types of RIO?

[clay lover]

I was told by an on line potter contact that shared a red recipe with me that it's failure to come out red, rather muddy brown instead, was due to me using Spanish red iron oxide. He said I needed Special red iron oxide, yes, that's it's name, SPECIAL.

I am aware of Crocus Martis as a more pure form, is that the same as Special RIO?

I googled it , no luck that I could understand, way over my head.

[Benhim]

According to my supplier:

 

Special is 97% pure Red Iron Oxide

 

Spanish is 82 - 86% Red Iron Oxide

 

I've heard it said several times that Spanish makes better black iron saturate glazes (reduction), and Special makes better red iron saturate glazes (oxidation).

 

Crocus Martis is an impure form of Red Iron Oxide which causes flecks or a speckled look.

[Denice]

Are you firing reduction or oxidation and at what cone? Denice