Junko Ordonez on tue 24 aug 04
Hello, I have a question about using glaze on heavily textured clay. I would like the texture to
show through the glaze, but I don't want to have glossy or translucent glaze, but rather a
matt or satin glaze lets the texture come through. Does this depend on the application, or are
there any particular glazes that can be used for this purpose?
Thank you,
Junko Ordonez
Mayssan Shora Farra on wed 25 aug 04
Junko Ordonez wrote:
>Hello, I have a question about using glaze on heavily textured clay. I
would like the texture to
>show through the glaze, but I don't want to have glossy or translucent
glaze, but rather a
>matt or satin glaze lets the texture come through. Does this depend on the
application, or are
>there any particular glazes that can be used for this purpose?
Hello Junko
It all depends,
If the texture is pretty deep, then a matte or semi/matte glaze would work.
I like the Pinnell weathered bronze green (you can find it on
frogpondpottery.com site, where John Hesselberth was gracious enough to
post a lot of useful glazes).
If the tecture is fine then a celadon type glaze would be your best bet to
show the datails. Or you can also use oxide or stain washes and if you add
some clay to the wash then it will stick and the piece would be as matt as
can be. And if you have a satiny clear glaze you can put on top of that,
but do add some water to it to make it thinner especially if you are
talking sculptural not functional.
I hope this helps some,
Mayssan,
http://www.clayvillepottery.com
Ron Roy on thu 26 aug 04
Hi Junko,
You will find that the rate of cooling will have a profound effect on what
you want to happen.
Many kilns cool fast - slow the cooling at the right time and you will have
much better results - especially when the clay is textured.
Go to our web site and see the difference in some glazes - when they are
fast and slow cooled.
www.masteringglazes.com
RR
>Hello, I have a question about using glaze on heavily textured clay. I
>would like the texture to
>show through the glaze, but I don't want to have glossy or translucent
>glaze, but rather a
>matt or satin glaze lets the texture come through. Does this depend on the
>application, or are
>there any particular glazes that can be used for this purpose?
>
>Thank you,
>Junko Ordonez
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Snail Scott on thu 26 aug 04
At 11:21 PM 8/24/2004 -0400, you wrote:
>Hello, I have a question about using glaze on heavily textured clay. I
would like the texture to
>show through the glaze, but I don't want to have glossy or translucent
glaze, but rather a
>matt or satin glaze lets the texture come through. Does this depend on the
application, or are
>there any particular glazes that can be used for this purpose?
A matte glaze can really obscure the subtle
texture of the clay, even more so than a
glossy transparent one. A thin, wiped-back
application may better emphasize your textures,
but test first - some glaze vary radically
when they are very thin, and give an unwanted
emphasis, rather than a smooth transition, to
the area between thick and wiped-off. Engobes
(semi-vitreous or truly flat) have less of this
tendency, and can be treated like slips. This
is often a great way to emphasize texture,
though it won't be a vitrified glaze surface.
It depends on your intentions for the piece.
-Snail Scott
David Beumee on fri 27 aug 04
Ron wrote,
> You will find that the rate of cooling will have a profound effect on what
> you want to happen.
Hi Ron,
Do I assume correctly then that a slower rate of cooling might help with eliminating pinholes for porcelain pots that have had thick clay body slip added (at greenware stage) to give texture? These are cone 10 reduction glazes that have no pinhole problems over untextured surfaces. I tried turning down the gas pressure to 2"W.C. at cone 10, which slowly fires down the kiln for half an hour to 1200 degrees C, and figured the off gassing, setting of the glazes would be complete by that time, but I can try firing down further if you think that might help with the pinholes. I use a fiber lined kiln which cools quickly, but again I've not had pinhole problems previously with the same glazes on unslipped surfaces.
Davd Beumee
> Hi Junko,
>
> You will find that the rate of cooling will have a profound effect on what
> you want to happen.
>
> Many kilns cool fast - slow the cooling at the right time and you will have
> much better results - especially when the clay is textured.
>
> Go to our web site and see the difference in some glazes - when they are
> fast and slow cooled.
>
> www.masteringglazes.com
>
> RR
>
> >Hello, I have a question about using glaze on heavily textured clay. I
> >would like the texture to
> >show through the glaze, but I don't want to have glossy or translucent
> >glaze, but rather a
> >matt or satin glaze lets the texture come through. Does this depend on the
> >application, or are
> >there any particular glazes that can be used for this purpose?
