Antoinette Badenhorst on tue 27 jun 06
Dear Clayarters, it's been a while since I posted and wonderful to be "back"
I've been making finer porcelain pieces than ever and I enjoy it
tremendously. The challenge is big and I enjoy that. I do have a serious
problem with firing though and I am considering building saggers to fire
these pieces in unless someone can help me slow down my electric kiln. I
loose too many pieces due to dunting.
I have a Bartlett controller on the kiln PLUS a kiln sitter. I've used the
L&L Kiln instructions to fire the kiln down and even though it does accept
the instructions, it does not work once the kiln sitter shuts down. I am
considering placing a very high cone (11 or 12) in the sitter and then baby
sit the kiln till it is done. Will that be a solution or is there something
much simpler that I do not know about? Also will the L&L instructions work
on the Bartlett as I hope it would?
As always...Thank you.
Do you need sharp trimming tools that will not wear out quickly? Contact me
for information.
Antoinette Badenhorst
105 Westwood Circle
Saltillo MS, 38866
662 869 1651
www.clayandcanvas.com
www.southernartistry.org
Stephen J Lewicki on wed 28 jun 06
Dear Antoinette -
We have several versions of our DynaTrol instructions that you can download
from our website (www.hotkilns.com). Depending on what version of the
Bartlett you have you should be able to find a version that comes close to
matching your Bartlett. The DynaTrol instructions are more comprehensive and
detailed than the similar Bartlett instructions so you may find them to be
useful. However, I would still get your hands on the correct set of
instructions from Bartlett for your exact controller. The folks at Bartlett
are very helpful and I'm sure they can help you with this.
It sounds like you have a manual kiln that is then in turned being
controlled with a separate Bartlett controller in a separate box. You will
not be able to control cool-down with this scheme (unlike if you had a fully
automatic kiln) if you use the kiln sitter to do the final shut-off. You
could try, however, to use the Dawson kiln sitter simply as high-limit
shut-off device. Put a cone in the Kiln Sitter that is two cones higher than
you want to go (so it doesn't shut off). Then use the control as your
shut-off device. If you do that you can program into the control a very nice
cool-down curve.
Best Regards,
Stephen Lewicki
President
L&L Kiln Mfg., Inc.
steve@hotkilns.com
www.hotkilns.com
Ron Roy on wed 28 jun 06
Hi Antoinette,
Tell me what kind of dunting -
Big or small pots -
Crackes open or closed -
Glaze at crack sharp or melted, (rounded not sharp)
Does it happen more often in certain places in your kiln -
Does it happen more with one particular glaze inside?
Does it happen more with a crazed glze on the ourside?
What clay are you using?
When a pot is cracked - it is always a good idea to brak it in two pieces
to see if the glaze is thick at certain places - at corners for instance -
can be an important clue. Some times changong the shape of a corner can
help.
I have assumed the problem is during a glaze fire cooling - porcelain can
also be problematic in a bisque firing during cooling - slowing down the
cooling during the quartz inversion is a good cure but there are others,
RR
>Dear Clayarters, it's been a while since I posted and wonderful to be "back"
>
>
>I've been making finer porcelain pieces than ever and I enjoy it
>tremendously. The challenge is big and I enjoy that. I do have a serious
>problem with firing though and I am considering building saggers to fire
>these pieces in unless someone can help me slow down my electric kiln. I
>loose too many pieces due to dunting.
>
>I have a Bartlett controller on the kiln PLUS a kiln sitter. I've used the
>L&L Kiln instructions to fire the kiln down and even though it does accept
>the instructions, it does not work once the kiln sitter shuts down. I am
>considering placing a very high cone (11 or 12) in the sitter and then baby
>sit the kiln till it is done. Will that be a solution or is there something
>much simpler that I do not know about? Also will the L&L instructions work
>on the Bartlett as I hope it would?
>
>As always...Thank you.
>
>
>
>
>
>Do you need sharp trimming tools that will not wear out quickly? Contact me
>for information.
