This color contains the following pigments:
hydrated iron, magnesium, aluminum and potassium silicates
Green earth is a natural pigment that varies from yellow and olive to blue-green in its composition and hues. It is semi-transparent, has low hiding power and tinting strength, muddies and darkens in oil, and is particularly good for tempera and fresco painting.
Green Earth has excellent permanence and lightfastness, although some varieties can be developed by light calcining. It is one of the most permanent pigments because Earths are not affected by sunlight or atmospheric conditions.
Green Earth has no significant hazards.
Terre verte is French for green earth. It was discovered in antiquity, and its use has been traced to the Ajanta caves in India and a variety of Roman sites, including Pompeii. Green Earth was very popular for underpainting flesh tones in medieval paintings because this green was the compliment to pink on the medieval color wheel. Its use declined after the Renaissance. The natural supplies of the pigment are mostly depleted, and manufacturers currently duplicate the hue using mineral bases like Viridian, iron oxide, or chromium oxide, or artificial ceramic colorants. Pigments sold under this name can also be the result of mixing Sienna and Phthalo Green.
Cr2O3 • 2 H2O or Cr2(OH3)
Viridian is the standard green and is stable, powerful, and cold with an emerald green undertone. It has a transparent hue, good tinting strength, a dark masstone that can be almost black at full strength, and a slow drying time in oil form. Viridian is commonly replaced by the darker, more saturated, and staining Phthalo Greens, but its properties make it a necessary part of the palette of an experienced landscape painter.
Viridian has excellent permanence, except in high-temperature work, and is highly valued as a glazing color.
Viridian is slightly toxic.
Viridian’s name comes from the Latin viridis, meaning green. The process for manufacturing Viridian, or Transparent Oxide of Chromium, was patented by Guignet in Paris in 1859. However, it had actually been discovered by Pannetier and Binet in 1838. Viridian replaced Verdigris, which was reactive and unstable, and Emerald Green, which was a poisonous copper aceto-arsenite used as a rat poison in the sewers of Paris.