> >
> >Thank you,
> >Junko Ordonez
>
> 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.
Ron Roy on fri 27 aug 04
Hi david,
Seems there might be something about that slip which could be the problem.
Is there iron in it? Could the slip be overfired?
If you care to send me the recipe for that slip I can compare it to a
similar clay body that I have test data for. I should then suggest changes
that might eliminate the problem.
Do you have solubles in the slip?
Firing down slow would not cure the problem if the slip was over mature -
or at least it would perhaps work better if you fast cooled for 100C then
slowed it down for 200C. Better to modify the slip.
RR
> Ron wrote,
>> You will find that the rate of cooling will have a profound effect on what
>> you want to happen.
>
>Hi Ron,
> Do I assume correctly then that a slower rate of cooling might help with
>eliminating pinholes for porcelain pots that have had thick clay body slip
>added (at greenware stage) to give texture? These are cone 10 reduction
>glazes that have no pinhole problems over untextured surfaces. I tried
>turning down the gas pressure to 2"W.C. at cone 10, which slowly fires
>down the kiln for half an hour to 1200 degrees C, and figured the off
>gassing, setting of the glazes would be complete by that time, but I can
>try firing down further if you think that might help with the pinholes. I
>use a fiber lined kiln which cools quickly, but again I've not had pinhole
>problems previously with the same glazes on unslipped surfaces.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
David Beumee on sat 28 aug 04
Ron wrote,
> Seems there might be something about that slip which could be the problem.
>
> Is there iron in it? Could the slip be overfired?
There's no iron in the body. It's possible the slip could be overfired.
> If you care to send me the recipe for that slip I can compare it to a
> similar clay body that I have test data for. I should then suggest changes
> that might eliminate the problem.
Unfortunately I don't have a recipe for the slip. It's made from slaked trimmings from Mile High P-60-S porcelain, 16% shrinkage @cone 10, 0% absorption @ cone 10, no warping or cracking, white fired color, fits GTS 3-10, (excellent glaze fit.)
Do you have solubles in the slip?
The trimmings are slaked in as little water as possible, and then sodium silicate is added in an amount necessary to make the slip usable, that is, thick enough to stay on the side of a leather hard pot when applied rather thickly. Hmmmm... Your question implies that solubles are a potential problem, and sodium silicate is surely soluble and would no doubt act as a strong flux. Perhaps there is another kind of deflocculant available that would work, or perhaps it's time to change clay bodies. Adding deflocculant to super thick slaked trimmings is the only way I have found to make a slip workable without adding more water, cutting down on shrinkage enough to make it able to be applied thick and not have it crack as the slip dries.
David Beumee
Earth Alchemy Pottery
Lafayette, CO
> Hi david,
>
> Seems there might be something about that slip which could be the problem.
>
> Is there iron in it? Could the slip be overfired?
>
> If you care to send me the recipe for that slip I can compare it to a
> similar clay body that I have test data for. I should then suggest changes
> that might eliminate the problem.
>
> Do you have solubles in the slip?
>
> Firing down slow would not cure the problem if the slip was over mature -
> or at least it would perhaps work better if you fast cooled for 100C then
> slowed it down for 200C. Better to modify the slip.
>
> RR
>
>
> > Ron wrote,
> >> You will find that the rate of cooling will have a profound effect on what
> >> you want to happen.
> >
> >Hi Ron,
> > Do I assume correctly then that a slower rate of cooling might help with
> >eliminating pinholes for porcelain pots that have had thick clay body slip
> >added (at greenware stage) to give texture? These are cone 10 reduction
> >glazes that have no pinhole problems over untextured surfaces. I tried
> >turning down the gas pressure to 2"W.C. at cone 10, which slowly fires
> >down the kiln for half an hour to 1200 degrees C, and figured the off
> >gassing, setting of the glazes would be complete by that time, but I can
> >try firing down further if you think that might help with the pinholes. I
> >use a fiber lined kiln which cools quickly, but again I've not had pinhole
> >problems previously with the same glazes on unslipped surfaces.
>
> 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.
Ron Roy on sun 29 aug 04
Hi David,
The most good will be done near the top temp - because that is where the
glaze is least viscose. The problem could be - if you hold up at the top
and the slip is overfiring it will not work.
