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Yellow Ochre

Alternate Names: Hydrated ferric oxide

Oxide Analysis Formula
CaO 0.23% 0.02
MgO 0.06% 0.01
Al2O3 19.92% 1.00
SiO2 57.78% 4.92
Fe2O3 22.01% 0.70
Oxide Weight 512.05
Formula Weight 512.05

Notes

A natural clay material containing yellow iron oxide, a hydrated ferric oxide, FeO(OH). Properties will vary in different areas. For many industries, this material is an inexpensive pigment (e.g. for staining cement and mortar). But for ceramics (e.g. as a colorant to produce iron tan, yellow and red-brown in slips and glazes), its iron content determines how useful it is compared to true iron oxide.

Material we have tested has low plasticity. Strangely, yellow iron can be even more plastic than yellow ochre, much stickier when wet.

Related Information

Yellow iron oxide vs. Yellow Ochre - fired at cone 6

The rear two samples are just dried. The fired iron oxide (front left) is clearly exhibiting a metallic sheen and has shrunk and become much more dense. And heavy. In the raw state, both exhibit a measure of plasticity when water is added. The yellow iron really holds on to the water, drying out much more slowly. The iron oxide densifies and shrinks even more by cone 8, taking on the characteristics of the metal.

Yellow ochre slurry color

Just been poured on to a plaster table. It has low plasticity and dewaters quickly.

Yellow Ochre as a low fire body colorant

It is bright yellow in the raw state, but it still fires red. 10% Yellow Ochre was added to a buff burning stoneware clay. Left is the dried clay. The center sample was fired to 1500F. The right sample was fired to 1850F.

The original container of a bag of Yellow Ochre

From Davis Colors

Links

Typecodes Clay Other
Clays that are not kaolins, ball clays or bentonites. For example, stoneware clays are mixtures of all of the above plus quartz, feldspar, mica and other minerals. There are also many clays that have high plasticity like bentonite but are much different mineralogically.
URLs https://www.nrochre.com/products/natural-iron-oxide-pigments
About natural iron oxide pigments: Ochre and Umber
Ochre (pronounced o’-ker) is a natural, mineral, earth pigment. Chemically, it is a hydrated ferric oxide, chemical formulation: FeO(OH). Ochre is inorganic, chemically inert, non-reactive with cement, mortar or brick, and non-toxic.
Materials Iron Oxide Yellow

By Tony Hansen


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