Katharine Beisner on fri 14 nov 03
Dear Ceramists,
I've just completed a coiled sculpture, 34" tall and 24" wide. The base =
and bottom walls are almost 3/4" thick, but mostly the walls are between =
1/2"- 3/8" thick. It was constructed with a high fire sculptural clay =
body including sand.
It's the largest piece I've ever built and I could use some advice on =
how to fire it.
* single fire vs. bisque?
Currently I'm planning to single fire it - I could bisque it in the gas =
kiln, but so far most advice has been to do a single firing.
* glazing green?
Here's where I really need help. I'd like to use high fire glazes, but =
I've been advised that it's dangerous to glaze green and I should =
consider slips and stains instead. I guess that putting the glaze on =
the piece could melt the greenware and stains are just more potent and =
can be applied without adding as much moisture. How dangerous is =
glazing green? What if the glaze is sprayed on, is that safer?
* super slow firing?
I am planning to follow the sculptural firing pattern described here =
http://nersp.nerdc.ufl.edu/~nan/tech7.html=20
Any advise on these subjects or on firing and glazing large pieces in =
general would be much appreciated.
Thanks,
Katharine Beisner
Austin, Texas
Snail Scott on sat 15 nov 03
At 07:14 AM 11/14/03 -0600, you wrote:
>I've just completed a coiled sculpture...
>single fire vs. bisque?
The reasons to bisque, in my opinion, are to make
the work non-water-soluble, so the glazing process
won't harm surface or details, to make the work
durable so it won't be as easily broken during
interim storage or the glazing process, and to
allow the use of glazes that fit poorly on green
clay. If none of these factors is significant in
your case, go ahead and single-fire it.
>* glazing green?
>Here's where I really need help. I'd like to use high fire glazes, but
I've been advised that it's dangerous to glaze green and I should consider
slips and stains instead. I guess that putting the glaze on the piece
could melt the greenware and stains are just more potent and can be applied
without adding as much moisture.
Phooey! (I find that it's the opposite, actually.)
There's no real difference between slips and glazes,
in terms of water content, but most applications of
stains will require more water for even application.
A lot does depend on your claybody, though, and your
form. Gritty clay is more likely to reabsorb water
from the glaze than a smooth clay. This is only a
real hazard if you have thin extremities or delicate
carving, though.
The best way to glaze green is to do it while the
piece is still stiff-leather-hard. In this state,
it will be its sturdiest, AND absorb the least water.
Glazes with a high clay content work best, but
most glazes do just fine on greenware.
>* super slow firing?
It doesn't need to be super-slow, unless it's super-
thick. Just fire as slowly as a normal bisque until
red heat is reached, then kick it up as fast as a
normal glaze firing. It's really just that simple.
-Snail
Stephani Stephenson on sat 15 nov 03
Katharine wrote:
"I've just completed a coiled sculpture, 34" tall and 24" wide. The base
and
bottom walls are almost 3/4" thick, but mostly the walls are between 1/2"-
3/8" thick. It was constructed with a high fire sculptural clay body
including sand......* single fire vs. bisque?"
HI Katharine
With a large piece, the shrinkage is much more noticeable. That +-10% ,
becomes quite a factor.
A large piece will literally need to 'move' in the kiln as it shrinks,
so you will need to think about how to allow it to do so,
in order to prevent cracking caused by part of the piece getting hung
up on the kiln shelf. So tip # 1 is to put a nice bed of grog down
on the shelf. Grog will act as a layer of 'ball bearings'
so that the base of the piece can contract as it is fired.
I can't advise as to single fire or bisque, as a lot of this is your choice and it
can be done either way.
However I would probably steer to doing a bisque on this first large piece ,
unless it is very difficult to load and handle and you absolutely do not want to
load and fire it a second time.
If the piece is well made and of a good clay body appropriate for this size sculpture
it should easily be able to withstand a bisque then a glaze fire.
I also say this because it sounds like you haven't single fired before, using glazes.
