BaldDragon on tue 31 oct 06
Hello, ask my kids would say, I'm a "n00b". I scanned the archives, but
didn't see anything that fit my situation. I've been doing pottery as a
hobby for about 6 months and finally got a kiln to fire my own stuff
(ancient one). So, here is what I'm running into.
I bisque fire to ^04, and then do a glaze fire to ^06. I'm using Duncan
Concepts underglazes and then use the clear dipping glaze for final coat.
What I've found is that the clear glaze crazes anywhere I don't have an
underglaze. The spots where I have the underglaze are fine. The bisque is
white, so I wasn't underglazing where I wanted white.
What is happening? Is the clear glaze not as resilient on it's own? Do I
have to use an underglaze?
Thanks,
BaldDragon
Hilltop Pottery on tue 31 oct 06
Bald
I don't fire at low temp but could the problem be that you are firing
your bisque at a hotter temperature than your glaze? With high fire
it's the opposite, you fire bisque to cone 06 or 04 and glaze is cones
higher. I use cone 04 for bisque and cone 6 for glaze maybe it's the
same for low fire?
Nancy
BaldDragon wrote:
> Hello, ask my kids would say, I'm a "n00b". I scanned the archives, but
> didn't see anything that fit my situation. I've been doing pottery as a
> hobby for about 6 months and finally got a kiln to fire my own stuff
> (ancient one). So, here is what I'm running into.
>
> I bisque fire to ^04, and then do a glaze fire to ^06. I'm using Duncan
> Concepts underglazes and then use the clear dipping glaze for final coat.
> What I've found is that the clear glaze crazes anywhere I don't have an
> underglaze. The spots where I have the underglaze are fine. The bisque is
> white, so I wasn't underglazing where I wanted white.
>
> What is happening? Is the clear glaze not as resilient on it's own? Do I
> have to use an underglaze?
>
> Thanks,
> BaldDragon
>
> ______________________________________________________________________________
> 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.
>
>
Alan Prestwich on tue 31 oct 06
Nancy,
The directions, and from my research, it says to fire the bisque 2 cones
higher than the glaze. This is to help reduce pinholing where the bisque is
still maturing during the glaze fire.
BaldDragon
On 10/31/06, Hilltop Pottery wrote:
>
> Bald
>
> I don't fire at low temp but could the problem be that you are firing
> your bisque at a hotter temperature than your glaze? With high fire
> it's the opposite, you fire bisque to cone 06 or 04 and glaze is cones
> higher. I use cone 04 for bisque and cone 6 for glaze maybe it's the
> same for low fire?
>
> Nancy
>
> BaldDragon wrote:
> > Hello, ask my kids would say, I'm a "n00b". I scanned the archives, but
> > didn't see anything that fit my situation. I've been doing pottery as a
> > hobby for about 6 months and finally got a kiln to fire my own stuff
> > (ancient one). So, here is what I'm running into.
> >
> > I bisque fire to ^04, and then do a glaze fire to ^06. I'm using Duncan
> > Concepts underglazes and then use the clear dipping glaze for final
> coat.
> > What I've found is that the clear glaze crazes anywhere I don't have an
> > underglaze. The spots where I have the underglaze are fine. The bisque
> is
> > white, so I wasn't underglazing where I wanted white.
> >
> > What is happening? Is the clear glaze not as resilient on it's own? Do I
> > have to use an underglaze?
> >
> > Thanks,
> > BaldDragon
> >
> >
> ______________________________________________________________________________
> > 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.
>
Snail Scott on tue 31 oct 06
>BaldDragon wrote:
>> I bisque fire to ^04, and then do a glaze fire to ^06. I'm using Duncan
>> Concepts underglazes and then use the clear dipping glaze for final coat.
>> What I've found is that the clear glaze crazes anywhere I don't have an
>> underglaze.
At 02:38 PM 10/31/2006 -0500, Nancy wrote:
>I don't fire at low temp but could the problem be that you are firing
>your bisque at a hotter temperature than your glaze?
Nope, BaldDragon has it right - low-fire
work does best when bisqued to a higher
cone than the final glaze firing. Otherwise
outgassing from the clay can fade out some
of the low-fire colorants.
Crazing is almost inevitable with most
low-fire ceramics - it results from a
combination of less-than optimum 'fit'
(compatible coefficient of expansion)
bewtween the clay and the glaze, and
the porous nature of the earthenware.
If bad fit doesn't cause crazing right
away, absorption of moisture will cause
it eventually.
