John Hesselberth on sat 8 aug 98

Chris,

I think this one may be a problem with Standard Ceramics 112 clay. I
used to use their 225 clay which they say is the same as 112 without the
manganese. While my problems weren't as severe as yours, the level of
bottom cracks was unacceptable. When I wrote my articles on cracking and
warping in Clay Times a few months ago, I made reference to a clay body
that I couldn't get to be crack free. I didn't name it in the article;
however it was 225. I switched to Standard's 306 and bottom cracks
rarely happen to me anymore. I strongly suggest you switch clays. If
you want the manganese speckles, try a different brand. If you can go
without them, try 306. I know there are lots of potters who use 112 in
the Eastern U.S. and my clay supplier said it didn't have this
reputation, but I don't buy it. Try switching clays and let me know what
happens.

I can't spot anything in your procedures that would cause this problem.
Sounds like you are doing everying right. I also agree with your
position that a bottom crack, even though small and not affecting
function, makes a pot a second. Since I don't have a seconds shelf, mine
get broken.

John Hesselberth

>----------------------------Original message----------------------------
>Anyone willing to have another go at the problem of cracks? I have
>read the archives and every book I can get my hands on and am still
>stymied. Specifically, these are small arc-shaped cracks (not
>fully-developed S's) that appear in the bottom of my pots, almost
>always in the very center, usually when they are bisqued, though
>sometimes also in greenware. The cracks virtually never go all
>the way through the bottom. I have more problems with
>plates or other large-bottomed pieces, but cracks also show up in
>small-bottomed work like mugs and vases.
>
>Here's what I do: I use Standard's 112 stoneware clay. I wedge. I
>throw as dry as I can and am careful about not leaving puddles
>sitting in the bottoms of pots while I'm throwing. I compress
>bottoms, with fingers and sometimes with a wooden rib. I cut off
>with a wire (I'm throwing on plastic bats), air-dry uncovered (in my
>damp basement studio) until pots are stiff enough to handle, then
>remove to plywood ware boards. I've tried bottom up and bottom down.
> Cover loosely with dry-cleaner's plastic until leather-hard, then
>trim. Sometimes foot and sometimes not. Return to boards, cover
>again, dry slowly, uncovering for a few hours at a time until they
>are mostly dry, then uncover completely until they are as dry as they
>get in my basement, then transport to the community studio, where
>they finish drying on an open shelf waiting to be fired.
>
>I've seen some improvement, but I'm still getting way too many
>cracks, which I find especially disheartening in larger pieces, even
>more so in pieces with lids and handles (casseroles, cookie jars)
>that take extra time to make. Can anyone suggest other ideas to
>try?? (Please don't answer this if you are one of those "Oh, I've
>never had a crack in my entire pottery career" people -- I need to
>hear from fellow sufferers who have licked this problem.)
>
>Oh, and by the way, (just in case I'm stuck with this malady
>forever) I've always assumed that even a tiny (less than 1/2 inch
>length, not obtrusive, not interfering with function) crack is
>grounds for a piece going to the seconds shelf. Is there a consensus
>on this??



John Hesselberth
Frog Pond Pottery
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com
visit my web site at http://www.frogpondpottery.com

"Why should we be in such desperate haste to succeed and in such
desperate enterprises? If a man does not keep pace with his companions,
perhaps it is because he hears a different drummer. Let him step to the
music he hears, however measured or far away." Henry David Thoreau,
Walden, 1854

Alex, Aurora and Leah Solla on sat 8 aug 98

At 02:09 PM 8/7/98 -0400, you wrote:
>----------------------------Original message----------------------------
>Anyone willing to have another go at the problem of cracks? The cracks
virtually never go all
>the way through the bottom. I have more problems with
>plates or other large-bottomed pieces, but cracks also show up in
>small-bottomed work like mugs and vases.
>

Chris-
having had cracks in a myriad of forms and claybodies, here's the way I
would attack the problem. First off, cut your pot in half so you can really
see the cross section. It could be that the thickness variation is too
great a stress for your claybody.

Second, if this is not the case, your drying process may be too slow. Yes,
you heard it right. Too slow drying can create wet spots and leatherhard
areas. Right where you dont want them. TO this end, try to flip your pots
as soon as they are dry enough to handle without distorting. At this point
you should still find the bottom quite wet. Hopefully this allows your
bottoms to catch up to the rims.

Lastly, when trimming, consider burnishing the inside of the footring after
trimming with either a rubber rib or a spoon or something convex.

Good luck and fear not. They pass and come again. Hopefully with some
learning in the process.

Alex in Logan UT where the heat wants to suck my brain dry.

