Mixing local earthenware and stoneware

[Earthandwater]

Hi!

I want to use more local materials in my work, but I only have access to a community studio kiln. We fire at cone 6/7 and the local blue and red clay we have here, would just melt. But! Is it possible to mix this local clay with stoneware? I have already tried, but there are so many variables and ways to mix it that I am not sure. I mixed just a teeny bit into some stoneware and threw a cup: it did sink a little bit, maybe bacause of the earthenware, but i am not sure. Do you think I could increase the local clay percentage? Is there any well known issues regarding this? I have searched, but I can't find anything relevant.

Best wishes,

earthandwater

[Sorcery]

I have been experimenting with 3 different local clays like this. 

I reckon the #1 underestimation is the longer bisque times in oxidation to burn out what is likely a higher impurities content. I have a photo here somewhere of a clay much less bloated with a longer burnout.

I've found most of the best effects of local materials are most easily had by using it to decorate the outside. For a slab builder like me, this means ribbing sand into the outside, using the clay as slip glaze, or carving depressions to rib the clay into. The benefit/hassle ratio here is 90/10.

Using it inside the clay, for an understandable use of local materials, is mathematically very unsound for finances, depending on the clay and situation of course. For my situation and clay, the benefit/hassle ratio is 10/90.

I don't believe this changes until your local clay is good stoneware and your closest supplier.....isn't.

Sorce

 

[Earthandwater]

Hello,

Thank you for your input! Yes, I also find it easier to use the local clay in the glazes, as slips and other decoration. But, I really want to use some of it in the clay body as well.

I did not quite understand what you meant about the bisque: does local clay have to be bisqued longer, to burn away impurities?

I do not think at all that collecting local clay will be financially a good idea, but i really like the tought of it and i am not afraid of some extra work:)

[Min]

You could do a line blend with a cone 10 claybody and your local clay, fire the test pieces in little shallow bowls to catch the ones that run. If you can get a dry mix cone 10 stoneware that would be the most accurate to measure out weights and combine the two evenly but even using wet clay will get you in the ballpark. I'ld start with 95:5 (cone 10 to local) then go by 5% increments until you get to 65:35. If you don't want to purchase a cone 10 stoneware its fairly simple to mix up a dry batch of cone 10 stoneware clay. 

[Earthandwater]

Thank you so much! I have been mixing with a stoneware that can be fired from cone 6-10 - do you think that can work? Or should it be specialized to cone 10?

[Callie Beller Diesel]

When clay companies call a clay “6-10”, it means it’s not really mature until cone 10, but will hold together for cone 6. You’re probably ok. 

[Earthandwater]

Ok, thank you! I have actually been wondering this: if the cone 6-10 clay fully vitrifies at cone 6. More to wonder about:)

[Min]

34 minutes ago, Earthandwater said:

More to wonder about:)

It's a good idea to test your claybody before you make a lot of pots with it, especially if you are making functional work like mugs and bowls. I would strongly suggest testing both the wide firing clay if you are using at cone 6/7 and the wild clay / commercial clay mix. The broad range commercial clay you could probably just test for absorption but the wild mix I would run a slumping test and an absorption test on once you get the tests narrowed down. If you need it there is a good article here that includes how to do these tests.

[Earthandwater]

Thank you so much for your help!

[Sorcery]

On 12/20/2020 at 10:23 AM, Earthandwater said:

, to burn away impurities?

Yeah. This is the same blend of local and commercial. The left spent less time between 1100F and 1800F. Large bloats.  The right spent more time through burn out. Almost no bloats. 

Sorce