Slate Writing
Slate writing was a popular effect of physical mediumship. Typically a pair of school slates (either separate or hinged) was employed. Placed on a table with a piece of chalk or slate pencil, and the spirits suitably invoked, the slates would in time be discovered with messages on them— purportedly from the spirit realm. (These modern slates show a short version of Houdini's anticipated message to his wife.)
To supposedly preclude trickery, the slates were often bound or even locked. But there were many means of circumventing the intended safeguards, ranging from substituting previously prepared slates to using specially gimmicked ones. (For a discussion, see Harry Houdini, Harry Houdini: A Magician Among the Spirits, 1924; reprinted New York: Arno Press, 1972.)