Sheilah Bliss on sat 8 aug 98

In a message dated 8/7/98 10:13:50 AM, you wrote:

<length, not obtrusive, not interfering with function) crack is
grounds for a piece going to the seconds shelf. Is there a consensus
on this??>>

Hi Chris -
I, too, tend to 2nd a piece that has even a minimal crack in it.
I've had some pieces that've cracked in bisque or glaze firing (^6 ox) "heal"
well by taking a piece of the the dried out clay and force the dried clay into
the crack by "scribbling" over it, forcing the fine clay particles inside
(some cracks need the clay packed in with a toothpick) and then re-fireed.
This seems to work best when no water used. Not all, but many pieces have
been resusitated this way. However, unless it's really, REALLY healed, I'll
often still 2nd the piece, just cause I know it was cracked. A lot of the
saved pieces that I don't feel right about selling, I still give as gifts and
they don't look like 2nds. :-)
Sheilah Bliss

Geoff Walker on sat 8 aug 98

Chris,

Sound very much like the clay is not suitable to me. I have a friend who
thows very large platters and bowls ... powerful pieces ... who had a
similar problem with one batch of clay. (One ton, I think.) 90% of the
pots she was making for an exhibition and another show cracked whilst
drying for the first time ever. I had had the same problem with one
batch of that particular commercial clay back in the 70's some time (but
that was a batch of 8 tons!), so sourced another clay. Although there
was then a period of some months of adjusting firings and glaze fit
etc., that particular problem went away.

I gave this lass a few hundred pounds of the clay we use, and everything
came through. No change in technique! As a matter of fact, if you get
the right clay, you should be able to skip all that compressing and slow
drying. I think the secret is to find a clay that does most of it's
shrinking in the firings and not in drying. You will find handles and
knobs easier to add as well.

Hope this helps ... from your description, I don't think the problem is
you, so don't be disheartened.

Best wishes,

Geoff Walker
Cronulla Pottery
Gold Coast
Australia.

Erikyu on sat 8 aug 98

Here is what worked for me...
I have always spiral wedged (Japanese style). I often had cracks.
I now wedge the same, ending with a somewhat cone shaped ball. The trick is
to put the cone on your wheel head point DOWN. This seems strange at first
but it is the only thing which works for me. I find that this is also
easier to center.
Good luck


Erikyu, aka Eric Haggin
Dublin, CA, USA

east@inreach.com

Yakimono Ya
Nendo ni Shimiiru
Kama no koe

Ron Roy on sat 8 aug 98

Hey Chris,

First of all, some clays are better than others at drying in a more even
way. The problem can be too little plasticity or too much.

I have two suggestions. First - when recompressing the bottoms while
throwing - move from the outside to the inside - this helps to compress the
inside of the bottom - do it 3 or 4 times using the flats of your fingers
or a rib - or both - fingers first then the rib.

Some will recommend putting an extra small ball of clay in the centre -
while throwing - and working it into the bottom - this has the same effect
as recommpressing the bottom.

It helps to have bats that have at least some absorbency and a good damp
cupboard.

The second: If pots dry unevenly the outside dries first - when the inside
clay tries to catch up - it tries to shrink but the outside won't let it.
Keep the drying even by covering well until you can get them off the bats
and turn them over. I work with porcelain which tends to dry unevenly - it
takes a lot of care - especially when the bottoms are wide as in platters
and plates.

The other option is to find another clay that has better drying characteristics.

>----------------------------Original message----------------------------
>Anyone willing to have another go at the problem of cracks? I have
>read the archives and every book I can get my hands on and am still
>stymied. Specifically, these are small arc-shaped cracks (not
>fully-developed S's) that appear in the bottom of my pots, almost
>always in the very center, usually when they are bisqued, though
>sometimes also in greenware. The cracks virtually never go all
>the way through the bottom. I have more problems with
>plates or other large-bottomed pieces, but cracks also show up in
>small-bottomed work like mugs and vases.

Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849

Web page: http://digitalfire.com/education/people/ronroy.htm

Stephen Mills on sun 9 aug 98

Chris,
I'm not familiar with the clay you are using (we don't get it
over here!) is it a very fine, fairly dense clay? and how thick
are the bottoms that crack?
When we come across this problem it is quite often (but of
course NOT always) a clay of the above type and/or too thick
bottoms. There is another possible area of enquiry: what is the
shrinkage (%) of this clay at ^8 for example? I had one clay
that had plus 14% shrinkage at^8 and that caused base S
cracking. We finally added about 20+% fine sand which cured the
problem.

Steve
Bath
UK


In message , Chris Schafale writes
>----------------------------Original message----------------------------
>Anyone willing to have another go at the problem of cracks? I have
>read the archives and every book I can get my hands on and am still
>stymied. Specifically, these are small arc-shaped cracks (not
>fully-developed S's) that appear in the bottom of my pots, almost
>always in the very center, usually when they are bisqued, though
>sometimes also in greenware. The cracks virtually never go all
>the way through the bottom. I have more problems with
>plates or other large-bottomed pieces, but cracks also show up in
>small-bottomed work like mugs and vases.
>
>Here's what I do: I use Standard's 112 stoneware clay. I wedge. I
>throw as dry as I can and am careful about not leaving puddles
>sitting in the bottoms of pots while I'm throwing. I compress
>bottoms, with fingers and sometimes with a wooden rib. I cut off
>with a wire (I'm throwing on plastic bats), air-dry uncovered (in my
>damp basement studio) until pots are stiff enough to handle, then
>remove to plywood ware boards. I've tried bottom up and bottom down.
> Cover loosely with dry-cleaner's plastic until leather-hard, then
>trim. Sometimes foot and sometimes not. Return to boards, cover
>again, dry slowly, uncovering for a few hours at a time until they
>are mostly dry, then uncover completely until they are as dry as they
>get in my basement, then transport to the community studio, where
>they finish drying on an open shelf waiting to be fired.
>
>I've seen some improvement, but I'm still getting way too many
>cracks, which I find especially disheartening in larger pieces, even
>more so in pieces with lids and handles (casseroles, cookie jars)
>that take extra time to make. Can anyone suggest other ideas to
>try?? (Please don't answer this if you are one of those "Oh, I've
>never had a crack in my entire pottery career" people -- I need to
>hear from fellow sufferers who have licked this problem.)
>
>Oh, and by the way, (just in case I'm stuck with this malady
>forever) I've always assumed that even a tiny (less than 1/2 inch
>length, not obtrusive, not interfering with function) crack is
>grounds for a piece going to the seconds shelf. Is there a consensus
>on this??
>
>Thanks in advance.
>
>Chris
>in NC where we've just had a few cool days to remind us that there is
>life after summer
>
>Light One Candle Pottery
>Fuquay-Varina, NC
>candle@nuteknet.com
>

