• Materials for Ceramics

Spanish Red Iron Oxide

Notes

Some suppliers claim that Crocus Martis and Spanish Red Iron are the same. However this material is said to be a very bright orange when raw and it is not the same. If you know more about this material, please let us know. It appears to be from Tierga Mines, the Santa Rosa mine in Zaragoza-Aragón, Spain. The deposit appears to be layered with dolomite (thus the unaccounted for 8%).
The material has some soluble salts (0.1% or more).

Tom Buck said this: "In Spain, there exists one large ore body assaying low amounts of iron sulfide (mostly), too inadequate for steel-making even with modern "float sink" technology. Long ago, however, an astute person noticed that rainwater would pool, then evaporate and leave behind a mineral that turned red on roasting. In time, it was discovered that a specific life-form (a bacterium, named bacillus ferro ferroxidans) used the iron sulfide as food (an energy source). The bacterium did its thing in water in contact with the iron mineral. The result is to solubilize the iron as Iron(II) Sulfate or FeSO₄. This solution is run into evaporation ponds, the green crystals recovered are then roasted to form Spanish red (iron oxide red). To keep costs as low as possible, the mine operators in Spain are happy with an Iron Oxide Red purity that ranges from 83 to 88 percent by weight. If you as a potter were able to obtain Spanish Red as such bag after bag, then you'd tweak your recipes to get the best glaze colour."

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