nori on mon 10 mar 08
Hey, everyone.
one of my studio mates returned from vacation today.
she was talking with her cousin, who is also a potter, about a glaze we
have that crazes.
her cousin suggested that we fire our bisque hotter. that a clay
manufacturer had suggested this to her.
hmmm.
i can't figure out why this would work.
as i understand it, crazing happens because the glaze shrinks more than
the clay during glaze firing. or something close to that!
and i know that my clay body doesn't shrink during bisque firing (thanks
to Dick Aerni for pointing this out... I STILL had to prove it to
myself)... so bisque firing at a hotter temperature wouldn't make the
clay shrink more than zero.
i can see that all other things being equal, the higher-fired bisque
would have a thinner layer of glaze, but why would that lessen crazing?
so... it sounds like a clay legend to me.
for the record, all of us (cousin included) are working with stoneware,
fired to cone 6 oxidation.
the cousin now bisques to cone 04; we bisque to cone 07.
any insight (pardon the glaze pun) would be greatly appreciated.
sabra in much warmer... and less snowy.... rochester ny
--
Clifton, Norwich & Sabra
My pottery cat clay
Our studio crocus clay works
My charity A little effort + no money = a big difference!
sample soap
David Hendley on tue 11 mar 08
Clay Legend. The temperature of the bisque firing, or
even lack of a bisque firing, makes no difference in the fit
of a glaze on the clay.
But, you are right, a very thin coating of glaze could be less
prone to developing noticeable crazing lines.
David Hendley
Maydelle, Texas
david(at)farmpots(dot)com
http://www.farmpots.com
----- Original Message -----
> one of my studio mates returned from vacation today.
> she was talking with her cousin, who is also a potter, about a glaze we
> have that crazes.
> her cousin suggested that we fire our bisque hotter. that a clay
> manufacturer had suggested this to her.
>
> hmmm.
> i can't figure out why this would work.
> as i understand it, crazing happens because the glaze shrinks more than
> the clay during glaze firing. or something close to that!
>
> i can see that all other things being equal, the higher-fired bisque
> would have a thinner layer of glaze, but why would that lessen crazing?
>
> so... it sounds like a clay legend to me.
David Hendley on wed 12 mar 08
Studio potters do not bisque fire to a higher temperature
than the glaze fire - I've never met one who did in all
my years in and around clay. I know that this is sometimes
the procedure in factory settings.
Raising the temperature of the hottest firing clay goes
through will affect glaze fit, but not previous firings to
lower temperatures. For studio potters, this
is the GLAZE firing, not the bisque firing, and this was
the context of the question I was answering.
David Hendley
Maydelle, Texas
david(at)farmpots(dot)com
http://www.farmpots.com
----- Original Message -----
> As I understand it, the higher the bisque temperature the higher the
> shrinkage of the clay (some porcelain bisque firings are to cone 10) - and
> thus less subsequent asorbsion of water. Since the shrinkage of a glaze is
> fixed at a specific temperature (given a temperature ramp), why would the
> temperature of a bisque not affect the crazing potential of the final
> product (glaze on a bisque fired clay)?
>
> Chris
Steve Mills on thu 13 mar 08
As a matter of interest, the High Bisc/Low Glaze is fairly common in the UK with Potters using white earthenware clays.
Due to their composition, these clays need a pretty high firing range; around the 1080 - 1200oC range to complete primary shrinkage, else glaze shivers off due to excessive compression. Consequently bisc is usually around 1120oC, and glaze at any temperature you like after that.
Steve
Bath
UK
----- Original Message ----
From: David Hendley
To: CLAYART@LSV.CERAMICS.ORG
Sent: Thursday, March 13, 2008 4:06:29 AM
Subject: Re: hotter bisque & glaze fit?
Studio potters do not bisque fire to a higher temperature
than the glaze fire - I've never met one who did in all
my years in and around clay. I know that this is sometimes
the procedure in factory settings.
Raising the temperature of the hottest firing clay goes
through will affect glaze fit, but not previous firings to
lower temperatures. For studio potters, this
is the GLAZE firing, not the bisque firing, and this was
the context of the question I was answering.
David Hendley
Maydelle, Texas
david(at)farmpots(dot)com
http://www.farmpots.com
----- Original Message -----
> As I understand it, the higher the bisque temperature the higher the
> shrinkage of the clay (some porcelain bisque firings are to cone 10) - and
> thus less subsequent asorbsion of water. Since the shrinkage of a glaze is
> fixed at a specific temperature (given a temperature ramp), why would the
> temperature of a bisque not affect the crazing potential of the final
> product (glaze on a bisque fired clay)?
>
> Chris
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Beth Spindler on thu 13 mar 08
several potters I know bisque at 03 or 04 and glaze at 06, this is stoneware and earthenware.? I do this as well..sometimes it seems to be too hot for the earthenware as the glaze doesn't cover well...........now I am puzzled.