>
>Antoinette Badenhorst
>
>105 Westwood Circle
>
>Saltillo MS, 38866
>
>662 869 1651
>
> www.clayandcanvas.com
>
> www.southernartistry.org
>
>______________________________________________________________________________
>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
Antoinette Badenhorst on wed 28 jun 06
Okay Roy, here goes:
I am working with Southern Ice. The most dunts this far were on small
bowls(cereal size) and while I am writing this to you, I realize that =
all
the bowls were glazed inside and not at all glazed on the outside (I =
went
outside to look at the pile of broken bowls.)It appears with my matt
strontium based glaze as well as my shiny white (wollistonite) glaze.(I =
only
use these 2 glazes)=20
The cracks are sharp on the edges and some pieces broke in 2. I found =
out
very quickly that I dare not dip-or pour-glaze these pieces. I have to =
spray
glaze. Some of them are thinner than a 1/16th of an inch and it just do =
not
tolerate glaze on it.
It happens anywhere in the kiln and it does not happen to all the =
pieces. In
other words; with some it is okay if I just glaze the inside. I've done =
them
as big as 12" x 9" without glaze on the outside very successfully. Of =
cause
when they become bigger, the clay walls are also thicker.
I am fairly sure that the problems occur during the cooling; otherwise I
would have had rounded edges right?
The bowls are open with narrow feet. The glaze does not pool in the =
bottom
and my throwing and trimming is fairly even. I trim a prominent foot =
rim.
Someone suggested to me to higher my bisque firing to ^04 or even =
higher. At
the moment I bisque at 05. That might cure the possibility of too much =
glaze
on the pieces right?
I think I covered all the information that you asked for.=20
Thanks for your interest in this problem.
Do you need sharp trimming tools that will not wear out quickly? Contact =
me
for information.=20
Antoinette Badenhorst
105 Westwood Circle
Saltillo MS, 38866
662 869 1651
www.clayandcanvas.com
www.southernartistry.org
=20
=20
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Ron Roy
Sent: Wednesday, June 28, 2006 3:01 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Slow cooling down in electric kiln for fine porcelain.
Hi Antoinette,
Tell me what kind of dunting -
Big or small pots -
Crackes open or closed -
Glaze at crack sharp or melted, (rounded not sharp)
Does it happen more often in certain places in your kiln -
Does it happen more with one particular glaze inside?
Does it happen more with a crazed glze on the ourside?
What clay are you using?
When a pot is cracked - it is always a good idea to brak it in two =
pieces
to see if the glaze is thick at certain places - at corners for instance =
-
can be an important clue. Some times changong the shape of a corner can
help.
I have assumed the problem is during a glaze fire cooling - porcelain =
can
also be problematic in a bisque firing during cooling - slowing down =
the
cooling during the quartz inversion is a good cure but there are others,
RR
>Dear Clayarters, it's been a while since I posted and wonderful to be
"back"
>
>
>I've been making finer porcelain pieces than ever and I enjoy it
>tremendously. The challenge is big and I enjoy that. I do have a =
serious
>problem with firing though and I am considering building saggers to =
fire
>these pieces in unless someone can help me slow down my electric kiln. =
I
>loose too many pieces due to dunting.
>
>I have a Bartlett controller on the kiln PLUS a kiln sitter. I've used =
the
>L&L Kiln instructions to fire the kiln down and even though it does =
accept
>the instructions, it does not work once the kiln sitter shuts down. I =
am
>considering placing a very high cone (11 or 12) in the sitter and then =
baby
>sit the kiln till it is done. Will that be a solution or is there =
something
>much simpler that I do not know about? Also will the L&L instructions =
work
>on the Bartlett as I hope it would?
>
>As always...Thank you.
>
>
>
>
>
>Do you need sharp trimming tools that will not wear out quickly? =
Contact me
>for information.
>
>Antoinette Badenhorst
>
>105 Westwood Circle
>
>Saltillo MS, 38866
>
>662 869 1651
>
> www.clayandcanvas.com
>
> www.southernartistry.org
>
>________________________________________________________________________=
___
___
>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
_________________________________________________________________________=
___
__
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.
Daniel Semler on wed 28 jun 06
Hi Antoinette,
OK so this is interesting. If I had to guess I'd go with expansion mismatch.
The effects of expansion mismatches are accentuated by a number of the factors
that you mention : extreme thinness of the body, glazing one side only,
and the
inherent expansion mismatch between the clay and glaze. The few tests
I've done
with Southern Ice would indicate that its expansion is much higher than
that of
the porcelain I normally use. We have a crackle celadon that pretty
much didn't
crackle at all on it, though it does on other bodies. It would be very
interesting to know the make up of the glazes.
