Dawn Christensen on mon 18 nov 02
Hi
The slabs I have been making ended up being 16 inches to start and I
have been drying them between drywall. I am flipping them day and night to
fresh drywall and opening them for extended time frames during the day. I
have laid plastic strips around the entire edge so they dried from the inside
out. My question now is to fire vertical or horizontal. I have been told
that people who do plates fire vertically. I have done dinner plates and
always did them horizontally. Cone? I was thinking, 05? I will smoke these
pieces before I draw and paint. Any suggestions or ideas. Thank you for
your answers and thoughts on the subject. Dawn
Saultman on tue 19 nov 02
on 11/18/02 7:35 PM, Dawn Christensen at DCHRis6788@AOL.COM wrote:
Hi Dawn,
I do 18" circular plaques. Tried firing them vertical. They warped.
I suggest firing them flat. I also spread silica sand on the kiln shelves
lightly so that as the large flat pieces shrink in the firing they don't
crack by pulling themselves apart due to shrinkage drag. Drywall sounds
interesting but in time drywall will warp, become quite wet and begin to
mildew. I let my slabs set on a sheet of newspaper for a day or two (I use
plastic on the edges too) then when firm enough to move place them on drying
racks. (keep using the plastic for the edges) I went to a used appliance
store and bought large stainless refrigerator shelves for $6 each.
Dan Saultman
Detroit
> Hi
> The slabs I have been making ended up being 16 inches to start and I
> have been drying them between drywall. I am flipping them day and night to
> fresh drywall and opening them for extended time frames during the day. I
> have laid plastic strips around the entire edge so they dried from the inside
> out. My question now is to fire vertical or horizontal. I have been told
> that people who do plates fire vertically. I have done dinner plates and
> always did them horizontally. Cone? I was thinking, 05? I will smoke these
> pieces before I draw and paint. Any suggestions or ideas. Thank you for
> your answers and thoughts on the subject. Dawn
>
Dale Duncan on fri 23 apr 04
Greetings Everyone....It's been a very long time since I've posted to =
the list, so an introduction is in order. My name is Dale Duncan,...Live =
in South Carolina and have been working in clay off and on since 1972. =
I've learned so much from the list over the years and I've decided its =
time to come out of "lurk mode" and be an active member. =20
To start things off I have a question that I hope some of you can help =
with. Next week, I'm going to fire some large textured paperclay slabs, =
11 x 14 in size. and about 1/2 thick...I have some concerns about =
cracking and warping. Those of you that fire large slabs, How are you =
stacking them in the kiln? I vaguely recall someone standing them on =
their edge and leaning them against the kiln wall....Does stacking this =
way cause the slab to bow in the middle? I have room to lay them flat =
on the kiln shelf but have heard of major cracking taking place in the =
middle of the slab. Any firing suggestions will be greatly =
appreciated......
Best Wishes ....Dale Duncan
Carolyn Bronowski on fri 23 apr 04
Hi--I put grog on my self and lay the large slabs flat, then I fire real
slow. Hope this helps. Carolyn
-----Original Message-----
From: Dale Duncan [mailto:duncan13@CETLINK.NET]
Sent: Friday, April 23, 2004 6:29 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Firing Large Slabs
Paul Gerhold on fri 23 apr 04
Dale,
Lay them flat on a shelf with a thin layer of silica or dry builders sand
underneath if you are primarily worried about warping, If your main concern is
cracking you are better off firing them as vertical as possible to equalize the
heat on both sides.
Paul
Dave Finkelnburg on fri 23 apr 04
Duncan,
Whether the slabs are glazed will have some bearing on how you fire
them.
I like standing large, unglazed, flat pieces as vertically as possible,
say between two stacks of kiln shelves. The more vertical, the less bow,
provided you don't overfire the clay body.
An option is to extrude coils or cut strips of slab about 1/4-inch to
1/2-inch or so diameter and lay the coils or strips out on the shelf about 1
to 2-inches apart, then set the slab on those. That way they allow the slab
to heat and cool fairly uniformly, because heat can get at the whole slab at
once, and leave at once. The kiln shelf keeps the bottom of the slab hot,
or cold, while the top is responding faster to the kiln temperature, so that
creates the problems you have heard about. The strips, if dipped in
alumina, will not stick to the shelf so they allow the slab to shrink, too.