--
Steve Mills
Bath
UK
home e-mail: stevemills@mudslinger.demon.co.uk
work e-mail: stevemills@bathpotters.demon.co.uk
own website: http://www.mudslinger.demon.co.uk
BPS website: http://www.bathpotters.demon.co.uk

John K. Dellow on sun 9 aug 98

Chris , if you can rule out the making & body as being the culprit, maybe
the plastic is the problem. I use hessian or cloth to cover your pots. The
plastic will slow the drying ,but the water released from the clay can
recondense on the plastic and drip back onto the ware.
John dellow the flower pot man

Kelley Webb Randel on sun 9 aug 98

Chris,
I commiserate, I have the same problem. My professor who is a zen master at
throwning, said I wasn't compressing the bottom enough, but that doesn't seem
to matter much. I compress with wooden rib, watched him, watched him,
compressed with a plastic rib, watched him... hell if i know whats wrong. And
yes, if there is just a small crack, it's a second.
good luck and let me know if you kick the problem! I'll be watching the mail
with much interest!
kelley / raku gddss@aol.com

Tom Wirt on sun 9 aug 98

Specifically, these are small arc-shaped cracks (not
fully-developed S's) that appear in the bottom of my pots, almost
always in the very center, usually when they are bisqued, though
sometimes also in greenware. The cracks virtually never go all
the way through the bottom. I have more problems with
plates or other large-bottomed pieces, but cracks also show up in
small-bottomed work like mugs and vases.

Hi Chris...
We do tons of plates, casseroles, etc. etc., and only occasionally have had
the problem you're encountering.....gotta be frustrating. I'd go through
the litany of how I process, but you've tried it all from your post....the
drying is critical, especially getting things turned over as soon as
[possible.....For bottom compression, I don't do anything special (just
normal going over bottoms after first opening a few times). One thing I've
seen with plastic bats is that when you cut off after throwing, let it dry
to near leather, then re-cut to get it off the bat, the wire may cut LOWER
than the original cut, leaving a thin skin between the two cuts. If you
don't trim all this skin away, and get back to the original wire cut, it
could cause the symptom you describe.

Which leaves me at THE CLAY for your problem. When we've had the problem,
m,y great suspicion has been that the clay wasn't well mixed and a
concentration of some ingredient has caused the problem.

Have you tried switching to another clay and seeing if the problems persist?

Hope this helps.

(PS> following Don Kopy's lead, we sell seconds by the pound. Saves
pricing. And mark them "seconds" with a magic marker).

Tom Wirt
claypot@hutchtel.net

Cindy on sun 9 aug 98

Chris,

I find that if the bottoms of my pots are thicker than the walls, they do
tend to crack. If even clay thickness, in addition to all the other things
you've been doing, doesn't work, I strongly suggest finding another clay.

As to whether your pots should go to the seconds pile for this particular
fault, I will say two things. First, few of your customers will either
notice or care about tiny, non-crippling cracks. Second, you have to decide
for yourself how you feel about this. It is *not* a moral issue. Most
potters choose not to sell imperfect pots, however I've seen very
attractive and functional, albeit imperfect, pots for sale. I do hate to
see perfectly good things (or people) wasted because of imperfections.

Since I don't have a lot of trouble with cracks, I tend to give those pots
that don't quite make the grade to friends who couldn't otherwise afford my
pottery. They like to receive it, I like to please them, and it cuts down
on my burgeoning cupboards.

