Rob Di Stasio on sun 10 apr 05
Newbie question here.
I am learning to throw on the wheel and sometimes I leave the pot's
bottom too thick. I try to dry them very slowly, in plastic over a
period of a few weeks but one of my best pieces to date has developed a
hairline crack in the bottom as it's dried.
I opened it up a bit and forced in more clay but it eventually came back.
I heard of mixing up some clay with a little vinegar and some shredded
tissue paper but haven't tried it yet.
I'd like the pot to be functional and watertight so I need to fill this
crack up enough that the glaze will seal it.
Any recommendations of a technique to use to keep the crack from
reappearing so I can get this bisqued and glazed?
Thanks, Rob
marianne kuiper milks on sun 10 apr 05
My Most Resouceful Friend Lori (who has workable
answers for everything :) ), suggested mixing equal
amounts of your fresh clay and powdered
(confectioner's) sugar. Make only a small amount,
since it hardens fast. Kneed it until is is too sticky
for any sane person to touch (yuck) and force it into
the crack once the pottery is dry. When the filler is
hard you can gently remove the excess, then fire. Or
(better) you can sand it after biscque. We've
discussed trying it after the first firing, but I'd
suggest NOT trying this on your favorite pot! On
greenware it works!!
By the way...why don't you trim the bottoms to desired
thickness once it is leatherhard?? I trim mine the
next day, sometimes the same. I have had cracking
problems myself, but only in pieplates. No pie for me!
Good luck. Marianne Kuiper Milks
--- Rob Di Stasio wrote:
> Newbie question here.
>
> I am learning to throw on the wheel and sometimes I
> leave the pot's
> bottom too thick. I try to dry them very slowly, in
> plastic over a
> period of a few weeks but one of my best pieces to
> date has developed a
> hairline crack in the bottom as it's dried.
>
> I opened it up a bit and forced in more clay but it
> eventually came back.
>
> I heard of mixing up some clay with a little vinegar
> and some shredded
> tissue paper but haven't tried it yet.
>
> I'd like the pot to be functional and watertight so
> I need to fill this
> crack up enough that the glaze will seal it.
>
> Any recommendations of a technique to use to keep
> the crack from
> reappearing so I can get this bisqued and glazed?
>
>
>
> Thanks, Rob
>
>
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> Send postings to clayart@lsv.ceramics.org
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Mark Pitney on sun 10 apr 05
Rob,
You could try lots and lots and lots of things and you will spend a lot of
time and energy doing this as a matter of fact in the time you spend trying to
save this very bestest piece that you will never ever be able to ever make
again you will probably make 20 or so pots that will be a lot better in the
trying. You are going to get lots of cracks and pieces will warp and glazes will
come out wrong but it is all part of the learning and will make you a better
clay artist for it! good luck
Mark and Cindy
The Mudpit
228 Manhattan Ave.
Brooklyn,NY. 11206
_www.mudpitnyc.com_ (http://www.mudpitnyc.com/)
718-218-9424
mudpitnyc@aol.com
Vince Pitelka on sun 10 apr 05
> I am learning to throw on the wheel and sometimes I leave the pot's
> bottom too thick. I try to dry them very slowly, in plastic over a
> period of a few weeks but one of my best pieces to date has developed a
> hairline crack in the bottom as it's dried.
Rob -
I can sympathize with your frustration over this problem, but I suggest that
the best solution is to address the problem in throwing, rather than
attempting to repair the cracks. With time, you will realize that repairing
cracks in greenware is rarely worthwhile - better to spend the time making
more pots. In the archives you can find plenty of information on s-cracks
and compressing bottoms. When you are throwing pots, be sure to measure the
bottom thickness with a needle tool, don't let yourself leave the bottom any
thicker than you want it to be, compress the bottom well by running your
fingertip gently from center to right-hand edge and back again a few times
as the wheel is spinning, and remove all water from the bottom before you
set the pot aside. Also, practice throwing as quickly as you can. This is
not a matter of production efficiency. The faster you throw, the less water
is absorbed, and the more the clay will behave and respond to your wishes.
These are things that will solve themselves as you throw more pots. The
solution is to throw lots more pots, and simply not let yourself get away
with leaving the bottoms thick, leaving the lower walls thick, etc. Even
after decades of making pots, I can distinctly remember the excitement of
conquering these problems.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Antoinette Badenhorst on sun 10 apr 05
Rob, if the bottom is too thick, chances that you might safe it from
cracking in the glaze firing is almost zero, But This can be a nice =
learning
experience for you. This is what I would do: Bisque fire the piece. Take =
a
sharp tool and open the crack just enough so that you can add some clay =
in
there. Mix the following together: Fine grounded bisque clay(from your
claybody, very soft plastic clay(you can add paperclay(which was what =
you
refered to when you mentioned tissue paper) and anything that will make =
it
stick......sugar, arabic gum, or cmc. Soak the pot before you fill the =
crack
up and then as the clay in the crack becomes dry, keep filling it up =
till
you do not see it any more. Scrape the access away with a sharp tool.=20
The reason why I will bisque it first, is because it takes you half way
through the shrinking process.
