Ron Collins on mon 18 feb 02
My porcelain body slumps and cannot be depended on at cone 6...I am so =
tired of never knowing if it will be ok, or not....I have a recipe for =
Birke's celadon, from clayart, which I use at cone 5 in the sitter, and =
the real cone 5 test cone is bent to about 2 o'clock. All the glazes I =
have mixed up, besides the Birke's, need a real cone 6....most of them =
are variations of Hesselberth site glazes....There is no point in trying =
the glazes in their book until I get a body that will not slump...I need =
this body not to melt down. My problem is unspecified =
materials...i.e.....feldspar. I don't know what kind it is, and they =
won't tell me, but it's my only source. What can I add to this body, =
to make it not melt so soon?? It does it mostly on hump molded bowls =
with a foot. It doesn't do it all the time...I never know, but I need =
more control in order to teach classes, and not ruin student work......
feldspar, unspecified 25
kaolin 20
silica 25
ball clay-Unimin 30
Calcium carbonate 2
bentonite 2
talc 5
fireclay- 3
loza-very fine grog =20
from toilet factory 5
It slumps...what can I do, to give it more strength? I was more =
concerned about a fully vitrified body, and now it seems over-vitrified =
and melts, depending on the shape of the thing.... So what do I do? =
Melinda Collins, Antigua, Guatemala....
Bryan on tue 19 feb 02
My initial thought was to get rid of the talc. That is what I did years ago
when I had trouble with overfiring. My second thought was " Why have
calcium carbonate and talc in a clay body?".
Bryan
----- Original Message -----
From: "Ron Collins"
To:
Sent: Monday, February 18, 2002 8:01 PM
Subject: slumping clay
My porcelain body slumps and cannot be depended on at cone 6...I am so tired
of never knowing if it will be ok, or not....I have a recipe for Birke's
celadon, from clayart, which I use at cone 5 in the sitter, and the real
cone 5 test cone is bent to about 2 o'clock. All the glazes I have mixed
up, besides the Birke's, need a real cone 6....most of them are variations
of Hesselberth site glazes....There is no point in trying the glazes in
their book until I get a body that will not slump...I need this body not to
melt down. My problem is unspecified materials...i.e.....feldspar. I don't
know what kind it is, and they won't tell me, but it's my only source.
What can I add to this body, to make it not melt so soon?? It does it
mostly on hump molded bowls with a foot. It doesn't do it all the time...I
never know, but I need more control in order to teach classes, and not ruin
student work......
feldspar, unspecified 25
kaolin 20
silica 25
ball clay-Unimin 30
Calcium carbonate 2
bentonite 2
talc 5
fireclay- 3
loza-very fine grog
from toilet factory 5
It slumps...what can I do, to give it more strength? I was more concerned
about a fully vitrified body, and now it seems over-vitrified and melts,
depending on the shape of the thing.... So what do I do? Melinda Collins,
Antigua, Guatemala....
____________________________________________________________________________
__
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Mark Mondloch on tue 19 feb 02
Hi Melinda,
I'm not qualified to answer this. I'm going to anyway. ;) Actually, I'd
like to find out if my thinking is off-base so here are my thoughts.
If your clay is over vitrified at your temp so you need to cut down on the
proportion of the fluxes. Your fluxes are the feldspar, calcium carb, and
talc. My understanding is that the calcium carb and talc are strong fluxes
with a short firing range compared to spar, so I think my first choice would
be to just eliminate them, especially if I'm mixing myself and would have to
try to get them blended in well. Unless there is some specific reason to
have them there- like talc= more thermal shock resistance? Another route
would be to decrease the % feldspar. I would guess at least 5% to make any
difference. Personally I'd replace the missing 5% with more fireclay since I
like a toothy body. If maintaining whiteness is important, replace it with
kaolin. If plasticity is an issue, then the ballclay.
I'll be watching to see what those more body knowledgeable have to say.
