Iron Oxide Red
Iron oxide, Fe2O3, Iron III Oxide, Hematite, Iron Sesquioxide)
Chemistry
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Volatiles
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Significant Temperatures
- 1550: Melts
Links to Other Materials
- Spanish Red Iron Oxide - Related
- Iron Oxide Black - Related
- Iron Sulphate - Related
- Harcros Yellow Iron Oxide - Related
- Iron Oxide Yellow - Related
- Natural Red Iron Oxide - Related
- Cache
Hazards
- Iron Oxide
Miscellaneous
- Family: Colorant
- Region: North America
- Mined At: Unspecified
- Raw Mineral: No
- Generic: Yes
Notes
Red iron oxide is the most common colorant in ceramics and has the highest amount of iron. It is available commercially as a soft and very fine powder made by grinding ore material or heat processing ferrous/ferric sulphate or ferric hydroxide. During firing all irons normally decompose and produce similar colors in glazes and clay bodies (although they have differing amounts of Fe metal per gram of powder).
In oxidation firing iron is an important source for tan, red-brown, and brown colors in glazes and bodies. Iron red colors, for example, are dependent on the crystallization of iron in a fluid glaze matrix and require large amounts of iron being present (eg. 25%). The red color of terra cotta bodies comes from iron, typically around 5% or more, and depends of the body being porous. As these bodies are fired to higher temperatures the color shifts to a deeper red and finally brown. The story is similar with medium fire bodies.
In reduction firing iron changes its personality to an incredible extent, it changes to a flux, a very active flux. Iron glazes that are stable at cone 6-10 in oxidation will run off the ware in reduction. The iron in reduction fired glazes is known for producing very attractive earthy brown tones. Greens, greys and reds can also be achieved depending on the chemistry of the glaze and the amount of iron. Ancient Chinese celadons, for example, contained around 2-3% iron. Particulate iron impurities in reduction clay bodies 'blossom' during firing, creating large specks that bleed right up through glazes.
The fine nature of red iron is a great asset in spreading it evenly throughout a glaze or body mix. It disperses better in glazes than does black iron. However, it is also a nuisance material for the same reason. In addition, larger amounts of iron oxide tend to gel glaze and body slurries, making them difficult to work with.
Red iron oxides are available in spheroidal, rhombohedral, and irregular particle shapes. Some high purity grades are specially controlled for heavy metals and are used in drugs, cosmetics, pet foods, and soft ferrites. Highly refined grades can have 98% Fe2O3 but typically red iron is about 95% pure and very fine (less than 1% 325 mesh). Some grades of red iron do have coarser specks in them and this can result in unwanted specking in glaze and bodies.
High iron materials or alternate names: burnt sienna, crocus martis, Indian red, red ochre, red oxide, Spanish red. Iron is the principle contaminant in most clay materials. A low iron content, for example, is very important in kaolins used for porcelain.
Properties
Surface Modifier - Variegation
When used with tin, iron can produce attractive mottled browns.
Data
- pH: 4-7
Linked Articles
Iron oxide and Hematite by Edouard Bastarache
Fe occurs in a number of natural forms, it is abundant in nature and an essential metal, however it can pose certain health hazards.
URLs
- A page showing the variety of colors iron is available in - http://www.sinopigments.com/irone.htm
- Wikipedia page - http://en.wikipedia.org/wiki/Iron(III)_oxide
Suppliers
- Generic
Authors
- Tony Hansen (Owner)
Pictures
-
Red iron oxide in a high temperature reduction fired glaze
XML
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<note>Red iron oxide is the most common colorant in ceramics and has the highest amount of iron. It is available commercially as a soft and very fine powder made by grinding ore material or heat processing ferrous/ferric sulphate or ferric hydroxide. During firing all irons normally decompose and produce similar colors in glazes and clay bodies (although they have differing amounts of Fe metal per gram of powder).
In oxidation firing iron is an important source for tan, red-brown, and brown colors in glazes and bodies. Iron red colors, for example, are dependent on the crystallization of iron in a fluid glaze matrix and require large amounts of iron being present (eg. 25%). The red color of terra cotta bodies comes from iron, typically around 5% or more, and depends of the body being porous. As these bodies are fired to higher temperatures the color shifts to a deeper red and finally brown. The story is similar with medium fire bodies.
In reduction firing iron changes its personality to an incredible extent, it changes to a flux, a very active flux. Iron glazes that are stable at cone 6-10 in oxidation will run off the ware in reduction. The iron in reduction fired glazes is known for producing very attractive earthy brown tones. Greens, greys and reds can also be achieved depending on the chemistry of the glaze and the amount of iron. Ancient Chinese celadons, for example, contained around 2-3% iron. Particulate iron impurities in reduction clay bodies \'blossom\' during firing, creating large specks that bleed right up through glazes.
The fine nature of red iron is a great asset in spreading it evenly throughout a glaze or body mix. It disperses better in glazes than does black iron. However, it is also a nuisance material for the same reason. In addition, larger amounts of iron oxide tend to gel glaze and body slurries, making them difficult to work with.
Red iron oxides are available in spheroidal, rhombohedral, and irregular particle shapes. Some high purity grades are specially controlled for heavy metals and are used in drugs, cosmetics, pet foods, and soft ferrites. Highly refined grades can have 98% Fe2O3 but typically red iron is about 95% pure and very fine (less than 1% 325 mesh). Some grades of red iron do have coarser specks in them and this can result in unwanted specking in glaze and bodies.
High iron materials or alternate names: burnt sienna, crocus martis, Indian red, red ochre, red oxide, Spanish red. Iron is the principle contaminant in most clay materials. A low iron content, for example, is very important in kaolins used for porcelain.
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