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A painted swatch of Cobalt green:
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The preparation of zinc oxide at the end of the eighteenth century made the development of cobalt green, also known as zinc green, possible. The Swedish chemist, Rinmann is credited with developing a process for making a compound of cobalt and zinc in 1780 that he published with the Stockholm Academy of Sciences. Arthur Herbert Church published Rinmann's process in his book, The Chemistry of Paints and Painting. According to Church, cobalt green was made with the compounds of oxides of zinc and cobalt by mixing them "with an alkaline carbonate" and then exposing the mixture to strong heat. After washing the sediment that resulted, the pigment was ready to grind. The pigment was always bluish-green in spite of the ability to widely vary the proportion of zinc to cobalt oxides in production. The compound that is formed is chemically joined.
Cobalt green was a semi-transparent, moderately bright green. Most sources cited considered it to be absolutely permanent as most pigments produced at high temperatures are. However, tests made in 1847 and published in 1910 showed a browning of the color in full-strength and a fading of it when mixed with lead white. The colormaker, Blockx, added that the date of the tests bears certainty that the green was made by Rinmann's process,
Artists did not favor cobalt green although it could safely be mixed with all other pigments and was a fast drier in oil. The poor tinting strength and high cost of cobalt green kept it in limited use. Field called it, "chemically good and artistically bad"
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When was Cobalt green used?
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