Pam Cresswell on sun 16 jan 05
Could an extremely cold kiln room cause glazes to shiver? Seriously, my last
two firings, the kiln room was at about 0 Celsius. I let the kiln cool
normally after reaching peak temperature. In other words, it probably
dropped like a rock, and in one case I had shattered pots, shattered
after/during cooling as glass was in sharp pieces, not melted drops. The
second firing, same glaze, the pots did not shatter, but the glaze has
shivered off. This is a glaze that worked great before. I am firing again
this weekend, and plan to do a slow ramp up, and then a ramp down. I have a
thick sculpture in the kiln, so I am being VERY VERY slow and cautious. I am
not using the shivery glaze this time, but I wonder if I need to dump this
glaze altogether, or if it is not the glaze but the weather.
I have been having trouble with my email, so I hope this one makes it to
the list!
Pam
dannon rhudy on sun 16 jan 05
> Could an extremely cold kiln room cause glazes to shiver?..>>>>
Shivering glazes and shattered pots are not caused by
ambient temperatures, but by poor fit between glaze and
clay. If the glaze you are using does not fit the clay you
are using, then you must either adjust the glaze or stop
using it; it will continue to shiver, a nasty flaw indeed.
If the glaze has worked on that clay in the past, then either
the glaze or something in it has changed, or the clay is not
the same.
regards
Dannon Rhudy
John Hesselberth on sun 16 jan 05
On Sunday, January 16, 2005, at 12:22 PM, Pam Cresswell wrote:
> . I am
> not using the shivery glaze this time, but I wonder if I need to dump
> this
> glaze altogether, or if it is not the glaze but the weather.
>
Hi Pam,
My opinion based on what you told us is that you need to dump this
glaze or modify it to get it away from the edge of disaster. You must
be right on the edge of shivering and the addition of a few degrees
lower temperature put you over the edge. If you want to post the
recipe or send it to me off-list I would be glad to offer a more
informed opinion. I'm sure others would also.
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Pam Cresswell on sun 16 jan 05
John,
Your help is most welcome! Here is the recipe:
Odyssey 04 Clear base
Earthenware cone 04
61.5 Laguna Borate
24.6 Kaolin--EPK
12.3 Flint
1.64 Lithium Carbonate
I got this from a very good book, The Ceramic Glaze Handbook, by Mark
Burleson
When I put it into Glazemaster, I got these #'s:
The Exp. Coeff is 69.48,
Sil to Al is 4.12
Pam the cold, shivery chick with the cold shivery glaze
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of John
Hesselberth
Sent: Sunday, January 16, 2005 5:55 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: does cold ambient temp affect glazes?
On Sunday, January 16, 2005, at 12:22 PM, Pam Cresswell wrote:
> . I am
> not using the shivery glaze this time, but I wonder if I need to dump
> this
> glaze altogether, or if it is not the glaze but the weather.
>
Hi Pam,
My opinion based on what you told us is that you need to dump this
glaze or modify it to get it away from the edge of disaster. You must
be right on the edge of shivering and the addition of a few degrees
lower temperature put you over the edge. If you want to post the
recipe or send it to me off-list I would be glad to offer a more
informed opinion. I'm sure others would also.
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
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Snail Scott on sun 16 jan 05
At 11:22 AM 1/16/2005 -0600, you wrote:
>Could an extremely cold kiln room cause glazes to shiver? Seriously, my=
last
>two firings, the kiln room was at about 0 Celsius...
Not likely. It's coming down from thousands of=20
degrees, after all, and the difference between=20
30=BAC and 0=BAC is nothing much compared to that.
Crash-cooling can be bad, but it's mainly a=20
cause of dunting, not shivering. There IS some=20
incompatibility between the expansion rates of=20
your clay and glaze. I know you said the glaze
is tried-and-true, but could anything have=20
changed? A fresh batch? A different clay body?
I've also seen shivering show up in 'borderline'=20
(but reliable) glazes when applied over dusty=20
slips, etc, which compromised the clay-glaze bond.
If not, perhaps the weather created just enough=20
stress to make a not-quite-bad-enough-to-notice=20
problem suddenly noticeable.
-Snail
Pam Cresswell on sun 16 jan 05
Thanks Dannon,
It is defiantly the same clay, even the same bag of clay. So if it was not
that the kiln cools off too quickly and caused thermal shock, and not the
clay, and the glaze worked fine in the past, then my glaze has changed
somehow? Very frustrating.
I even went and dug out the pots with this glaze that I fired a few weeks
ago, and they look fine.
(yes I know, test test test)
Pam, headed back to the drawing board
> Could an extremely cold kiln room cause glazes to shiver?..>>>>
Shivering glazes and shattered pots are not caused by
ambient temperatures, but by poor fit between glaze and
clay. If the glaze you are using does not fit the clay you
are using, then you must either adjust the glaze or stop
using it; it will continue to shiver, a nasty flaw indeed.