If you do want to try it I would suggest experimenting with the technique on some smaller
pieces first. Glazes are absorbed differently in raw v. bisque applications.
Glazes don't 'melt' the raw clay but they do make it slightly more vulnerable for a time..
generally about 15-20 minutes, while the water in the glaze is absorbed into the clay,
so you need to let a piece dry again after application, before you handle it again.
In general, you cannot handle a piece the same way you handle a bisque piece during glazing
...it is just a matter of timing and experience. The shape and weight of the piece determines
how you handle it. You can spray glazes onto a piece to be single fired, and this is definitely
a good option for larger pieces ... but again I would advise doing some
test pieces to see how your glazes respond to the raw clay application...
Glazing a large bisque piece can still be a challenge,
especially if you are use to dipping and pouring.
Still , handling a bisque piece is a bit more forgiving. also you have options such as applying
then washing off glaze, leaving glaze in the crevices of the coils and allowing bare clay
to show through on outer part of the coil, spraying, etc.
The only other thing I would add is that your glazes may look and act differently on
a large piece. The way they run, the way they look and behave on a large expanse... a
charming glossy glaze on a small pot can look garish on a large one, unevenness in glaze application
can show up to a greater degree .If you have a vertical drop of 2-3 feet your glaze
may run more...I have seen large pots where the glaze all ends up at the bottom of the pot, or on
the kiln shelf...so give the glaze 'room to run'. select a glaze that will not run,
and think about how you will protect your kiln shelve or kiln bottom
in the event that glazes do run.
Conversely the dynamic nature of
glazes moving, interacting on a large piece can be nice,
as can be flashing on the piece from the fire..
sincerely
Stephani Stephenson
steph@alchemiestudio.com
Tony Ferguson on sat 15 nov 03
One can glaze at the leather or bone dry stage. Only in the case of rubbing
in a glaze and the sponging it off to leave it in depressions or some other
very unusual method of glazing requires a bisque. Everybody is freaked out
about single firing. Don't freak until you've learned from someone who
knows what is going on.
The majority of glazing processes do not harm the surface and do not require
a bisque--most of us have learned the institutional way as the only way or
inherited knowledge about the glazing process which is limited without
knowledge of the traditional way of firing. Biquing is as new to clay
artists as computers are to the modern age in terms of ceramic history.
Bisquing is a convenience, a waste of fuel and your time. If you were to
learn to single fire, looking at what you create over your life time, you
would make more work and develop faster. Your timeline would be
accelerated.
If you are careful in glazing and storing, you will not break the work.
Most glazes, Linda Blossom will attest to this with her tile work as well as
many others, do not require any changes made to them other than adding
something to them to make them stick better to the surface such as CMC or
VeegumT. Any glaze with 15% ball clay usually does not require any
adjustments. The only way to know is to test because it depends on the
claybody. This is why I said spray the glaze--you almost can never go wrong
spraying a glaze on green ware unless you oversaturate a specific area on
the work. It is not a no-brainer--it does require developed skill, but it
is not unaccessable to anyone who works in clay. It require effort and
intent and can produce results not attainable from a bisque piece.
In terms of the speed of the firing--it all depends on moisture content of
the piece, thickness of the clay wall--difference in variation of wall
thickness through the entire piece--its also a mass thing--heating up a
scultpure is different than heating up a load of pots and kiln furnature--I
would not fire according to the same schedule--go a bit slower, why risk all
those hours of work. Every subsequent scultpure, reduce the time a bit to
see how fast you can go. If you don't care about this piece, than fire as
usual and see if you can pull it off--you may be surprised at the results.
Test test test like anything else. Good glazing and firing and to you.
Thank you.
Tony Ferguson (who out of necessity packs up a kiln load of greenware
pottery and sculpture and hauls it 2.5 hours away to be wadded outside and
loaded into the anagama). Am I NUTS????????
