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.
Electrochromic devices
The history of coloration goes back to 1704 when Diesbach discovered Prussian blue (hexacyanoferrate), which changes the color from transparent to blue under oxidation of iron. In the 1930s, Kobosew and Nekrassow first noted electrochemical coloration in bulk tungsten oxide. While working at Balzers in Lichtenstein, T. Kraus provided a detailed description of electrochemical coloration in thin film of tungsten trioxide (WO) on 30 July 1953. In 1969, S. K. Deb demonstrated electrochromic coloration in WO thin films. Deb observed electrochromic color by applying electric field of the order of 10 Vcm across WO thin film. In fact, the real birth of the EC technology is usually attributed to S. K. Deb’s seminal paper of 1973, wherein he described the coloration mechanism in WO. The electrochromism occurs due to the electrochemical redox reactions that take place in electrochromic materials. Various types of materials and structures can be used to construct electrochromic devices, depending on the specific applications.