|Monthly Tech-Tip |
Alternate Names: Hydrated ferric oxide
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.
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.
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.
From Davis Colors
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.
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|