Apryl Tackett on sat 31 mar 07
Hi all,
I'm de-lurking to ask (what I hope isn't an overly obvious) question =20
about porcelain. I've just moved from Appalachia (with our wonderful =20
70-98% humidity and mountains) to coastal southern Ca (with an =20
interesting 40% humidity thing going on and I'm right on the =20
coastline, so not much altitude). The problem is - my porcelain work =20
now blows (er, my terra cottas and stonewares have never looked better =20
though). Is there some info anyone could share with me about porcelain =20
that I'm missing? It's all over the place! It cracks, crumbles, =20
shatters - you name it. I've messed with the water content as much as =20
I know how to no avail (the humidity was the only thing I could think =20
of that would totally throw my work like this). I think the best was a =20
gargoyle that I did. When I bisque fired it the body crumbled, the =20
wings exploded, and when I opened the kiln there was a wonderful =20
little head looking up accusingly at me - it, the ears (at different =20
points in the kiln) and a couple of feet survived the carnage. I'm =20
used to working with very thin porcelain walls - but here I've doubled =20
and trippled the wall depth just to keep it upright enough to air dry =20
- and even that hasn't worked. I can go into more detail - but =20
basically it looks and feels right wet - but when it dries it might as =20
well be baby powder and spit...and stingy with the spit.
Thanks in advance!
AprylRae
Matthew Katz on sun 1 apr 07
Hi Apryl,
Wow, sound like you hit a gold mine of problems, sorry to hear that.
I have to say that I'm not sure that they are all related, but let's start
at the beginning.
I can sympathize with the humidity problems. I am from the North East, and I
went out to Colorado for Grad school and I had a lot of problems with the
low humidity when I started. But there are a few ways to overcome the
problems. Now all of these are going to take some experimentation to get
right, but I can promise that in the end they will work.
The thing about drying in a dry climate is that you have to take an almost
obsessive role in controlling the drying, and that you either have to do it
extremely fast or extremely slow, or as I used a combination of the two. For
slow drying, your best option is cheese cloth. Moist (not wet) cheese cloth
wrapped loosely around the work will keep the relative humidity of the piece
constant and slowly let the work acclimate to the low environmental
humidity. To go really slow use a plastic bag over that and occasionally
spritz the cloth with water. I would recommend using high thread count
cheese cloth (NOT what is sold at Jo-ann Fabrics) I buy mine at a chef's
supply store.
The fast method is to use an oscillating fan. This takes a lot of tending
because the work will need to be watched and turned (particularly on the
bottom). to ensure even drying and avoid shrinkage differentials to avoid
cracking. By keeping the fan moving it will be pretty even, but you will
have to figure out how it effects your work. This is a method that replaces
the traditional Hot Box, avoid Hot boxes at all costs! They cause a lot more
problems than they are worth because they create steam within you body which
can cause failure. The fan works with the natural capillary action of the
clay, all it does it to exchange the moist air surrounding the piece with
fresh low humidity air, which then naturally draws water out of the piece
even faster than a hot box. This works extremely fast, I use this all the
time to make something in the morning and have it in a bisque that night.
But make sure to monitor the ware.
Both of these methods are extremely effective. Now that I am back east. I
still use them and they work great.
I need to know a little more information about your other problems to
accurately diagnose them.
Did your piece explode or did it just crumble? If it exploded, than the work
was not dry. Explosions are fairly simple and are always cause by moisture
remaining in the work. Again, the heat turns it to steam and it rushes to
get out of the body. But pressure builds up and it explodes to relieve the
pressure.
As far as the work feeling like power, Are you making your own clay or are
you buying box? Is it the same clay that you were using back east? I have a
few theories, but I need a little more information first.
Keep on fighting the good fight, everything will be alright in the end.
Best,
Matt
On 3/31/07, Apryl Tackett wrote:
>
> Hi all,
>
> I'm de-lurking to ask (what I hope isn't an overly obvious) question
> about porcelain. I've just moved from Appalachia (with our wonderful
> 70-98% humidity and mountains) to coastal southern Ca (with an
> interesting 40% humidity thing going on and I'm right on the
> coastline, so not much altitude). The problem is - my porcelain work
> now blows (er, my terra cottas and stonewares have never looked better
> though). Is there some info anyone could share with me about porcelain
> that I'm missing? It's all over the place! It cracks, crumbles,
> shatters - you name it. I've messed with the water content as much as
> I know how to no avail (the humidity was the only thing I could think
> of that would totally throw my work like this). I think the best was a
> gargoyle that I did. When I bisque fired it the body crumbled, the
> wings exploded, and when I opened the kiln there was a wonderful
> little head looking up accusingly at me - it, the ears (at different
> points in the kiln) and a couple of feet survived the carnage. I'm
> used to working with very thin porcelain walls - but here I've doubled
> and trippled the wall depth just to keep it upright enough to air dry
> - and even that hasn't worked. I can go into more detail - but
> basically it looks and feels right wet - but when it dries it might as
> well be baby powder and spit...and stingy with the spit.