I am interested by your comment that :
> I found out
> very quickly that I dare not dip-or pour-glaze these pieces. I have to spray
> glaze. Some of them are thinner than a 1/16th of an inch and it just do not
> tolerate glaze on it.
Did the glaze simply not adhere well or fall off, or was there some other
probem ?
One interesting test would be to glaze both inside and out and see what
happens.
Another question is, did all the small thin bowls done this way crack before
the kiln was opened or are some ok ? If so a freeze boil test on one -
with due
caution - would be interesting also. Or perhaps on a decent sized fragment.
Thanx
D
Antoinette Badenhorst on thu 29 jun 06
Hi Daniel, I've considered all the factors that you've mentioned. I have
several glazed in full, without any dunting.=20
For one, the pieces are some so thin that they become wet before the =
glaze
adhere to it. Also, since I do consider the mismatch of clay and glaze, =
I am
particularly careful not to put too much glaze on the pieces.(learned =
that
the hard way!)
I still believe the firing process should be much more controlled.I did =
not
have enough breakages to discourage me, but too much.....you get my =
point? I
spend way too many hours on one piece to end up with breakages.
It would not do harm though to discuss my glazes. (Ron I am sure you are
interested!) It is no secret; in fact I think the strontium based one is
after a barium glaze published in the Potters Dictionary. The other one =
is a
basic white glaze that I used in South Africa for years and had to =
adjust
here in the USA. Be warned, I seldom do things to the book. My recipes =
is by
weight and not by %
=20
White:
=20
P Feldspar 950
EPK 350
Wollistanite 675
Zircopax 250
Fritt 3195 275 (there is probably better fritts to use, but this is =
the
one I started out with when I had to adjust the recipe and I can not
remember how I came to choose this one)
Also I am wondering about the silica content.
=20
Strontium Base Glaze:
=20
Neph. Sye. 2040
P. Feldspar 300
EPK 720
Silica 420
Strontium carb. 1346
Whiting 300
Lith Carb. 180
=20
As I mentioned, I spay the glaze on and keep it subtle and I fire to =
^10.
What makes it very curious is that not every piece I make that way =
dunts. I
had a few that literally fell apart in 2 pieces. I do think that was a =
glaze
mismatch, because I pour glazed it, but then I made a series of 9 bowls =
with
wide rims, narrow bottoms (I have images if you're interested).The =
dunting
was in different "shard-like" shapes and not straight. The pieces also =
did
not fall apart. That is what made me think it is a lack of heat control. =
On
the Potters council website
http://www.ceramics.org/potterscouncil/gallery.asp are images of SI =
pieces
that I've done successfully over and over, but then I had a few,( I =
think it
was during the cooler months)that fell apart in the kiln even before I
opened it. Those were a little thicker; I'd say just over a 1/16th of an
inch.
Thanks for your interest also Daniel. I hope this will have benefits for
more than just me.
Do you need sharp trimming tools that will not wear out quickly? Contact =
me
for information.=20
Antoinette Badenhorst
105 Westwood Circle
Saltillo MS, 38866
662 869 1651
www.clayandcanvas.com
www.southernartistry.org
=20
=20
=20
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Daniel =
Semler
Sent: Wednesday, June 28, 2006 9:20 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Slow cooling down in electric kiln for fine porcelain.
=20
Hi Antoinette,
=20
OK so this is interesting. If I had to guess I'd go with expansion
mismatch.
The effects of expansion mismatches are accentuated by a number of the
factors
that you mention : extreme thinness of the body, glazing one side only,
and the
inherent expansion mismatch between the clay and glaze. The few tests
I've done
with Southern Ice would indicate that its expansion is much higher than
that of
the porcelain I normally use. We have a crackle celadon that pretty
much didn't
crackle at all on it, though it does on other bodies. It would be very
interesting to know the make up of the glazes.
=20
I am interested by your comment that :
=20
> I found out
> very quickly that I dare not dip-or pour-glaze these pieces. I have to
spray
> glaze. Some of them are thinner than a 1/16th of an inch and it just =
do
not
> tolerate glaze on it.
=20
Did the glaze simply not adhere well or fall off, or was there some =
other
probem ?
=20
One interesting test would be to glaze both inside and out and see =
what
happens.
