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.
A sample of a commercial cobalt blue pigment
|sRGBB (r, g, b)||(0, 71, 171)|
|CMYKH (c, m, y, k)||(1, 1, 0, 0)|
|HSV (h, s, v)||(215°, 100%, 67%)|
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H: Normalized to [0–100] (hundred)
Historical uses and productionEdit
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 cultureEdit
- 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 and 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.
- Because of its chemical stability in the presence of alkali, cobalt blue is used as a pigment in blue concrete.
- 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.
- 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.
- Two Major League Soccer teams have cobalt blue as a secondary color: Real Salt Lake from its inception and Sporting Kansas City on its home uniforms since 2008.
- Several countries including the Netherlands and Romania, and a U.S. state – Nevada – have cobalt blue as one of three shades of their flags.
- Sega's official logo color is cobalt blue. Sonic the Hedgehog, Sega's current mascot, was colored to match.
Cobalt blue is toxic when inhaled or ingested. Potters who fail to take adequate precautions when using cobalt blue may succumb to cobalt poisoning.
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The spectral power distribution of light reflected by cobalt blue is in the purple region of the visible spectrum.[clarification needed] Purple is commonly defined[by whom?] as a mixture of blue and red colours. Cobalt blue strongly absorbs all wavelengths of light between blue and infra-red, and reflects wavelengths at the lower bound and at the upper bound of wavelengths human visual sensors can detect. The human visual system treats the visible spectrum as circular, in the range of approximately 400-700nm. Cobalt blue is therefore perceived as primarily blue but with a degree of purple. The degree of purple (as a percentage, reported by studies of color naming) is subject to individual variation. Individuals that are red-green colour blind (that is, who are red-weak) will not see the purple component and simply see cobalt blue as blue. A degree of red-weakness will vary the degree to which an individual perceives the purple component.[clarification needed] As the reflected wavelengths are at the periphery of human perception, the colour is perceived as quite pure (equivalent to a spectral colour). The sample shown by the spectral power distribution diagram has a dominant wavelength of 456nm with a saturation of 93.8% (which means the sample measured is equivalent to a spectral colour which has been mixed with a small amount (6.2%) of white light). Some digital cameras[which?] are insensitive to the peripheral wavelengths and as a result produce images that show cobalt blue as a dark blue.
- Kerr, Rose; Wood, Nigel (2004), Science and Civilisation in China Volume 5. Part 12, Ceramic Technology, Cambridge: Cambridge University Press, pp. 658–692, ISBN 0-521-83833-9.
- Gehlen, A.F. (1803). "Ueber die Bereitung einer blauen Farbe aus Kobalt, die eben so schön ist wie Ultramarin. Vom Bürger Thenard". Neues allgemeines Journal der Chemie, Band 2. H. Frölich. Archived from the original on 2018-02-10. German translation from Thénard, L.J. (1803 (Brumaire, XII)), "Considérations générales sur les couleurs, suivies d'un procédé pour préparer une couleur bleue aussi belle que l'outremer" (PDF), Journal des Mines, 86: 128–136, archived (PDF) from the original on 2012-03-29 Check date values in:
- Maerz and Paul. A Dictionary of Color. New York (1930). McGraw-Hill. p. 91; Color Sample of Cobalt Blue: Page 131 Plate 34 Color Sample L7
- ""J Varley's List of Colours". The British Museum. Archived from the original on 2016-09-20. Retrieved 2016-07-22.
- "Cobalt blue". ColourLex. Archived from the original on 2015-04-15. Retrieved 7 June 2018.
- "Chinese pottery: The Yuan dynasty (1206–1368)". Archived 2017-12-29 at the Wayback Machine. Encyclopædia Britannica Online. Accessed 7 June 2018.
- Halpin, Jeff. "Introducing Utah's team: Real Salt Lake". Major League Soccer. Archived from the original on August 19, 2007. Retrieved June 9, 2015.
- "Wizards unveil new look for '08 season". Kansas City Wizards Media Relations, January 20, 2008.[permanent dead link]
- Sheffield, Brandon. "Out of the Blue: Naoto Ohshima Speaks". Gamasutra. Archived from the original on 16 July 2015. Retrieved 12 August 2013.
Well, he's blue because that's Sega's more-or-less official company color
- Roy, A. "Cobalt blue", in Artists' Pigments, Berrie, B. H., Ed., National Gallery of Art, Washington, D.C., 2007