Types of Pigments

Natural Mineral Colors - The earth colors [ochers, umbers, and so on] are mined from beds of earth and have been given their color by the presence in the local soil of iron compounds [iron oxides and iron hydroxides], along with varying amount of clay, chalk, and silica. The color, transparency, and strength tend to vary with the different deposits, some yielding more desirable colors than do others. These colors have been in use since prehistoric times and have been found to be permanent in all techniques. They must be well washed and purified of any foreign materials that might adversely affect the colors' permanence.

Although their collective color character tends toward a brown quality [brick reds, sandy yellows, burnt oranges], they have sufficient life and variety to produce rich and handsome harmonies, even when used in a painting to the exclusion of most other pigments.

When the natural earths are roasted or calcined, they change their colors, usually to deeper, warmer tones: thus raw sienna becomes burnt sienna; raw umber, burnt umber; and so on. These varieties are also permanent in all techniques.

The earth pigments include:

Yellow Ocher
Burnt and Raw Sienna
Burnt and Raw Umber
Light Red
Indian Red
Venetian Red
Terra Rosa
Terra Verte
Burnt Terre Verte

Factory-made Mineral Colors- This group of colors, products of the laboratory and industrial process, contains many permanent and important additions to the painter's palette, such as viridian or cobalt blue. On the other hand, not all artificial metallic colors are permanent and stable--for example, chrome yellow [lead chromate] which frequently darkens.

Factory-made equivalents of the burnt and raw earth colors have been available since the middle of the nineteenth century. Today they are generally called Mars colors, such as Mars yellow, Mars red, Mars brown, etc. Like their natural counterparts, they are permanent in all techniques and are somewhat freer from undesirable impurities than are the natural earth colors.

Viridian
Cobalt Blue
Chrome Yellow [impermanent]
Mars Colors

Artificial Organic Colors - These, like the natural organic colors, are compounds containing carbon. Although many [such as mauve and magenta, discovered in the nineteenth century] are fugitive, some [such as phthalocyanine blue and alizarin] are sufficiently permanent for artists' use. Since 1960 a growing list of artificial organic colors, demonstrating increased permanence, has gained acceptance by artists and manufacturers of artists' colors. [p. 7]

Natural Organic Colors - These are of vegetable or animal origin, such as bitumen or sepia. They are rarely permanent enough for artists' use.

2. Many artificial mineral colors are permanent.

3. Quite a few artificial organic colors are permanent.

4. Very few natural organic colors are permanent.