Jennifer Buckner on wed 9 jul 03
Here's a question from a novice potter who's having problems with glazes
crazing. I've tested Tig's celadon, Alisa Claussen's versions of Burke's
celadon (both light and dark), the Mastering ^6 Glazes Oatmeal, and Glossy
Clear Liner, as well as Tony Hanson's 5 x 20 on a Sheffield clay called
W1A. They refer to this as a vitreous, porcelainous stoneware. I'm
getting horrible crazing with all of the above.
In a private post, someone from this list suggested I ask Sheffield for the
make-up of W1A. I did this but they have refused to give me this
information, saying only that it contains some silica, ball clay and
kaolin. When pressed, he said that the silica content is less than 20%,
which my correspondent says will automatically create problems with glaze fit.
The one solution that Sheffield offered is that they makes their own clear
glaze, formulated for W1A, which I can purchase. Not quite the response I
was looking for, but one I may have to go with until I run out of this
particular clay. I have 1000 lbs which I bought last fall, making it less
than likely that Sheffield will accept it back on a trade.
Can anyone give me any more information on this clay? Anyone worked with
it and solved the clay/glaze lack of fit?
Jennifer
Jennifer G. Buckner jenniverre@earthlink.net
Lee Love on wed 9 jul 03
----- Original Message -----
From: "Jennifer Buckner"
To:
Sent: Wednesday, July 09, 2003 10:08 PM
Subject: crazing problems
> Here's a question from a novice potter who's having problems with glazes
> crazing. I've tested Tig's celadon, Alisa Claussen's versions of Burke's
> celadon (both light and dark), the Mastering ^6 Glazes Oatmeal, and Glossy
> Clear Liner, as well as Tony Hanson's 5 x 20 on a Sheffield clay called
> W1A. They refer to this as a vitreous, porcelainous stoneware. I'm
> getting horrible crazing with all of the above.
Jennifer, Have you tried glaze recipes made for this type of clay? I
can't help you at cone 6, but it has been my experience that often, my stoneware
glazes do not fit my porcelain or porcelainous clay bodies.
~~~~~~~Lee In Mashiko, Japan http://hachiko.com ~~~~~~~~~~~~~~~~~~
* *
* Every man has enough power left to carry out that of *
* which he is convinced. *
~~~~~~~~~~ Johann Wolfgang von Goethe~~~~~~~~~~~~~~~~~~~~~~
piedpotterhamelin@COMCAST.NET on wed 9 jul 03
Contact General Frit, Fusion Ceramic or Ferro and ask about a low expansion
frit to incrementally add to your glaze. Fusion is great to work with. They
have several boron, non-boron, zinc frits to work with.
> Here's a question from a novice potter who's having problems with glazes
> crazing. I've tested Tig's celadon, Alisa Claussen's versions of Burke's
> celadon (both light and dark), the Mastering ^6 Glazes Oatmeal, and Glossy
> Clear Liner, as well as Tony Hanson's 5 x 20 on a Sheffield clay called
> W1A. They refer to this as a vitreous, porcelainous stoneware. I'm
> getting horrible crazing with all of the above.
>
> In a private post, someone from this list suggested I ask Sheffield for the
> make-up of W1A. I did this but they have refused to give me this
> information, saying only that it contains some silica, ball clay and
> kaolin. When pressed, he said that the silica content is less than 20%,
> which my correspondent says will automatically create problems with glaze fit.
>
> The one solution that Sheffield offered is that they makes their own clear
> glaze, formulated for W1A, which I can purchase. Not quite the response I
> was looking for, but one I may have to go with until I run out of this
> particular clay. I have 1000 lbs which I bought last fall, making it less
> than likely that Sheffield will accept it back on a trade.
>
> Can anyone give me any more information on this clay? Anyone worked with
> it and solved the clay/glaze lack of fit?
>
> Jennifer
>
> Jennifer G. Buckner jenniverre@earthlink.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.
CLAYART@LSV.CERAMICS.ORG on wed 9 jul 03
You need to pick a good glaze and adjust it to fit.
Here is how:
http://www.digitalfire.ab.ca/cermat/education/4.php
-------8<--------
Here\'s a question from a novice potter who\'s having problems with glazes
crazing. I\'ve tested Tig\'s celadon, Alisa Claussen\'s versions of Burke\'s
celadon (both light and dark), the Mastering ^6 Glazes Oatmeal, and Glossy
Clear Liner, as well as Tony Hanson\'s 5 x 20 on a Sheffield clay called
W1A. They refer to this as a vitreous, porcelainous stoneware. I\'m
getting horrible crazing with all of the above.
In a private post, someone from this list suggested I ask Sheffield for the
make-up of W1A. I did this but they have refused to give me this
information, saying only that it contains some silica, ball clay and
kaolin. When pressed, he said that the silica content is less than 20%,
which my correspondent says will automatically create problems with glaze fit.
