Need help with cone 10 claybody

[Anonymous]

I have been using this very dark colored claybody for all of my work. I
have been firing at cone 10, but only at a glaze reduction, not body
reduction, and getting great results--though not always constant. Anyhow, I have
always loved the deep chocolate color I get, but when I fire it with a body
reduction it bloats.

This is the recipe that I have been using:

Red-Brown Stoneware Throwing Body Cone 10
Shrinkage 9.8%, plasticity 11, glaze rating 11.1

Jordan clay* 30.0
Redart clay 27.0
Kentucky ball clay #4 18.0
Feldspar (Buckingham) 5.0
Silica Sand 15.0
Fire clay (calcined)* 5.0

I have been substituting *Fire clay (calcined) with AP Green and *Jordan
clay with Goldart.

I believe that the AP Green is fine, but is the Goldart the wrong choice for
a cone 10 body reduction firing? What can I use instead? Cedar Heights
fire clay? EPK?

Maybe the Goldart isn't the problem after all? This recipe has an awful lot
of Redart in it, could this cause the bloating? What do you think about
adding manganese to a cone 10 claybody for color? Is this something I
should avoid if possible (due to health reasons)? What alternatives do I
have?

What I need is a DARK claybody (I don't always use glazes) that can
withstand a cone 10 body reduction. Can you help me change this recipe so
that I can get my desired results? Maybe you have a recipe that I might be
able to try. *NOTE: I want to throw and sculpt with this body.

Thanks in advance for any help that you may have to offer,

Greyfolk

[imported_aclift]

Hi Greyfolk,
You ask some good questions. Your clay body is fine. The way you fire it is what needs to be adapted. I would say stop doing a body reduction. There is some great information on the following pages:

Bloating and Black Coring
http://www.lagunaclay.com/support/articles/bloating.htm

clayart digest - bloating
http://www.potters.org/subject47914.htm
http://www.potters.org/subject01094.htm

As far as maganese goes. Personally I am reluctant to put in into my clay. Granular perahps, fine maganese, no thanks. Although, if it will do something for your work that you really want and you protect yourself, perhaps it would be all right. See the Links below on Maganese.

PPP: Influences on Clay Color
http://www.ceramicindustry.com/CDA/A...,88297,00.html

My Story of Manganese and Parkinsons: Jane Watkins
http://ceramic-materials.com/cermat/education/147.html
Potters Manganese Toxicity by Elke Blodgett
http://ceramic-materials.com/cermat/education/139.html
Good Luck to you,
Andy

[Anonymous]

Your clay body is fine. The way you fire it is what needs to be adapted. I would say stop doing a body reduction.

Thanks Andy,

I would really like to learn how to make this body adaptable to the body reduction. All the other clay bodies in the firing do very well. Is it possible that the goldart had been contaminated with sulfur?

Thanks,
Craig