A SURPRISE SLATE TRICK
From Sellers' Secrets, 1931.
Although Sellers uses a slate - a natural prop of that time - there are alternatives that can make a message appear. For close-up a double lift with a blank business card will work. (PD)
A clean slate is shown to the spectators. A number of cards are exhibited bearing such names as "Sahara," Indian Ocean," "Vesuvius," "CoraL Islands," Red Sea," etc., etc. One is selected. The name of the selected card is shown on the slate in a surprising manner.
A flap slate. A number of cards as above, say about twelve. Under the flap with a piece of red chalk write a large letter C. You are now ready to perform.
Show slate and lay on table. Now show cards and have one selected. Forcing the card with the name, "The Red Sea," receive it back and shuffle into the remaining cards.
Now ask the spectator to name the card he selected, and on his answering "The Red Sea" show the large red C on the slate.