Cerulean, also spelled caerulean, is a shade of blue ranging between azure and a darker sky blue.

"Cerulean blue" is the name of a pigment. The pigment was discovered in the late eighteenth century and designated as cerulean blue in the nineteenth century.

The pigment Cerulean blue was discovered in 1789 by the Swiss chemist Albrecht HΓΆpfner. Subsequently, there was a limited German production under the name of CΓΆlinblau.

When the pigment cerulean blue was discovered, it became a useful addition to Prussian blue, cobalt blue and synthetic ultramarine which already had superseded the prior pigments.

It is particularly valuable for artistic painting of skies because of its hue, its permanence, and its opaqueness. Berthe Morisot painted the blue coat of the woman in her 'Summer's Day', 1879 in cerulean blue in conjunction with artificial ultramarine and cobalt blue.

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