Dean on tue 2 sep 08
Since the rim of the plate is in the air it dries faster, both sides are exposed. The bottom dries slower, only one side exposed. Hence the rim dries and shrinks first and cracks result. The bigger your plate the more drying stress this creates. Find a way to even things out. Run a thick twisted cutoff wire under your plate to create little ventilating grooves under the plates when wet. Dry under plastic till you can handle the plates, soft to medium leather hard. If you're trimming, trim as soon as possible to remove excess wet clay from the bottom and have a uniform thickness throughout.. There is hardly any shrinkage till the clay gets to a firm leather stage. Then:
1. flip the plate over and dry upside down. No elevated rim so the entire bottom surface right out to the rim dries evenly.
Or:
2. elevate the plate on props so there is air flow under the whole plate
Or:
3. dry on a perforated surface like pegboard that has holes all over it with some airspace under it to allow moisture to escape from the bottom of the plate
Also I dry my pots under perforated plastic that is used to cover bananas while they're shipped. You can get this from super markets. Lets a nice slow even moisture release from the whole piece. Like a portable damp room. Nice even drying.
All that being said, getting cracks like that in a 4 lb plate seems extreme. If you're not wedded to that clay you might try another body with more benign drying habits.
I have been working on a series of 12-15 lb platters in stoneware. Much easier clay, for sure, but all the same problems magnified. There's a couple of smaller ones on my website.
Solve the drying problem now and you'll be able to make any size platters you want. I also had a similar problem getting cracks during firing and now I set my platters on coils to fire with equal airflow over and under the platters.
Blessings from Kauai
Dean
lightwavepottery.com
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