Chevreul discovered that two colors juxtaposed, slightly overlapping or very close together, would have the effect of another color when seen from a distance.

After looking at a red object, one may see a cyan echo/halo of the original object.

In his works, Chevreul advised artists to think and paint not just the color of the central object, but to add colors and make appropriate adjustments to achieve a harmony among colors. It seems that the harmony Chevreul wrote about is what Seurat came to call "emotion".

Chromoluminarism (also called Divisionism) used individual dots or patches of color which interacted optically to create colors rather than mixing the colors on the palette. Chromoluminarists believed this gave their paintings the maximum luminosity scientifically possible. It was this use of the scientific rules and theories of colors that separated the Chromoluminariists from the Impressionists who used instinct and intuition to create colors in their paintings.

Motivated by study in optical and color theory, Seurat contrasted miniature dots or small brushstrokes of colors that when unified optically in the human eye were perceived as a single shade or hue. He believed that this form of painting, called divisionism at the time but now known as pointillism, would make the colors more brilliant and powerful than standard brush strokes. The use of dots of almost uniform size came in the second year of his work on the painting, 1885–86. To make the experience of the painting even more vivid, he surrounded it with a frame of painted dots, which in turn he enclosed with a pure white, wooden frame, which is how the painting is exhibited today at the Art Institute of Chicago.

He believed that a painter could use color to create harmony and emotion in art in the same way that a musician uses counterpoint and variation to create harmony in music. He theorized that the scientific application of color was like any other natural law, and he was driven to prove this conjecture. He thought that the knowledge of perception and optical laws could be used to create a new language of art based on its own set of heuristics and he set out to show this language using lines, color intensity and color schema. Seurat called this language Chromoluminarism.

The emotion of gaiety can be achieved by the domination of luminous hues, by the predominance of warm colors, and by the use of lines directed upward. Calm is achieved through an equivalence/balance of the use of the light and the dark, by the balance of warm and cold colors, and by lines that are horizontal. Sadness is achieved by using dark and cold colors and by lines pointing downward.

Techniquie: Cross hatching
Done before A sunday afternoon
But you can see how Seurat mixes paints so that the colour and light blends in one's eye.
1884

A sunday afternoon 1884 - 18866