Randy McCall on wed 16 jun 04
I have been having some s cracks in small salad bowls. I am trying some =
suggestions I got out of the archives on compression. I also have made =
a drying rack with plastic sheeting. =20
Small bowls here in SC have been drying in about two days, but I was =
having a lot of cracks. Over 50%.
I have set up a drying rack and pieces now are drying very slowly, but =
humidity now is much higher due to the fact it is raining every =
afternoon.
Is there any specific drying time that I should be shooting for to help =
with the cracks? Using Highwater Desert Buff.
Antoinette Badenhorst on wed 16 jun 04
Randy, S-cracks is not caused by drying, but by the way that you
compress your clay after opening. If you throw off the hump you have to
make extra sure to compact the clay in the bottom. After you opened up
your clay, run a few times on a radius in the bottom of your bowl and
make sure that there is no water to weaken the clay. Straight cracks are
caused by water and s-cracks are because of clay not compressed enough.
Make sure that the walls and bottom of your pots are of even thickness.
V-cracks on the rim of a pot are caused by uneven drying (take note not
fast drying) Hope this helps you.
Nice evening.
Antoinette Badenhorst
105 Westwood Circle
Saltillo MS
38866
662 869 1651
www.clayandcanvas.com
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Randy
McCall
Sent: Wednesday, June 16, 2004 6:18 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Drying salad bowls??????????
I have been having some s cracks in small salad bowls. I am trying some
suggestions I got out of the archives on compression. I also have made
a drying rack with plastic sheeting.
Small bowls here in SC have been drying in about two days, but I was
having a lot of cracks. Over 50%.
I have set up a drying rack and pieces now are drying very slowly, but
humidity now is much higher due to the fact it is raining every
afternoon.
Is there any specific drying time that I should be shooting for to help
with the cracks? Using Highwater Desert Buff.
________________________________________________________________________
______
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.
Jennifer Boyer on wed 16 jun 04
Compression is indeed one cause of s cracks, but some clay bodies are
very prone to s cracking, especially if you throw off the hump. My
solution to this problem(I had s cracks even with a lot of compression)
came from a Clayart suggestion: I top my ware racks with pieces of
sheet rock and dry my pots on them. The sheetrock speeds the drying
rate of the pot bottoms so they catch up a bit with the walls that are
getting more air circulation. Works like a charm.
Jennifer
On Jun 16, 2004, at 7:59 PM, Antoinette Badenhorst wrote:
> Randy, S-cracks is not caused by drying, but by the way that you
> compress your clay after opening. If you throw off the hump you have to
> make extra sure to compact the clay in the bottom. After you opened up
> your clay, run a few times on a radius in the bottom of your bowl and
> make sure that there is no water to weaken the clay. Straight cracks
> are
> caused by water and s-cracks are because of clay not compressed enough.
> Make sure that the walls and bottom of your pots are of even thickness.
> V-cracks on the rim of a pot are caused by uneven drying (take note not
> fast drying) Hope this helps you.
> Nice evening.
> Antoinette Badenhorst
> 105 Westwood Circle
> Saltillo MS
> 38866
> 662 869 1651
> www.clayandcanvas.com
>
> -----Original Message-----
> From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Randy
> McCall
> Sent: Wednesday, June 16, 2004 6:18 PM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Drying salad bowls??????????
>
> I have been having some s cracks in small salad bowls. I am trying
> some
> suggestions I got out of the archives on compression. I also have made
> a drying rack with plastic sheeting.
>
>
************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
Dave Finkelnburg on wed 16 jun 04
Dear Randy,
I have to disagree slightly with my friend Antoinette here about the
"cause" of S-cracks. I believe in the potters' adage, "The last part to dry
is the first part to crack." IF the bottom is thick, or the rim dries
faster than the bottom, you will tend to get S-cracks because the rim is
shrinking in and literally pulling out on the center of the still-soft base.
It literally pulls the base in two!
Antoinette has suggested some remedies...keeping the bottom the same
thickness as the walls, making sure the bottom is well burnished during
throwing to heal micro-tears in the clay caused during opening.
I would note it is hard (as in impossible) to throw the bottom thin if
you want to make a trimmed foot. So, you need to get the bowls turned over
as soon as possible, so the bottom can begin drying, if you plan to trim the
bottom. Even with a potter's foot turn the pot over soon. If necessary,
cover the rims as you are doing to prevent them from drying faster than the
feet. IF you trim a foot, make sure the thickness of the foot is close to
the same thickness as the walls of the bowl.
