Brief description of Cobalt blue:
Very costly and extraordinary stable pigment of pure blue colour discovered by Thénard in 1802. It is now the most important of the cobalt pigments.
Alternative names: Thénards blue, Dresden blue
Word origin: The name "Cobalt blue" comes from Middle High German kobolt = an underground goblin (cobalt was thought to be detrimental to silver ores).
Chemical name: Cobalt(II) oxide-aluminum oxide
Example of use by artists:
The Umbrellas (Les Parapluies)
Renoir, Pierre-Auguste
c. 1881-85
This painting was painted during the restless period in Renoir's work. It is immediately apparent that the picture exhibits two distinct styles. The group of figures on the right is painted in a soft feathery style reminiscent of his work of the later 1870s, while the umbrellas and the couple on the left are painted in a harder manner with more distinct outlines and subdued steely colors. The exact date of the painting is not known, but it is generally accepted that it was worked on over a period of several years.
Notice how the fashions illustrated in the Umbrellas differs. The women in Renoir's paintings are usually dressed in the latest styles. The dresses and hats worn by the figures at the right conform to a fashion that appeared in 1881 and which became popular in 1882. The vogue was superseded the following year by a more sever style of dress with simple straight lines. THe woman with the band-box is dressed in this latter style which was the height of fashion in 1885-6, but which had fallen out of favor by 1887.
Renoir appears to have changed his palette significantly between the two stages. Examination of the cross-sections has shown that in the earlier phase he used exclusively cobalt blue, his habitual choice during the 1870's and early 1880's, but in finishing and revising the composition he used only French ultramarine.
History of Cobalt blue:
Although smalt, a pigment made from cobalt blue glass has been known at least since the Middle Ages, the cobalt blue established in the nineteenth century was a greatly improved one.
The isolation of the blue color of smalt was discovered in the first half of the eighteenth century by the Swedish chemist Brandt. In 1777, Gahn and Wenzel found cobalt aluminate during research on cobalt compounds. Their discovery was made during experimentation with a soldering blowpipe. The color was not manufactured commercially until late in 1803 or 1804.
The Minister of the French government, Chaptal, appointed Louis Jaques Thénard and Mérimée to look into the improvement of artists' colors. Thenard developed this new cobalt blue by his observations at the Sevres porcelain factory. He experimented with roasting cobalt arsenate and cobalt phosphate with alumina in a furnace. He published his results in late 1803-4 in the Journal des mines, "Sur les couleurs, suives d'un procédé pour préparer une couleur bleue aussi belle que l'outremer."
Thénard tried the blue in oil and gum media and by the time his report was published, the color had not changed after a two-month exposure test. Production began in France in 1807. Most sources cited regard Thenard as the inventor of the blue. However, Leithner of Vienna is also mentioned as one who developed cobalt arsenate as early as 1775.
Cobalt blue was generally regarded as durable in the nineteenth century. It requires one hundred percent of oil to grind it as an oil paint otherwise its cool tone can turn greenish due to the yellowing of linseed oil. To avoid the yellowing, Laurie suggested that it be used as a glaze color or mixing it with white. It is totally stable in watercolor and fresco techniques. Field called it a "modern, improved blue". John J. Varley, author of List of Colours, recommended it as a good substitution for ultramarine blue for painting skies.
