Cerulean

Cerulean (/səˈruːliən/), also spelled caerulean, is a shade of blue ranging between azure and a darker sky blue. The first recorded use of cerulean as a colour name in English was in 1590. The word is derived from the Latin word caeruleus, "dark blue, blue, or blue-green", which in turn probably derives from caerulum, diminutive of caelum, "heaven, sky".

"Cerulean blue" is the name of a blue-green pigment consisting of cobalt stannate (Co
₂SnO
₄). The pigment was first synthesized in the late eighteenth century by Albrecht Höpfner, a Swiss chemist, and it was known as Höpfner blue during the first half of the nineteenth century. Art suppliers began referring to cobalt stannate as cerulean in the second half of the nineteenth century. It was not widely used by artists until the 1870s when it became available in oil paint.