Good potting!
Dave Finkelnburg in very dry Idaho where speed drying is available
year round!
----- Original Message -----
From: "Antoinette Badenhorst"
Sent: Wednesday, June 16, 2004 5:59 PM
> Randy, S-cracks is not caused by drying, but by the way that you
> compress your clay after opening.
Veena Raghavan on thu 17 jun 04
I have found that compressing the bottoms, when the bowls are leatherhard=
,
using a rubber rib or a wooden tool, prevents s-cracks. I do this most of=
the time and have never had cracking problems.
Hope this helps.
Veena
Veena Raghavan
75124.2520@compuserve.com
Lee Love on thu 17 jun 04
Clay makes a big difference. I've seen large platters made of
Mashiko nami clay, dried from the rim in without cracking on the
bottom. Mashiko clay has a lot of sand in it. I have some dug out
from in front of Hamada's pottery when they were putting sewer drain
in. The clay seam was about 2 meters down and was sandwiched between
layers of yellowish/reddish sand.
My shigaraki clay on the other hand, will often "S" crack no matter
how careful you are. You sometimes get hairline cracks on rims and
lid galleries. I have been adding han-jiki (half porcelain, half
Mashiko nami) to help give it more resistance. Will see what it
does to the fire color.
--
in Mashiko, Japan http://mashiko.org
http://journals.fotki.com/togeika/Mashiko/ Commentary On Pottery
Antoinette Badenhorst on thu 17 jun 04
Dear Dave, You do not disagree with me, I've said the same as you've
said, maybe just a little different angle. I did say a few key things:
even walls (meant after trimming- many s-cracks appear only after
firing) Throw the bottom 2 times as thick as the walls and trim 50% away
to leave a good foot rim.(in my terms and throwing stoneware it would be
maybe just over a 1/4" before trimming) That will give enough space
between the shelf surface and the bowl bottom to glaze and will assure
even thickness of the piece everywhere (after trimming). If the bottom
is thrown too thick, it will definitely cause cracks from uneven drying.
(Note I did not say fast drying) Randy said that he leave the pieces 2
days to dry slowly. Slow drying will not help at all if the piece is not
of even thickness and compressed enough. If he said "drying out over 2
days", I assume he has done what he had to do and is preparing the
pieces to go in the kiln. There are several ways to dry the piece
evenly. The sheet rock idea is perfect. I use backer board, which is
even better, since it dries clay faster than plaster. I throw recently
on plaster bats, which is very nice since one do not have to remove the
piece till it is ready to trim.
It is also a good idea to smooth out with a rib or even a finger after
trimming, in particular if the clay is still fairly soft and the
trimming disturbed the clay on the bottom.
Antoinette Badenhorst(who learned about these things the hard way about
24 years ago but is only speaking English regularly the past 5 years.)
105 Westwood Circle
Saltillo MS
38866
662 869 1651
www.clayandcanvas.com
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Dave
Finkelnburg
Sent: Wednesday, June 16, 2004 9:51 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Drying salad bowls??????????
Dear Randy,
I have to disagree slightly with my friend Antoinette here about the
"cause" of S-cracks. I believe in the potters' adage, "The last part to
dry
is the first part to crack." IF the bottom is thick, or the rim dries
faster than the bottom, you will tend to get S-cracks because the rim is
shrinking in and literally pulling out on the center of the still-soft
base.
It literally pulls the base in two!
Antoinette has suggested some remedies...keeping the bottom the same
thickness as the walls, making sure the bottom is well burnished during
throwing to heal micro-tears in the clay caused during opening.
I would note it is hard (as in impossible) to throw the bottom thin
if
you want to make a trimmed foot. So, you need to get the bowls turned
over
as soon as possible, so the bottom can begin drying, if you plan to trim
the
bottom. Even with a potter's foot turn the pot over soon. If
necessary,
cover the rims as you are doing to prevent them from drying faster than
the
feet. IF you trim a foot, make sure the thickness of the foot is close
to
the same thickness as the walls of the bowl.
Good potting!
Dave Finkelnburg in very dry Idaho where speed drying is
available
year round!
----- Original Message -----
From: "Antoinette Badenhorst"
Sent: Wednesday, June 16, 2004 5:59 PM
> Randy, S-cracks is not caused by drying, but by the way that you
> compress your clay after opening.
