Plates Lifting During Drying

[tomhumf]

This is a two part question.

 

I've not made many dinner plates, but have a set of four drying currently that I have trimmed. I have quite a damp studio/ garage so things dry slow. During drying some of my plates lifted in the centre. I've now put some weights on them to counter this. These ones have flat bottoms - no footring. I've had the problem before.

 

So firstly is this lifting of plates common, if so how do you avoid it? Maybe it's the way I have trimmed them.

 

And secondly do you think footrings are better than flat bottoms - may this be the cause? If I trimmed footrings without any nubbin / centre support I wouldnt be able to weigh them down to prevent lifting really. Otherwise the weight would push the centre area I would need to leave free for glaze onto the shelf...

[Mark C.]

Yes I think flat bottoms are helping warp them.

I have some questions ? what diameter are these plates and what was the weight you started with (like 5#s of clay for example)

What was you bat material and did you wire them off right after throwing or later?stoneware or porcelain?

I just threw a bunch of plates that where on plastic bats. 11.3 inches wide (these fire to 10 inch)-cut them right away-started with #6 lbs of clay.

flipped them as soon as I could and trimmed them when they where ready. Dried them right side top no weights and they are fine. (porcelain )

I trim out a foot and leave a small nubbin in center (I have a post with photos on plates a year or two ago)

[tomhumf]

After doing some more reading I guess it's the rims drying faster then base which causes the lifting. Does everyone cover their rims with plastic?

[tomhumf]

Marc, I posted that before I saw your reply... I will answer your questions..

[tomhumf]

They were thrown to 30cm diameter from 2kg lumps, the bottoms are as flat as I could make, around 1cm deep thrown. I cut them from bat straight after throwing, then trimmed a little off bottom leaving about 0.5cm thickness. They are stoneware.

 

The bats are plywood, about half inch thick. I have seen your plates during reading about this - very nice.

[Mark C.]

Most common plate mistakes are 

 

not using enough clay to start with

to thin bottoms

to thin lips

I converted your metrics 30cm+11.8 inch wide using 2kg=4.4Lbs of clay

my guess is you are using way to little clay for a 30 cm plate

 

I never cover anything right after throwing but I get back to it when its ready as thats my full time job.

what I do is place pots  up or down in shop as the warmth is higher up and the cool is lower thats how I control doing in winter.

I always want the stuff done sooner than later so covering only slows me down.

I do cover handled forms right after attaching handles for 1 night to equalize moisture.This safes cracking on porcelain but stoneware is so bullet proof no need for that.

[Roberta12]

I make a lot of trays this time of year.  Many of them have flat bottoms.  I have bags of rice that I place in the center while they are drying.  I live in a fairly dry climate so I do cover them for a couple of days, but then start easing the plastic off.  For me, unless I trim a foot on a plate, the bags of rice, help keep things flat.

 

Roberta

[Mark C.]

I make lots of pie plates with untrimmed flat bottoms. They rarely lift but my climate is dry only 5 months of the year.I keep the humidly at around 50-60% in winter with the gas heater going.

I think getting the plates turned over as soon as you can then drying them right side up after any trimming along with even wall thickness is key . Or at least it works for me. If the bottoms are thin they can bow up. Getting them even wall thickness is a key point,

[tomhumf]

Thanks everyone. I guess I will try using a bit more clay, and try putting a footring on. How thick would you say your bases are after trimming Mark? And how much clearance do you have between the footring and base?

[Marcia Selsor]

I keep my plates upside down after trimming so they dry evenly. I sandwich them between 2 bats and flip them over.

Marcia

[Mark C.]

I have plenty of space so the bottom can be glazed (makes them stronger) at least a 1/4 inch of space under the foot for glaze.

I have not cut a plate in 1/2 in decades so I cannot say on thickness.I used to make my plates very thin and they did not hold up (broke easy)-now that are made thicker to last.

I am still using plates I made in the 70's on a daily basis.

The plate ,bowl or cup should all have a wall thickness thats the same everywhere. That is the goal for the best work.

[Marcia Selsor]

There is a big difference in the way various climates affect drying. In Montana I could throw , trim and pull handle for mugs in one day. In Southern Ill. I had to wait 4-5 days before the clay was stiff enough to trim. Since I use A/C in Brownsville, I can control the drying with tupperware containers over the pots.So you'll have to add that equation into your drying system.

 

 

Marcia

[Mark C.]

I'm assuming your spot in the UK is a damp climate?

[tomhumf]

Ok thanks Marcia and Marc. My studio is an old external garage with no insulation, and ground level halfway up the walls on two sides. It's damp even in summer. I need to take ware in the house to dry fully. Since I only manage to do a couple of hours every other evening its actually not too bad having slow drying.

[Mark C.]

slow drying should help you.

I'm on the other end as I dry things as fast as I can.I keep my humidity low in studio in winter for drying and dry all wares outside in summer when I can. 

[preeta]

i came across this today. interesting information half way through this video.