hi - i'm new to slab work. does anyone have a trick for keeping a round vase (with two vertical seams) from warping itself out of round? i've covered it in plastic, and let it dry for many days, but no luck. any help is appreciated. (using porcelain clay)
Posted 18 January 2014 - 02:38 PM
I think that folks need a little more information on you slab rolling and assembly technique. Do you use a tube form to work around, are you putting the piece together when the clay is stiffer, or when it first comes off of the roller. How tall are you working. All of these things might help to pinpoint some areas of improvement.
Posted 18 January 2014 - 03:18 PM
Posted 18 January 2014 - 03:50 PM
What about after rolling it out, you wrap it around your form and let it dry a bit? it could even be dried sideways around the form, so it wouldn't sag in it's more flexible state. You wouldn't even have to connect the ends at this point. Once it has dried slightly, slightly then connect the ends, via your stated method. It will be tougher to cut the miter in this manner, but it should help resolve your issue.
Posted 18 January 2014 - 04:22 PM
I do a lot of slab work, including cylinders 15+ inches. I make my slabs larger than the forms planned and I place the slab on a piece of foam and roll it with the paper form -- that gives the slab a new memory. By making the slab larger than needed, you can cut away the ends of the slab that will want to pull back and which don't get as much new memory from rolling as the interior of the slab.
I form my slabs around thick paper tubes -- the inside tubes found in rolls of shrink wrap; I also put the paper tube inside a cheap knee-high nylon that is tied at the top; the clay does not stick to the nylon and you don't have to keep wrapping the tube in newspaper, etc. I only use one seam, beveled, scored and slipped (I use magic water in my joining slips). I use a 60 degree bevel, not 45 degree bevel because it gives you more overlap. If I want to keep a round form, and while the cylinder is still wrapped around the form, I will add a bottom and then I will take strips of newspaper or plastic bag and wrap them around the outside and fasten down the ends with masking tape. These strips provide just enough tension at the outset that it helps keep the clay memory from wanting to pull apart at the seam; as the clay becomes leather-hard, the bands will loosen. I let the cylinder set up for a while before removing the paper tube. Overnight, I place a plastic bag (generally the ones newspapers are delivered in) over the cylinder to slow drying.
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Posted 18 January 2014 - 04:40 PM
Posted 18 January 2014 - 05:41 PM
It is possible the outside of your slabs feels drier than the inside is, and that your tall pieces are slumping. If I make slabs in advance, I put a sheet of plastic between the clay and each piece of Sheetrock. The clay does not dry out, and the Sheetrock does not mildew. I can uncover the slab to dry a bit and then re-cover it to reach moisture consistency. Assorted sponges are good for propping things up while they dry.
Dry Ridge Pottery
Posted 19 January 2014 - 01:08 PM
Also ... How on earth do you drywall lovers handle the extra weight of those things when they are wet? Where do you store them between uses? How do you move around a slab of clay sandwiched between two of them?
They just seem to be a 'solution' that creates several other problems ... But then, I admit to being lazy anyhow. I cannot imagine hauling drywall around in an effort to deal with slab warping problems.
Contemporary Fine Colored Porcelain
TRY ... FAIL ... LEARN ... REPEAT
" ... If a sufficient number of people are different, no one has to be normal"
Posted 19 January 2014 - 02:44 PM
Posted 19 January 2014 - 04:02 PM
My fantasy is a pottery fairy who comes during the night and leaves behind perfectly wedged clay and several nice slabs, ready for use.
Dry Ridge Pottery
Posted 19 January 2014 - 04:14 PM
I will also make multiple slabs and store them in plastic bins with covers, with a piece of plastic between slabs. You can stack 4 or 5 without them squishing the bottom one. I place a piece of plastic large enough the cover the top of the bin before putting on the lid.
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