In the history of painting, the work of Georges Seurat (1859-1891) stands out as being a unique synthesis of both science and art, as articulated for example in his masterpiece A Sunday Afternoon on the Island of the Grande Jatte of 1886 (fig.2). By incorporating the cutting-edge color science of the day, in a new technique referred to as divisionism or pointillism (image above), Seurat and his followers, the Neo-Impressionists, are credited with creating some of the most luminous and vibrant paintings in the history of art.
However, there is one small problem with this oft cited description – the paintings are neither bright nor luminous, and the technique suffers from a misunderstanding of color science rather than a practical application color theory. More surprising however, is the fact that the lack of luminosity found in the paintings and the scientific misunderstanding behind them, has not affected their reputation in this respect, as can be seen by the countless books, essays, and exhibitions by historians and experts that continually tout the unique luminosity and ‘scientific’ basis of the work .
Fig. 2 Georges Seurat. A Sunday Afternoon on the Island of the Grande Jatte (1886). The Art Institute of Chicago.
Central to this dilemma is the concept of optical color mixing. Seurat developed a method of juxtaposing small dabs and dots of color on his canvases that, when seen from a distance, would combine in the eye of the viewer to form distinct colors that were more vibrant and luminous than colors combined through traditional mixing on the palette. Through his reading of Charles Blanc’s, The Grammar of Painting and Engraving (1867) and Ogden Rood’s, Modern Chromatics, (1879) he was introduced to the ideas of Michel Chevreul and Hermann von Helmholtz, especially their theories of simultaneous contrast and additive color mixing. From Rood, he discovered that surface colors can be additively combined either by placing them on spinning disks, or juxtaposing them in small dots that at a distance would merge in the viewer’s eye; from Chevreul he learned that complementary, or opposite colors, when placed next to each other, tended to enhance each other. The Divisionist technique of juxtaposing small dots of ‘pure’ color is said to create colors that are “brighter or more luminous than can be obtained by a mixture on the palette”  , and that because, according to Seurat’s friend and critic Félix Fénéon, whose description of his technique he endorsed , “these colors, isolated on the canvas, recombine on the retina; we have therefore not a mixture of material colors (pigments), but a mixture of differently colored rays of light… It is also generally understood that the luminosity of optical mixtures is always superior to that of material mixtures” .
The problem is that Seurat had either misread, or misunderstood Blanc and Rood, as no such claims are made in their texts. What Rood was describing was a particular case of additive mixing, known as partitive or additive-averaging mixing. In such cases, the light from a reflective surface, as in spinning discs or juxtaposed dots, is not only additive, meaning blue and yellow, when combined, will make white not green, but also that the properties of the different colors will be “averaged over the area of the object instead of simply being added. An optical mixture [additive] of two or more paints is certainly higher in value than a physical mixture of the same paints, but optical mixtures, as a whole are not lighter or more chromatic than physical mixtures. Indeed, optical mixtures of varied paint colours tend, due to the averaging principle, to lie towards the middle of colour space, i.e. medium value and low to medium chroma” . Add to this the use of juxtaposed complements by many of the Neo-Impressionists, as seen for example in the work of Paul Signac, (fig. 3), and you get a neutralizing effect, rather than an increase in luminosity .
Fig. 3 Paul Signac The Breakfast, 1887, Otterlo Kröller-Müller Museum. “In a detail from Signac’s Breakfast (right), we can see orange dots in the bluish shade of the cup on the tablecloth; similarly, there are red dots amongst the green reflections of the saucer”, Georges Roque, Chevreul’s Colour Theory and its Consequences for Artists (2010)
Though complements will additively mix to white, a partitive mixture, due to spatial averaging, reduces the chroma and the lightness contrast relative to the mixture components separately (fig 4) .
Fig 4. An example, using stripes, of partitive mixing of additive complementary colors. ©David Briggs 2007
So rather than developing a method for creating luminous colors that are capable of reproducing the brilliance of sunlight, the divisionist technique of Seurat and his followers actually created a degree of dullness and greyness in the colors used. In Seurat’s case, this result is even further exacerbated through his use of unstable colors, such as zinc yellow, that have darkened and dulled considerably over time. To see an interesting digital reconstruction of Seurat’s masterpiece, in its original state – I refer you to the work of Roy Berns and his research on the Grande Jatte at the Art Institute of Chicago .
Seurat’s work has many other attributes that qualify him as a significant painter in the history of art, but on this account, he and his followers were clearly mistaken. You can forgive a young painter (he died at age 31) for misunderstanding the science of his time, concerned as he was with experimentation and development, but the continued propagation of such falsehoods by art historians and experts is unforgivable. With more than 100 years of hindsight, historians and institutions should know better. The real tragedy is not Seurat's misunderstanding of color science but the absence of awareness about it from future generations. What this demonstrates is how received ideas and theory can eclipse what we actually perceive with our eyes. A triumph of theory over experience, that constitutes the real Seurat Delusion.
 Such as Arnason’s, History of Modern Art (London 1977 p.44) and Gombrich’s, The Image and the Eye (Oxford 1982 p238), as well as the Tate Gallery’s website (http://www.tate.org.uk/art/art-terms/n/neo-impressionism) to name a few
 Lee, A. (1987), Seurat and Science. Art History, 10: 203–226. doi: 10.1111/j.1467-8365.1987.tb00250.
 letter to Maurice Beauborg (August 28, 1890) in Herbert, R. L., (1991) Georges Seurat, 1859-1891, New York, Metropolitan Museum of Art, New York
 Feneon, F., Les Impressionistes en 1886, La Vogue. June 1886 pp 261-75
 Briggs, D., retrieved from http://www.huevaluechroma.com/044.php
 Roque, G. (2010) Chevreul’s Colour Theory and its Consequences for Artists, the Colour Group (Great Britain) http://www.colour.org.uk/Chevreuls%20Law%20F1%20web%20good.pdf
 Berns, R., Rejuvenating Seurat’s Palette Using Color and Imaging Science: A Simulation. retrieved from http://www.cis.rit.edu/people/faculty/berns/seurat/Seurat_Berns_Essay_small.pdf