by U.S. Geological Survey Friday, May 8, 2015
Arnold O. Tanner, a mineral commodity specialist for the U.S. Geological Survey, compiled the following information on iron oxide pigments.
Prior to the 2011 royal wedding, the roads and walkways around Buckingham Palace in London were resurfaced with stone mastic asphalt dyed red with a synthetic iron oxide pigment. Credit: ©Misterweiss.
Iron oxide pigments, natural or synthetic, are inorganic materials commonly used as coloring agents. They are valued for their resistance to color-change (especially from exposure to sunlight), chemical resistance, stability under ambient environmental conditions, nontoxicity and relatively low cost.
Major minerals comprising the natural iron oxide pigments are hematite for red pigments; goethite and limonite (hydrated iron oxides) for the yellow and brown pigments commonly occurring in the iron oxide-rich ochres, siennas, and umbers; and magnetite for black pigments. Natural iron oxide pigments were used as colorants in early civilizations for body decoration and paintings on cave walls, which reveal details of prehistoric cultures.
Synthetic iron oxide pigments, first developed in the early 20th century by the chemical industry, surpass pigments produced from natural iron oxide minerals in uniformity, color quality and variety, and chemical purity. They are manufactured under controlled conditions to accurately replicate particle size, distribution and shape.
The leading use today for iron oxide pigments, both natural and synthetic, is in providing color in construction materials and in paints and coatings. Construction applications include brick; concrete products such as paving stones, roofing tiles, and other precast products of various sizes or dimensions; mortar; and ready-mixed concrete. Other end uses include colorants for ceramics, glass, paper, plastics, rubber, and textiles; in foundry sands and industrial chemicals; and in animal feed, cosmetics, fertilizers, and magnetic ink and toner.
Natural pigments are often used in applications that demand less color consistency, such as in primers and undercoats, but synthetic pigments command a larger market share for most applications. In paints and coatings, the overlapping alignment of flakey particles of micaceous iron oxide greatly increases the materials' resistance to moisture and gas penetration — preventing corrosion and rusting of metals — as well as to blistering, cracking and peeling.
Iron oxide pigments are produced from natural deposits in many countries, including Austria, Cyprus, Germany, India, Pakistan, Spain, Turkey and the United States. Many countries produce synthetic iron oxide pigments.
For more information on iron oxide pigments and other mineral resources, visit: minerals.usgs.gov/minerals.
In 2014, the United States produced about 50,000 metric tons of finished natural and synthetic iron oxide pigments.
In 2014, the United States exported about 60,000 metric tons of all grades of iron oxides and hydroxides, mostly to China, Spain, Canada and Mexico.
India was the world’s leading producer of natural (ochre) iron oxide pigments in 2014, generating about 1.4 million metric tons.
Pigment and paint grinding equipment estimated to be 350,000 to 400,000 years old was found in a cave near Lusaka, Zambia, in the mid-1990s.
A team of Spanish and Finnish researchers demonstrated in 2011 that atmospheric sulfur dioxide is likely responsible for turning red iron oxide pigments to blackened splotches (by reducing hematite to magnetite) in paintings in the ruins of Pompeii, Italy.
In recent years, remediation of contaminated soils and water from acid coal mine drainage has increasingly become a “green” source of iron oxide pigment, some of which is used to produce artists' oils and acrylic paints.
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