Daniel Semler on mon 21 feb 05
Hi All,
Clay Planet in San Jose, CA offers this porcelain so I tried some out. David
Pier designed it and so I made a bunch of tests including shrinkage and
absorption.
Shrinkage :
Made three sticks of clay about 12-13 cm long marked a 100mm line in them.
Average line length at :
bone dry : 94 mm
bisqued : 93.67 mm
cone 10 : 85.67 mm
So that's 14.33 % shrinkage at cone 10.
Absorption :
Using the same three sticks above.
OK, the usual practice seems to be to take the still warm tiles from the kiln
and weigh them, then begin the two hour boil. Well, I did not unload this kiln
and the tiles had been outside for a while (several days) under cover but open
to the air. So I did the following :
Weighed them as is.
Baked in oven at about 300-325F for three hours.
Reweighed - no change.
Returned to the oven, same temp. for a further 4 hours.
Reweighed - no change.
Then boiled for two hours, keeping them covered with water.
I came up with :
Test piece A : 0.124%
Test piece B : 0.136%
Test piece C : 0.119%
Thus an average of 0.126% absorption at cone 10. I have read David Beumee's
killer article on claybodies in Studio Potter Dec 2003 and these numbers seem
to indicate that, at least by the standards in the article, this is pretty much
what you'd want in a cone 10 porcelain. Incidentally, David, if you read this,
thanks for that article, great stuff. I'm doing some simple claybody trials now
- will have questions later, no doubt :)
The question is, is the method of baking the pieces above the boiling point of
water reasonable ? I assume that given the time and the fact that no detectable
weight change (scales only measure to 0.1g) that this should be ok.
Thanx
D
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David Beumee on tue 22 feb 05
Hi Daniel,
It's gratifying to see you be so conscientious about your testing methods, and kudos to David Pier for his obvious care in formulating the porcelain body for Clay Planet. Now it's up to the clay manufacturer to be conscientious about the consistency of their mixing methods.
Your absorption results are exactly the kind of numbers I try to achieve for a cone 10 porcelain body; just enough spar in the recipe to very close to zero absorption. Once the absorption tests show a flat zero, there's no way to tell if the body is unnecessarily over fluxed. Your absorption results for this body are why it didn't matter that the tests were outside for awhile after the firing, and why it was not dangerous to bake them above the boiling point of water.
Very glad to hear you are benifitting from the Studio Potter article. Don't hesitate to email me with questions.
David Beumee
DavidBeumee.com
david@davidbeumee.com
Lafayette, CO
-------------- Original message ----------------------
From: Daniel Semler
> Hi All,
>
> Clay Planet in San Jose, CA offers this porcelain so I tried some out. David
> Pier designed it and so I made a bunch of tests including shrinkage and
> absorption.
>
> Shrinkage :
>
> Made three sticks of clay about 12-13 cm long marked a 100mm line in them.
>
> Average line length at :
> bone dry : 94 mm
> bisqued : 93.67 mm
> cone 10 : 85.67 mm
>
> So that's 14.33 % shrinkage at cone 10.
>
> Absorption :
>
> Using the same three sticks above.
>
> OK, the usual practice seems to be to take the still warm tiles from the kiln
> and weigh them, then begin the two hour boil. Well, I did not unload this kiln
> and the tiles had been outside for a while (several days) under cover but open
> to the air. So I did the following :
>
> Weighed them as is.
> Baked in oven at about 300-325F for three hours.
> Reweighed - no change.
> Returned to the oven, same temp. for a further 4 hours.
> Reweighed - no change.
> Then boiled for two hours, keeping them covered with water.
>
> I came up with :
>
> Test piece A : 0.124%
> Test piece B : 0.136%
> Test piece C : 0.119%
>
> Thus an average of 0.126% absorption at cone 10. I have read David Beumee's
> killer article on claybodies in Studio Potter Dec 2003 and these numbers seem
> to indicate that, at least by the standards in the article, this is pretty much
> what you'd want in a cone 10 porcelain. Incidentally, David, if you read this,
> thanks for that article, great stuff. I'm doing some simple claybody trials now
> - will have questions later, no doubt :)
>
> The question is, is the method of baking the pieces above the boiling point of
> water reasonable ? I assume that given the time and the fact that no detectable
> weight change (scales only measure to 0.1g) that this should be ok.
