Slate Writing or psychography is very old school, possibly even before the Séance Trumpet.

A Medium would take two school slates, placing a piece of chalk between them and binding them together with a rubber band, piece of string or ribbon.  They would then hold the slates between their hands allowing Spirit to write. 

Physicist Johann Zollner, an expert, wrote a book, "Transcendental Physics" in which he declared that Writing Slates, Séance Trumpets and Mediumship were not tricks at all but the real thing.

   Writing Slates,              20.00
   includes chalk, coupling bands and bag