The one solution that Sheffield offered is that they makes their own clear
glaze, formulated for W1A, which I can purchase. Not quite the response I
was looking for, but one I may have to go with until I run out of this
particular clay. I have 1000 lbs which I bought last fall, making it less
than likely that Sheffield will accept it back on a trade.
Can anyone give me any more information on this clay? Anyone worked with
it and solved the clay/glaze lack of fit?
Jennifer
Jennifer G. Buckner jenniverre@earthlink.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.
--------
Tony Hansen, Digitalfire Corp.
David Hewitt on thu 10 jul 03
Jennifer,
I have no experience of clay W1A. I presume that it must have a very low
expansion from what you have experienced. It would be nice, of course if
the supplier would give you a coefficient of expansion figure for this
clay, but not many suppliers are obliging in this respect.
I do, however, have a very low expansion clear shiny cone 6 glaze which
I use on the porcelain that I get - Potclays 1149. As an indication of
its fit for the clay that I use, I can glaze the inside only of a vase
without a problem of it splitting the pot. It has a C. of E. of 4.239 x
10-6/oC linear, Appen. If you are interested in trying this glaze,
please contact me direct and I will let you have the recipe. I would of
course be interested in knowing the result.
If you want to judge the significance of this C.of E. you might like to
look at my web site under Pottery Techniques / Calculating Crazing.
Alternatively, I include this glaze recipe, LEF4, in the recipes that
come supplied with the glaze program CeramDat.
David
In message , Jennifer Buckner writes
>Here's a question from a novice potter who's having problems with glazes
>crazing. I've tested Tig's celadon, Alisa Claussen's versions of Burke's
>celadon (both light and dark), the Mastering ^6 Glazes Oatmeal, and Glossy
>Clear Liner, as well as Tony Hanson's 5 x 20 on a Sheffield clay called
>W1A. They refer to this as a vitreous, porcelainous stoneware. I'm
>getting horrible crazing with all of the above.
>
>In a private post, someone from this list suggested I ask Sheffield for the
>make-up of W1A. I did this but they have refused to give me this
>information, saying only that it contains some silica, ball clay and
>kaolin. When pressed, he said that the silica content is less than 20%,
>which my correspondent says will automatically create problems with glaze fit.
>
>The one solution that Sheffield offered is that they makes their own clear
>glaze, formulated for W1A, which I can purchase. Not quite the response I
>was looking for, but one I may have to go with until I run out of this
>particular clay. I have 1000 lbs which I bought last fall, making it less
>than likely that Sheffield will accept it back on a trade.
>
>Can anyone give me any more information on this clay? Anyone worked with
>it and solved the clay/glaze lack of fit?
>
>Jennifer
>
>Jennifer G. Buckner jenniverre@earthlink.net
--
David Hewitt
David Hewitt Pottery
7 Fairfield Road, Caerleon, Newport,
South Wales, NP18 3DQ.
Tel:- +44 (0) 1633 420647
Fax:- +44 (0) 870 1617274
Web:- http://www.dhpot.demon.co.uk
Ron Roy on sun 13 jul 03
Hi Jennifer,
It is not true that 20% silica will automatically create fit problems. In
fact adding silica to a clay body will help solve crazing. I am not saying
this is always the right thing to do - there are exceptions.
I just checked all the glazes you mentioned and they will fit most cone 6
bodies without crazing. Seems you are working with a clay body is out of
the ordinary.
We must make sure we are talking about crazing and not shivering to start with.
Have you done the freezing and boiling water test?
In mastering cone 6 glazes there is a series of glazes designed to find out
the expansion rate of clays. I suggest you mix up the medium (#3), medium
low (#2) and low expansion (#1) glazes and put them on some of that clay.
Once we know what expansion is needed for a none grazing glaze we can make
some.
Both High Calcium base glazes in our book have quite a low expansion rate -
try one without any colouring oxides. If they still craze then you do have
a strange clay to work with - if it's really crazing we are dealing with.
RR
>Here's a question from a novice potter who's having problems with glazes
>crazing. I've tested Tig's celadon, Alisa Claussen's versions of Burke's
>celadon (both light and dark), the Mastering ^6 Glazes Oatmeal, and Glossy
>Clear Liner, as well as Tony Hanson's 5 x 20 on a Sheffield clay called
>W1A. They refer to this as a vitreous, porcelainous stoneware. I'm
>getting horrible crazing with all of the above.
>
>In a private post, someone from this list suggested I ask Sheffield for the
>make-up of W1A. I did this but they have refused to give me this
>information, saying only that it contains some silica, ball clay and
>kaolin. When pressed, he said that the silica content is less than 20%,
>which my correspondent says will automatically create problems with glaze fit.
