Crocus Martis

Description: Anhydrous Ferrous Sulphate FeSo4, Calcined Copperas

Oxide	Analysis	Formula
Fe2O3	41.64%	1.00
FeO	37.48%	1.76
SO3	20.88%	n/a
Oxide Weight		304.02
Formula Weight		384.25

Notes

Has been used in glazes as a substitute for red iron oxide.

There are varying ideas from country to country about what this material is. Historically it was just a naturally-occurring red iron oxide containing impurities (i.e. clay minerals) or an ultra-high iron clay. Today, Crocus Martis sold by ceramic suppliers is more likely to be a soluble synthetic impure red iron sulphate or a calcined-at-900C version of the sulphate (it is insoluble). This material is not normally highly processed and therefore can produce iron specking in glazes. Normal iron oxides can be used as a substitute (although less will be needed since this material has a significant weight loss during firing).

Sulphur is released during firing and it does not decompose fully until as high at 1200C.

Related Information

Links

Materials	Spanish Red Iron Oxide
Typecodes	Colorant Metallic based materials that impart fired color to glazes and bodies.

By Tony Hansen
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