slow cooling with digital electric kiln

I have a new Paragon Electric Kiln with a digital controler. I program
it for cone #5 with a 10 minute hold for my glazing. What slower
cooling rate than the normal cool down should I use to allow crystal
glazes to work and help keep Greenware from cracking?
Reply to
Mel
I can't give specifics on crystal glazes since I've never done these. But I do know that it is a *very* finicky process to get nice crystal growth. There are books devoted to the subject, and Web sites. This is probably not an area to dive right into if you are just starting out... get comfortable with conventional glazes first.
It's not just because it's hard to get good crystals, it's because crystal glazes have to be very runny... they almost always flow down the pot and run off the bottom. Those who work with crystal glazes have to put little saucers under their pots to keep the run-off from flowing onto the kiln shelves. Afterward they have to break off the glazed-on saucer and grind the foot of the pot smooth.
I'm not sure what you mean by greenware cracking. Greenware is unfired ware. Some people use this term to refer to undried ware (Hamer and Hamer, in "The Potter's Dictionary"), but I think it's more commonly applied to dried but unfired ware. So the cool-down curve clearly doesn't apply here.
As far as simple cracking from thermal shock, this will never be an issue. You don't need to program anything for it, because the kiln will naturally cool *way* slower than needed to prevent thermal cracking. (Assuming you allow things to cool naturally until you can touch the ware... never try to remove hot ware from the kiln unless you are doing raku or something like that, and know what you are doing.)
That doesn't mean you'll never get cracking, just that any cracking you get will have other causes like stress left over from the making, or too much thickness difference between parts of the ware, or bad glaze fit, etc.
Best regards,
Bob Masta DAQARTA v4.51 Data AcQuisition And Real-Time Analysis
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Reply to
Bob Masta
I don't know what kind of controller you have, but it should provide a function that will slow down cooling. The Mastering Cone 6 Glaze Book specifies some good rates of cooling that bring out the crystals in the recipes they have. The elements actually come back on to do this. You'll need to find out what works for your glazes and how to program your controller.
Best, Sue
Reply to
Sue Roessel Dura
rote:
From what I have heard for Crystal formation after you reach your high temperature you then drop down about 100 degrees and then hold that temp for 1 to 2 hours, then you can shut off and let the kiln cool on its own (no open draft holes).
Reply to
btpanek09
Hi Folks,
I don't check this list very often and am sorry to see it's pretty much trashed. Where is everyone else getting advice?
My question right now is that I have a gig at a local private school that is part of its fundraiser. Apparently, they get artists in to create a project with their students so that the result will raise money at auction. My idea is to make a punch bowl that will be rather nice, have the kids make cups to go with it using yogurt containers as molds (did you know that 8oz containers are now passe???). Then we will use hands in the glazes to put hand prints on these pieces. I've gotten making the cups down to 6 steps and the glaze part to 2 steps. Has anyone tried anything like this???
Please let me know if I am crazy to try a project like this with 5th graders!!!
Best to all, Sue
Reply to
Sue Roessel Dura
On Wed, 11 Mar 2009 18:08:51 -0500, Sue Roessel
To get the clay off of the outside of the yogurt containers quickly, try wrapping the container with a layer of old newspaper first. You might want to make a template and pre-cut a bunch of sheets for this. Wrap the paper on the container and tape it to itself... no tape on the container. Then the clay and paper will slip off together after forming. (As long as you don't wait so long that the paper is saturated.)
Another tip is to use "tarpaper" (roofing felt) to make templates of the mugs. This is sold in big rolls at building supply stores. Get the 15# stuff (30# may be too stiff). Your template will end up being 2 pieces: A disk for the bottom of the mug and a curvey piece like a windshield for the body (plus a handle piece, if you want.) Use plain paper to make the master template, and expect a few trial runs until you get it the shape and size you want, then cut the working template(s) from the tarpaper.
These templates will be for the *outside* of the piece. Roll out a slab between sticks the thickness you want the mug walls to be, wet the template pieces, roll them into the slab to get them to stick, then use a blunt pin tool or even a butter knife to cut out the clay+template pieces. The tarpaper is stiff enough to make a guide, so the kids can do this themselves (assuming you trust them with the cutting tool... butterknives may be better than pin tools for that aspect!).
Now you can pick up the tarpaper+clay pieces and assemble them onto the yogurt containers. Note that since the templates are outside the clay, which is probably a 1/4 inch thick slab (or whatever you like), they must be enough bigger than the container that the *inside* will fit. That's why you might need some trial and error designing the templates.
But as it happens, you may not even need the containers as a mold, since the tarpaper+clay is pretty much self-supporting for this small size... I have done this without using a container or other form, and all it means is that you spend a moment making the circumference round after joining, instead of whatever oval it just happened to come out as... you can use this as an opportunity for creative expression!
Use a toothbrush dipped in water to roughen and wet the seams before joining. Join the semi-cylindrical wall portion of the mug first, then wet and roughen the bottom and join that. You can leave the tarpaper forms on for as long as it takes for things to stiffen up a bit, since they are on the outside. (They are waterproof, though, so you need to remove them for complete drying.)
Tarpaper templates can be washed and stored for re-use. They last a long time. And you can make all kinds of shapes. A nice simple project I once did with my young nephew was a butter dish. It's made from simple rectangular shapes you can lay out on graph paper to make the master template, without much trial and error stuff. And the pieces are small, so they are easy to handle with the clay attached. I made the lid as one folded piece... a long rectangle with "ears" for the sides. When you fold this up, you first score some V-shaped grooves at the joints and roughen and moisten as usual, then fold and press. The tarpaper on the outside holds everything together, and if you don't make the V grooves too deep there will be enough clay on the corners to give a nice rounded appearance.
Best regards,
Bob Masta DAQARTA v4.51 Data AcQuisition And Real-Time Analysis
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Scope, Spectrum, Spectrogram, Sound Level Meter FREE Signal Generator Science with your sound card!
Reply to
Bob Masta
Thanks Bob! I did the project today and did a lot of what you suggested. We used a heavy tissue paper over the cups and I had pre-cut 'windsheilds' of clay. It was easy to get a pattern by rolling the cup on a slab, cutting out the result, checking the fit and then tracing it on paper. The kids worked as partners with one holding the cup steady while the other wrapped the clay around it. They switched roles, then added the bottom, made with a biscuit cutter. The cup slid right off and they worked the inside and the rim. I was happy with how well they did! I like the idea of the toothbrush and tarpaper - may use it next time so we don't have to collect so many cups ;-) Best, Sue
Reply to
Sue Roessel Dura

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