Issue With Rio In Black Gloss ^6 Glaze

[Frankiegirl]

Hello. Hopefully someone here can help me because I am scratching my head. I use a black gloss cone 6 glaze and recently had an issue with it - it came out a strange sort of light brownish/bluish color (not unpleasing but odd and not at all the gloss black I have used and require). I recently relocated and purchased the iron oxide from a different place than usual and it was the Red variety. I normally use Spanish RIO for this recipe but didn't have any on hand so used the more expensive RIO. Even though I have never substituted it before I didn't think it would make a difference. Am I missing something here? Could that have been my issue or should I be looking at some other error?

 

Here is what I used:

 

Silica: 26

FF 3134: 26

Custer Felspar: 22

EPK: 17

Talc: 5

Whiting: 4

 

RIO: 9

Cobalt Carb: 1

 

 

[neilestrick]

http://mobile.ceramicartsdaily.org/wp-content/uploads/2011/03/cmtechnofileiron.pdf

 

Iron oxide can vary greatly in purity. I would run some tests, increasing the iron in 1% increments up to 14%.