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warping platters


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#1 alligator alley

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Posted 31 January 2012 - 04:24 PM

I am having a major problem with warping platters and plates as they are drying, I use just a lot of different vessels as my molds, even glazed pieces, I try to keep them covered as they are drying. I use cone 6 clay from Standard, sometimes white and other times brown; I am getting to the point of giving up,as I am pretty new to this mud business, don't seem to be getting the hang of it. Any help will be appreciated

#2 neilestrick

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Posted 31 January 2012 - 04:38 PM

Describe the warp. Is the foot humping up as they dry upside down? If so, the bottom is too thick, or too thick in the middle. I have also seen this problem if the bottom is too wet while trimming. Sometimes I'll trim it, then trim it again after it dries a bit more.
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#3 Mark C.

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Posted 31 January 2012 - 07:33 PM

It sounds like you are draping slabs over molds?
Are the slabs made with rolling clay from 1 side only?
Give us more info on how and what you are doing so we can help
mark
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#4 Pres

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Posted 01 February 2012 - 09:26 AM

I am having a major problem with warping platters and plates as they are drying, I use just a lot of different vessels as my molds, even glazed pieces, I try to keep them covered as they are drying. I use cone 6 clay from Standard, sometimes white and other times brown; I am getting to the point of giving up,as I am pretty new to this mud business, don't seem to be getting the hang of it. Any help will be appreciated


Yes, as Mark says, give us more info. 1) How thick and how large are you making the platters? 2)How are you rolling out the slabs-one direction, two directions or multi? 3)What sort of supports are you putting on them(foot ring, knob feet, etc) 4) Are you placing them directly on the mold form or using paper or powdered clay between. I think if you can answer those questions we can give you some possible solutions to your problem.

Simply retired teacher, not dead, living the dream. on and on and. . . . on. . . .                                                                                 http://picworkspottery.blogspot.com/


#5 bciskepottery

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Posted 01 February 2012 - 07:40 PM

Some general considerations for slabs . . .

If you are hand forming/rolling your slab, be sure to rotate the slab as you form it. Avoid stretching/rolling it in only one direction. If you are using a slab roller, roll the slab back and forth at least twice to get an even slab, if possible, rotate the slab 90 degrees so you stretch it in all directions. If you can't rotate it on the slab roller, take a rolling pin and roll it in opposite directions.

You want to keep the slab flat at all times if you want to make flat-ware (plates, platters). I roll my slabs between two pieces of canvass. After rolling on the slab roller, I remove the top canvass and use a dry wall trowel/scraper to remove any texture from the canvass. Then, I place clean newsprint on top of the slab, put a ware board on top of the newsprint, fold the edges of the canvass over the back of the ware board and flip it. The canvass holds the slab flat against the ware board. Remove the bottom canvass and clean up the texture with the dry wall tool or rib. Then I carry the slab on the ware board over to the table where I work. Using a sandwich approach to flipping the slab helps prevent warping when the slab is drying. Clay has memory; if you bend it, it will want to go back to that memory/shape later on.

A good way to compress a slab, once it is made, is to take the ware board with the slab, hold it at about waist high, and drop it flat on the floor. Noisy, yes, but rather effective.

If you are using a non-porous item for the mold (i.e., glazed wares, plastic tray, glass platter, etc.), the clay slab will stick and, as it dries, warp. Dust the surfaces of your non-porous molds with corn starch, place some cheese cloth between the mold and clay, or spray with Pam. These will act to prevent the clay from sticking to the mold surface as it dries. Watch for any undercuts in your molds; another place where the clay can get hung up while drying and warp.

I use a sandbag -- a half cup or so of sand on some plastic wrap, tied up, then placed in an old piece of table napkin or tee shirt that is also tied up -- to press my slabs into a mold. (Actually, you need two sand bags, one for white clay, one for brown/red.) The sandbag allows you to shape the slab without leaving fingerprints or marring texture.

When picking up a slab to carry it, use two paint sticks -- one under the edge, the other on top -- to pick up the slab. That distributes the pressure from lifting and carrying and avoids tears.

Check out Youtube . . . search for slab built pottery, platters, etc. You may find some videos that show how to make, use slabs. Visuals often work better than words when explaining this process.

No need to give up. Learn from your experiences.

