Mars Brown has similar general properties to the pure red oxides, and it is often a mix of synthetic forms of oxides such as PY42, PR101, and PBk11. Its tinting strength is low, and it dries quickly. Hues vary based on manufacturer.
Mars Brown has excellent permanence and lightfastness, with outstanding resistance to chemicals, heat, and weather.
Mars Brown is not considered toxic, although care should be taken not to breathe its dust.
CoO • ZnO
Cobalt Green is a pure, fairly opaque, moderately bright bluish-green with a low tinting strength and limited hiding power. It makes valuable grays and muted, minimalistic greens when mixed with other pigments. However, it can brown at full strength and fade when mixed with lead based whites. It is quick drying in oil form and is not widely used because its hue can easily be matched by mixing green and blue pigments with superior painting properties. It is currently not in wide use.
Cobalt Green is completely lightfast. Its permanence is excellent, so it can be used in all painting techniques.
Cobalt Green is moderately toxic if inhaled or ingested. It is slightly toxic if it comes into contact with skin.
Cobalt comes from the Middle High German word kobolt, an underground goblin, because miners thought cobalt harmed silver ores. In 1780, the Swedish chemist Sven Rinmann developed a process for making a compound of cobalt and zinc (zinc oxide). It was introduced as a pigment in 1835, but poor tinting strength and high cost kept it in limited use throughout the next centuries. It gained some popularity among 19th century landscape painters.