Tuesday, March 10, 2009

Clay trouble

Well the title says it all. We are planning on mixing all of our own clay, but last year just got a little too crazy and we didn't have time to mix enough clay up to last us over the winter. We fired our little test kiln last week. Quite a few of the pots had large bloats on them, between an inch and two inches in diameter. Here is a picture of a pot we broke, kind of a cut away view of one of the bloats:

Here is a piece from one of the bloated pots:

I'm guessing our clay supplier is have pieces of metal (iron) falling off of his clay mixing equipment into the clay body. Does anybody else out there have any experience with this, or any advice? We do fire the little gas test kiln pretty quickly. We are hoping in the extended firing of the wood kiln we can fire slow enough and keep it in oxidation long enough that the bloating will not be a problem. Still a little worrisome though as all the pots that we have made so far are made with this clay body. As soon as the weather warms up a little more we will be getting back to mixing our own clay!


Linda Starr said...

That is so terrible; hope slowing the firing down helps. I saw a guy on flickr, Glenn D Hudson, actually puts iron into his pots and woodfires them but they don't look like yours - but maybe some do - I saw his pots on flickr here is the link to see his pots with iron shavings added:

brandon phillips said...

do you raw glaze? i had this happen once when i used to raw glaze and then it never happened again. though mine weren't as large. my theory was that i reduced too early or fired too fast and gasses got trapped, couldn't be sure though. i don't think it has anything to do with the iron though. are they mixing your body or are you using a premixed? i've heard things about goldart causing bloating but i've never really looked into it.

Alex Solla said...

Having seen this a few times, I would hazard to guess that somehow, a lower temp clay (or claybody) was inadvertently mixed into your claybody. It happens. Did it my very first batch of mud I mixed up. Looked just like your samples. At this point, I would see if your supplier would take the clay back, if not, see how it behaves at lower temps. Might end up being unuseable at higher temps. Certainly not worth more than a sample test.

With regard to fast firing... it can cause some bloating, but usually only in once-fired pots. And what you have in your sample is a hollow bloat, as opposed to a carbon-core bloat (which is what I have usually seen in single fire problems.

Hope this helps. Good luck and I hope you are able to salvage something from this catastrophe.

Joe and Christy said...

Thanks everyone for the advice. I guess it would have been good for me to say from the start that we are glazing everything leather hard and once firing. Thanks again.

Michael Mahan said...

I can remember this happening to me when I was raw glazing and firing in a small electric kiln which fires rather fast.

Hopefully, a slower firing will solve it.

Good luck.