#6 earthquake

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Posted 01 February 2012 - 09:03 PM

I am having a major problem with warping platters and plates as they are drying, I use just a lot of different vessels as my molds, even glazed pieces, I try to keep them covered as they are drying. I use cone 6 clay from Standard, sometimes white and other times brown; I am getting to the point of giving up,as I am pretty new to this mud business, don't seem to be getting the hang of it. Any help will be appreciated



#7 earthquake

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Posted 01 February 2012 - 09:07 PM

I have had the same problem with Standard Clay #181 White. I was also having a problem with cracking while drying. I did everything "by the book". I was telling a potter friend ...just casually...and she said...thank you, thank you..she was having the same problem. I have stopped using that clay for slab built plates and platters. I called the company. There response was..yes , we are aware of the problem. Sometimes it cracks and sometimes it doesn't. Well...i won't buy the product any more.

#8 neilestrick

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Posted 02 February 2012 - 12:56 PM

I have had the same problem with Standard Clay #181 White. I was also having a problem with cracking while drying. I did everything "by the book". I was telling a potter friend ...just casually...and she said...thank you, thank you..she was having the same problem. I have stopped using that clay for slab built plates and platters. I called the company. There response was..yes , we are aware of the problem. Sometimes it cracks and sometimes it doesn't. Well...i won't buy the product any more.


Standard #181 is a very smooth body, and is not good for slab work at all. I would go with #182, which is very smooth to the touch, but does have some fireclay in it, which greatly reduces warping and cracking.
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#9 alligator alley

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Posted 02 February 2012 - 10:25 PM

Some general considerations for slabs . . .Thanks for the help, I use a slabroller and turn the clay as I go, rotating, I then pick the clay up and turn it over, don't know why i started doing this. I have always just picked the clay up and place on mold ,which I do spray with Pam.I don't have feet at this time, attach before real leather. I roll out to about 1/4 inch

If you are hand forming/rolling your slab, be sure to rotate the slab as you form it. Avoid stretching/rolling it in only one direction. If you are using a slab roller, roll the slab back and forth at least twice to get an even slab, if possible, rotate the slab 90 degrees so you stretch it in all directions. If you can't rotate it on the slab roller, take a rolling pin and roll it in opposite directions.

You want to keep the slab flat at all times if you want to make flat-ware (plates, platters). I roll my slabs between two pieces of canvass. After rolling on the slab roller, I remove the top canvass and use a dry wall trowel/scraper to remove any texture from the canvass. Then, I place clean newsprint on top of the slab, put a ware board on top of the newsprint, fold the edges of the canvass over the back of the ware board and flip it. The canvass holds the slab flat against the ware board. Remove the bottom canvass and clean up the texture with the dry wall tool or rib. Then I carry the slab on the ware board over to the table where I work. Using a sandwich approach to flipping the slab helps prevent warping when the slab is drying. Clay has memory; if you bend it, it will want to go back to that memory/shape later on.

A good way to compress a slab, once it is made, is to take the ware board with the slab, hold it at about waist high, and drop it flat on the floor. Noisy, yes, but rather effective.

If you are using a non-porous item for the mold (i.e., glazed wares, plastic tray, glass platter, etc.), the clay slab will stick and, as it dries, warp. Dust the surfaces of your non-porous molds with corn starch, place some cheese cloth between the mold and clay, or spray with Pam. These will act to prevent the clay from sticking to the mold surface as it dries. Watch for any undercuts in your molds; another place where the clay can get hung up while drying and warp.

I use a sandbag -- a half cup or so of sand on some plastic wrap, tied up, then placed in an old piece of table napkin or tee shirt that is also tied up -- to press my slabs into a mold. (Actually, you need two sand bags, one for white clay, one for brown/red.) The sandbag allows you to shape the slab without leaving fingerprints or marring texture.

When picking up a slab to carry it, use two paint sticks -- one under the edge, the other on top -- to pick up the slab. That distributes the pressure from lifting and carrying and avoids tears.

Check out Youtube . . . search for slab built pottery, platters, etc. You may find some videos that show how to make, use slabs. Visuals often work better than words when explaining this process.

No need to give up. Learn from your experiences.



#10 alligator alley

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Posted 02 February 2012 - 10:53 PM

It sounds like you are draping slabs over molds?
Are the slabs made with rolling clay from 1 side only?
Give us more info on how and what you are doing so we can help
mark


I am draping over molds, but I do roll on both sides and try to pay careful attention to rolling at different angles, but I do pick the clay up without the sticks, have never done that, something else new to learn, haha, that's probably where I'm creating the problem, since clay does have a memory; also I roll to about 1/4 to 1/2 thickness

#11 alligator alley

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Posted 02 February 2012 - 11:07 PM

Describe the warp. Is the foot humping up as they dry upside down? If so, the bottom is too thick, or too thick in the middle. I have also seen this problem if the bottom is too wet while trimming. Sometimes I'll trim it, then trim it again after it dries a bit more.