On Lake Superior, where the sky meets the Lake
Custom & Manufactured Kiln Design
Stoneware, Porcelain, Raku and more
by Coleman, Ferguson, Winchester...
http://www.aquariusartgallery.com
218-727-6339
315 N. Lake Ave
Apt 312
Duluth, MN 55806
----- Original Message -----
From: "Snail Scott"
To:
Sent: Saturday, November 15, 2003 11:27 AM
Subject: Re: firing a BIG piece
> At 07:14 AM 11/14/03 -0600, you wrote:
> >I've just completed a coiled sculpture...
> >single fire vs. bisque?
>
>
> The reasons to bisque, in my opinion, are to make
> the work non-water-soluble, so the glazing process
> won't harm surface or details, to make the work
> durable so it won't be as easily broken during
> interim storage or the glazing process, and to
> allow the use of glazes that fit poorly on green
> clay. If none of these factors is significant in
> your case, go ahead and single-fire it.
>
>
> >* glazing green?
> >Here's where I really need help. I'd like to use high fire glazes, but
> I've been advised that it's dangerous to glaze green and I should consider
> slips and stains instead. I guess that putting the glaze on the piece
> could melt the greenware and stains are just more potent and can be
applied
> without adding as much moisture.
>
>
> Phooey! (I find that it's the opposite, actually.)
> There's no real difference between slips and glazes,
> in terms of water content, but most applications of
> stains will require more water for even application.
>
> A lot does depend on your claybody, though, and your
> form. Gritty clay is more likely to reabsorb water
> from the glaze than a smooth clay. This is only a
> real hazard if you have thin extremities or delicate
> carving, though.
>
> The best way to glaze green is to do it while the
> piece is still stiff-leather-hard. In this state,
> it will be its sturdiest, AND absorb the least water.
> Glazes with a high clay content work best, but
> most glazes do just fine on greenware.
>
>
> >* super slow firing?
>
> It doesn't need to be super-slow, unless it's super-
> thick. Just fire as slowly as a normal bisque until
> red heat is reached, then kick it up as fast as a
> normal glaze firing. It's really just that simple.
>
> -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.
>
Tony Ferguson on sat 15 nov 03
Katharine,
Spray your glaze on. Be careful not to get it too wet--let it dry in
between coats for extra insurance. You could bisque if you want to.
Fire slowly whatever you do and don't open the kiln for at least a few
days--slow cool. 3 or 4 days is better or until its room temperature.
Thank you.
Tony Ferguson
On Lake Superior, where the sky meets the Lake
Custom & Manufactured Kiln Design
Stoneware, Porcelain, Raku and more
by Coleman, Ferguson, Winchester...
http://www.aquariusartgallery.com
218-727-6339
315 N. Lake Ave
Apt 312
Duluth, MN 55806
----- Original Message -----
From: "Katharine Beisner"
To:
Sent: Friday, November 14, 2003 7:14 AM
Subject: firing a BIG piece
Dear Ceramists,
I've just completed a coiled sculpture, 34" tall and 24" wide. The base and
bottom walls are almost 3/4" thick, but mostly the walls are between 1/2"-
3/8" thick. It was constructed with a high fire sculptural clay body
including sand.
It's the largest piece I've ever built and I could use some advice on how to
fire it.
* single fire vs. bisque?
Currently I'm planning to single fire it - I could bisque it in the gas
kiln, but so far most advice has been to do a single firing.
* glazing green?
Here's where I really need help. I'd like to use high fire glazes, but I've
been advised that it's dangerous to glaze green and I should consider slips
and stains instead. I guess that putting the glaze on the piece could melt
the greenware and stains are just more potent and can be applied without
adding as much moisture. How dangerous is glazing green? What if the glaze
is sprayed on, is that safer?
* super slow firing?
I am planning to follow the sculptural firing pattern described here
http://nersp.nerdc.ufl.edu/~nan/tech7.html
Any advise on these subjects or on firing and glazing large pieces in
general would be much appreciated.
Thanks,
Katharine Beisner
Austin, Texas
____________________________________________________________________________
__
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.
| |
|
