Martin Howard on fri 1 dec 00
I have had pots crack at leather hard when glazed.
BUT that only showed that there was an imbalance in the form of the pot
OR that the rims were too thin
OR that the amount of water in the slip and the glaze together was too much
for that particular pot
OR I had just missed leather and was into black leather stage.
But I am persevering with raw glazing, sometimes glazing at leather,
sometimes spray glazing at bone dry if I missed the leather stage.
It does mean that I use 117 units of electricity for each kiln load, instead
of 2 lots of 100, a saving of 83 units for each lot of pots. I ramp slowly
to enable the leather hard pots to completely dry out during the first night
in the kiln. Top is open until 500 C and I do not look through the spyholes
now, because that seems to cause a draught affecting those pots nearest the
front of the kiln.
The students more often bisque glaze than leather glaze, but that is no
problem, because the kiln is at the same setting for both. Pots for bisque
firing mix with leather glazed at the bottom of the kiln, where it only
reaches cone 1. The top reaches 3.
Martin Howard
Webb's Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
England
martin@webbscottage.co.uk
Cindy Strnad on mon 4 dec 00
Hi, MaryBeth.
I'm so glad to hear your firing went well! A little tip I read about raw
glazing teapots, which may be of interest to you:
If I remember right . . . glaze the inside of the pot (no spout or strainer
holes). Add the spout and, if desired, strainer holes. Glaze the outside,
being careful to get glaze inside the spout only up to the strainer holes.
Handy little trick, only for raw glazers, so I haven't tried it. Sounds like
it would be cool, though.
Obviously, this must be done at the leather hard stage. I read it in "The
Self-Sufficient Potter".
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
earthenv@gwtc.net
http://www.earthenvesselssd.com
MaryBeth Bishop on mon 4 dec 00
hi again,
I just completed my first two glaze firings in my Skutt 1027. It was new two
years ago and I finally got around to mixing and sieving my old glazes and
giving it all a go. Since I have never really been "into" electric firing, I
have been making things and bisque firing them to carry off for wood firings
or salt or whatever. Anyway, finally I decided to get with it and begin to
learn this kiln and stop being such a primadonna or whatever. So, after I
got the Thanksgiving dishes washed, I went to work in the garage. It is cold
here by the way, so lots of layers of clothing and hot water carried from the
house. Anyway, to the point.
I did two mixed firings back to back. Bisque ware in with raw ware and
refires. The raw pots were all bone dry when I glazed them. I used the
same glazes on the whole batch. If you set them side by side it is almost
impossible to tell the difference. I can tell because I think the glaze and
clay form a more "organic" union when put together in the raw state and of
course I know which pieces were which. The other thing is that I brush
teapots rather than dip them. This makes them a bit "blotchy". Actually I
find these easy to accept as I really like the movement in glazes that comes
from reduction firing. Of course everything was dry by the time I actually
started the kiln but in slow mode I had no failures. I really think a
bisque firing is unnecessary unless a piece is fragile, complex or needing to
be transported for firing. Other than that, I have to choose between
dipping, brushing with a big sloppy paint brush or spraying depending on my
ability to handle the piece in and out of the glaze bucket. Tongs are
obviously out for raw glazing. And of course you need to be able to control
the firing. Slow, somewhere under 200 degrees an hour has been safe for me.
Of course, after I get past 1200 or so I am dealing with bisque pots all and
can speed up a bit if necessary.
Anyway, just a little summary of my first efforts in some time. The good
news is the pots came out fine. Ready to be sorted into groups:
acceptable/sellable/ponderable and landfill.
Now I am moving to a corner in our new group studio...Claymakers...for the
winter. I haven't really shivered in years but was definitely shaking on
Friday by the time I finished loading the kiln the second time. Saturday I
moved indoors to begin a winter of handbuilding at Claymakers and stopped
just short of complaining because I was hot. So, all a ramble here, but my
position on Bisque fire...an option. Surely not a necessity. In group
situations however it is probably a good safety measure. The only problems I
have ever seen were with ware that wasn't completely dry coupled with a kiln
which moved up at a "normal" rate...whatever that is.
Mary Beth Bishop
Durham, NC. The snow missed us but it is definitely cold.
Nancy Galland on mon 18 dec 00
Has anyone ever single fired porcelain?
BTu1690922@AOL.COM on tue 19 dec 00
Hi,
I just tried two porcelain bowls with sprayed and dipped glazes. One had
cracking which appeared to happen on the way up (no glaze over the cracks)
(correct me if I'm wrong). The other had an opaque glaze, no cracking was
apparent. The glazes seemed to fit well, no apparent difference from other
bisqued and glazed pieces. I think I'll try it again, results seem promising.
