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|This is the chemistry of the material (the formula compares numbers of molecules, the analysis compares them by weight). In glazes, the composite chemistry of the mix is the main factor shaping fired properties (e.g. color, melting temperature, surface). In bodies we are interested in their physical properties (e.g. shrinkage, porosity, strength), these are a product of the mineralogy of the materials.|
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.
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