>
>The one solution that Sheffield offered is that they makes their own clear
>glaze, formulated for W1A, which I can purchase. Not quite the response I
>was looking for, but one I may have to go with until I run out of this
>particular clay. I have 1000 lbs which I bought last fall, making it less
>than likely that Sheffield will accept it back on a trade.
>
>Can anyone give me any more information on this clay? Anyone worked with
>it and solved the clay/glaze lack of fit?
>
>Jennifer
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Jennifer Buckner on sun 13 jul 03
Hi Ron,
Many thanks for responding. I'll answer your questions and comments
throughout your message.
At 02:15 PM 7/13/2003, you wrote:
>Hi Jennifer,
>
>It is not true that 20% silica will automatically create fit problems. In
>fact adding silica to a clay body will help solve crazing. I am not saying
>this is always the right thing to do - there are exceptions.
Actually, the person who wrote said that *less than* 20% silica would
create a problem, and Sheffield, the clay supplier has said that my clay
does, in fact, contain less than 20%.
>We must make sure we are talking about crazing and not shivering to start
>with.
I looked up the definitions in "Clay and Glazes for the Potter". Crazing,
defined as "...a fine network of cracks" is what I see on my test tiles and
pots. It looks like old Chinese pots. Shivering, defined as "...sharp
slivers or flakes of glaze" that come off the object is not happening.
>Have you done the freezing and boiling water test?
I ran these tests on Caribbean Sea Green, Waterfall and a clear Ravenscrag
slip glaze as well as this clear base with 3% each of rutile, cobalt
carbonate and titanium. No crazing seen after 4 repeats. I didn't feel I
needed to test the tiles with Glossy Clear Liner #2, Oatmeal, and the
celadons because the crazing was visible as they were taken from my kiln.
Oddly enough, I tested Tony Hanson's 5 x 20 on several practice
pots. There was a lot of obvious crazing almost immediately. I added 10%
Mason stains to several batches of the 5 x 20 and fired some test tiles. I
can see no crazing months after firing them. I haven't done the
freezer/boiling water tests on these tiles.
>In mastering cone 6 glazes there is a series of glazes designed to find out
>the expansion rate of clays. I suggest you mix up the medium (#3), medium
>low (#2) and low expansion (#1) glazes and put them on some of that clay.
>Once we know what expansion is needed for a none grazing glaze we can make
>some.
I'll do this some time during the next week and let you know.
>Both High Calcium base glazes in our book have quite a low expansion rate -
>try one without any colouring oxides.
I'll do this at the same time.
>If they still craze then you do have
>a strange clay to work with - if it's really crazing we are dealing with.
If it's not crazing and not shivering, what could it be?
By the way, I've had some very good luck with your Variegated Blue, and
just pulled some pots with Caribbean Sea Green out of the kiln on
Saturday. I had some crawling (again, definition looked up in Rhodes) but
not too much and I think perhaps I'd put it on too thickly in places.
I'll get back to you as soon as I have some results to report.
Many thanks again for your help.
Jennifer
>RR
>
> >Here's a question from a novice potter who's having problems with glazes
> >crazing. I've tested Tig's celadon, Alisa Claussen's versions of Burke's
> >celadon (both light and dark), the Mastering ^6 Glazes Oatmeal, and Glossy
> >Clear Liner, as well as Tony Hanson's 5 x 20 on a Sheffield clay called
> >W1A. They refer to this as a vitreous, porcelainous stoneware. I'm
> >getting horrible crazing with all of the above.
> >
> >In a private post, someone from this list suggested I ask Sheffield for the
> >make-up of W1A. I did this but they have refused to give me this
> >information, saying only that it contains some silica, ball clay and
> >kaolin. When pressed, he said that the silica content is less than 20%,
> >which my correspondent says will automatically create problems with
> glaze fit.
> >
> >The one solution that Sheffield offered is that they makes their own clear
> >glaze, formulated for W1A, which I can purchase. Not quite the response I
> >was looking for, but one I may have to go with until I run out of this
> >particular clay. I have 1000 lbs which I bought last fall, making it less
> >than likely that Sheffield will accept it back on a trade.
> >
> >Can anyone give me any more information on this clay? Anyone worked with
> >it and solved the clay/glaze lack of fit?
> >
> >Jennifer
>
>Ron Roy
>RR#4
>15084 Little Lake Road
>Brighton, Ontario
>Canada
>K0K 1H0
>Phone: 613-475-9544
>Fax: 613-475-3513
>
>______________________________________________________________________________
>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.
Jennifer G. Buckner jenniverre@earthlink.net
Ron Roy on wed 16 jul 03
Hi Jennifer,
I look after bodies that have no silica and those that have 25% silica and
all the amounts in between. I was just trying to make the point that who
ever said that simply does not know what they are talking about. It's
probably because they don't know how to cure the problem by altering the
glaze. There are many in this business - working for suppliers - that just
don't have the necessary understanding to solve the problems. We have to
understand all that so we can get on with solving the problems.
