What Are Earth Pigments? Exploring the Geology of Natural Earth Pigments
Natural earth pigments range in color—from warm yellows, burnt reds, browns, earth greens, and even blue. These naturally occurring phenomena get their colors from minerals, and in the studio, they transform into the most beautiful artistic colors that reveal the hidden beauty of iron.
Discovering the Geological Makeup of Natural Earth Pigments
There are three primary components that create the color you see in natural earth pigments, the principal coloring-producing agent, the secondary or modifying coloring agent, and the base filler, diluent, or carrier of the color.
The Principal Coloring-Producing Agent
The principal coloring-producing agent is responsible for the main color you can see. In earth pigments, this is usually iron oxide (iron + oxygen). Earth pigments may contain any degree of iron, however, this does not affect the superiority of the colors. Iron oxides are widespread in nature and play an important role in geological and biological processes. In total there are 16 iron oxides, hydroxides, and oxyhydroxides, but only 3 are considered the principal iron ores.
Hematite (Fe2O3) - Red Iron Oxide Pigments
Limonite (2Fe2O3h2o - Fe2o34H20) - Yellow and Brown Iron Oxide Pigments
Magnetite (Fe304 or FeOFe2O3) - Black Iron Oxide Pigments
The Secondary or Modifying Coloring Producing Agent
The secondary or modifying coloring agent in simple terms alters or tints the iron oxide color. Things like calcium, manganese, oxides, carbon or organic materials, silica, and limestone can all cause different colored results.
Base Filler, Diluent, or Carrier
Lastly, the base filler, diluent, or carrier of the colors is the material that holds the colored mineral together. Clay is the most commonly found in natural earth pigments. Pure clay can often lighten the colors of iron oxides creating pinks, creams, and light yellows.
Identifying Earth Pigment Colors
Ochre, sienna, and umber are all common color names in the artist palette. Each color is a naturally occurring pigment that is comprised of the above formula—a principal coloring agent, a secondary coloring agent, and a base.
Ochres
Ochre’s principal coloring-producing agent is the hydrated iron hydroxide limonite, one of the three principal types of iron oxide. Ochres that appear redder have a higher quantity of hematite, an anhydrous iron oxide.
Siennas
Sienna is a color that is created from limonite iron oxide and manganese. It can be darkened to create burnt sienna by calcination or heating it in a furnace.
Umber
Umber is also colored from iron oxide and manganese. Umbers typically have a higher amount of manganese which results in its darker brown color.
Without iron, we wouldn’t have natural earth pigments. Combined with air, water, and a few additional minerals you can find earth pigments in just about any shade of the rainbow.
