Dave Finkelnburg on sun 8 oct 00
Gene,
Either your attachment technique is weak and the pieces are cracked and
you don't see it, or your pre-heat temperature is too high.
You are doing everything right--drying the pieces carefully and
equalizing the moisture, then letting them dry well. How do you know the
preheat is at 200 degrees F? Most pyrometers are only accurate to about
plus or minus 10 degrees. Sometimes they are less accurate at low
temperatures. To be on the safe side, try your preheat at about 180
degrees. That's plenty high and allows more margin for error.
You don't say how you attach, so it's hard to tell if that might be a
source of problems. Try things one at a time. Do the preheat again, only
this time open the kiln and check the ware before firing on up through your
bisque cycle. That way, if anything fails, you will have a better idea when
the failure happened.
I hope this helps.
Dave Finkelnburg in Idaho
-----Original Message-----
From: Arnolds Home Improvements
To: CLAYART@LSV.CERAMICS.ORG
Date: Sunday, October 08, 2000 9:19 PM
Subject: knobs blowing off my lids
>This may be a rookie question but after all I am one!!
>I have just begun to make pots with lids and knobs. After applying the
>handles and knob I cover the pots in plastic for a few days, then I uncover
>the pots and allow them to dry to what I perceive to be bone dry. I bisque
>fired the pots to cone 07 and allowed it to cool. when I opened the kiln
out
>of 7 pots the knobs had blown off 3 of them. I'm sure moisture is the
>problem but my question is how can this be prevented or how can I tell if
>the pots and knobs are totally dry.
>
>I bisque fired on slow bisque with a 3 hour pre-heat at 200 degrees.
>
>Thanks in advance for any help!!!!
>
>
>Gene Arnold
>playing in the mud in North Carolina
>mudduck@advi.net
>
>___________________________________________________________________________
___
>Send postings to clayart@lsv.ceramics.org
>
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>
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melpots@pclink.com.
>
Snail Scott on sun 8 oct 00
At 04:17 PM 10/8/00 -0400, you wrote:
>This may be a rookie question but after all I am one!!
>I have just begun to make pots with lids and knobs. After applying the
>handles and knob I cover the pots in plastic for a few days, then I uncover
>the pots and allow them to dry to what I perceive to be bone dry. I bisque
>fired the pots to cone 07 and allowed it to cool. when I opened the kiln out
>of 7 pots the knobs had blown off 3 of them...
Did you score-and-slip the joint? If so, make sure
those score marks are totally filled with slip. Air
pockets in the score marks (or anywhere else) become
little steam-filled bombs when heated. The tiny pores
in the solid clay aren't any drier, but they can't
build up enough localized pressure to blow stuff up
unless it's pretty wet. If you are using a needle tool
or fettling knife to score the joint, you may be making
thin, crevice-like scores that are hard to fill to their
bottoms with slip. Try a fork with blunt tines - you
probably won't score as deeply or narrowly, the scores
will easily fill with slip, and you can cut your scoring
effort in half! (Not a big concern with teapot knobs,
but I'm a coil-builder. I LOOVE my fork!)
-Snail
Elca Branman on sun 8 oct 00
Try using a pin tool on the inside of the lid, going up into the knob,
but not through tpo the other side. This will allow drying to be more
efficient and when you subsequesntly glaze the bisque pieces, the hole
will be fuilled..Don't be stingy..depending on the size of the knob ,
maybe 2 or 3 stabs..
Elca Branman
elcab1 @juno .com
On Sun, 8 Oct 2000 16:17:16 -0400 Arnolds Home Improvements
writes:
> knobs had blown off 3 of them. I'm sure moisture is
> the
> problem but my question is how can this be prevented or how can I
> tell if
> the pots and knobs are totally dry.
>
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Arnolds Home Improvements on sun 8 oct 00
This may be a rookie question but after all I am one!!
I have just begun to make pots with lids and knobs. After applying the
handles and knob I cover the pots in plastic for a few days, then I uncover
the pots and allow them to dry to what I perceive to be bone dry. I bisque
fired the pots to cone 07 and allowed it to cool. when I opened the kiln out
of 7 pots the knobs had blown off 3 of them. I'm sure moisture is the
problem but my question is how can this be prevented or how can I tell if
the pots and knobs are totally dry.
I bisque fired on slow bisque with a 3 hour pre-heat at 200 degrees.
Thanks in advance for any help!!!!
Gene Arnold
playing in the mud in North Carolina
mudduck@advi.net
Jennifer F Boyer on mon 9 oct 00
I've had this problem in the past when I'm sure I was using good
attachment procedures. Slow heating was the key for me.
Sometimes I turn my loaded bisk kiln on for an hour on very low
the day before I bisk. Then turn it off when I leave the studio
with the spies open and the lid shut. The next day I start with
a slow pre-heat, but check the open spy with a mirror to see
what kind of moisture is coming out as the kiln starts to heat.
I don't start turning up switches till the mist on the mirror
clears in under 10 seconds after I take it away from the spy. If
the moisture is on the mirror in droplets, I know I have a way
to go.....after a few firings with the mirror test you'll be
able to make your own guidleines for what you need to be safe..
Jennifer, off to unload a bisk kiln.
PS another way I dry out a bisk load is to set a small fan
pointing down into it after loading(lid open), leaving the fan
going over night. I don't like heating a damp bisk load since
the escaping moisture doesn't do the kiln any favors...but we
all get in a jam and have to do it sometimes. The fan helps a lot.
Snail Scott wrote:
>
> At 04:17 PM 10/8/00 -0400, you wrote:
> >This may be a rookie question but after all I am one!!
