Cobalt blue is a blue pigment made from a variety of cobalt, aluminum, and oxygen combinations. Cobalt pigments produce a cool blue color, and painters like Maxfield Parrish used them to paint skies. It’s also a popular traditional Chinese porcelain pigment.
The pigment cobalt blue is made up of cobalt(II) oxide-aluminum oxide or cobalt(II) aluminate. These pigments have slightly different chemical compositions, but they’re both made from finely ground cobalt oxide and aluminum oxide, or alumina, which are joined together through a process called “sintering.” To bond the two substances, pigment manufacturers grind them together, mix them together, and then heat them to a high temperature.
The main pigment in qing-hua or “blue flower” porcelain, a distinctive Chinese blue and white porcelain, is cobalt blue. Although examples of cobalt-based blue pigments can be found in ancient Greece, Egypt, and the Middle East, the earliest known examples of this type of pigment date from the seventh century in China. To make pigment, porcelain manufacturers imported cobalt from the Middle East. To decorate porcelain, potters first created the vessels, then decorated them by hand before glazing. Smaltite, a type of cobalt oxide, is used in Chinese blue-and-white pottery pigments, whereas cobalt aluminate is used in most modern cobalt-based pigments.
Despite the fact that cobalt blue pigment had been used in Chinese porcelain for centuries, it was only recently discovered in Europe. Small amounts of smaltite were added to quartz and potassium carbonate by medieval European glassmakers to make the ingredients for smalt, a dark blue glass. Smalt-based pigments were unsuitable for painting because of their tendency to fade over time, despite producing a deep blue color in glass.
Louis Jacques Thénard, a French chemist, discovered a slightly different form of the pigment in 1802, which became popular among painters. The majority of Europe’s cobalt was mined in Norway and Germany, and these countries were known for their cobalt pigments. The pigment most commonly referred to as “cobalt blue” is made up of cobalt aluminate.
For a long time, European miners had been aware of the existence of cobalt. The word “cobalt” is derived from the German word “kobold,” which refers to a type of nefarious goblin. Cobalt ores such as cobaltite and smaltite are common but difficult to work with. They contaminate other ores, are difficult to smelt, and emit highly toxic dust. These ores were named after the pesky underground goblins because of their “mischievous” natures.