COREY J SCHMIDT on mon 5 jul 04
OK, I have been doing Raku pottery (american style) for five years now.
Just when I think I get something down, it seems all the rules change
(without anyone telling me), and I have to rethink things all over again.
Here is my current problems.
1). It seems that I have hit and miss breakage rates with my pots. I seem
to be doing everything consistent, and I have good building techniques.
When I fire the first load from a cold kiln everything comes out nice, and
not broken. But as the kiln warms up and I put other pieces into the hot
kiln things go amiss. Have I missed something here? Surly everyone isn't
letting the kilns cool down between firings! Do you stilt the pots, or use
sand or something to buffer the bottoms of the pots where they contact the
kiln shelf? This was not so much a problem with my first type of clay
Seattle Pottery's Columbia Buff with extra grog ^10 and bisqued to ^06-05.
And I was throwing smaller pieces. Now I have switched to what I thought
was a better Raku clay, Seattle Pottery's Raku 2 ^06-1 with the same bisque
temp (although I think it has WAY too much grog) and even some of my smaller
pots are cracking in the kiln (the first cold firing still turns out good).
I fire with a home made fiber kiln and propane venture burner. My fire
cycles run about 15-20 minutes between kiln loads, and I preheat the next
batch on top of the kiln (they usually get too hot to touch with bare hands.
Any ideas, comments, or suggestions.
2). Also about glazes going bad. I have heard that glazes go bad. And on
some firings I thought they have, but not wanting to waist anything I have
later glazed a pot or two using that very same glaze it turns out just
great. Again, any ideas, comments, or suggestions.
thanks,
Corey
Craig Dunn Clark on mon 5 jul 04
Corey, sounds like your clay body ain't doin what it's sposed to be doing.
Don't know anything about your particular body but I do know that a properly
formulated raku body will survive firings when placed into a "hot" kiln. I
use Lagunas WSO and or my own special blend (100lbs Hawthorn Bond, 50lbs
Gold Art, 50lbs Ball Clay and from 15% to 25% grog and kyanite.....the
varying percentages are based on what type and how big the pieces on plan on
throwing or building will be.)
As to a buffer between the shelf and the pots either fiber or soft brick
work well. I just let the kiln cool down enough to where the shelf is no
longer glowing red before putting in the next round of pots, especially if
they are larger and/or open forms. When I don't I have a higher loss rate
than I would like, especially with footed forms. It also sounds like that 15
to 20 minute cycle is a bit fast. Try slowing things down some and see if
that helps.Do you need to have that quick a turn around time? One more
suggestion is to bisque fire to cone 04 rather than 06. The higher bisque
temp gives you a bit more strenght and the cost difference in the firing is
not substantial.
I have literally had a glaze sitting around for a year that I did not
use very frequently, remixed and sieved and did not have any problems. There
is a lot more room for running free and loose with things in raku. Don't
think this would be the same case with a high fire glaze.
Hope this helps
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
----- Original Message -----
From: "COREY J SCHMIDT"
To:
Sent: Monday, July 05, 2004 4:43 PM
Subject: Some Raku Questions
> OK, I have been doing Raku pottery (american style) for five years now.
> Just when I think I get something down, it seems all the rules change
> (without anyone telling me), and I have to rethink things all over again.
> Here is my current problems.
> 1). It seems that I have hit and miss breakage rates with my pots. I
seem
> to be doing everything consistent, and I have good building techniques.
> When I fire the first load from a cold kiln everything comes out nice, and
> not broken. But as the kiln warms up and I put other pieces into the hot
> kiln things go amiss. Have I missed something here? Surly everyone isn't
> letting the kilns cool down between firings! Do you stilt the pots, or
use
> sand or something to buffer the bottoms of the pots where they contact the
> kiln shelf? This was not so much a problem with my first type of clay
> Seattle Pottery's Columbia Buff with extra grog ^10 and bisqued to ^06-05.
> And I was throwing smaller pieces. Now I have switched to what I thought
> was a better Raku clay, Seattle Pottery's Raku 2 ^06-1 with the same
bisque
> temp (although I think it has WAY too much grog) and even some of my
smaller
> pots are cracking in the kiln (the first cold firing still turns out
good).
> I fire with a home made fiber kiln and propane venture burner. My fire
> cycles run about 15-20 minutes between kiln loads, and I preheat the next
> batch on top of the kiln (they usually get too hot to touch with bare
hands.
> Any ideas, comments, or suggestions.
> 2). Also about glazes going bad. I have heard that glazes go bad. And
on
> some firings I thought they have, but not wanting to waist anything I have
> later glazed a pot or two using that very same glaze it turns out just
> great. Again, any ideas, comments, or suggestions.
>
> thanks,
> Corey
>
>
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william schran on mon 5 jul 04
Corey wrote:>When I fire the first load from a cold kiln everything
comes out nice, and
not broken. But as the kiln warms up and I put other pieces into the hot
kiln things go amiss.<
Try using some broken/scrap IFB, or cut some new ones in half and
stilt all of you work on them. This will help eliminate the sudden
temperature change when the relatively cool pot hits the very hot
kiln shelf.
Have several pieces of brick so you can let one set cool while the
other is in the kiln.
Bill
Ron & Nancy Hughes on mon 5 jul 04
Dear Corey
I use all the shards from previous firings that I made before I learned
to put the shards under my pots in the kiln after previous firings
Nancy
sdr on mon 5 jul 04
Corey said:
> 1). It seems that I have hit and miss breakage rates with my pots.....
When you load your second lot of pots, put a piece of
broken kiln shelf or a half brick or something on the hot
shelf, to buffer the cold pot from the hot shelf. Your breakage
rate will shrink to nothing.
Decide ahead of time where to put the HOT kiln shelf/brick
pieces when you remove them from the kiln, so that they are
well away from your traffic path. I've seen a zillion people
just drop them in front of the kiln, making a lovely hot spot
on which to trip, burn shoes/feet, do generally dumb stuff.
Remember that you'll be putting a fresh cool piece in EACH
time you load a new lot of pots.
regards
Dannon Rhudy
Ron Roy on wed 7 jul 04
Here is what I said.
Hi Corey,
Get the silica out of the clay body - it's probably the thermal shock when
the clay goes through the quartz inversion at 573C.
RR
>lost a post from ron.
>breaking pots may be due to silica..thermal shock.
>mel
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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