The art of painting underwent a revolution starting in the 1860s.  The cumulative result of a systematic study of light and color, coupled to a rising interest in scientific observation and the preference by artists for on-site plein-air painting, modified the age-old effort of trying to capture or duplicate the true, natural representation of light to that of representing the effect of light in terms of an optical stimulus/response sensation.

This revolution in art was spurred by numerous scientific color theories that were circulated in the latter part of the 19th century.  This trend was manifested by newly published scientific investigations of physiological optics and, most importantly, in the active involvement of the artists in these fields.  The artistic inheritors of this revolution were the Impressionists, in the early 1870s, and more so, the Neo-Impressionists in the 1880s.

Among the many color theories that influenced art in the late nineteenth century, the most popular were those of Eugene Chevreul, originally published in French in 1839, with an English translation appearing in 1872.  Chevreul was a consulting chemist who was asked to improve the quality of dyes used in a tapestry factory.  He conducted many experiments, looking for ways to produce colors that were more vivid.  He deduced that the role of the chemist was not as important as the role of the artist, and that more potent dye formulations would not significantly improve results as effectively as proper color placement.  Thus evolved Chevreul's Law of Simultaneous Contrast of Colors.  It states, in part, "The apparent intensity of color does not depend as much on the inherent pigmentation...as it does on the hue of the neighboring color."  Furthermore, Chevreul adds, "When two colored objects are scrutinized together, the color of each will be influenced by the complementary color of its neighbor."  Moreover, "In the case where the eye sees at the same time two contiguous colors, they will appear as dissimilar as possible, both in their optical composition and in the height of their tone."  The distinction of Chevreul’s work is that it took into consideration the physiological processes by which the human eye receives color and the way that information is interpreted by the brain.

Chevreul's work was truly revolutionary because of its basis in recent advancements in the scientific study of physiological optics.  His law explored the role of color as a stimulus on the human eye, not necessarily on its role in nature.  He advised the artist to realize that, "There are colors inherent to the model which the painter cannot change without being unfaithful to nature (and) there are others at his disposal which must be chosen so as to harmonize with the first."  In addition, he cautioned, "The greater the difference between the colors, the more they mutually beautify each other; and inversely, the less the difference there is, the more they will tend to injure one another."

Chevreul’s color theories, as well as an assortment of other scientific approaches, were scrutinized and systematized by the Impressionists in the early 1870s and to a greater degree by the Neo-Impressionists, followers of Georges Seurat (1859-1891), in the 1880s.  The immediate outcome of this scientific infusion in art was the appearance of intensely bright paintings, particularly in the representation of sunlit outdoor scenes.  The utilization of the previously discussed laws of color contrast and color harmony enabled the artist to present the effect of intense sunlight and at the same time, the effect of cool, lively shade, without arbitrarily darkening the shadow.  Overall, the Impressionist painting was designed to create movement on the optical plane by the juxtaposition of selected color patches, a movement which closely approximated the natural fluidity of light.

The concerns of artistic methodology and preference of subject matter caused the Impressionists to part company with the Realists.  Technically speaking, the Realism of Courbet and the Romantic-Realism of Theodore Rousseau and Charles-Francois Daubigny (1817-1878) were more or less academic approaches, differing only in subject matter and objective content.  Impressionism, by contrast, repudiated most of the tenets of the Academy.  The time consuming, over-worked method of painting which required days or weeks to produce a painting was spurned by the Impressionists.  They lamented the artificiality of light and color which often characterized an academic canvas, a consequence of painting in the studio.  Impressionists preferred instead to paint directly on primed canvas and to set the easel out-of-doors.