slow cooling with digital electric kiln

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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?

Re: slow cooling with digital electric kiln
On Fri, 6 Feb 2009 07:55:23 -0800 (PST), Mel

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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
 
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Re: slow cooling with digital electric kiln

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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

Re: slow cooling with digital electric kiln
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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).

Teaching 5th graders
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

Re: Teaching 5th graders
On Wed, 11 Mar 2009 18:08:51 -0500, Sue Roessel

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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
 
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Re: Teaching 5th graders
On Thu, 19 Mar 2009 12:34:37 GMT, snipped-for-privacy@daqarta.com (Bob Masta) wrote:

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

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Re: Teaching 5th graders

 Sue

Any way you could post a pic?

Love to see their work!

Rox


Re: Teaching 5th graders

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We should finish up in a couple of weeks, then I'll take some photos.  Best, Sue

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