It seems less crazed over the underglaze
for two reasons: first, glaze tends to go
on thinner over underglaze, and a thinner
coating will make finer (less visible)
crazing. It's still there, though. Second,
dark colored areas simply show the crazing
less. It's just harder to see.
You can try a different clay body, to try
and get a better glaze fit than your current
combination, or a different clear glaze, but
eventually even a good-fitting glaze will
craze on earthenware. The more transparent
the glaze, and the thicker the application,
the more visible it will be. Basically, it's
the price you pay for using clear glaze on
unvitrified clay. One reason among many that
most professionals end up using higher-fired
clay with less absorbency (like stoneware),
or using opaque glazes that don't show the
crazing as obviously.
A traditional way to get a white-and-color
design on earthenware is with majolica (or
majolica-style) glazes: using an opaque
white glaze all over, and painting the
designs with colored glazes on top. I
believe several of the commercial
manufacturers make majolica-style glazes
that work pretty well. These can be fired
the same way you are firing your current
work, and it's a technique with a long and
wonderful history.
-Snail
Overall's on tue 31 oct 06
I suspect it's your clay body.
Are you using a low fire clay, or is it stoneware or
porcelain?
Kim in Houston
http://www.houstonpotters.com
--- BaldDragon wrote:
> Hello, ask my kids would say, I'm a "n00b". I
> scanned the archives, but
> didn't see anything that fit my situation. I've been
> doing pottery as a
> hobby for about 6 months and finally got a kiln to
> fire my own stuff
> (ancient one). So, here is what I'm running into.
>
> I bisque fire to ^04, and then do a glaze fire to
> ^06. I'm using Duncan
> Concepts underglazes and then use the clear dipping
> glaze for final coat.
> What I've found is that the clear glaze crazes
> anywhere I don't have an
> underglaze. The spots where I have the underglaze
> are fine. The bisque is
> white, so I wasn't underglazing where I wanted
> white.
>
> What is happening? Is the clear glaze not as
> resilient on it's own? Do I
> have to use an underglaze?
>
> Thanks,
> BaldDragon
>
>
______________________________________________________________________________
> 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.
>
Kim Overall
http://www.houstonpotters.com
Eleanora Eden on tue 31 oct 06
Actually, crazing is not inevitable at all on low fire work, old or new.
I am using in my own kitchen low fire wares that I made in the
'80s and 90's....dishes still craze free for sure. I do know the lore
says this but it isn't necessarily so.
I agree that it must be a clay body that doesn't fit with the glaze, and
the extra flux in the Concepts make the fit okay where they are underneath.
You should go back to your supplier and make sure the clay they are selling
you is compatible with the glaze they are selling you. Perhaps you could tell
this list what you know about the clay you are using.
Eleanora
Crazing is almost inevitable with most
low-fire ceramics - it results from a
combination of less-than optimum 'fit'
(compatible coefficient of expansion)
bewtween the clay and the glaze, and
the porous nature of the earthenware.
If bad fit doesn't cause crazing right
away, absorption of moisture will cause
it eventually.
--
Bellows Falls Vermont
www.eleanoraeden.com
Hilltop Pottery on tue 31 oct 06
Ok so that makes sense. I was having a problem with a Jon's Clear glass
that I purchased from Laguna. It was having fits on me with bubbling
where there was underglaze and being somewhat okay where there wasn't.
And also turning my green stains to puke browns. I called Laguna and
spoke with someone who told me they didn't recommended Jon's Clear for
cone 6 firing even though it is sold as a cone 5-10 glaze. He then
recommended I either use my underglaze on bisque and refire to cone 06
OR paint directly on greenware. He said at cone 6 there wasn't time for
the chemicals in the underglaze to burn out before the kiln shut off and
the glaze started to cool. I don't know if this will work or not but in
my next glaze firing (hopefully tomorrow) my first piece trying this
method isgoing into the kiln. Could you call the manufacturer of the
product and share your concern? I've found most of them are really helpful.
Nancy
Alan Prestwich wrote:
> Nancy,
> The directions, and from my research, it says to fire the bisque 2 cones
> higher than the glaze. This is to help reduce pinholing where the
> bisque is
> still maturing during the glaze fire.
>
> BaldDragon
>
>
>
> On 10/31/06, Hilltop Pottery wrote:
>>
>> Bald
>>
>> I don't fire at low temp but could the problem be that you are firing
>> your bisque at a hotter temperature than your glaze? With high fire
>> it's the opposite, you fire bisque to cone 06 or 04 and glaze is cones
>> higher. I use cone 04 for bisque and cone 6 for glaze maybe it's the
>> same for low fire?