Sylvia
---
Mark & Sylvia Mondloch
Silver Creek Pottery & Forge
W6725 Hwy 144
Random Lake ,Wi 53075
HotArt@silvercreekpottery.com
http://www.silvercreekpottery.com
----- Original Message -----
From: "Ron Collins"
To:
Sent: Monday, February 18, 2002 8:01 PM
Subject: slumping clay
My porcelain body slumps and cannot be depended on at cone 6...I am so tired
of never knowing if it will be ok, or not....I have a recipe for Birke's
celadon, from clayart, which I use at cone 5 in the sitter, and the real
cone 5 test cone is bent to about 2 o'clock. All the glazes I have mixed
up, besides the Birke's, need a real cone 6....most of them are variations
of Hesselberth site glazes....There is no point in trying the glazes in
their book until I get a body that will not slump...I need this body not to
melt down. My problem is unspecified materials...i.e.....feldspar. I don't
know what kind it is, and they won't tell me, but it's my only source.
What can I add to this body, to make it not melt so soon?? It does it
mostly on hump molded bowls with a foot. It doesn't do it all the time...I
never know, but I need more control in order to teach classes, and not ruin
student work......
feldspar, unspecified 25
kaolin 20
silica 25
ball clay-Unimin 30
Calcium carbonate 2
bentonite 2
talc 5
fireclay- 3
loza-very fine grog
from toilet factory 5
It slumps...what can I do, to give it more strength? I was more concerned
about a fully vitrified body, and now it seems over-vitrified and melts,
depending on the shape of the thing.... So what do I do? Melinda Collins,
Antigua, Guatemala....
Ron Collins on tue 19 feb 02
> I read that if you cannot get neph.sye, you should not count on getting a
> fully vitrified body from the usual mix of equal parts feldspar, silica,
> kaolin and ball clay--a standard cone 10 porcelain body. So, I also read
> that if you add talc, in a 1:5 ration to the feldspar, you get a lower
> vitrification on the body, ie cone 6, without neph sye, so that's what I
> did. It seemed to work. I added the calcium carbonate-whiting-because
> someone in ceramics monthly did, so that's what I will eliminate first.
> That may be the culprit. I put the grog and fireclay in because I thought
> that might help the slumping, as well as help plasticity. It hasn't helped
> the strength enouch to matter, but has helped, I think, with plasticity.
> Trouble is, I'm running out of fireclay, and can't buy more here, so it's
> out eventually anyway. I use a rather hit and miss approach, and seem to
> be missing the mark..the first to go will be cal.carb, and second,
increase
> the ratio more of ball clay to kaolin. I think there is something to the
> talc/feldspar ratio bit, and will try and keep the talc in. Thanks for
> help, and any more help appreciated. I don't have a way to de-air, which
> would help plasticity. So, rambling on, I'll keep trying.....any help, or
> suggestions, as I said, appreciated....melinda
>
Steven Goldate on sun 31 aug 03
This is a question for any clay experts out there. I have a porcelain that slumps at
the maturing temperature. I realize I could fire it lower, but what could I add to
stiffen it, without losing too much of its other porcelain-related qualities? Calcined
alumina? Some other ingredient?
thanks for any suggestions,
Steven.
-----------------------------------------
Steven Goldate
Editor
Ceramics Today
http://www.ceramicstoday.com
ceramics@ceramicstoday.com
-----------------------------------------
John Rodgers on sun 31 aug 03
Steven, there are some funny things that can happen to porcelain when
fired. I have had parts all of off porcelain figurines when fired to
maturity.
What kind of kiln do you use? Do you use an electronic controller
(computer) or a Dawson Kiln Sitter. My experience in recent years has
been such that I no longer trust Computer controllers or Kiln Sitters
and their mini-cones.
I was grumbling to a hobby ceramics Old Timer one day ( over 50 years
in the business) and she told me two things that have changed and
improved the quality of my firings and my finished work.
"First," she said: "Forget all the fancy-schmancy extra equipment on a
kiln, and use your eyeball and a shelf cone as the final say-so as to
whether the load has reached maturity".
I now do that and my firings are ...to take a quote from a scene in a
funny movie -- "dead on balls accurate" and I am getting perfection
every time.
Second, she said, "Always leave the bottom plug out of the kiln
(electric kilns) through the complete firing. This will even the heat
throughout the kiln during the firing." I now leave the plug out, and
that combined with the eyeball/cone thing is giving me the best firings
I have ever had, and it shows in the work.