A way to help you improve the thickness of your bottoms is to measure =
the
average thickness of your walls when you throw. When you open your clay =
on
the wheel,before you start pulling the walls up, you can measure the
thickness of the bottom with a needle tool, by pushing it right through =
the
bottom. If you plan on trimming a footrim, the bottom should be double =
the
thickness of your average wall and if you do not trim a footrim, it =
should
be more ore less the same thickness as your average walls. If you do =
trim a
footrim, you would know that you can go halfway into the bottom, without
fear of going right through.
Here is a tip on helping you to trim your bottoms better: Take a =
toothpick
and break the tip off. It must be as long as the thickness of the rim of
your pot. Push this tip from the inside into the bottom of your pot =
before
you trim it. When you trim the bottom, you can keep on trimming till you =
hit
the toothpick. You can leave it there to burn away or push it out with a
needle tool.
Hope all this would help you.
Regards.
Antoinette Badenhorst
105 Westwood Circle
Saltillo MS, 38866
www.clayandcanvas.com
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Rob Di =
Stasio
Sent: Sunday, April 10, 2005 1:18 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Repairing cracks in greenware?
Newbie question here.
I am learning to throw on the wheel and sometimes I leave the pot's
bottom too thick. I try to dry them very slowly, in plastic over a
period of a few weeks but one of my best pieces to date has developed a
hairline crack in the bottom as it's dried.
I opened it up a bit and forced in more clay but it eventually came =
back.
I heard of mixing up some clay with a little vinegar and some shredded
tissue paper but haven't tried it yet.
I'd like the pot to be functional and watertight so I need to fill this
crack up enough that the glaze will seal it.
Any recommendations of a technique to use to keep the crack from
reappearing so I can get this bisqued and glazed?
Thanks, Rob
_________________________________________________________________________=
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__
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You may look at the archives for the list or change your subscription
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melpots@pclink.com.
Earl Brunner on sun 10 apr 05
Technically speaking, if it is too thick and has a crack, then it probably
isn't one of your "best" pieces. You are too emotionally attached to it.
Learn to trim better (or throw thinner to begin with). Use a needle tool if
you have to, to check thickness as you throw. A small hole is nothing
compared to a crack.
If you can learn not to spend a lot of time fixing pots and use more time to
make them you will be ahead. (that said, even I sometimes try to fix pots
that I like). The problem is that you are trying to put wet material into a
previously shrunk, dry piece, and the wet stuff shrinks as it dries. Bisque
some powdered clay of the same type. Glaze and fire your pot. Glaze fire
some of the powder as well. If the crack isn't healed at that point, mix a
little of the glaze in with the glaze fired powder and work it into the
crack, then refire.
Earl Brunner
Las Vegas, NV
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Rob Di Stasio
Sent: Saturday, April 09, 2005 11:18 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Repairing cracks in greenware?
Newbie question here.
I am learning to throw on the wheel and sometimes I leave the pot's
bottom too thick. I try to dry them very slowly, in plastic over a
period of a few weeks but one of my best pieces to date has developed a
hairline crack in the bottom as it's dried.
I opened it up a bit and forced in more clay but it eventually came back.
I heard of mixing up some clay with a little vinegar and some shredded
tissue paper but haven't tried it yet.
I'd like the pot to be functional and watertight so I need to fill this
crack up enough that the glaze will seal it.
Any recommendations of a technique to use to keep the crack from
reappearing so I can get this bisqued and glazed?
Thanks, Rob
____________________________________________________________________________
__
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.
Cindy in SD on sun 10 apr 05
Dear Rob,
I know how you feel. I remember feeling the same way. Some pottery
teachers have been known to require students to discard all work until
the work reaches the teacher's standards for kiln worthiness. This
sounds harsh, but I tried it at one time and found it liberating. When
you know the pot you're making will be going right to the slop bucket,
you are free to test your limits. You're not worried about whether one
more pass will ruin the piece. There is no pressure to produce work you
will be proud of in ten or even two years. From my experience, I can
tell you that in five years, if you stick with making pottery, you will
want to search and destroy any early work you gave to your relatives.
If you decide to do this, take a wire or a thin-bladed knife and cut
through the pieces from top to bottom before you toss them. This gives
you a good picture of the wall thickness you're achieving. Generally,
the piece will be pretty fat at the base. Sometimes the bottom will be
too thick, but more often it will be too wimpy. Remember that when
cutting a pot off, particularly one with a broad base, the cutting wire
will rise a little bit in the middle, so you need to make the base a
little thicker than you want to end up with (unless you're using plaster
bats, of course). Then, if you intend to trim a foot ring, that requires
extra clay as well.