>>
>> Nancy
>>
>> BaldDragon wrote:
>> > Hello, ask my kids would say, I'm a "n00b". I scanned the archives,
>> but
>> > didn't see anything that fit my situation. I've been doing pottery
>> as a
>> > hobby for about 6 months and finally got a kiln to fire my own stuff
>> > (ancient one). So, here is what I'm running into.
>> >
>> > I bisque fire to ^04, and then do a glaze fire to ^06. I'm using
>> Duncan
>> > Concepts underglazes and then use the clear dipping glaze for final
>> coat.
>> > What I've found is that the clear glaze crazes anywhere I don't
>> have an
>> > underglaze. The spots where I have the underglaze are fine. The bisque
>> is
>> > white, so I wasn't underglazing where I wanted white.
>> >
>> > What is happening? Is the clear glaze not as resilient on it's own?
>> Do I
>> > have to use an underglaze?
>> >
>> > Thanks,
>> > BaldDragon
>> >
>> >
>> ______________________________________________________________________________
>>
>> > 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.
>>
>
> ______________________________________________________________________________
>
> 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.
>
Alan on wed 1 nov 06
I'm using Mili Hi Ceramics CT3 clay. It has 9% shrinkage, and their info is
pretty generic.
http://www.milehiceramics.com/claydescriptions.htm
**CT-3 (Cone 06-2)
Our most popular low fire white earthenware.* CT-3 is a smooth, strong,
very plastic, white earthenware clay body that is excellent for school use,
especially elementary age. It is also used for taxidermy clay. Available
with grog for larger sculpture and tiles.
It would be great if glaze manufactures could state the common shrinkage as
well :)
BaldDragon
On 10/31/06, Hilltop Pottery wrote:
>
> Ok so that makes sense. I was having a problem with a Jon's Clear glass
> that I purchased from Laguna. It was having fits on me with bubbling
> where there was underglaze and being somewhat okay where there wasn't.
> And also turning my green stains to puke browns. I called Laguna and
> spoke with someone who told me they didn't recommended Jon's Clear for
> cone 6 firing even though it is sold as a cone 5-10 glaze. He then
> recommended I either use my underglaze on bisque and refire to cone 06
> OR paint directly on greenware. He said at cone 6 there wasn't time for
> the chemicals in the underglaze to burn out before the kiln shut off and
> the glaze started to cool. I don't know if this will work or not but in
> my next glaze firing (hopefully tomorrow) my first piece trying this
> method isgoing into the kiln. Could you call the manufacturer of the
> product and share your concern? I've found most of them are really
> helpful.
>
> Nancy
>
> Alan Prestwich wrote:
> > Nancy,
> > The directions, and from my research, it says to fire the bisque 2 cones
> > higher than the glaze. This is to help reduce pinholing where the
> > bisque is
> > still maturing during the glaze fire.
> >
> > BaldDragon
> >
> >
> >
> > On 10/31/06, Hilltop Pottery wrote:
> >>
> >> Bald
> >>
> >> I don't fire at low temp but could the problem be that you are firing
> >> your bisque at a hotter temperature than your glaze? With high fire
> >> it's the opposite, you fire bisque to cone 06 or 04 and glaze is cones
> >> higher. I use cone 04 for bisque and cone 6 for glaze maybe it's the
> >> same for low fire?
> >>
> >> Nancy
> >>
> >> BaldDragon wrote:
> >> > Hello, ask my kids would say, I'm a "n00b". I scanned the archives,
> >> but
> >> > didn't see anything that fit my situation. I've been doing pottery
> >> as a
> >> > hobby for about 6 months and finally got a kiln to fire my own stuff
> >> > (ancient one). So, here is what I'm running into.
> >> >
> >> > I bisque fire to ^04, and then do a glaze fire to ^06. I'm using
> >> Duncan
> >> > Concepts underglazes and then use the clear dipping glaze for final
> >> coat.
> >> > What I've found is that the clear glaze crazes anywhere I don't
> >> have an
> >> > underglaze. The spots where I have the underglaze are fine. The
> bisque
> >> is
> >> > white, so I wasn't underglazing where I wanted white.
> >> >
> >> > What is happening? Is the clear glaze not as resilient on it's own?
> >> Do I
> >> > have to use an underglaze?
> >> >
> >> > Thanks,
> >> > BaldDragon
> >> >
> >> >
> >>
> ______________________________________________________________________________
> >>
> >> > 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.
> >>
> >
> >
> ______________________________________________________________________________
> >
> > 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.
>
Snail Scott on wed 1 nov 06
At 08:32 PM 10/31/2006 -0400, you wrote:
>Actually, crazing is not inevitable at all on low fire work, old or new.
