Iron Oxide Red
Synthetic Hematite
Formula: Fe2O3
Synthetic 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). Red iron oxide is available in many different shades from a bright light red at a deep red maroon, these are normally designated by a scale from about 120-180 (this number designation should be on the bags from the manufacturer, darker colors are higher numbers), however in ceramics these different grades should all fire to a similar temperature since they have the same amount iron. The different raw colors are a product of the degree of grinding.
In oxidation firing iron is very refractory, so much so that it is impossible, even in a highly melted frit, to produce a metallic glaze. It 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 become 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 can melt and become fluid during firing, creating specks that can bleed up through glazes. This phenomenon is a highly desirable aesthetic in certain types of ceramics, when the particles are quite large the resultant blotch in the glaze surface is called a blossom.
Iron oxide can gel glaze and clay slurries making them difficult to work with (this is especially a problem where the slurry is deflocculated).
Iron oxide particles are very small, normally 100% of the material will pass a 325 mesh screen (this is part of the reason iron is such a nuisance dust). As with other powders of exceedingly small particle size, agglomeration of the the particles into larger ones can be a real problem. These particles can resist break down, even a powerful electric mixer is not enough to disperse them (black iron oxide can be even more difficult). In such cases screening a glaze will break them down. However screening finer than 80 mesh is difficult, this is not fine enough to eliminate the speckles that iron can produce. Thus ball milling may be the only solution if the speckle is undesired.
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 (see picture).
High iron raw 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.
One method of producing synthetic iron oxide is by burning solutions of Ferric Chloride (spent pickle liquor from the steel industry) to produce Hydrochloric Acid (their main product) and Hematite (a byproduct). 100% pure material contains 69.9% Fe.
Mechanisms
Out Bound Links
In Bound Links
- (Materials - Related)
Iron Oxide Black - Fe3O4 - Ferrous ferric oxide, Synthetic Magnetite
Fe3O4, Black Iron Oxide, BIO, Magnetite Powder, Iron(II,III) Oxide
- (Materials - Related)
Hematite - High iron mineral
- (Oxides - Closest material equivalent)
Fe2O3 - Iron Oxide, Ferric Oxide
Pictures
This is what about 8% iron can do in a transparent base glaze with slow cooling at cone 10R on a refined porcelain.
Since iron oxide is a flux in reduction, overglaze iron based pigments run if applied to thickly
An oxidiation transparent glaze with iron added produces an amber
Red iron oxide in a high temperature reduction fired glaze
Celadon cone 10R glaze (about 3.5% iron oxide) with G1947U transparent liner glaze
A cone 10 reduction tenmoku glaze with about 10% iron oxide.
Cone 10 reduction fired crystallizing kaki glaze (about 12% iron oxide).
4% red iron oxides from two different manufacturers in a cone 6 ravenscrag slip based glaze. The one of the left has a coarser grain size.
Example of how iron turns to a flux in reduction firing and makes the glaze melt much more fluid.
5 different brand names of iron oxide at 4% in G1214W cone 5 transparent glaze. The specks are not due to particle size, but differences in agglomeration of particles.
Five different brand names of iron oxide at 4% in G1214W cone 5 transparent glaze. The glazes have been sieved to 100 mesh but remaining specks are still due to agglomeration of particles, not particle size differences.
An example of how iron stone concretions contained within two clay bodies (a white and brown stoneware) blossom and produce speckle at cone 10 reduction.
Example of 5% black iron oxide (left), right iron oxide (center) and yellow iron oxide (right) added to G1214W glaze, sieved to 100 mesh and fired to cone 8. The black is slightly darker, the yellow has no color? Do you know why?
Metallic oxides with 50% Ferro frit 3134 in crucibles at cone 6ox. Chrome and rutile have not melted, copper and cobalt are extremely active melters. Cobalt and copper have crystallized during cooling, manganese has formed an iridescent glass.
XML for Import into INSIGHT
<?xml version="1.0" encoding="UTF-8"?>
<material name="Iron Oxide Red" descrip="Synthetic Hematite" searchkey="Ferric Oxide, Red Iron Oxide, RIO, Iron(III) oxide, Fe2O3, Hematite" loi="0.00" casnumber="1345-25-1">
<oxides>
<oxide symbol="Fe2O3" name="Iron Oxide, Ferric Oxide" status="" percent="95.000" tolerance=""/>
</oxides>
<volatiles>
<volatile symbol="H2O" name="Water" percent="5.000" tolerance=""/>
</volatiles>
</material> | 
The future of ceramic recipe, material and physical testing record keeping is here.
Maintain your recipe database on-line
- Login to a private account or work with others in a group account (e.g. university).
- Nothing to install (access it using your web browser). It is always the latest version.
- Easy to import your existing data.
- As many side-by-side recipes as you want.
- Many ways to search and classify glaze and body recipes.
- Glaze and body recipes are robust, with units-of-measure, unlimited pictures with individual titles and descriptions.
- Add variations to a recipe; each with its own pictures, descriptions and name/code-number extensions.
- Recipes can link to typecodes, projects and firing schedules (all managed in their own areas).
- Standard reports and mix ticket reports with last-minute-totalling; variations report as if they are a complete recipe.
- Video tutorials, help system, contact form on every page, dedicated messaging and support ticket systems.
- It is an industrial-strength database system (unlimited capacity, fast, reliable, scalable).
Imports many file formats
- Glaze recipe formats supported: HyperGlaze, GlazeGhem, GlazeMaster, Matrix, INSIGHT XML recipes (single and multiple), INSIGHT SQLite DB files.
- Assign a batch number to imports, and later search by batch.
- Assign multiple typecodes to imported glaze and body batches (to classify) and search on these later.
- Prepend character sequences to glaze recipe names during import.
- Import the pictures and pair them to their corresponding records automatically.
- One click to automatically export the database to an SQLite DB database file and download it (for use with desktop INSIGHT or just as a backup).
- Export and import individual glaze recipes as text or XML.
Perfect for Education
- Ceramic study programs can now accumulate material, recipe and testing data year-after-year, students can login and together build a valuable ceramic glaze and body knowledge resource.
- Students already have internet connected devices, computers are not even needed in the class.
- The Reference Manager gives you quick access to the Digitalfire Ceramic Reference Database.
Learn more..
|
Watch the video or sign-up at http://insight-live.com.