After a couple of weeks (or even a couple of days) of doing this, I
guarantee you will find your work improving. It is absolutely worth the
pain. Your goal for small pieces is to have even walls all the way to
the bat. For larger pieces, you will need a slight increase in wall
thickness as you approach the base--how much depends in the form and on
the size of the piece. Wide, shallow bowls and broad-rimmed plates
require a little extra support at the bottom, some of which you may want
to trim off later.
That said, here are some tips for keeping your bases from cracking:
1. When you're throwing the pot, don't allow water to sit in the base
for long periods of time. This weakens the base. If you throw
fast, you can use lots of water, but if you throw slowly, you need
to consider what that moisture is doing to the base of your pot.
2. At some point during the throwing process, you need to "compress"
the base. We've had long discussions of this matter, and perhaps
compress is the wrong word, but most people agree that going over
the base with your fingers several times while applying firm
pressure tends to keep the cracks down.
3. Remove the piece from the bat as soon as possible, unless you are
using plaster bats for relatively light pieces. I haven't yet
discovered whether cement board bats provide this same advantage,
because I no longer use bats for small pieces. When pieces sit on
the bat, their bases cannot dry at the same rate as their other
parts. Also, they tend to stick, which adds extra stress when
shrinkage is occurring.
4. If you still have trouble, dry the ware more slowly.
5. If this doesn't work, try turning your kneaded clay on its spiral
end and then rolling it into a log along its cross axis instead of
along its length. Cut your pieces from this log, and you will help
to defeat the clay's "memory" of spiral stress lines.
If none of this works (as it sometimes will not), and you still get
cracking, then put the piece in the slop bucket and make another piece.
There are all sorts of crack remedies out there, and some of them will
actually work on some clays some of the time, but they're really not
worth the trouble.
Best wishes,
Cindy in SD
Malcolm Schosha on mon 11 apr 05
Rob,
The main reason for S cracks in the foot of the pot is not
compressing the the bottom when opening the ball of clay. This is
important. Many potters who throw off the hump have this problem
chronically because in that configuration there is no way to compress
the clay.
Re-cycle the pots with cracks and remember to compress the clay in
the foot of the pot with your thumb when throwing, and the problem
will probabily go away.
Of course, avoid leaving excessive thickness on the bottom also.
Malcolm Schosha
--- In clayart@yahoogroups.com, Rob Di Stasio wrote:
> Newbie question here.
>
> I am learning to throw on the wheel and sometimes I leave the pot's
> bottom too thick. I try to dry them very slowly, in plastic over a
> period of a few weeks but one of my best pieces to date has
developed a
> hairline crack in the bottom as it's dried.
>
> I opened it up a bit and forced in more clay but it eventually came
back.
>
> I heard of mixing up some clay with a little vinegar and some
shredded
> tissue paper but haven't tried it yet.
>
> I'd like the pot to be functional and watertight so I need to fill
this
> crack up enough that the glaze will seal it.
>
> Any recommendations of a technique to use to keep the crack from
> reappearing so I can get this bisqued and glazed?
>
>
>
> Thanks, Rob
>
>
______________________________________________________________________
________
> Send postings to clayart@l...
>
> 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@p...
Eric on sun 17 apr 05
This may be too late, but... (and I'm surprised no one else suggested this)
There are a number of products you can buy which are specifically for
mending greenware or bisqueware cracks. The one that I have used is
called Aztec Mender. You mix it with some slip or clay which matches
your claybody, fill the crack, and fire. It works wonderfully. You can
even use it to reattach pieces of a pot broken clean through. The only
trace of a seam depends on how well you clean clean it up before firing.
If you google on "Aztec mender" you'll find several places online were
you can buy small jar of it for a few bucks. A broader search on
"pottery mender" will lead you to several similar products as well.
Rob Di Stasio wrote:
> Newbie question here.
>
> I am learning to throw on the wheel and sometimes I leave the pot's
> bottom too thick. I try to dry them very slowly, in plastic over a
> period of a few weeks but one of my best pieces to date has developed a
> hairline crack in the bottom as it's dried.
>
> I opened it up a bit and forced in more clay but it eventually came back.
>
> I heard of mixing up some clay with a little vinegar and some shredded
> tissue paper but haven't tried it yet.
>
> I'd like the pot to be functional and watertight so I need to fill this
> crack up enough that the glaze will seal it.
>
> Any recommendations of a technique to use to keep the crack from
> reappearing so I can get this bisqued and glazed?
>
>
>
> Thanks, Rob
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