A semi-transparent, bright, bluish-green with a low tinting strength, cobalt green is extremely permanent – like many pigments produced at high temperatures.
In 1780, the process for making a compound of cobalt and zinc was developed by the Swedish chemist Sven Rinman. A mixture of cobalt and zinc was exposed to strong heat, then washed, and the cobalt green pigment was ready to grind.
Although available from 1835, cobalt green pigment was not widely used until after 1860, when zinc oxide became more readily available. Arthur Church, the chemist and amateur painter, published Rinman’s process in his book, The Chemistry of Paints and Painting (London, 1901), praising cobalt green as “chemically and artistically perfect”.
Cobalt green provides an option for the painter to the more widely used phthalo-based greens or chromium oxide. A fast drier in oil, in watercolour cobalt green has the characteristic of “granulating” in washes, in a similar way to ultramarine.