>I am using in my own kitchen low fire wares that I made in the
>'80s and 90's....dishes still craze free for sure. I do know the lore
>says this but it isn't necessarily so.
I think vitrification has a big role
in this, as well as the clay body
composition. (I was oversimplifying,
before.) Low-fire bodies can still
have greater or lesser degrees of
vitrification, and the more vitrified,
the less they seem to craze.
Talc-based bodies also seem to craze
less.
-Snail
Heather Pedersen on wed 1 nov 06
I use underglaze infrequently, but I have observed that the underglaze will
sometimes melt into the glaze, which could change the properties of the
glaze in that area.
So at a guess, it sounds like your clay and the clear glaze do not have a
good fit, except in places where the underglaze has melted into the glaze a
bit.
An alternate explanation would be that the underglaze is forming a buffer
between the clay and the glaze to reduce the stress between the two. Same
root cause though.
I am assuming that if you fire a piece with only clear glaze, and no
underglaze, the whole thing has crackles?
-= Heather
On Tue, 31 Oct 2006 12:51:57 -0500, BaldDragon wrote:
>Hello, ask my kids would say, I'm a "n00b". I scanned the archives, but
>didn't see anything that fit my situation. I've been doing pottery as a
>hobby for about 6 months and finally got a kiln to fire my own stuff
>(ancient one). So, here is what I'm running into.
>
>I bisque fire to ^04, and then do a glaze fire to ^06. I'm using Duncan
>Concepts underglazes and then use the clear dipping glaze for final coat.
>What I've found is that the clear glaze crazes anywhere I don't have an
>underglaze. The spots where I have the underglaze are fine. The bisque is
>white, so I wasn't underglazing where I wanted white.
>
>What is happening? Is the clear glaze not as resilient on it's own? Do I
>have to use an underglaze?
>
>Thanks,
>BaldDragon
>
>___________________________________________________________________________
___
>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.
Bunny Lemak on wed 1 nov 06
What you are doing sounds correct.
But, you did not tell us how you are firing your ware. The ^04, did you
fire fast, Medium or slow? Same with the glaze firing ^06, fast, Med or
slow?
A few years back they all had to change their formula's and take out most
of the lead in the glazes. Lead in the glaze was great only because it
hid most of these common errors, now they are showing up, but don't
dispare there is a solution to making this work.
Please let me know how you fired both loads, this will help a lot in your
answer.
Crazing usually comes from the first fire - you did not get all the gasses
out, and therefore it will show up in the final produce. No you cannot re-
fire to get rid of the crazing. The piece is now lost, but chalk it up to
experience.
Please let me know. Thanks!
Bunny
Alan on wed 1 nov 06
That's along the lines of what I was thinking. That the underglaze changes
the chemical composition of the dipping glaze. So far everything has had an
underglaze on atleast some of the body. But, from what I've seen (like the
whole inside of a pitcher) everything on straight bisque is has the fine
cracks. I looked real closely at the portion with underglaze and I don't see
any cracks there, but they could be really fine.
No biggy on loosing the piece. It's just a hobby, and right now I'm focusing
mostly on my throwing.
Alan.
On 11/1/06, Heather Pedersen wrote:
>
> I use underglaze infrequently, but I have observed that the underglaze
> will
> sometimes melt into the glaze, which could change the properties of the
> glaze in that area.
> So at a guess, it sounds like your clay and the clear glaze do not have a
> good fit, except in places where the underglaze has melted into the glaze
> a
> bit.
> An alternate explanation would be that the underglaze is forming a buffer
> between the clay and the glaze to reduce the stress between the two. Same
> root cause though.
>
> I am assuming that if you fire a piece with only clear glaze, and no
> underglaze, the whole thing has crackles?
>
> -= Heather
>
> On Tue, 31 Oct 2006 12:51:57 -0500, BaldDragon
> wrote:
>
> >Hello, ask my kids would say, I'm a "n00b". I scanned the archives, but
> >didn't see anything that fit my situation. I've been doing pottery as a
> >hobby for about 6 months and finally got a kiln to fire my own stuff
> >(ancient one). So, here is what I'm running into.
> >
> >I bisque fire to ^04, and then do a glaze fire to ^06. I'm using Duncan
> >Concepts underglazes and then use the clear dipping glaze for final coat.
> >What I've found is that the clear glaze crazes anywhere I don't have an
> >underglaze. The spots where I have the underglaze are fine. The bisque is
> >white, so I wasn't underglazing where I wanted white.
> >
> >What is happening? Is the clear glaze not as resilient on it's own? Do I
> >have to use an underglaze?
