings or oil slicks.
Williamsburg Iridescent and Interference paints are permanent, lightfast materials made from metal oxide coated mica flakes ground in Alkali Refined Linseed Oil. They produce angle dependent colors, which shift in intensity and color depending on the angle at which the surface is viewed. Their special color effects work by reflecting and refracting light off and through the very thin oxide coating on the mica flakes. The color emitted depends on the thickness and type of oxide used. These colors are translucent when viewed straight on, but can look slightly more opaque when viewed from an angle.
These paints are coarse and granular when squeezed out of the tube. For optimal color effects, the mica particles must be left larger in size and are shaped like flat platelets that tend to cluster together. Also, mica is fragile and would get crushed with milling, so these paints are only mixed and not milled using the three-roll mill. Williamsburg Iridescent and Interference colors are categorized as a medium grind. You’ll find that with knifing or the addition of thinner or medium, that the clustered mica particles relax and these paints become similar in consistency to the other colors in that grind category. For dramatic metallic texture, the Iridescent colors can be brushed or knifed right out of the tube. When used in this way, the iridescent texture catches light like actual metal dust ground in oil to create rough metallic passages, translucent enough to show previously painted layers. To increase translucency and create a more smooth, uniform metallic layer, simply mix a small amount of medium or thinner into the paint with a palette knife or brush.
Interference colors are a special type of iridescent known for their ability to shift from one shimmering color to another as the surface is turned toward and away from a light source. Our interference colors shift from a dominant color, as it is named on the tube, to its compliment. The shift is most dramatic when interference colors are painted over lighter colors or white. When painted over dark colors, especially black, interference colors display their dominant color with an almost holographic radiance, but with no compliment color flip. Interference colors work best when painted thinly. Unlike the Iridescents, they do not display color effects well in thicker applications, but rather tend to look cloudy and coarse.
Both Iridescent and Interference colors can be blended with other colors to create beautiful, shimmering mixtures. They mix best with transparent colors, but can be used in any proportion with any paint. Their color effects can be easily obscured by mixing, so you will need to experiment with different proportions to find what works best for you. Start by adding a tiny amount of color to your iridescent to see how they blend, then try thinning with medium and brushing out over different colors for a variety of effects. Adding medium will bring out the shimmer in the mixture and increase translucency, but medium rich mixtures should be brushed out thinly to reduce the risk of wrinkling and yellowing. Both Interference and Iridescent colors tint mixtures toward their dominant color. Think of them as normal mixing colors with shimmer. For example, mixing a small amount of Ultramarine Blue into Iridescent Copper makes a sparkling Mars Violet Deep masstone with a blue undertone or when mixed with Interference Red, makes an pearlescent, electric bluish-purple with a blue undertone over white and a reddish undertone over black.
Experimenting with Iridescent and Interference colors can open up a whole new range of color and add life to your palette. Unlike with the use of metal foils or glitter, these colors can be used without concern for tarnishing or lightfastness. They can also be used during any stage of the painting, keeping in mind the general rule of fat over lean. These paints are classified as medium to slow driers, which can be adjusted by thinness or thickness of application, the addition of thinner, medium, fast drying medium or the drying tendencies of colors you mix with them. ENJOY!
For a more in depth description of how Iridescent and interference colors create their special color effects, see this earlier Just Paint article called “Iridescent Mediums” from 1987: https://www.justpaint.org/wp-content/uploads/2015/11/jp02.pdf