The Story of Cobalt

Cobalt blue in impure forms has long been used in Chinese blue and white porcelain, beginning in the late 8th or 9th century. 

Persian Ceramics

It originally came from mines in Persia, now in Iran. It was the Persians who really found out how good Cobalt was as a glaze. They used it for the blue tiles for their mosques, representing the heavens. When heated with copper, makes a turquoise, remembering the green on the prophets cloak. The results are spectacular. When traveller Robert Brian visited the town of Herat in the 1930s, he described the blue on the tomb of the Gawhar Shad as the most beautiful example colour in architecture ever devised by man, to the glory of God and himself.

English Name - Gremlins

Cobalt is an ore that often attracts arsenic. So the German silver miners who often came across it, hated it and gave it the name of a gremlin Kobalt. For centuries, they threw it away before it ate their feet and attacked their lungs.

Secret Messages

During the 17th century, people discovered its propensity to change colour on heating it and used it in invisible inks. When a plain paper is held over fire, it would magically turn green, where secret messages had been traced. 

Smalt - Ground Glass

Smalt has been used since 1500’s, a finely ground blue glass (a mixture of cobalt and potassium). It is a very transparent pigment, which is easily overwhelmed in mixtures due to its weak tinting strength. Depending on how fine the powder is ground depending how dark it is. Dark smalt is larger particles (200 mesh) the finer particles make a lighter colour (400 mesh). An affordable blue compared to the alternative Lapis Lazuli from Afghanistan.

Smalt works better in water based mediums (acrylic and watercolour) rather than oil were it may fade due to the oil reacting with potassium particularly in a damp environment. Smalt PB32

Blue Pigment

Cobalt had been used in paint for many years, it didn't reach European paint boxes until the 19th century after a scientist called Louis Jacques Thenard managed to make it into a pigment in 1802.

Commercial production began in 1807, and the leading manufacturer of cobalt blue was in Norway, known as the Blue Colour Works. Original Cobalt Blue PB28 and other modern Cobalt Blue pigments

Range of Colours

Since then cobalt has been calcined (heated) with other metals to produce a range of colours in varying shades of blue, yellow red and green. Five Cobalt Colours

As a Watercolour Pigment

The watercolourist, John Varley, suggested cobalt blue as a good substitution for ultramarine for painting skies, writing in his List of Colours from 1818, "Best 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 tints when too heavy, and for tints in drapery, et cetera. Capable, by its superior brilliance and contrast, to subdue the brightness of other blues."

As a watercolour all cobalt based pigments tends to granulate in Watercolour. 

Cobalt in Oil

When Cobalt is used in oil it requires a lot less oil than other pigments and dries quite quickly as it is a siccative.

All the cobalt pigments are exceptionally light fast, but also very expensive depending on the colour.