Gail
Gilchrist, Tx
Snail Scott on tue 19 dec 00
At 09:27 PM 12/18/00 -0400, you wrote:
>Has anyone ever single fired porcelain?
>
This works better than single-firing just
about anything else! Porcelain seems to
handle being glazed 'green' better than
other clays. Go for it!
-Snail
Jim Cullen on tue 19 dec 00
I single-fire Tucker's MCS Cone 6 Porcelain. Firing isn't the problem,
glazing is. Nothing worse than pouring the inside of a vase, setting it
aside to dry, coming back and seeing the pot split from top to bottom. This
happens often enough that I've started to bisque fir those pots that I feel
might not make through glazing, thin, tall or difficult to reproduce.
I'll be taking Steven Hill's week-long workshop this summer and hopefully
learn some of his tricks to prevent this problem. I know he sprays his
glazes, as do I, but I'm not sure how he glazes the interior of his pots.
One other thing, I've feel porcelain gives me the ability to fire faster. I
usually candle for at least an hour, longer if I'm glazing and putting pots
directly into the kiln for firing the next day. The I set the kiln on HI and
let it go. I use a pyrometer and carefully watch the last 200 degrees F. I
then check the cones for the final 30 minutes, checking every 10 minutes and
watching the 5 cone.
I also soak for 30 minutes after the 6 cone bends to 9 o'clock. (more like
9:30, It'll be at 9:00 after the soak).
Try it, but Be Careful Out There.
KEEP CENTERED
Cullen
Naperville, Illinois
mail to: jcullen845@ameritech.net
----- Original Message -----
From: "Nancy Galland"
To:
Sent: Monday, December 18, 2000 7:27 PM
Subject: Re: Is the Bisque firing a necessity
> Has anyone ever single fired porcelain?
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
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> You may look at the archives for the list or change your subscription
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> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
Mike O'Brien on wed 20 dec 00
Hi Nancy,
I have been once-firing bathroom sinks for about 20 years. I call it
porcelain, some call it semi porcelain, some call it vitreous china. Anyway
its a cone six white body.
I have never bisque fired. When I started it just seemed a big waste. Let
me know if I can help.
Mike O'Brien
O'Brien Porcelain/semi porcelain/vitreous china Co.
WHC228@AOL.COM on wed 20 dec 00
Nancy
I haven't fired a bisk for nearly 20 years except for some really complicated
pieces. I even single fire my crystalline glazes.
When I was at Kholer they didn't bisk so I figured that I didn't need to
either. The advantages are obvious.
Bill Campbell
Paul Taylor on wed 20 dec 00
Dear nacy
Yes Its the same as stoneware. Look in archive for more info.
Regards from Paul Taylor
http://www.anu.ie/westportpottery
> From: Nancy Galland
> Reply-To: Ceramic Arts Discussion List
> Date: Mon, 18 Dec 2000 21:27:44 -0400
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: Is the Bisque firing a necessity
>
> Has anyone ever single fired porcelain?
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
Mike O'Brien on mon 1 jan 01
Hi Nanci,
Sorry about the delay. All my kids were home for the holidays. Now I have to
get back to my 780 clayart e-mails.
I have a mold making book called "PLASTER MOLD AND MODEL MAKING".
Authors "Chaney & Skee". Published by Litton Educational Publishing, Inc.
It's pretty good, but trial and error is how I have learned almost everything
I know.
I have found that books mean much until you start doing a process. After you
learn how to do something and go back and reread the book, it makes perfect
sense. However, it is the best place to start if you don't have someone you
can watch.
I usually make my models and master molds and then take them to Glendale
Molds in LA and have them make the Blocks and Cases and production molds. It
takes a lot of space for a complete mold shop. Maybe some day.
It sounds like your corner sink would be a two part mold without a backsplash
and a three or four part mold with a backsplash. The problem is your two
main mold parts will require about 100 lbs of plaster each. You need a large
mixer to mix that much.
You can make one if you are mechanically inclined.
You first have to make a model. That is you have to have something to make a
mold of. Generally, you make it 10% larger than you want the finished
product to allow for shrinkage. You can make it out of plaster or wood or
sometimes flat surfaces are best done with Corian or some other countertop
material. It works great because plaster doesn't stick to it. (a necessity)
I would make the top and splash and bowl 1/2" thick and the apron maybe 1"
thick for support. When you slipcast the 1" thick part will end up being
hollow.
If you don't know anything about plaster, you have a lot of learning to do.
I don't know where you live, but I would start by looking for a mold maker in
the nearest large city.
Let me know if I can be of further help.
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