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Cobalt blue
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Hex triplet
#0047AB
CMYK (c, m, y, k)
(0.17, , , )
sRGB (r, g, b)
(0, 71, 171)
HSV (h, s, v)
(215°, 100%, 67%)
Cobalt blue is a blue pigment made by sintering cobalt(II) oxide with alumina at 1200 °C. Chemically, cobalt blue pigment is cobalt(II) oxide-aluminium oxide, or cobalt(II) aluminate, CoAl2O4. Cobalt blue is lighter and less intense than the (iron-cyanide based) pigment Prussian blue. It is extremely stable and has historically been used as a coloring agent in ceramics (especially Chinese porcelain), jewelry, and paint. Transparent glasses are tinted with the silica-based cobalt pigment smalt.
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.
In human culture
Art
Watercolorist and astrologer John Varley suggested cobalt blue as a good substitution for ultramarine for painting skies, writing in his "List of Colours" from 1818: "Used as a substitute for Ultramarine in its brightness of colour, and superior when used in skies and other objects, which require even tints; used occasionally in retrieving the brightness of those tints when too heavy, and for tints in drapery, etc. Capable, by its superior brilliancy and contrast, to subdue the brightness of other blues."
Cobalt blue has been used in paintings since its discovery by Thénard by painters such as Turner, the Impressionists such as Renoir, Monet and Post-Impressionists such as Van Gogh. It is stable and lightfast and also compatible with all other pigments.
Maxfield Parrish, famous partly for the intensity of his skyscapes, used cobalt blue, and cobalt blue is sometimes called Parrish blue as a result.
Cobalt blue was the primary blue pigment used in Chinese blue and white porcelain for centuries, beginning in the late 8th or early 9th century.
Automobiles
Several car manufacturers including Jeep and Bugatti have cobalt blue as one paint options.
Construction
Because of its chemical stability in the presence of alkali, cobalt blue is used as a pigment in blue concrete.
Glassmaking
The blue seen on many glassware pieces is cobalt blue, and it is used widely by artists in many other fields.
Cobalt glass almost perfectly filters out the bright yellow emission of ionized sodium.
Ophthalmology
Cobalt blue is used as a filter used in ophthalmoscopes, and is used to illuminate the cornea of the eye following application of fluorescein dye which is used to detect corneal ulcers and scratches.
