Cobalt blue is the cool blue colour of the pigments made using cobalt salts of alumina. Cobalt blue pigments are extremely stable, and have historically been used as colouring agents in ceramics, (especially Chinese porcelain), jewelry, and paint. Transparent glasses are tinted with the silica-based cobalt pigment smalt.
Chemically, cobalt blue pigment is a cobalt(II) oxide-aluminium oxide, or cobalt(II) aluminate, CoAl2O4. The compound is made by sintering finely ground CoO and Al2O3 (alumina) at 1200 °C. Cobalt blue is lighter and less intense than (iron-cyanide based) Prussian blue.
Historical uses and production
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 colour 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.
Cobalt blue in human culture
- Watercolourist and astrologer John Varley suggested cobalt blue as a good substitution for ultramarine for painting skies, writing in his “List of Colours” from 1816: “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 tines when too heavy, and for tints in drapery, etc. Capable, by its superior brilliancy and contrast, to subdue the brightness of other blues.”
- 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.
- Several car manufacturers including Jeep and Bugatti have cobalt blue as one paint options.
- 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.
- Major League Soccer’s Kansas City Wizards have had cobalt blue as the secondary colour of 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 colour is cobalt blue. Sonic the Hedgehog, Sega’s current mascot, was coloured 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.