Dale Cochoy on wed 30 jan 02
I've been thinking about the solutions I got for reducing foot assy
firing/drying cracks on lg. slab builts. Everyone who responded mentioned
rolling a slab of same clay to dry, bisque and high fire on to shrink at
same rate. Some mentioned also putting sand/grog under those lg. slabs .
I just rolled out a couple 1/4" thick slabs for two big pots I already made
and are drying. I am drying them on paper or plastic sheets on my hospital
trays. I'll try these slabs with bisque and glaze fire, but, I'm wondering.
This takes ( wastes) a lot of clay. Has anyone tried making 4 tiles a
little bigger than the feet to set them on? Wouldn't this actually be about
the same process in shrinking/moving and much less clay? A small tile should
shrink the same % as big tile if made of same clay as pot? Or, am I missing
something.?
I'll be testing these two theories in about a week.
Regards,
Dale
Terrance Lazaroff on thu 31 jan 02
Dale;
Your thinking may work providing you grog the shelf under the four tiles.
The most important drying time is probably in the first few hours of the
construction. It is here that we must be sure that the feet can move with
the shrinkage.
I suggest you try both methods and see what works for you.
Terrance
----- Original Message -----
From: "Dale Cochoy"
To:
Sent: Wednesday, January 30, 2002 6:56 PM
Subject: Foot cracks problem, another idea
> I've been thinking about the solutions I got for reducing foot assy
> firing/drying cracks on lg. slab builts. Everyone who responded mentioned
> rolling a slab of same clay to dry, bisque and high fire on to shrink at
> same rate. Some mentioned also putting sand/grog under those lg. slabs
.
> I just rolled out a couple 1/4" thick slabs for two big pots I already
made
> and are drying. I am drying them on paper or plastic sheets on my
hospital
> trays. I'll try these slabs with bisque and glaze fire, but, I'm
wondering.
> This takes ( wastes) a lot of clay. Has anyone tried making 4 tiles a
> little bigger than the feet to set them on? Wouldn't this actually be
about
> the same process in shrinking/moving and much less clay? A small tile
should
> shrink the same % as big tile if made of same clay as pot? Or, am I
missing
> something.?
> I'll be testing these two theories in about a week.
> Regards,
> Dale
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
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>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Marsh Pottery on thu 31 jan 02
Try drying bigger leather pots on wire shelving, or old wire sink bottom
things, raised up on stilts so air can circulate underneath.
Also try firing the big, very heavy pots on several, evenly spaced posts.
I have found that my thick porcelain pet memorials don't crack when I do
that. They did crack when I used just sand. Their own weight was causing
the cracking - They pushed out / expanded in the heat and were too heavy to
move in as the clay shrank again.
Marsha
Marsh Pottery Studio
Check me out at:
http://www.marshpottery.com
Dale Cochoy on thu 31 jan 02
Thanks Terrance.
Yes, I dry very slowly, especially first week using big plastic bags over
work.
As I said, I have two lg. slabs now rolled for two big pots made the other
day. I'm making another tonite so I think I'll try the 4-tiles thing w/ fine
grog under. Unless, of course, someone has tried that and it doesn't work
like the larger slab trick.
Dale
----- Original Message -----
From: "Terrance Lazaroff"
Subject: Re: Foot cracks problem, another idea
> Dale;
>
> Your thinking may work providing you grog the shelf under the four tiles.
>
> The most important drying time is probably in the first few hours of the
> construction. It is here that we must be sure that the feet can move with
> the shrinkage.
>
> I suggest you try both methods and see what works for you.
>
> Terrance
> ----- Original Message -----
> From: "Dale Cochoy"
> To:
> Sent: Wednesday, January 30, 2002 6:56 PM
> Subject: Foot cracks problem, another idea
>
>
> > I've been thinking about the solutions I got for reducing foot assy
> > firing/drying cracks on lg. slab builts. Everyone who responded
mentioned
> > rolling a slab of same clay to dry, bisque and high fire on to shrink at
> > same rate. Some mentioned also putting sand/grog under those lg.
slabs
> .
> > I just rolled out a couple 1/4" thick slabs for two big pots I already
> made
> > and are drying. I am drying them on paper or plastic sheets on my
> hospital
> > trays. I'll try these slabs with bisque and glaze fire, but, I'm
> wondering.
> > This takes ( wastes) a lot of clay. Has anyone tried making 4 tiles a
> > little bigger than the feet to set them on? Wouldn't this actually be
> about
> > the same process in shrinking/moving and much less clay? A small tile
> should
> > shrink the same % as big tile if made of same clay as pot? Or, am I
> missing
> > something.?
> > I'll be testing these two theories in about a week.
> > Regards,
> > Dale
Susan on thu 31 jan 02
----- Original Message -----
> I am drying them on paper or plastic sheets on my
> hospital
>> trays.
perhaps that is the problem. You don't get uniform drying...thus causing
cracking. I would not dry on plastic sheets/plastic hospital trays...the
underneath side will dry slower than the top.
potterybydai on thu 31 jan 02
Dale - I think the idea of the whole-slab thing is that the shrinkage takes
place BETWEEN the feet, thus causing a drag on the feet as they try to move
inwards during the firing. If you put the feet on their own little pads,
they wouldn't help with that---unless you had lots of placer sand underneath
for the pads to slide on. I think it would depend on how heavy your piece
was; if it was very heavy the separate pads probably wouldn't work. On the
other hand, I'm not very good at physics, I don't think
Dai in Kelowna, BC
potterybydai@shaw.ca
Life is 10% what happens to you, and 90% how you
respond to it.
