Ferric oxide

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Benin iron altar
MFA# 1992.400


An insoluble dark red powder that occurs naturally as Hematite. Red iron oxide has been used since antiquity as a permanent red pigment in paints and glazes (see Red ocher). In the late 1700s, ferric oxide was manufactured as a red pigment. This synthetic, intense red pigment with a uniform particle size is now called Mars red. Ferric oxide is also found in the form of Rust. Rust is a corrosion product that readily occurs on Iron and some steels in the presence of Oxygen and moisture. Fine powdered ferric oxide, called Jewelers' rouge, is also used as an Abrasive for Glass, precious metals and diamonds. Ferric oxide is also the most common material used in magnetic coatings on audio and video tapes.

Ferric oxide

Synonyms and Related Terms

ferric sesquioxide; jeweler's rouge; red iron oxide; red iron trioxide; ferric trioxide; Venetian red; Tuscan red; Indian red; Persian red; crocus martis


  • Overexposure to dust may result in x-ray shadows due to apparently benign lung pigmentation.
  • Fisher Scientific: MSDS

Physical and Chemical Properties

Soluble in acids. Insoluble in water.

Composition Fe2O3
CAS 1309-37-1
Melting Point 1565 C
Density 5.12-5.24 g/ml
Molecular Weight 159.69


Properties of Common Abrasives

Resources and Citations

  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Robert Fournier, Illustrated Dictionary of Practical Pottery, Chilton Book Company, Radnor, PA, 1992
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 4072
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
  • Michael McCann, Artist Beware, Watson-Guptill Publications, New York City, 1979
  • Susan E. Schur, Conservation Terminology: A review of Past & Current Nomenclature of Materials, Technology and Conservation, Spring (p.34-39); Summer (p.35-38); Fall (p.25-36), 1985