Making a cone 04 clay go to cone 10

[Mullins Pottery]

I've got this native clay that I've been working with for a couple years and it's a fantastic clay that fires beautifully to cone 04. When I first began testing this clay body i tested it at both 04 and cone 10. At cone 04 its a soft salmon color and it works great with cone 04-06 glazes. in a cone 10 gas reduction firing it turns black and seems to be too vitrified and brittle but there is no bloating. At this temperature it does not receive cone 10 glazes at all. All the test tiles I made with this clay glazed crumbled/shot off into hundreds of pieces. I know that there are some clay bodies that can be adjusted to work well at low and high fire temperatures.  I'm wanting to find out what could be added to this clay body to make it a proper fit for cone 10 glazes and perhaps still work well at 04.

[glazenerd]

Just now, Mullins Pottery said:

I've got this native clay that I've been working with for a couple years and it's a fantastic clay that fires beautifully to cone 04. When I first began testing this clay body i tested it at both 04 and cone 10. At cone 04 its a soft salmon color ( indication of iron/ magnesium/ carbons)and it works great with cone 04-06 glazes. in a cone 10 gas reduction firing it turns black and seems to be too vitrified and brittle ( indication of higher iron levels, probably hematite) but there is no bloating. At this temperature it does not receive cone 10 glazes at all. ( because the body is maturing well below this cone, sealing the pores of the clay/ glaze interface) All the test tiles I made with this clay glazed crumbled/shot off into hundreds of pieces. I know that there are some clay bodies that can be adjusted to work well at low and high fire temperatures.( a myth, clay bodies might work, but not work well)   I'm wanting to find out what could be added to this clay body to make it a proper fit for cone 10 glazes and perhaps still work well at 04.( by your comments thus far, suspect high iron content; which means cone 6 would be the top range.)

 

[neilestrick]

If you want it to go hotter, try cutting it with some kaolin, ball clay, or fireclay.

[Mullins Pottery]

Thanks guys I appreciate the suggestions. I'm definitely going to give kaolin a try. 

 

[tinbucket]

Not only try "cutting it" with a high temperature clay, do a line blend! At least 20/80, 50/50, and 80/20. Absorption/shrinkage bars should give you some idea of what's going on. Also, I'm assuming you are firing cone 10 reduction, and cone reduction will effect the fluxing action of iron more than oxidation will, I'm sure others can give a better explanation of this - my understanding iron in reduction = more melty/stronger fluxing