=20
Another question is, did all the small thin bowls done this way crack
before
the kiln was opened or are some ok ? If so a freeze boil test on one -
with due
caution - would be interesting also. Or perhaps on a decent sized =
fragment.
=20
Thanx
D
=20
_________________________________________________________________________=
___
__
Send postings to clayart@lsv.ceramics.org
=20
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
=20
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Daniel Semler on thu 29 jun 06
Hi Antoinette,
Thank you for this. I would not necessarily take my own word on this I must
say, I'm sure Ron will answer also. However, what you say here confirms some
of my concerns about this clay glaze combination. I will run some numbers of
the glazes tonight or tomorrow to see further what I think. My current
suspicion is that you are close to the limits of this particular combination.
By combination I mean, body, glaze, form, thickness. Firing control may help
you get more out of the kiln, but I am concerned about thermal shocks to the
bowls during use (are they functional ware or decorative ?), and about delayed
effects. That is why I think the freeze/boil stuff may be worth a shot. It may
not be too hard to slightly modify the glazes to pull you back from the edge
here a bit, to give you more latitude.
I had a look at the photos you sent. I very much like the contrast of the
white porcelain and the blue inside. And with the carving I can see why you
don't want breakage. They are lovely pieces. Oh just a thought, are the pieces
that are dunting carved and if so are any breaking along the carving lines ?
Thanx
D
Antoinette Badenhorst on thu 29 jun 06
Hi Daniel, no my work is meant to be for decoration only. I think the =
narrow
foot( and the price!) pushes it outside the range of utilarian use. =
Also:
the ones that you looked at were glazed with barium in the glaze, before =
I
adjusted to strontium. Well, that is typically me; I always push the =
medium
to its limits. I am glad that we can discuss all the possibilities, =
because
as I go deeper into evaluating the work, I realize that it is only the =
open
bowls that I have trouble with. More closed shapes, bottles and teapots =
(too
small for use....and I do NOT glaze them inside) did not show any =
problem of
this kind.It is only on the open bowl shapes that I have this dunting
problem and also only the extreme thin ones. I started using SI a year =
ago
and I have to say that the clay itself is extremely tedious to work =
with!
The pieces were not carved, but washed away in the wax resist method =
(just
as tedious to do). One would think that it should dunt along the =
textural
lines, but it does not.=20
You keep mentioning the freeze/boil effect. I will do that next week to
eliminate that possible problem. At ^ 10 I can tell you, the clay has =
the
appearance as if it is glazed. Another interesting thing that I =
discovered
along the way with SI, is that it do not tolerate much of multiple =
firing.
Two ^10 firings and you have the clay bloating.
I would appreciate it if we can check the glazes for a fit. Since it is =
not
meant to hold food, I did not worry, too much about crackling, but if =
that
is the possible cause of the dunting, I have to eliminate that.
One last remark that I did not mention yet: My kilns are very lightly
packed. Remember these pieces are light and it takes me a week to create =
10
small bowls, so there is lots of air flow around the pieces. I try to =
pack
as evenly as possible, but I even considered that as a possible problem.
Thanks again for your responses. I am very curious to hear what Ron Roy =
has
to say after all this discussion.
Do you need sharp trimming tools that will not wear out quickly? Contact =
me
for information.=20
Antoinette Badenhorst
105 Westwood Circle
Saltillo MS, 38866
662 869 1651
www.clayandcanvas.com
www.southernartistry.org
=20
=20
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Daniel =
Semler
Sent: Thursday, June 29, 2006 10:58 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Slow cooling down in electric kiln for fine porcelain.
Hi Antoinette,
Thank you for this. I would not necessarily take my own word on this I
must
say, I'm sure Ron will answer also. However, what you say here confirms
some
of my concerns about this clay glaze combination. I will run some =
numbers of
the glazes tonight or tomorrow to see further what I think. My current
suspicion is that you are close to the limits of this particular
combination.
By combination I mean, body, glaze, form, thickness. Firing control may =
help
you get more out of the kiln, but I am concerned about thermal shocks to =
the
bowls during use (are they functional ware or decorative ?), and about
delayed
effects. That is why I think the freeze/boil stuff may be worth a shot. =
It
may
not be too hard to slightly modify the glazes to pull you back from the =
edge
here a bit, to give you more latitude.