Dale Cochoy on thu 31 jan 02
----- Original Message -----
From: "Susan"
Subject: Re: Foot cracks problem, another idea
> ----- Original Message -----
> > I am drying them on paper or plastic sheets on my
> > hospital
> >> trays.
>
> perhaps that is the problem. You don't get uniform drying...thus causing
> cracking. I would not dry on plastic sheets/plastic hospital trays...the
> underneath side will dry slower than the top.
Susan,
Funny, several people said the cure was drying on plastic ( bags) or paper.
I do ( have done) both , but that , the paper or plastic, (usually paper) is
on the trays. BUT, I flip the trays several times a day, so drying IS even.
I love that putting a tray on top of piece the "flipping" trays/piece when
I get up to about 30 lbs! So far so good.:>)
My problems with foot cracks are definitely from firing.
Dale
claybair on fri 1 feb 02
What about drying the pot upside down part of the time?
Re: firing,
I just had a thought..... what if the pot was supported by some slabs
between the feet during bisque firing and stilts during glaze firing? This
would put no pressure on the feet.
Warping??? Dunno
Gayle Bair
Bainbridge Island, WA
http://claybair.com
Terrance Lazaroff on fri 1 feb 02
I think we are missing the point here. I believe the problem is feet. That
means the base of the pot is not touching the support. Thus plastic allows
the shrinkage to occur because the two layers of plastic will slid as the
pot shrinks.
I am unsure about how it would work with a base touching the support.
However on paper it has always worked for me.
Terrance
----- Original Message -----
From: "Dale Cochoy"
To:
Sent: Thursday, January 31, 2002 7:08 PM
Subject: Re: Foot cracks problem, another idea
> ----- Original Message -----
> From: "Susan"
> Subject: Re: Foot cracks problem, another idea
>
>
> > ----- Original Message -----
> > > I am drying them on paper or plastic sheets on my
> > > hospital
> > >> trays.
> >
> > perhaps that is the problem. You don't get uniform drying...thus causing
> > cracking. I would not dry on plastic sheets/plastic hospital trays...the
> > underneath side will dry slower than the top.
>
> Susan,
> Funny, several people said the cure was drying on plastic ( bags) or
paper.
> I do ( have done) both , but that , the paper or plastic, (usually paper)
is
> on the trays. BUT, I flip the trays several times a day, so drying IS
even.
> I love that putting a tray on top of piece the "flipping" trays/piece
when
> I get up to about 30 lbs! So far so good.:>)
> My problems with foot cracks are definitely from firing.
> Dale
>
>
____________________________________________________________________________
__
> 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.
Dale Cochoy on fri 1 feb 02
I gotcha Terrance. I understood that, and there is no friction betwen the
two sheets. I just made a large pot last nite and that's exactly what I'm
doing today. it is resting on two trash bags and covered losely by a third.
I had commonly used paper on my trays until pots were pretty well dried
before.
Dale
----- Original Message -----
From: "Terrance Lazaroff"
To:
Sent: Friday, February 01, 2002 12:57 AM
Subject: Re: Foot cracks problem, another idea
> I think we are missing the point here. I believe the problem is feet.
That
> means the base of the pot is not touching the support. Thus plastic
allows
> the shrinkage to occur because the two layers of plastic will slid as the
> pot shrinks.
>
> I am unsure about how it would work with a base touching the support.
> However on paper it has always worked for me.
>
> Terrance
Cindy Strnad on fri 1 feb 02
Hello, Dale.
If you have uneven drying, this can cause foot (or
other) cracks, and they may not show up until
after the glaze firing. As much trouble as we put
into drying these large pieces, we can still have
uneven drying. If you encase the piece totally in
a couple of plastic bags, you can still have
uneven drying. It's frustrating. I've been reading
Vince's book and I think I'll build myself a moist
drying cabinet. It sounds like this could work,
and I think it's worth a try. But it's vital to
keep the stress off during firing as well. The
clay cookie idea seems like an excellent one both
for stress-free drying and firing. I would go with
the whole cookie, though, and make sure there's
room for air to pass between the piece you're
firing and the cookie. Let's keep one-another
informed.
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
cindy@earthen-vessels-pottery.com
http://www.earthen-vessels-pottery.com
Dale Cochoy on sat 2 feb 02
----- Original Message -----
From: "claybair"
Subject: Re: Foot cracks problem, another idea
> What about drying the pot upside down part of the time?
I do that, at least once a day, usually more.
>
> Re: firing,
> I just had a thought..... what if the pot was supported by some slabs
> between the feet during bisque firing and stilts during glaze firing? This
> would put no pressure on the feet.
> Warping??? Dunno
> Gayle Bair
I won't fire anything on stilts anymore. To much stuff warped that way. Even
slightly and it's "Landfill Fodder".
Dale
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