Cobalt blue

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.

When was Cobalt blue used?