I had a look at the photos you sent. I very much like the contrast of =
the
white porcelain and the blue inside. And with the carving I can see why =
you
don't want breakage. They are lovely pieces. Oh just a thought, are the
pieces
that are dunting carved and if so are any breaking along the carving =
lines ?
Thanx
D
_________________________________________________________________________=
___
__
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.
Daniel Semler on fri 30 jun 06
Hi Antoinette,
Ok you said something here that rather threw a spanner into my
theory. But ...
I have a backup theory. My first theory was that the glaze mismatch was such
that the glazes were in such compression as to shatter the body because of its
thinness and the cooling characteristics. Having a loosely packed load it
should cool faster.
But then you said "Since it is not meant to hold food, I did not worry, too
much about crackling, ....". Well if they are crazing then they're not in
compression. Theory blown ! But snatching a new theory from the ashes of the
old, it is worth noting that crazed glazes can dramatically weaken the piece
overall. I believe the theory is that the cracks in the glaze penetrate the
body to some degree. So the body is weaker, you have a loose pack which cools
comparatively quickly, and you have thin pieces which in themselves will lose
heat quickly, and the piece cracks. You made one other comment that intrigued
me and which might support my conjectures : "The dunting was in different
"shard-like" shapes and not straight. The pieces also did not fall apart." Do
the shapes look like craze lines might if a piece broke along them ?
Of course the question is, are the glazes crazed, or is it just me ? If they
are then this may not be too far off. The small footed bowl that
cracked in two
might simply have been the foot cooling more slowly that the rest of the bowl
because of the shelf beneath it.
> Another interesting thing that I discovered
> along the way with SI, is that it do not tolerate much of multiple firing.
> Two ^10 firings and you have the clay bloating.
Given how it matures this makes sense.
I looked at the CTE of the glazes assuming potash spar was custer and would
expect the strontium glaze to craze but I'm not sure about the other one, but
it might. Am I close ?
As an aside have you seen the work of Victor Greenaway ?
Thanx
D
Chris Campbell on fri 30 jun 06
Forgive me if my answer is off or late but
I have not read all of the posts and do not
currently have time to ...
I reduced all my cracks, dunts, slumps etc.,
almost completely when I started firing down
after high fires. No other changes at all.
This is with Southern Ice and with usually only
the inside surface glazed.
Chris Campbell - in North Carolina - gone for
a week so will not be able to follow this up for
that time.
Chris Campbell Pottery LLC
9417 Koupela Drive
Raleigh NC 27615-2233
Fine Colored Porcelain since 1989
1-800-652-1008
Fax : 919-676-2062
website: www.ccpottery.com
wholesale : www.wholesalecrafts.com
Ron Roy on mon 3 jul 06
Hi Antoinette,
Excuse my lateness - just got behind - take one day off and it just piles
up around here.
I have calculated both glazes and neither has a low enough expansion to be
what I would call a potential problem.
The strontium glaze has a very high expansion rate - which means it will be
crazing badly.
Keep in mind - that when a glaze crazes it also crakes the clay a little -
along the craze lines. That is the reason pots with crazed glazes on them
weaker than pots with glazes that fit properly. Properly means glazes that
don't craze but the glaze expansion/contraction is not so low that
shivering and dunting are the result.
I can imagine the micro crackes caused by a crazing glazes could be a
factor in cracking of the ware - if the clay was thin enough.
The question now becomes - just how thin are your pots?
Are the pots that are cracking thiner than the ones that are not? Perhaps
you will have to break one that has not cracked? Maybe you can tell - by
weighing cracked and uncracked of the same size?
The other factor which is worth looking into - is your clay properly
vitrified at cone 10 - porcelain usually has a lot of free quartz in it -
if that quartz has not been converted to amorphous slica - your problem may
be directly related to the free quartz still in the body which converts
back to alpha at 573C - if your pots are cracked when you open your kiln.
It could even be a combination of the two factors.
I see also that the Barium glaze has over the 2% lithium that some of us
think is too much - and can cause strange fir problems with some clays.
Perhaps a sub in of spodumene so you can lower the amount of Lithium Carb
would be fruitful?
Let me know if you waht to try that - I would probably need to change some
clay to ball so I need to know what ball clay you have - and perhaps some
bentonite?
This looks like a glaze that could easily deflocculate.
RR
>Hi Daniel, I've considered all the factors that you've mentioned. I have
>several glazed in full, without any dunting.