________________________________________________________________________
______
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
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Cat Jarosz on thu 17 jun 04
I dont know if this will help much with out a visual but here goes
nuttin.... when I throw anything with a wide bottom or if I know it stands a chance
of s cracking. I use my screw driver handle to pound the bottom of the pot
when I am first opening the form. I pound it a bit before I get to the
depth I will want it to be.... Have not had an S crack in 20 yrs and I use
that same poor screw driver on everything... ( it gets bats off wheel head )
ps that wall board stuff is good to have also but for me it's a fairly new
addition ( under 6 yrs) but I do have alot of unpainted worktables that did
the same thing ...drying wide bottoms upside down is tricky as the bottom
tends to pull up for some mysterious reason. you would need to watch it like a
hawk and flip often ( that is not always an option)
Even drying is important also. know your enviroment and time of yr
situation.. I live in south and its so dang humid you could drown standing on top
of a mountain in the winter I have a gas heater in a small space , the
difference in drying rate is HUGE.... and there is spring and fall ...
I swear Clay keeps us humble and on our toes .... good potting to
all... gotta go save my sneaker from the jaws of death !!!!
V)''(V curly & cat >^..^< "Chicks with beards rule !!!"
(_o_)
\||/
Ron Roy on fri 18 jun 04
Hi Randy,
Read the section on cracks in the Hamer dictionary - 8 pages on cracking -
you find the crack that looks like yours and h they explain why it
happened.
S cracks usually show up on ware thrown off the hump - because the clay is
twisted during centering and throwing.
If the same type of crack shows up in ware not thrown off the hump it is
usually straight.
The causes are the same - pot dries faster than the bottom - bottom has to
shrink more as it catches up to the sides - sides won't let it.
Also - the bottom clay does not get the same kind of compression and
particle arrangement as the sides and that results in different rates of
shrinkage in the two.
That is why recompessing the bottom when you open helps cure the problem.
Slow even drying will help as well.
If your bowls are thrown off the hump - compression from the outside -
where you are cutting off will help - as will not leaving the bottom too
thick.
Certainly getting the bowls over on the rim will help the bottom clay catch
up with the sides - and slow down the drying.
Changing clay will sometimes help as clay that has a high (or low)
shrinkage is more difficult to deal with. Adding grog also helps ware dry
more evenly.
RR
>I have been having some s cracks in small salad bowls. I am trying some
>suggestions I got out of the archives on compression. I also have made a
>drying rack with plastic sheeting.
>
>
>Small bowls here in SC have been drying in about two days, but I was
>having a lot of cracks. Over 50%.
>
>I have set up a drying rack and pieces now are drying very slowly, but
>humidity now is much higher due to the fact it is raining every afternoon.
>
>Is there any specific drying time that I should be shooting for to help
>with the cracks? Using Highwater Desert Buff.
>
>______________________________________________________________________________
>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.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Randy McCall on sat 19 jun 04
Thanks for the response. I have made the adjustments on a group of =
bowls where I used the compression techniques that everyone has =
suggested plus set up drying shelves. Those pots have been drying for a =
week and not a crack so far.
Thanks everyone for the suggestions.....................
Randy McCall
----- Original Message -----=20
From: Tracy Wilson=20
To: CLAYART@LSV.CERAMICS.ORG=20
Sent: Saturday, June 19, 2004 6:58 PM
Subject: Re: Drying salad bowls??????????
Compression of the bottom is VERY important as is slow drying =
but...another
thing I've learned over the last 25 years is it's important how you =
put the
lump of clay on the wheel. If you use a pugmill, the clay pug should =
go on
the wheel (or bat) at 90 degrees (perpendicular) from the way it's
extruded. Seems more important with porcelain than stoneware but the =
clay
twists as it moves through the machine and encourages 's' cracks. The =
same
holds true for wedging. Take note of the way you wedge and adjust
accordingly.
Tracy Wilson
Saltbox Pottery
www.saltboxpottery.com
=
_________________________________________________________________________=
_____
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.
Tracy Wilson on sat 19 jun 04
Compression of the bottom is VERY important as is slow drying but...another
thing I've learned over the last 25 years is it's important how you put the
lump of clay on the wheel. If you use a pugmill, the clay pug should go on
the wheel (or bat) at 90 degrees (perpendicular) from the way it's
extruded. Seems more important with porcelain than stoneware but the clay
twists as it moves through the machine and encourages 's' cracks. The same
holds true for wedging. Take note of the way you wedge and adjust
accordingly.
Tracy Wilson
Saltbox Pottery
www.saltboxpottery.com
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