Editing Georges Seurat (section)

===Contemporary ideas===
[[File:Seurat-La Parade detail.jpg|thumb|upright|Detail from ''[[Parade de cirque|Circus Sideshow (Parade de Cirque)]]'' (1889) showing pointillism and color theory]]

During the 19th century, scientist-writers such as [[Michel Eugène Chevreul]], [[Ogden Rood]] and David Sutter wrote treatises on colour, [[optical]] effects and [[perception]]. They adapted the scientific research of [[Hermann von Helmholtz]] and [[Isaac Newton]] into a form accessible to laypeople.<ref name="Robert Herbert">Herbert, Robert L., ''Neo-impressionism'', New York, Solomon R. Guggenheim Foundation, 1968</ref> Artists followed new discoveries in perception with great interest.<ref name="Robert Herbert" />

Chevreul was perhaps the most important influence on artists at the time; his great contribution was producing a colour wheel of primary and intermediary hues. Chevreul was a French [[chemist]] who restored [[tapestries]]. During his restorations he noticed that the only way to restore a section properly was to take into account the influence of the colours around the missing [[wool]]; he could not produce the right hue unless he recognized the surrounding [[dye]]s. Chevreul discovered that two colours juxtaposed, slightly overlapping or very close together, would have the effect of another colour when seen from a distance. The discovery of this phenomenon became the basis for the pointillist technique of the Neo-Impressionist painters.<ref name="Robert Herbert" />

Chevreul also realized that the "halo" that one sees after looking at a colour is the opposing colour (also known as [[complementary color]]). For example: After looking at a red object, one may see a cyan echo/halo of the original object. This complementary colour (as an example, cyan for red) is due to [[retina]]l persistence. Neo-Impressionist painters interested in the interplay of colours made extensive use of complementary colors in their paintings. In his works, Chevreul advised artists to think and paint not just the colour of the central object, but to add colours and make appropriate adjustments to achieve a harmony among colours. It seems that the harmony Chevreul wrote about is what Seurat came to call "emotion".<ref name="Robert Herbert" />

It is not clear whether Seurat read all of Chevreul's book on colour contrast, published in 1859, but he did copy out several paragraphs from the chapter on painting, and he had read [[Charles Blanc]]'s ''Grammaire des arts du dessin'' (1867),<ref name=techbull/> which cites Chevreul's work. Blanc's book was directed at artists and art connoisseurs. Because of colour's emotional significance to him, he made explicit recommendations that were close to the theories later adopted by the Neo-Impressionists. He said that colour should not be based on the "judgment of taste", but rather it should be close to what we experience in reality. Blanc did not want artists to use equal intensities of colour, but to consciously plan and understand the role of each hue in creating a whole.<ref name="Robert Herbert" />

While Chevreul based his theories on Newton's thoughts on the mixing of light, Ogden Rood based his writings on the work of Helmholtz. He analyzed the effects of mixing and juxtaposing material pigments. Rood valued as [[primary colors]] red, green and blue-violet. Like Chevreul, he said that if two colours are placed next to each other, from a distance they look like a third distinctive colour. He also pointed out that the juxtaposition of primary hues next to each other would create a far more intense and pleasing colour, when perceived by the eye and mind, than the corresponding color made simply by mixing paint. Rood advised artists to be aware of the difference between additive and subtractive qualities of colour, since material pigments and optical pigments (light) do not mix in the same way:

*Material pigments: Red + Yellow + Blue = Black ( [[CMY color model|Magenta, Yellow and Cyan]] give a true black when mixed; Red, Yellow and Blue generally do not.)
*Optical / Light : Red + Green + Blue = White

Seurat was also influenced by Sutter's ''Phenomena of Vision'' (1880), in which he wrote that "the laws of harmony can be learned as one learns the laws of harmony and music".<ref>{{cite book|first=Sam|last=Hunter|author-link=Sam Hunter (art historian)|chapter=Georges Seurat|title=Modern Art |url=https://archive.org/details/modernartpaintin00hunt|url-access=registration|location=New York|publisher=[[Harry N. Abrams]] |year=1992|page=[https://archive.org/details/modernartpaintin00hunt/page/27 27]|isbn=9780810936096}}</ref> He heard lectures in the 1880s by the mathematician [[Charles Henry (librarian)|Charles Henry]] at the [[University of Paris|Sorbonne]], who discussed the [[emotion]]al properties and symbolic meaning of lines and colour. There remains controversy over the extent to which Henry's ideas were adopted by Seurat.<ref name="Robert Herbert" />