Most contemporary technologies of color image reproduction use optical mixing to obtain a full range of colors. Four-color process printing, CRT, LCD and plasma displays, all reproduce a wide gamut of hues and values using tiny dots of ink or luminous pixels in just three or four colors. The colors remain discrete in the image, and are only blended in the eye. The illustration below shows a detail of a printed color picture, with inks of cyan, magenta, yellow and black in dots of variable size. A color monitor performs a similar trick with glowing red, green and blue dots of variable brightness.
The old masters who developed the craft of pictorial oil painting did not, as far as I know, ever consciously use the phenomenon of optical color mixing. Most of them used some variation of the technique of grisaille, or painting in black and white (or sometimes in greens or earth tones), then adding color by applying thin transparent glazes over this monochrome foundation. Jan Van Eyck is often considered the first master of this technique, and it’s still commonly used by painters who follow the classical methods. Here are two versions of a painting by Jean Auguste Dominique Ingres, the first version in grisaille, and the second with color glazes applied.
The great virtue of this method is to achieve a feeling of solidity and luminosity. The grisaille painting allows for a sculptural rendition of values, and the white of the grisaille reflects all wavelengths of light, which are then subtly filtered by the glazes. Light penetrates the transparent surface layer of the painting and reflects back to us from a deeper level, tinged as the setting sun or the distant mountain are tinged by the intervening atmosphere.
Directly mixing pigments on the palette or on the canvas, on the other hand, tends to give dull and flat colors. Every opaque blend of two pigments has less brightness and less intensity of color than either of its components. The natural mineral pigments available to painters before the industrial revolution were extremely limited, so the glazing technique was often the only way to achieve color that was both vivid and subtle in its gradations.
In the nineteenth century, several technological innovations led to a completely new approach to color in painting. Photography quickly surpassed the painters in its ability to render monochromatic values. This made painters strive to reproduce the more vibrant effects of color that photography still could not capture. Modern industrial chemistry discovered new synthetic pigments that were both permanent and far more vivid than the classical artists’ pigments. All those paints with chemical sounding names like alizarin and phthalocyanine are products of the new chemistry. Pre-mixed paints in squeezable metal tubes were yet another nineteenth century development that made it much easier for an artist to leave the studio and study the colors of nature and the effects of light outdoors, or en plein air.
French Impressionism was the product of all these changes. The old methods started to seem stodgy and lacking in spontaneity, and in any case were unsuited to plein air painting. You can observe optical color mixing effects starting from the beginnings of the impressionist movement, as in this Renoir painting.
In the detail below, you can see that the clothing and shadows on the ground are painted with various bright colors in close proximity, colors that do not correspond with the actual surface colors of the objects being depicted. The overall impression of the colors in the painting is vibrant but not unnatural.
Monet painted haystacks in a field and the facade of Rouen Cathedral over and over again, trying to capture the ever-changing subtleties of light and air. [Both links in the preceding sentence are well worth a click!] Here the haystack contains dabs of red, olive, lavender, violet and black.
Artists such as Edgar Degas and Mary Cassatt used optical mixes of odd colors like greens and purples to depict flesh tones.
George Seurat studied the science of color perception, and developed an analytical approach to painting with optically mixing colors. He called his method chromoluminarism, though it’s better known today as pointillism, a word originally coined by critics. Here’s one of his mural-scale canvases, followed by a detail of a face in profile, showing the discrete dots of color.
What Seurat does with analytical coolness, Vincent van Gogh does with fiery intensity.
Optical mixing of colors also interested abstract expressionists such as Joan Mitchell.
Chuck Close is the heir to Seurat’s analytical approach, as in this monumental self-portrait.
For my own work in color, I usually use aquarelle crayons on toothy charcoal paper. The crayons deposit bits of pigmented wax on the ridges of the paper. Going over an area with more than one color leaves the markings separate, and the colors mix optically. Here’s a detail of the portrait of Alley featured at the top of this post. You can see that the flesh tones are made up of strokes of blue gray, pink, yellow, light blue, reddish brown and white, on a neutral gray paper. The technique is particularly effective at depicting reflected light in shadow areas.
Here’s a quicker figure sketch, followed by an enlarged detail. Here the colors making up the flesh tones include turquoise, orange, fuschia, and yellow.
Mixing colors in the eye, rather than on the palette, produces color impressions that are bright and shimmery, that suggest not only the effects of light but the slippery nature of flesh tones. The actual colors of living human skin are subtle to the point of elusiveness. Skin is translucent, imbued with underlying colors of blood and fat. Its surface is nearly iridescent, and reflects and refracts the colors of surrounding objects and lights. Flat colors cannot capture this subtlety. Grisaille and glazing can, and so can optical mixing, in a very different way.
All the images in this post, besides those of my own work, were found on the web. Clicking on the pictures will take you to their source pages, and in many cases, to larger versions of the images.