Marcia Selsor on sat 10 aug 02
You can start by adding 5% bentonite to your glazes. that will help the glaze
shrink with the pieces.
Marcia
Valerie Johnson wrote:
> I have made some sculptures that I am considering once firing b/c I don't
> want to handle them much and risk loss. My books are very thin on advice for
> once firing; tried to search the archives but the site was apparently down
> today.
>
> I understand a very slow start would be needed, but how would a cone 10 glaze
> be altered, if at all? I have once fired a few items and was disapposed in
> the thinness of the glaze in the finished pieces. Are there some basic
> tenets to follow in formulating glazes for once firing? Or do you just glaze
> thickly?
>
> Thanks!
> Valerie Johnson
> Eads, Tennessee
>
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Valerie Johnson on sat 10 aug 02
I have made some sculptures that I am considering once firing b/c I don't
want to handle them much and risk loss. My books are very thin on advice for
once firing; tried to search the archives but the site was apparently down
today.
I understand a very slow start would be needed, but how would a cone 10 glaze
be altered, if at all? I have once fired a few items and was disapposed in
the thinness of the glaze in the finished pieces. Are there some basic
tenets to follow in formulating glazes for once firing? Or do you just glaze
thickly?
Thanks!
Valerie Johnson
Eads, Tennessee
Stephani Stephenson on sun 11 aug 02
Valerie
I once -fire or raw -glaze much of my work.
I apply glaze to bone dry work, but most of the work is 3/4 " thick
it is not thin-walled, delicate stuff.
I sometimes pour or dip pieces, sometimes spray pieces. forms such as
pierced pieces which may not survive dipping or are difficult to handle
while pouring, I spray. also sometimes I paint, using a viscous glaze,
and floating the glaze onto surface.
Glazes are somewhat thicker, more like heavy cream, but certainly
nowhere near yogurt! and of course, glazes are thinned for spraying.
if you have to do a couple of different pours, or handle the piece in
between glaze maneuvers, or move the piece
either do it all together, fairly quickly, right after glazing , or let
the piece sit for 1/2 hour or so to completely dry in between
maneuvers.
Pieces are most susceptible to breaking 5-15 minutes after glazing,
when whatever water has soaked in is at its most saturated level.
If you handle work quickly, the water will not have soaked in ,as
greenware is less porous than bisqueware. If you let it sit, be sure you
let it sit long enough so that the water has evaporated once again.
I personally have less success with getting an even glaze coat when
working with leather hard rather than bone dry clay... but this may be a
technique used by those who work with thinner walled ware. Perhaps
Tony could speak to this.
My glazes have 10-20% clay, EPK, ball clay or Red Art, or a
combination.... also I add 1-3% bentonite. And other glazes contain
gerstley, which seems to keep ingredients suspended and stick to
surface. also I do not fire to cone 10 so am dealing with less shrinkage
I go through first part of firing same rate as If I was firing a
bisque, the rest of the firing as if I were doing a glaze fire!
hope this helps
Stephani Stephenson
Carlsbad CA
Tony Ferguson on sun 11 aug 02
Valerie,
Try applying the glaze while the sculpture is leather hard. Depending on
what kind of texture, whether you want a crawly, crackly texture or a smooth
surface, you will vary your thickness. Whatever you apply when it is
leather hard must be able to shrink with the shrinking body--which will be
much more than if you glaze bone dry which the glaze will not have to shrink
as much. It would be best to do some tests before committing your finer
pieces and letting it be a crap shoot. I would really need to see the
recipes to tell which to alter: ball clay or kaolin or the addition of 2.5
to 5% bentonite. I never have used more than 3% but then you might have an
unsual recipes where more bentonite may be appropriate.
Bentonite will help your glaze stick (it is a very stickly clay) as well as
shrink with the piece. As a general rule of thumb, if you have 15% or more
ball clay in the glaze recipe you should be fine. Sometime all you need to
do is convert the kaolin to ball clay or add bentonite as I suggested. Some
folks add CMC gum or another "sticker" to the glaze and the glaze requires
no further messing around. A method my friend Ernest Miller, a crystalline
porcelain artists uses, is he sprays the glaze on the work. If the glaze
starts to lift or show signs of poor fit, he adds more CMC gum to the
original glaze batch and so on and so on until the sprayed coats stays on
smooth. Good experimentation to you and consider letting me know how it
turns out.
Thank you.
Tony Ferguson
Stoneware, Porcelain, Raku
www.aquariusartgallery.com
218-727-6339
315 N. Lake Ave
Apt 312
Duluth, MN 55806
----- Original Message -----
From: "Valerie Johnson"
To:
Sent: Saturday, August 10, 2002 7:21 PM
Subject: once firing advice needed for glazes
> I have made some sculptures that I am considering once firing b/c I don't
> want to handle them much and risk loss. My books are very thin on advice
for
> once firing; tried to search the archives but the site was apparently down
> today.
>
> I understand a very slow start would be needed, but how would a cone 10
glaze
> be altered, if at all? I have once fired a few items and was disapposed
in
> the thinness of the glaze in the finished pieces. Are there some basic
> tenets to follow in formulating glazes for once firing? Or do you just
glaze
> thickly?
>
> Thanks!
> Valerie Johnson
> Eads, Tennessee
>
>
____________________________________________________________________________
__
> 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 mon 12 aug 02
At 10:21 PM 8/10/02 EDT, you wrote:
>I have made some sculptures that I am considering once firing b/c I don't
>want to handle them much and risk loss...
>I understand a very slow start would be needed, but how would a cone 10 glaze
>be altered, if at all?
Once-firing is just like doing bisque and glaze at the
same time. Start firing exactly as you would for bisque,
then when you've reached bisque temperatures (just red
heat, no need for a specific cone/temp), continue firing
just as you would for a glaze firing 'til done. It will
be a longer firing than either a bisque or a glaze firing
would be alone, but uses less time and fuel than doing
them separately. And, as you observed, it reduces the
handling of the pieces. (That's one of the reasons I
choose to once-fire, when I do.)
The best glazes for once-fire are those containing large
amounts of clay, as this allows the art and the glaze
to move together while drying. It's a great opportunity
for using slip-glazes. (Any recipe containing calcined
clays is also a good contender; just use regular clay
instead.) Many of the glazes you are using on bisque may
be suitable; test them and see. Many glazes do fine on
both greenware and bisque. A little extra bentonite can
help, too. (The final appearance will be very similar.
Any variation will probably have more to do with
application and thickness, since greenware is less absorbent
than bisque.)
I prefer to glaze greenware while still leather-hard, to
avoid the weird problems caused by re-wetting bone-dry
clay. It depends on the clay body, though, how big a
problem it really is.
-Snail
-Snail
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