Books with pages that magically change their contents—text, drawings, color, blank, etc.—began to be mentioned and explained in the 1500s. The earliest mention was by Gerolamo Cardano in his 1550 work, De subtilitate: “Formas varias in uno eodemque libello ostendunt, semper prioribus abscedentibus.” (Conjurers show changing forms in one and the same book, with the earlier ones always vanishing.)
Descriptions giving the method of the gimmicked books appeared in 1584 by J. Prevost in La Premiere partie des subtiles, et plaisantes inventions, p. 56; and Reginald Scot in his Discoverie of Witchcraft, book 13, chapter 33, p. 343. Expressing a high degree of certainty, Scot credited a person named Clarvis (probably a conjurer) with the invention of the book, but we have no other substantiation of this, nor is a conjurer named Clarvis elsewhere recorded. (For further information on early descriptions of this trick book, see Pierre Tailefer's “Mysteries of the Agrippa Blow Book” in Gibecière, Vol. 12 No. 2, Summer 2017, p. 14.)
The name “Blow Book” is said to have come from the practice of conjurers blowing on the book, or having spectators do so, as the magical means of effecting the transformations on its pages. The secret was a system of subtly (and sometimes not so subtly) trimmed page edges. When the pages were flipped through at particular positions on their edges, only certain pages were exposed to view.
The Blow Book has remained in conjurer's repertoires through the centuries, its most popular modern incarnation being the Magic Coloring Book, a staple with children's magicians.
The principle of short and long pages has been varied and reapplied many times, especially to playing cards (see Svengali Deck) and pads used to force a word, number or image (see Svengali Forcing Pad).