Locking Spirit Slates. British, 1940s. A gimmicked set of apparently innocent school slates that allows the magician or medium to materialize ?spirit messages" on the surfaces of the chalkboards. Hardwood construction, with several flaps and old handwritten instructions. Slates 11 ? x 9". With a note in Eddie Dawes' hand that states both ?Trevor Hall Slates" and ?Thayer Slates," but likely neither of these, as the Hall slates were sold in our first auction from the Dawes collection, and the Thayer-made slates were of a different construction (though contained the same internal mechanism).