If the glaze has worked on that clay in the past, then either
the glaze or something in it has changed, or the clay is not
the same.
regards
Dannon Rhudy
Ron Roy on mon 17 jan 05
Hi Pam,
Send me the recipe for the shivering glaze - the calculated expansion will
probably tell the tale - and even point to the solution.
RR
>Could an extremely cold kiln room cause glazes to shiver? Seriously, my last
>two firings, the kiln room was at about 0 Celsius. I let the kiln cool
>normally after reaching peak temperature. In other words, it probably
>dropped like a rock, and in one case I had shattered pots, shattered
>after/during cooling as glass was in sharp pieces, not melted drops. The
>second firing, same glaze, the pots did not shatter, but the glaze has
>shivered off. This is a glaze that worked great before. I am firing again
>this weekend, and plan to do a slow ramp up, and then a ramp down. I have a
>thick sculpture in the kiln, so I am being VERY VERY slow and cautious. I am
>not using the shivery glaze this time, but I wonder if I need to dump this
>glaze altogether, or if it is not the glaze but the weather.
> I have been having trouble with my email, so I hope this one makes it to
>the list!
>Pam
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
John Hesselberth on mon 17 jan 05
Hi Pam,
I am not that familiar with earthenware glazes, but this one does have
a lower calculated expansion (69 on the scale I use) than those I am
familiar with. So I do suspect this glaze has been on the edge of a
problem all along. It is unusual in that it has lots of low expansion
materials (boron, alumina, silica and lithia) and little higher
expansion material like sodium and potassium. Just removing the lithium
carbonate won't move it very much since there is not much there.
Therefore my approach would be to take out some of the boron and
replace it with an alkaline frit like Ferro 3110. Going to
Laguna Borate 50
Frit 3110 11.5
Lithium Carbonate 1.6
Kaolin 24.6
Silica 6.0
would give you enough higher expansion (74.6) that you should get away
from the edge. You could also replace some of the Laguna Borate with
neph sy, but you would have to jiggle the kaolin and silica a bit to
keep the alumina and silica numbers about the same. Hopefully some
people with more earthenware experience will offer some additional
proposals.
Just as a note to someone who might read this from the archives in the
future--this is not a good durable glaze for functional work--it is
probably fine on sculptural or decorative work.
Regards,
John
On Sunday, January 16, 2005, at 08:47 PM, Pam Cresswell wrote:
> John,
>
> Your help is most welcome! Here is the recipe:
>
> Odyssey 04 Clear base
> Earthenware cone 04
>
> 61.5 Laguna Borate
> 24.6 Kaolin--EPK
> 12.3 Flint
> 1.64 Lithium Carbonate
>
>
> I got this from a very good book, The Ceramic Glaze Handbook, by Mark
> Burleson
> When I put it into Glazemaster, I got these #'s:
> The Exp. Coeff is 69.48,
> Sil to Al is 4.12
>
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Ron Roy on tue 18 jan 05
Hi Pam,
the expansion of that glaze is not that low - considering it has over 20%
boron in it.
I suspect the solubles from the Lithium carb and the Laguna borate are
getting together somehow to cause the problem.
Here is the glaze without the lithium - worth a try!
Laguna Borate - 65.5
EPK - 23.0
Silica - 11.5
Total - 100.0
RR
>Your help is most welcome! Here is the recipe:
>
>Odyssey 04 Clear base
> Earthenware cone 04
>
> 61.5 Laguna Borate
> 24.6 Kaolin--EPK
> 12.3 Flint
> 1.64 Lithium Carbonate
>
>
>I got this from a very good book, The Ceramic Glaze Handbook, by Mark
>Burleson
>When I put it into Glazemaster, I got these #'s:
>The Exp. Coeff is 69.48,
>Sil to Al is 4.12
>
>Pam the cold, shivery chick with the cold shivery glaze
>
>-----Original Message-----
>From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of John
>Hesselberth
>Sent: Sunday, January 16, 2005 5:55 PM
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: does cold ambient temp affect glazes?
>
>On Sunday, January 16, 2005, at 12:22 PM, Pam Cresswell wrote:
>
>> . I am
>> not using the shivery glaze this time, but I wonder if I need to dump
>> this
>> glaze altogether, or if it is not the glaze but the weather.
>>
>
>Hi Pam,
>
>My opinion based on what you told us is that you need to dump this
>glaze or modify it to get it away from the edge of disaster. You must
>be right on the edge of shivering and the addition of a few degrees
>lower temperature put you over the edge. If you want to post the
>recipe or send it to me off-list I would be glad to offer a more
>informed opinion. I'm sure others would also.
>
>Regards,
>
>John
>
>John Hesselberth
>http://www.frogpondpottery.com
>http://www.masteringglazes.com
>
>____________________________________________________________________________
>__
>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.
>
>______________________________________________________________________________
>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.
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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