Beth in VA...still with head reeling about glazes and now these wad thingys????? what the heck are these????
-----Original Message-----
From: Steve Mills
To: CLAYART@LSV.CERAMICS.ORG
Sent: Thu, 13 Mar 2008 5:00 am
Subject: Re: hotter bisque & glaze fit?
As a matter of interest, the High Bisc/Low Glaze is fairly common in the UK with
Potters using white earthenware clays.
Due to their composition, these clays need a pretty high firing range; around
the 1080 - 1200oC range to complete primary shrinkage, else glaze shivers off
due to excessive compression. Consequently bisc is usually around 1120oC, and
glaze at any temperature you like after that.
Steve
Bath
UK
----- Original Message ----
From: David Hendley
To: CLAYART@LSV.CERAMICS.ORG
Sent: Thursday, March 13, 2008 4:06:29 AM
Subject: Re: hotter bisque & glaze fit?
Studio potters do not bisque fire to a higher temperature
than the glaze fire - I've never met one who did in all
my years in and around clay. I know that this is sometimes
the procedure in factory settings.
Raising the temperature of the hottest firing clay goes
through will affect glaze fit, but not previous firings to
lower temperatures. For studio potters, this
is the GLAZE firing, not the bisque firing, and this was
the context of the question I was answering.
David Hendley
Maydelle, Texas
david(at)farmpots(dot)com
http://www.farmpots.com
----- Original Message -----
> As I understand it, the higher the bisque temperature the higher the
> shrinkage of the clay (some porcelain bisque firings are to cone 10) - and
> thus less subsequent asorbsion of water. Since the shrinkage of a glaze is
> fixed at a specific temperature (given a temperature ramp), why would the
> temperature of a bisque not affect the crazing potential of the final
> product (glaze on a bisque fired clay)?
>
> Chris
______________________________________________________________________________
Clayart members may send postings to: clayart@lsv.ceramics.org
You may look at the archives for the list, post messages, change your
subscription settings or unsubscribe/leave the list here: http://www.acers.org/cic/clayart/
Moderator of the list is Mel Jacobson who may be reached at melpots2@visi.com
____________________________________________________________________________________
Never miss a thing. Make Yahoo your home page.
http://www.yahoo.com/r/hs
______________________________________________________________________________
Clayart members may send postings to: clayart@lsv.ceramics.org
You may look at the archives for the list, post messages, change your
subscription settings or unsubscribe/leave the list here: http://www.acers.org/cic/clayart/
Moderator of the list is Mel Jacobson who may be reached at melpots2@visi.com
Eleanora Eden on fri 14 mar 08
As far as I know most earthenware work is done this way.
I bisc fire at ^04 and glaze fire at ^06.
Eleanora
>As a matter of interest, the High Bisc/Low Glaze is fairly common in the UK with Potters using white earthenware clays.
>Due to their composition, these clays need a pretty high firing range; around the 1080 - 1200oC range to complete primary shrinkage, else glaze shivers off due to excessive compression. Consequently bisc is usually around 1120oC, and glaze at any temperature you like after that.
>
>Steve
>Bath
>UK
>
>
>
>----- Original Message ----
>From: David Hendley
>To: CLAYART@LSV.CERAMICS.ORG
>Sent: Thursday, March 13, 2008 4:06:29 AM
>Subject: Re: hotter bisque & glaze fit?
>
>Studio potters do not bisque fire to a higher temperature
>than the glaze fire - I've never met one who did in all
>my years in and around clay. I know that this is sometimes
>the procedure in factory settings.
--
Bellows Falls Vermont
www.eleanoraeden.com
Lee on fri 14 mar 08
On Thu, Mar 13, 2008 at 11:58 PM, Eleanora Eden wrote=
:
> As far as I know most earthenware work is done this way.
> I bisc fire at ^04 and glaze fire at ^06.
>
I am thinking about single fire earthenware to cone1 in soda. Will do
impression and inlay along with hakeme. Bought a 50lb bag of smooth
lowfire white to use as slip. Might be interesting to try it as a flashing
slip in highfire wood. Hope to do a test.
--=20
Lee, a Mashiko potter in Minneapolis
http://mashikopots.blogspot.com/
"Ta tIr na n-=F3g ar chul an tI=97tIr dlainn trina ch=E9ile"=97that is, "Th=
e land of
eternal youth is behind the house, a beautiful land fluent within itself."
-- John O'Donohue
Snail Scott on fri 14 mar 08
>
> From: David Hendley
> Sent: Thursday, March 13, 2008 4:06:29 AM
> Studio potters do not bisque fire to a higher temperature
> than the glaze fire - I've never met one who did in all
> my years in and around clay...Raising the temperature of the hottest
> firing clay goes
> through will affect glaze fit, but not previous firings to
> lower temperatures.
