Cobalt Green Light Pigment

Rublev Colours Cobalt Green Light pigment is a green cobalt zinc oxide, semi-transparent of limited hiding power discovered by Rinmann in 1780. Due to its permanence, it can be used in all painting techniques. The poor tinting strength and high cost of cobalt green kept it in limited use. Field called it, “chemically good and artistically bad.”

History and Origin

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.

Source

Cobalt Green is a synthetic inorganic pigment composed of an isomorphous mixture of cobalt zincate and zinc oxide heated at high temperatures which cannot be chemically separated. Paler tints require greater amounts of zinc oxide.

How cobalt green is made can be seen from webexhibits.org.

Permanence and Compatibility

Cobalt Green is considered permanent in all painting techniques.

Oil Absorption and Grinding

Cobalt Green absorbs a moderate amount of oil (34 to 37 grams per 100 grams of pigment), which slows the drying of oil paint and yet is a moderately fast-drying oil color. It disperses well in both oil- and water-based paints and is easy to mull by hand to a smooth paste.

Toxicity

Cobalt Green ;is not considered toxic, but care should be used in handling the dry powder pigment to avoid inhaling respirable dust particles. May contain trace amounts of soluble cobalt, but should not be a hazard in normal artist use. Avoid dust, avoid spraying, don't use your mouth to point your brushes.

Ecology

Very toxic to aquatic life with long-lasting effects.