cone firing

i don't know how lucky i've been, BUT i've used cone 6 porcelain slip castings fired at cone 10 a few times - using cone 10 glases. maybe 8 times i've tried this. the overall result is sure beautiful. but i recognize that this may be a form of russian roulete...

i don't know if the higher temp glazes insulate somehow (i would have thought they would flux the clay body downward), or if true porcelain has a stuborn affect on overfirings.

just a piece of data....

steve

steve graber

"Stu" wrote in news: snipped-for-privacy@corp.supernews.com:

A cone 5 clay seems to be a bit of an orphan, but now you've got it, keep it and use it. The clay will fire over a large range of temperatures.

You should do some firing tests on the clay by putting some small pieces into the next cone 10 firing. As it will be a formulated white stoneware clay and not a terra cotta it is more than likely the clay will fire well at cone 10 and will be hard and well vitrified Large thin bowls might slump a bit. For the stoneware clay to vitrify at cone 5 there will be a quantity of some sort of frit in it to bring its vitrifying temperature down.

I fire a cone 6 white clay to cone 10 and 11 in oxidation, reduction and anagama. Works well across the range and has excellent colour response. Some of the areas on the potts seem to self glaze. I imagine that this is caused by the addition of the frit or frits in the body. Good responce from manganese dioxide and ash in the anagama

Secondly you could treat it as an earthernware clay. Bisque to 1000 and glaze with standard earthernware glazes.

Happy daze

John W

temperature

The folks that write books are generally very experienced. Certainly there are different ways of doing things, but info in books is likely to be "best practice". For example, a well formulated cone 6 stoneware clay will be well vitrified at cone 6. If fired to ^10 it will almost certainly be overfire and slumping (or worse). If a clay labeled cone 6 fires well to cone 10, it is very unlikely that it would properly vitrify at cone 6.

deg

this thread is a bit difficult to follow, you appear first under "Stu", then under "Kathrin Fields" and then under "Kathy", you never sign your postings with a name, it took me a while to realize this is all the same person.

What is written in the available books usually _is_ experienced reality. People who haven't experienced reality unsually don't write books. And pottery is _not_ a simple craft by no means. Read the books carefully and then experiment on your own, it takes time to find out what _your_ clay, _your_ glazes, do. I, for example, have a clay which i couldn't possibly fire only one cone higher than supposed, it very quickly melts into a glaze. Other clays have a firing range of several cones without any noticable effects. Most of it is trial and error, make one small piece, fire it at cone xxx and see what happens. Here in the newsgroup, you get people from all over the world, using different clays, different glazes, there is no way we can tell you what your clay will do under what conditions. Experimenting is fun! Sometimes you find things totally unexpected, for better or worse! Enjoy it!

Monika

-- Monika Schleidt snipped-for-privacy@schleidt.org

Just one or two things I might add to this thread...

Before Kathy (or Stu) experiments with cone 5 clay in a cone 10 kiln, he/she should find out if it's permitted by the school doing the firing (I recall in the original post she/he mentioned using a school's kiln). The school where I take my classes has a very strict policy about only firing cone 10 claybodies in their kilns. There have been some disasters involving melting or exploding pieces when people haven't followed this policy, and unfortunately the disasters don't only affect the work of the person using the lower cone clay. Experimentation is a good thing, but not when it can ruin a kiln's worth of other peoples pieces! I know I spent a good amount of time with a Dremel getting rid of chunks of someone's exploded piece in a set of mugs I had done on commission. Not fun. You don't want to be banned from using the kiln over 5 lbs of cone 5 clay. It's not worth it!

Deb R.

Sorry about the name switching. I'm Kathy (Stu is my husband who communicates with newsgroups related to homebuilt rotorcraft and machining.Check out our web site,

) Took these several changes to get my "signature" block corrected for this group. Kathryn Fields is just a formalization of course, so the choice to change made sense to me this am.

All of your contributions are quite helpful. Certainly, I would discuss firing this clay with who ever controls/fires any of the available kilns. Was just wondering whether to put the clay away until a better time, using other clays which I have and know they will work in our resources.

I'm too new to this to buy a kiln -- unless there is a very small kiln which would cover small quantity testing, yet had a wide range of heating possibilities. As you point out, pottery is not a simple craft and requires a good deal of study along with all the shere practice I can muster. Developing throwing skills, glazing, building and understanding clays fully occuppies my attention, without crowding in this entire further study of kilns.

Anyway the point is I really appreciate all your contributions to my education and searing.

Kathy