It sounds like the best solution would be to make the slip more refractory
- or do as some potters do - make pinholes desirable.
I can remember a problem someone was having with pin holes at the rims only
- the salts were overfiring the clay - we solved it by taking some of the
Epsom salts out of the body - solubles can be the source of many problems
so understanding how they affect melting becomes important. We could have
solved the problem by drying the ware upside down as well but then sticking
to the shelves might have become the problem.
The more I think about it the more I think the solution is in fixing the slip.
RR
>Hi Ron,
> Do I assume correctly then that a slower rate of cooling might help with
>eliminating pinholes for porcelain pots that have had thick clay body slip
>added (at greenware stage) to give texture? These are cone 10 reduction
>glazes that have no pinhole problems over untextured surfaces. I tried
>turning down the gas pressure to 2"W.C. at cone 10, which slowly fires
>down the kiln for half an hour to 1200 degrees C, and figured the off
>gassing, setting of the glazes would be complete by that time, but I can
>try firing down further if you think that might help with the pinholes. I
>use a fiber lined kiln which cools quickly, but again I've not had pinhole
>problems previously with the same glazes on unslipped surfaces.
>
>Davd Beumee
>
>
>> Hi Junko,
>>
>> You will find that the rate of cooling will have a profound effect on what
>> you want to happen.
>>
>> Many kilns cool fast - slow the cooling at the right time and you will have
>> much better results - especially when the clay is textured.
>>
>> Go to our web site and see the difference in some glazes - when they are
>> fast and slow cooled.
>>
>> www.masteringglazes.com
>>
>> RR
>>
>> >Hello, I have a question about using glaze on heavily textured clay. I
>> >would like the texture to
>> >show through the glaze, but I don't want to have glossy or translucent
>> >glaze, but rather a
>> >matt or satin glaze lets the texture come through. Does this depend on the
>> >application, or are
>> >there any particular glazes that can be used for this purpose?
>> >
>> >Thank you,
>> >Junko Ordonez
>>
>> 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
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on mon 30 aug 04
I am having further thoughts on this - It could also be that the slip is
being made more refractory with the additions of stains - the solution to
the problem will be testing in both directions - adding kaolin to the slip
to make it more refractory - or adding spar to make it less refractory.
Some stains can be melters, others can be refractory - testing each in
slips of different refractoryness will give the clues necessary to find the
right combinations.
I also recommend using Darvan 7 as a deflocculent - less is needed than
sodium silicate. It is also less forgiving in terms of over deflocculation.
RR
> > Seems there might be something about that slip which could be the problem.
>>
>> Is there iron in it? Could the slip be overfired?
>
>There's no iron in the body. It's possible the slip could be overfired.
>
>> If you care to send me the recipe for that slip I can compare it to a
>> similar clay body that I have test data for. I should then suggest changes
>> that might eliminate the problem.
>
>Unfortunately I don't have a recipe for the slip. It's made from slaked
>trimmings from Mile High P-60-S porcelain, 16% shrinkage @cone 10, 0%
>absorption @ cone 10, no warping or cracking, white fired color, fits GTS
>3-10, (excellent glaze fit.)
>
> Do you have solubles in the slip?
>
>The trimmings are slaked in as little water as possible, and then sodium
>silicate is added in an amount necessary to make the slip usable, that is,
>thick enough to stay on the side of a leather hard pot when applied rather
>thickly. Hmmmm... Your question implies that solubles are a potential
>problem, and sodium silicate is surely soluble and would no doubt act as a
>strong flux. Perhaps there is another kind of deflocculant available that
>would work, or perhaps it's time to change clay bodies. Adding
>deflocculant to super thick slaked trimmings is the only way I have found
>to make a slip workable without adding more water, cutting down on
>shrinkage enough to make it able to be applied thick and not have it
>crack as the slip dries.
>
>David Beumee
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on mon 30 aug 04
Hi David,
The overall shrinkage seems high for that clay - normal overall shrinkage
for a throwing body should be in the range of 12 to 13%.
Could it be that it is overfired to start with? The problem with finding an
absorption of 0% is that you don't know if the clay is over fired. If you
had an absorption amount for cone 8 you would know for sure. If it's 0% at
eight it means the body should perhaps be a little more refractory to start
with. I am assuming High Water is not testing for absorption and shrinkage?
