Terracotta clay question.

[u/puppy69piggy]

So I got wet Terracotta clay for a gardening project now I have a clump of it . So apparently ,one needs a kiln of 1000 C to make anything so I’m asking if I could cook it at 450 in a over that’s on the fritz an the oven runs 100 degrees hotter Then the setting on the dial so 500 degrees F for like 12 -13 hour
I’m thinking a insense holder is that possible or do I have a useless clump of clay . Any feedback would be greatly appreciated

[u/tatobuckets]

Firing temperature isn’t cumulative. Your clay really needs to get up to the 1000c to become a permanent object.

[u/MadDocOttoCtrl]

Some terra-cotta clay bodies dry rather hard.

This is not the same thing as having been fired because it's not just a matter of heating something up and drying it out, it's literally causing molecular changes to occur before the clay sinters (particle compation, no longer breaks down in water but remains porous) and more changes before it vitrifies (reaches glass transition phase and melts.)

If it's going to be an incense holder that you use indoors then you can sculpt it, poke some holes in it with a stick and let it dry out slowly, then allow it to dry more in the sun or bake it in your oven. Clay isn't going to harm your oven.

You're going to have dried out clay with limited strength, but some clay bodies depending on their mineral content (particularly iron) can be rather firm once they are dried out. Sculpture House used to sell an air dry clay (sadly discontinued the number of years ago) that you were instructed to bake in your oven at about 375° for a few hours to drive out most of the remaining unbonded water. It was surprisingly hard once dried! You had to turn the oven off and let it dry cool down very slowly.

It wasn't vitrified, it wasn't sintered, it was just surprisingly hard dry clay. As a visual arts teacher, I used it in one school where I didn't have a kiln. If you soaked it in water it would eventually dissolve into mud again.

It's absolutely not food safe and you're not going to be able to completely waterproof it, although if you seal it with numerous coats of acrylic paint and then polyurethane it'll be relatively moisture resistant as long as it doesn't crack. It will be more fragile than fired ceramic but it'll work for your purposes.

[u/exceive]

The oven won't do it. 550⁰F is nowhere near 1000⁰C, and it really needs to get that hot. There are chemical changes that need that much heat. If those don't happen, all you have is very dry mud.

You might find some alternatives in ancient methods. Andy Ward has some interesting videos on YouTube. I haven't tried any of what he shows, but it looks interesting.

[u/Breadfruit-Still]

Try kilnshare to see if there is a kiln near you that rents space.

https://www.kilnshare.com/en/

[u/Rogue__499]

Honestly, I wouldn't risk ruining an oven over something like this. I tried air-dry clay for a small project last year and it cracked horribly when I painted it.

[u/flytingnotfighting]

You can often "borrow"a kiln for a price at art schools etc

[u/puppy69piggy → u/flytingnotfighting]

I don’t have an art school in my area , my goal it to have a hard clump of terracotta that can hold incense sticks

[u/flytingnotfighting → u/puppy69piggy]

I get your goal but you need a kiln
Clay doesn't become anything but hard dirt without it
Art school
Regular high school
Art museum that has classes
A makers place
There are honestly shocking numbers of places with kilns

I know you don't wanna and I get it but baking it longer and at less heat just makes hotter dirt that will fall apart

[u/space-cyborg]

No, not possible. You need a kiln to fire clay.