Barbrox@aol.com on wed 29 jan 97
Dear Ron
I appreciate your taking the time to respond to my problem. I believe that
you are correct regarding what will happen to my re-fires as I have indeed
tried this and the results have truly been worse. What I am still having some
problems understanding is why previous use of the same clay and the same
glaze worked just fine. (I did just buy a new batch of the glaze.) As I await
the arrival of my new Skutt 1027 complete with Envirovent and automatic
controls, can I assume that this system will control the fire as you
described? Well, I suppose that I will try firing a bisque load again. P.S. I
do not have an element out.Thanks again- Barbara
Gordana Ricijas on thu 7 feb 02
We have problem with blisters after inglaze decor
firing at 1260-1300°C (cone 8/10). The atmosphere in
the kiln is oxidation.
We produce high-fired hotel porcelain. Temperature of
our glaze kiln is 1360°C (cone 12/13), oxidation and
reduction atmosphere.
Characteristic of glaze:
- sintering 1170°C
- softening 1180°C
- 1/2 sphere 1290°C
- fusion 1310°C
What do you sugest us to solve this problem?
__________________________________________________
Do You Yahoo!?
Send FREE Valentine eCards with Yahoo! Greetings!
http://greetings.yahoo.com
Gordana Ricijas on mon 4 mar 02
Hi!
I found a glaze recipe on internet with wollastonite:
Recipe:
20,5 Kaolin
26,5 Silica
27,0 Custer feldspar
23,5 Wollastonite
2,5 Zinc Oxide
Add:
0,5 Soda
I didn't use ZnO, I use higher silica. Kiln: gass kiln ox. and reduction, 1360°C.
I have a big problem with wollastonite. It settled down so I have to mix the slurry strong.
Do any of you have similar experience? What do you sugest to do?
It is interesting that blisters after inglaze decor firing at 1270°C appear only on plates, on the bottom of plates (not on cups and bowls), so we have to fire most of decors at 1300°C instead at lower temperature. This blisters look like a craters. When we refired plate with blisters in decor kiln, some blisters disepear.
If it is problem in glaze recipe, why blisters don't appear on cups and bowls? What do you think?
---------------------------------
Do You Yahoo!?
Yahoo! Sports - Sign up for Fantasy Baseball
Cindy Strnad on mon 4 mar 02
Dear Gordana,
Blisters can be caused when gasses and trapped air move upward from the body,
and then through the glaze. If the glaze is thick, the blisters will be worse.
Make sure you do not apply the glaze more thickly on the plates than on the
bowls and cups. If a pottery piece has thicker walls, the glaze will go on more
thickly when you apply it to the pot. This may be the problem with your plates.
Are they thicker than your cups and bowls?
To get rid of blisters: Soak the kiln at top temperature and cool very slowly--
OR: Fire and cool quickly so that the air and gasses do not have time to collect
and rise through the glaze.
Apply glazes more thinly
Fire to a higher bisque temperature. This may help to burn off gasses in the
clay. You could also soak the bisque load at top temperature to give gasses more
time to escape.
Wollastonite is a good and reliable material, but it is inconvenient to use. If
you are using wollastonite, you must sieve or strain your glazes. Once you have
done this, the wollastonite (by itself) will give you no more problems.
Sometimes other chemical reactions may cause crystals to grow in your glaze. If
this happens, you will need to sieve the glaze again. I use an 80 mesh sieve.
You will need a fine sieve, but I do not think you will need one as fine as 80
mesh.
Best wishes,
=====================================
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
cindy@earthen-vessels-pottery.com
http://www.earthen-vessels-pottery.com
CM Critique discussion forum
http://www.earthen-vessels-pottery.com/toforum.html
MJ on mon 15 nov 10
Hello - I just finished a cone 6 firing using the schedule in MC6G book.
Some of the glazes came out quite good, and others had some blistering. A
couple of the glazes were actually Amaco or Laguna glazes rated to cone
5. I had used them previously at cone 5 and just did not like the results,
so decided to test them at cone 6 using the MC6G firing schedule. There wa=
s
a fair amount of blistering on those glazes so my guess is that they cannot
handle going higher than cone 5. I would like to understand blistering mor=
e
as to what causes it and ways to avoid it. Also, if you get blistering, is
there a way to refire to correct the problem?
