Linda M on sat 7 aug 04
I am relatively new in this art and I am having problems since I have my
own studio now with a new L&L kiln with digatrol. I never had this problem
when using a friends studio and her kiln.
My problem is: After bisque firing when I open the kiln I have 2 out of 3
sculpture pieces that have cracks where I have added on an eye, a belly, a
tail, etc. or the whole add on piece has broken off. I use newspaper in the
main body to fill the empty cavity and I realize that this takes longer to
dry but pieces sit for a couple of weeks before I load them in the kiln.
(We do have humidity here that ranges from 70% to 95%. However, my studio
is not in a cement basement. It is a separate struture from house that is
designed like a guest house). Could it be that my pieces are not totally
dry? Or could I be leaving air spaces where I attach the additions? I don't
use slip unless the clay has dryed out some. I normally just attach the
addition on to the body because the body is still very moist. Could this be
my problem? I am getting so discouraged after spending hours on a sculpture
to have this happen to so many of them. Can someone tell me what I could be
doing wrong? Thank you for any advise you can give me.
Linda Marcoux
Kathie Johannes on sun 8 aug 04
I had the same problem and lost alot of really good work being in to much
of a hurry, I slowed my firing way------------- down. And of course be
double careful of air pockets.Kathie Johannes
>From: Linda M
>Reply-To: Clayart
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Pop offs & cracking when bisque firing
>Date: Sat, 7 Aug 2004 20:12:04 -0400
>
>I am relatively new in this art and I am having problems since I have my
>own studio now with a new L&L kiln with digatrol. I never had this problem
>when using a friends studio and her kiln.
>My problem is: After bisque firing when I open the kiln I have 2 out of 3
>sculpture pieces that have cracks where I have added on an eye, a belly, a
>tail, etc. or the whole add on piece has broken off. I use newspaper in the
>main body to fill the empty cavity and I realize that this takes longer to
>dry but pieces sit for a couple of weeks before I load them in the kiln.
>(We do have humidity here that ranges from 70% to 95%. However, my studio
>is not in a cement basement. It is a separate struture from house that is
>designed like a guest house). Could it be that my pieces are not totally
>dry? Or could I be leaving air spaces where I attach the additions? I don't
>use slip unless the clay has dryed out some. I normally just attach the
>addition on to the body because the body is still very moist. Could this be
>my problem? I am getting so discouraged after spending hours on a sculpture
>to have this happen to so many of them. Can someone tell me what I could be
>doing wrong? Thank you for any advise you can give me.
>Linda Marcoux
>
>______________________________________________________________________________
>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.
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Mike Gordon on sun 8 aug 04
Linda,
Whenever you add one piece of clay to another it is always a good idea
to score each piece and either use slip or water.Otherwise as the clay
dries they move away from each other and cracks appear after the firing
expansion and contraction phase. My students did all the time, and when
you looked at the piece after firing you could see that the only thing
keeping the two pieces together in the first place was a thin film of
clay which dried faster than the clay around it and it cracked. Mike
Gorodn
On Aug 7, 2004, at 5:12 PM, Linda M wrote:
> I am relatively new in this art and I am having problems since I have
> my
> own studio now with a new L&L kiln with digatrol. I never had this
> problem
> when using a friends studio and her kiln.
> My problem is: After bisque firing when I open the kiln I have 2 out
> of 3
> sculpture pieces that have cracks where I have added on an eye, a
> belly, a
> tail, etc. or the whole add on piece has broken off. I use newspaper
> in the
> main body to fill the empty cavity and I realize that this takes
> longer to
> dry but pieces sit for a couple of weeks before I load them in the
> kiln.
> (We do have humidity here that ranges from 70% to 95%. However, my
> studio
> is not in a cement basement. It is a separate struture from house that
> is
> designed like a guest house). Could it be that my pieces are not
> totally
> dry? Or could I be leaving air spaces where I attach the additions? I
> don't
> use slip unless the clay has dryed out some. I normally just attach the
> addition on to the body because the body is still very moist. Could
> this be
> my problem? I am getting so discouraged after spending hours on a
> sculpture
> to have this happen to so many of them. Can someone tell me what I
> could be
> doing wrong? Thank you for any advise you can give me.
> Linda Marcoux
>
> _______________________________________________________________________
> _______
> 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.
>
Snail Scott on sun 8 aug 04
At 08:12 PM 8/7/2004 -0400, you wrote:
>...I have 2 out of 3
>sculpture pieces that have cracks where I have added on an eye, a belly, a
>tail, etc. or the whole add on piece has broken off...Could it be that my
pieces are not totally
>dry? Or could I be leaving air spaces where I attach the additions? I don't
>use slip unless the clay has dryed out some. I normally just attach the
>addition on to the body because the body is still very moist. Could this be
>my problem?
You are on the right track here. While it is often
possible to attach wet clay to wet clay without
slip or scoring, the fact that you have parts
cracking off shows that, at least in this instance,
it's not sufficient. Remember, it's not slip that
holds the parts together. It's the scoring that
allows the platelets of clay to intermingle and
'grab' onto one another; the slip exists merely to
fil any gaps that might have been created in the
process. Scoring doesn't need to be elaborate. A
few good 'scrubs' on each part with an old wet
toothbrush is often sufficient. Go ahead and give
it a try - it won't slow you doen much at all,
and it might just cure the problem all by itself.
Also, take a good look at your wet-clay joining
technique - are you digging into the thickness of
the clay ('luting'), or just mooshing the edges
to make smooth-looking connection? This will often
suffice in low-stress firing situations, but it's
not a strong joint.
You mentioned that this cracking is a new problem,
which started when you began using another kiln.
It's likely that you are now firing a little
faster than before, and that extra stress is
exposing all the weaknesses of technique that
weren't evident before. Residual moisture may not
have time to escape safely anymore. No clay is ever
perfectly dry, and you're right about newspaper
holding moisture for a long, long time.
Slowing down the firing will probably help, but
strengthening your joints with a little scoring
will be a worthwhile effort, too.
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