Some Notes about the Geology Behind
Poetic Earth: The Memory of Land
by Catherine Nash, M.F.A.
Earth pigments, used since the beginning of human history, are still considered the most permanent, despite the predominant use of synthetic colors in the commercial marketplace. Author Anne Wall Thomas states that, “They are not affected by sunlight or by atmospheric conditions humidity, temperature, and impurities. They remain unaltered by contact with alkalis and dilute acids...[they] do not react with solvents and they have reasonable tinting strength and covering power. They have the capacity to screen harmful ultraviolet rays...and are invariably the least expensive pigments available. These characteristics account for their popularity with manufacturers of protective coatings for both wood and metal.” Indeed, the most common house colors one sees everywhere in Norway and Sweden are yellow ochre and röd farg, a deep, rich red. I was told it is because these earth colored paints withstand the harsh Scandinavian winters for many years.
Different oxidation levels and levels of quality cause variance in the colors of earth pigments making it impossible to reproduce exact hues. Because iron is a relatively reactive metal, chemists have controlled it for specific and reproducible synthetic color results. Iron oxides are inorganic pigments whose color can range from brown to red to yellow to green (umber to red oxide to ochre to terra verte) due to the amount of iron present, but they vary depending upon the earth in which they are found. Other minerals found in a sample of iron oxide such as carbonic materials, limestone, calcium, and manganese oxides also affect the specific color of the pigment. Almost all naturally occurring iron oxides have a clay base (an eroded product of silicate rocks) which also influences the ultimate color.
Iron oxides were used by prehistoric cave dwellers symbolically for cultural and spiritual rituals. There is evidence that prehistoric man traveled many miles to mine iron oxides, perhaps sought for their qualities of durability and richness of color. Some of the world’s oldest prehistoric cave paintings have been found in the south of France. The paintings at Lascaux, perhaps the most famous of these, were created more than 16,000 years ago.
Durability, permanence, and light fastness still make these pigments important for today’s artist. A wonderful green earth that I dug just north of Moab in Utah is from the Brushy Basin member of the Morrison Formation and is dated to the Jurassic era, about 135,230 million years ago. A sedimentary rock, it contains quite a bit of clay. The green is iron that was not oxidized, which means it was laid down in a low oxidized environment (i.e., into water). Geologists have determined that a huge lake measuring 500 miles long and 300 miles wide covered a great deal of the Four Corners area (where the states of Utah, Colorado, New Mexico, and Arizona all meet). Volcanoes all along the western shore of this lake spewed alkaline ash into the water, where it settled. Different levels of salinity resulted in varied shades of green: bluish green can be found near Durango, Colorado, for instance.
©Catherine Nash_Eroding hills of green sedimentary clay earth near Tuba City, Arizona.
In contrast, the red earth of Sedona is a fine grained sedimentary sandstone. The magnificent rock formations in this area are similar to those of Utah’s Monument Valley. A second, a purple grey, gathered from a highway road cut near the Painted Desert, is from Jurassic and Triassic sedimentary layers. The site is specifically known as the Owl Rock member of the Chinle Formation, along the road just west of Tuba City. It is an incredible area of petrified trees, fossils, and dinosaur tracks.
Like the different colors found in iron oxides, colorful horizontal banding of sandstone and mudstone layers of the Chinle Formation resulted from a varying mineral content in the sediments and also from how quickly they were laid down. Concentrations of slowly deposited oxides of iron and aluminum create red, orange, and pink hues. A rapid sediment buildup, perhaps from a flood, caused oxygen to be removed from the soil and formed pale aqua, gray, and lavender layers.
Lifting Fog was painted with watercolors mulled from chrysocolla, malachite, green clay from Utah, limonite found on the shore of Lake Mead, white sandstone from near Page, red sandstone from Sedona, etc. Every painting in this installation was created from earth pigments found by the artist with a few exceptions in purchases of the rarer palettes: blue and green vivianites from Australia, Glauconite green from Russia, and lazurite and azurites blues from Afghanistan.
[Lifting Fog, Watercolor and ink on cotton rag handmade paper. 15.5”H x 18”W.]
The entire southwestern desert is a visual wonder of varied hues, whether marveled at from a distance or explored up close. I find it fascinating to ponder the ancient earths and the magnitude of geological time. The immensity of it feeds my creative ideas. Using pigments from the earth gives a personal layer of meaning and imbues my experiences into my images. Just as the act of gathering a specific plant from a particular location to make paper permeates my sheet, the earth pigments I have dug, filtered, and ground imbue it with the ancient.
Painting Below the Rim...a time lapse~
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1 Thomas, Anne Wall. Colors from the Earth: The Artists’ Guide to Collecting, Preparing,and Using Them, Van Nostrand Reinhold Co., New York, New York: 1980. pg. 24.
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2 From a conversation with Murray Shoemaker, Park Ranger, Arches National Park, Moab, Utah.
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3 National Park Service web site, Geology. < https://www.nps.gov/pefo/learn/nature/geologicformations.htm >