This is related to the porcelain slumping problem in that there is not
much room in terms of time/temperature between being not yet mature and
beyond the pale........if you get my meaning. There needs to be really
tight accuracy in the maturing process so that you catch and stop the
process in the pinnacle of maturation. If you could consider the
porcelain to have a maturity range, so you have a situation of mature
but less so, and assign a number of 10, and mature, but more so, and
assign a number of 20, then anything in between the two numbers is
considered mature. However, the lower side - 10 - while mature, is more
stable, and there is less movement, while the higher side - 20 - is more
mature, has been exposed to the heat longer, and particles in the clay
are melting more with more movement as a consequence - i.e., slumping.
If you consider that the particles in the porcelain have corners and
points on them, in the non mature state the points contact one another
and on a microscopic scale for interstices in between, i.e., spaces. As
the material reaches maturity, the points begin to melt and the
interstices begin to close. The longer the exposure to the heat, the
more the melting takes place, and the more the collapse of the
interstices, i.e. the more movement you will have, and the more slumping
occurs.
So, I perceive on the basis of my own experience, that you will need to
play with the process a bit, and find at just what point of cone bending
you will actually get a satisfactory level of maturity of the porcelain,
without slumping. This knowledge will not come quickly as you will need
to do several tests to get it right. Write now all the data of your
parameters over the period of time when the firing takes place. I find
that my pyrometer is always off and doesn't match the cone so far as
temperature is concerned. That is, there is always some variation in the
numbers when the pyrometer says the right temperature has been arrived
at. Since heatwork is the real indicator, do not depend solely on a
pyrometer, or a computer, or a kiln sitter. As the time for maturity
approaches, start opening that peep hole and look a the cone(s). They
will give you the true story.
Currently my best example of this type of firing procedure is my work
with Floating Blue glaze. Some sources say fire to cone 6. For me, that
produces a glaze that is green and runs off the pots. I tried cone 5,
and used the procedure of firing until the cone tip was down and
touching the base. Better but still a little greenish in spots, some
pooling but no runs. Final solution, also arrived at by testing. Fire
the FB to cone 5, bent horizontal, bottom kiln plug open. With that, I
get perfect floating blue every time.
So, my point is, test, test, test. And don't depend on the gadgets on
the kiln to give you the answers. Your eyeball, shelf cones, and a good
brain for sound reasoning will do the trick.
Regards,
John Rodgers
Birmingham, AL
Steven Goldate wrote:
>This is a question for any clay experts out there. I have a porcelain that slumps at
>the maturing temperature. I realize I could fire it lower, but what could I add to
>stiffen it, without losing too much of its other porcelain-related qualities? Calcined
>alumina? Some other ingredient?
>
>thanks for any suggestions,
>Steven.
>-----------------------------------------
>Steven Goldate
>Editor
>Ceramics Today
>http://www.ceramicstoday.com
>ceramics@ceramicstoday.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.
>
>
>
Tony Hansen on mon 1 sep 03
Steve\'s point about the form is good.
The porcelain manufacturers pay a lot of attention to
the cross section and shape of ware and in keeping the
shelves perfectly flat. When ware is fired in special
setters that support it on every side more design
effort goes into the setter than the plates themselves.
-------8<--------
Hi Steven,
You might consider a change in the form to make it more stable. (I dont
know your work) Some forms are more resistant to slumping than others.
Alternatively, the problem might be related to the kiln shelves that
you are firing the work on.
Warping can be caused by setting the work on a uneven surface.
Try making some porcelain setters that will shrink at the same rate as
the pot. You should be careful to ensure that the foot is turned as
flat as your skill level will allow. After glazing, set the glazed,
bisqued pot on a fresh, raw porcelain clay setter that is well coated
with alumina wash. gently press the pot onto the setter. ( a setter is
a small clay disc, like a pan cake.) You can even glue the pot onto the
setter using PVA glue on the foot.