>
> Thanks in advance!
> AprylRae
>
>
> ______________________________________________________________________________
> 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.
>
--
Matthew Katz
Alfred, NY
Apryl Tackett on sun 1 apr 07
Thanks so much Matt!
I have been systematically going nuts trying to get my porcelain =20
straightened out, and I really appreciate the help. I've been able to =20
slow down the drying a little this past week using a light cloth, =20
wadded up damp papertowels and a plastic bag...so I think the fine =20
cheesecloth may do the trick. I was hoping that it was something I'd =20
just have to experimant with, but after the whole "gargoyle of doom" =20
incident in my kiln I was ready to throw the towel in on porcelain.
I'll break down different things that have happened so it will be =20
easier to identify the problems. Oh - right now I'm using a domestic =20
porcelain from Great Lakes (link: =20
http://www.greatclay.com/Merchant2/merchant.mvc?Screen=3DPROD&Product_Code=
=3DMCL330&Category_Code=3DMCP&Product_Count=3D0 ) I had it shipped out here =
so I could start out with familiar clay. Our studio is small, so right now w=
e're using =20
premixed.
1) Thrown pieces (and tall thin hand built ones) have had to be =20
thicker to stand up straight while air drying. When I've done pieces =20
as thin as I'm used to they fold in on themselves, or flop over in =20
half. I've had pieces stay upright and nice for hours, then open the =20
studio in the morning and find a mess of pieces flopped over. =20
Basically, anything over 8 inches tall stands a 50% chance of folding. =20
I had one stay nice by lightly poking a paper towel down the middle - =20
it was still thicker than I like, but not horribly so.
2)Flat pieces have bowed - even if I flip them while drying. The best =20
example of this is a plaque (oval, about 1/4 inch thick, 9 inch wide, =20
5 inch tall). I had it covered with a lightly damp cloth, sitting on =20
another dry cloth, and a bag over it. I flipped about 6 hours after =20
setting it out to dry, and again before closing. Everything was fine =20
for the day, next morning it looked like a sled runner. I sponged =20
water onto the concave side and it went flat again. Ultimatly it =20
cracked in four pieces and got ground to slip.
3) Flat pieces that don't bow crumble. I had a larger rectangular =20
piece (roughly 12inch x 16 inch, 1/2 inch thick at the edges) that =20
dried nicely. When I picked it up to hold it to my face it felt nice, =20
no bows, no cool spots. I walked it to the open kiln, holding it by =20
the bottom like an offering plate, leaned over to put it in and a =20
couple inched from the kilnshelf it crumbled in my hands. *crumbled* I =20
was all O_o huh!?!?
4) Thicker pieces - I just don't know! I think the statue/bookend =20
exploded (I *hope* it exploded - I can explain that!). The body part =20
(well, the debris) lookled like the platter that crumbled, but the =20
wings certainly had some trajectory. Since the ears were under the =20
kiln shelf, and I found a foot dangling from the oposite side of =20
another piece I'm leaning toward explosion. It felt totally dry, =20
pieces I've done that size before have dried in less time, and just to =20
make sure I left it in a plastic bag for a couple of days after I =20
thought it was dry and checked it again. I think that poor piece was =20
just my last straw.
5) When I join leather pieces with slip they rarely join right, and I =20
have to use a LOT of slip. When I put on what I'm used to using it =20
dries almost immediatly, so I gob it on, join it, let it dry to icing =20
consistancy and trim it a little. Once it is totally dry I file it =20
down flush. I pop it in a bag to dry so the slip moisture is pulled =20
through the piece and can balance out. It may or may not stick - =20
they've been getting better here lately.
I think that coveres the big problems...unless my kiln has a haint ;) =20
Seriously though - my stoneware and terra cottas are turning out =20
better than ever, it's just the porcelain that's racking my brain.
Thanks again for looking at this for me!
Leigh Whitaker on sun 1 apr 07
This may be a dumb idea, but is there any way you can get a humidifier for
your studio? (An alien idea to me, having grown up in Alabama.) That's
assuming the humidity is the problem. I have absolutely no idea about that, since
I have no experience with porcelain.
My husband recently had to have some expensive repairs done on his Martin
Guitar, which he had been storing hanging on the wall. The repair guy gently
chastised him for not keeping the Martin in a humidified case. My husband was
surprised that they didn't tell him this when he bought the guitar, but he
bought it in Knoxville, TN, so I doubt it was as much of a problem there! He
how has a special guitar humidifier that he keeps inside the guitar. I
didn't even know they made such a thing.