Good luck with your project!
Dave Finkelnburg in Idaho
----- Original Message -----
From: "Dale Duncan"
Sent: Friday, April 23, 2004 7:29 AM
I'm going to fire some large textured paperclay slabs, 11 x 14 in size.
and about 1/2 thick...I have some concerns about cracking and warping.
Karen Sullivan on sun 25 apr 04
It is an interesting process to
learn rules...and then go through
the process of breaking those rules....
The resulting wisdom is what makes
one's judgement and skill have value...
experience
So...a rule...clay moves when it
is fired to cone 10...and therefore
you need to design the form architecturally
to survive the fire...temperature...
Think of steel beam construction...
they are formed into the shape of an
H with right angles....the right angle
is the structural part of the beam that
maintains the straight shape...
so...
in constructing ceramic forms that will
be exposed to high temperature there
are forces on the clay that warp the form...
nothing happens much at bisque temps...
so you don't know how effective the construction
is until the last firing...
So...I noticed a couple of problems with your
response to the advice you have been given...
Your slabs should either be fired flat on
alumina or sand so they float...without a part of
the slab sticking to a drop of glaze on the shelf and
sticking...then shrinking and pulling causing a crack...
Or loaded vertically...so the pressure of the weight
is stacked in a straight line...I have found problems
with this strategy at high temps...
I made a large slab...then was stupid to lean clay
bars against the slab...what I got was a slab in
the shape of a "C"...not what I wanted...The pressure on
the slab folded the form...
So...do tests...
I go with the float technique...
you can lay alumina on a shelf...then comb through
with a trowel...the trowel used for mastic in setting
tile floors...so it has grooves...with grooves in the
alumina you will allow heat to reach the bottom...
best of luck
bamboo karen
wayneinkeywest on fri 30 apr 04
Susan:
You can still do the half shelf the same way...
just follow the perimeter of whatever shelf you're using.
The trick with using half shelves, of course, is not to
have any one piece sit on (span) two of them. If you
have to do so, because of the size of the piece, I
recommend building up a "thicker" layer of the alumina,
and planning and placing pieces carefully onto the
shelf/shelves, and not moving it afterward (prior to firing).
After the firing, it's an easy matter to vacuum
up the kiln, even as you unload. One tip...if you
have access to, or own one of those "dustbuster"
style hand vacuums, and use it "clean", you can
recycle and re-use the alumina. That's what I do,
because I'm a cheap bastard, er, because my
supplier is so far away :>)
Best Regards,
Wayne Seidl
Key West, Florida, USA
North America, Terra
Latitude 81.8, Longitude 24.4
Elevation 3.1 feet (1m)
----- Original Message -----
From: "Susan Fox-Hirschmann" >
<< A "dam" if you will, of clay wadding such as one can find the
recipe
> for in the archives placed around the edges of the shelf on which
> you spread the alumina will usually keep it confined, if you're
> doing the entire shelf. >>
>
>
> yeah, I get it, but it is the 1/2 shelves, where I see there might
be a
> problem of alumina eking its way to the pieces beneath...any ideas
here?
> Thanks for you help.
> You clayart people are the BEST!
> sincerely
> Susan
> Annandale, VA
> Where latitude and longitude are outta reach,
> just know it as 20 mi from the crazy seat of power in this
country, D.C.
Susan Fox-Hirschmann on fri 30 apr 04
In a message dated 4/25/2004 1:00:55 PM Eastern Daylight Time,
xkwinnies@EARTHLINK.NET writes:
<< I go with the float technique...
you can lay alumina on a shelf...then comb through
with a trowel...the trowel used for mastic in setting
tile floors...so it has grooves...with grooves in the
alumina you will allow heat to reach the bottom... >>
I will be doing just this in the next month...with of all things...porcelain.
My concern here is that none of the alumina "migrates" between shelves to
become
a part of the glazed piece beneath. How do you keep that from happening?