Thanks in advance for any help on this. MJ
ronnie beezer on tue 16 nov 10
Hi Ron,
I read MJ's post this morning and it so happens that the exact thing happen=
ed to
me this last firing. I also use Laguna glazes and I just bought a beautiful
Amaco glaze for cone 5. I have an electronic Skutt kiln and since I don't r=
eally
know how to use ramp firing I just press cone 5 at medium speed and that'=
s it.
I also used witness cones on every shelf and they bent perfectly to cone 5.=
The
plates that I used the Amaco glaze on blistered all over but the rest of th=
e
pots didn't. I had previously tested the glaze on test tiles and there was =
no
blistering or pin holes. What is very strange is that two days later the ar=
eas
on the plates that had the blisters became smooth (no blisters)but did have
some pinholes. I would appreciate it if you can shed some light on this and=
what
I can do to prevent it from happening again.
Thank you,
Ronnie
________________________________
From: Ron Roy
To: Clayart@LSV.CERAMICS.ORG
Sent: Tue, November 16, 2010 2:30:22 PM
Subject: Re: blisters
Hi MJ,
There are different reasons for blistering - some are related to the
glaze formulation but it can also be the clay.
If clay is being overfired it will start to breakdown and produce
gases. Because this happens at the end of a firing - when glazes are
sealed over - the escaping gas from the overfired clay can produce
blistering.
Most glazes go through bubbling stages - if a firing is stopped during
one of those episodes - pin holes, bubbles and broken blisters can
result.
Sometimes the cure is to fire lower or higher or just add a long enough soa=
k.
My favorite cure is to let the final temperature drop 50C (100F) and
hold for a period of time (start at 15 Min). This gives the glaze a
chance to heal over but stops the gases being generated that are
causing the problem.
The best way to cure the problem is to reformulate the glaze or - if
it's the clay - use another body that is more suited to your glaze
temperature.
Can I assume it was not any of the MC6G's that blistered and that you
are using cones to monitor your end temperature?
It would also be helpful to know if the problem happens more in one
place in your kiln and if you can fire with cones on each shelf so we
know what temperature you are getting to in all parts of the kiln.
I can send instructions on how to test your clay to see if that is the
problem.
RR
Quoting MJ :
> Hello - I just finished a cone 6 firing using the schedule in MC6G book.
> Some of the glazes came out quite good, and others had some blistering. A
> couple of the glazes were actually Amaco or Laguna glazes rated to cone
> 5. I had used them previously at cone 5 and just did not like the result=
s,
> so decided to test them at cone 6 using the MC6G firing schedule. There =
was
> a fair amount of blistering on those glazes so my guess is that they cann=
ot
> handle going higher than cone 5. I would like to understand blistering m=
ore
> as to what causes it and ways to avoid it. Also, if you get blistering, =
is
> there a way to refire to correct the problem?
>
> Thanks in advance for any help on this. MJ
>
Ron Roy on tue 16 nov 10
Hi MJ,
There are different reasons for blistering - some are related to the
glaze formulation but it can also be the clay.
If clay is being overfired it will start to breakdown and produce
gases. Because this happens at the end of a firing - when glazes are
sealed over - the escaping gas from the overfired clay can produce
blistering.
Most glazes go through bubbling stages - if a firing is stopped during
one of those episodes - pin holes, bubbles and broken blisters can
result.
Sometimes the cure is to fire lower or higher or just add a long enough soa=
k.
My favorite cure is to let the final temperature drop 50C (100F) and
hold for a period of time (start at 15 Min). This gives the glaze a
chance to heal over but stops the gases being generated that are
causing the problem.
The best way to cure the problem is to reformulate the glaze or - if
it's the clay - use another body that is more suited to your glaze
temperature.
Can I assume it was not any of the MC6G's that blistered and that you
are using cones to monitor your end temperature?
It would also be helpful to know if the problem happens more in one
place in your kiln and if you can fire with cones on each shelf so we
know what temperature you are getting to in all parts of the kiln.
I can send instructions on how to test your clay to see if that is the
problem.
RR
Quoting MJ :
> Hello - I just finished a cone 6 firing using the schedule in MC6G book.