>
> Thanx
> D
>
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> This message was sent using IMP, the Internet Messaging Program.
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
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> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy on thu 24 feb 05
Hi Daniel,
The absorption rates look OK but - in order to asertain if your heating was
enough to remove all moisture from a clay body before weighing dry you
will need to take some clay that has more absorbency than the porclain -
like 2 or 3 percent - to see if the heating would be enough.
I would say the shrinkage of over 14% is high - better to have 12%
shrinkage and work with aged clay or at least clay which has been
flocculated with Epsom salts.
RR
>Hi All,
>
> Clay Planet in San Jose, CA offers this porcelain so I tried some out. David
>Pier designed it and so I made a bunch of tests including shrinkage and
>absorption.
>
>Shrinkage :
>
> Made three sticks of clay about 12-13 cm long marked a 100mm line in them.
>
> Average line length at :
> bone dry : 94 mm
> bisqued : 93.67 mm
> cone 10 : 85.67 mm
>
> So that's 14.33 % shrinkage at cone 10.
>
>Absorption :
>
> Using the same three sticks above.
>
> OK, the usual practice seems to be to take the still warm tiles from the kiln
>and weigh them, then begin the two hour boil. Well, I did not unload this kiln
>and the tiles had been outside for a while (several days) under cover but open
>to the air. So I did the following :
>
> Weighed them as is.
> Baked in oven at about 300-325F for three hours.
> Reweighed - no change.
> Returned to the oven, same temp. for a further 4 hours.
> Reweighed - no change.
> Then boiled for two hours, keeping them covered with water.
>
> I came up with :
>
> Test piece A : 0.124%
> Test piece B : 0.136%
> Test piece C : 0.119%
>
> Thus an average of 0.126% absorption at cone 10. I have read David Beumee's
>killer article on claybodies in Studio Potter Dec 2003 and these numbers seem
>to indicate that, at least by the standards in the article, this is pretty much
>what you'd want in a cone 10 porcelain. Incidentally, David, if you read this,
>thanks for that article, great stuff. I'm doing some simple claybody trials now
>- will have questions later, no doubt :)
>
> The question is, is the method of baking the pieces above the boiling
>point of
>water reasonable ? I assume that given the time and the fact that no detectable
>weight change (scales only measure to 0.1g) that this should be ok.
>
>Thanx
>D
>
>----------------------------------------------------------------
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>
>______________________________________________________________________________
>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
Daniel Semler on fri 25 feb 05
Hi Ron,
Thanx.
I have some stoneware samples coming up so I'll try these.
My basic approach is to weigh it, heat it for a while, weigh it and repeat
until the weight stops changing. With Pier porcelain that happened right off.
I'll see with the stoneware. If I can come up with a valid method for this in
which I can have confidence it will be helpful.
I don't quite follow this comment :
> I would say the shrinkage of over 14% is high - better to have 12%
> shrinkage and work with aged clay or at least clay which has been
> flocculated with Epsom salts.
Does aging or flocculation have an effect on shrinkage ?
Thanx for your comments.
D
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Daniel Semler on fri 25 feb 05
Hi Ron,
I think the coffee is hitting the neurons now.
Is this because aging or flocculation would acheive similar plasticity but
with lower water content, thus leading to lower shrinkage ?
> I would say the shrinkage of over 14% is high - better to have 12%
> shrinkage and work with aged clay or at least clay which has been
> flocculated with Epsom salts.
Would wet mixing work as well ? I guess you'd have more water to start with,
and then have to let it dry for a while, which would be aging, really.
Thanx
D
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Ron Roy on sat 26 feb 05
Hi Daniel,
12% overall shrinkage is the ideal shrinkage for a throwing clay but when
you keep it that low for porcelain - especially the white types - you may
have some problems with it being short.
Adding epsom salts when making the clay flocculates the clay and improves
workability a lot - without increasing shrinkage very much - aging on top
of that makes it even better.
The reason so many porcelain bodies shrink so much is because they are
expected to be used soon after making. It is also the reason that cracking
and warping are problems with those kinds of bodies.
RR
> I don't quite follow this comment :
>
>> I would say the shrinkage of over 14% is high - better to have 12%
>> shrinkage and work with aged clay or at least clay which has been
>> flocculated with Epsom salts.
>
> Does aging or flocculation have an effect on shrinkage ?