Cindy Strnad
Earthen Vessels
Custer, SD
USA http://blackhills-info.com/a/cindys/menu.htm

----------
> From: Chris Schafale
> To: CLAYART@LSV.UKY.EDU
> Subject: The cracks that won't quit
> Date: Friday, August 07, 1998 12:09 PM
>
> ----------------------------Original message----------------------------
> Anyone willing to have another go at the problem of cracks? I have
> read the archives and every book I can get my hands on and am still
> stymied. Specifically, these are small arc-shaped cracks (not
> fully-developed S's) that appear in the bottom of my pots, almost
> always in the very center, usually when they are bisqued, though
> sometimes also in greenware. The cracks virtually never go all
> the way through the bottom. I have more problems with
> plates or other large-bottomed pieces, but cracks also show up in
> small-bottomed work like mugs and vases.
>
> Here's what I do: I use Standard's 112 stoneware clay. I wedge. I
> throw as dry as I can and am careful about not leaving puddles
> sitting in the bottoms of pots while I'm throwing. I compress
> bottoms, with fingers and sometimes with a wooden rib. I cut off
> with a wire (I'm throwing on plastic bats), air-dry uncovered (in my
> damp basement studio) until pots are stiff enough to handle, then
> remove to plywood ware boards. I've tried bottom up and bottom down.
> Cover loosely with dry-cleaner's plastic until leather-hard, then
> trim. Sometimes foot and sometimes not. Return to boards, cover
> again, dry slowly, uncovering for a few hours at a time until they
> are mostly dry, then uncover completely until they are as dry as they
> get in my basement, then transport to the community studio, where
> they finish drying on an open shelf waiting to be fired.
>
> I've seen some improvement, but I'm still getting way too many
> cracks, which I find especially disheartening in larger pieces, even
> more so in pieces with lids and handles (casseroles, cookie jars)
> that take extra time to make. Can anyone suggest other ideas to
> try?? (Please don't answer this if you are one of those "Oh, I've
> never had a crack in my entire pottery career" people -- I need to
> hear from fellow sufferers who have licked this problem.)
>
> Oh, and by the way, (just in case I'm stuck with this malady
> forever) I've always assumed that even a tiny (less than 1/2 inch
> length, not obtrusive, not interfering with function) crack is
> grounds for a piece going to the seconds shelf. Is there a consensus
> on this??
>
> Thanks in advance.
>
> Chris
> in NC where we've just had a few cool days to remind us that there is
> life after summer
>
> Light One Candle Pottery
> Fuquay-Varina, NC
> candle@nuteknet.com

Jeremy M. Hellman on sun 9 aug 98

Hi Eric-

I haven't been in the chat room, and the last time I was there, about 3
months ago, no one else was there. I thought of you recently because I
finally got around to starting to use that oxblood red ^6 ox glaze you'd
forwarded to me. It's a real winner, although quite sensitive to
thickness of application. Too thin and it's ugly; too thick and it runs.
Needs to be thick, but not too thick. Breaks beautifully on edges.

I hope you, your wife and baby, now probably a year old, are all well.

Is there any time in your life for pottery?

Bonnie

>----------------------------Original message----------------------------
>Here is what worked for me...
> I have always spiral wedged (Japanese style). I often had cracks.
>I now wedge the same, ending with a somewhat cone shaped ball. The trick is
>to put the cone on your wheel head point DOWN. This seems strange at first
>but it is the only thing which works for me. I find that this is also
>easier to center.
>Good luck
>
>
>Erikyu, aka Eric Haggin
>Dublin, CA, USA
>
>east@inreach.com
>
>Yakimono Ya
>Nendo ni Shimiiru
>Kama no koe


"Outside a dog, a book is a man's best friend. Inside a dog, it's too
dark to read" Groucho Marx

" " Harpo Marx

"Time flies like an arrow. Fruit flies like a banana" Att. to GM

"You can tune a piano but you cant tune a fish" Old Proverb

"By the time they had diminished from 50 to 8, the other dwarves
began to suspect 'Hungry' ..." -- Gary Larson, "The Far Side"

Knox Steinbrecher on mon 10 aug 98

I use Standard 112 on bowls, plates. platters etc. and have not had the same
experience with cracks. Couldn't tell you why.....I just don't have trouble
with cracks. Luck of the ignorant ?

Knox in Marietta Ga

C Pike on tue 11 aug 98

Hi
Has anyone tried to fill these s cracks after the high fire. I've tried using
epoxy and adding acrylic paint to tint it but it doesn't make it a first.
Connie

------------------------------------------------------------------------------
Bob & Connie Pike pikec@cadvision.com
1303 10th Ave SE High River,Alberta T1V 1L4 Canada (403-652-5255)
----------------------------------------------------------------------------
--

Joseph Herbert on tue 11 aug 98

Chris Schafale generated many responses with the cracks that won t quit post.
I am responding mostly so I can make up a fake pottery name after my signature
but there could be some real information in here, too.

It is easy to state that all cracks in clay and clay products are caused by
uneven volume changes, shrinkage during drying and some firing, expansion
during crystal phase changes. During drying, some part of the clay mass or
pot or tile shrinks more than some other part and the material fails in
tension and cracks. We are all familiar with the shrinkage of clay from the
wet state to bone dry and then the additional shrinkage during firing. Even
the dreaded cristobalite squeeze and the inconvenient quartz inversions are
volume change events when some part of the clay object shrinks or expands more
than another. The things crack, sometimes explosively.

Having said that, the pursuit of crackless pottery can be a frustrating
experience. I have had three times when inexplicable cracks plagued me.
Because I often travel and do pottery in different places, I have used lots of
different clay bodies that are fired by many different people. Over the years
of learning, I had (have) developed a way of working that produced fairly
sturdy pots that didn t crack on drying, were strong enough in the bone dry
state to withstand moderately careless handling, and of a form and thickness
that didn t encourage cracks during firing. Just a happy boy having a good
time in the mud.