Leigh
************************************** See what's free at http://www.aol.com.
John Hesselberth on sun 1 apr 07
On Apr 1, 2007, at 3:54 PM, Apryl Tackett wrote:
> Thanks so much Matt!
>
> I have been systematically going nuts trying to get my porcelain
> straightened out, and I really appreciate the help. I've been able
> to slow down the drying a little this past week using a light
> cloth, wadded up damp papertowels and a plastic bag...so I think
> the fine cheesecloth may do the trick. I was hoping that it was
> something I'd just have to experimant with, but after the whole
> "gargoyle of doom" incident in my kiln I was ready to throw the
> towel in on porcelain.
>
> I'll break down different things that have happened so it will be
> easier to identify the problems. Oh - right now I'm using a
> domestic porcelain from Great Lakes (link: http://www.greatclay.com/
> Merchant2/merchant.mvc?
> Screen=PROD&Product_Code=MCL330&Category_Code=MCP&Product_Count=0 )
> I had it shipped out here so I could start out with familiar clay.
> Our studio is small, so right now we're using premixed.
>
> 1) Thrown pieces (and tall thin hand built ones) have had to be
> thicker to stand up straight while air drying. When I've done
> pieces as thin as I'm used to they fold in on themselves, or flop
> over in half. I've had pieces stay upright and nice for hours, then
> open the studio in the morning and find a mess of pieces flopped
> over. Basically, anything over 8 inches tall stands a 50% chance of
> folding. I had one stay nice by lightly poking a paper towel down
> the middle - it was still thicker than I like, but not horribly so.
>
> 2)Flat pieces have bowed - even if I flip them while drying. The
> best example of this is a plaque (oval, about 1/4 inch thick, 9
> inch wide, 5 inch tall). I had it covered with a lightly damp
> cloth, sitting on another dry cloth, and a bag over it. I flipped
> about 6 hours after setting it out to dry, and again before
> closing. Everything was fine for the day, next morning it looked
> like a sled runner. I sponged water onto the concave side and it
> went flat again. Ultimatly it cracked in four pieces and got ground
> to slip.
>
> 3) Flat pieces that don't bow crumble. I had a larger rectangular
> piece (roughly 12inch x 16 inch, 1/2 inch thick at the edges) that
> dried nicely. When I picked it up to hold it to my face it felt
> nice, no bows, no cool spots. I walked it to the open kiln, holding
> it by the bottom like an offering plate, leaned over to put it in
> and a couple inched from the kilnshelf it crumbled in my hands.
> *crumbled* I was all O_o huh!?!?
>
> 4) Thicker pieces - I just don't know! I think the statue/bookend
> exploded (I *hope* it exploded - I can explain that!). The body
> part (well, the debris) lookled like the platter that crumbled, but
> the wings certainly had some trajectory. Since the ears were under
> the kiln shelf, and I found a foot dangling from the oposite side
> of another piece I'm leaning toward explosion. It felt totally dry,
> pieces I've done that size before have dried in less time, and just
> to make sure I left it in a plastic bag for a couple of days after
> I thought it was dry and checked it again. I think that poor piece
> was just my last straw.
>
> 5) When I join leather pieces with slip they rarely join right, and
> I have to use a LOT of slip. When I put on what I'm used to using
> it dries almost immediatly, so I gob it on, join it, let it dry to
> icing consistancy and trim it a little. Once it is totally dry I
> file it down flush. I pop it in a bag to dry so the slip moisture
> is pulled through the piece and can balance out. It may or may not
> stick - they've been getting better here lately.
>
> I think that coveres the big problems...unless my kiln has a
> haint ;) Seriously though - my stoneware and terra cottas are
> turning out better than ever, it's just the porcelain that's
> racking my brain.
>
> Thanks again for looking at this for me!
>
> ______________________________________________________________________
> ________
> 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.
Vince Pitelka on sun 1 apr 07
Leigh Whitaker wrote:
> This may be a dumb idea, but is there any way you can get a humidifier for
> your studio? (An alien idea to me, having grown up in Alabama.) That's
> assuming the humidity is the problem. I have absolutely no idea about
> that, since
> I have no experience with porcelain.
Leigh -
Actually, that is a very sound suggestion. I had a studio in Northern
California about five miles up the valley of the Mad River, in the town of
Blue Lake. In the summertime things were very dry, and in order to slow
down drying, I humidified one of the rooms in my studio with a standard
cold-mist humidifier, and an occasional bucket of water just sloshed across
the concrete slab floor. In the winter it is very damp on the north Pacific
Coast, and I used a dehumidifier. Worked great.
- 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/
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