> >
> >Thanks,
> >BaldDragon
> >
>
> >___________________________________________________________________________
> ___
> >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.
>
Alan on wed 1 nov 06
Currently, I'm firing for both bisque and glaze the same. I do 1 hr on low
with lid propped open and top hole unplugged, the next 2 hrs are on medium
leaving top propped open and top hole unplugged, then I go to high until the
witness cone is bent correctly. I would assume that is slow...
Alan.
On 11/1/06, Bunny Lemak wrote:
>
> What you are doing sounds correct.
>
> But, you did not tell us how you are firing your ware. The ^04, did you
> fire fast, Medium or slow? Same with the glaze firing ^06, fast, Med or
> slow?
>
> A few years back they all had to change their formula's and take out most
> of the lead in the glazes. Lead in the glaze was great only because it
> hid most of these common errors, now they are showing up, but don't
> dispare there is a solution to making this work.
>
> Please let me know how you fired both loads, this will help a lot in your
> answer.
>
> Crazing usually comes from the first fire - you did not get all the gasses
> out, and therefore it will show up in the final produce. No you cannot
> re-
> fire to get rid of the crazing. The piece is now lost, but chalk it up to
> experience.
>
> Please let me know. Thanks!
> Bunny
>
>
> ______________________________________________________________________________
> 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.
>
Bunny Lemak on wed 1 nov 06
On Wed, 1 Nov 2006 12:12:16 -0700, Alan wrote:
>Currently, I'm firing for both bisque and glaze the same. I do 1 hr on low
>with lid propped open and top hole unplugged, the next 2 hrs are on medium
>leaving top propped open and top hole unplugged, then I go to high until
the
>witness cone is bent correctly. I would assume that is slow...
>
>Alan.
>
>>
Well your firing sounds correct too.
How thick is your glaze? Glaze should be the consistency of milk. You
only need 2-3 coats depending on how heavy/light you glaze.
You may also want to try holding at the end of your ^06 firing for 10-15
minutes.
If all else fails, call Duncan they have a toll free # that is either on
their site or in their catalog.
I personally prefer Mayco products over Duncan, but we buy what we were
taught on.
If you want to contact me off list, please feel free to do so. This is
not a huge problem, we just have to find out what is wrong and correct it.
I have many pieces back from the 1970's and they are not crazed. We will
get to the bottom of this!!
Bunny
tlemak@cox.net
Snail Scott on wed 1 nov 06
At 12:12 PM 11/1/2006 -0700, you wrote:
>Currently, I'm firing for both bisque and glaze the same. I do 1 hr on low
>with lid propped open and top hole unplugged, the next 2 hrs are on medium
>leaving top propped open and top hole unplugged, then I go to high until the
>witness cone is bent correctly. I would assume that is slow...
What's 'slow' depends on how thick your
work is, and what kind of clay body it is.
Personally, I'd spend longer on 'low'
instead of leaving the lid up for 'medium';
that gets pretty uneven - dead cool on
top but pretty hot on the bottom. Keeping
the lid down will keep the temperature
more even, once the moisture has left.
Some time on 'low' with the lid up, then
some with the lid down, then to 'medium'
and then 'high'.
As for firing greenware and low-fire
glaze ware together, that depends on the
glazes. Many can handle it, but some,
especially the cadmium-colored ones, will
tend to burn out if exposed to the
outgassing from greenware. If you aren't
using sensitive glazes, then go ahead and
put it all together, with one warning: If
your clay needs to go to ^04 for optimum
vitrification (like some commercial
bodies), you will have weaker, more
porous clay if you only go to ^06. And
if the glaze is rated for ^06 (like many
commercial ones), it can get too runny
at ^04. And so on.
If you have a clay and glaze that both
optimize at the same temperature and do
not have burnout problems, then you might
as well go ahead and fire together. The
comments above are mainly aimed at the
folks who are using the commercial stuff.
(Though a lot of those so-called ^04
bodies do fine or even better at higher
cones, and many low glazes also are fine
at other cones. Just 'cause the package
says so doesn't make it true. One of my
favorite ^1 clays says ^04 on the bag.)
-Snail
Alan on thu 2 nov 06
I sent an email to Duncan and they agreed with you. I'll try your suggestion
the next time I glaze fire.
From Duncan
"Thank you very much for your e-mail. When you fire your bisque how long do
you fire in low and how long in medium before it goes to high to finish
firing. I think that the problem could be underfired bisque. IN1001 is
lead free and very susceptible to underfired bisque and will craze or get
craters. The Concepts do not have that problem so that is why you are not
getting crazing on the underglaze. When firing your greenware to bisque you
need to fire for 2 hours in low, 2 hours in medium, then switch to high to
finish firing to cone 04. This should take care of the crazing."