I was making pots in my motel room on the shore of the Gulf of Mexico in
Palacios, Texas. It says paradise but it isn t really. The throwing and
drying were as expected, I put the pots on the top of my kitchenette
refrigerator, without problems. Transporting greenware three hundred miles to
Dallas seemed like a foolish thing to try, so I went to the local CERAMICS
lady and asked her to fire my pots to an 04 bisque. She required convincing
that the two things, my pots and her conch shell tissue box covers, were the
same material but I prevailed and she fired my bowls as she fired her old man
of the sea fighting the gale with the windjammer spoked wheel tied down. I
got DUNTING. Some of the bowls, about two per firing cracked across the foot
so the crack ran from the center of the bottom to a region near the rim
without ever actually crossing the rim. After some reflection (years of it) I
have decided that her slip cast objects were of a consistent and constant (and
thin) wall thickness and my bowls weren t. She fired her kiln very rapidly
and, since her pieces were all of one thickness of clay, they would expand and
contract evenly and not break. There may have been a component of
Cristobalite development in my clay body and not in her slip that added to the
problem. I was sort of mystified by the events at the time and never could
get her to slow down her firing (or cooling?) enough to not break at least one
piece per load. Not a single case of dunting before or since. Hummm.

So, I am later in Wallingford, Pa. between Swarthmore, of art paper fame and
that town that is the source of all our national ills, Media, working at the
community art center there. This is all cone 6 electric firing but the people
there had really put effort into their glazes and the fired results were often
wonderful. In the normal course of events, I made many pots there and had no
problem with cracking. However, one week there comes a chance to get into a
wood firing up by Chester Springs, Pa. and I don t have anything bisqued and
ready to go. So, I go to the Wallingford art center and throw a series of
cups off the hump - something I don t often do. About half of these cups,
even though I thought I treated them more or less like my other thrown
objects, developed S cracks. After reflection, I decided that the way I was
throwing these off the hump had lead to the bottoms being much wetter than
when I worked in other ways. I suppose if I were to throw off the hump more
often, I would develop a pattern of working that would reduce the wetness of
the vessel bottoms and eliminate the S cracks. When I have thrown off the
hump using other clay bodies, I have not had this problem. Hummm.

Later still, last year, I am working at a museum in Racine, Wisconsin using a
cone 5 raku body. Everything that I made that was larger than a teacup S
cracked in the bisque so badly that, on the larger pieces, you might drop a
penny through the crack. I believe that for the 8 sessions I went there I got
three bowls that made it through the entire process. Other people in the
class didn t have this problem. My way of working, which mostly succeeds, was
so at odds with this clay body so much that I couldn t get a finished piece to
save my life.

This museum is the Wustum and it has a pottery collection that is worth
finding if you ever find yourself in Racine. Soldner, Orr, Grubey, Gustin.

What little point there is to this rambling is that we have to find an
intersection of our ways of working with what the clay will stand. Different
clay bodies respond differently to different ways of working and drying and
firing. The differences in a pattern of working that allows one person to
succeed while the person beside them to fail can be so subtle as to lead to
magical beliefs. Many of the standard prescriptions for curing cracking are
suggested patterns of work that will make the difference. In reality all the
prescirber can say is, "This works for me." without really being sure of what
"This" is. That certainly doesn t assure it will work for anyone else.
Having been confronted with several cases of mysterious cracking, I think the
easiest thing to change is the clay body. If you have established firm habits
of work and are in a settled place where you do things the same way
repeatedly, see if you can t find a clay that fits your existing work patterns
rather than making endless different incantations in hopes that one will
magically work. If you get the same cracking problems using other clay
bodies, then you will probably have to analyze your processes, perhaps
minutely, and change your work habits until you conform to the expectations of
the clay.

Long ago in a computer programming class I came to look on the distant
computer (this was before everyone had one) as the ultimate critic. "I submit
my small pile of cards to you, great critic, in hopes that you will look with
favor on my humble efforts." Often the reply came thundering back on a single
sheet of green and white paper - SYNTAX ERROR AT LINE 400 - like a dagger to
the heart. When my efforts were correct in all respects, the great critic
would be my tame calculator of sums and manipulator of arrays. In a sense the
clay is here the critic. If you don t work it right, it lets you know. You
can change the clay body - which wasn t possible with the computer, or you can
slowly mold your ways of work to the dictates of the clay - the ultimate
critic of workmanship.

Having rambled on for so long, I will make my small joke and end.

Joseph Herbert
JJHerb@aol.com
Curse-the-Dark Pottery
Irving, Texas

Abbey of New Clairvaux on tue 11 aug 98

Dear Bonnie,

Would you be able and willing to share the "oxblood red cone 6 oxidation
glaze" that you mentioned?

