Clay slabs are great to use to construct masks, serving dishes, and other functional and decorative pieces. Plus, kids can make clay slabs to press leaves, lace and stamps!! It's truly amazing what a little clay and a rolling pin can do.
To ensure an even thickness to the clay slab, use same-thickness shims on each side of the clay, so the rolling pin will sit on top of the shims. Make sure the shims don't exceed 1/4 inch thickness (3/8 inch for larger forms).
Once the slab has been rolled to the desired thickness, flip the slab over, and rotate it 90 degrees from its origin. Re-roll the slab. This helps to relieve some of the stresses on the clay.
If using stamps or something else to impress into the clay, spray the face of the piece that will impress into the clay with WD-40. You'll get a cleaner press, and the WD-40 fires out of the clay.
When the creation is completed, do two things. First of all, make sure the creation is placed on a surface where the piece won't stick--a wood board or a dry wall board work great!! As the piece dries, the clay shrinks. If the piece sticks, the shrinking clay will have nowhere to go!! Secondly, drape plastic over the piece. Dry the piece slowly. Check the piece daily, to ensure no condensation is building up on the inside between the creation and the plastic. Leave the plastic on for a couple of days, up to a week for larger pieces.
When working with a full load of slab ware, bring the kiln up to temperature more slowly. Slab ware usually uses a thicker clay body and requires more time to get the extra water and volatile chemical molecules out of it.
For larger pieces, sprinkle 90 mesh sand under the piece. The sand acts as roller bearings as the clay shrinks.