>
>For one, the pieces are some so thin that they become wet before the glaze
>adhere to it. Also, since I do consider the mismatch of clay and glaze, I am
>particularly careful not to put too much glaze on the pieces.(learned that
>the hard way!)
>
>I still believe the firing process should be much more controlled.I did not
>have enough breakages to discourage me, but too much.....you get my point? I
>spend way too many hours on one piece to end up with breakages.
>
>It would not do harm though to discuss my glazes. (Ron I am sure you are
>interested!) It is no secret; in fact I think the strontium based one is
>after a barium glaze published in the Potters Dictionary. The other one is a
>basic white glaze that I used in South Africa for years and had to adjust
>here in the USA. Be warned, I seldom do things to the book. My recipes is by
>weight and not by %
>
>
>
>White:
>
>
>
>P Feldspar 950
>
>EPK 350
>
>Wollistanite 675
>
>Zircopax 250
>
>Fritt 3195 275 (there is probably better fritts to use, but this is the
>one I started out with when I had to adjust the recipe and I can not
>remember how I came to choose this one)
>
>Also I am wondering about the silica content.
>
>
>
>Strontium Base Glaze:
>
>
>
>Neph. Sye. 2040
>
>P. Feldspar 300
>
>EPK 720
>
>Silica 420
>
>Strontium carb. 1346
>
>Whiting 300
>
>Lith Carb. 180
>
>
>
>As I mentioned, I spay the glaze on and keep it subtle and I fire to ^10.
>What makes it very curious is that not every piece I make that way dunts. I
>had a few that literally fell apart in 2 pieces. I do think that was a glaze
>mismatch, because I pour glazed it, but then I made a series of 9 bowls with
>wide rims, narrow bottoms (I have images if you're interested).The dunting
>was in different "shard-like" shapes and not straight. The pieces also did
>not fall apart. That is what made me think it is a lack of heat control. On
>the Potters council website
>http://www.ceramics.org/potterscouncil/gallery.asp are images of SI pieces
>that I've done successfully over and over, but then I had a few,( I think it
>was during the cooler months)that fell apart in the kiln even before I
>opened it. Those were a little thicker; I'd say just over a 1/16th of an
>inch.
>
>Thanks for your interest also Daniel. I hope this will have benefits for
>more than just me.
>
>Do you need sharp trimming tools that will not wear out quickly? Contact me
>for information.
>
>Antoinette Badenhorst
>
>105 Westwood Circle
>
>Saltillo MS, 38866
>
>662 869 1651
>
>www.clayandcanvas.com
>
>www.southernartistry.org
>
>
>
>
>
>
>
>-----Original Message-----
>From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Daniel Semler
>Sent: Wednesday, June 28, 2006 9:20 PM
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: Slow cooling down in electric kiln for fine porcelain.
>
>
>
>Hi Antoinette,
>
>
>
> OK so this is interesting. If I had to guess I'd go with expansion
>mismatch.
>
>The effects of expansion mismatches are accentuated by a number of the
>factors
>
>that you mention : extreme thinness of the body, glazing one side only,
>
>and the
>
>inherent expansion mismatch between the clay and glaze. The few tests
>
>I've done
>
>with Southern Ice would indicate that its expansion is much higher than
>
>that of
>
>the porcelain I normally use. We have a crackle celadon that pretty
>
>much didn't
>
>crackle at all on it, though it does on other bodies. It would be very
>
>interesting to know the make up of the glazes.
>
>
>
>I am interested by your comment that :
>
>
>
>> I found out
>
>> very quickly that I dare not dip-or pour-glaze these pieces. I have to
>spray
>
>> glaze. Some of them are thinner than a 1/16th of an inch and it just do
>not
>
>> tolerate glaze on it.
>
>
>
> Did the glaze simply not adhere well or fall off, or was there some other
>
>probem ?
>
>
>
> One interesting test would be to glaze both inside and out and see what
>
>happens.
>
>
>
> Another question is, did all the small thin bowls done this way crack
>before
>
>the kiln was opened or are some ok ? If so a freeze boil test on one -
>
>with due
>
>caution - would be interesting also. Or perhaps on a decent sized fragment.
>
>
>
>Thanx
>
>D
>
>
>
>____________________________________________________________________________
>__
>
>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
| |
|
