I make a lot of flat pieces, using slabs of clay. I thought I would talk for a bit about a problem I have run into with the slabs. During the drying stage certain pieces want to warp and twist. I use dishes and forms to slump into, so it is important to me to know when to take a piece out of the form, and when it is better to leave it in.
The first method makes use of my left-over clay pieces. I make clay "biscuits" out of them to weight my slabs down. They can be bisque fired or just left in the dry state, and used over and over. I have bowls of them in the studio.
In the pictures above I am making a cocktail plate. First I spritz the form with water, then I spread a piece of thin plastic wrap (like Sarah wrap) to keep the clay from sticking to the form. This one is plastic, which I like because I can give it a good "thump" with the sheet of clay and it will drape nicely into the form. I also thump the glass ones if they are sturdy. Once the excess clay is trimmed away and the piece has texture applied, I drape a sheet of tissue paper over the clay, then lay down my clay biscuits. They seem to suck some of the moisture out of the clay and swiften the drying time. Even if I take the piece out when leatherhard to clean up the edges, I will replace the biscuits until it is bone dry.