Alan.
On 11/1/06, Snail Scott wrote:
>
> At 12:12 PM 11/1/2006 -0700, you wrote:
> >Currently, I'm firing for both bisque and glaze the same. I do 1 hr on
> low
> >with lid propped open and top hole unplugged, the next 2 hrs are on
> medium
> >leaving top propped open and top hole unplugged, then I go to high until
> the
> >witness cone is bent correctly. I would assume that is slow...
>
>
>
> What's 'slow' depends on how thick your
> work is, and what kind of clay body it is.
> Personally, I'd spend longer on 'low'
> instead of leaving the lid up for 'medium';
> that gets pretty uneven - dead cool on
> top but pretty hot on the bottom. Keeping
> the lid down will keep the temperature
> more even, once the moisture has left.
> Some time on 'low' with the lid up, then
> some with the lid down, then to 'medium'
> and then 'high'.
>
> As for firing greenware and low-fire
> glaze ware together, that depends on the
> glazes. Many can handle it, but some,
> especially the cadmium-colored ones, will
> tend to burn out if exposed to the
> outgassing from greenware. If you aren't
> using sensitive glazes, then go ahead and
> put it all together, with one warning: If
> your clay needs to go to ^04 for optimum
> vitrification (like some commercial
> bodies), you will have weaker, more
> porous clay if you only go to ^06. And
> if the glaze is rated for ^06 (like many
> commercial ones), it can get too runny
> at ^04. And so on.
>
> If you have a clay and glaze that both
> optimize at the same temperature and do
> not have burnout problems, then you might
> as well go ahead and fire together. The
> comments above are mainly aimed at the
> folks who are using the commercial stuff.
> (Though a lot of those so-called ^04
> bodies do fine or even better at higher
> cones, and many low glazes also are fine
> at other cones. Just 'cause the package
> says so doesn't make it true. One of my
> favorite ^1 clays says ^04 on the bag.)
>
> -Snail
>
>
> ______________________________________________________________________________
> 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.
>
Sheryl McMonigal on thu 2 nov 06
man is this a subject of irritation for me. I drive total 450 mile round
trip and ask all the appropriate questions about the clays and glazes I buy
at the clay store only to make a bunch of neat stuff to have my glaze fall
off or the clay to crumble with the glaze I put on it. and I try to
investigate thoroughly on laguna's web site as that is mainly the clay that
is available and I usually use their glazes cause I can buy in bulk. a
couple of my latest failures have been with the b3-brown which I bought
1000lbs. of, all the glazes I put on it evidently the glaze is shrinkking
more than the clay. I open up the kiln and all looks cool but when I pick
it up it crumbles in my hands. I want to make tiles from this clay for my
kitchen but am afraid. I need at least a clear on top for my countertops
and this is the only black clay available to me. the other mishap is
crackle glazes flake right of the white clays and the black clay. aaagh.
boy does this piss me off. when I happen back to the store they have no
good answers and I can not return the clay. I've only been at this for a
couple years and do not want to be restricted to blah glazes. most of my
stuff is just ornamental in nature.
sheryl mc.
----- Original Message -----
From: "Alan"
To:
Sent: Wednesday, November 01, 2006 7:46 AM
Subject: Re: Dipping glaze on bare bisque
> I'm using Mili Hi Ceramics CT3 clay. It has 9% shrinkage, and their info
is
> pretty generic.
> http://www.milehiceramics.com/claydescriptions.htm
>
> **CT-3 (Cone 06-2)
> Our most popular low fire white earthenware.* CT-3 is a smooth, strong,
> very plastic, white earthenware clay body that is excellent for school
use,
> especially elementary age. It is also used for taxidermy clay. Available
> with grog for larger sculpture and tiles.
>
> It would be great if glaze manufactures could state the common shrinkage
as
> well :)
>
> BaldDragon
>
>
> On 10/31/06, Hilltop Pottery wrote:
> >
> > Ok so that makes sense. I was having a problem with a Jon's Clear glass
> > that I purchased from Laguna. It was having fits on me with bubbling
> > where there was underglaze and being somewhat okay where there wasn't.
> > And also turning my green stains to puke browns. I called Laguna and
> > spoke with someone who told me they didn't recommended Jon's Clear for
> > cone 6 firing even though it is sold as a cone 5-10 glaze. He then
> > recommended I either use my underglaze on bisque and refire to cone 06
> > OR paint directly on greenware. He said at cone 6 there wasn't time for
> > the chemicals in the underglaze to burn out before the kiln shut off and
> > the glaze started to cool. I don't know if this will work or not but in
> > my next glaze firing (hopefully tomorrow) my first piece trying this
> > method isgoing into the kiln. Could you call the manufacturer of the
> > product and share your concern? I've found most of them are really
> > helpful.