> >I have just begun to make pots with lids and knobs. After applying the
> >handles and knob I cover the pots in plastic for a few days, then I uncover
> >the pots and allow them to dry to what I perceive to be bone dry. I bisque
> >fired the pots to cone 07 and allowed it to cool. when I opened the kiln out
> >of 7 pots the knobs had blown off 3 of them...
>
~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
Jennifer Boyer jboyer@adelphia.net
Thistle Hill Pottery
95 Powder Horn Glen Rd
Montpelier, VT 05602 USA
802-223-8926
http://www.thistlehillpottery.com/
Check out this searchable sites about web hoaxes:
http://urbanlegends.about.com/science/urbanlegends/library/blhoax.htm
~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
Cindy Strnad on mon 9 oct 00
Hello, Gene.
I'd certainly think a 3 hour pre-heat at 200 degrees F. ought to insure your
knobs would be dry. Apparently not, though. Here are a few things you can
try:
Pierce the knobs with a needle tool. You don't need to go all the way to the
outside. If you do, the hole will show. This is Murphy's law of holes and
glazes: If you want the hole to remain a hole, it will fill with glaze. If
you want the hole to fill with glaze, it will remain a fully functional
hole. However, a hole or two from the inside of the lid to near the tip of
the knob may help to release the gasses which are causing your knobs to
blow.
Consider hollow knobs (for larger projects). If you're already making hollow
knobs, be sure to pierce the lid from the underside at the attachment site.
It is possible to fire hollow pieces without piercing, but they must be
fired very slowly the whole way up. Easier to just make a hole.
Here's a quick test of bone dryness. Assuming your clay room isn't as chilly
as mine currently is, feel the ware. If your piece is cool to the touch at
all, it isn't dry.
For thicker pieces, I pre-heat for 4-6 hours at 180F, then heat at 150F per
hour up to 500F. There's very little science involved there--just my own
desperate attempts to make things work. This routine does work for me,
though. It may be over-kill, but it does work. I haven't had a piece--any
piece--blow up in bisque for a very long time. (crossing my fingers,
knocking on wood, throwing salt over my shoulder . . . .) I use 180F because
at my mile high altitude, water boils at 210F, and I've seen the kiln
fluctuate as much as 15 degrees F while holding. So, just to be safe . . . .
If none of this works, consider adding some grog to your clay. A more open
clay body will exhaust gasses more easily, and with less destruction. An
open body is also desirable for pieces, such as casseroles, which will be
used in an oven.
Hoping some of this helps,
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
earthenv@gwtc.net
http://www.earthenvesselssd.com
WHew536674@CS.COM on mon 9 oct 00
Gene,
My first reaction would be that the knobs are still damp on the inside.
There are all kinds of knobs to be made and we don't know what kind you made,
or how. That would help. I'm assuming you attached them separately after
you made the lid. Another possibility is that they may not have been
attached sufficiently. If I am attaching something separately, I score the
places that will meet, add slip, press gently to make sure no air is trapped,
then put a coil around the entire attachment, and fuse the coil to the top of
the lid, in this case and the knob. Still damp, trapped air, or not
sufficiently fused would be my 3 guesses.
Joyce A.
Mission TX
Martin Howard on tue 10 oct 00
I looked hard at throwing lids and came to the idea of throwing lid and knob
in one. It seemed the obvious choice.
It is so similar to throwing egg cups with attached groovy container for the
shell bits.
Centre the clay to the dimension of the width of the opening to be lidded.
Just open up the clay with two fingers; one for the centre of the knob and
the other the middle of the groovy bit.
Bring up the centre walls and enclose the knob form into the shape wanted.
Leave a central hole in the top if required.
Bring up the outside walls and bend over to make the flange.
No problem then with knobs blowing off.
Martin Howard
Webb's Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
England
martin@webbscottage.co.uk
KLeSueur@AOL.COM on tue 10 oct 00
I do lots of casseroles and have had this problem also. I have decided that
firing is the problem and have taken the following course to fix it.
I give the pots extra time to dry. I assume that there is some moisture
somehow trapped in the knob. Since I'm luck to have a controller on my kiln I
set it for a 50 degree climb per hour. After three hours I increase that rate
to 100 degrees. When the kiln reaches 700 degrees I increase the rate to 185
degrees and let it finish at that rate. It's slow, but when I take the time I
don't blow any knobs.
Kathi LeSueur
Ann Arbor, Mi
James E. Simmons on tue 10 oct 00
Dear Gene,
I too am a rookie, but having had a similar experience, I may have an answer
for you. On the knobs, take a needle tool and make a small hole through the
lid from the inside, up toward the area where the knob is attached. This
will vent any vapor, or air pockets. Doesn't affect the lid. Hope it works
for you.
Muddpuppy (Angela)
-----Original Message-----
From: Arnolds Home Improvements
To: CLAYART@LSV.CERAMICS.ORG
Date: Sunday, October 08, 2000 10:34 PM
Subject: knobs blowing off my lids
>This may be a rookie question but after all I am one!!
>I have just begun to make pots with lids and knobs. After applying the
>handles and knob I cover the pots in plastic for a few days, then I uncover
>the pots and allow them to dry to what I perceive to be bone dry. I bisque
>fired the pots to cone 07 and allowed it to cool. when I opened the kiln
out
>of 7 pots the knobs had blown off 3 of them. I'm sure moisture is the
>problem but my question is how can this be prevented or how can I tell if
>the pots and knobs are totally dry.
>
>I bisque fired on slow bisque with a 3 hour pre-heat at 200 degrees.
>
>Thanks in advance for any help!!!!
>
>
>Gene Arnold
>playing in the mud in North Carolina
>mudduck@advi.net
>
>___________________________________________________________________________
___
>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.
>
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