marci Boskie's Mama =3D^..^=3D on sun 13 feb 11
Speakingof cracks on handles, I have an odd issue with some of my
jewelry pieces:
I use Laguna frost cone 6 porcelain, rolled very thin with a rolling
pin into an oval-y shape, then I flip the top edge over so that it
forms a loop that a chain can be run through . I stack them in pizza
boxes to dry ...
The odd thing is that some of them will develop a crack right in
the center of the part where it loops over , not where the end of
the loop over attachs to the body . ( I use a small amount if slurry
to attach ) ( Picture a taco where instead of folding it in half,
you roll one edge over to only about 1/5 of the way down and attach
the rolled over part to the body of the taco ...Thats sorta what
they look like and the crack forms right at the top edge of where
the taco is rolled over ) ...
The thing is: If cracks form because of variations in dampness,
whats going on here? I do the roll over as soon as I get the clay
rolled to the desired thinness, and its the same piece of clay so Im
not attaching things that are different degrees of dry... and it
doesnt happen on all of them ... some turn out just fine ..
Would covering them with plastic help? Would the act of laying
them out on cardboard be enough to draw more moisture out of the body
of the piece , leaving the roll-over part just wet enough to crack? (
These are VERY thin )
Marci the baffled chinapainter
marci Boskie's Mama =3D^..^=3D on sun 13 feb 11
At 11:03 AM 2/13/2011, James Freeman wrote:
>The same thing is happening to your loop. It seems the easiest
>solution to your problem would be to simply roll the loop, but do
>not attach the rolled edge to the base piece. This will allow it to
>move freely as it shrinks, and should still be sufficiently "closed"
>to hold onto the chain or cord. Any small gap which opened up would
>likely be sealed with glaze anyway. A second option, if sealing the
>rolled loop is in fact necessary, might be to elevate the piece as
>it dries so that air can get to all sides of the loop evenly. A
>third option might be to dry the pieces on a plaster slab so that
>the plaster is drawing moisture from the back of the loop while the
>top air dries. I am sure you will get many other good suggestions.
Hi James.
I tried the ' not attaching' thing and the loop springs up to
form too large a gap.
However , your last two suggestions might be the answer ..Sounds like
I was thinking backwards... thinking that the cardboard from the
pizza boxes I lay them out in was pulling more moisture from the back
....Ill try the elevating thing and the plaster slab thing ... Thanks...
If youre coming to NCECA, I owe you a beer :O) .. ( or a taco ) ...
Marci the chinapanter
Birgit Wright on sun 13 feb 11
Hi Marci=3D3B Something I find happens when I am handbuilding is that if I=
f=3D
old something over more than 90 degrees=3D2Clike an L shape and then on to =
co=3D
mpletely in half like a taco=3D2C even with soft clay=3D2C the clay at the=
fol=3D
d opens like fish scales=3D2C as if the bending fish turned but the ridgid =
fi=3D
ns would fan open. If you were to take your finger or a sponge and smooth=
=3D
the clay around the bend you close the "scales" and smooth them out and t=
=3D
hey may not crack. With your discs being so small and thin you might not p=
=3D
erceive the cracks with your eye but they will be there. Maybe this will b=
=3D
e useful.
=3D20
Cheers=3D2C Birgit Wright=3D20
=3D20
> Date: Sun=3D2C 13 Feb 2011 10:25:03 -0600
> From: marci@PPIO.COM
> Subject: Re: cracks not on handles
> To: Clayart@LSV.CERAMICS.ORG
>=3D20
> Speakingof cracks on handles=3D2C I have an odd issue with some of my
> jewelry pieces:
> I use Laguna frost cone 6 porcelain=3D2C rolled very thin with a rolling
> pin into an oval-y shape=3D2C then I flip the top edge over so that it
> forms a loop that a chain can be run through . I stack them in pizza
> boxes to dry ...
> The odd thing is that some of them will develop a crack right in
> the center of the part where it loops over =3D2C not where the end of
> the loop over attachs to the body . ( I use a small amount if slurry
> to attach ) ( Picture a taco where instead of folding it in half=3D2C
> you roll one edge over to only about 1/5 of the way down and attach
> the rolled over part to the body of the taco ...Thats sorta what
> they look like and the crack forms right at the top edge of where
> the taco is rolled over ) ...
> The thing is: If cracks form because of variations in dampness=3D2C
> whats going on here? I do the roll over as soon as I get the clay
> rolled to the desired thinness=3D2C and its the same piece of clay so Im
> not attaching things that are different degrees of dry... and it
> doesnt happen on all of them ... some turn out just fine ..
> Would covering them with plastic help? Would the act of laying
> them out on cardboard be enough to draw more moisture out of the body
> of the piece =3D2C leaving the roll-over part just wet enough to crack? (
> These are VERY thin )
> Marci the baffled chinapainter
=3D
James Freeman on sun 13 feb 11
On Sun, Feb 13, 2011 at 11:25 AM, marci Boskie's Mama =3D^..^=3D o.com
> wrote:
> Speakingof cracks on handles, I have an odd issue with some of my
> jewelry pieces:
> I use Laguna frost cone 6 porcelain, rolled very thin with a rolling
> pin into an oval-y shape, then I flip the top edge over so that it
> forms a loop that a chain can be run through . I stack them in pizza
> boxes to dry ...