If you go to this trouble, your pot should stay flat and unwarped.
regards
Steve Harrison
On Sunday, August 31, 2003, at 03:42 PM, Steven Goldate wrote:
> This is a question for any clay experts out there. I have a porcelain
> that slumps at
> the maturing temperature. I realize I could fire it lower, but what
> could I add to
> stiffen it, without losing too much of its other porcelain-related
> qualities? Calcined
> alumina? Some other ingredient?
>
> thanks for any suggestions,
> Steven.
> -----------------------------------------
> Steven Goldate
> Editor
> Ceramics Today
> http://www.ceramicstoday.com
> ceramics@ceramicstoday.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.
--------
Tony Hansen, Digitalfire Corp.
iandol on mon 1 sep 03
Dear Steven Goldate,=20
We seem to be having an epidemic! Do you know the precise composition of =
your clay or is it a commercial product?
I recently, in a private mail suggested changing techniques and adopting =
the High Bisque-Low Glaze option.
If this is done it becomes possible to fire in saggars and use contoured =
setters to support fragile ware using a separator bed of pure fused =
alumina grain.
If you are in control of body composition one solution is to reduce the =
amount of Felspar. another is to incorporate Molochite Grog. I would not =
recommend using Pitchers of identical composition since these would =
possible have a lower thermal activation temperature. I feel this would =
exaggerate the problem rather than cure it.
Best regards,
Ivor Lewis. Redhill, South Australia
Ababi on mon 1 sep 03
Hello Steven
With my very humble porcelaneous knowledge I shall try to help you.
I would not go to the alumina solution unless the ware would have to be
used for crystal glazes.
If you make the claybody yourself try to add molochite.
Try some batches of adding 5% and up to 10%
Or better 2 to 10% of the claybody.
You can do it this way for easier calculations in the future: Claybody
98% molochite2% and so on.
If you use a commercially prepared you must dry it first.
Ababi Sharon
Glaze addict
Kibbutz Shoval Israel
ababisha@shoval.org.il
http://members4.clubphoto.com/ababi306910
http://www.matrix2000.co.nz/Matrix%20Demo/Ababi.htm
.
steve harrison on mon 1 sep 03
Hi Steven,
If you add something to make the body more refractory, it will make it
less translucent.
Try firing just a bit lower, you will find that at some point the clay
will still be translucent but firm enough to hold most of its form.
Porcelain will always have just a little change in form when it becomes
glassy enough to be translucent. It's a trade off. The more translucent
, the more change in form.
You might consider a change in the form to make it more stable. (I dont
know your work) Some forms are more resistant to slumping than others.
Alternatively, the problem might be related to the kiln shelves that
you are firing the work on.
Warping can be caused by setting the work on a uneven surface.
Try making some porcelain setters that will shrink at the same rate as
the pot. You should be careful to ensure that the foot is turned as
flat as your skill level will allow. After glazing, set the glazed,
bisqued pot on a fresh, raw porcelain clay setter that is well coated
with alumina wash. gently press the pot onto the setter. ( a setter is
a small clay disc, like a pan cake.) You can even glue the pot onto the
setter using PVA glue on the foot.
If you go to this trouble, your pot should stay flat and unwarped.
regards
Steve Harrison
On Sunday, August 31, 2003, at 03:42 PM, Steven Goldate wrote:
> This is a question for any clay experts out there. I have a porcelain
> that slumps at
> the maturing temperature. I realize I could fire it lower, but what
> could I add to
> stiffen it, without losing too much of its other porcelain-related
> qualities? Calcined
> alumina? Some other ingredient?
>
> thanks for any suggestions,
> Steven.
> -----------------------------------------
> Steven Goldate
> Editor
> Ceramics Today
> http://www.ceramicstoday.com
> ceramics@ceramicstoday.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 tue 2 sep 03
HI Steven,
What I need to make a suggestion is - the recipe and the cone fired to and
perhaps some analysis of some of your local materials.
If it is a purchased body - then I would need to know by what means you
intend to mix in another material - calcined kaolin would be an option for
instance?
RR
>This is a question for any clay experts out there. I have a porcelain that
>slumps at
>the maturing temperature. I realize I could fire it lower, but what could
>I add to
>stiffen it, without losing too much of its other porcelain-related
>qualities? Calcined
>alumina? Some other ingredient?
>
>thanks for any suggestions,
>Steven.
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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