If a body calls for 0% absorption - then it necessary to test it at a lower
cone as well to maintain correct absorption at the top temperature the clay
is rated for.
RR
>Ron wrote,
> > Seems there might be something about that slip which could be the problem.
>>
>> Is there iron in it? Could the slip be overfired?
>
>There's no iron in the body. It's possible the slip could be overfired.
>
>> If you care to send me the recipe for that slip I can compare it to a
>> similar clay body that I have test data for. I should then suggest changes
>> that might eliminate the problem.
>
>Unfortunately I don't have a recipe for the slip. It's made from slaked
>trimmings from Mile High P-60-S porcelain, 16% shrinkage @cone 10, 0%
>absorption @ cone 10, no warping or cracking, white fired color, fits GTS
>3-10, (excellent glaze fit.)
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
David Beumee on tue 31 aug 04
Hi Ron,
This is a (commercial) porcelain body, and the shrikage is naturally going to be higher than 12 or 13%. If you know of a cone 10 porcelain body with 12% shrinkage please let me know.
It's unlikely in this case that the body is overfired at cone 10. Although Mile Hi P-60-S has 0% shrikage at cone 10, I have had no slumping problems with the tall vertical forms I have been making with this body, and I see no evidence of a shiny or glassy test bar. But you're right. 0% absorption can certainly mean the possibility of an overfired body. I always try for an absortion percentage of 0.1 or 0.2% for the porcelain bodies I formulate, which tells me I've added just enough spar and not too much. Mile Hi's (Denver) catalog lists P-60-S porcelain at 15% shrinkage and does not supply an absorption %. It is listed for use at cone 8-10.
I will make up slip with no added anything, slip with added percentages of spar and slip with added percentages of kaolin. I have not had pinhole problems with glazes used over colored slips, all of which are colored with various percentages of iron, meaning perhaps that more flux is desirable in this case to solve the pinhole problem.
David Beumee
Earth Alchemy Pottery
Lafayette, CO
> Hi David,
>
> The overall shrinkage seems high for that clay - normal overall shrinkage
> for a throwing body should be in the range of 12 to 13%.
>
> Could it be that it is overfired to start with? The problem with finding an
> absorption of 0% is that you don't know if the clay is over fired. If you
> had an absorption amount for cone 8 you would know for sure. If it's 0% at
> eight it means the body should perhaps be a little more refractory to start
> with. I am assuming High Water is not testing for absorption and shrinkage?
>
> If a body calls for 0% absorption - then it necessary to test it at a lower
> cone as well to maintain correct absorption at the top temperature the clay
> is rated for.
>
> RR
>
>
>
> >Ron wrote,
> > > Seems there might be something about that slip which could be the problem.
> >>
> >> Is there iron in it? Could the slip be overfired?
> >
> >There's no iron in the body. It's possible the slip could be overfired.
> >
> >> If you care to send me the recipe for that slip I can compare it to a
> >> similar clay body that I have test data for. I should then suggest changes
> >> that might eliminate the problem.
> >
> >Unfortunately I don't have a recipe for the slip. It's made from slaked
> >trimmings from Mile High P-60-S porcelain, 16% shrinkage @cone 10, 0%
> >absorption @ cone 10, no warping or cracking, white fired color, fits GTS
> >3-10, (excellent glaze fit.)
>
> 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.
Ron Roy on thu 2 sep 04
Hi David,
Tuckers makes 4 cone 10 porcelains - 3 have an overall average shrinkage
(wet to dry + fired) of 12 % - the other one (grolleg based) has a little
higher shrinkage of 13%. I make adjustments now and then but hardly ever.
The wet to dry shrinkage is consistent between the 4 bodies - between 5 and 6%.
The only way a porcelain body should have an over all shrinkage of 16%
would be if 1. The wet to dry is too much or - 2. the body is overfired at
the recommended cone - or 3 - both the wet and fired shrinkage are too
high.
If the clay is over mature at glaze temperature the last kind of forms to
deform because the clay is too soft would be vertical forms. You would
notice it more on bowls or extended rims - like on plates.
I would tend to agree - if the problem is not happening when you add iron -
and are reduction firing (iron fluxes in reduction) then perhaps it is
because the stains are making the slip more refractory. Let us know what
you find out.
RR
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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