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Cobalt blue is a blue pigment made from one of a number of combinations of cobalt, aluminum and oxygen. Cobalt pigments produce a cool blue color, and were favored by painters such as Maxfield Parrish for painting skies. It is also an important traditional pigment in Chinese porcelain.
Cobalt blue pigment consists either of cobalt(II) oxide-aluminum oxide or cobalt(II) aluminate. These pigments are slightly different in their chemical composition, but both are the product of finely ground cobalt oxide and aluminum oxide, or alumina, being joined by a process known as "sintering." Pigment manufacturers grind the two substances, mix them together, and subject them to intense heat to bond them.
Cobalt blue is the main pigment used in distinctive Chinese blue and white porcelain, known as qing-hua or "blue flower" porcelain. The earliest known examples of this type of pigment date from the seventh century in China, although examples of cobalt-based blue pigments are known from ancient Greece, Egypt and the middle east. Porcelain manufacturers imported cobalt from the middle east to make pigment. To decorate porcelain, potters first made the vessels themselves, then applied decoration by hand before glazing. Chinese blue-and-white pottery pigments are made from smaltite, a form of cobalt oxide, whereas most modern cobalt-based pigment uses cobalt aluminate.
Although Chinese porcelain had been made using cobalt blue pigment for centuries, cobalt blue emerged in Europe independently. Medieval European glassmakers added small amounts of smaltite to quartz and potassium carbonate to make the ingredients for a dark blue glass known as smalt. Although it produced a deep blue color in glass, smalt-based pigments were unsuitable for painting because of their tendency to fade over time.
In 1802, French chemist Louis Jacques Thénard discovered a slightly different form of the pigment, which became popular among painters. Mines in Norway and Germany produced the majority of Europe's cobalt, and these countries were known for their cobalt pigments. This pigment, based on cobalt aluminate, is the pigment most commonly referred to as "cobalt blue."
European miners had been aware of the existence of cobalt for some time. The name "cobalt" comes from the German word "kobold," which is the name of a type of mischievous goblin. Cobaltite and smaltite are common cobalt ores which are very difficult to work with. They contaminate other ores, can be difficult to smelt and can release highly poisonous dust. Due to the "mischievous" natures of these ores, they were named after the pesky underground goblins.
Frequently Asked Questions
What is cobalt blue and how is it made?
Cobalt blue is a deep blue pigment made by sintering cobalt(II) oxide with alumina at 1200°C. The resultant compound, cobalt aluminate (CoAl2O4), is then ground into a fine powder. This vibrant blue hue has been prized for centuries for its stability and resistance to fading. It was first used in Chinese porcelain before becoming popular in Western art.
Can cobalt blue be naturally found or is it always synthetic?
Cobalt blue is typically synthesized, as the process of sintering cobalt(II) oxide with alumina is necessary to produce the pigment. While cobalt salts can occur naturally, the specific vibrant shade known as cobalt blue is the result of a controlled chemical process. Natural cobalt is usually found in combination with other metals in ores like cobaltite.
What are the common uses of cobalt blue in art and design?
Cobalt blue has been widely used in various forms of art and design, including ceramics, glassware, painting, and enameling. Its intense color and durability make it a favorite among artists for creating striking blue hues that do not fade over time. It was famously used by painters such as Vincent van Gogh and has become a staple in the palettes of contemporary artists as well.
Is cobalt blue safe to use in all applications?
While cobalt blue pigment is generally considered safe for use in art and design, cobalt itself can be toxic if ingested or inhaled in significant quantities. Therefore, precautions should be taken when handling the raw pigment powder to avoid inhalation or ingestion. However, once the pigment is bound in a medium, such as ceramic glaze or paint, it is largely inert and safe for handling and everyday use.
How does cobalt blue compare to ultramarine and other blue pigments?
Cobalt blue is distinct from ultramarine and other blue pigments in its composition and color properties. Ultramarine, traditionally made from lapis lazuli, has a slightly violet undertone, while cobalt blue is a truer blue. Cobalt blue also offers excellent lightfastness and opacity compared to other blues like Prussian blue, which can be more transparent. Each blue pigment has unique characteristics that artists may choose based on the desired effect in their work.