Plates must be dried very slowly and evenly (minimum of 1 week). Wrap in plastic to control the drying. Dry on wire racks, or pegboard to allow air flow. If your racks leave marks, use fiberglass screen door screening on the racks. Or place small objects under the piece to prop it up and allow the foot and bottom to dry at the page rate as the top and sides. You might want to make some small bisque pieces for this purpose. Uneven drying can set up stresses that don’t show themselves until the final glaze firing.
To reduce chances of cracking, it can help if the rim does not dry faster than the center. To do this, cut a round hole in the plastic about 3-4 inches in diameter over the center of the plate. Once the center is dry enough, cover the whole pot loosely for 1-2 weeks. See illustrations below.
drying large thrown pot drying large thrown platter
Some people use water based wax to coat the rims during drying, to prevent them from drying too quickly.
The general process is: Throw the plate, wire it free from the bat, and set on a shelf. (Note, running a wire through a large plate, it is bound to rise up in the middle even if you pull tightly, so make sure your plate is thrown very thick and plan to trim a lot. An alternative is using plaster bats which will release on their own.) Dry slowly and evenly, and don’t let the rim dry out first. As soon as the bottom is hard enough to support itself, flip the platter over sandwiching a bat on top and flip. Take what was the throwing bat off. Let her dry open to trimming stage. After trimming, place on a shelf rim down, cover to dry.
Another innovative solution to the above problem, besides using plaster bats, is using oiled masonite bats, ½” thick (so they are completely inflexible). The clay releases itself from the oiled bat.
Use socks filled with rice as weights to make sure plates stay nice and flat when they are drying.