Cobalt blue
Cobalt blue in impure forms had long been used in Chinese porcelain, but it was independently discovered as a pure alumina-based pigment by Louis Jacques Thénard in 1802. Commercial production began in France in 1807. The first recorded use of "cobalt blue" as a color name in English was in 1777. The leading world manufacturer of cobalt blue in the 19th century was Benjamin Wegner's Norwegian company Blaafarveværket ("blue colour works" in Dano-Norwegian). Germany was also famous for production, especially the blue colour works ("Blaufarbenwerke") in the Ore Mountains of Saxony.
Blue
Another important influence on painting in the 19th century was the theory of complementary colours, developed by the French chemist Michel Eugene Chevreul in 1828 and published in 1839. He demonstrated that placing complementary colours, such as blue and yellow-orange or ultramarine and yellow, next to each other heightened the intensity of each colour "to the apogee of their tonality." In 1879 an American physicist, Ogden Rood, published a book charting the complementary colours of each colour in the spectrum. This principle of painting was used by Claude Monet in his "Impression – Sunrise – Fog" (1872), where he put a vivid blue next to a bright orange sun, (1872) and in "Régate à Argenteuil" (1872), where he painted an orange sun against blue water. The colours brighten each other. Renoir used the same contrast of cobalt blue water and an orange sun in "Canotage sur la Seine" (1879–1880). Both Monet and Renoir liked to use pure colours, without any blending.