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Rick Wise

Best way to dry plates?

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I lose a lot of plates during the time after trimming them and before bisque firing.  They develop S cracks while reaching the bone dry stage.  I know the usual cautions about good compression, slow drying,  even drying, etc.  What I need advice on is this: 

1. Should the plate be face up or  inverted while drying, and 

2. What sort of surface should it sit on?  A bat?  A wire rack to allow air underneath?  Sand or powder to prevent "drag" as it shrinks?

Thanks so much for any help!  My wife is going to kill me if I dont get these plates done on time.

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On all my porcelain plates and I made 28 last week for a show this past weekend -after timming I put them foot down on a flat bat and dried them in the sun. I had one  plate thgat died out of 28. 

I do not baby them -my guess is its a body or thionckness issues for you. I just never get s cracks these days.

I cut them off with a wire as soon as they are thrown while still on the wheel

Edited by Mark C.

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Hi Rick!

fwiw, I place trimmed plate on a plaster slab; I'm trimming a wide foot ring, hence only the ring is in contact with the plaster. A light spin and a look assures me the entire ring is in contact with the surface - no high spots or curling. I'm putting all wet/damp pieces in a still spot where the sun doesn't shine (oh stop!).

Compression is the word, however, I'm not believing that exerting pressure on clay causes any reduction in volume, hence not actually "compression" imo. No, what I believe occurs is more along the "alignment" line. Any road, several of the forum regulars point out that "compressing" in to out should be complimented by out to in.

Other factors I) allowing water to accumulate and sit in the vessel is bad, many say II) variance in thickness; the portion S cracking should be about the same thickness as the walls, eh?

After trimming, I'm thoroughly burnishing the foot ring, all three sides, and the space within the foot ring as well, with a metal rib and/or the rounded edge of a loop tool. Burnishing makes smooth - also stronger? It don't hurt.

From there, I'm interested to see what others may offer.

No doubt there's much to read here inna archives as well...

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When I put a foot ring in, I leave a button in the middle that is level with the foot so the middle can't sag as it dries.

I compress the crap out of my plate bottoms!  Unlike @Hulk I do believe clay can be compressed because it contains water and the water can be forced out. 

Wire them off the bats after throwing while it's easy, with all the downward pressure of compressing, the bottoms will be really stiff and difficult to wire through later.

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Even drying is going to help with other issues but S cracks start their life during the throwing stage. Might be noticed when drying or during the bisque or glaze fire but they have their beginnings from the throwing part of the process.  

Different rates of shrinkage between the base and the walls results if not enough of the the clay platelets are in the same plane as the direction of the wheel. Compressing the clay gets the platelets on the surface aligned but often doesn’t go deep enough into the clay on the wheelhead. If you think about it when you pull up a wall you are compressing both sides of the clay as the wheel is turning therefore getting clay platelets well aligned, in the floor of a pot you can only get at one side.   I’m making a hunch that you don’t cone your clay? Try coning the clay and keeping an eye on even thickness between walls and base of the plates. Coning well really works to prevent S cracks, no volcano tops when you cone. 

To dry evenly I cover the rims of platters with plastic film, right side up, and leave the middles open. This slows the rims from drying out way before the middles do. 

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drywall is my favorite drying base.  and yes, compression  - whatever you think it does.  throwing without lots of water.  evenness of throwing.  when making a plate, have you ever sliced upwards from the wheelhead with a wire to see what is happening to the clay?

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Min -- thanks for the reminder re coning.  I do sometimes forget.  Will re-double my efforts. 

Also am trying this:  I cut a circle of cardboard a little larger than the plate, then cut out the center of the cardboard so that I have a ring.  I coverthe ring with aluminum foil so that it does not absorb. The ring goes on to the plate while drying.  Center of plate is exposed and while rim is covered.  Hope this promotes even drying.

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I'm still not believing volume of clay changing (much) due to pressure exerted; volume of clay changing due to percent water reduced, of course! …"much" as in significant, like water itself doesn't compress much either - lots of volume change related to temperature - pressure alone, very little, "Water is essentially incompressible, especially under normal conditions." Clay responds to pressure, aye.

Regarding sun and/or air movement whilst drying, avoiding both as I typically don't want to do the turn turn turn that's required - indoors (in my studio), the sun comes from the side and I don't want any air currents (dust); outside is another ballgame, entire.

As for surfaces and/or positions, the foot ring being thicker than the rim portion and the center portion, I'm looking to help it along, that is, dry faster, hence the plaster bat (else fiber bat, else newsprint) - yep, absorb water from the foot ring. Slowing down drying rate on the rim and center portions, similar strategy there, imo.

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If you do not belive in coppression try throwing lids off the hump without taping the centers-100% s cracks vs using a tool to tap/compress cneter after cutting off-100% no s cracks

Water does not compress but think about water filling the micro voids between the clay particles-the more water the more space (more weaker when its drys off)More space between particles.

 

Edited by Mark C.

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Hi Rick, I have been throwing a lot of Patens (plates) for communion sets. These usually are with in 12-14" in diameter for use with whole loaf type communion. I throw all of my plates with wetter than usual clay, wedged well, and coned on the wheel a few times up and down. then I use my rt fist and lft hand to push the clay downward into a low compressed 1-2 inch thick flat form on the wheel, then Using my hands I pull  the outer band outward from the center to get about a 1/2" thickness across the area leaving a little more clay to pull the rim on the outside of the form I finish this area with a large slightly bowed wooden rib compressing a little thinner. This area I stamp with stamps, slip, and decorate even overlapping that thicker edge. Then I use a wooden rib to add a slight undercut to the outer edge as if cutting the form off of the wheel.Lastly I pull the outer thicker area upward and outward to from the lip about 2-3" rising from the wheel head for easy lifting of the form when used in communion. The rim gets a little thickening with a chamois, and some decorative lines on the rim diameter.  Then I use my cutting wire to separate the plate from the bat, and remove the bat for the rim to stiffen up for flipping on another bat before trimming when leather hard. I trim with a double foot ring, narrow 2-2 1?2 diameter in center and one at outer edge.

 

best,

Pres

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I put 2 foot rings on porcelain dinner plates. Probably serves the same function as Liam's button. I also trim when the clay is a bit stiff. Cut off the plate.  I place a soft piece foam the keep the center from slumping if the clay is soft. Sandwich the plate with another bat and flip. Put it on the wheel trim and start drying. I flip the plates several times during the drying and dry them in a bakers rack wrapped with plastic. In Texas it was humid. In Montana it is dry. All depends on your studio atmosphere. Avoid drafts.

Marcia

 

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Plastic bats seem to cause more cracking than plaster or masonite bats. If I have to use plastic, I wire it off immediately after throwing, and flip it onto it's rim when the rim is strong enough to support itself.  If the base is too soft to flip and will sag, then I transfer the plate to a board with newspaper so the base can move easier as it dries and contracts.

With plaster or masonite bats, I think they wick away enough moisture from the bottom of the plate to avoid the stress from uneven drying on the rim and the foot, and I don't have to be as careful.

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