Susan
Annandale, VA
Susan Fox Hirschmann
Art Pottery
please visit http://www.silverhawk.com/ex99/hirschmann
wayneinkeywest on fri 30 apr 04
Susan:
A "dam" if you will, of clay wadding such as one can find the recipe
for in the archives placed around the edges of the shelf on which
you spread the alumina will usually keep it confined, if you're
doing the entire shelf.
Or, (like me), you can just be damn careful about sprinkling the
alumina ONLY where you want it. I use an old parmesan cheese
shaker, and shake carefully. Remove the shelves only after
unloading the pots and spraying lightly with water to "hold" the
powder, and do so carefully as well. A good misting with a spray
bottle is usually sufficient to "stick" the powder long enough to
get the shelf out of the kiln. If you fire with a vent (I do not)
you might want to use the dam method.
Not sure how much air flow there is with a vent.
Hope that helps,
Wayne Seidl
Key West, Florida, USA
North America, Terra
Latitude 81.8, Longitude 24.4
Elevation 3.1 feet (1m)
> In a message dated 4/25/2004 1:00:55 PM Eastern Daylight Time,
> xkwinnies@EARTHLINK.NET writes:
>
> << I go with the float technique...
> you can lay alumina on a shelf...then comb through
> with a trowel...the trowel used for mastic in setting
> tile floors...so it has grooves...with grooves in the
> alumina you will allow heat to reach the bottom... >>
>
>
> I will be doing just this in the next month...with of all
things...porcelain.
> My concern here is that none of the alumina "migrates" between
shelves to
> become
> a part of the glazed piece beneath. How do you keep that from
happening?
> Susan
> Annandale, VA
Susan Fox-Hirschmann on fri 30 apr 04
In a message dated 4/30/2004 5:24:18 PM Eastern Daylight Time,
wayneinkeywest@BELLSOUTH.NET writes:
<< A "dam" if you will, of clay wadding such as one can find the recipe
for in the archives placed around the edges of the shelf on which
you spread the alumina will usually keep it confined, if you're
doing the entire shelf. >>
yeah, I get it, but it is the 1/2 shelves, where I see there might be a
problem of alumina eking its way to the pieces beneath...any ideas here?
Thanks for you help.
You clayart people are the BEST!
sincerely
Susan
Annandale, VA
Where latitude and longitude are outta reach,
just know it as 20 mi from the crazy seat of power in this country, D.C.
Susan Fox-Hirschmann on sat 1 may 04
Hi!
Yes, I am doing 1/2 shelves and yes every piece will span two shelves....
What kind of alumina do you buy?
Thanks for your help!
I am designing and creating a porcelain (and handmade paper) wall mosaic that
measures (finished size)----8 ft. wide by 6 feet high! It is challenging,
fun, and taking tons of time....but hell it is also paying the bills.
Warm regards,
Susan
Annandale, VA
wayneinkeywest on sun 2 may 04
Susan:
At the risk of incurring the wrath of those who know "more betterer"
:>) I just use the alumina hydrate that I buy for glazes.
BTW, I forgot to mention that I do not use the alumina (hydrate) for
glazes after using it in the kiln. Don't rightly know why, I just
keep it in reserve for use as "shelf liner" over and over.
Does anyone on the list use alumina oxide?
Hope that helps,
Wayne Seidl
Key West, Florida, USA
North America, Terra
Latitude 81.8, Longitude 24.4
Elevation 3.1 feet (1m)
----- Original Message -----
From: "Susan Fox-Hirschmann"
To:
Sent: Saturday, May 01, 2004 8:21 PM
Subject: Re: firing large slabs
> Hi!
> Yes, I am doing 1/2 shelves and yes every piece will span two
shelves....
> What kind of alumina do you buy?
> Thanks for your help!
> I am designing and creating a porcelain (and handmade paper) wall
mosaic that
> measures (finished size)----8 ft. wide by 6 feet high! It is
challenging,
> fun, and taking tons of time....but hell it is also paying the
bills.