Fr. |Anthony

> -----Original Message-----
> From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.UKY.EDU]On Behalf
> Of Jeremy M. Hellman
> Sent: Sunday, August 09, 1998 8:54 AM
> To: CLAYART@LSV.UKY.EDU
> Subject: Re: The cracks that won't quit
>
>
> ----------------------------Original message----------------------------
> Hi Eric-
>
> I haven't been in the chat room, and the last time I was there, about 3
> months ago, no one else was there. I thought of you recently because I
> finally got around to starting to use that oxblood red ^6 ox glaze you'd
> forwarded to me. It's a real winner, although quite sensitive to
> thickness of application. Too thin and it's ugly; too thick and it runs.
> Needs to be thick, but not too thick. Breaks beautifully on edges.
>
> I hope you, your wife and baby, now probably a year old, are all well.
>
> Is there any time in your life for pottery?
>
> Bonnie
>
> >----------------------------Original message----------------------------
> >Here is what worked for me...
> > I have always spiral wedged (Japanese style). I often had cracks.
> >I now wedge the same, ending with a somewhat cone shaped ball.
> The trick is
> >to put the cone on your wheel head point DOWN. This seems
> strange at first
> >but it is the only thing which works for me. I find that this is also
> >easier to center.
> >Good luck
> >
> >
> >Erikyu, aka Eric Haggin
> >Dublin, CA, USA
> >
> >east@inreach.com
> >
> >Yakimono Ya
> >Nendo ni Shimiiru
> >Kama no koe
>
>
> "Outside a dog, a book is a man's best friend. Inside a dog, it's too
> dark to read" Groucho Marx
>
> " " Harpo Marx
>
> "Time flies like an arrow. Fruit flies like a banana" Att. to GM
>
> "You can tune a piano but you cant tune a fish" Old Proverb
>
> "By the time they had diminished from 50 to 8, the other dwarves
> began to suspect 'Hungry' ..." -- Gary Larson, "The Far Side"
>

MRS SANDRA L BURKE on tue 11 aug 98

Ron,
I'm hoping you can help with a question that is not really related to
this discussion, but it does have to do with clay bodies.
I am an adjunct insturctor at two different colleges. This fall I
will be teaching ceramics at both schools. One of the colleges is
currently using two different clay bodies; one for cone 10 reduction
and an earthenware body for pit firing and raku. Since it is an hours
drive between the two schools, I was wondering if there is a clay
body that will serve both purposes. That is one clay body that can be
both high fire and raku.
Thanks
Sandy Burke

Bob&Hulda on tue 11 aug 98

Jim,
I sometimes get this when my clay is too fresh, I just centre the
clay as usual,wire it off,turn it upside down and throw,result= no S cracks
anymore.
Bob Hollis

Kim Marie on tue 11 aug 98

I switched from Miller 60 clay to Standard 112 approximately 6 months ago.
I don't have the cracking problems now and though I didn't have as many
problems at the onset, I did have some cracking. For me it seemed to be 2
factors. one was 'the thick and thin of it'. I like a raised foot on my
bowls so I throw them more thickly on the bottom. As long as I trim them the
next day and make sure I don't have too thick an area at the transition
section between the bottom of the bowl and its body, I don't have the
problem. I too use plastic bats. Many pieces stay on the bat 'til the next
day and I do recut them with my wire. If I doing pieces that won't be
trimmed, I have to make sure the bottoms aren't thick. When they were, they
cracked.

Factor 2 is the drying. Some of my work has additions of clay that I later
carve. When I do this, I will loosely wrap the piece in plastic one day,
the next day I'll check it and just drape the plastic over it. I leave it
like this until the color starts to change to a greenware look and then
remove the plastic entirely and let it dry completely. I've never turned
any of my pieces over except for plates or platters. ON day one of making
plates, I place some plastic loosely over them when I leave the studio for
the day. I uncover them in the morning of day 2 and hopefully by afternoon i
can trim. After trimming, they are loosely covered when I leave. Sometimes
(depending on our humidity factor) by day 3 I can turn them over. At this
point they stay loosely covered until mostly dry.

I'm a bit more careful of the drying with 112 and can't push it like I used
to rush the drying of miller 60 but I don't baby it either. There are so
many more advantages to the 112 in comparison to the 60 so I'm glad to do
it. I would wonder if you are trying to dry too slowly. I worked in a
basement for about 6 months and would bring my pieces up at the end of a day.

Since you are working in your basement, I hope you have done a radon test.
It's inexpensive and well worth the peace of mind. I found the basement I
worked in was 54.3 and anything over 4.0 is NOT good. The environmental
dept. thought I did the test wrong and had me do it over. Same results. We
bought a different house after having the basement checked.

Olivia T Cavy on wed 12 aug 98

Joseph,

Thanks for taking the time to share with the group your personal
failures. It's been said that we learn more from our failures, and your
lesson that we need to match our working style with a clay that works is
important. Probably not a beginner lesson, but the original posting
wasn't really a beginner problem. It was good to read that an experienced
potter such as yourself still (occasionally) ran into a clay (or a kiln
firing) he didn't like!

Actually, I can see you're following the Mellon Bank approach to bad bank
loans of the 1980's, when they took all of their bad (mostly real estate)
loans, and gave them to a "new" bank, so Mellon could get them off their
Balance Sheet and make Mellon look better. By establishing your
Curse-the-Dark Pottery you could give them all of your seconds (and
thirds) and other pots that didn't quite make it, and sell them. Only
your closest friends would know that JJ Herbert was the supplier for
Curse-the-Dark Pottery!

