Slate Writing is a popular mentalism effect in which writing mysteriuously appear on a slate, a little blackboard.
The medium and the sitter take seats at opposite ends of a table, each grasping a corner of an ordinary school slate (little blackboards) that they hold firmly pressed against the underside of the table. A small fragment of slate-pencil is first enclosed between slate and table. A scratching sound, as of someone writing on a slate, is heard, with three loud raps indicating the conclusion of the message. On the withdrawal of the slate, it is found to have a message, usually an answer to some question previously written down by the sitter.
Another presentation is to wrap two slates face to face with a chalk inside.