I do, sometimes, but I'm not a potter. I occasionally
want to have the look of high-fired bare clay with
localized areas of a low-fire glaze, so I high-fire,
then apply the glaze and re-fire lower.
David is right, though, in regards to the original
question. Let's set aside the 'bisque' and 'glaze firing'
terminology, which is really misleading. What counts
is how high the highest firing went, relative to the
maturation temperature of the clay and coatings.
-Snail
Daphne Vega on sat 29 mar 08
I've been meaning to pose this question here for some time, this seems
like a good topic to put it in.
Why are low fire clays bisqued to 04 then fired to 05 (at least that is
the manufacturing recommended firing instructions)? In all the studios I
learned in all the clay was bisqued to 08, then fired to their proper
glaze temp. I have always worked in the cone 5-10 range but I don't
remember the low fire people having any trouble. I have looked through my
books and briefly online but haven't found anything specifically
discussing this detail. I now work in a small community studio and go back
and forth with the other instructor about bisquing temp, she fires to cone
04 and my pots come out of the glaze firing looking weak because I am
expecting them to take the glaze the same as when they are fired (when I
do it) to cone 08. Am I compromising the everyone's 05 work when I bisque
to 08?
Thanks in advance for all help with this-
Daphne
William & Susan Schran User on sat 29 mar 08
On 3/29/08 6:19 PM, "Daphne Vega" wrote:
> Why are low fire clays bisqued to 04 then fired to 05 (at least that is
> the manufacturing recommended firing instructions)? In all the studios I
> learned in all the clay was bisqued to 08, then fired to their proper
> glaze temp.
Firing the bisque a bit hotter strengthens the clay a bit more and may
assist in preventing crazing of the glazes.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
John Britt on sun 30 mar 08
Daphne,
One reason some people fire the bisque higher at low fire is so that all
the gases are out before the glaze firing. For example, majolica folks
like to bisque to 04 and fire to 05 so that they don't get pinholes.
Bisque firing higher will reduce the absorption rate of your piece so you
may have to mix your glazes thicker in order to get the same glaze
thickness with the same dipping time.
John Britt
Ron Roy on mon 31 mar 08
Hi Daphne,
I have always bisqued to 04 - for several reasons - just take some of the
water off your glazes to make them thicker.
08 for bisque can be problematic - it's hard to get all the organics out
and - larger ware can dunt in the bisque firing because the clay is too
weak to take the cooling stresses.
RR
>I've been meaning to pose this question here for some time, this seems
>like a good topic to put it in.
>Why are low fire clays bisqued to 04 then fired to 05 (at least that is
>the manufacturing recommended firing instructions)? In all the studios I
>learned in all the clay was bisqued to 08, then fired to their proper
>glaze temp. I have always worked in the cone 5-10 range but I don't
>remember the low fire people having any trouble. I have looked through my
>books and briefly online but haven't found anything specifically
>discussing this detail. I now work in a small community studio and go back
>and forth with the other instructor about bisquing temp, she fires to cone
>04 and my pots come out of the glaze firing looking weak because I am
>expecting them to take the glaze the same as when they are fired (when I
>do it) to cone 08. Am I compromising the everyone's 05 work when I bisque
>to 08?
>
>Thanks in advance for all help with this-
>
>Daphne
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Brant Palley NMCLAY.com on thu 3 apr 08
In Low Fire ceramics using commercial glazes we fire bisque to cone 04 and
the glazes are fired 2 cones lower to cone 06.
The clays we make for low fire have a particular expansion that matches
the glazes when properly fired. If you fire hotter you will experience
shivering, lower you get crazing.
If you bisque lower than the glaze fire you will get blistering and
bubbling in the glaze caused by new gasses being forced out of the clay
through the now molten glaze.
Hope this helps.
Brant Palley
www.nmclay.com
Eleanora Eden on wed 9 apr 08
Also the commercial underglazes for lowfire want to be bisqued at ^04 before
glazing at ^06. All the instructions indicate that. If they aren't bisqued at a
higher temperature than the glaze they will move, and also crawling.
But even if you aren't using any underglazes, the clay won't be adequately
vitrified after a ^08 bisque. There will probably be more warping as well as
pinholing, problems with glaze fit, everything the other posts have covered.
Eleanora
>In Low Fire ceramics using commercial glazes we fire bisque to cone 04 and
>the glazes are fired 2 cones lower to cone 06.
>
>The clays we make for low fire have a particular expansion that matches
>the glazes when properly fired. If you fire hotter you will experience
>shivering, lower you get crazing.
>
>If you bisque lower than the glaze fire you will get blistering and
>bubbling in the glaze caused by new gasses being forced out of the clay
>through the now molten glaze.
>
>Hope this helps.
>
>Brant Palley
>www.nmclay.com
--
Bellows Falls Vermont
www.eleanoraeden.com
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