> >
> > Nancy
> >
> > Alan Prestwich wrote:
> > > Nancy,
> > > The directions, and from my research, it says to fire the bisque 2
cones
> > > higher than the glaze. This is to help reduce pinholing where the
> > > bisque is
> > > still maturing during the glaze fire.
> > >
> > > BaldDragon
> > >
> > >
> > >
> > > On 10/31/06, Hilltop Pottery wrote:
> > >>
> > >> Bald
> > >>
> > >> I don't fire at low temp but could the problem be that you are firing
> > >> your bisque at a hotter temperature than your glaze? With high fire
> > >> it's the opposite, you fire bisque to cone 06 or 04 and glaze is
cones
> > >> higher. I use cone 04 for bisque and cone 6 for glaze maybe it's the
> > >> same for low fire?
> > >>
> > >> Nancy
> > >>
> > >> BaldDragon wrote:
> > >> > Hello, ask my kids would say, I'm a "n00b". I scanned the archives,
> > >> but
> > >> > didn't see anything that fit my situation. I've been doing pottery
> > >> as a
> > >> > hobby for about 6 months and finally got a kiln to fire my own
stuff
> > >> > (ancient one). So, here is what I'm running into.
> > >> >
> > >> > I bisque fire to ^04, and then do a glaze fire to ^06. I'm using
> > >> Duncan
> > >> > Concepts underglazes and then use the clear dipping glaze for final
> > >> coat.
> > >> > What I've found is that the clear glaze crazes anywhere I don't
> > >> have an
> > >> > underglaze. The spots where I have the underglaze are fine. The
> > bisque
> > >> is
> > >> > white, so I wasn't underglazing where I wanted white.
> > >> >
> > >> > What is happening? Is the clear glaze not as resilient on it's own?
> > >> Do I
> > >> > have to use an underglaze?
> > >> >
> > >> > Thanks,
> > >> > BaldDragon
> > >> >
> > >> >
> > >>
> >
____________________________________________________________________________
__
> > >>
> > >> > 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.
> > >>
> > >
> > >
> >
____________________________________________________________________________
__
> > >
> > > 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.
> >
>
>
____________________________________________________________________________
__
> 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.
Donald G. Goldsobel on thu 2 nov 06
Sheryl,
Laguna has a tech advisor. Last person in the job I spoke to was JOHN
PACHINI TECH ADVICE-CLAY AND MINERALS.
I don't have an 800# for them-only the local California one. They were very
helpful and can offer glaze adjustments or whatever they feel the problem
may be. They know their products and are generally supportive.
Good luck
Donald
Jon Pacini on thu 2 nov 06
Greetings All----
A couple of things have come up on this thread that need to be addressed.
Jon's Clear is a glaze I developed back in the 70's for a predecessor
company of Laguna's, Westwood Ceramic Supply. It was developed to primarily
fit the throwing porcelains that Westwood made for ^5 and a casting
porcelain at ^6. As it worked out it was a bit Chun-like/cloudy at ^4-5 but
was more transparent from ^6 up to ^10. The thicker it was, the more cloudy,
and the thinner, the more transparent. And this is pretty much what you can
still expect from this particular glaze. If it's bubbling on you, it is
either under fired or the material under the glaze is gassing or both.
B-3 Brown clay is a son of a gun to get a glaze fit on. Particularly if you
are only glazing one side of the ware. The COE of this body is quite High,
7.27x 10-6. The reason for this is the high metallic oxide content used to
make the clay Black. Most stonewares are in the 4-5+ range and many glazes
can be expected to fit most of those bodies. However with B-3 you tend to
get a lot of dunting because of the high COE and the stresses that are
developed when only one side of the ware is glazed with a glaze that does
not come close to fitting it. Your best served to either glaze both sides of
B-3 with the same glaze or not to glaze it at all.
For novice potters who figure that all clays and glazes made by a company
should each fit each other, this is a real problem. All glazes do not fit
all clays, period, exclamation point! Never have--- never will. And for the
most part we here at Laguna do not have a master list of what works with
what. I do have the COE's for all the clays, but because there are so many
glazes and frankly I don't have the staff to do the work, no attempt has
been made to develop a COE chart of them. Maybe someday.