Sometimes - when the glaze winds up too big for the clay (shivering) it
does look like crazing - we just have to make sure before we starting
fixing the glazes.
Are you soaking at the end of the firing at all - how fast at the end - for
the last hour. At what temperature do you start fast cooling your kiln -
like spy holes open or lid open a bit?
RR
>Many thanks for responding. I'll answer your questions and comments
>throughout your message.
>
>At 02:15 PM 7/13/2003, you wrote:
>>Hi Jennifer,
>>
>>It is not true that 20% silica will automatically create fit problems. In
>>fact adding silica to a clay body will help solve crazing. I am not saying
>>this is always the right thing to do - there are exceptions.
>
>Actually, the person who wrote said that *less than* 20% silica would
>create a problem, and Sheffield, the clay supplier has said that my clay
>does, in fact, contain less than 20%.
>
>>We must make sure we are talking about crazing and not shivering to start
>>with.
>
>I looked up the definitions in "Clay and Glazes for the Potter". Crazing,
>defined as "...a fine network of cracks" is what I see on my test tiles and
>pots. It looks like old Chinese pots. Shivering, defined as "...sharp
>slivers or flakes of glaze" that come off the object is not happening.
>
>>Have you done the freezing and boiling water test?
>
>I ran these tests on Caribbean Sea Green, Waterfall and a clear Ravenscrag
>slip glaze as well as this clear base with 3% each of rutile, cobalt
>carbonate and titanium. No crazing seen after 4 repeats. I didn't feel I
>needed to test the tiles with Glossy Clear Liner #2, Oatmeal, and the
>celadons because the crazing was visible as they were taken from my kiln.
>
>Oddly enough, I tested Tony Hanson's 5 x 20 on several practice
>pots. There was a lot of obvious crazing almost immediately. I added 10%
>Mason stains to several batches of the 5 x 20 and fired some test tiles. I
>can see no crazing months after firing them. I haven't done the
>freezer/boiling water tests on these tiles.
>
>>In mastering cone 6 glazes there is a series of glazes designed to find out
>>the expansion rate of clays. I suggest you mix up the medium (#3), medium
>>low (#2) and low expansion (#1) glazes and put them on some of that clay.
>>Once we know what expansion is needed for a none grazing glaze we can make
>>some.
>
>I'll do this some time during the next week and let you know.
>
>
>>Both High Calcium base glazes in our book have quite a low expansion rate -
>>try one without any colouring oxides.
>
>I'll do this at the same time.
>
>>If they still craze then you do have
>>a strange clay to work with - if it's really crazing we are dealing with.
>
>If it's not crazing and not shivering, what could it be?
>
>By the way, I've had some very good luck with your Variegated Blue, and
>just pulled some pots with Caribbean Sea Green out of the kiln on
>Saturday. I had some crawling (again, definition looked up in Rhodes) but
>not too much and I think perhaps I'd put it on too thickly in places.
>
>I'll get back to you as soon as I have some results to report.
>
>Many thanks again for your help.
>
>Jennifer
>
>
>>RR
>>
>> >Here's a question from a novice potter who's having problems with glazes
>> >crazing. I've tested Tig's celadon, Alisa Claussen's versions of Burke's
>> >celadon (both light and dark), the Mastering ^6 Glazes Oatmeal, and Glossy
>> >Clear Liner, as well as Tony Hanson's 5 x 20 on a Sheffield clay called
>> >W1A. They refer to this as a vitreous, porcelainous stoneware. I'm
>> >getting horrible crazing with all of the above.
>> >
>> >In a private post, someone from this list suggested I ask Sheffield for the
>> >make-up of W1A. I did this but they have refused to give me this
>> >information, saying only that it contains some silica, ball clay and
>> >kaolin. When pressed, he said that the silica content is less than 20%,
>> >which my correspondent says will automatically create problems with
>> glaze fit.
>> >
>> >The one solution that Sheffield offered is that they makes their own clear
>> >glaze, formulated for W1A, which I can purchase. Not quite the response I
>> >was looking for, but one I may have to go with until I run out of this
>> >particular clay. I have 1000 lbs which I bought last fall, making it less
>> >than likely that Sheffield will accept it back on a trade.
>> >
>> >Can anyone give me any more information on this clay? Anyone worked with
>> >it and solved the clay/glaze lack of fit?
>> >
>> >Jennifer
>>
>>Ron Roy
>>RR#4
>>15084 Little Lake Road
>>Brighton, Ontario
>>Canada
>>K0K 1H0
>>Phone: 613-475-9544
>>Fax: 613-475-3513
>>
>>______________________________________________________________________________
>>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.
>
>Jennifer G. Buckner jenniverre@earthlink.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.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
| |
|