I am picking the slab up as soon as I get finished with the slabbing, not letting the clay set_up a while to firm somewhat, just read that I should do this. Thanks fo any input

#12 Benhim

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Posted 03 February 2012 - 02:02 AM

1) If you have a wheel my advice is to make slabs on the wheel. It's very quick using soft clay to slab it out on a wheel. The slabbed product has better aligned particles that will resist warping much better than anything rolled with a rolling device of any kind.

2) Make a plaster bisque of anything that's already glazed if you like it that much. My best slump or hump molds are made with bisque, but if you're not able or just have a shape you like plaster cement like hydrostone works pretty well. I dislike No. 1 Pottery Plaster as it's too soft for this type of mold.

3) Use porous molds to allow quicker setting and more even drying. Uneven drying will cause warping as the outside dries the surface in contact can't dry. Then when the wetter surface later does dry it pulls on the already drier surface causing warping. You can't really combat this except to not do it in the first place.

BenCo Ceramics


#13 Mark C.

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Posted 03 February 2012 - 03:20 AM


It sounds like you are draping slabs over molds?
Are the slabs made with rolling clay from 1 side only?
Give us more info on how and what you are doing so we can help
mark


I am draping over molds, but I do roll on both sides and try to pay careful attention to rolling at different angles, but I do pick the clay up without the sticks, have never done that, something else new to learn, haha, that's probably where I'm creating the problem, since clay does have a memory; also I roll to about 1/4 to 1/2 thickness


We make many slab items here from one of a kind fish to production baking dishes
we use a bailey slab roller which has two rollers for even pressing
hump molds need to have clay removed as soon as its dry and none to past that as they get caught up on mold while shrinking
slump molds are more forgiving as clay shrinks away from mold walls
we use cloth on one surface and a (slab mat) brand heavy cardboard texture free for the other side
the clay is firm from the bag so before flipping large slabs into molds is easy-also we cut them down to just over size so there is less to handle
most of ours are 1/4 to no more than 3/8ths thick
As soon as they are dry enough to come out of molds we handle them then lay a stick on handles to keep them from lifting-dry them slow at first
The problems we have had is only with the clay body itself-it took some tests to find the right body
we fire cone 11 porcelain reduction fires mostly and most of the slab work is with a Laguna clay body called 1/2 and 1/2 they make two of these bodies the one that works best for slabs has grog not fine sand in it
They may make this in mid range temperature
I feel it may be your clay body after hearing the story-I would try another body
Mark
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#14 DAY

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Posted 03 February 2012 - 10:02 AM

I have had a different experience with Standard's 181. I built hundreds and hundreds of bird feeders over a 10 year period, and had no problems. Of course that was after (circa 1990) complaining about cracking- and after that Standard began putting molochite in the mix.


I use a Bailey double roller to make my slabs. And Tyvek as a support. My 12"-15" circles, 3/8" thick, are prepared on a piece of Tyvek, which I pick up by the "ears", and drape over the mold. The clay sticks to the Tyvek, so there is no stress on the clay.

#15 alligator alley

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Posted 03 February 2012 - 07:01 PM

1) If you have a wheel my advice is to make slabs on the wheel. It's very quick using soft clay to slab it out on a wheel. The slabbed product has better aligned particles that will resist warping much better than anything rolled with a rolling device of any kind.

2) Make a plaster bisque of anything that's already glazed if you like it that much. My best slump or hump molds are made with bisque, but if you're not able or just have a shape you like plaster cement like hydrostone works pretty well. I dislike No. 1 Pottery Plaster as it's too soft for this type of mold.

3) Use porous molds to allow quicker setting and more even drying. Uneven drying will cause warping as the outside dries the surface in contact can't dry. Then when the wetter surface later does dry it pulls on the already drier surface causing warping. You can't really combat this except to not do it in the first place.



#16 alligator alley

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Posted 03 February 2012 - 07:04 PM


1) If you have a wheel my advice is to make slabs on the wheel. It's very quick using soft clay to slab it out on a wheel. The slabbed product has better aligned particles that will resist warping much better than anything rolled with a rolling device of any kind.

2) Make a plaster bisque of anything that's already glazed if you like it that much. My best slump or hump molds are made with bisque, but if you're not able or just have a shape you like plaster cement like hydrostone works pretty well. I dislike No. 1 Pottery Plaster as it's too soft for this type of mold.

3) Use porous molds to allow quicker setting and more even drying. Uneven drying will cause warping as the outside dries the surface in contact can't dry. Then when the wetter surface later does dry it pulls on the already drier surface causing warping. You can't really combat this except to not do it in the first place.


I thank you for the tips, making my own molds seems to be the best all around for me, again thanks




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