>
>Thanx for your comments.
>D
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on sat 26 feb 05
HI Daniel - again,
Just remember - clay does not "age" in the liquid form.
Well aged clay is always the best solution to improve workability. I think
it is much more important than how wet the mix is. Epsom salts is also more
important than wet mixing in my opinion.
It is also important to have the clay well mixed no matter how it is mixed
- and deairing also improves workability.
Best regards Daniel - your attitude is inspiring - RR
> I think the coffee is hitting the neurons now.
> Is this because aging or flocculation would acheive similar plasticity but
>with lower water content, thus leading to lower shrinkage ?
>
>> I would say the shrinkage of over 14% is high - better to have 12%
>> shrinkage and work with aged clay or at least clay which has been
>> flocculated with Epsom salts.
>
> Would wet mixing work as well ? I guess you'd have more water to start with,
>and then have to let it dry for a while, which would be aging, really.
>
>Thanx
>D
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
David Beumee on sun 27 feb 05
Ron wrote,
"> The reason so many porcelain bodies shrink so much is because they are
> expected to be used soon after making."
I don't understand what the effect of aging would have on reducing the shrinkage of a porcelain body. Please explain.
David Beumee
Lafayette, CO
-------------- Original message ----------------------
From: Ron Roy
> Hi Daniel,
>
> 12% overall shrinkage is the ideal shrinkage for a throwing clay but when
> you keep it that low for porcelain - especially the white types - you may
> have some problems with it being short.
>
> Adding epsom salts when making the clay flocculates the clay and improves
> workability a lot - without increasing shrinkage very much - aging on top
> of that makes it even better.
>
> The reason so many porcelain bodies shrink so much is because they are
> expected to be used soon after making. It is also the reason that cracking
> and warping are problems with those kinds of bodies.
>
> RR
>
>
> > I don't quite follow this comment :
> >
> >> I would say the shrinkage of over 14% is high - better to have 12%
> >> shrinkage and work with aged clay or at least clay which has been
> >> flocculated with Epsom salts.
> >
> > Does aging or flocculation have an effect on shrinkage ?
> >
> >Thanx for your comments.
> >D
>
> 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.
Ben on tue 1 mar 05
because they are not allowed to age in order to improve their plasticity,
they are formulated with a higher percentage of plastic materials which have
an inherently higher shrinkage rate.
> Ron wrote,
> "> The reason so many porcelain bodies shrink so much is because they are
>> expected to be used soon after making."
>
> I don't understand what the effect of aging would have on reducing the
> shrinkage of a porcelain body. Please explain.
>
> David Beumee
> Lafayette, CO
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> -------------- Original message ----------------------
> From: Ron Roy
>> Hi Daniel,
>>
>> 12% overall shrinkage is the ideal shrinkage for a throwing clay but when
>> you keep it that low for porcelain - especially the white types - you may
>> have some problems with it being short.
>>
>> Adding epsom salts when making the clay flocculates the clay and improves
>> workability a lot - without increasing shrinkage very much - aging on top
>> of that makes it even better.
>>
>> The reason so many porcelain bodies shrink so much is because they are
>> expected to be used soon after making. It is also the reason that
>> cracking
>> and warping are problems with those kinds of bodies.
>>
>> RR
>>
>>
>> > I don't quite follow this comment :
>> >
>> >> I would say the shrinkage of over 14% is high - better to have 12%
>> >> shrinkage and work with aged clay or at least clay which has been
>> >> flocculated with Epsom salts.
>> >
>> > Does aging or flocculation have an effect on shrinkage ?
>> >
>> >Thanx for your comments.
>> >D
>>
>> 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.
>
> ______________________________________________________________________________
> 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 on wed 2 mar 05
Hi David,
Aging does not increase or decrease shrinkage - it only aids in
flocculating or defloculating clay.
I am trying to explain that - if you have flocculated clay you don't need
the high shrinkage for workability.
Make the clay have the right overall shrinkage to begin with and use the
right clays to get the best plasticity - then find the way to help the clay
flocculate using an agent or time - or both.
RR
>Ron wrote,
> "> The reason so many porcelain bodies shrink so much is because they are
>> expected to be used soon after making."
>
>I don't understand what the effect of aging would have on reducing the
>shrinkage of a porcelain body. Please explain.
>
>David Beumee
>Lafayette, CO
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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