> Warm regards,
> Susan
> Annandale, VA
>
>
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>
Lee Love on sun 2 may 04
What I use under large flat platters is nukabai, ricehull ash. I
recall someone here mentioning that it is used in America as sweeping
compound. Ricehull ash is primarily silica. My teacher used it
on the floor of the yohen chamber in his noborigama and I got the idea
from his use.
--
in Mashiko, Japan http://mashiko.org
http://potters.blogspot.com/ Commentary On Pottery
Eleanora Eden on sun 13 jun 04
>Hi Dale and all,
Hope your slabs went well......I was saving this thread till I had time to
go through it and it occurs to me that one point was not mentioned: when I
fire large platters or larger slabs I do it flat but I build a wall around
it like sort of a saggar so that the heat gets to the piece more
indirectly. Seems to help alot.
Also am reminded that I learned from a Ron Roy post a long time ago to
put my large flat stuff only in the top of the kiln so it won't cool too
quickly.
Since I started practicing these two steps I have had much better success
rate.
Eleanora
>
>
>To start things off I have a question that I hope some of you can help
>with. Next week, I'm going to fire some large textured paperclay
>slabs, 11 x 14 in size. and about 1/2 thick...I have some concerns about
>cracking and warping. Those of you that fire large slabs, How are you
>stacking them in the kiln? I vaguely recall someone standing them on their
>edge and leaning them against the kiln wall....Does stacking this way
>cause the slab to bow in the middle? I have room to lay them flat on the
>kiln shelf but have heard of major cracking taking place in the middle of
>the slab. Any firing suggestions will be greatly appreciated......
>Best Wishes ....Dale Duncan
>
>______________________________________________________________________________
>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.
Deborah Thuman on wed 20 feb 08
I've done that a few times. I cut out my slab. I put a piece of
newspaper on a board, put the slab on the board, put a piece of
newspaper over the slab, and put a board on top. It's important to dry
this slab slowly - always a fun trick when you live in a desert like I
do. I've had some very flat slabs fired to ^10.
Deb
http://debthumansblog.blogspot.com/
stephani stephenson on thu 21 feb 08
whether the original inquiry was with regard to paper
clay or regular slabs:
large slabs generally dry and fire wonderfully on
edge...with exception,possibly ,of slabs that are
thick and heavy yet have thin, fragile edges, and even
fragile edged slabs do OK if they are lightweight
throughout...
so it is worth bisque firing them this way even if you
don't glaze fire them this way....you can even get
away with light glaze coat firing pieces this way....
depending also on temp , thickness, nature of clay,
etc, of course (and all the usual disclaimers about
testing this yourself...)
often they don't even need much support, and even if
they do , they can be supported on either side with
kiln brick, shelves, etc.... think firing them like
pieces of bread in a loaf...standing upright....
also reduces that problem of having to have a kiln
shelf which can accommodate that big green slab
properly.
so this would be my first suggestion
if glazing and you need to fire them flat, try
supporting them on
clay supports...i roll out a thin slab then sllice
the slab into strips and support the piece on the
strips...have also seen people use coils and even
balls of clay...using a very open bodied clay...piece
is placed on the
strips,coils or balls while they are wet, right on the
kiln shelf...
use a clay which is not vitreous at the temp you fire
to, a good sculpture body, cheaper than alumina wads,
or use alumina variations if need be...
i like this method as well, though it seems more labor
intensive, strips can be reused and the piece is not
resting directly on the shelf... sometimes i even make
gutters in the edge strips if I am edge glazing.
or let the piece overhang abit , and if the glaze
forms a little glaze drip on the edge of the slab, cut
it off with a tile saw afterwards... elevating the
piece saves on glaze drips on shelve as well, when
edge glazing low flat pieces so saves on kiln shelf
clean up .
also using the clay strips reduces the surface contact
of piece with the shelf and the accompanying
drag..clay strips shring with the slab...
and
allows even heating top and bottom,
unlike coating shelf with silica sand, which i also do
,or use to do.... reduces problem of sand falling onto
glazed work below, even though you are as careful as
you can be,
It is pretty problem free, unless perhaps you are
using a clay that
is quite thin and prone to slumping if not supported
every square millimeter.....
Stephani Stephenson
http://www.revivaltileworks.com
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