> Some of the glazes came out quite good, and others had some blistering. A
> couple of the glazes were actually Amaco or Laguna glazes rated to cone
> 5. I had used them previously at cone 5 and just did not like the result=
s,
> so decided to test them at cone 6 using the MC6G firing schedule. There =
was
> a fair amount of blistering on those glazes so my guess is that they cann=
ot
> handle going higher than cone 5. I would like to understand blistering m=
ore
> as to what causes it and ways to avoid it. Also, if you get blistering, =
is
> there a way to refire to correct the problem?
>
> Thanks in advance for any help on this. MJ
>
Ron Roy on wed 17 nov 10
Hi Ronnie,
You say the blisters disappeared? You mean there is no trace of them
at all? I cannot even imagine that happening - were there any flakes
of glaze around?
It is possible that blisters could form on a flat surface rather than
a vertical one - some glazes rely on gravity to help heal over
imperfections.
I recommend you read your manual that came with your controller and
learn to program your own firings - that way you can slowdown the
heating rate - especially near the end of your firings - which might
solve the problem.
There are many on this list who can help you with programing - just ask.
RR
Quoting ronnie beezer :
> Hi Ron,
>
> I read MJ's post this morning and it so happens that the exact thing
> happened to
> me this last firing. I also use Laguna glazes and I just bought a beautif=
ul
> Amaco glaze for cone 5. I have an electronic Skutt kiln and since I
> don't really
> know how to use ramp firing I just press cone 5 at medium speed
> and that's it.
> I also used witness cones on every shelf and they bent perfectly to
> cone 5. The
> plates that I used the Amaco glaze on blistered all over but the rest of =
the
> pots didn't. I had previously tested the glaze on test tiles and there wa=
s no
> blistering or pin holes. What is very strange is that two days later
> the areas
> on the plates that had the blisters became smooth (no blisters)but did ha=
ve
> some pinholes. I would appreciate it if you can shed some light on
> this and what
> I can do to prevent it from happening again.
>
>
> Thank you,
> Ronnie
>
>
>
>
> ________________________________
> From: Ron Roy
> To: Clayart@LSV.CERAMICS.ORG
> Sent: Tue, November 16, 2010 2:30:22 PM
> Subject: Re: blisters
>
> Hi MJ,
>
> There are different reasons for blistering - some are related to the
> glaze formulation but it can also be the clay.
>
> If clay is being overfired it will start to breakdown and produce
> gases. Because this happens at the end of a firing - when glazes are
> sealed over - the escaping gas from the overfired clay can produce
> blistering.
>
> Most glazes go through bubbling stages - if a firing is stopped during
> one of those episodes - pin holes, bubbles and broken blisters can
> result.
>
> Sometimes the cure is to fire lower or higher or just add a long enough s=
oak.
>
> My favorite cure is to let the final temperature drop 50C (100F) and
> hold for a period of time (start at 15 Min). This gives the glaze a
> chance to heal over but stops the gases being generated that are
> causing the problem.
>
> The best way to cure the problem is to reformulate the glaze or - if
> it's the clay - use another body that is more suited to your glaze
> temperature.
>
> Can I assume it was not any of the MC6G's that blistered and that you
> are using cones to monitor your end temperature?
>
> It would also be helpful to know if the problem happens more in one
> place in your kiln and if you can fire with cones on each shelf so we
> know what temperature you are getting to in all parts of the kiln.
>
> I can send instructions on how to test your clay to see if that is the
> problem.
>
> RR
>
>
> Quoting MJ :
>
>> Hello - I just finished a cone 6 firing using the schedule in MC6G book.
>> Some of the glazes came out quite good, and others had some blistering. =
A
>> couple of the glazes were actually Amaco or Laguna glazes rated to cone
>> 5. I had used them previously at cone 5 and just did not like the resul=
ts,
>> so decided to test them at cone 6 using the MC6G firing schedule. There=
was
>> a fair amount of blistering on those glazes so my guess is that they can=
not
>> handle going higher than cone 5. I would like to understand blistering =
more
>> as to what causes it and ways to avoid it. Also, if you get blistering,=
is
>> there a way to refire to correct the problem?
>>
>> Thanks in advance for any help on this. MJ
>>
>
>
>
>
| |
|