Bonnie

Bonnie D. Hellman
Pittsburgh, PA
work email: bdh@firstcaptl.com or oliviatcavy@juno.com
home email: mou10man@sgi.net

On Tue, 11 Aug 1998 09:19:34 EDT Joseph Herbert writes:
>----------------------------Original
>message----------------------------
>Chris Schafale generated many responses with the cracks that won t
>quit post.
>I am responding mostly so I can make up a fake pottery name after my
>signature
>but there could be some real information in here, too.
>
>It is easy to state that all cracks in clay and clay products are
>caused by
>uneven volume changes, shrinkage during drying and some firing,
>expansion
>during crystal phase changes. During drying, some part of the clay
>mass or
>pot or tile shrinks more than some other part and the material fails
>in
>tension and cracks. We are all familiar with the shrinkage of clay
>from the
>wet state to bone dry and then the additional shrinkage during firing.
> Even
>the dreaded cristobalite squeeze and the inconvenient quartz
>inversions are
>volume change events when some part of the clay object shrinks or
>expands more
>than another. The things crack, sometimes explosively.
>
>Having said that, the pursuit of crackless pottery can be a
>frustrating
>experience. I have had three times when inexplicable cracks plagued
>me.
>Because I often travel and do pottery in different places, I have used
>lots of
>different clay bodies that are fired by many different people. Over
>the years
>of learning, I had (have) developed a way of working that produced
>fairly
>sturdy pots that didn t crack on drying, were strong enough in the
>bone dry
>state to withstand moderately careless handling, and of a form and
>thickness
>that didn t encourage cracks during firing. Just a happy boy having a
>good
>time in the mud.
>
>I was making pots in my motel room on the shore of the Gulf of Mexico
>in
>Palacios, Texas. It says paradise but it isn t really. The throwing
>and
>drying were as expected, I put the pots on the top of my kitchenette
>refrigerator, without problems. Transporting greenware three hundred
>miles to
>Dallas seemed like a foolish thing to try, so I went to the local
>CERAMICS
>lady and asked her to fire my pots to an 04 bisque. She required
>convincing
>that the two things, my pots and her conch shell tissue box covers,
>were the
>same material but I prevailed and she fired my bowls as she fired her
>old man
>of the sea fighting the gale with the windjammer spoked wheel tied
>down. I
>got DUNTING. Some of the bowls, about two per firing cracked across
>the foot
>so the crack ran from the center of the bottom to a region near the
>rim
>without ever actually crossing the rim. After some reflection (years
>of it) I
>have decided that her slip cast objects were of a consistent and
>constant (and
>thin) wall thickness and my bowls weren t. She fired her kiln very
>rapidly
>and, since her pieces were all of one thickness of clay, they would
>expand and
>contract evenly and not break. There may have been a component of
>Cristobalite development in my clay body and not in her slip that
>added to the
>problem. I was sort of mystified by the events at the time and never
>could
>get her to slow down her firing (or cooling?) enough to not break at
>least one
>piece per load. Not a single case of dunting before or since. Hummm.
>
>So, I am later in Wallingford, Pa. between Swarthmore, of art paper
>fame and
>that town that is the source of all our national ills, Media, working
>at the
>community art center there. This is all cone 6 electric firing but
>the people
>there had really put effort into their glazes and the fired results
>were often
>wonderful. In the normal course of events, I made many pots there and
>had no
>problem with cracking. However, one week there comes a chance to get
>into a
>wood firing up by Chester Springs, Pa. and I don t have anything
>bisqued and
>ready to go. So, I go to the Wallingford art center and throw a
>series of
>cups off the hump - something I don t often do. About half of these
>cups,
>even though I thought I treated them more or less like my other thrown
>objects, developed S cracks. After reflection, I decided that the way
>I was
>throwing these off the hump had lead to the bottoms being much wetter
>than
>when I worked in other ways. I suppose if I were to throw off the
>hump more
>often, I would develop a pattern of working that would reduce the
>wetness of
>the vessel bottoms and eliminate the S cracks. When I have thrown off
>the
>hump using other clay bodies, I have not had this problem. Hummm.
>
>Later still, last year, I am working at a museum in Racine, Wisconsin
>using a
>cone 5 raku body. Everything that I made that was larger than a
>teacup S
>cracked in the bisque so badly that, on the larger pieces, you might
>drop a
>penny through the crack. I believe that for the 8 sessions I went
>there I got
>three bowls that made it through the entire process. Other people in
>the
>class didn t have this problem. My way of working, which mostly
>succeeds, was
>so at odds with this clay body so much that I couldn t get a finished
>piece to
>save my life.
>
>This museum is the Wustum and it has a pottery collection that is
>worth
>finding if you ever find yourself in Racine. Soldner, Orr, Grubey,
>Gustin.
>
>What little point there is to this rambling is that we have to find an
>intersection of our ways of working with what the clay will stand.
>Different
>clay bodies respond differently to different ways of working and
>drying and
>firing. The differences in a pattern of working that allows one
>person to
>succeed while the person beside them to fail can be so subtle as to
>lead to
>magical beliefs. Many of the standard prescriptions for curing
>cracking are
>suggested patterns of work that will make the difference. In reality
>all the
>prescirber can say is, "This works for me." without really being sure
>of what
>"This" is. That certainly doesn t assure it will work for anyone
>else.
>Having been confronted with several cases of mysterious cracking, I
>think the
>easiest thing to change is the clay body. If you have established
>firm habits
>of work and are in a settled place where you do things the same way
>repeatedly, see if you can t find a clay that fits your existing work
>patterns
>rather than making endless different incantations in hopes that one
>will
>magically work. If you get the same cracking problems using other
>clay
>bodies, then you will probably have to analyze your processes, perhaps
>minutely, and change your work habits until you conform to the
>expectations of
>the clay.
>
>Long ago in a computer programming class I came to look on the distant
>computer (this was before everyone had one) as the ultimate critic.
>"I submit
>my small pile of cards to you, great critic, in hopes that you will
>look with
>favor on my humble efforts." Often the reply came thundering back on
>a single
>sheet of green and white paper - SYNTAX ERROR AT LINE 400 - like a
>dagger to
>the heart. When my efforts were correct in all respects, the great
>critic
>would be my tame calculator of sums and manipulator of arrays. In a
>sense the
>clay is here the critic. If you don t work it right, it lets you
>know. You
>can change the clay body - which wasn t possible with the computer, or
>you can
>slowly mold your ways of work to the dictates of the clay - the
>ultimate
>critic of workmanship.
>
>Having rambled on for so long, I will make my small joke and end.
>
>Joseph Herbert
>JJHerb@aol.com
>Curse-the-Dark Pottery
>Irving, Texas
>