And finally --- before you get real carried away with producing ware ---test
what you have in mind to do. This is something that gets said quite often,
but apparently there are a lot of wannabe potters out there who still don't
do it. There are way to many ways to work with clay to cover all
contingencies in a catalog or website.Test everything under YOUR conditions
before you commit to production. We test all the clays and glazes that we
produce. Every batch of glaze and clay has a number stamped on it and a
Quality Control sheet that follows it through production and testing. And
they do not go out unless they are approved. They work under the conditions
we test them. You have to make sure the products work under the conditions
you use. If you don't, you're going to have problems.
And remember ---things will always go wrong right before a big show or sale
because you are rushed or cutting corners. Take your time, be consistent
with your work habits and your kilns will come out fine. If you don't
believe me, ask somebody else who's been a potter forever like Mel or one of
the many others on the list, and they will explain it to you.
Best regards,
Jon Pacini
Clay Manager
Laguna Clay Co
Snail Scott on thu 2 nov 06
At 09:54 AM 11/2/2006 -0800, you wrote:
>...I want to make tiles from this clay for my
>kitchen but am afraid. I need at least a clear on top for my countertops
>and this is the only black clay available to me...
Black clays - they can be tough to glaze,
all right. Any special reason you want a
clear glaze over black clay, instead of a
black glaze (or a clear glaze over black
slip) over a white or red body?
-Snail
Sheryl McMonigal on thu 2 nov 06
I like the richness of that particalar clay is the #1 reason for chosing
that clay' the texture and plasticity is another reason. I will rub a
reddish orange into the recesses "design" then I will need to have a glaze
overall and I wanted the black of the clay to show thru which is a total
different look from black glaze. also as it is going to be a countertop I
cannot leave the clay unglazed for food contamination issues. I've had clay
and glaze not be a good fit before and usually my glaze will be the one to
show the stress. it is like the clay is extremely brittle after I glaze
fire. i've tried changing cones up and down to no avail. also I've tried
using a thin layer of glaze to some success, also if it is a vessel it does
not like glaze on inside and outside.
thanks for your help snail.
sheryl mc.
----- Original Message -----
From: "Snail Scott"
To:
Sent: Thursday, November 02, 2006 1:23 PM
Subject: Re: Dipping glaze on bare bisque
> At 09:54 AM 11/2/2006 -0800, you wrote:
> >...I want to make tiles from this clay for my
> >kitchen but am afraid. I need at least a clear on top for my countertops
> >and this is the only black clay available to me...
>
>
> Black clays - they can be tough to glaze,
> all right. Any special reason you want a
> clear glaze over black clay, instead of a
> black glaze (or a clear glaze over black
> slip) over a white or red body?
>
> -Snail
>
>
____________________________________________________________________________
__
> 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.
Snail Scott on fri 3 nov 06
At 04:28 PM 11/2/2006 -0800, you wrote:
>I like the richness of that particalar clay is the #1 reason for chosing
>that clay' the texture and plasticity is another reason. I will rub a
>reddish orange into the recesses "design" then I will need to have a glaze
>overall and I wanted the black of the clay to show thru which is a total
>different look from black glaze.
I'd try using a more conventional clay body,
adequately grogged to reduce drying issues
with your flat tiles. A black slip should
be indistinguishable from a black clay body,
and if brushing it on interferes with your
texture, try spraying, or even dipping. A
thin coat should cover adequately without
clogging your texture. If you apply the slip
on greenware, you should be able to do your
orange wipe in your usual way after bisque.
You will have many more possibilities for a
good-fitting, durable glaze by using a more
conventional clay.
Getting good fit on a black clay is a bitch;
it's worth trying other options, even if they
seem like more work up front.
I'd save heavily colored clay bodies like
that one for non-functional work, where the
clay can be left bare. (It IS nice looking.)
-Snail
Russel Fouts on sat 4 nov 06
>> B-3 Brown clay is a son of a gun to get a glaze fit on. Particularly
if you are only glazing one side of the ware. The COE of this body is
quite High, 7.27x 10-6. The reason for this is the high metallic oxide
content used to make the clay Black. Most stonewares are in the 4-5+
range and many glazes can be expected to fit most of those bodies.
However with B-3 you tend to get a lot of dunting because of the high
COE and the stresses that are developed when only one side of the ware
is glazed with a glaze that does not come close to fitting it. Your best
served to either glaze both sides of B-3 with the same glaze or not to
glaze it at all. <<
Just to emphasize Jon's point. I have a wonderful Maiolica glaze from
Matthias Ostermann's book, that when applied too thick or to only one
side (inside or outside) of a pot, can break it to pieces quite smartly.
It's all in knowing your materials.
Russel
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