> The odd thing is that some of them will develop a crack right in
> the center of the part where it loops over , not where the end of
> the loop over attachs to the body .
>
Marci...
Cracks don't form from variations in moisture content per se. The cracking
that was being discussed, where a handle is adjoined to a pot, is caused by
variations in shrinkage of the respective parts, and this variation in
shrinkage is caused by the variation in moisture content.
In the case of an attached handle, the mug body is leather hard, meaning it
has already done about half of it's total shrinkage. You attach a handle
made of much fresher, much wetter clay. As the piece continues to dry, the
mug body does not shrink much more since it has gotten much of it's
shrinkage out of the way already, but the handle still has all of it's
shrinking to do, so it shrinks quite a bit more than the piece to which it
is attached. Since the handle shrinks more than the clay to which it was
attached, it must pull away to relieve the stress.
In the case of your rolled tacos, the cause is also likely differential
shrinkage caused by differential moisture content, but the cause of this
moisture differential is not the same as in the handle case. When you roll
and attach the edge of the clay disc to form your loop, and then set the
piece flat in your drying box, the clay forming the exposed portion of the
loop can dry much faster than the clay forming the back of the loop, since
this part is laying flat on your drying surface. Therefore, the clay
forming the exposed part of the loop can start to shrink before the back of
the loop does, and since it does not have enough mechanical strength to ben=
d
the larger, damper part of the loop, it must instead crack to relieve the
stress.
Picture this: Suppose you have two leather hard thrown pots standing on
your table several inches apart, and you connect them with a strap of fresh
clay. As your clay strap shrinks, it must either pull the two pots to whic=
h
it is attached closer together, or, failing that, it must crack in two or
separate from one of the pots. It has no other choices as it gets shorter.
Either the gap must shrink with it, or it must give.
The same thing is happening to your loop. It seems the easiest solution to
your problem would be to simply roll the loop, but do not attach the rolled
edge to the base piece. This will allow it to move freely as it shrinks,
and should still be sufficiently "closed" to hold onto the chain or cord.
Any small gap which opened up would likely be sealed with glaze anyway. A
second option, if sealing the rolled loop is in fact necessary, might be to
elevate the piece as it dries so that air can get to all sides of the loop
evenly. A third option might be to dry the pieces on a plaster slab so tha=
t
the plaster is drawing moisture from the back of the loop while the top air
dries. I am sure you will get many other good suggestions.
Good luck.
...James
James Freeman
"...outsider artists, caught in the bog of their own consciousness, too
preciously idiosyncratic to be taken seriously."
"All I say is by way of discourse, and nothing by way of advice. I should
not speak so boldly if it were my due to be believed."
-Michel de Montaigne
http://www.jamesfreemanstudio.com
http://www.flickr.com/photos/jamesfreemanstudio/
http://www.jamesfreemanstudio.com/resources
marci Boskie's Mama =3D^..^=3D on sun 13 feb 11
At 11:26 AM 2/13/2011, Birgit Wright wrote:
>Hi Marci; Something I find happens when I am handbuilding is that
>if I fold something over more than 90 degrees,like an L shape and
>then on to completely in half like a taco, even with soft clay, the
>clay at the fold opens like fish scales, as if the bending fish
>turned but the ridgid fins would fan open. If you were to take
>your finger or a sponge and smooth the clay around the bend you
>close the "scales" and smooth them out and they may not
>crack. With your discs being so small and thin you might not
>perceive the cracks with your eye but they will be there. Maybe
>this will be useful.
>
>Cheers, Birgit Wright
Hi Birgit,
Thanks! Yes, another possibility . I'll try that too ...
Marci
monkeymind88@COMCAST.NET on mon 14 feb 11
>Hi Marci; Something I find happens when I am handbuilding is that
>if I fold something over more than 90 degrees,like an L shape and
>then on to completely in half like a taco, even with soft clay, the
>clay at the fold opens like fish scales, as if the bending fish
>turned but the ridgid fins would fan open. If you were to take
>your finger or a sponge and smooth the clay around the bend you
>close the "scales" and smooth them out and they may not crack.
>With your discs being so small and thin you might not perceive the
>cracks with your eye but they will be there. Maybe this will be
>useful.
Better yet, in the act of bending clay, you need to 'coax' it into
shape. Make the part that will have the most alteration slightly
thicker than the rest, then using a very light touch and a series of
alterations--nothing drastic, but slowly in steps--maneuver the clay
into the shape you want. This way, the thickness will be more
uniform and less is asked of the interior structure of the clay in
the alteration of it.
--
Jeanette Harris in Poulsbo WA
http://www.jeanetteharrisblog.blogspot.com
http://fiberneedlethread.blogspot.com/
http://www.washingtonpotters.org/WPA_Gallery.htm
http://www.southernarizonaclayartists.org/gallery/jeanette-harris
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