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Jennifer M. Dubats on wed 12 aug 98

Sandy,

At the studio I took classes at they used a white stoneware body from
Campbell's Ceramic supply in Richmond. It can be used for Raku or fired at
cone 6 or used at cone 10 in reduction. The range is cone 6 to 10 but it
worked fine for Raku at a lower temp. It works great at high temperature. I
personally did not care for it fired at cone 6 in oxidation. (the pieces fired
at ^6 crazed with time, I think the body was not matured enough for functional
ware at that temp. too high of absorption rate at ^6)
The Raku looked good and almost no losses even with beginners work.
Try using some of the cone 10 clay to Raku if you can. I bet you will have
good results.


Jenny Dubats
in hot and humid VA.

Ron Roy on wed 12 aug 98

Hi Sandy,

While I don't think this was directed at me - I can say tes to this - try
the cone 10 body in raku - it will probably work. Don't try the earthenware
at cone 10.

When I did my raku 25 years ago - I used a heavily grogged porcelain - that
way I could have the white show through the clear glaze and the black
cracks were the decoration.

>----------------------------Original message----------------------------
>Ron,
>I'm hoping you can help with a question that is not really related to
>this discussion, but it does have to do with clay bodies.
>I am an adjunct insturctor at two different colleges. This fall I
>will be teaching ceramics at both schools. One of the colleges is
>currently using two different clay bodies; one for cone 10 reduction
>and an earthenware body for pit firing and raku. Since it is an hours
>drive between the two schools, I was wondering if there is a clay
>body that will serve both purposes. That is one clay body that can be
>both high fire and raku.
>Thanks
>Sandy Burke

Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849

Web page: http://digitalfire.com/education/people/ronroy.htm

Cindy on wed 12 aug 98

Connie,

You can't make an s-cracked piece a first. To make it useable, fill the
crack with kiln cement after the glaze firing, then cover the inside of the
cracked area with more glaze and re-fire. If you use brown clay, color the
kiln cement by adding a little iron oxide.

Cindy Strnad
Earthen Vessels
Custer, SD
USA http://blackhills-info.com/a/cindys/menu.htm

----------
> From: C Pike
> To: CLAYART@LSV.UKY.EDU
> Subject: The cracks that won't quit
> Date: Tuesday, August 11, 1998 7:17 AM
>
> ----------------------------Original message----------------------------
> Hi
> Has anyone tried to fill these s cracks after the high fire. I've tried
using
> epoxy and adding acrylic paint to tint it but it doesn't make it a first.
> Connie
>
>
----------------------------------------------------------------------------
--
> Bob & Connie Pike pikec@cadvision.com
> 1303 10th Ave SE High River,Alberta T1V 1L4 Canada (403-652-5255)
>
----------------------------------------------------------------------------

> --

Steve McNutt on wed 12 aug 98

It occurred to me to add this bit on covering pieces to manage drying prior to
trimming:

About a year ago, one of the women in our studio went on a campaign to
acquaint us with the benefits of covering bowls and plates with light weight
cotton squares instead of plastic. I use this on anything with a rim and
think it works better.

The other "covering" hint I have gleaned over the years is to place a sheet of
newsprint over the wet rim to stabilize it for moving off the bat.

All this is a bit off the subject, but I usually just lurk thinking I have
nothing new to add. I thought I'd take the plunge and see how it goes.
Thanks to all of you who spend so much time helping the rest of us.

Mary Beth Bishop
MBBishop00@aol.com